Add dependencies/vendor (whatsapp)

60 files changed, 13398 insertions, 0 deletions

diff --git a/vendor/golang.org/x/mod/LICENSE b/vendor/golang.org/x/mod/LICENSE
new file mode 100644
index 00000000..6a66aea5
--- /dev/null
+++ b/vendor/golang.org/x/mod/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2009 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/vendor/golang.org/x/mod/PATENTS b/vendor/golang.org/x/mod/PATENTS
new file mode 100644
index 00000000..73309904
--- /dev/null
+++ b/vendor/golang.org/x/mod/PATENTS
@@ -0,0 +1,22 @@
+Additional IP Rights Grant (Patents)
+
+"This implementation" means the copyrightable works distributed by
+Google as part of the Go project.
+
+Google hereby grants to You a perpetual, worldwide, non-exclusive,
+no-charge, royalty-free, irrevocable (except as stated in this section)
+patent license to make, have made, use, offer to sell, sell, import,
+transfer and otherwise run, modify and propagate the contents of this
+implementation of Go, where such license applies only to those patent
+claims, both currently owned or controlled by Google and acquired in
+the future, licensable by Google that are necessarily infringed by this
+implementation of Go.  This grant does not include claims that would be
+infringed only as a consequence of further modification of this
+implementation.  If you or your agent or exclusive licensee institute or
+order or agree to the institution of patent litigation against any
+entity (including a cross-claim or counterclaim in a lawsuit) alleging
+that this implementation of Go or any code incorporated within this
+implementation of Go constitutes direct or contributory patent
+infringement, or inducement of patent infringement, then any patent
+rights granted to you under this License for this implementation of Go
+shall terminate as of the date such litigation is filed.
diff --git a/vendor/golang.org/x/mod/semver/semver.go b/vendor/golang.org/x/mod/semver/semver.go
new file mode 100644
index 00000000..7be398f8
--- /dev/null
+++ b/vendor/golang.org/x/mod/semver/semver.go
@@ -0,0 +1,411 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package semver implements comparison of semantic version strings.
+// In this package, semantic version strings must begin with a leading "v",
+// as in "v1.0.0".
+//
+// The general form of a semantic version string accepted by this package is
+//
+//	vMAJOR[.MINOR[.PATCH[-PRERELEASE][+BUILD]]]
+//
+// where square brackets indicate optional parts of the syntax;
+// MAJOR, MINOR, and PATCH are decimal integers without extra leading zeros;
+// PRERELEASE and BUILD are each a series of non-empty dot-separated identifiers
+// using only alphanumeric characters and hyphens; and
+// all-numeric PRERELEASE identifiers must not have leading zeros.
+//
+// This package follows Semantic Versioning 2.0.0 (see semver.org)
+// with two exceptions. First, it requires the "v" prefix. Second, it recognizes
+// vMAJOR and vMAJOR.MINOR (with no prerelease or build suffixes)
+// as shorthands for vMAJOR.0.0 and vMAJOR.MINOR.0.
+package semver
+
+import "sort"
+
+// parsed returns the parsed form of a semantic version string.
+type parsed struct {
+	major      string
+	minor      string
+	patch      string
+	short      string
+	prerelease string
+	build      string
+	err        string
+}
+
+// IsValid reports whether v is a valid semantic version string.
+func IsValid(v string) bool {
+	_, ok := parse(v)
+	return ok
+}
+
+// Canonical returns the canonical formatting of the semantic version v.
+// It fills in any missing .MINOR or .PATCH and discards build metadata.
+// Two semantic versions compare equal only if their canonical formattings
+// are identical strings.
+// The canonical invalid semantic version is the empty string.
+func Canonical(v string) string {
+	p, ok := parse(v)
+	if !ok {
+		return ""
+	}
+	if p.build != "" {
+		return v[:len(v)-len(p.build)]
+	}
+	if p.short != "" {
+		return v + p.short
+	}
+	return v
+}
+
+// Major returns the major version prefix of the semantic version v.
+// For example, Major("v2.1.0") == "v2".
+// If v is an invalid semantic version string, Major returns the empty string.
+func Major(v string) string {
+	pv, ok := parse(v)
+	if !ok {
+		return ""
+	}
+	return v[:1+len(pv.major)]
+}
+
+// MajorMinor returns the major.minor version prefix of the semantic version v.
+// For example, MajorMinor("v2.1.0") == "v2.1".
+// If v is an invalid semantic version string, MajorMinor returns the empty string.
+func MajorMinor(v string) string {
+	pv, ok := parse(v)
+	if !ok {
+		return ""
+	}
+	i := 1 + len(pv.major)
+	if j := i + 1 + len(pv.minor); j <= len(v) && v[i] == '.' && v[i+1:j] == pv.minor {
+		return v[:j]
+	}
+	return v[:i] + "." + pv.minor
+}
+
+// Prerelease returns the prerelease suffix of the semantic version v.
+// For example, Prerelease("v2.1.0-pre+meta") == "-pre".
+// If v is an invalid semantic version string, Prerelease returns the empty string.
+func Prerelease(v string) string {
+	pv, ok := parse(v)
+	if !ok {
+		return ""
+	}
+	return pv.prerelease
+}
+
+// Build returns the build suffix of the semantic version v.
+// For example, Build("v2.1.0+meta") == "+meta".
+// If v is an invalid semantic version string, Build returns the empty string.
+func Build(v string) string {
+	pv, ok := parse(v)
+	if !ok {
+		return ""
+	}
+	return pv.build
+}
+
+// Compare returns an integer comparing two versions according to
+// semantic version precedence.
+// The result will be 0 if v == w, -1 if v < w, or +1 if v > w.
+//
+// An invalid semantic version string is considered less than a valid one.
+// All invalid semantic version strings compare equal to each other.
+func Compare(v, w string) int {
+	pv, ok1 := parse(v)
+	pw, ok2 := parse(w)
+	if !ok1 && !ok2 {
+		return 0
+	}
+	if !ok1 {
+		return -1
+	}
+	if !ok2 {
+		return +1
+	}
+	if c := compareInt(pv.major, pw.major); c != 0 {
+		return c
+	}
+	if c := compareInt(pv.minor, pw.minor); c != 0 {
+		return c
+	}
+	if c := compareInt(pv.patch, pw.patch); c != 0 {
+		return c
+	}
+	return comparePrerelease(pv.prerelease, pw.prerelease)
+}
+
+// Max canonicalizes its arguments and then returns the version string
+// that compares greater.
+//
+// Deprecated: use Compare instead. In most cases, returning a canonicalized
+// version is not expected or desired.
+func Max(v, w string) string {
+	v = Canonical(v)
+	w = Canonical(w)
+	if Compare(v, w) > 0 {
+		return v
+	}
+	return w
+}
+
+// ByVersion implements sort.Interface for sorting semantic version strings.
+type ByVersion []string
+
+func (vs ByVersion) Len() int      { return len(vs) }
+func (vs ByVersion) Swap(i, j int) { vs[i], vs[j] = vs[j], vs[i] }
+func (vs ByVersion) Less(i, j int) bool {
+	cmp := Compare(vs[i], vs[j])
+	if cmp != 0 {
+		return cmp < 0
+	}
+	return vs[i] < vs[j]
+}
+
+// Sort sorts a list of semantic version strings using ByVersion.
+func Sort(list []string) {
+	sort.Sort(ByVersion(list))
+}
+
+func parse(v string) (p parsed, ok bool) {
+	if v == "" || v[0] != 'v' {
+		p.err = "missing v prefix"
+		return
+	}
+	p.major, v, ok = parseInt(v[1:])
+	if !ok {
+		p.err = "bad major version"
+		return
+	}
+	if v == "" {
+		p.minor = "0"
+		p.patch = "0"
+		p.short = ".0.0"
+		return
+	}
+	if v[0] != '.' {
+		p.err = "bad minor prefix"
+		ok = false
+		return
+	}
+	p.minor, v, ok = parseInt(v[1:])
+	if !ok {
+		p.err = "bad minor version"
+		return
+	}
+	if v == "" {
+		p.patch = "0"
+		p.short = ".0"
+		return
+	}
+	if v[0] != '.' {
+		p.err = "bad patch prefix"
+		ok = false
+		return
+	}
+	p.patch, v, ok = parseInt(v[1:])
+	if !ok {
+		p.err = "bad patch version"
+		return
+	}
+	if len(v) > 0 && v[0] == '-' {
+		p.prerelease, v, ok = parsePrerelease(v)
+		if !ok {
+			p.err = "bad prerelease"
+			return
+		}
+	}
+	if len(v) > 0 && v[0] == '+' {
+		p.build, v, ok = parseBuild(v)
+		if !ok {
+			p.err = "bad build"
+			return
+		}
+	}
+	if v != "" {
+		p.err = "junk on end"
+		ok = false
+		return
+	}
+	ok = true
+	return
+}
+
+func parseInt(v string) (t, rest string, ok bool) {
+	if v == "" {
+		return
+	}
+	if v[0] < '0' || '9' < v[0] {
+		return
+	}
+	i := 1
+	for i < len(v) && '0' <= v[i] && v[i] <= '9' {
+		i++
+	}
+	if v[0] == '0' && i != 1 {
+		return
+	}
+	return v[:i], v[i:], true
+}
+
+func parsePrerelease(v string) (t, rest string, ok bool) {
+	// "A pre-release version MAY be denoted by appending a hyphen and
+	// a series of dot separated identifiers immediately following the patch version.
+	// Identifiers MUST comprise only ASCII alphanumerics and hyphen [0-9A-Za-z-].
+	// Identifiers MUST NOT be empty. Numeric identifiers MUST NOT include leading zeroes."
+	if v == "" || v[0] != '-' {
+		return
+	}
+	i := 1
+	start := 1
+	for i < len(v) && v[i] != '+' {
+		if !isIdentChar(v[i]) && v[i] != '.' {
+			return
+		}
+		if v[i] == '.' {
+			if start == i || isBadNum(v[start:i]) {
+				return
+			}
+			start = i + 1
+		}
+		i++
+	}
+	if start == i || isBadNum(v[start:i]) {
+		return
+	}
+	return v[:i], v[i:], true
+}
+
+func parseBuild(v string) (t, rest string, ok bool) {
+	if v == "" || v[0] != '+' {
+		return
+	}
+	i := 1
+	start := 1
+	for i < len(v) {
+		if !isIdentChar(v[i]) && v[i] != '.' {
+			return
+		}
+		if v[i] == '.' {
+			if start == i {
+				return
+			}
+			start = i + 1
+		}
+		i++
+	}
+	if start == i {
+		return
+	}
+	return v[:i], v[i:], true
+}
+
+func isIdentChar(c byte) bool {
+	return 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' || c == '-'
+}
+
+func isBadNum(v string) bool {
+	i := 0
+	for i < len(v) && '0' <= v[i] && v[i] <= '9' {
+		i++
+	}
+	return i == len(v) && i > 1 && v[0] == '0'
+}
+
+func isNum(v string) bool {
+	i := 0
+	for i < len(v) && '0' <= v[i] && v[i] <= '9' {
+		i++
+	}
+	return i == len(v)
+}
+
+func compareInt(x, y string) int {
+	if x == y {
+		return 0
+	}
+	if len(x) < len(y) {
+		return -1
+	}
+	if len(x) > len(y) {
+		return +1
+	}
+	if x < y {
+		return -1
+	} else {
+		return +1
+	}
+}
+
+func comparePrerelease(x, y string) int {
+	// "When major, minor, and patch are equal, a pre-release version has
+	// lower precedence than a normal version.
+	// Example: 1.0.0-alpha < 1.0.0.
+	// Precedence for two pre-release versions with the same major, minor,
+	// and patch version MUST be determined by comparing each dot separated
+	// identifier from left to right until a difference is found as follows:
+	// identifiers consisting of only digits are compared numerically and
+	// identifiers with letters or hyphens are compared lexically in ASCII
+	// sort order. Numeric identifiers always have lower precedence than
+	// non-numeric identifiers. A larger set of pre-release fields has a
+	// higher precedence than a smaller set, if all of the preceding
+	// identifiers are equal.
+	// Example: 1.0.0-alpha < 1.0.0-alpha.1 < 1.0.0-alpha.beta <
+	// 1.0.0-beta < 1.0.0-beta.2 < 1.0.0-beta.11 < 1.0.0-rc.1 < 1.0.0."
+	if x == y {
+		return 0
+	}
+	if x == "" {
+		return +1
+	}
+	if y == "" {
+		return -1
+	}
+	for x != "" && y != "" {
+		x = x[1:] // skip - or .
+		y = y[1:] // skip - or .
+		var dx, dy string
+		dx, x = nextIdent(x)
+		dy, y = nextIdent(y)
+		if dx != dy {
+			ix := isNum(dx)
+			iy := isNum(dy)
+			if ix != iy {
+				if ix {
+					return -1
+				} else {
+					return +1
+				}
+			}
+			if ix {
+				if len(dx) < len(dy) {
+					return -1
+				}
+				if len(dx) > len(dy) {
+					return +1
+				}
+			}
+			if dx < dy {
+				return -1
+			} else {
+				return +1
+			}
+		}
+	}
+	if x == "" {
+		return -1
+	} else {
+		return +1
+	}
+}
+
+func nextIdent(x string) (dx, rest string) {
+	i := 0
+	for i < len(x) && x[i] != '.' {
+		i++
+	}
+	return x[:i], x[i:]
+}
diff --git a/vendor/golang.org/x/sys/execabs/execabs.go b/vendor/golang.org/x/sys/execabs/execabs.go
new file mode 100644
index 00000000..78192498
--- /dev/null
+++ b/vendor/golang.org/x/sys/execabs/execabs.go
@@ -0,0 +1,102 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package execabs is a drop-in replacement for os/exec
+// that requires PATH lookups to find absolute paths.
+// That is, execabs.Command("cmd") runs the same PATH lookup
+// as exec.Command("cmd"), but if the result is a path
+// which is relative, the Run and Start methods will report
+// an error instead of running the executable.
+//
+// See https://blog.golang.org/path-security for more information
+// about when it may be necessary or appropriate to use this package.
+package execabs
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"path/filepath"
+	"reflect"
+	"unsafe"
+)
+
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+// It is an alias for exec.ErrNotFound.
+var ErrNotFound = exec.ErrNotFound
+
+// Cmd represents an external command being prepared or run.
+// It is an alias for exec.Cmd.
+type Cmd = exec.Cmd
+
+// Error is returned by LookPath when it fails to classify a file as an executable.
+// It is an alias for exec.Error.
+type Error = exec.Error
+
+// An ExitError reports an unsuccessful exit by a command.
+// It is an alias for exec.ExitError.
+type ExitError = exec.ExitError
+
+func relError(file, path string) error {
+	return fmt.Errorf("%s resolves to executable in current directory (.%c%s)", file, filepath.Separator, path)
+}
+
+// LookPath searches for an executable named file in the directories
+// named by the PATH environment variable. If file contains a slash,
+// it is tried directly and the PATH is not consulted. The result will be
+// an absolute path.
+//
+// LookPath differs from exec.LookPath in its handling of PATH lookups,
+// which are used for file names without slashes. If exec.LookPath's
+// PATH lookup would have returned an executable from the current directory,
+// LookPath instead returns an error.
+func LookPath(file string) (string, error) {
+	path, err := exec.LookPath(file)
+	if err != nil {
+		return "", err
+	}
+	if filepath.Base(file) == file && !filepath.IsAbs(path) {
+		return "", relError(file, path)
+	}
+	return path, nil
+}
+
+func fixCmd(name string, cmd *exec.Cmd) {
+	if filepath.Base(name) == name && !filepath.IsAbs(cmd.Path) {
+		// exec.Command was called with a bare binary name and
+		// exec.LookPath returned a path which is not absolute.
+		// Set cmd.lookPathErr and clear cmd.Path so that it
+		// cannot be run.
+		lookPathErr := (*error)(unsafe.Pointer(reflect.ValueOf(cmd).Elem().FieldByName("lookPathErr").Addr().Pointer()))
+		if *lookPathErr == nil {
+			*lookPathErr = relError(name, cmd.Path)
+		}
+		cmd.Path = ""
+	}
+}
+
+// CommandContext is like Command but includes a context.
+//
+// The provided context is used to kill the process (by calling os.Process.Kill)
+// if the context becomes done before the command completes on its own.
+func CommandContext(ctx context.Context, name string, arg ...string) *exec.Cmd {
+	cmd := exec.CommandContext(ctx, name, arg...)
+	fixCmd(name, cmd)
+	return cmd
+
+}
+
+// Command returns the Cmd struct to execute the named program with the given arguments.
+// See exec.Command for most details.
+//
+// Command differs from exec.Command in its handling of PATH lookups,
+// which are used when the program name contains no slashes.
+// If exec.Command would have returned an exec.Cmd configured to run an
+// executable from the current directory, Command instead
+// returns an exec.Cmd that will return an error from Start or Run.
+func Command(name string, arg ...string) *exec.Cmd {
+	cmd := exec.Command(name, arg...)
+	fixCmd(name, cmd)
+	return cmd
+}
diff --git a/vendor/golang.org/x/tools/AUTHORS b/vendor/golang.org/x/tools/AUTHORS
new file mode 100644
index 00000000..15167cd7
--- /dev/null
+++ b/vendor/golang.org/x/tools/AUTHORS
@@ -0,0 +1,3 @@
+# This source code refers to The Go Authors for copyright purposes.
+# The master list of authors is in the main Go distribution,
+# visible at http://tip.golang.org/AUTHORS.
diff --git a/vendor/golang.org/x/tools/CONTRIBUTORS b/vendor/golang.org/x/tools/CONTRIBUTORS
new file mode 100644
index 00000000..1c4577e9
--- /dev/null
+++ b/vendor/golang.org/x/tools/CONTRIBUTORS
@@ -0,0 +1,3 @@
+# This source code was written by the Go contributors.
+# The master list of contributors is in the main Go distribution,
+# visible at http://tip.golang.org/CONTRIBUTORS.
diff --git a/vendor/golang.org/x/tools/LICENSE b/vendor/golang.org/x/tools/LICENSE
new file mode 100644
index 00000000..6a66aea5
--- /dev/null
+++ b/vendor/golang.org/x/tools/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2009 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/vendor/golang.org/x/tools/PATENTS b/vendor/golang.org/x/tools/PATENTS
new file mode 100644
index 00000000..73309904
--- /dev/null
+++ b/vendor/golang.org/x/tools/PATENTS
@@ -0,0 +1,22 @@
+Additional IP Rights Grant (Patents)
+
+"This implementation" means the copyrightable works distributed by
+Google as part of the Go project.
+
+Google hereby grants to You a perpetual, worldwide, non-exclusive,
+no-charge, royalty-free, irrevocable (except as stated in this section)
+patent license to make, have made, use, offer to sell, sell, import,
+transfer and otherwise run, modify and propagate the contents of this
+implementation of Go, where such license applies only to those patent
+claims, both currently owned or controlled by Google and acquired in
+the future, licensable by Google that are necessarily infringed by this
+implementation of Go.  This grant does not include claims that would be
+infringed only as a consequence of further modification of this
+implementation.  If you or your agent or exclusive licensee institute or
+order or agree to the institution of patent litigation against any
+entity (including a cross-claim or counterclaim in a lawsuit) alleging
+that this implementation of Go or any code incorporated within this
+implementation of Go constitutes direct or contributory patent
+infringement, or inducement of patent infringement, then any patent
+rights granted to you under this License for this implementation of Go
+shall terminate as of the date such litigation is filed.
diff --git a/vendor/golang.org/x/tools/go/gcexportdata/gcexportdata.go b/vendor/golang.org/x/tools/go/gcexportdata/gcexportdata.go
new file mode 100644
index 00000000..fc8beea5
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/gcexportdata/gcexportdata.go
@@ -0,0 +1,133 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package gcexportdata provides functions for locating, reading, and
+// writing export data files containing type information produced by the
+// gc compiler.  This package supports go1.7 export data format and all
+// later versions.
+//
+// Although it might seem convenient for this package to live alongside
+// go/types in the standard library, this would cause version skew
+// problems for developer tools that use it, since they must be able to
+// consume the outputs of the gc compiler both before and after a Go
+// update such as from Go 1.7 to Go 1.8.  Because this package lives in
+// golang.org/x/tools, sites can update their version of this repo some
+// time before the Go 1.8 release and rebuild and redeploy their
+// developer tools, which will then be able to consume both Go 1.7 and
+// Go 1.8 export data files, so they will work before and after the
+// Go update. (See discussion at https://golang.org/issue/15651.)
+//
+package gcexportdata // import "golang.org/x/tools/go/gcexportdata"
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"go/token"
+	"go/types"
+	"io"
+	"io/ioutil"
+
+	"golang.org/x/tools/go/internal/gcimporter"
+)
+
+// Find returns the name of an object (.o) or archive (.a) file
+// containing type information for the specified import path,
+// using the workspace layout conventions of go/build.
+// If no file was found, an empty filename is returned.
+//
+// A relative srcDir is interpreted relative to the current working directory.
+//
+// Find also returns the package's resolved (canonical) import path,
+// reflecting the effects of srcDir and vendoring on importPath.
+func Find(importPath, srcDir string) (filename, path string) {
+	return gcimporter.FindPkg(importPath, srcDir)
+}
+
+// NewReader returns a reader for the export data section of an object
+// (.o) or archive (.a) file read from r.  The new reader may provide
+// additional trailing data beyond the end of the export data.
+func NewReader(r io.Reader) (io.Reader, error) {
+	buf := bufio.NewReader(r)
+	_, err := gcimporter.FindExportData(buf)
+	// If we ever switch to a zip-like archive format with the ToC
+	// at the end, we can return the correct portion of export data,
+	// but for now we must return the entire rest of the file.
+	return buf, err
+}
+
+// Read reads export data from in, decodes it, and returns type
+// information for the package.
+// The package name is specified by path.
+// File position information is added to fset.
+//
+// Read may inspect and add to the imports map to ensure that references
+// within the export data to other packages are consistent.  The caller
+// must ensure that imports[path] does not exist, or exists but is
+// incomplete (see types.Package.Complete), and Read inserts the
+// resulting package into this map entry.
+//
+// On return, the state of the reader is undefined.
+func Read(in io.Reader, fset *token.FileSet, imports map[string]*types.Package, path string) (*types.Package, error) {
+	data, err := ioutil.ReadAll(in)
+	if err != nil {
+		return nil, fmt.Errorf("reading export data for %q: %v", path, err)
+	}
+
+	if bytes.HasPrefix(data, []byte("!<arch>")) {
+		return nil, fmt.Errorf("can't read export data for %q directly from an archive file (call gcexportdata.NewReader first to extract export data)", path)
+	}
+
+	// The App Engine Go runtime v1.6 uses the old export data format.
+	// TODO(adonovan): delete once v1.7 has been around for a while.
+	if bytes.HasPrefix(data, []byte("package ")) {
+		return gcimporter.ImportData(imports, path, path, bytes.NewReader(data))
+	}
+
+	// The indexed export format starts with an 'i'; the older
+	// binary export format starts with a 'c', 'd', or 'v'
+	// (from "version"). Select appropriate importer.
+	if len(data) > 0 && data[0] == 'i' {
+		_, pkg, err := gcimporter.IImportData(fset, imports, data[1:], path)
+		return pkg, err
+	}
+
+	_, pkg, err := gcimporter.BImportData(fset, imports, data, path)
+	return pkg, err
+}
+
+// Write writes encoded type information for the specified package to out.
+// The FileSet provides file position information for named objects.
+func Write(out io.Writer, fset *token.FileSet, pkg *types.Package) error {
+	if _, err := io.WriteString(out, "i"); err != nil {
+		return err
+	}
+	return gcimporter.IExportData(out, fset, pkg)
+}
+
+// ReadBundle reads an export bundle from in, decodes it, and returns type
+// information for the packages.
+// File position information is added to fset.
+//
+// ReadBundle may inspect and add to the imports map to ensure that references
+// within the export bundle to other packages are consistent.
+//
+// On return, the state of the reader is undefined.
+//
+// Experimental: This API is experimental and may change in the future.
+func ReadBundle(in io.Reader, fset *token.FileSet, imports map[string]*types.Package) ([]*types.Package, error) {
+	data, err := ioutil.ReadAll(in)
+	if err != nil {
+		return nil, fmt.Errorf("reading export bundle: %v", err)
+	}
+	return gcimporter.IImportBundle(fset, imports, data)
+}
+
+// WriteBundle writes encoded type information for the specified packages to out.
+// The FileSet provides file position information for named objects.
+//
+// Experimental: This API is experimental and may change in the future.
+func WriteBundle(out io.Writer, fset *token.FileSet, pkgs []*types.Package) error {
+	return gcimporter.IExportBundle(out, fset, pkgs)
+}
diff --git a/vendor/golang.org/x/tools/go/gcexportdata/importer.go b/vendor/golang.org/x/tools/go/gcexportdata/importer.go
new file mode 100644
index 00000000..efe221e7
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/gcexportdata/importer.go
@@ -0,0 +1,73 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gcexportdata
+
+import (
+	"fmt"
+	"go/token"
+	"go/types"
+	"os"
+)
+
+// NewImporter returns a new instance of the types.Importer interface
+// that reads type information from export data files written by gc.
+// The Importer also satisfies types.ImporterFrom.
+//
+// Export data files are located using "go build" workspace conventions
+// and the build.Default context.
+//
+// Use this importer instead of go/importer.For("gc", ...) to avoid the
+// version-skew problems described in the documentation of this package,
+// or to control the FileSet or access the imports map populated during
+// package loading.
+//
+func NewImporter(fset *token.FileSet, imports map[string]*types.Package) types.ImporterFrom {
+	return importer{fset, imports}
+}
+
+type importer struct {
+	fset    *token.FileSet
+	imports map[string]*types.Package
+}
+
+func (imp importer) Import(importPath string) (*types.Package, error) {
+	return imp.ImportFrom(importPath, "", 0)
+}
+
+func (imp importer) ImportFrom(importPath, srcDir string, mode types.ImportMode) (_ *types.Package, err error) {
+	filename, path := Find(importPath, srcDir)
+	if filename == "" {
+		if importPath == "unsafe" {
+			// Even for unsafe, call Find first in case
+			// the package was vendored.
+			return types.Unsafe, nil
+		}
+		return nil, fmt.Errorf("can't find import: %s", importPath)
+	}
+
+	if pkg, ok := imp.imports[path]; ok && pkg.Complete() {
+		return pkg, nil // cache hit
+	}
+
+	// open file
+	f, err := os.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	defer func() {
+		f.Close()
+		if err != nil {
+			// add file name to error
+			err = fmt.Errorf("reading export data: %s: %v", filename, err)
+		}
+	}()
+
+	r, err := NewReader(f)
+	if err != nil {
+		return nil, err
+	}
+
+	return Read(r, imp.fset, imp.imports, path)
+}
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/bexport.go b/vendor/golang.org/x/tools/go/internal/gcimporter/bexport.go
new file mode 100644
index 00000000..072005af
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/bexport.go
@@ -0,0 +1,854 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Binary package export.
+// This file was derived from $GOROOT/src/cmd/compile/internal/gc/bexport.go;
+// see that file for specification of the format.
+
+package gcimporter
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"go/ast"
+	"go/constant"
+	"go/token"
+	"go/types"
+	"math"
+	"math/big"
+	"sort"
+	"strings"
+)
+
+// If debugFormat is set, each integer and string value is preceded by a marker
+// and position information in the encoding. This mechanism permits an importer
+// to recognize immediately when it is out of sync. The importer recognizes this
+// mode automatically (i.e., it can import export data produced with debugging
+// support even if debugFormat is not set at the time of import). This mode will
+// lead to massively larger export data (by a factor of 2 to 3) and should only
+// be enabled during development and debugging.
+//
+// NOTE: This flag is the first flag to enable if importing dies because of
+// (suspected) format errors, and whenever a change is made to the format.
+const debugFormat = false // default: false
+
+// If trace is set, debugging output is printed to std out.
+const trace = false // default: false
+
+// Current export format version. Increase with each format change.
+// Note: The latest binary (non-indexed) export format is at version 6.
+//       This exporter is still at level 4, but it doesn't matter since
+//       the binary importer can handle older versions just fine.
+// 6: package height (CL 105038) -- NOT IMPLEMENTED HERE
+// 5: improved position encoding efficiency (issue 20080, CL 41619) -- NOT IMPLEMEMTED HERE
+// 4: type name objects support type aliases, uses aliasTag
+// 3: Go1.8 encoding (same as version 2, aliasTag defined but never used)
+// 2: removed unused bool in ODCL export (compiler only)
+// 1: header format change (more regular), export package for _ struct fields
+// 0: Go1.7 encoding
+const exportVersion = 4
+
+// trackAllTypes enables cycle tracking for all types, not just named
+// types. The existing compiler invariants assume that unnamed types
+// that are not completely set up are not used, or else there are spurious
+// errors.
+// If disabled, only named types are tracked, possibly leading to slightly
+// less efficient encoding in rare cases. It also prevents the export of
+// some corner-case type declarations (but those are not handled correctly
+// with with the textual export format either).
+// TODO(gri) enable and remove once issues caused by it are fixed
+const trackAllTypes = false
+
+type exporter struct {
+	fset *token.FileSet
+	out  bytes.Buffer
+
+	// object -> index maps, indexed in order of serialization
+	strIndex map[string]int
+	pkgIndex map[*types.Package]int
+	typIndex map[types.Type]int
+
+	// position encoding
+	posInfoFormat bool
+	prevFile      string
+	prevLine      int
+
+	// debugging support
+	written int // bytes written
+	indent  int // for trace
+}
+
+// internalError represents an error generated inside this package.
+type internalError string
+
+func (e internalError) Error() string { return "gcimporter: " + string(e) }
+
+func internalErrorf(format string, args ...interface{}) error {
+	return internalError(fmt.Sprintf(format, args...))
+}
+
+// BExportData returns binary export data for pkg.
+// If no file set is provided, position info will be missing.
+func BExportData(fset *token.FileSet, pkg *types.Package) (b []byte, err error) {
+	if !debug {
+		defer func() {
+			if e := recover(); e != nil {
+				if ierr, ok := e.(internalError); ok {
+					err = ierr
+					return
+				}
+				// Not an internal error; panic again.
+				panic(e)
+			}
+		}()
+	}
+
+	p := exporter{
+		fset:          fset,
+		strIndex:      map[string]int{"": 0}, // empty string is mapped to 0
+		pkgIndex:      make(map[*types.Package]int),
+		typIndex:      make(map[types.Type]int),
+		posInfoFormat: true, // TODO(gri) might become a flag, eventually
+	}
+
+	// write version info
+	// The version string must start with "version %d" where %d is the version
+	// number. Additional debugging information may follow after a blank; that
+	// text is ignored by the importer.
+	p.rawStringln(fmt.Sprintf("version %d", exportVersion))
+	var debug string
+	if debugFormat {
+		debug = "debug"
+	}
+	p.rawStringln(debug) // cannot use p.bool since it's affected by debugFormat; also want to see this clearly
+	p.bool(trackAllTypes)
+	p.bool(p.posInfoFormat)
+
+	// --- generic export data ---
+
+	// populate type map with predeclared "known" types
+	for index, typ := range predeclared() {
+		p.typIndex[typ] = index
+	}
+	if len(p.typIndex) != len(predeclared()) {
+		return nil, internalError("duplicate entries in type map?")
+	}
+
+	// write package data
+	p.pkg(pkg, true)
+	if trace {
+		p.tracef("\n")
+	}
+
+	// write objects
+	objcount := 0
+	scope := pkg.Scope()
+	for _, name := range scope.Names() {
+		if !ast.IsExported(name) {
+			continue
+		}
+		if trace {
+			p.tracef("\n")
+		}
+		p.obj(scope.Lookup(name))
+		objcount++
+	}
+
+	// indicate end of list
+	if trace {
+		p.tracef("\n")
+	}
+	p.tag(endTag)
+
+	// for self-verification only (redundant)
+	p.int(objcount)
+
+	if trace {
+		p.tracef("\n")
+	}
+
+	// --- end of export data ---
+
+	return p.out.Bytes(), nil
+}
+
+func (p *exporter) pkg(pkg *types.Package, emptypath bool) {
+	if pkg == nil {
+		panic(internalError("unexpected nil pkg"))
+	}
+
+	// if we saw the package before, write its index (>= 0)
+	if i, ok := p.pkgIndex[pkg]; ok {
+		p.index('P', i)
+		return
+	}
+
+	// otherwise, remember the package, write the package tag (< 0) and package data
+	if trace {
+		p.tracef("P%d = { ", len(p.pkgIndex))
+		defer p.tracef("} ")
+	}
+	p.pkgIndex[pkg] = len(p.pkgIndex)
+
+	p.tag(packageTag)
+	p.string(pkg.Name())
+	if emptypath {
+		p.string("")
+	} else {
+		p.string(pkg.Path())
+	}
+}
+
+func (p *exporter) obj(obj types.Object) {
+	switch obj := obj.(type) {
+	case *types.Const:
+		p.tag(constTag)
+		p.pos(obj)
+		p.qualifiedName(obj)
+		p.typ(obj.Type())
+		p.value(obj.Val())
+
+	case *types.TypeName:
+		if obj.IsAlias() {
+			p.tag(aliasTag)
+			p.pos(obj)
+			p.qualifiedName(obj)
+		} else {
+			p.tag(typeTag)
+		}
+		p.typ(obj.Type())
+
+	case *types.Var:
+		p.tag(varTag)
+		p.pos(obj)
+		p.qualifiedName(obj)
+		p.typ(obj.Type())
+
+	case *types.Func:
+		p.tag(funcTag)
+		p.pos(obj)
+		p.qualifiedName(obj)
+		sig := obj.Type().(*types.Signature)
+		p.paramList(sig.Params(), sig.Variadic())
+		p.paramList(sig.Results(), false)
+
+	default:
+		panic(internalErrorf("unexpected object %v (%T)", obj, obj))
+	}
+}
+
+func (p *exporter) pos(obj types.Object) {
+	if !p.posInfoFormat {
+		return
+	}
+
+	file, line := p.fileLine(obj)
+	if file == p.prevFile {
+		// common case: write line delta
+		// delta == 0 means different file or no line change
+		delta := line - p.prevLine
+		p.int(delta)
+		if delta == 0 {
+			p.int(-1) // -1 means no file change
+		}
+	} else {
+		// different file
+		p.int(0)
+		// Encode filename as length of common prefix with previous
+		// filename, followed by (possibly empty) suffix. Filenames
+		// frequently share path prefixes, so this can save a lot
+		// of space and make export data size less dependent on file
+		// path length. The suffix is unlikely to be empty because
+		// file names tend to end in ".go".
+		n := commonPrefixLen(p.prevFile, file)
+		p.int(n)           // n >= 0
+		p.string(file[n:]) // write suffix only
+		p.prevFile = file
+		p.int(line)
+	}
+	p.prevLine = line
+}
+
+func (p *exporter) fileLine(obj types.Object) (file string, line int) {
+	if p.fset != nil {
+		pos := p.fset.Position(obj.Pos())
+		file = pos.Filename
+		line = pos.Line
+	}
+	return
+}
+
+func commonPrefixLen(a, b string) int {
+	if len(a) > len(b) {
+		a, b = b, a
+	}
+	// len(a) <= len(b)
+	i := 0
+	for i < len(a) && a[i] == b[i] {
+		i++
+	}
+	return i
+}
+
+func (p *exporter) qualifiedName(obj types.Object) {
+	p.string(obj.Name())
+	p.pkg(obj.Pkg(), false)
+}
+
+func (p *exporter) typ(t types.Type) {
+	if t == nil {
+		panic(internalError("nil type"))
+	}
+
+	// Possible optimization: Anonymous pointer types *T where
+	// T is a named type are common. We could canonicalize all
+	// such types *T to a single type PT = *T. This would lead
+	// to at most one *T entry in typIndex, and all future *T's
+	// would be encoded as the respective index directly. Would
+	// save 1 byte (pointerTag) per *T and reduce the typIndex
+	// size (at the cost of a canonicalization map). We can do
+	// this later, without encoding format change.
+
+	// if we saw the type before, write its index (>= 0)
+	if i, ok := p.typIndex[t]; ok {
+		p.index('T', i)
+		return
+	}
+
+	// otherwise, remember the type, write the type tag (< 0) and type data
+	if trackAllTypes {
+		if trace {
+			p.tracef("T%d = {>\n", len(p.typIndex))
+			defer p.tracef("<\n} ")
+		}
+		p.typIndex[t] = len(p.typIndex)
+	}
+
+	switch t := t.(type) {
+	case *types.Named:
+		if !trackAllTypes {
+			// if we don't track all types, track named types now
+			p.typIndex[t] = len(p.typIndex)
+		}
+
+		p.tag(namedTag)
+		p.pos(t.Obj())
+		p.qualifiedName(t.Obj())
+		p.typ(t.Underlying())
+		if !types.IsInterface(t) {
+			p.assocMethods(t)
+		}
+
+	case *types.Array:
+		p.tag(arrayTag)
+		p.int64(t.Len())
+		p.typ(t.Elem())
+
+	case *types.Slice:
+		p.tag(sliceTag)
+		p.typ(t.Elem())
+
+	case *dddSlice:
+		p.tag(dddTag)
+		p.typ(t.elem)
+
+	case *types.Struct:
+		p.tag(structTag)
+		p.fieldList(t)
+
+	case *types.Pointer:
+		p.tag(pointerTag)
+		p.typ(t.Elem())
+
+	case *types.Signature:
+		p.tag(signatureTag)
+		p.paramList(t.Params(), t.Variadic())
+		p.paramList(t.Results(), false)
+
+	case *types.Interface:
+		p.tag(interfaceTag)
+		p.iface(t)
+
+	case *types.Map:
+		p.tag(mapTag)
+		p.typ(t.Key())
+		p.typ(t.Elem())
+
+	case *types.Chan:
+		p.tag(chanTag)
+		p.int(int(3 - t.Dir())) // hack
+		p.typ(t.Elem())
+
+	default:
+		panic(internalErrorf("unexpected type %T: %s", t, t))
+	}
+}
+
+func (p *exporter) assocMethods(named *types.Named) {
+	// Sort methods (for determinism).
+	var methods []*types.Func
+	for i := 0; i < named.NumMethods(); i++ {
+		methods = append(methods, named.Method(i))
+	}
+	sort.Sort(methodsByName(methods))
+
+	p.int(len(methods))
+
+	if trace && methods != nil {
+		p.tracef("associated methods {>\n")
+	}
+
+	for i, m := range methods {
+		if trace && i > 0 {
+			p.tracef("\n")
+		}
+
+		p.pos(m)
+		name := m.Name()
+		p.string(name)
+		if !exported(name) {
+			p.pkg(m.Pkg(), false)
+		}
+
+		sig := m.Type().(*types.Signature)
+		p.paramList(types.NewTuple(sig.Recv()), false)
+		p.paramList(sig.Params(), sig.Variadic())
+		p.paramList(sig.Results(), false)
+		p.int(0) // dummy value for go:nointerface pragma - ignored by importer
+	}
+
+	if trace && methods != nil {
+		p.tracef("<\n} ")
+	}
+}
+
+type methodsByName []*types.Func
+
+func (x methodsByName) Len() int           { return len(x) }
+func (x methodsByName) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
+func (x methodsByName) Less(i, j int) bool { return x[i].Name() < x[j].Name() }
+
+func (p *exporter) fieldList(t *types.Struct) {
+	if trace && t.NumFields() > 0 {
+		p.tracef("fields {>\n")
+		defer p.tracef("<\n} ")
+	}
+
+	p.int(t.NumFields())
+	for i := 0; i < t.NumFields(); i++ {
+		if trace && i > 0 {
+			p.tracef("\n")
+		}
+		p.field(t.Field(i))
+		p.string(t.Tag(i))
+	}
+}
+
+func (p *exporter) field(f *types.Var) {
+	if !f.IsField() {
+		panic(internalError("field expected"))
+	}
+
+	p.pos(f)
+	p.fieldName(f)
+	p.typ(f.Type())
+}
+
+func (p *exporter) iface(t *types.Interface) {
+	// TODO(gri): enable importer to load embedded interfaces,
+	// then emit Embeddeds and ExplicitMethods separately here.
+	p.int(0)
+
+	n := t.NumMethods()
+	if trace && n > 0 {
+		p.tracef("methods {>\n")
+		defer p.tracef("<\n} ")
+	}
+	p.int(n)
+	for i := 0; i < n; i++ {
+		if trace && i > 0 {
+			p.tracef("\n")
+		}
+		p.method(t.Method(i))
+	}
+}
+
+func (p *exporter) method(m *types.Func) {
+	sig := m.Type().(*types.Signature)
+	if sig.Recv() == nil {
+		panic(internalError("method expected"))
+	}
+
+	p.pos(m)
+	p.string(m.Name())
+	if m.Name() != "_" && !ast.IsExported(m.Name()) {
+		p.pkg(m.Pkg(), false)
+	}
+
+	// interface method; no need to encode receiver.
+	p.paramList(sig.Params(), sig.Variadic())
+	p.paramList(sig.Results(), false)
+}
+
+func (p *exporter) fieldName(f *types.Var) {
+	name := f.Name()
+
+	if f.Anonymous() {
+		// anonymous field - we distinguish between 3 cases:
+		// 1) field name matches base type name and is exported
+		// 2) field name matches base type name and is not exported
+		// 3) field name doesn't match base type name (alias name)
+		bname := basetypeName(f.Type())
+		if name == bname {
+			if ast.IsExported(name) {
+				name = "" // 1) we don't need to know the field name or package
+			} else {
+				name = "?" // 2) use unexported name "?" to force package export
+			}
+		} else {
+			// 3) indicate alias and export name as is
+			// (this requires an extra "@" but this is a rare case)
+			p.string("@")
+		}
+	}
+
+	p.string(name)
+	if name != "" && !ast.IsExported(name) {
+		p.pkg(f.Pkg(), false)
+	}
+}
+
+func basetypeName(typ types.Type) string {
+	switch typ := deref(typ).(type) {
+	case *types.Basic:
+		return typ.Name()
+	case *types.Named:
+		return typ.Obj().Name()
+	default:
+		return "" // unnamed type
+	}
+}
+
+func (p *exporter) paramList(params *types.Tuple, variadic bool) {
+	// use negative length to indicate unnamed parameters
+	// (look at the first parameter only since either all
+	// names are present or all are absent)
+	n := params.Len()
+	if n > 0 && params.At(0).Name() == "" {
+		n = -n
+	}
+	p.int(n)
+	for i := 0; i < params.Len(); i++ {
+		q := params.At(i)
+		t := q.Type()
+		if variadic && i == params.Len()-1 {
+			t = &dddSlice{t.(*types.Slice).Elem()}
+		}
+		p.typ(t)
+		if n > 0 {
+			name := q.Name()
+			p.string(name)
+			if name != "_" {
+				p.pkg(q.Pkg(), false)
+			}
+		}
+		p.string("") // no compiler-specific info
+	}
+}
+
+func (p *exporter) value(x constant.Value) {
+	if trace {
+		p.tracef("= ")
+	}
+
+	switch x.Kind() {
+	case constant.Bool:
+		tag := falseTag
+		if constant.BoolVal(x) {
+			tag = trueTag
+		}
+		p.tag(tag)
+
+	case constant.Int:
+		if v, exact := constant.Int64Val(x); exact {
+			// common case: x fits into an int64 - use compact encoding
+			p.tag(int64Tag)
+			p.int64(v)
+			return
+		}
+		// uncommon case: large x - use float encoding
+		// (powers of 2 will be encoded efficiently with exponent)
+		p.tag(floatTag)
+		p.float(constant.ToFloat(x))
+
+	case constant.Float:
+		p.tag(floatTag)
+		p.float(x)
+
+	case constant.Complex:
+		p.tag(complexTag)
+		p.float(constant.Real(x))
+		p.float(constant.Imag(x))
+
+	case constant.String:
+		p.tag(stringTag)
+		p.string(constant.StringVal(x))
+
+	case constant.Unknown:
+		// package contains type errors
+		p.tag(unknownTag)
+
+	default:
+		panic(internalErrorf("unexpected value %v (%T)", x, x))
+	}
+}
+
+func (p *exporter) float(x constant.Value) {
+	if x.Kind() != constant.Float {
+		panic(internalErrorf("unexpected constant %v, want float", x))
+	}
+	// extract sign (there is no -0)
+	sign := constant.Sign(x)
+	if sign == 0 {
+		// x == 0
+		p.int(0)
+		return
+	}
+	// x != 0
+
+	var f big.Float
+	if v, exact := constant.Float64Val(x); exact {
+		// float64
+		f.SetFloat64(v)
+	} else if num, denom := constant.Num(x), constant.Denom(x); num.Kind() == constant.Int {
+		// TODO(gri): add big.Rat accessor to constant.Value.
+		r := valueToRat(num)
+		f.SetRat(r.Quo(r, valueToRat(denom)))
+	} else {
+		// Value too large to represent as a fraction => inaccessible.
+		// TODO(gri): add big.Float accessor to constant.Value.
+		f.SetFloat64(math.MaxFloat64) // FIXME
+	}
+
+	// extract exponent such that 0.5 <= m < 1.0
+	var m big.Float
+	exp := f.MantExp(&m)
+
+	// extract mantissa as *big.Int
+	// - set exponent large enough so mant satisfies mant.IsInt()
+	// - get *big.Int from mant
+	m.SetMantExp(&m, int(m.MinPrec()))
+	mant, acc := m.Int(nil)
+	if acc != big.Exact {
+		panic(internalError("internal error"))
+	}
+
+	p.int(sign)
+	p.int(exp)
+	p.string(string(mant.Bytes()))
+}
+
+func valueToRat(x constant.Value) *big.Rat {
+	// Convert little-endian to big-endian.
+	// I can't believe this is necessary.
+	bytes := constant.Bytes(x)
+	for i := 0; i < len(bytes)/2; i++ {
+		bytes[i], bytes[len(bytes)-1-i] = bytes[len(bytes)-1-i], bytes[i]
+	}
+	return new(big.Rat).SetInt(new(big.Int).SetBytes(bytes))
+}
+
+func (p *exporter) bool(b bool) bool {
+	if trace {
+		p.tracef("[")
+		defer p.tracef("= %v] ", b)
+	}
+
+	x := 0
+	if b {
+		x = 1
+	}
+	p.int(x)
+	return b
+}
+
+// ----------------------------------------------------------------------------
+// Low-level encoders
+
+func (p *exporter) index(marker byte, index int) {
+	if index < 0 {
+		panic(internalError("invalid index < 0"))
+	}
+	if debugFormat {
+		p.marker('t')
+	}
+	if trace {
+		p.tracef("%c%d ", marker, index)
+	}
+	p.rawInt64(int64(index))
+}
+
+func (p *exporter) tag(tag int) {
+	if tag >= 0 {
+		panic(internalError("invalid tag >= 0"))
+	}
+	if debugFormat {
+		p.marker('t')
+	}
+	if trace {
+		p.tracef("%s ", tagString[-tag])
+	}
+	p.rawInt64(int64(tag))
+}
+
+func (p *exporter) int(x int) {
+	p.int64(int64(x))
+}
+
+func (p *exporter) int64(x int64) {
+	if debugFormat {
+		p.marker('i')
+	}
+	if trace {
+		p.tracef("%d ", x)
+	}
+	p.rawInt64(x)
+}
+
+func (p *exporter) string(s string) {
+	if debugFormat {
+		p.marker('s')
+	}
+	if trace {
+		p.tracef("%q ", s)
+	}
+	// if we saw the string before, write its index (>= 0)
+	// (the empty string is mapped to 0)
+	if i, ok := p.strIndex[s]; ok {
+		p.rawInt64(int64(i))
+		return
+	}
+	// otherwise, remember string and write its negative length and bytes
+	p.strIndex[s] = len(p.strIndex)
+	p.rawInt64(-int64(len(s)))
+	for i := 0; i < len(s); i++ {
+		p.rawByte(s[i])
+	}
+}
+
+// marker emits a marker byte and position information which makes
+// it easy for a reader to detect if it is "out of sync". Used for
+// debugFormat format only.
+func (p *exporter) marker(m byte) {
+	p.rawByte(m)
+	// Enable this for help tracking down the location
+	// of an incorrect marker when running in debugFormat.
+	if false && trace {
+		p.tracef("#%d ", p.written)
+	}
+	p.rawInt64(int64(p.written))
+}
+
+// rawInt64 should only be used by low-level encoders.
+func (p *exporter) rawInt64(x int64) {
+	var tmp [binary.MaxVarintLen64]byte
+	n := binary.PutVarint(tmp[:], x)
+	for i := 0; i < n; i++ {
+		p.rawByte(tmp[i])
+	}
+}
+
+// rawStringln should only be used to emit the initial version string.
+func (p *exporter) rawStringln(s string) {
+	for i := 0; i < len(s); i++ {
+		p.rawByte(s[i])
+	}
+	p.rawByte('\n')
+}
+
+// rawByte is the bottleneck interface to write to p.out.
+// rawByte escapes b as follows (any encoding does that
+// hides '$'):
+//
+//	'$'  => '|' 'S'
+//	'|'  => '|' '|'
+//
+// Necessary so other tools can find the end of the
+// export data by searching for "$$".
+// rawByte should only be used by low-level encoders.
+func (p *exporter) rawByte(b byte) {
+	switch b {
+	case '$':
+		// write '$' as '|' 'S'
+		b = 'S'
+		fallthrough
+	case '|':
+		// write '|' as '|' '|'
+		p.out.WriteByte('|')
+		p.written++
+	}
+	p.out.WriteByte(b)
+	p.written++
+}
+
+// tracef is like fmt.Printf but it rewrites the format string
+// to take care of indentation.
+func (p *exporter) tracef(format string, args ...interface{}) {
+	if strings.ContainsAny(format, "<>\n") {
+		var buf bytes.Buffer
+		for i := 0; i < len(format); i++ {
+			// no need to deal with runes
+			ch := format[i]
+			switch ch {
+			case '>':
+				p.indent++
+				continue
+			case '<':
+				p.indent--
+				continue
+			}
+			buf.WriteByte(ch)
+			if ch == '\n' {
+				for j := p.indent; j > 0; j-- {
+					buf.WriteString(".  ")
+				}
+			}
+		}
+		format = buf.String()
+	}
+	fmt.Printf(format, args...)
+}
+
+// Debugging support.
+// (tagString is only used when tracing is enabled)
+var tagString = [...]string{
+	// Packages
+	-packageTag: "package",
+
+	// Types
+	-namedTag:     "named type",
+	-arrayTag:     "array",
+	-sliceTag:     "slice",
+	-dddTag:       "ddd",
+	-structTag:    "struct",
+	-pointerTag:   "pointer",
+	-signatureTag: "signature",
+	-interfaceTag: "interface",
+	-mapTag:       "map",
+	-chanTag:      "chan",
+
+	// Values
+	-falseTag:    "false",
+	-trueTag:     "true",
+	-int64Tag:    "int64",
+	-floatTag:    "float",
+	-fractionTag: "fraction",
+	-complexTag:  "complex",
+	-stringTag:   "string",
+	-unknownTag:  "unknown",
+
+	// Type aliases
+	-aliasTag: "alias",
+}
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/bimport.go b/vendor/golang.org/x/tools/go/internal/gcimporter/bimport.go
new file mode 100644
index 00000000..b0231200
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/bimport.go
@@ -0,0 +1,1040 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file is a copy of $GOROOT/src/go/internal/gcimporter/bimport.go.
+
+package gcimporter
+
+import (
+	"encoding/binary"
+	"fmt"
+	"go/constant"
+	"go/token"
+	"go/types"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"unicode"
+	"unicode/utf8"
+)
+
+type importer struct {
+	imports    map[string]*types.Package
+	data       []byte
+	importpath string
+	buf        []byte // for reading strings
+	version    int    // export format version
+
+	// object lists
+	strList       []string           // in order of appearance
+	pathList      []string           // in order of appearance
+	pkgList       []*types.Package   // in order of appearance
+	typList       []types.Type       // in order of appearance
+	interfaceList []*types.Interface // for delayed completion only
+	trackAllTypes bool
+
+	// position encoding
+	posInfoFormat bool
+	prevFile      string
+	prevLine      int
+	fake          fakeFileSet
+
+	// debugging support
+	debugFormat bool
+	read        int // bytes read
+}
+
+// BImportData imports a package from the serialized package data
+// and returns the number of bytes consumed and a reference to the package.
+// If the export data version is not recognized or the format is otherwise
+// compromised, an error is returned.
+func BImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (_ int, pkg *types.Package, err error) {
+	// catch panics and return them as errors
+	const currentVersion = 6
+	version := -1 // unknown version
+	defer func() {
+		if e := recover(); e != nil {
+			// Return a (possibly nil or incomplete) package unchanged (see #16088).
+			if version > currentVersion {
+				err = fmt.Errorf("cannot import %q (%v), export data is newer version - update tool", path, e)
+			} else {
+				err = fmt.Errorf("cannot import %q (%v), possibly version skew - reinstall package", path, e)
+			}
+		}
+	}()
+
+	p := importer{
+		imports:    imports,
+		data:       data,
+		importpath: path,
+		version:    version,
+		strList:    []string{""}, // empty string is mapped to 0
+		pathList:   []string{""}, // empty string is mapped to 0
+		fake: fakeFileSet{
+			fset:  fset,
+			files: make(map[string]*token.File),
+		},
+	}
+
+	// read version info
+	var versionstr string
+	if b := p.rawByte(); b == 'c' || b == 'd' {
+		// Go1.7 encoding; first byte encodes low-level
+		// encoding format (compact vs debug).
+		// For backward-compatibility only (avoid problems with
+		// old installed packages). Newly compiled packages use
+		// the extensible format string.
+		// TODO(gri) Remove this support eventually; after Go1.8.
+		if b == 'd' {
+			p.debugFormat = true
+		}
+		p.trackAllTypes = p.rawByte() == 'a'
+		p.posInfoFormat = p.int() != 0
+		versionstr = p.string()
+		if versionstr == "v1" {
+			version = 0
+		}
+	} else {
+		// Go1.8 extensible encoding
+		// read version string and extract version number (ignore anything after the version number)
+		versionstr = p.rawStringln(b)
+		if s := strings.SplitN(versionstr, " ", 3); len(s) >= 2 && s[0] == "version" {
+			if v, err := strconv.Atoi(s[1]); err == nil && v > 0 {
+				version = v
+			}
+		}
+	}
+	p.version = version
+
+	// read version specific flags - extend as necessary
+	switch p.version {
+	// case currentVersion:
+	// 	...
+	//	fallthrough
+	case currentVersion, 5, 4, 3, 2, 1:
+		p.debugFormat = p.rawStringln(p.rawByte()) == "debug"
+		p.trackAllTypes = p.int() != 0
+		p.posInfoFormat = p.int() != 0
+	case 0:
+		// Go1.7 encoding format - nothing to do here
+	default:
+		errorf("unknown bexport format version %d (%q)", p.version, versionstr)
+	}
+
+	// --- generic export data ---
+
+	// populate typList with predeclared "known" types
+	p.typList = append(p.typList, predeclared()...)
+
+	// read package data
+	pkg = p.pkg()
+
+	// read objects of phase 1 only (see cmd/compile/internal/gc/bexport.go)
+	objcount := 0
+	for {
+		tag := p.tagOrIndex()
+		if tag == endTag {
+			break
+		}
+		p.obj(tag)
+		objcount++
+	}
+
+	// self-verification
+	if count := p.int(); count != objcount {
+		errorf("got %d objects; want %d", objcount, count)
+	}
+
+	// ignore compiler-specific import data
+
+	// complete interfaces
+	// TODO(gri) re-investigate if we still need to do this in a delayed fashion
+	for _, typ := range p.interfaceList {
+		typ.Complete()
+	}
+
+	// record all referenced packages as imports
+	list := append(([]*types.Package)(nil), p.pkgList[1:]...)
+	sort.Sort(byPath(list))
+	pkg.SetImports(list)
+
+	// package was imported completely and without errors
+	pkg.MarkComplete()
+
+	return p.read, pkg, nil
+}
+
+func errorf(format string, args ...interface{}) {
+	panic(fmt.Sprintf(format, args...))
+}
+
+func (p *importer) pkg() *types.Package {
+	// if the package was seen before, i is its index (>= 0)
+	i := p.tagOrIndex()
+	if i >= 0 {
+		return p.pkgList[i]
+	}
+
+	// otherwise, i is the package tag (< 0)
+	if i != packageTag {
+		errorf("unexpected package tag %d version %d", i, p.version)
+	}
+
+	// read package data
+	name := p.string()
+	var path string
+	if p.version >= 5 {
+		path = p.path()
+	} else {
+		path = p.string()
+	}
+	if p.version >= 6 {
+		p.int() // package height; unused by go/types
+	}
+
+	// we should never see an empty package name
+	if name == "" {
+		errorf("empty package name in import")
+	}
+
+	// an empty path denotes the package we are currently importing;
+	// it must be the first package we see
+	if (path == "") != (len(p.pkgList) == 0) {
+		errorf("package path %q for pkg index %d", path, len(p.pkgList))
+	}
+
+	// if the package was imported before, use that one; otherwise create a new one
+	if path == "" {
+		path = p.importpath
+	}
+	pkg := p.imports[path]
+	if pkg == nil {
+		pkg = types.NewPackage(path, name)
+		p.imports[path] = pkg
+	} else if pkg.Name() != name {
+		errorf("conflicting names %s and %s for package %q", pkg.Name(), name, path)
+	}
+	p.pkgList = append(p.pkgList, pkg)
+
+	return pkg
+}
+
+// objTag returns the tag value for each object kind.
+func objTag(obj types.Object) int {
+	switch obj.(type) {
+	case *types.Const:
+		return constTag
+	case *types.TypeName:
+		return typeTag
+	case *types.Var:
+		return varTag
+	case *types.Func:
+		return funcTag
+	default:
+		errorf("unexpected object: %v (%T)", obj, obj) // panics
+		panic("unreachable")
+	}
+}
+
+func sameObj(a, b types.Object) bool {
+	// Because unnamed types are not canonicalized, we cannot simply compare types for
+	// (pointer) identity.
+	// Ideally we'd check equality of constant values as well, but this is good enough.
+	return objTag(a) == objTag(b) && types.Identical(a.Type(), b.Type())
+}
+
+func (p *importer) declare(obj types.Object) {
+	pkg := obj.Pkg()
+	if alt := pkg.Scope().Insert(obj); alt != nil {
+		// This can only trigger if we import a (non-type) object a second time.
+		// Excluding type aliases, this cannot happen because 1) we only import a package
+		// once; and b) we ignore compiler-specific export data which may contain
+		// functions whose inlined function bodies refer to other functions that
+		// were already imported.
+		// However, type aliases require reexporting the original type, so we need
+		// to allow it (see also the comment in cmd/compile/internal/gc/bimport.go,
+		// method importer.obj, switch case importing functions).
+		// TODO(gri) review/update this comment once the gc compiler handles type aliases.
+		if !sameObj(obj, alt) {
+			errorf("inconsistent import:\n\t%v\npreviously imported as:\n\t%v\n", obj, alt)
+		}
+	}
+}
+
+func (p *importer) obj(tag int) {
+	switch tag {
+	case constTag:
+		pos := p.pos()
+		pkg, name := p.qualifiedName()
+		typ := p.typ(nil, nil)
+		val := p.value()
+		p.declare(types.NewConst(pos, pkg, name, typ, val))
+
+	case aliasTag:
+		// TODO(gri) verify type alias hookup is correct
+		pos := p.pos()
+		pkg, name := p.qualifiedName()
+		typ := p.typ(nil, nil)
+		p.declare(types.NewTypeName(pos, pkg, name, typ))
+
+	case typeTag:
+		p.typ(nil, nil)
+
+	case varTag:
+		pos := p.pos()
+		pkg, name := p.qualifiedName()
+		typ := p.typ(nil, nil)
+		p.declare(types.NewVar(pos, pkg, name, typ))
+
+	case funcTag:
+		pos := p.pos()
+		pkg, name := p.qualifiedName()
+		params, isddd := p.paramList()
+		result, _ := p.paramList()
+		sig := types.NewSignature(nil, params, result, isddd)
+		p.declare(types.NewFunc(pos, pkg, name, sig))
+
+	default:
+		errorf("unexpected object tag %d", tag)
+	}
+}
+
+const deltaNewFile = -64 // see cmd/compile/internal/gc/bexport.go
+
+func (p *importer) pos() token.Pos {
+	if !p.posInfoFormat {
+		return token.NoPos
+	}
+
+	file := p.prevFile
+	line := p.prevLine
+	delta := p.int()
+	line += delta
+	if p.version >= 5 {
+		if delta == deltaNewFile {
+			if n := p.int(); n >= 0 {
+				// file changed
+				file = p.path()
+				line = n
+			}
+		}
+	} else {
+		if delta == 0 {
+			if n := p.int(); n >= 0 {
+				// file changed
+				file = p.prevFile[:n] + p.string()
+				line = p.int()
+			}
+		}
+	}
+	p.prevFile = file
+	p.prevLine = line
+
+	return p.fake.pos(file, line, 0)
+}
+
+// Synthesize a token.Pos
+type fakeFileSet struct {
+	fset  *token.FileSet
+	files map[string]*token.File
+}
+
+func (s *fakeFileSet) pos(file string, line, column int) token.Pos {
+	// TODO(mdempsky): Make use of column.
+
+	// Since we don't know the set of needed file positions, we
+	// reserve maxlines positions per file.
+	const maxlines = 64 * 1024
+	f := s.files[file]
+	if f == nil {
+		f = s.fset.AddFile(file, -1, maxlines)
+		s.files[file] = f
+		// Allocate the fake linebreak indices on first use.
+		// TODO(adonovan): opt: save ~512KB using a more complex scheme?
+		fakeLinesOnce.Do(func() {
+			fakeLines = make([]int, maxlines)
+			for i := range fakeLines {
+				fakeLines[i] = i
+			}
+		})
+		f.SetLines(fakeLines)
+	}
+
+	if line > maxlines {
+		line = 1
+	}
+
+	// Treat the file as if it contained only newlines
+	// and column=1: use the line number as the offset.
+	return f.Pos(line - 1)
+}
+
+var (
+	fakeLines     []int
+	fakeLinesOnce sync.Once
+)
+
+func (p *importer) qualifiedName() (pkg *types.Package, name string) {
+	name = p.string()
+	pkg = p.pkg()
+	return
+}
+
+func (p *importer) record(t types.Type) {
+	p.typList = append(p.typList, t)
+}
+
+// A dddSlice is a types.Type representing ...T parameters.
+// It only appears for parameter types and does not escape
+// the importer.
+type dddSlice struct {
+	elem types.Type
+}
+
+func (t *dddSlice) Underlying() types.Type { return t }
+func (t *dddSlice) String() string         { return "..." + t.elem.String() }
+
+// parent is the package which declared the type; parent == nil means
+// the package currently imported. The parent package is needed for
+// exported struct fields and interface methods which don't contain
+// explicit package information in the export data.
+//
+// A non-nil tname is used as the "owner" of the result type; i.e.,
+// the result type is the underlying type of tname. tname is used
+// to give interface methods a named receiver type where possible.
+func (p *importer) typ(parent *types.Package, tname *types.Named) types.Type {
+	// if the type was seen before, i is its index (>= 0)
+	i := p.tagOrIndex()
+	if i >= 0 {
+		return p.typList[i]
+	}
+
+	// otherwise, i is the type tag (< 0)
+	switch i {
+	case namedTag:
+		// read type object
+		pos := p.pos()
+		parent, name := p.qualifiedName()
+		scope := parent.Scope()
+		obj := scope.Lookup(name)
+
+		// if the object doesn't exist yet, create and insert it
+		if obj == nil {
+			obj = types.NewTypeName(pos, parent, name, nil)
+			scope.Insert(obj)
+		}
+
+		if _, ok := obj.(*types.TypeName); !ok {
+			errorf("pkg = %s, name = %s => %s", parent, name, obj)
+		}
+
+		// associate new named type with obj if it doesn't exist yet
+		t0 := types.NewNamed(obj.(*types.TypeName), nil, nil)
+
+		// but record the existing type, if any
+		tname := obj.Type().(*types.Named) // tname is either t0 or the existing type
+		p.record(tname)
+
+		// read underlying type
+		t0.SetUnderlying(p.typ(parent, t0))
+
+		// interfaces don't have associated methods
+		if types.IsInterface(t0) {
+			return tname
+		}
+
+		// read associated methods
+		for i := p.int(); i > 0; i-- {
+			// TODO(gri) replace this with something closer to fieldName
+			pos := p.pos()
+			name := p.string()
+			if !exported(name) {
+				p.pkg()
+			}
+
+			recv, _ := p.paramList() // TODO(gri) do we need a full param list for the receiver?
+			params, isddd := p.paramList()
+			result, _ := p.paramList()
+			p.int() // go:nointerface pragma - discarded
+
+			sig := types.NewSignature(recv.At(0), params, result, isddd)
+			t0.AddMethod(types.NewFunc(pos, parent, name, sig))
+		}
+
+		return tname
+
+	case arrayTag:
+		t := new(types.Array)
+		if p.trackAllTypes {
+			p.record(t)
+		}
+
+		n := p.int64()
+		*t = *types.NewArray(p.typ(parent, nil), n)
+		return t
+
+	case sliceTag:
+		t := new(types.Slice)
+		if p.trackAllTypes {
+			p.record(t)
+		}
+
+		*t = *types.NewSlice(p.typ(parent, nil))
+		return t
+
+	case dddTag:
+		t := new(dddSlice)
+		if p.trackAllTypes {
+			p.record(t)
+		}
+
+		t.elem = p.typ(parent, nil)
+		return t
+
+	case structTag:
+		t := new(types.Struct)
+		if p.trackAllTypes {
+			p.record(t)
+		}
+
+		*t = *types.NewStruct(p.fieldList(parent))
+		return t
+
+	case pointerTag:
+		t := new(types.Pointer)
+		if p.trackAllTypes {
+			p.record(t)
+		}
+
+		*t = *types.NewPointer(p.typ(parent, nil))
+		return t
+
+	case signatureTag:
+		t := new(types.Signature)
+		if p.trackAllTypes {
+			p.record(t)
+		}
+
+		params, isddd := p.paramList()
+		result, _ := p.paramList()
+		*t = *types.NewSignature(nil, params, result, isddd)
+		return t
+
+	case interfaceTag:
+		// Create a dummy entry in the type list. This is safe because we
+		// cannot expect the interface type to appear in a cycle, as any
+		// such cycle must contain a named type which would have been
+		// first defined earlier.
+		// TODO(gri) Is this still true now that we have type aliases?
+		// See issue #23225.
+		n := len(p.typList)
+		if p.trackAllTypes {
+			p.record(nil)
+		}
+
+		var embeddeds []types.Type
+		for n := p.int(); n > 0; n-- {
+			p.pos()
+			embeddeds = append(embeddeds, p.typ(parent, nil))
+		}
+
+		t := newInterface(p.methodList(parent, tname), embeddeds)
+		p.interfaceList = append(p.interfaceList, t)
+		if p.trackAllTypes {
+			p.typList[n] = t
+		}
+		return t
+
+	case mapTag:
+		t := new(types.Map)
+		if p.trackAllTypes {
+			p.record(t)
+		}
+
+		key := p.typ(parent, nil)
+		val := p.typ(parent, nil)
+		*t = *types.NewMap(key, val)
+		return t
+
+	case chanTag:
+		t := new(types.Chan)
+		if p.trackAllTypes {
+			p.record(t)
+		}
+
+		dir := chanDir(p.int())
+		val := p.typ(parent, nil)
+		*t = *types.NewChan(dir, val)
+		return t
+
+	default:
+		errorf("unexpected type tag %d", i) // panics
+		panic("unreachable")
+	}
+}
+
+func chanDir(d int) types.ChanDir {
+	// tag values must match the constants in cmd/compile/internal/gc/go.go
+	switch d {
+	case 1 /* Crecv */ :
+		return types.RecvOnly
+	case 2 /* Csend */ :
+		return types.SendOnly
+	case 3 /* Cboth */ :
+		return types.SendRecv
+	default:
+		errorf("unexpected channel dir %d", d)
+		return 0
+	}
+}
+
+func (p *importer) fieldList(parent *types.Package) (fields []*types.Var, tags []string) {
+	if n := p.int(); n > 0 {
+		fields = make([]*types.Var, n)
+		tags = make([]string, n)
+		for i := range fields {
+			fields[i], tags[i] = p.field(parent)
+		}
+	}
+	return
+}
+
+func (p *importer) field(parent *types.Package) (*types.Var, string) {
+	pos := p.pos()
+	pkg, name, alias := p.fieldName(parent)
+	typ := p.typ(parent, nil)
+	tag := p.string()
+
+	anonymous := false
+	if name == "" {
+		// anonymous field - typ must be T or *T and T must be a type name
+		switch typ := deref(typ).(type) {
+		case *types.Basic: // basic types are named types
+			pkg = nil // // objects defined in Universe scope have no package
+			name = typ.Name()
+		case *types.Named:
+			name = typ.Obj().Name()
+		default:
+			errorf("named base type expected")
+		}
+		anonymous = true
+	} else if alias {
+		// anonymous field: we have an explicit name because it's an alias
+		anonymous = true
+	}
+
+	return types.NewField(pos, pkg, name, typ, anonymous), tag
+}
+
+func (p *importer) methodList(parent *types.Package, baseType *types.Named) (methods []*types.Func) {
+	if n := p.int(); n > 0 {
+		methods = make([]*types.Func, n)
+		for i := range methods {
+			methods[i] = p.method(parent, baseType)
+		}
+	}
+	return
+}
+
+func (p *importer) method(parent *types.Package, baseType *types.Named) *types.Func {
+	pos := p.pos()
+	pkg, name, _ := p.fieldName(parent)
+	// If we don't have a baseType, use a nil receiver.
+	// A receiver using the actual interface type (which
+	// we don't know yet) will be filled in when we call
+	// types.Interface.Complete.
+	var recv *types.Var
+	if baseType != nil {
+		recv = types.NewVar(token.NoPos, parent, "", baseType)
+	}
+	params, isddd := p.paramList()
+	result, _ := p.paramList()
+	sig := types.NewSignature(recv, params, result, isddd)
+	return types.NewFunc(pos, pkg, name, sig)
+}
+
+func (p *importer) fieldName(parent *types.Package) (pkg *types.Package, name string, alias bool) {
+	name = p.string()
+	pkg = parent
+	if pkg == nil {
+		// use the imported package instead
+		pkg = p.pkgList[0]
+	}
+	if p.version == 0 && name == "_" {
+		// version 0 didn't export a package for _ fields
+		return
+	}
+	switch name {
+	case "":
+		// 1) field name matches base type name and is exported: nothing to do
+	case "?":
+		// 2) field name matches base type name and is not exported: need package
+		name = ""
+		pkg = p.pkg()
+	case "@":
+		// 3) field name doesn't match type name (alias)
+		name = p.string()
+		alias = true
+		fallthrough
+	default:
+		if !exported(name) {
+			pkg = p.pkg()
+		}
+	}
+	return
+}
+
+func (p *importer) paramList() (*types.Tuple, bool) {
+	n := p.int()
+	if n == 0 {
+		return nil, false
+	}
+	// negative length indicates unnamed parameters
+	named := true
+	if n < 0 {
+		n = -n
+		named = false
+	}
+	// n > 0
+	params := make([]*types.Var, n)
+	isddd := false
+	for i := range params {
+		params[i], isddd = p.param(named)
+	}
+	return types.NewTuple(params...), isddd
+}
+
+func (p *importer) param(named bool) (*types.Var, bool) {
+	t := p.typ(nil, nil)
+	td, isddd := t.(*dddSlice)
+	if isddd {
+		t = types.NewSlice(td.elem)
+	}
+
+	var pkg *types.Package
+	var name string
+	if named {
+		name = p.string()
+		if name == "" {
+			errorf("expected named parameter")
+		}
+		if name != "_" {
+			pkg = p.pkg()
+		}
+		if i := strings.Index(name, "·"); i > 0 {
+			name = name[:i] // cut off gc-specific parameter numbering
+		}
+	}
+
+	// read and discard compiler-specific info
+	p.string()
+
+	return types.NewVar(token.NoPos, pkg, name, t), isddd
+}
+
+func exported(name string) bool {
+	ch, _ := utf8.DecodeRuneInString(name)
+	return unicode.IsUpper(ch)
+}
+
+func (p *importer) value() constant.Value {
+	switch tag := p.tagOrIndex(); tag {
+	case falseTag:
+		return constant.MakeBool(false)
+	case trueTag:
+		return constant.MakeBool(true)
+	case int64Tag:
+		return constant.MakeInt64(p.int64())
+	case floatTag:
+		return p.float()
+	case complexTag:
+		re := p.float()
+		im := p.float()
+		return constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
+	case stringTag:
+		return constant.MakeString(p.string())
+	case unknownTag:
+		return constant.MakeUnknown()
+	default:
+		errorf("unexpected value tag %d", tag) // panics
+		panic("unreachable")
+	}
+}
+
+func (p *importer) float() constant.Value {
+	sign := p.int()
+	if sign == 0 {
+		return constant.MakeInt64(0)
+	}
+
+	exp := p.int()
+	mant := []byte(p.string()) // big endian
+
+	// remove leading 0's if any
+	for len(mant) > 0 && mant[0] == 0 {
+		mant = mant[1:]
+	}
+
+	// convert to little endian
+	// TODO(gri) go/constant should have a more direct conversion function
+	//           (e.g., once it supports a big.Float based implementation)
+	for i, j := 0, len(mant)-1; i < j; i, j = i+1, j-1 {
+		mant[i], mant[j] = mant[j], mant[i]
+	}
+
+	// adjust exponent (constant.MakeFromBytes creates an integer value,
+	// but mant represents the mantissa bits such that 0.5 <= mant < 1.0)
+	exp -= len(mant) << 3
+	if len(mant) > 0 {
+		for msd := mant[len(mant)-1]; msd&0x80 == 0; msd <<= 1 {
+			exp++
+		}
+	}
+
+	x := constant.MakeFromBytes(mant)
+	switch {
+	case exp < 0:
+		d := constant.Shift(constant.MakeInt64(1), token.SHL, uint(-exp))
+		x = constant.BinaryOp(x, token.QUO, d)
+	case exp > 0:
+		x = constant.Shift(x, token.SHL, uint(exp))
+	}
+
+	if sign < 0 {
+		x = constant.UnaryOp(token.SUB, x, 0)
+	}
+	return x
+}
+
+// ----------------------------------------------------------------------------
+// Low-level decoders
+
+func (p *importer) tagOrIndex() int {
+	if p.debugFormat {
+		p.marker('t')
+	}
+
+	return int(p.rawInt64())
+}
+
+func (p *importer) int() int {
+	x := p.int64()
+	if int64(int(x)) != x {
+		errorf("exported integer too large")
+	}
+	return int(x)
+}
+
+func (p *importer) int64() int64 {
+	if p.debugFormat {
+		p.marker('i')
+	}
+
+	return p.rawInt64()
+}
+
+func (p *importer) path() string {
+	if p.debugFormat {
+		p.marker('p')
+	}
+	// if the path was seen before, i is its index (>= 0)
+	// (the empty string is at index 0)
+	i := p.rawInt64()
+	if i >= 0 {
+		return p.pathList[i]
+	}
+	// otherwise, i is the negative path length (< 0)
+	a := make([]string, -i)
+	for n := range a {
+		a[n] = p.string()
+	}
+	s := strings.Join(a, "/")
+	p.pathList = append(p.pathList, s)
+	return s
+}
+
+func (p *importer) string() string {
+	if p.debugFormat {
+		p.marker('s')
+	}
+	// if the string was seen before, i is its index (>= 0)
+	// (the empty string is at index 0)
+	i := p.rawInt64()
+	if i >= 0 {
+		return p.strList[i]
+	}
+	// otherwise, i is the negative string length (< 0)
+	if n := int(-i); n <= cap(p.buf) {
+		p.buf = p.buf[:n]
+	} else {
+		p.buf = make([]byte, n)
+	}
+	for i := range p.buf {
+		p.buf[i] = p.rawByte()
+	}
+	s := string(p.buf)
+	p.strList = append(p.strList, s)
+	return s
+}
+
+func (p *importer) marker(want byte) {
+	if got := p.rawByte(); got != want {
+		errorf("incorrect marker: got %c; want %c (pos = %d)", got, want, p.read)
+	}
+
+	pos := p.read
+	if n := int(p.rawInt64()); n != pos {
+		errorf("incorrect position: got %d; want %d", n, pos)
+	}
+}
+
+// rawInt64 should only be used by low-level decoders.
+func (p *importer) rawInt64() int64 {
+	i, err := binary.ReadVarint(p)
+	if err != nil {
+		errorf("read error: %v", err)
+	}
+	return i
+}
+
+// rawStringln should only be used to read the initial version string.
+func (p *importer) rawStringln(b byte) string {
+	p.buf = p.buf[:0]
+	for b != '\n' {
+		p.buf = append(p.buf, b)
+		b = p.rawByte()
+	}
+	return string(p.buf)
+}
+
+// needed for binary.ReadVarint in rawInt64
+func (p *importer) ReadByte() (byte, error) {
+	return p.rawByte(), nil
+}
+
+// byte is the bottleneck interface for reading p.data.
+// It unescapes '|' 'S' to '$' and '|' '|' to '|'.
+// rawByte should only be used by low-level decoders.
+func (p *importer) rawByte() byte {
+	b := p.data[0]
+	r := 1
+	if b == '|' {
+		b = p.data[1]
+		r = 2
+		switch b {
+		case 'S':
+			b = '$'
+		case '|':
+			// nothing to do
+		default:
+			errorf("unexpected escape sequence in export data")
+		}
+	}
+	p.data = p.data[r:]
+	p.read += r
+	return b
+
+}
+
+// ----------------------------------------------------------------------------
+// Export format
+
+// Tags. Must be < 0.
+const (
+	// Objects
+	packageTag = -(iota + 1)
+	constTag
+	typeTag
+	varTag
+	funcTag
+	endTag
+
+	// Types
+	namedTag
+	arrayTag
+	sliceTag
+	dddTag
+	structTag
+	pointerTag
+	signatureTag
+	interfaceTag
+	mapTag
+	chanTag
+
+	// Values
+	falseTag
+	trueTag
+	int64Tag
+	floatTag
+	fractionTag // not used by gc
+	complexTag
+	stringTag
+	nilTag     // only used by gc (appears in exported inlined function bodies)
+	unknownTag // not used by gc (only appears in packages with errors)
+
+	// Type aliases
+	aliasTag
+)
+
+var predeclOnce sync.Once
+var predecl []types.Type // initialized lazily
+
+func predeclared() []types.Type {
+	predeclOnce.Do(func() {
+		// initialize lazily to be sure that all
+		// elements have been initialized before
+		predecl = []types.Type{ // basic types
+			types.Typ[types.Bool],
+			types.Typ[types.Int],
+			types.Typ[types.Int8],
+			types.Typ[types.Int16],
+			types.Typ[types.Int32],
+			types.Typ[types.Int64],
+			types.Typ[types.Uint],
+			types.Typ[types.Uint8],
+			types.Typ[types.Uint16],
+			types.Typ[types.Uint32],
+			types.Typ[types.Uint64],
+			types.Typ[types.Uintptr],
+			types.Typ[types.Float32],
+			types.Typ[types.Float64],
+			types.Typ[types.Complex64],
+			types.Typ[types.Complex128],
+			types.Typ[types.String],
+
+			// basic type aliases
+			types.Universe.Lookup("byte").Type(),
+			types.Universe.Lookup("rune").Type(),
+
+			// error
+			types.Universe.Lookup("error").Type(),
+
+			// untyped types
+			types.Typ[types.UntypedBool],
+			types.Typ[types.UntypedInt],
+			types.Typ[types.UntypedRune],
+			types.Typ[types.UntypedFloat],
+			types.Typ[types.UntypedComplex],
+			types.Typ[types.UntypedString],
+			types.Typ[types.UntypedNil],
+
+			// package unsafe
+			types.Typ[types.UnsafePointer],
+
+			// invalid type
+			types.Typ[types.Invalid], // only appears in packages with errors
+
+			// used internally by gc; never used by this package or in .a files
+			anyType{},
+		}
+		predecl = append(predecl, additionalPredeclared()...)
+	})
+	return predecl
+}
+
+type anyType struct{}
+
+func (t anyType) Underlying() types.Type { return t }
+func (t anyType) String() string         { return "any" }
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/exportdata.go b/vendor/golang.org/x/tools/go/internal/gcimporter/exportdata.go
new file mode 100644
index 00000000..f33dc561
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/exportdata.go
@@ -0,0 +1,93 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file is a copy of $GOROOT/src/go/internal/gcimporter/exportdata.go.
+
+// This file implements FindExportData.
+
+package gcimporter
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
+	// See $GOROOT/include/ar.h.
+	hdr := make([]byte, 16+12+6+6+8+10+2)
+	_, err = io.ReadFull(r, hdr)
+	if err != nil {
+		return
+	}
+	// leave for debugging
+	if false {
+		fmt.Printf("header: %s", hdr)
+	}
+	s := strings.TrimSpace(string(hdr[16+12+6+6+8:][:10]))
+	size, err = strconv.Atoi(s)
+	if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
+		err = fmt.Errorf("invalid archive header")
+		return
+	}
+	name = strings.TrimSpace(string(hdr[:16]))
+	return
+}
+
+// FindExportData positions the reader r at the beginning of the
+// export data section of an underlying GC-created object/archive
+// file by reading from it. The reader must be positioned at the
+// start of the file before calling this function. The hdr result
+// is the string before the export data, either "$$" or "$$B".
+//
+func FindExportData(r *bufio.Reader) (hdr string, err error) {
+	// Read first line to make sure this is an object file.
+	line, err := r.ReadSlice('\n')
+	if err != nil {
+		err = fmt.Errorf("can't find export data (%v)", err)
+		return
+	}
+
+	if string(line) == "!<arch>\n" {
+		// Archive file. Scan to __.PKGDEF.
+		var name string
+		if name, _, err = readGopackHeader(r); err != nil {
+			return
+		}
+
+		// First entry should be __.PKGDEF.
+		if name != "__.PKGDEF" {
+			err = fmt.Errorf("go archive is missing __.PKGDEF")
+			return
+		}
+
+		// Read first line of __.PKGDEF data, so that line
+		// is once again the first line of the input.
+		if line, err = r.ReadSlice('\n'); err != nil {
+			err = fmt.Errorf("can't find export data (%v)", err)
+			return
+		}
+	}
+
+	// Now at __.PKGDEF in archive or still at beginning of file.
+	// Either way, line should begin with "go object ".
+	if !strings.HasPrefix(string(line), "go object ") {
+		err = fmt.Errorf("not a Go object file")
+		return
+	}
+
+	// Skip over object header to export data.
+	// Begins after first line starting with $$.
+	for line[0] != '$' {
+		if line, err = r.ReadSlice('\n'); err != nil {
+			err = fmt.Errorf("can't find export data (%v)", err)
+			return
+		}
+	}
+	hdr = string(line)
+
+	return
+}
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/gcimporter.go b/vendor/golang.org/x/tools/go/internal/gcimporter/gcimporter.go
new file mode 100644
index 00000000..e8cba6b2
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/gcimporter.go
@@ -0,0 +1,1078 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file is a modified copy of $GOROOT/src/go/internal/gcimporter/gcimporter.go,
+// but it also contains the original source-based importer code for Go1.6.
+// Once we stop supporting 1.6, we can remove that code.
+
+// Package gcimporter provides various functions for reading
+// gc-generated object files that can be used to implement the
+// Importer interface defined by the Go 1.5 standard library package.
+package gcimporter // import "golang.org/x/tools/go/internal/gcimporter"
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"go/build"
+	"go/constant"
+	"go/token"
+	"go/types"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"sort"
+	"strconv"
+	"strings"
+	"text/scanner"
+)
+
+// debugging/development support
+const debug = false
+
+var pkgExts = [...]string{".a", ".o"}
+
+// FindPkg returns the filename and unique package id for an import
+// path based on package information provided by build.Import (using
+// the build.Default build.Context). A relative srcDir is interpreted
+// relative to the current working directory.
+// If no file was found, an empty filename is returned.
+//
+func FindPkg(path, srcDir string) (filename, id string) {
+	if path == "" {
+		return
+	}
+
+	var noext string
+	switch {
+	default:
+		// "x" -> "$GOPATH/pkg/$GOOS_$GOARCH/x.ext", "x"
+		// Don't require the source files to be present.
+		if abs, err := filepath.Abs(srcDir); err == nil { // see issue 14282
+			srcDir = abs
+		}
+		bp, _ := build.Import(path, srcDir, build.FindOnly|build.AllowBinary)
+		if bp.PkgObj == "" {
+			id = path // make sure we have an id to print in error message
+			return
+		}
+		noext = strings.TrimSuffix(bp.PkgObj, ".a")
+		id = bp.ImportPath
+
+	case build.IsLocalImport(path):
+		// "./x" -> "/this/directory/x.ext", "/this/directory/x"
+		noext = filepath.Join(srcDir, path)
+		id = noext
+
+	case filepath.IsAbs(path):
+		// for completeness only - go/build.Import
+		// does not support absolute imports
+		// "/x" -> "/x.ext", "/x"
+		noext = path
+		id = path
+	}
+
+	if false { // for debugging
+		if path != id {
+			fmt.Printf("%s -> %s\n", path, id)
+		}
+	}
+
+	// try extensions
+	for _, ext := range pkgExts {
+		filename = noext + ext
+		if f, err := os.Stat(filename); err == nil && !f.IsDir() {
+			return
+		}
+	}
+
+	filename = "" // not found
+	return
+}
+
+// ImportData imports a package by reading the gc-generated export data,
+// adds the corresponding package object to the packages map indexed by id,
+// and returns the object.
+//
+// The packages map must contains all packages already imported. The data
+// reader position must be the beginning of the export data section. The
+// filename is only used in error messages.
+//
+// If packages[id] contains the completely imported package, that package
+// can be used directly, and there is no need to call this function (but
+// there is also no harm but for extra time used).
+//
+func ImportData(packages map[string]*types.Package, filename, id string, data io.Reader) (pkg *types.Package, err error) {
+	// support for parser error handling
+	defer func() {
+		switch r := recover().(type) {
+		case nil:
+			// nothing to do
+		case importError:
+			err = r
+		default:
+			panic(r) // internal error
+		}
+	}()
+
+	var p parser
+	p.init(filename, id, data, packages)
+	pkg = p.parseExport()
+
+	return
+}
+
+// Import imports a gc-generated package given its import path and srcDir, adds
+// the corresponding package object to the packages map, and returns the object.
+// The packages map must contain all packages already imported.
+//
+func Import(packages map[string]*types.Package, path, srcDir string, lookup func(path string) (io.ReadCloser, error)) (pkg *types.Package, err error) {
+	var rc io.ReadCloser
+	var filename, id string
+	if lookup != nil {
+		// With custom lookup specified, assume that caller has
+		// converted path to a canonical import path for use in the map.
+		if path == "unsafe" {
+			return types.Unsafe, nil
+		}
+		id = path
+
+		// No need to re-import if the package was imported completely before.
+		if pkg = packages[id]; pkg != nil && pkg.Complete() {
+			return
+		}
+		f, err := lookup(path)
+		if err != nil {
+			return nil, err
+		}
+		rc = f
+	} else {
+		filename, id = FindPkg(path, srcDir)
+		if filename == "" {
+			if path == "unsafe" {
+				return types.Unsafe, nil
+			}
+			return nil, fmt.Errorf("can't find import: %q", id)
+		}
+
+		// no need to re-import if the package was imported completely before
+		if pkg = packages[id]; pkg != nil && pkg.Complete() {
+			return
+		}
+
+		// open file
+		f, err := os.Open(filename)
+		if err != nil {
+			return nil, err
+		}
+		defer func() {
+			if err != nil {
+				// add file name to error
+				err = fmt.Errorf("%s: %v", filename, err)
+			}
+		}()
+		rc = f
+	}
+	defer rc.Close()
+
+	var hdr string
+	buf := bufio.NewReader(rc)
+	if hdr, err = FindExportData(buf); err != nil {
+		return
+	}
+
+	switch hdr {
+	case "$$\n":
+		// Work-around if we don't have a filename; happens only if lookup != nil.
+		// Either way, the filename is only needed for importer error messages, so
+		// this is fine.
+		if filename == "" {
+			filename = path
+		}
+		return ImportData(packages, filename, id, buf)
+
+	case "$$B\n":
+		var data []byte
+		data, err = ioutil.ReadAll(buf)
+		if err != nil {
+			break
+		}
+
+		// TODO(gri): allow clients of go/importer to provide a FileSet.
+		// Or, define a new standard go/types/gcexportdata package.
+		fset := token.NewFileSet()
+
+		// The indexed export format starts with an 'i'; the older
+		// binary export format starts with a 'c', 'd', or 'v'
+		// (from "version"). Select appropriate importer.
+		if len(data) > 0 && data[0] == 'i' {
+			_, pkg, err = IImportData(fset, packages, data[1:], id)
+		} else {
+			_, pkg, err = BImportData(fset, packages, data, id)
+		}
+
+	default:
+		err = fmt.Errorf("unknown export data header: %q", hdr)
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Parser
+
+// TODO(gri) Imported objects don't have position information.
+//           Ideally use the debug table line info; alternatively
+//           create some fake position (or the position of the
+//           import). That way error messages referring to imported
+//           objects can print meaningful information.
+
+// parser parses the exports inside a gc compiler-produced
+// object/archive file and populates its scope with the results.
+type parser struct {
+	scanner    scanner.Scanner
+	tok        rune                      // current token
+	lit        string                    // literal string; only valid for Ident, Int, String tokens
+	id         string                    // package id of imported package
+	sharedPkgs map[string]*types.Package // package id -> package object (across importer)
+	localPkgs  map[string]*types.Package // package id -> package object (just this package)
+}
+
+func (p *parser) init(filename, id string, src io.Reader, packages map[string]*types.Package) {
+	p.scanner.Init(src)
+	p.scanner.Error = func(_ *scanner.Scanner, msg string) { p.error(msg) }
+	p.scanner.Mode = scanner.ScanIdents | scanner.ScanInts | scanner.ScanChars | scanner.ScanStrings | scanner.ScanComments | scanner.SkipComments
+	p.scanner.Whitespace = 1<<'\t' | 1<<' '
+	p.scanner.Filename = filename // for good error messages
+	p.next()
+	p.id = id
+	p.sharedPkgs = packages
+	if debug {
+		// check consistency of packages map
+		for _, pkg := range packages {
+			if pkg.Name() == "" {
+				fmt.Printf("no package name for %s\n", pkg.Path())
+			}
+		}
+	}
+}
+
+func (p *parser) next() {
+	p.tok = p.scanner.Scan()
+	switch p.tok {
+	case scanner.Ident, scanner.Int, scanner.Char, scanner.String, '·':
+		p.lit = p.scanner.TokenText()
+	default:
+		p.lit = ""
+	}
+	if debug {
+		fmt.Printf("%s: %q -> %q\n", scanner.TokenString(p.tok), p.scanner.TokenText(), p.lit)
+	}
+}
+
+func declTypeName(pkg *types.Package, name string) *types.TypeName {
+	scope := pkg.Scope()
+	if obj := scope.Lookup(name); obj != nil {
+		return obj.(*types.TypeName)
+	}
+	obj := types.NewTypeName(token.NoPos, pkg, name, nil)
+	// a named type may be referred to before the underlying type
+	// is known - set it up
+	types.NewNamed(obj, nil, nil)
+	scope.Insert(obj)
+	return obj
+}
+
+// ----------------------------------------------------------------------------
+// Error handling
+
+// Internal errors are boxed as importErrors.
+type importError struct {
+	pos scanner.Position
+	err error
+}
+
+func (e importError) Error() string {
+	return fmt.Sprintf("import error %s (byte offset = %d): %s", e.pos, e.pos.Offset, e.err)
+}
+
+func (p *parser) error(err interface{}) {
+	if s, ok := err.(string); ok {
+		err = errors.New(s)
+	}
+	// panic with a runtime.Error if err is not an error
+	panic(importError{p.scanner.Pos(), err.(error)})
+}
+
+func (p *parser) errorf(format string, args ...interface{}) {
+	p.error(fmt.Sprintf(format, args...))
+}
+
+func (p *parser) expect(tok rune) string {
+	lit := p.lit
+	if p.tok != tok {
+		p.errorf("expected %s, got %s (%s)", scanner.TokenString(tok), scanner.TokenString(p.tok), lit)
+	}
+	p.next()
+	return lit
+}
+
+func (p *parser) expectSpecial(tok string) {
+	sep := 'x' // not white space
+	i := 0
+	for i < len(tok) && p.tok == rune(tok[i]) && sep > ' ' {
+		sep = p.scanner.Peek() // if sep <= ' ', there is white space before the next token
+		p.next()
+		i++
+	}
+	if i < len(tok) {
+		p.errorf("expected %q, got %q", tok, tok[0:i])
+	}
+}
+
+func (p *parser) expectKeyword(keyword string) {
+	lit := p.expect(scanner.Ident)
+	if lit != keyword {
+		p.errorf("expected keyword %s, got %q", keyword, lit)
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Qualified and unqualified names
+
+// PackageId = string_lit .
+//
+func (p *parser) parsePackageID() string {
+	id, err := strconv.Unquote(p.expect(scanner.String))
+	if err != nil {
+		p.error(err)
+	}
+	// id == "" stands for the imported package id
+	// (only known at time of package installation)
+	if id == "" {
+		id = p.id
+	}
+	return id
+}
+
+// PackageName = ident .
+//
+func (p *parser) parsePackageName() string {
+	return p.expect(scanner.Ident)
+}
+
+// dotIdentifier = ( ident | '·' ) { ident | int | '·' } .
+func (p *parser) parseDotIdent() string {
+	ident := ""
+	if p.tok != scanner.Int {
+		sep := 'x' // not white space
+		for (p.tok == scanner.Ident || p.tok == scanner.Int || p.tok == '·') && sep > ' ' {
+			ident += p.lit
+			sep = p.scanner.Peek() // if sep <= ' ', there is white space before the next token
+			p.next()
+		}
+	}
+	if ident == "" {
+		p.expect(scanner.Ident) // use expect() for error handling
+	}
+	return ident
+}
+
+// QualifiedName = "@" PackageId "." ( "?" | dotIdentifier ) .
+//
+func (p *parser) parseQualifiedName() (id, name string) {
+	p.expect('@')
+	id = p.parsePackageID()
+	p.expect('.')
+	// Per rev f280b8a485fd (10/2/2013), qualified names may be used for anonymous fields.
+	if p.tok == '?' {
+		p.next()
+	} else {
+		name = p.parseDotIdent()
+	}
+	return
+}
+
+// getPkg returns the package for a given id. If the package is
+// not found, create the package and add it to the p.localPkgs
+// and p.sharedPkgs maps. name is the (expected) name of the
+// package. If name == "", the package name is expected to be
+// set later via an import clause in the export data.
+//
+// id identifies a package, usually by a canonical package path like
+// "encoding/json" but possibly by a non-canonical import path like
+// "./json".
+//
+func (p *parser) getPkg(id, name string) *types.Package {
+	// package unsafe is not in the packages maps - handle explicitly
+	if id == "unsafe" {
+		return types.Unsafe
+	}
+
+	pkg := p.localPkgs[id]
+	if pkg == nil {
+		// first import of id from this package
+		pkg = p.sharedPkgs[id]
+		if pkg == nil {
+			// first import of id by this importer;
+			// add (possibly unnamed) pkg to shared packages
+			pkg = types.NewPackage(id, name)
+			p.sharedPkgs[id] = pkg
+		}
+		// add (possibly unnamed) pkg to local packages
+		if p.localPkgs == nil {
+			p.localPkgs = make(map[string]*types.Package)
+		}
+		p.localPkgs[id] = pkg
+	} else if name != "" {
+		// package exists already and we have an expected package name;
+		// make sure names match or set package name if necessary
+		if pname := pkg.Name(); pname == "" {
+			pkg.SetName(name)
+		} else if pname != name {
+			p.errorf("%s package name mismatch: %s (given) vs %s (expected)", id, pname, name)
+		}
+	}
+	return pkg
+}
+
+// parseExportedName is like parseQualifiedName, but
+// the package id is resolved to an imported *types.Package.
+//
+func (p *parser) parseExportedName() (pkg *types.Package, name string) {
+	id, name := p.parseQualifiedName()
+	pkg = p.getPkg(id, "")
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+// BasicType = identifier .
+//
+func (p *parser) parseBasicType() types.Type {
+	id := p.expect(scanner.Ident)
+	obj := types.Universe.Lookup(id)
+	if obj, ok := obj.(*types.TypeName); ok {
+		return obj.Type()
+	}
+	p.errorf("not a basic type: %s", id)
+	return nil
+}
+
+// ArrayType = "[" int_lit "]" Type .
+//
+func (p *parser) parseArrayType(parent *types.Package) types.Type {
+	// "[" already consumed and lookahead known not to be "]"
+	lit := p.expect(scanner.Int)
+	p.expect(']')
+	elem := p.parseType(parent)
+	n, err := strconv.ParseInt(lit, 10, 64)
+	if err != nil {
+		p.error(err)
+	}
+	return types.NewArray(elem, n)
+}
+
+// MapType = "map" "[" Type "]" Type .
+//
+func (p *parser) parseMapType(parent *types.Package) types.Type {
+	p.expectKeyword("map")
+	p.expect('[')
+	key := p.parseType(parent)
+	p.expect(']')
+	elem := p.parseType(parent)
+	return types.NewMap(key, elem)
+}
+
+// Name = identifier | "?" | QualifiedName .
+//
+// For unqualified and anonymous names, the returned package is the parent
+// package unless parent == nil, in which case the returned package is the
+// package being imported. (The parent package is not nil if the name
+// is an unqualified struct field or interface method name belonging to a
+// type declared in another package.)
+//
+// For qualified names, the returned package is nil (and not created if
+// it doesn't exist yet) unless materializePkg is set (which creates an
+// unnamed package with valid package path). In the latter case, a
+// subsequent import clause is expected to provide a name for the package.
+//
+func (p *parser) parseName(parent *types.Package, materializePkg bool) (pkg *types.Package, name string) {
+	pkg = parent
+	if pkg == nil {
+		pkg = p.sharedPkgs[p.id]
+	}
+	switch p.tok {
+	case scanner.Ident:
+		name = p.lit
+		p.next()
+	case '?':
+		// anonymous
+		p.next()
+	case '@':
+		// exported name prefixed with package path
+		pkg = nil
+		var id string
+		id, name = p.parseQualifiedName()
+		if materializePkg {
+			pkg = p.getPkg(id, "")
+		}
+	default:
+		p.error("name expected")
+	}
+	return
+}
+
+func deref(typ types.Type) types.Type {
+	if p, _ := typ.(*types.Pointer); p != nil {
+		return p.Elem()
+	}
+	return typ
+}
+
+// Field = Name Type [ string_lit ] .
+//
+func (p *parser) parseField(parent *types.Package) (*types.Var, string) {
+	pkg, name := p.parseName(parent, true)
+
+	if name == "_" {
+		// Blank fields should be package-qualified because they
+		// are unexported identifiers, but gc does not qualify them.
+		// Assuming that the ident belongs to the current package
+		// causes types to change during re-exporting, leading
+		// to spurious "can't assign A to B" errors from go/types.
+		// As a workaround, pretend all blank fields belong
+		// to the same unique dummy package.
+		const blankpkg = "<_>"
+		pkg = p.getPkg(blankpkg, blankpkg)
+	}
+
+	typ := p.parseType(parent)
+	anonymous := false
+	if name == "" {
+		// anonymous field - typ must be T or *T and T must be a type name
+		switch typ := deref(typ).(type) {
+		case *types.Basic: // basic types are named types
+			pkg = nil // objects defined in Universe scope have no package
+			name = typ.Name()
+		case *types.Named:
+			name = typ.Obj().Name()
+		default:
+			p.errorf("anonymous field expected")
+		}
+		anonymous = true
+	}
+	tag := ""
+	if p.tok == scanner.String {
+		s := p.expect(scanner.String)
+		var err error
+		tag, err = strconv.Unquote(s)
+		if err != nil {
+			p.errorf("invalid struct tag %s: %s", s, err)
+		}
+	}
+	return types.NewField(token.NoPos, pkg, name, typ, anonymous), tag
+}
+
+// StructType = "struct" "{" [ FieldList ] "}" .
+// FieldList  = Field { ";" Field } .
+//
+func (p *parser) parseStructType(parent *types.Package) types.Type {
+	var fields []*types.Var
+	var tags []string
+
+	p.expectKeyword("struct")
+	p.expect('{')
+	for i := 0; p.tok != '}' && p.tok != scanner.EOF; i++ {
+		if i > 0 {
+			p.expect(';')
+		}
+		fld, tag := p.parseField(parent)
+		if tag != "" && tags == nil {
+			tags = make([]string, i)
+		}
+		if tags != nil {
+			tags = append(tags, tag)
+		}
+		fields = append(fields, fld)
+	}
+	p.expect('}')
+
+	return types.NewStruct(fields, tags)
+}
+
+// Parameter = ( identifier | "?" ) [ "..." ] Type [ string_lit ] .
+//
+func (p *parser) parseParameter() (par *types.Var, isVariadic bool) {
+	_, name := p.parseName(nil, false)
+	// remove gc-specific parameter numbering
+	if i := strings.Index(name, "·"); i >= 0 {
+		name = name[:i]
+	}
+	if p.tok == '.' {
+		p.expectSpecial("...")
+		isVariadic = true
+	}
+	typ := p.parseType(nil)
+	if isVariadic {
+		typ = types.NewSlice(typ)
+	}
+	// ignore argument tag (e.g. "noescape")
+	if p.tok == scanner.String {
+		p.next()
+	}
+	// TODO(gri) should we provide a package?
+	par = types.NewVar(token.NoPos, nil, name, typ)
+	return
+}
+
+// Parameters    = "(" [ ParameterList ] ")" .
+// ParameterList = { Parameter "," } Parameter .
+//
+func (p *parser) parseParameters() (list []*types.Var, isVariadic bool) {
+	p.expect('(')
+	for p.tok != ')' && p.tok != scanner.EOF {
+		if len(list) > 0 {
+			p.expect(',')
+		}
+		par, variadic := p.parseParameter()
+		list = append(list, par)
+		if variadic {
+			if isVariadic {
+				p.error("... not on final argument")
+			}
+			isVariadic = true
+		}
+	}
+	p.expect(')')
+
+	return
+}
+
+// Signature = Parameters [ Result ] .
+// Result    = Type | Parameters .
+//
+func (p *parser) parseSignature(recv *types.Var) *types.Signature {
+	params, isVariadic := p.parseParameters()
+
+	// optional result type
+	var results []*types.Var
+	if p.tok == '(' {
+		var variadic bool
+		results, variadic = p.parseParameters()
+		if variadic {
+			p.error("... not permitted on result type")
+		}
+	}
+
+	return types.NewSignature(recv, types.NewTuple(params...), types.NewTuple(results...), isVariadic)
+}
+
+// InterfaceType = "interface" "{" [ MethodList ] "}" .
+// MethodList    = Method { ";" Method } .
+// Method        = Name Signature .
+//
+// The methods of embedded interfaces are always "inlined"
+// by the compiler and thus embedded interfaces are never
+// visible in the export data.
+//
+func (p *parser) parseInterfaceType(parent *types.Package) types.Type {
+	var methods []*types.Func
+
+	p.expectKeyword("interface")
+	p.expect('{')
+	for i := 0; p.tok != '}' && p.tok != scanner.EOF; i++ {
+		if i > 0 {
+			p.expect(';')
+		}
+		pkg, name := p.parseName(parent, true)
+		sig := p.parseSignature(nil)
+		methods = append(methods, types.NewFunc(token.NoPos, pkg, name, sig))
+	}
+	p.expect('}')
+
+	// Complete requires the type's embedded interfaces to be fully defined,
+	// but we do not define any
+	return newInterface(methods, nil).Complete()
+}
+
+// ChanType = ( "chan" [ "<-" ] | "<-" "chan" ) Type .
+//
+func (p *parser) parseChanType(parent *types.Package) types.Type {
+	dir := types.SendRecv
+	if p.tok == scanner.Ident {
+		p.expectKeyword("chan")
+		if p.tok == '<' {
+			p.expectSpecial("<-")
+			dir = types.SendOnly
+		}
+	} else {
+		p.expectSpecial("<-")
+		p.expectKeyword("chan")
+		dir = types.RecvOnly
+	}
+	elem := p.parseType(parent)
+	return types.NewChan(dir, elem)
+}
+
+// Type =
+//	BasicType | TypeName | ArrayType | SliceType | StructType |
+//      PointerType | FuncType | InterfaceType | MapType | ChanType |
+//      "(" Type ")" .
+//
+// BasicType   = ident .
+// TypeName    = ExportedName .
+// SliceType   = "[" "]" Type .
+// PointerType = "*" Type .
+// FuncType    = "func" Signature .
+//
+func (p *parser) parseType(parent *types.Package) types.Type {
+	switch p.tok {
+	case scanner.Ident:
+		switch p.lit {
+		default:
+			return p.parseBasicType()
+		case "struct":
+			return p.parseStructType(parent)
+		case "func":
+			// FuncType
+			p.next()
+			return p.parseSignature(nil)
+		case "interface":
+			return p.parseInterfaceType(parent)
+		case "map":
+			return p.parseMapType(parent)
+		case "chan":
+			return p.parseChanType(parent)
+		}
+	case '@':
+		// TypeName
+		pkg, name := p.parseExportedName()
+		return declTypeName(pkg, name).Type()
+	case '[':
+		p.next() // look ahead
+		if p.tok == ']' {
+			// SliceType
+			p.next()
+			return types.NewSlice(p.parseType(parent))
+		}
+		return p.parseArrayType(parent)
+	case '*':
+		// PointerType
+		p.next()
+		return types.NewPointer(p.parseType(parent))
+	case '<':
+		return p.parseChanType(parent)
+	case '(':
+		// "(" Type ")"
+		p.next()
+		typ := p.parseType(parent)
+		p.expect(')')
+		return typ
+	}
+	p.errorf("expected type, got %s (%q)", scanner.TokenString(p.tok), p.lit)
+	return nil
+}
+
+// ----------------------------------------------------------------------------
+// Declarations
+
+// ImportDecl = "import" PackageName PackageId .
+//
+func (p *parser) parseImportDecl() {
+	p.expectKeyword("import")
+	name := p.parsePackageName()
+	p.getPkg(p.parsePackageID(), name)
+}
+
+// int_lit = [ "+" | "-" ] { "0" ... "9" } .
+//
+func (p *parser) parseInt() string {
+	s := ""
+	switch p.tok {
+	case '-':
+		s = "-"
+		p.next()
+	case '+':
+		p.next()
+	}
+	return s + p.expect(scanner.Int)
+}
+
+// number = int_lit [ "p" int_lit ] .
+//
+func (p *parser) parseNumber() (typ *types.Basic, val constant.Value) {
+	// mantissa
+	mant := constant.MakeFromLiteral(p.parseInt(), token.INT, 0)
+	if mant == nil {
+		panic("invalid mantissa")
+	}
+
+	if p.lit == "p" {
+		// exponent (base 2)
+		p.next()
+		exp, err := strconv.ParseInt(p.parseInt(), 10, 0)
+		if err != nil {
+			p.error(err)
+		}
+		if exp < 0 {
+			denom := constant.MakeInt64(1)
+			denom = constant.Shift(denom, token.SHL, uint(-exp))
+			typ = types.Typ[types.UntypedFloat]
+			val = constant.BinaryOp(mant, token.QUO, denom)
+			return
+		}
+		if exp > 0 {
+			mant = constant.Shift(mant, token.SHL, uint(exp))
+		}
+		typ = types.Typ[types.UntypedFloat]
+		val = mant
+		return
+	}
+
+	typ = types.Typ[types.UntypedInt]
+	val = mant
+	return
+}
+
+// ConstDecl   = "const" ExportedName [ Type ] "=" Literal .
+// Literal     = bool_lit | int_lit | float_lit | complex_lit | rune_lit | string_lit .
+// bool_lit    = "true" | "false" .
+// complex_lit = "(" float_lit "+" float_lit "i" ")" .
+// rune_lit    = "(" int_lit "+" int_lit ")" .
+// string_lit  = `"` { unicode_char } `"` .
+//
+func (p *parser) parseConstDecl() {
+	p.expectKeyword("const")
+	pkg, name := p.parseExportedName()
+
+	var typ0 types.Type
+	if p.tok != '=' {
+		// constant types are never structured - no need for parent type
+		typ0 = p.parseType(nil)
+	}
+
+	p.expect('=')
+	var typ types.Type
+	var val constant.Value
+	switch p.tok {
+	case scanner.Ident:
+		// bool_lit
+		if p.lit != "true" && p.lit != "false" {
+			p.error("expected true or false")
+		}
+		typ = types.Typ[types.UntypedBool]
+		val = constant.MakeBool(p.lit == "true")
+		p.next()
+
+	case '-', scanner.Int:
+		// int_lit
+		typ, val = p.parseNumber()
+
+	case '(':
+		// complex_lit or rune_lit
+		p.next()
+		if p.tok == scanner.Char {
+			p.next()
+			p.expect('+')
+			typ = types.Typ[types.UntypedRune]
+			_, val = p.parseNumber()
+			p.expect(')')
+			break
+		}
+		_, re := p.parseNumber()
+		p.expect('+')
+		_, im := p.parseNumber()
+		p.expectKeyword("i")
+		p.expect(')')
+		typ = types.Typ[types.UntypedComplex]
+		val = constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
+
+	case scanner.Char:
+		// rune_lit
+		typ = types.Typ[types.UntypedRune]
+		val = constant.MakeFromLiteral(p.lit, token.CHAR, 0)
+		p.next()
+
+	case scanner.String:
+		// string_lit
+		typ = types.Typ[types.UntypedString]
+		val = constant.MakeFromLiteral(p.lit, token.STRING, 0)
+		p.next()
+
+	default:
+		p.errorf("expected literal got %s", scanner.TokenString(p.tok))
+	}
+
+	if typ0 == nil {
+		typ0 = typ
+	}
+
+	pkg.Scope().Insert(types.NewConst(token.NoPos, pkg, name, typ0, val))
+}
+
+// TypeDecl = "type" ExportedName Type .
+//
+func (p *parser) parseTypeDecl() {
+	p.expectKeyword("type")
+	pkg, name := p.parseExportedName()
+	obj := declTypeName(pkg, name)
+
+	// The type object may have been imported before and thus already
+	// have a type associated with it. We still need to parse the type
+	// structure, but throw it away if the object already has a type.
+	// This ensures that all imports refer to the same type object for
+	// a given type declaration.
+	typ := p.parseType(pkg)
+
+	if name := obj.Type().(*types.Named); name.Underlying() == nil {
+		name.SetUnderlying(typ)
+	}
+}
+
+// VarDecl = "var" ExportedName Type .
+//
+func (p *parser) parseVarDecl() {
+	p.expectKeyword("var")
+	pkg, name := p.parseExportedName()
+	typ := p.parseType(pkg)
+	pkg.Scope().Insert(types.NewVar(token.NoPos, pkg, name, typ))
+}
+
+// Func = Signature [ Body ] .
+// Body = "{" ... "}" .
+//
+func (p *parser) parseFunc(recv *types.Var) *types.Signature {
+	sig := p.parseSignature(recv)
+	if p.tok == '{' {
+		p.next()
+		for i := 1; i > 0; p.next() {
+			switch p.tok {
+			case '{':
+				i++
+			case '}':
+				i--
+			}
+		}
+	}
+	return sig
+}
+
+// MethodDecl = "func" Receiver Name Func .
+// Receiver   = "(" ( identifier | "?" ) [ "*" ] ExportedName ")" .
+//
+func (p *parser) parseMethodDecl() {
+	// "func" already consumed
+	p.expect('(')
+	recv, _ := p.parseParameter() // receiver
+	p.expect(')')
+
+	// determine receiver base type object
+	base := deref(recv.Type()).(*types.Named)
+
+	// parse method name, signature, and possibly inlined body
+	_, name := p.parseName(nil, false)
+	sig := p.parseFunc(recv)
+
+	// methods always belong to the same package as the base type object
+	pkg := base.Obj().Pkg()
+
+	// add method to type unless type was imported before
+	// and method exists already
+	// TODO(gri) This leads to a quadratic algorithm - ok for now because method counts are small.
+	base.AddMethod(types.NewFunc(token.NoPos, pkg, name, sig))
+}
+
+// FuncDecl = "func" ExportedName Func .
+//
+func (p *parser) parseFuncDecl() {
+	// "func" already consumed
+	pkg, name := p.parseExportedName()
+	typ := p.parseFunc(nil)
+	pkg.Scope().Insert(types.NewFunc(token.NoPos, pkg, name, typ))
+}
+
+// Decl = [ ImportDecl | ConstDecl | TypeDecl | VarDecl | FuncDecl | MethodDecl ] "\n" .
+//
+func (p *parser) parseDecl() {
+	if p.tok == scanner.Ident {
+		switch p.lit {
+		case "import":
+			p.parseImportDecl()
+		case "const":
+			p.parseConstDecl()
+		case "type":
+			p.parseTypeDecl()
+		case "var":
+			p.parseVarDecl()
+		case "func":
+			p.next() // look ahead
+			if p.tok == '(' {
+				p.parseMethodDecl()
+			} else {
+				p.parseFuncDecl()
+			}
+		}
+	}
+	p.expect('\n')
+}
+
+// ----------------------------------------------------------------------------
+// Export
+
+// Export        = "PackageClause { Decl } "$$" .
+// PackageClause = "package" PackageName [ "safe" ] "\n" .
+//
+func (p *parser) parseExport() *types.Package {
+	p.expectKeyword("package")
+	name := p.parsePackageName()
+	if p.tok == scanner.Ident && p.lit == "safe" {
+		// package was compiled with -u option - ignore
+		p.next()
+	}
+	p.expect('\n')
+
+	pkg := p.getPkg(p.id, name)
+
+	for p.tok != '$' && p.tok != scanner.EOF {
+		p.parseDecl()
+	}
+
+	if ch := p.scanner.Peek(); p.tok != '$' || ch != '$' {
+		// don't call next()/expect() since reading past the
+		// export data may cause scanner errors (e.g. NUL chars)
+		p.errorf("expected '$$', got %s %c", scanner.TokenString(p.tok), ch)
+	}
+
+	if n := p.scanner.ErrorCount; n != 0 {
+		p.errorf("expected no scanner errors, got %d", n)
+	}
+
+	// Record all locally referenced packages as imports.
+	var imports []*types.Package
+	for id, pkg2 := range p.localPkgs {
+		if pkg2.Name() == "" {
+			p.errorf("%s package has no name", id)
+		}
+		if id == p.id {
+			continue // avoid self-edge
+		}
+		imports = append(imports, pkg2)
+	}
+	sort.Sort(byPath(imports))
+	pkg.SetImports(imports)
+
+	// package was imported completely and without errors
+	pkg.MarkComplete()
+
+	return pkg
+}
+
+type byPath []*types.Package
+
+func (a byPath) Len() int           { return len(a) }
+func (a byPath) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a byPath) Less(i, j int) bool { return a[i].Path() < a[j].Path() }
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/iexport.go b/vendor/golang.org/x/tools/go/internal/gcimporter/iexport.go
new file mode 100644
index 00000000..be8b7459
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/iexport.go
@@ -0,0 +1,911 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Indexed binary package export.
+// This file was derived from $GOROOT/src/cmd/compile/internal/gc/iexport.go;
+// see that file for specification of the format.
+
+package gcimporter
+
+import (
+	"bytes"
+	"encoding/binary"
+	"go/ast"
+	"go/constant"
+	"go/token"
+	"go/types"
+	"io"
+	"math/big"
+	"reflect"
+	"sort"
+
+	"golang.org/x/tools/internal/typeparams"
+)
+
+// Current bundled export format version. Increase with each format change.
+// 0: initial implementation
+const bundleVersion = 0
+
+// IExportData writes indexed export data for pkg to out.
+//
+// If no file set is provided, position info will be missing.
+// The package path of the top-level package will not be recorded,
+// so that calls to IImportData can override with a provided package path.
+func IExportData(out io.Writer, fset *token.FileSet, pkg *types.Package) error {
+	return iexportCommon(out, fset, false, []*types.Package{pkg})
+}
+
+// IExportBundle writes an indexed export bundle for pkgs to out.
+func IExportBundle(out io.Writer, fset *token.FileSet, pkgs []*types.Package) error {
+	return iexportCommon(out, fset, true, pkgs)
+}
+
+func iexportCommon(out io.Writer, fset *token.FileSet, bundle bool, pkgs []*types.Package) (err error) {
+	if !debug {
+		defer func() {
+			if e := recover(); e != nil {
+				if ierr, ok := e.(internalError); ok {
+					err = ierr
+					return
+				}
+				// Not an internal error; panic again.
+				panic(e)
+			}
+		}()
+	}
+
+	p := iexporter{
+		fset:        fset,
+		allPkgs:     map[*types.Package]bool{},
+		stringIndex: map[string]uint64{},
+		declIndex:   map[types.Object]uint64{},
+		typIndex:    map[types.Type]uint64{},
+	}
+	if !bundle {
+		p.localpkg = pkgs[0]
+	}
+
+	for i, pt := range predeclared() {
+		p.typIndex[pt] = uint64(i)
+	}
+	if len(p.typIndex) > predeclReserved {
+		panic(internalErrorf("too many predeclared types: %d > %d", len(p.typIndex), predeclReserved))
+	}
+
+	// Initialize work queue with exported declarations.
+	for _, pkg := range pkgs {
+		scope := pkg.Scope()
+		for _, name := range scope.Names() {
+			if ast.IsExported(name) {
+				p.pushDecl(scope.Lookup(name))
+			}
+		}
+
+		if bundle {
+			// Ensure pkg and its imports are included in the index.
+			p.allPkgs[pkg] = true
+			for _, imp := range pkg.Imports() {
+				p.allPkgs[imp] = true
+			}
+		}
+	}
+
+	// Loop until no more work.
+	for !p.declTodo.empty() {
+		p.doDecl(p.declTodo.popHead())
+	}
+
+	// Append indices to data0 section.
+	dataLen := uint64(p.data0.Len())
+	w := p.newWriter()
+	w.writeIndex(p.declIndex)
+
+	if bundle {
+		w.uint64(uint64(len(pkgs)))
+		for _, pkg := range pkgs {
+			w.pkg(pkg)
+			imps := pkg.Imports()
+			w.uint64(uint64(len(imps)))
+			for _, imp := range imps {
+				w.pkg(imp)
+			}
+		}
+	}
+	w.flush()
+
+	// Assemble header.
+	var hdr intWriter
+	if bundle {
+		hdr.uint64(bundleVersion)
+	}
+	hdr.uint64(iexportVersion)
+	hdr.uint64(uint64(p.strings.Len()))
+	hdr.uint64(dataLen)
+
+	// Flush output.
+	io.Copy(out, &hdr)
+	io.Copy(out, &p.strings)
+	io.Copy(out, &p.data0)
+
+	return nil
+}
+
+// writeIndex writes out an object index. mainIndex indicates whether
+// we're writing out the main index, which is also read by
+// non-compiler tools and includes a complete package description
+// (i.e., name and height).
+func (w *exportWriter) writeIndex(index map[types.Object]uint64) {
+	// Build a map from packages to objects from that package.
+	pkgObjs := map[*types.Package][]types.Object{}
+
+	// For the main index, make sure to include every package that
+	// we reference, even if we're not exporting (or reexporting)
+	// any symbols from it.
+	if w.p.localpkg != nil {
+		pkgObjs[w.p.localpkg] = nil
+	}
+	for pkg := range w.p.allPkgs {
+		pkgObjs[pkg] = nil
+	}
+
+	for obj := range index {
+		pkgObjs[obj.Pkg()] = append(pkgObjs[obj.Pkg()], obj)
+	}
+
+	var pkgs []*types.Package
+	for pkg, objs := range pkgObjs {
+		pkgs = append(pkgs, pkg)
+
+		sort.Slice(objs, func(i, j int) bool {
+			return indexName(objs[i]) < indexName(objs[j])
+		})
+	}
+
+	sort.Slice(pkgs, func(i, j int) bool {
+		return w.exportPath(pkgs[i]) < w.exportPath(pkgs[j])
+	})
+
+	w.uint64(uint64(len(pkgs)))
+	for _, pkg := range pkgs {
+		w.string(w.exportPath(pkg))
+		w.string(pkg.Name())
+		w.uint64(uint64(0)) // package height is not needed for go/types
+
+		objs := pkgObjs[pkg]
+		w.uint64(uint64(len(objs)))
+		for _, obj := range objs {
+			w.string(indexName(obj))
+			w.uint64(index[obj])
+		}
+	}
+}
+
+// indexName returns the 'indexed' name of an object. It differs from
+// obj.Name() only for type parameter names, where we include the subscripted
+// type parameter ID.
+//
+// TODO(rfindley): remove this once we no longer need subscripts.
+func indexName(obj types.Object) (res string) {
+	if _, ok := obj.(*types.TypeName); ok {
+		if tparam, ok := obj.Type().(*typeparams.TypeParam); ok {
+			return types.TypeString(tparam, func(*types.Package) string { return "" })
+		}
+	}
+	return obj.Name()
+}
+
+type iexporter struct {
+	fset *token.FileSet
+	out  *bytes.Buffer
+
+	localpkg *types.Package
+
+	// allPkgs tracks all packages that have been referenced by
+	// the export data, so we can ensure to include them in the
+	// main index.
+	allPkgs map[*types.Package]bool
+
+	declTodo objQueue
+
+	strings     intWriter
+	stringIndex map[string]uint64
+
+	data0     intWriter
+	declIndex map[types.Object]uint64
+	typIndex  map[types.Type]uint64
+}
+
+// stringOff returns the offset of s within the string section.
+// If not already present, it's added to the end.
+func (p *iexporter) stringOff(s string) uint64 {
+	off, ok := p.stringIndex[s]
+	if !ok {
+		off = uint64(p.strings.Len())
+		p.stringIndex[s] = off
+
+		p.strings.uint64(uint64(len(s)))
+		p.strings.WriteString(s)
+	}
+	return off
+}
+
+// pushDecl adds n to the declaration work queue, if not already present.
+func (p *iexporter) pushDecl(obj types.Object) {
+	// Package unsafe is known to the compiler and predeclared.
+	assert(obj.Pkg() != types.Unsafe)
+
+	if _, ok := p.declIndex[obj]; ok {
+		return
+	}
+
+	p.declIndex[obj] = ^uint64(0) // mark n present in work queue
+	p.declTodo.pushTail(obj)
+}
+
+// exportWriter handles writing out individual data section chunks.
+type exportWriter struct {
+	p *iexporter
+
+	data       intWriter
+	currPkg    *types.Package
+	prevFile   string
+	prevLine   int64
+	prevColumn int64
+}
+
+func (w *exportWriter) exportPath(pkg *types.Package) string {
+	if pkg == w.p.localpkg {
+		return ""
+	}
+	return pkg.Path()
+}
+
+func (p *iexporter) doDecl(obj types.Object) {
+	w := p.newWriter()
+	w.setPkg(obj.Pkg(), false)
+
+	switch obj := obj.(type) {
+	case *types.Var:
+		w.tag('V')
+		w.pos(obj.Pos())
+		w.typ(obj.Type(), obj.Pkg())
+
+	case *types.Func:
+		sig, _ := obj.Type().(*types.Signature)
+		if sig.Recv() != nil {
+			panic(internalErrorf("unexpected method: %v", sig))
+		}
+
+		// Function.
+		if typeparams.ForSignature(sig).Len() == 0 {
+			w.tag('F')
+		} else {
+			w.tag('G')
+		}
+		w.pos(obj.Pos())
+		// The tparam list of the function type is the
+		// declaration of the type params. So, write out the type
+		// params right now. Then those type params will be
+		// referenced via their type offset (via typOff) in all
+		// other places in the signature and function that they
+		// are used.
+		if tparams := typeparams.ForSignature(sig); tparams.Len() > 0 {
+			w.tparamList(tparams, obj.Pkg())
+		}
+		w.signature(sig)
+
+	case *types.Const:
+		w.tag('C')
+		w.pos(obj.Pos())
+		w.value(obj.Type(), obj.Val())
+
+	case *types.TypeName:
+		t := obj.Type()
+
+		if tparam, ok := t.(*typeparams.TypeParam); ok {
+			w.tag('P')
+			w.pos(obj.Pos())
+			w.typ(tparam.Constraint(), obj.Pkg())
+			break
+		}
+
+		if obj.IsAlias() {
+			w.tag('A')
+			w.pos(obj.Pos())
+			w.typ(t, obj.Pkg())
+			break
+		}
+
+		// Defined type.
+		named, ok := t.(*types.Named)
+		if !ok {
+			panic(internalErrorf("%s is not a defined type", t))
+		}
+
+		if typeparams.ForNamed(named).Len() == 0 {
+			w.tag('T')
+		} else {
+			w.tag('U')
+		}
+		w.pos(obj.Pos())
+
+		if typeparams.ForNamed(named).Len() > 0 {
+			w.tparamList(typeparams.ForNamed(named), obj.Pkg())
+		}
+
+		underlying := obj.Type().Underlying()
+		w.typ(underlying, obj.Pkg())
+
+		if types.IsInterface(t) {
+			break
+		}
+
+		n := named.NumMethods()
+		w.uint64(uint64(n))
+		for i := 0; i < n; i++ {
+			m := named.Method(i)
+			w.pos(m.Pos())
+			w.string(m.Name())
+			sig, _ := m.Type().(*types.Signature)
+			w.param(sig.Recv())
+			w.signature(sig)
+		}
+
+	default:
+		panic(internalErrorf("unexpected object: %v", obj))
+	}
+
+	p.declIndex[obj] = w.flush()
+}
+
+func (w *exportWriter) tag(tag byte) {
+	w.data.WriteByte(tag)
+}
+
+func (w *exportWriter) pos(pos token.Pos) {
+	if iexportVersion >= iexportVersionPosCol {
+		w.posV1(pos)
+	} else {
+		w.posV0(pos)
+	}
+}
+
+func (w *exportWriter) posV1(pos token.Pos) {
+	if w.p.fset == nil {
+		w.int64(0)
+		return
+	}
+
+	p := w.p.fset.Position(pos)
+	file := p.Filename
+	line := int64(p.Line)
+	column := int64(p.Column)
+
+	deltaColumn := (column - w.prevColumn) << 1
+	deltaLine := (line - w.prevLine) << 1
+
+	if file != w.prevFile {
+		deltaLine |= 1
+	}
+	if deltaLine != 0 {
+		deltaColumn |= 1
+	}
+
+	w.int64(deltaColumn)
+	if deltaColumn&1 != 0 {
+		w.int64(deltaLine)
+		if deltaLine&1 != 0 {
+			w.string(file)
+		}
+	}
+
+	w.prevFile = file
+	w.prevLine = line
+	w.prevColumn = column
+}
+
+func (w *exportWriter) posV0(pos token.Pos) {
+	if w.p.fset == nil {
+		w.int64(0)
+		return
+	}
+
+	p := w.p.fset.Position(pos)
+	file := p.Filename
+	line := int64(p.Line)
+
+	// When file is the same as the last position (common case),
+	// we can save a few bytes by delta encoding just the line
+	// number.
+	//
+	// Note: Because data objects may be read out of order (or not
+	// at all), we can only apply delta encoding within a single
+	// object. This is handled implicitly by tracking prevFile and
+	// prevLine as fields of exportWriter.
+
+	if file == w.prevFile {
+		delta := line - w.prevLine
+		w.int64(delta)
+		if delta == deltaNewFile {
+			w.int64(-1)
+		}
+	} else {
+		w.int64(deltaNewFile)
+		w.int64(line) // line >= 0
+		w.string(file)
+		w.prevFile = file
+	}
+	w.prevLine = line
+}
+
+func (w *exportWriter) pkg(pkg *types.Package) {
+	// Ensure any referenced packages are declared in the main index.
+	w.p.allPkgs[pkg] = true
+
+	w.string(w.exportPath(pkg))
+}
+
+func (w *exportWriter) qualifiedIdent(obj types.Object) {
+	// Ensure any referenced declarations are written out too.
+	w.p.pushDecl(obj)
+	w.string(indexName(obj))
+	w.pkg(obj.Pkg())
+}
+
+func (w *exportWriter) typ(t types.Type, pkg *types.Package) {
+	w.data.uint64(w.p.typOff(t, pkg))
+}
+
+func (p *iexporter) newWriter() *exportWriter {
+	return &exportWriter{p: p}
+}
+
+func (w *exportWriter) flush() uint64 {
+	off := uint64(w.p.data0.Len())
+	io.Copy(&w.p.data0, &w.data)
+	return off
+}
+
+func (p *iexporter) typOff(t types.Type, pkg *types.Package) uint64 {
+	off, ok := p.typIndex[t]
+	if !ok {
+		w := p.newWriter()
+		w.doTyp(t, pkg)
+		off = predeclReserved + w.flush()
+		p.typIndex[t] = off
+	}
+	return off
+}
+
+func (w *exportWriter) startType(k itag) {
+	w.data.uint64(uint64(k))
+}
+
+func (w *exportWriter) doTyp(t types.Type, pkg *types.Package) {
+	switch t := t.(type) {
+	case *types.Named:
+		if targs := typeparams.NamedTypeArgs(t); targs.Len() > 0 {
+			w.startType(instanceType)
+			// TODO(rfindley): investigate if this position is correct, and if it
+			// matters.
+			w.pos(t.Obj().Pos())
+			w.typeList(targs, pkg)
+			w.typ(typeparams.NamedTypeOrigin(t), pkg)
+			return
+		}
+		w.startType(definedType)
+		w.qualifiedIdent(t.Obj())
+
+	case *typeparams.TypeParam:
+		w.startType(typeParamType)
+		w.qualifiedIdent(t.Obj())
+
+	case *types.Pointer:
+		w.startType(pointerType)
+		w.typ(t.Elem(), pkg)
+
+	case *types.Slice:
+		w.startType(sliceType)
+		w.typ(t.Elem(), pkg)
+
+	case *types.Array:
+		w.startType(arrayType)
+		w.uint64(uint64(t.Len()))
+		w.typ(t.Elem(), pkg)
+
+	case *types.Chan:
+		w.startType(chanType)
+		// 1 RecvOnly; 2 SendOnly; 3 SendRecv
+		var dir uint64
+		switch t.Dir() {
+		case types.RecvOnly:
+			dir = 1
+		case types.SendOnly:
+			dir = 2
+		case types.SendRecv:
+			dir = 3
+		}
+		w.uint64(dir)
+		w.typ(t.Elem(), pkg)
+
+	case *types.Map:
+		w.startType(mapType)
+		w.typ(t.Key(), pkg)
+		w.typ(t.Elem(), pkg)
+
+	case *types.Signature:
+		w.startType(signatureType)
+		w.setPkg(pkg, true)
+		w.signature(t)
+
+	case *types.Struct:
+		w.startType(structType)
+		w.setPkg(pkg, true)
+
+		n := t.NumFields()
+		w.uint64(uint64(n))
+		for i := 0; i < n; i++ {
+			f := t.Field(i)
+			w.pos(f.Pos())
+			w.string(f.Name())
+			w.typ(f.Type(), pkg)
+			w.bool(f.Anonymous())
+			w.string(t.Tag(i)) // note (or tag)
+		}
+
+	case *types.Interface:
+		w.startType(interfaceType)
+		w.setPkg(pkg, true)
+
+		n := t.NumEmbeddeds()
+		w.uint64(uint64(n))
+		for i := 0; i < n; i++ {
+			ft := t.EmbeddedType(i)
+			tPkg := pkg
+			if named, _ := ft.(*types.Named); named != nil {
+				w.pos(named.Obj().Pos())
+			} else {
+				w.pos(token.NoPos)
+			}
+			w.typ(ft, tPkg)
+		}
+
+		n = t.NumExplicitMethods()
+		w.uint64(uint64(n))
+		for i := 0; i < n; i++ {
+			m := t.ExplicitMethod(i)
+			w.pos(m.Pos())
+			w.string(m.Name())
+			sig, _ := m.Type().(*types.Signature)
+			w.signature(sig)
+		}
+
+	case *typeparams.Union:
+		w.startType(unionType)
+		nt := t.Len()
+		w.uint64(uint64(nt))
+		for i := 0; i < nt; i++ {
+			term := t.Term(i)
+			w.bool(term.Tilde())
+			w.typ(term.Type(), pkg)
+		}
+
+	default:
+		panic(internalErrorf("unexpected type: %v, %v", t, reflect.TypeOf(t)))
+	}
+}
+
+func (w *exportWriter) setPkg(pkg *types.Package, write bool) {
+	if write {
+		w.pkg(pkg)
+	}
+
+	w.currPkg = pkg
+}
+
+func (w *exportWriter) signature(sig *types.Signature) {
+	w.paramList(sig.Params())
+	w.paramList(sig.Results())
+	if sig.Params().Len() > 0 {
+		w.bool(sig.Variadic())
+	}
+}
+
+func (w *exportWriter) typeList(ts *typeparams.TypeList, pkg *types.Package) {
+	w.uint64(uint64(ts.Len()))
+	for i := 0; i < ts.Len(); i++ {
+		w.typ(ts.At(i), pkg)
+	}
+}
+
+func (w *exportWriter) tparamList(list *typeparams.TypeParamList, pkg *types.Package) {
+	ll := uint64(list.Len())
+	w.uint64(ll)
+	for i := 0; i < list.Len(); i++ {
+		w.typ(list.At(i), pkg)
+	}
+}
+
+func (w *exportWriter) paramList(tup *types.Tuple) {
+	n := tup.Len()
+	w.uint64(uint64(n))
+	for i := 0; i < n; i++ {
+		w.param(tup.At(i))
+	}
+}
+
+func (w *exportWriter) param(obj types.Object) {
+	w.pos(obj.Pos())
+	w.localIdent(obj)
+	w.typ(obj.Type(), obj.Pkg())
+}
+
+func (w *exportWriter) value(typ types.Type, v constant.Value) {
+	w.typ(typ, nil)
+
+	switch b := typ.Underlying().(*types.Basic); b.Info() & types.IsConstType {
+	case types.IsBoolean:
+		w.bool(constant.BoolVal(v))
+	case types.IsInteger:
+		var i big.Int
+		if i64, exact := constant.Int64Val(v); exact {
+			i.SetInt64(i64)
+		} else if ui64, exact := constant.Uint64Val(v); exact {
+			i.SetUint64(ui64)
+		} else {
+			i.SetString(v.ExactString(), 10)
+		}
+		w.mpint(&i, typ)
+	case types.IsFloat:
+		f := constantToFloat(v)
+		w.mpfloat(f, typ)
+	case types.IsComplex:
+		w.mpfloat(constantToFloat(constant.Real(v)), typ)
+		w.mpfloat(constantToFloat(constant.Imag(v)), typ)
+	case types.IsString:
+		w.string(constant.StringVal(v))
+	default:
+		if b.Kind() == types.Invalid {
+			// package contains type errors
+			break
+		}
+		panic(internalErrorf("unexpected type %v (%v)", typ, typ.Underlying()))
+	}
+}
+
+// constantToFloat converts a constant.Value with kind constant.Float to a
+// big.Float.
+func constantToFloat(x constant.Value) *big.Float {
+	x = constant.ToFloat(x)
+	// Use the same floating-point precision (512) as cmd/compile
+	// (see Mpprec in cmd/compile/internal/gc/mpfloat.go).
+	const mpprec = 512
+	var f big.Float
+	f.SetPrec(mpprec)
+	if v, exact := constant.Float64Val(x); exact {
+		// float64
+		f.SetFloat64(v)
+	} else if num, denom := constant.Num(x), constant.Denom(x); num.Kind() == constant.Int {
+		// TODO(gri): add big.Rat accessor to constant.Value.
+		n := valueToRat(num)
+		d := valueToRat(denom)
+		f.SetRat(n.Quo(n, d))
+	} else {
+		// Value too large to represent as a fraction => inaccessible.
+		// TODO(gri): add big.Float accessor to constant.Value.
+		_, ok := f.SetString(x.ExactString())
+		assert(ok)
+	}
+	return &f
+}
+
+// mpint exports a multi-precision integer.
+//
+// For unsigned types, small values are written out as a single
+// byte. Larger values are written out as a length-prefixed big-endian
+// byte string, where the length prefix is encoded as its complement.
+// For example, bytes 0, 1, and 2 directly represent the integer
+// values 0, 1, and 2; while bytes 255, 254, and 253 indicate a 1-,
+// 2-, and 3-byte big-endian string follow.
+//
+// Encoding for signed types use the same general approach as for
+// unsigned types, except small values use zig-zag encoding and the
+// bottom bit of length prefix byte for large values is reserved as a
+// sign bit.
+//
+// The exact boundary between small and large encodings varies
+// according to the maximum number of bytes needed to encode a value
+// of type typ. As a special case, 8-bit types are always encoded as a
+// single byte.
+//
+// TODO(mdempsky): Is this level of complexity really worthwhile?
+func (w *exportWriter) mpint(x *big.Int, typ types.Type) {
+	basic, ok := typ.Underlying().(*types.Basic)
+	if !ok {
+		panic(internalErrorf("unexpected type %v (%T)", typ.Underlying(), typ.Underlying()))
+	}
+
+	signed, maxBytes := intSize(basic)
+
+	negative := x.Sign() < 0
+	if !signed && negative {
+		panic(internalErrorf("negative unsigned integer; type %v, value %v", typ, x))
+	}
+
+	b := x.Bytes()
+	if len(b) > 0 && b[0] == 0 {
+		panic(internalErrorf("leading zeros"))
+	}
+	if uint(len(b)) > maxBytes {
+		panic(internalErrorf("bad mpint length: %d > %d (type %v, value %v)", len(b), maxBytes, typ, x))
+	}
+
+	maxSmall := 256 - maxBytes
+	if signed {
+		maxSmall = 256 - 2*maxBytes
+	}
+	if maxBytes == 1 {
+		maxSmall = 256
+	}
+
+	// Check if x can use small value encoding.
+	if len(b) <= 1 {
+		var ux uint
+		if len(b) == 1 {
+			ux = uint(b[0])
+		}
+		if signed {
+			ux <<= 1
+			if negative {
+				ux--
+			}
+		}
+		if ux < maxSmall {
+			w.data.WriteByte(byte(ux))
+			return
+		}
+	}
+
+	n := 256 - uint(len(b))
+	if signed {
+		n = 256 - 2*uint(len(b))
+		if negative {
+			n |= 1
+		}
+	}
+	if n < maxSmall || n >= 256 {
+		panic(internalErrorf("encoding mistake: %d, %v, %v => %d", len(b), signed, negative, n))
+	}
+
+	w.data.WriteByte(byte(n))
+	w.data.Write(b)
+}
+
+// mpfloat exports a multi-precision floating point number.
+//
+// The number's value is decomposed into mantissa × 2**exponent, where
+// mantissa is an integer. The value is written out as mantissa (as a
+// multi-precision integer) and then the exponent, except exponent is
+// omitted if mantissa is zero.
+func (w *exportWriter) mpfloat(f *big.Float, typ types.Type) {
+	if f.IsInf() {
+		panic("infinite constant")
+	}
+
+	// Break into f = mant × 2**exp, with 0.5 <= mant < 1.
+	var mant big.Float
+	exp := int64(f.MantExp(&mant))
+
+	// Scale so that mant is an integer.
+	prec := mant.MinPrec()
+	mant.SetMantExp(&mant, int(prec))
+	exp -= int64(prec)
+
+	manti, acc := mant.Int(nil)
+	if acc != big.Exact {
+		panic(internalErrorf("mantissa scaling failed for %f (%s)", f, acc))
+	}
+	w.mpint(manti, typ)
+	if manti.Sign() != 0 {
+		w.int64(exp)
+	}
+}
+
+func (w *exportWriter) bool(b bool) bool {
+	var x uint64
+	if b {
+		x = 1
+	}
+	w.uint64(x)
+	return b
+}
+
+func (w *exportWriter) int64(x int64)   { w.data.int64(x) }
+func (w *exportWriter) uint64(x uint64) { w.data.uint64(x) }
+func (w *exportWriter) string(s string) { w.uint64(w.p.stringOff(s)) }
+
+func (w *exportWriter) localIdent(obj types.Object) {
+	// Anonymous parameters.
+	if obj == nil {
+		w.string("")
+		return
+	}
+
+	name := indexName(obj)
+	if name == "_" {
+		w.string("_")
+		return
+	}
+
+	w.string(name)
+}
+
+type intWriter struct {
+	bytes.Buffer
+}
+
+func (w *intWriter) int64(x int64) {
+	var buf [binary.MaxVarintLen64]byte
+	n := binary.PutVarint(buf[:], x)
+	w.Write(buf[:n])
+}
+
+func (w *intWriter) uint64(x uint64) {
+	var buf [binary.MaxVarintLen64]byte
+	n := binary.PutUvarint(buf[:], x)
+	w.Write(buf[:n])
+}
+
+func assert(cond bool) {
+	if !cond {
+		panic("internal error: assertion failed")
+	}
+}
+
+// The below is copied from go/src/cmd/compile/internal/gc/syntax.go.
+
+// objQueue is a FIFO queue of types.Object. The zero value of objQueue is
+// a ready-to-use empty queue.
+type objQueue struct {
+	ring       []types.Object
+	head, tail int
+}
+
+// empty returns true if q contains no Nodes.
+func (q *objQueue) empty() bool {
+	return q.head == q.tail
+}
+
+// pushTail appends n to the tail of the queue.
+func (q *objQueue) pushTail(obj types.Object) {
+	if len(q.ring) == 0 {
+		q.ring = make([]types.Object, 16)
+	} else if q.head+len(q.ring) == q.tail {
+		// Grow the ring.
+		nring := make([]types.Object, len(q.ring)*2)
+		// Copy the old elements.
+		part := q.ring[q.head%len(q.ring):]
+		if q.tail-q.head <= len(part) {
+			part = part[:q.tail-q.head]
+			copy(nring, part)
+		} else {
+			pos := copy(nring, part)
+			copy(nring[pos:], q.ring[:q.tail%len(q.ring)])
+		}
+		q.ring, q.head, q.tail = nring, 0, q.tail-q.head
+	}
+
+	q.ring[q.tail%len(q.ring)] = obj
+	q.tail++
+}
+
+// popHead pops a node from the head of the queue. It panics if q is empty.
+func (q *objQueue) popHead() types.Object {
+	if q.empty() {
+		panic("dequeue empty")
+	}
+	obj := q.ring[q.head%len(q.ring)]
+	q.head++
+	return obj
+}
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/iimport.go b/vendor/golang.org/x/tools/go/internal/gcimporter/iimport.go
new file mode 100644
index 00000000..1fcc87e5
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/iimport.go
@@ -0,0 +1,845 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Indexed package import.
+// See cmd/compile/internal/gc/iexport.go for the export data format.
+
+// This file is a copy of $GOROOT/src/go/internal/gcimporter/iimport.go.
+
+package gcimporter
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"go/constant"
+	"go/token"
+	"go/types"
+	"io"
+	"sort"
+
+	"golang.org/x/tools/internal/typeparams"
+)
+
+type intReader struct {
+	*bytes.Reader
+	path string
+}
+
+func (r *intReader) int64() int64 {
+	i, err := binary.ReadVarint(r.Reader)
+	if err != nil {
+		errorf("import %q: read varint error: %v", r.path, err)
+	}
+	return i
+}
+
+func (r *intReader) uint64() uint64 {
+	i, err := binary.ReadUvarint(r.Reader)
+	if err != nil {
+		errorf("import %q: read varint error: %v", r.path, err)
+	}
+	return i
+}
+
+// Keep this in sync with constants in iexport.go.
+const (
+	iexportVersionGo1_11 = 0
+	iexportVersionPosCol = 1
+	// TODO: before release, change this back to 2.
+	iexportVersionGenerics = iexportVersionPosCol
+
+	iexportVersionCurrent = iexportVersionGenerics
+)
+
+type ident struct {
+	pkg  string
+	name string
+}
+
+const predeclReserved = 32
+
+type itag uint64
+
+const (
+	// Types
+	definedType itag = iota
+	pointerType
+	sliceType
+	arrayType
+	chanType
+	mapType
+	signatureType
+	structType
+	interfaceType
+	typeParamType
+	instanceType
+	unionType
+)
+
+// IImportData imports a package from the serialized package data
+// and returns 0 and a reference to the package.
+// If the export data version is not recognized or the format is otherwise
+// compromised, an error is returned.
+func IImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (int, *types.Package, error) {
+	pkgs, err := iimportCommon(fset, imports, data, false, path)
+	if err != nil {
+		return 0, nil, err
+	}
+	return 0, pkgs[0], nil
+}
+
+// IImportBundle imports a set of packages from the serialized package bundle.
+func IImportBundle(fset *token.FileSet, imports map[string]*types.Package, data []byte) ([]*types.Package, error) {
+	return iimportCommon(fset, imports, data, true, "")
+}
+
+func iimportCommon(fset *token.FileSet, imports map[string]*types.Package, data []byte, bundle bool, path string) (pkgs []*types.Package, err error) {
+	const currentVersion = 1
+	version := int64(-1)
+	if !debug {
+		defer func() {
+			if e := recover(); e != nil {
+				if version > currentVersion {
+					err = fmt.Errorf("cannot import %q (%v), export data is newer version - update tool", path, e)
+				} else {
+					err = fmt.Errorf("cannot import %q (%v), possibly version skew - reinstall package", path, e)
+				}
+			}
+		}()
+	}
+
+	r := &intReader{bytes.NewReader(data), path}
+
+	if bundle {
+		bundleVersion := r.uint64()
+		switch bundleVersion {
+		case bundleVersion:
+		default:
+			errorf("unknown bundle format version %d", bundleVersion)
+		}
+	}
+
+	version = int64(r.uint64())
+	switch version {
+	case /* iexportVersionGenerics, */ iexportVersionPosCol, iexportVersionGo1_11:
+	default:
+		if version > iexportVersionGenerics {
+			errorf("unstable iexport format version %d, just rebuild compiler and std library", version)
+		} else {
+			errorf("unknown iexport format version %d", version)
+		}
+	}
+
+	sLen := int64(r.uint64())
+	dLen := int64(r.uint64())
+
+	whence, _ := r.Seek(0, io.SeekCurrent)
+	stringData := data[whence : whence+sLen]
+	declData := data[whence+sLen : whence+sLen+dLen]
+	r.Seek(sLen+dLen, io.SeekCurrent)
+
+	p := iimporter{
+		exportVersion: version,
+		ipath:         path,
+		version:       int(version),
+
+		stringData:  stringData,
+		stringCache: make(map[uint64]string),
+		pkgCache:    make(map[uint64]*types.Package),
+
+		declData: declData,
+		pkgIndex: make(map[*types.Package]map[string]uint64),
+		typCache: make(map[uint64]types.Type),
+		// Separate map for typeparams, keyed by their package and unique
+		// name (name with subscript).
+		tparamIndex: make(map[ident]types.Type),
+
+		fake: fakeFileSet{
+			fset:  fset,
+			files: make(map[string]*token.File),
+		},
+	}
+
+	for i, pt := range predeclared() {
+		p.typCache[uint64(i)] = pt
+	}
+
+	pkgList := make([]*types.Package, r.uint64())
+	for i := range pkgList {
+		pkgPathOff := r.uint64()
+		pkgPath := p.stringAt(pkgPathOff)
+		pkgName := p.stringAt(r.uint64())
+		_ = r.uint64() // package height; unused by go/types
+
+		if pkgPath == "" {
+			pkgPath = path
+		}
+		pkg := imports[pkgPath]
+		if pkg == nil {
+			pkg = types.NewPackage(pkgPath, pkgName)
+			imports[pkgPath] = pkg
+		} else if pkg.Name() != pkgName {
+			errorf("conflicting names %s and %s for package %q", pkg.Name(), pkgName, path)
+		}
+
+		p.pkgCache[pkgPathOff] = pkg
+
+		nameIndex := make(map[string]uint64)
+		for nSyms := r.uint64(); nSyms > 0; nSyms-- {
+			name := p.stringAt(r.uint64())
+			nameIndex[name] = r.uint64()
+		}
+
+		p.pkgIndex[pkg] = nameIndex
+		pkgList[i] = pkg
+	}
+
+	if bundle {
+		pkgs = make([]*types.Package, r.uint64())
+		for i := range pkgs {
+			pkg := p.pkgAt(r.uint64())
+			imps := make([]*types.Package, r.uint64())
+			for j := range imps {
+				imps[j] = p.pkgAt(r.uint64())
+			}
+			pkg.SetImports(imps)
+			pkgs[i] = pkg
+		}
+	} else {
+		if len(pkgList) == 0 {
+			errorf("no packages found for %s", path)
+			panic("unreachable")
+		}
+		pkgs = pkgList[:1]
+
+		// record all referenced packages as imports
+		list := append(([]*types.Package)(nil), pkgList[1:]...)
+		sort.Sort(byPath(list))
+		pkgs[0].SetImports(list)
+	}
+
+	for _, pkg := range pkgs {
+		if pkg.Complete() {
+			continue
+		}
+
+		names := make([]string, 0, len(p.pkgIndex[pkg]))
+		for name := range p.pkgIndex[pkg] {
+			names = append(names, name)
+		}
+		sort.Strings(names)
+		for _, name := range names {
+			p.doDecl(pkg, name)
+		}
+
+		// package was imported completely and without errors
+		pkg.MarkComplete()
+	}
+
+	for _, typ := range p.interfaceList {
+		typ.Complete()
+	}
+
+	return pkgs, nil
+}
+
+type iimporter struct {
+	exportVersion int64
+	ipath         string
+	version       int
+
+	stringData  []byte
+	stringCache map[uint64]string
+	pkgCache    map[uint64]*types.Package
+
+	declData    []byte
+	pkgIndex    map[*types.Package]map[string]uint64
+	typCache    map[uint64]types.Type
+	tparamIndex map[ident]types.Type
+
+	fake          fakeFileSet
+	interfaceList []*types.Interface
+}
+
+func (p *iimporter) doDecl(pkg *types.Package, name string) {
+	// See if we've already imported this declaration.
+	if obj := pkg.Scope().Lookup(name); obj != nil {
+		return
+	}
+
+	off, ok := p.pkgIndex[pkg][name]
+	if !ok {
+		errorf("%v.%v not in index", pkg, name)
+	}
+
+	r := &importReader{p: p, currPkg: pkg}
+	r.declReader.Reset(p.declData[off:])
+
+	r.obj(name)
+}
+
+func (p *iimporter) stringAt(off uint64) string {
+	if s, ok := p.stringCache[off]; ok {
+		return s
+	}
+
+	slen, n := binary.Uvarint(p.stringData[off:])
+	if n <= 0 {
+		errorf("varint failed")
+	}
+	spos := off + uint64(n)
+	s := string(p.stringData[spos : spos+slen])
+	p.stringCache[off] = s
+	return s
+}
+
+func (p *iimporter) pkgAt(off uint64) *types.Package {
+	if pkg, ok := p.pkgCache[off]; ok {
+		return pkg
+	}
+	path := p.stringAt(off)
+	errorf("missing package %q in %q", path, p.ipath)
+	return nil
+}
+
+func (p *iimporter) typAt(off uint64, base *types.Named) types.Type {
+	if t, ok := p.typCache[off]; ok && (base == nil || !isInterface(t)) {
+		return t
+	}
+
+	if off < predeclReserved {
+		errorf("predeclared type missing from cache: %v", off)
+	}
+
+	r := &importReader{p: p}
+	r.declReader.Reset(p.declData[off-predeclReserved:])
+	t := r.doType(base)
+
+	if base == nil || !isInterface(t) {
+		p.typCache[off] = t
+	}
+	return t
+}
+
+type importReader struct {
+	p          *iimporter
+	declReader bytes.Reader
+	currPkg    *types.Package
+	prevFile   string
+	prevLine   int64
+	prevColumn int64
+}
+
+func (r *importReader) obj(name string) {
+	tag := r.byte()
+	pos := r.pos()
+
+	switch tag {
+	case 'A':
+		typ := r.typ()
+
+		r.declare(types.NewTypeName(pos, r.currPkg, name, typ))
+
+	case 'C':
+		typ, val := r.value()
+
+		r.declare(types.NewConst(pos, r.currPkg, name, typ, val))
+
+	case 'F', 'G':
+		var tparams []*typeparams.TypeParam
+		if tag == 'G' {
+			tparams = r.tparamList()
+		}
+		sig := r.signature(nil)
+		typeparams.SetForSignature(sig, tparams)
+		r.declare(types.NewFunc(pos, r.currPkg, name, sig))
+
+	case 'T', 'U':
+		// Types can be recursive. We need to setup a stub
+		// declaration before recursing.
+		obj := types.NewTypeName(pos, r.currPkg, name, nil)
+		named := types.NewNamed(obj, nil, nil)
+		// Declare obj before calling r.tparamList, so the new type name is recognized
+		// if used in the constraint of one of its own typeparams (see #48280).
+		r.declare(obj)
+		if tag == 'U' {
+			tparams := r.tparamList()
+			typeparams.SetForNamed(named, tparams)
+		}
+
+		underlying := r.p.typAt(r.uint64(), named).Underlying()
+		named.SetUnderlying(underlying)
+
+		if !isInterface(underlying) {
+			for n := r.uint64(); n > 0; n-- {
+				mpos := r.pos()
+				mname := r.ident()
+				recv := r.param()
+				msig := r.signature(recv)
+
+				// If the receiver has any targs, set those as the
+				// rparams of the method (since those are the
+				// typeparams being used in the method sig/body).
+				targs := typeparams.NamedTypeArgs(baseType(msig.Recv().Type()))
+				if targs.Len() > 0 {
+					rparams := make([]*typeparams.TypeParam, targs.Len())
+					for i := range rparams {
+						// TODO(rfindley): this is less tolerant than the standard library
+						// go/internal/gcimporter, which calls under(...) and is tolerant
+						// of nil rparams. Bring them in sync by making the standard
+						// library importer stricter.
+						rparams[i] = targs.At(i).(*typeparams.TypeParam)
+					}
+					typeparams.SetRecvTypeParams(msig, rparams)
+				}
+
+				named.AddMethod(types.NewFunc(mpos, r.currPkg, mname, msig))
+			}
+		}
+
+	case 'P':
+		// We need to "declare" a typeparam in order to have a name that
+		// can be referenced recursively (if needed) in the type param's
+		// bound.
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected type param type")
+		}
+		name0, sub := parseSubscript(name)
+		tn := types.NewTypeName(pos, r.currPkg, name0, nil)
+		t := typeparams.NewTypeParam(tn, nil)
+		if sub == 0 {
+			errorf("name %q missing subscript", name)
+		}
+
+		// TODO(rfindley): can we use a different, stable ID?
+		// t.SetId(sub)
+
+		// To handle recursive references to the typeparam within its
+		// bound, save the partial type in tparamIndex before reading the bounds.
+		id := ident{r.currPkg.Name(), name}
+		r.p.tparamIndex[id] = t
+
+		typeparams.SetTypeParamConstraint(t, r.typ())
+
+	case 'V':
+		typ := r.typ()
+
+		r.declare(types.NewVar(pos, r.currPkg, name, typ))
+
+	default:
+		errorf("unexpected tag: %v", tag)
+	}
+}
+
+func (r *importReader) declare(obj types.Object) {
+	obj.Pkg().Scope().Insert(obj)
+}
+
+func (r *importReader) value() (typ types.Type, val constant.Value) {
+	typ = r.typ()
+
+	switch b := typ.Underlying().(*types.Basic); b.Info() & types.IsConstType {
+	case types.IsBoolean:
+		val = constant.MakeBool(r.bool())
+
+	case types.IsString:
+		val = constant.MakeString(r.string())
+
+	case types.IsInteger:
+		val = r.mpint(b)
+
+	case types.IsFloat:
+		val = r.mpfloat(b)
+
+	case types.IsComplex:
+		re := r.mpfloat(b)
+		im := r.mpfloat(b)
+		val = constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
+
+	default:
+		if b.Kind() == types.Invalid {
+			val = constant.MakeUnknown()
+			return
+		}
+		errorf("unexpected type %v", typ) // panics
+		panic("unreachable")
+	}
+
+	return
+}
+
+func intSize(b *types.Basic) (signed bool, maxBytes uint) {
+	if (b.Info() & types.IsUntyped) != 0 {
+		return true, 64
+	}
+
+	switch b.Kind() {
+	case types.Float32, types.Complex64:
+		return true, 3
+	case types.Float64, types.Complex128:
+		return true, 7
+	}
+
+	signed = (b.Info() & types.IsUnsigned) == 0
+	switch b.Kind() {
+	case types.Int8, types.Uint8:
+		maxBytes = 1
+	case types.Int16, types.Uint16:
+		maxBytes = 2
+	case types.Int32, types.Uint32:
+		maxBytes = 4
+	default:
+		maxBytes = 8
+	}
+
+	return
+}
+
+func (r *importReader) mpint(b *types.Basic) constant.Value {
+	signed, maxBytes := intSize(b)
+
+	maxSmall := 256 - maxBytes
+	if signed {
+		maxSmall = 256 - 2*maxBytes
+	}
+	if maxBytes == 1 {
+		maxSmall = 256
+	}
+
+	n, _ := r.declReader.ReadByte()
+	if uint(n) < maxSmall {
+		v := int64(n)
+		if signed {
+			v >>= 1
+			if n&1 != 0 {
+				v = ^v
+			}
+		}
+		return constant.MakeInt64(v)
+	}
+
+	v := -n
+	if signed {
+		v = -(n &^ 1) >> 1
+	}
+	if v < 1 || uint(v) > maxBytes {
+		errorf("weird decoding: %v, %v => %v", n, signed, v)
+	}
+
+	buf := make([]byte, v)
+	io.ReadFull(&r.declReader, buf)
+
+	// convert to little endian
+	// TODO(gri) go/constant should have a more direct conversion function
+	//           (e.g., once it supports a big.Float based implementation)
+	for i, j := 0, len(buf)-1; i < j; i, j = i+1, j-1 {
+		buf[i], buf[j] = buf[j], buf[i]
+	}
+
+	x := constant.MakeFromBytes(buf)
+	if signed && n&1 != 0 {
+		x = constant.UnaryOp(token.SUB, x, 0)
+	}
+	return x
+}
+
+func (r *importReader) mpfloat(b *types.Basic) constant.Value {
+	x := r.mpint(b)
+	if constant.Sign(x) == 0 {
+		return x
+	}
+
+	exp := r.int64()
+	switch {
+	case exp > 0:
+		x = constant.Shift(x, token.SHL, uint(exp))
+		// Ensure that the imported Kind is Float, else this constant may run into
+		// bitsize limits on overlarge integers. Eventually we can instead adopt
+		// the approach of CL 288632, but that CL relies on go/constant APIs that
+		// were introduced in go1.13.
+		//
+		// TODO(rFindley): sync the logic here with tip Go once we no longer
+		// support go1.12.
+		x = constant.ToFloat(x)
+	case exp < 0:
+		d := constant.Shift(constant.MakeInt64(1), token.SHL, uint(-exp))
+		x = constant.BinaryOp(x, token.QUO, d)
+	}
+	return x
+}
+
+func (r *importReader) ident() string {
+	return r.string()
+}
+
+func (r *importReader) qualifiedIdent() (*types.Package, string) {
+	name := r.string()
+	pkg := r.pkg()
+	return pkg, name
+}
+
+func (r *importReader) pos() token.Pos {
+	if r.p.exportVersion >= iexportVersionPosCol {
+		r.posv1()
+	} else {
+		r.posv0()
+	}
+
+	if r.prevFile == "" && r.prevLine == 0 && r.prevColumn == 0 {
+		return token.NoPos
+	}
+	return r.p.fake.pos(r.prevFile, int(r.prevLine), int(r.prevColumn))
+}
+
+func (r *importReader) posv0() {
+	delta := r.int64()
+	if delta != deltaNewFile {
+		r.prevLine += delta
+	} else if l := r.int64(); l == -1 {
+		r.prevLine += deltaNewFile
+	} else {
+		r.prevFile = r.string()
+		r.prevLine = l
+	}
+}
+
+func (r *importReader) posv1() {
+	delta := r.int64()
+	r.prevColumn += delta >> 1
+	if delta&1 != 0 {
+		delta = r.int64()
+		r.prevLine += delta >> 1
+		if delta&1 != 0 {
+			r.prevFile = r.string()
+		}
+	}
+}
+
+func (r *importReader) typ() types.Type {
+	return r.p.typAt(r.uint64(), nil)
+}
+
+func isInterface(t types.Type) bool {
+	_, ok := t.(*types.Interface)
+	return ok
+}
+
+func (r *importReader) pkg() *types.Package { return r.p.pkgAt(r.uint64()) }
+func (r *importReader) string() string      { return r.p.stringAt(r.uint64()) }
+
+func (r *importReader) doType(base *types.Named) types.Type {
+	switch k := r.kind(); k {
+	default:
+		errorf("unexpected kind tag in %q: %v", r.p.ipath, k)
+		return nil
+
+	case definedType:
+		pkg, name := r.qualifiedIdent()
+		r.p.doDecl(pkg, name)
+		return pkg.Scope().Lookup(name).(*types.TypeName).Type()
+	case pointerType:
+		return types.NewPointer(r.typ())
+	case sliceType:
+		return types.NewSlice(r.typ())
+	case arrayType:
+		n := r.uint64()
+		return types.NewArray(r.typ(), int64(n))
+	case chanType:
+		dir := chanDir(int(r.uint64()))
+		return types.NewChan(dir, r.typ())
+	case mapType:
+		return types.NewMap(r.typ(), r.typ())
+	case signatureType:
+		r.currPkg = r.pkg()
+		return r.signature(nil)
+
+	case structType:
+		r.currPkg = r.pkg()
+
+		fields := make([]*types.Var, r.uint64())
+		tags := make([]string, len(fields))
+		for i := range fields {
+			fpos := r.pos()
+			fname := r.ident()
+			ftyp := r.typ()
+			emb := r.bool()
+			tag := r.string()
+
+			fields[i] = types.NewField(fpos, r.currPkg, fname, ftyp, emb)
+			tags[i] = tag
+		}
+		return types.NewStruct(fields, tags)
+
+	case interfaceType:
+		r.currPkg = r.pkg()
+
+		embeddeds := make([]types.Type, r.uint64())
+		for i := range embeddeds {
+			_ = r.pos()
+			embeddeds[i] = r.typ()
+		}
+
+		methods := make([]*types.Func, r.uint64())
+		for i := range methods {
+			mpos := r.pos()
+			mname := r.ident()
+
+			// TODO(mdempsky): Matches bimport.go, but I
+			// don't agree with this.
+			var recv *types.Var
+			if base != nil {
+				recv = types.NewVar(token.NoPos, r.currPkg, "", base)
+			}
+
+			msig := r.signature(recv)
+			methods[i] = types.NewFunc(mpos, r.currPkg, mname, msig)
+		}
+
+		typ := newInterface(methods, embeddeds)
+		r.p.interfaceList = append(r.p.interfaceList, typ)
+		return typ
+
+	case typeParamType:
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected type param type")
+		}
+		pkg, name := r.qualifiedIdent()
+		id := ident{pkg.Name(), name}
+		if t, ok := r.p.tparamIndex[id]; ok {
+			// We're already in the process of importing this typeparam.
+			return t
+		}
+		// Otherwise, import the definition of the typeparam now.
+		r.p.doDecl(pkg, name)
+		return r.p.tparamIndex[id]
+
+	case instanceType:
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected instantiation type")
+		}
+		// pos does not matter for instances: they are positioned on the original
+		// type.
+		_ = r.pos()
+		len := r.uint64()
+		targs := make([]types.Type, len)
+		for i := range targs {
+			targs[i] = r.typ()
+		}
+		baseType := r.typ()
+		// The imported instantiated type doesn't include any methods, so
+		// we must always use the methods of the base (orig) type.
+		// TODO provide a non-nil *Environment
+		t, _ := typeparams.Instantiate(nil, baseType, targs, false)
+		return t
+
+	case unionType:
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected instantiation type")
+		}
+		terms := make([]*typeparams.Term, r.uint64())
+		for i := range terms {
+			terms[i] = typeparams.NewTerm(r.bool(), r.typ())
+		}
+		return typeparams.NewUnion(terms)
+	}
+}
+
+func (r *importReader) kind() itag {
+	return itag(r.uint64())
+}
+
+func (r *importReader) signature(recv *types.Var) *types.Signature {
+	params := r.paramList()
+	results := r.paramList()
+	variadic := params.Len() > 0 && r.bool()
+	return types.NewSignature(recv, params, results, variadic)
+}
+
+func (r *importReader) tparamList() []*typeparams.TypeParam {
+	n := r.uint64()
+	if n == 0 {
+		return nil
+	}
+	xs := make([]*typeparams.TypeParam, n)
+	for i := range xs {
+		// Note: the standard library importer is tolerant of nil types here,
+		// though would panic in SetTypeParams.
+		xs[i] = r.typ().(*typeparams.TypeParam)
+	}
+	return xs
+}
+
+func (r *importReader) paramList() *types.Tuple {
+	xs := make([]*types.Var, r.uint64())
+	for i := range xs {
+		xs[i] = r.param()
+	}
+	return types.NewTuple(xs...)
+}
+
+func (r *importReader) param() *types.Var {
+	pos := r.pos()
+	name := r.ident()
+	typ := r.typ()
+	return types.NewParam(pos, r.currPkg, name, typ)
+}
+
+func (r *importReader) bool() bool {
+	return r.uint64() != 0
+}
+
+func (r *importReader) int64() int64 {
+	n, err := binary.ReadVarint(&r.declReader)
+	if err != nil {
+		errorf("readVarint: %v", err)
+	}
+	return n
+}
+
+func (r *importReader) uint64() uint64 {
+	n, err := binary.ReadUvarint(&r.declReader)
+	if err != nil {
+		errorf("readUvarint: %v", err)
+	}
+	return n
+}
+
+func (r *importReader) byte() byte {
+	x, err := r.declReader.ReadByte()
+	if err != nil {
+		errorf("declReader.ReadByte: %v", err)
+	}
+	return x
+}
+
+func baseType(typ types.Type) *types.Named {
+	// pointer receivers are never types.Named types
+	if p, _ := typ.(*types.Pointer); p != nil {
+		typ = p.Elem()
+	}
+	// receiver base types are always (possibly generic) types.Named types
+	n, _ := typ.(*types.Named)
+	return n
+}
+
+func parseSubscript(name string) (string, uint64) {
+	// Extract the subscript value from the type param name. We export
+	// and import the subscript value, so that all type params have
+	// unique names.
+	sub := uint64(0)
+	startsub := -1
+	for i, r := range name {
+		if '₀' <= r && r < '₀'+10 {
+			if startsub == -1 {
+				startsub = i
+			}
+			sub = sub*10 + uint64(r-'₀')
+		}
+	}
+	if startsub >= 0 {
+		name = name[:startsub]
+	}
+	return name, sub
+}
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/newInterface10.go b/vendor/golang.org/x/tools/go/internal/gcimporter/newInterface10.go
new file mode 100644
index 00000000..8b163e3d
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/newInterface10.go
@@ -0,0 +1,22 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.11
+// +build !go1.11
+
+package gcimporter
+
+import "go/types"
+
+func newInterface(methods []*types.Func, embeddeds []types.Type) *types.Interface {
+	named := make([]*types.Named, len(embeddeds))
+	for i, e := range embeddeds {
+		var ok bool
+		named[i], ok = e.(*types.Named)
+		if !ok {
+			panic("embedding of non-defined interfaces in interfaces is not supported before Go 1.11")
+		}
+	}
+	return types.NewInterface(methods, named)
+}
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/newInterface11.go b/vendor/golang.org/x/tools/go/internal/gcimporter/newInterface11.go
new file mode 100644
index 00000000..49984f40
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/newInterface11.go
@@ -0,0 +1,14 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.11
+// +build go1.11
+
+package gcimporter
+
+import "go/types"
+
+func newInterface(methods []*types.Func, embeddeds []types.Type) *types.Interface {
+	return types.NewInterfaceType(methods, embeddeds)
+}
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/support_go117.go b/vendor/golang.org/x/tools/go/internal/gcimporter/support_go117.go
new file mode 100644
index 00000000..817a147e
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/support_go117.go
@@ -0,0 +1,16 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !typeparams || !go1.18
+// +build !typeparams !go1.18
+
+package gcimporter
+
+import "go/types"
+
+const iexportVersion = iexportVersionGo1_11
+
+func additionalPredeclared() []types.Type {
+	return nil
+}
diff --git a/vendor/golang.org/x/tools/go/internal/gcimporter/support_go118.go b/vendor/golang.org/x/tools/go/internal/gcimporter/support_go118.go
new file mode 100644
index 00000000..e6b81fc5
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/gcimporter/support_go118.go
@@ -0,0 +1,20 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build typeparams && go1.18
+// +build typeparams,go1.18
+
+package gcimporter
+
+import "go/types"
+
+const iexportVersion = iexportVersionGenerics
+
+// additionalPredeclared returns additional predeclared types in go.1.18.
+func additionalPredeclared() []types.Type {
+	return []types.Type{
+		// comparable
+		types.Universe.Lookup("comparable").Type(),
+	}
+}
diff --git a/vendor/golang.org/x/tools/go/internal/packagesdriver/sizes.go b/vendor/golang.org/x/tools/go/internal/packagesdriver/sizes.go
new file mode 100644
index 00000000..18a002f8
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/internal/packagesdriver/sizes.go
@@ -0,0 +1,49 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package packagesdriver fetches type sizes for go/packages and go/analysis.
+package packagesdriver
+
+import (
+	"context"
+	"fmt"
+	"go/types"
+	"strings"
+
+	"golang.org/x/tools/internal/gocommand"
+)
+
+var debug = false
+
+func GetSizesGolist(ctx context.Context, inv gocommand.Invocation, gocmdRunner *gocommand.Runner) (types.Sizes, error) {
+	inv.Verb = "list"
+	inv.Args = []string{"-f", "{{context.GOARCH}} {{context.Compiler}}", "--", "unsafe"}
+	stdout, stderr, friendlyErr, rawErr := gocmdRunner.RunRaw(ctx, inv)
+	var goarch, compiler string
+	if rawErr != nil {
+		if rawErrMsg := rawErr.Error(); strings.Contains(rawErrMsg, "cannot find main module") || strings.Contains(rawErrMsg, "go.mod file not found") {
+			// User's running outside of a module. All bets are off. Get GOARCH and guess compiler is gc.
+			// TODO(matloob): Is this a problem in practice?
+			inv.Verb = "env"
+			inv.Args = []string{"GOARCH"}
+			envout, enverr := gocmdRunner.Run(ctx, inv)
+			if enverr != nil {
+				return nil, enverr
+			}
+			goarch = strings.TrimSpace(envout.String())
+			compiler = "gc"
+		} else {
+			return nil, friendlyErr
+		}
+	} else {
+		fields := strings.Fields(stdout.String())
+		if len(fields) < 2 {
+			return nil, fmt.Errorf("could not parse GOARCH and Go compiler in format \"<GOARCH> <compiler>\":\nstdout: <<%s>>\nstderr: <<%s>>",
+				stdout.String(), stderr.String())
+		}
+		goarch = fields[0]
+		compiler = fields[1]
+	}
+	return types.SizesFor(compiler, goarch), nil
+}
diff --git a/vendor/golang.org/x/tools/go/packages/doc.go b/vendor/golang.org/x/tools/go/packages/doc.go
new file mode 100644
index 00000000..4bfe28a5
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/packages/doc.go
@@ -0,0 +1,221 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package packages loads Go packages for inspection and analysis.
+
+The Load function takes as input a list of patterns and return a list of Package
+structs describing individual packages matched by those patterns.
+The LoadMode controls the amount of detail in the loaded packages.
+
+Load passes most patterns directly to the underlying build tool,
+but all patterns with the prefix "query=", where query is a
+non-empty string of letters from [a-z], are reserved and may be
+interpreted as query operators.
+
+Two query operators are currently supported: "file" and "pattern".
+
+The query "file=path/to/file.go" matches the package or packages enclosing
+the Go source file path/to/file.go.  For example "file=~/go/src/fmt/print.go"
+might return the packages "fmt" and "fmt [fmt.test]".
+
+The query "pattern=string" causes "string" to be passed directly to
+the underlying build tool. In most cases this is unnecessary,
+but an application can use Load("pattern=" + x) as an escaping mechanism
+to ensure that x is not interpreted as a query operator if it contains '='.
+
+All other query operators are reserved for future use and currently
+cause Load to report an error.
+
+The Package struct provides basic information about the package, including
+
+  - ID, a unique identifier for the package in the returned set;
+  - GoFiles, the names of the package's Go source files;
+  - Imports, a map from source import strings to the Packages they name;
+  - Types, the type information for the package's exported symbols;
+  - Syntax, the parsed syntax trees for the package's source code; and
+  - TypeInfo, the result of a complete type-check of the package syntax trees.
+
+(See the documentation for type Package for the complete list of fields
+and more detailed descriptions.)
+
+For example,
+
+	Load(nil, "bytes", "unicode...")
+
+returns four Package structs describing the standard library packages
+bytes, unicode, unicode/utf16, and unicode/utf8. Note that one pattern
+can match multiple packages and that a package might be matched by
+multiple patterns: in general it is not possible to determine which
+packages correspond to which patterns.
+
+Note that the list returned by Load contains only the packages matched
+by the patterns. Their dependencies can be found by walking the import
+graph using the Imports fields.
+
+The Load function can be configured by passing a pointer to a Config as
+the first argument. A nil Config is equivalent to the zero Config, which
+causes Load to run in LoadFiles mode, collecting minimal information.
+See the documentation for type Config for details.
+
+As noted earlier, the Config.Mode controls the amount of detail
+reported about the loaded packages. See the documentation for type LoadMode
+for details.
+
+Most tools should pass their command-line arguments (after any flags)
+uninterpreted to the loader, so that the loader can interpret them
+according to the conventions of the underlying build system.
+See the Example function for typical usage.
+
+*/
+package packages // import "golang.org/x/tools/go/packages"
+
+/*
+
+Motivation and design considerations
+
+The new package's design solves problems addressed by two existing
+packages: go/build, which locates and describes packages, and
+golang.org/x/tools/go/loader, which loads, parses and type-checks them.
+The go/build.Package structure encodes too much of the 'go build' way
+of organizing projects, leaving us in need of a data type that describes a
+package of Go source code independent of the underlying build system.
+We wanted something that works equally well with go build and vgo, and
+also other build systems such as Bazel and Blaze, making it possible to
+construct analysis tools that work in all these environments.
+Tools such as errcheck and staticcheck were essentially unavailable to
+the Go community at Google, and some of Google's internal tools for Go
+are unavailable externally.
+This new package provides a uniform way to obtain package metadata by
+querying each of these build systems, optionally supporting their
+preferred command-line notations for packages, so that tools integrate
+neatly with users' build environments. The Metadata query function
+executes an external query tool appropriate to the current workspace.
+
+Loading packages always returns the complete import graph "all the way down",
+even if all you want is information about a single package, because the query
+mechanisms of all the build systems we currently support ({go,vgo} list, and
+blaze/bazel aspect-based query) cannot provide detailed information
+about one package without visiting all its dependencies too, so there is
+no additional asymptotic cost to providing transitive information.
+(This property might not be true of a hypothetical 5th build system.)
+
+In calls to TypeCheck, all initial packages, and any package that
+transitively depends on one of them, must be loaded from source.
+Consider A->B->C->D->E: if A,C are initial, A,B,C must be loaded from
+source; D may be loaded from export data, and E may not be loaded at all
+(though it's possible that D's export data mentions it, so a
+types.Package may be created for it and exposed.)
+
+The old loader had a feature to suppress type-checking of function
+bodies on a per-package basis, primarily intended to reduce the work of
+obtaining type information for imported packages. Now that imports are
+satisfied by export data, the optimization no longer seems necessary.
+
+Despite some early attempts, the old loader did not exploit export data,
+instead always using the equivalent of WholeProgram mode. This was due
+to the complexity of mixing source and export data packages (now
+resolved by the upward traversal mentioned above), and because export data
+files were nearly always missing or stale. Now that 'go build' supports
+caching, all the underlying build systems can guarantee to produce
+export data in a reasonable (amortized) time.
+
+Test "main" packages synthesized by the build system are now reported as
+first-class packages, avoiding the need for clients (such as go/ssa) to
+reinvent this generation logic.
+
+One way in which go/packages is simpler than the old loader is in its
+treatment of in-package tests. In-package tests are packages that
+consist of all the files of the library under test, plus the test files.
+The old loader constructed in-package tests by a two-phase process of
+mutation called "augmentation": first it would construct and type check
+all the ordinary library packages and type-check the packages that
+depend on them; then it would add more (test) files to the package and
+type-check again. This two-phase approach had four major problems:
+1) in processing the tests, the loader modified the library package,
+   leaving no way for a client application to see both the test
+   package and the library package; one would mutate into the other.
+2) because test files can declare additional methods on types defined in
+   the library portion of the package, the dispatch of method calls in
+   the library portion was affected by the presence of the test files.
+   This should have been a clue that the packages were logically
+   different.
+3) this model of "augmentation" assumed at most one in-package test
+   per library package, which is true of projects using 'go build',
+   but not other build systems.
+4) because of the two-phase nature of test processing, all packages that
+   import the library package had to be processed before augmentation,
+   forcing a "one-shot" API and preventing the client from calling Load
+   in several times in sequence as is now possible in WholeProgram mode.
+   (TypeCheck mode has a similar one-shot restriction for a different reason.)
+
+Early drafts of this package supported "multi-shot" operation.
+Although it allowed clients to make a sequence of calls (or concurrent
+calls) to Load, building up the graph of Packages incrementally,
+it was of marginal value: it complicated the API
+(since it allowed some options to vary across calls but not others),
+it complicated the implementation,
+it cannot be made to work in Types mode, as explained above,
+and it was less efficient than making one combined call (when this is possible).
+Among the clients we have inspected, none made multiple calls to load
+but could not be easily and satisfactorily modified to make only a single call.
+However, applications changes may be required.
+For example, the ssadump command loads the user-specified packages
+and in addition the runtime package.  It is tempting to simply append
+"runtime" to the user-provided list, but that does not work if the user
+specified an ad-hoc package such as [a.go b.go].
+Instead, ssadump no longer requests the runtime package,
+but seeks it among the dependencies of the user-specified packages,
+and emits an error if it is not found.
+
+Overlays: The Overlay field in the Config allows providing alternate contents
+for Go source files, by providing a mapping from file path to contents.
+go/packages will pull in new imports added in overlay files when go/packages
+is run in LoadImports mode or greater.
+Overlay support for the go list driver isn't complete yet: if the file doesn't
+exist on disk, it will only be recognized in an overlay if it is a non-test file
+and the package would be reported even without the overlay.
+
+Questions & Tasks
+
+- Add GOARCH/GOOS?
+  They are not portable concepts, but could be made portable.
+  Our goal has been to allow users to express themselves using the conventions
+  of the underlying build system: if the build system honors GOARCH
+  during a build and during a metadata query, then so should
+  applications built atop that query mechanism.
+  Conversely, if the target architecture of the build is determined by
+  command-line flags, the application can pass the relevant
+  flags through to the build system using a command such as:
+    myapp -query_flag="--cpu=amd64" -query_flag="--os=darwin"
+  However, this approach is low-level, unwieldy, and non-portable.
+  GOOS and GOARCH seem important enough to warrant a dedicated option.
+
+- How should we handle partial failures such as a mixture of good and
+  malformed patterns, existing and non-existent packages, successful and
+  failed builds, import failures, import cycles, and so on, in a call to
+  Load?
+
+- Support bazel, blaze, and go1.10 list, not just go1.11 list.
+
+- Handle (and test) various partial success cases, e.g.
+  a mixture of good packages and:
+  invalid patterns
+  nonexistent packages
+  empty packages
+  packages with malformed package or import declarations
+  unreadable files
+  import cycles
+  other parse errors
+  type errors
+  Make sure we record errors at the correct place in the graph.
+
+- Missing packages among initial arguments are not reported.
+  Return bogus packages for them, like golist does.
+
+- "undeclared name" errors (for example) are reported out of source file
+  order. I suspect this is due to the breadth-first resolution now used
+  by go/types. Is that a bug? Discuss with gri.
+
+*/
diff --git a/vendor/golang.org/x/tools/go/packages/external.go b/vendor/golang.org/x/tools/go/packages/external.go
new file mode 100644
index 00000000..7242a0a7
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/packages/external.go
@@ -0,0 +1,101 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file enables an external tool to intercept package requests.
+// If the tool is present then its results are used in preference to
+// the go list command.
+
+package packages
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	exec "golang.org/x/sys/execabs"
+	"os"
+	"strings"
+)
+
+// The Driver Protocol
+//
+// The driver, given the inputs to a call to Load, returns metadata about the packages specified.
+// This allows for different build systems to support go/packages by telling go/packages how the
+// packages' source is organized.
+// The driver is a binary, either specified by the GOPACKAGESDRIVER environment variable or in
+// the path as gopackagesdriver. It's given the inputs to load in its argv. See the package
+// documentation in doc.go for the full description of the patterns that need to be supported.
+// A driver receives as a JSON-serialized driverRequest struct in standard input and will
+// produce a JSON-serialized driverResponse (see definition in packages.go) in its standard output.
+
+// driverRequest is used to provide the portion of Load's Config that is needed by a driver.
+type driverRequest struct {
+	Mode LoadMode `json:"mode"`
+	// Env specifies the environment the underlying build system should be run in.
+	Env []string `json:"env"`
+	// BuildFlags are flags that should be passed to the underlying build system.
+	BuildFlags []string `json:"build_flags"`
+	// Tests specifies whether the patterns should also return test packages.
+	Tests bool `json:"tests"`
+	// Overlay maps file paths (relative to the driver's working directory) to the byte contents
+	// of overlay files.
+	Overlay map[string][]byte `json:"overlay"`
+}
+
+// findExternalDriver returns the file path of a tool that supplies
+// the build system package structure, or "" if not found."
+// If GOPACKAGESDRIVER is set in the environment findExternalTool returns its
+// value, otherwise it searches for a binary named gopackagesdriver on the PATH.
+func findExternalDriver(cfg *Config) driver {
+	const toolPrefix = "GOPACKAGESDRIVER="
+	tool := ""
+	for _, env := range cfg.Env {
+		if val := strings.TrimPrefix(env, toolPrefix); val != env {
+			tool = val
+		}
+	}
+	if tool != "" && tool == "off" {
+		return nil
+	}
+	if tool == "" {
+		var err error
+		tool, err = exec.LookPath("gopackagesdriver")
+		if err != nil {
+			return nil
+		}
+	}
+	return func(cfg *Config, words ...string) (*driverResponse, error) {
+		req, err := json.Marshal(driverRequest{
+			Mode:       cfg.Mode,
+			Env:        cfg.Env,
+			BuildFlags: cfg.BuildFlags,
+			Tests:      cfg.Tests,
+			Overlay:    cfg.Overlay,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("failed to encode message to driver tool: %v", err)
+		}
+
+		buf := new(bytes.Buffer)
+		stderr := new(bytes.Buffer)
+		cmd := exec.CommandContext(cfg.Context, tool, words...)
+		cmd.Dir = cfg.Dir
+		cmd.Env = cfg.Env
+		cmd.Stdin = bytes.NewReader(req)
+		cmd.Stdout = buf
+		cmd.Stderr = stderr
+
+		if err := cmd.Run(); err != nil {
+			return nil, fmt.Errorf("%v: %v: %s", tool, err, cmd.Stderr)
+		}
+		if len(stderr.Bytes()) != 0 && os.Getenv("GOPACKAGESPRINTDRIVERERRORS") != "" {
+			fmt.Fprintf(os.Stderr, "%s stderr: <<%s>>\n", cmdDebugStr(cmd), stderr)
+		}
+
+		var response driverResponse
+		if err := json.Unmarshal(buf.Bytes(), &response); err != nil {
+			return nil, err
+		}
+		return &response, nil
+	}
+}
diff --git a/vendor/golang.org/x/tools/go/packages/golist.go b/vendor/golang.org/x/tools/go/packages/golist.go
new file mode 100644
index 00000000..0e1e7f11
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/packages/golist.go
@@ -0,0 +1,1099 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packages
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"go/types"
+	"io/ioutil"
+	"log"
+	"os"
+	"path"
+	"path/filepath"
+	"reflect"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"unicode"
+
+	exec "golang.org/x/sys/execabs"
+	"golang.org/x/tools/go/internal/packagesdriver"
+	"golang.org/x/tools/internal/gocommand"
+	"golang.org/x/tools/internal/packagesinternal"
+	"golang.org/x/xerrors"
+)
+
+// debug controls verbose logging.
+var debug, _ = strconv.ParseBool(os.Getenv("GOPACKAGESDEBUG"))
+
+// A goTooOldError reports that the go command
+// found by exec.LookPath is too old to use the new go list behavior.
+type goTooOldError struct {
+	error
+}
+
+// responseDeduper wraps a driverResponse, deduplicating its contents.
+type responseDeduper struct {
+	seenRoots    map[string]bool
+	seenPackages map[string]*Package
+	dr           *driverResponse
+}
+
+func newDeduper() *responseDeduper {
+	return &responseDeduper{
+		dr:           &driverResponse{},
+		seenRoots:    map[string]bool{},
+		seenPackages: map[string]*Package{},
+	}
+}
+
+// addAll fills in r with a driverResponse.
+func (r *responseDeduper) addAll(dr *driverResponse) {
+	for _, pkg := range dr.Packages {
+		r.addPackage(pkg)
+	}
+	for _, root := range dr.Roots {
+		r.addRoot(root)
+	}
+}
+
+func (r *responseDeduper) addPackage(p *Package) {
+	if r.seenPackages[p.ID] != nil {
+		return
+	}
+	r.seenPackages[p.ID] = p
+	r.dr.Packages = append(r.dr.Packages, p)
+}
+
+func (r *responseDeduper) addRoot(id string) {
+	if r.seenRoots[id] {
+		return
+	}
+	r.seenRoots[id] = true
+	r.dr.Roots = append(r.dr.Roots, id)
+}
+
+type golistState struct {
+	cfg *Config
+	ctx context.Context
+
+	envOnce    sync.Once
+	goEnvError error
+	goEnv      map[string]string
+
+	rootsOnce     sync.Once
+	rootDirsError error
+	rootDirs      map[string]string
+
+	goVersionOnce  sync.Once
+	goVersionError error
+	goVersion      int // The X in Go 1.X.
+
+	// vendorDirs caches the (non)existence of vendor directories.
+	vendorDirs map[string]bool
+}
+
+// getEnv returns Go environment variables. Only specific variables are
+// populated -- computing all of them is slow.
+func (state *golistState) getEnv() (map[string]string, error) {
+	state.envOnce.Do(func() {
+		var b *bytes.Buffer
+		b, state.goEnvError = state.invokeGo("env", "-json", "GOMOD", "GOPATH")
+		if state.goEnvError != nil {
+			return
+		}
+
+		state.goEnv = make(map[string]string)
+		decoder := json.NewDecoder(b)
+		if state.goEnvError = decoder.Decode(&state.goEnv); state.goEnvError != nil {
+			return
+		}
+	})
+	return state.goEnv, state.goEnvError
+}
+
+// mustGetEnv is a convenience function that can be used if getEnv has already succeeded.
+func (state *golistState) mustGetEnv() map[string]string {
+	env, err := state.getEnv()
+	if err != nil {
+		panic(fmt.Sprintf("mustGetEnv: %v", err))
+	}
+	return env
+}
+
+// goListDriver uses the go list command to interpret the patterns and produce
+// the build system package structure.
+// See driver for more details.
+func goListDriver(cfg *Config, patterns ...string) (*driverResponse, error) {
+	// Make sure that any asynchronous go commands are killed when we return.
+	parentCtx := cfg.Context
+	if parentCtx == nil {
+		parentCtx = context.Background()
+	}
+	ctx, cancel := context.WithCancel(parentCtx)
+	defer cancel()
+
+	response := newDeduper()
+
+	state := &golistState{
+		cfg:        cfg,
+		ctx:        ctx,
+		vendorDirs: map[string]bool{},
+	}
+
+	// Fill in response.Sizes asynchronously if necessary.
+	var sizeserr error
+	var sizeswg sync.WaitGroup
+	if cfg.Mode&NeedTypesSizes != 0 || cfg.Mode&NeedTypes != 0 {
+		sizeswg.Add(1)
+		go func() {
+			var sizes types.Sizes
+			sizes, sizeserr = packagesdriver.GetSizesGolist(ctx, state.cfgInvocation(), cfg.gocmdRunner)
+			// types.SizesFor always returns nil or a *types.StdSizes.
+			response.dr.Sizes, _ = sizes.(*types.StdSizes)
+			sizeswg.Done()
+		}()
+	}
+
+	// Determine files requested in contains patterns
+	var containFiles []string
+	restPatterns := make([]string, 0, len(patterns))
+	// Extract file= and other [querytype]= patterns. Report an error if querytype
+	// doesn't exist.
+extractQueries:
+	for _, pattern := range patterns {
+		eqidx := strings.Index(pattern, "=")
+		if eqidx < 0 {
+			restPatterns = append(restPatterns, pattern)
+		} else {
+			query, value := pattern[:eqidx], pattern[eqidx+len("="):]
+			switch query {
+			case "file":
+				containFiles = append(containFiles, value)
+			case "pattern":
+				restPatterns = append(restPatterns, value)
+			case "": // not a reserved query
+				restPatterns = append(restPatterns, pattern)
+			default:
+				for _, rune := range query {
+					if rune < 'a' || rune > 'z' { // not a reserved query
+						restPatterns = append(restPatterns, pattern)
+						continue extractQueries
+					}
+				}
+				// Reject all other patterns containing "="
+				return nil, fmt.Errorf("invalid query type %q in query pattern %q", query, pattern)
+			}
+		}
+	}
+
+	// See if we have any patterns to pass through to go list. Zero initial
+	// patterns also requires a go list call, since it's the equivalent of
+	// ".".
+	if len(restPatterns) > 0 || len(patterns) == 0 {
+		dr, err := state.createDriverResponse(restPatterns...)
+		if err != nil {
+			return nil, err
+		}
+		response.addAll(dr)
+	}
+
+	if len(containFiles) != 0 {
+		if err := state.runContainsQueries(response, containFiles); err != nil {
+			return nil, err
+		}
+	}
+
+	// Only use go/packages' overlay processing if we're using a Go version
+	// below 1.16. Otherwise, go list handles it.
+	if goVersion, err := state.getGoVersion(); err == nil && goVersion < 16 {
+		modifiedPkgs, needPkgs, err := state.processGolistOverlay(response)
+		if err != nil {
+			return nil, err
+		}
+
+		var containsCandidates []string
+		if len(containFiles) > 0 {
+			containsCandidates = append(containsCandidates, modifiedPkgs...)
+			containsCandidates = append(containsCandidates, needPkgs...)
+		}
+		if err := state.addNeededOverlayPackages(response, needPkgs); err != nil {
+			return nil, err
+		}
+		// Check candidate packages for containFiles.
+		if len(containFiles) > 0 {
+			for _, id := range containsCandidates {
+				pkg, ok := response.seenPackages[id]
+				if !ok {
+					response.addPackage(&Package{
+						ID: id,
+						Errors: []Error{{
+							Kind: ListError,
+							Msg:  fmt.Sprintf("package %s expected but not seen", id),
+						}},
+					})
+					continue
+				}
+				for _, f := range containFiles {
+					for _, g := range pkg.GoFiles {
+						if sameFile(f, g) {
+							response.addRoot(id)
+						}
+					}
+				}
+			}
+		}
+		// Add root for any package that matches a pattern. This applies only to
+		// packages that are modified by overlays, since they are not added as
+		// roots automatically.
+		for _, pattern := range restPatterns {
+			match := matchPattern(pattern)
+			for _, pkgID := range modifiedPkgs {
+				pkg, ok := response.seenPackages[pkgID]
+				if !ok {
+					continue
+				}
+				if match(pkg.PkgPath) {
+					response.addRoot(pkg.ID)
+				}
+			}
+		}
+	}
+
+	sizeswg.Wait()
+	if sizeserr != nil {
+		return nil, sizeserr
+	}
+	return response.dr, nil
+}
+
+func (state *golistState) addNeededOverlayPackages(response *responseDeduper, pkgs []string) error {
+	if len(pkgs) == 0 {
+		return nil
+	}
+	dr, err := state.createDriverResponse(pkgs...)
+	if err != nil {
+		return err
+	}
+	for _, pkg := range dr.Packages {
+		response.addPackage(pkg)
+	}
+	_, needPkgs, err := state.processGolistOverlay(response)
+	if err != nil {
+		return err
+	}
+	return state.addNeededOverlayPackages(response, needPkgs)
+}
+
+func (state *golistState) runContainsQueries(response *responseDeduper, queries []string) error {
+	for _, query := range queries {
+		// TODO(matloob): Do only one query per directory.
+		fdir := filepath.Dir(query)
+		// Pass absolute path of directory to go list so that it knows to treat it as a directory,
+		// not a package path.
+		pattern, err := filepath.Abs(fdir)
+		if err != nil {
+			return fmt.Errorf("could not determine absolute path of file= query path %q: %v", query, err)
+		}
+		dirResponse, err := state.createDriverResponse(pattern)
+
+		// If there was an error loading the package, or the package is returned
+		// with errors, try to load the file as an ad-hoc package.
+		// Usually the error will appear in a returned package, but may not if we're
+		// in module mode and the ad-hoc is located outside a module.
+		if err != nil || len(dirResponse.Packages) == 1 && len(dirResponse.Packages[0].GoFiles) == 0 &&
+			len(dirResponse.Packages[0].Errors) == 1 {
+			var queryErr error
+			if dirResponse, queryErr = state.adhocPackage(pattern, query); queryErr != nil {
+				return err // return the original error
+			}
+		}
+		isRoot := make(map[string]bool, len(dirResponse.Roots))
+		for _, root := range dirResponse.Roots {
+			isRoot[root] = true
+		}
+		for _, pkg := range dirResponse.Packages {
+			// Add any new packages to the main set
+			// We don't bother to filter packages that will be dropped by the changes of roots,
+			// that will happen anyway during graph construction outside this function.
+			// Over-reporting packages is not a problem.
+			response.addPackage(pkg)
+			// if the package was not a root one, it cannot have the file
+			if !isRoot[pkg.ID] {
+				continue
+			}
+			for _, pkgFile := range pkg.GoFiles {
+				if filepath.Base(query) == filepath.Base(pkgFile) {
+					response.addRoot(pkg.ID)
+					break
+				}
+			}
+		}
+	}
+	return nil
+}
+
+// adhocPackage attempts to load or construct an ad-hoc package for a given
+// query, if the original call to the driver produced inadequate results.
+func (state *golistState) adhocPackage(pattern, query string) (*driverResponse, error) {
+	response, err := state.createDriverResponse(query)
+	if err != nil {
+		return nil, err
+	}
+	// If we get nothing back from `go list`,
+	// try to make this file into its own ad-hoc package.
+	// TODO(rstambler): Should this check against the original response?
+	if len(response.Packages) == 0 {
+		response.Packages = append(response.Packages, &Package{
+			ID:              "command-line-arguments",
+			PkgPath:         query,
+			GoFiles:         []string{query},
+			CompiledGoFiles: []string{query},
+			Imports:         make(map[string]*Package),
+		})
+		response.Roots = append(response.Roots, "command-line-arguments")
+	}
+	// Handle special cases.
+	if len(response.Packages) == 1 {
+		// golang/go#33482: If this is a file= query for ad-hoc packages where
+		// the file only exists on an overlay, and exists outside of a module,
+		// add the file to the package and remove the errors.
+		if response.Packages[0].ID == "command-line-arguments" ||
+			filepath.ToSlash(response.Packages[0].PkgPath) == filepath.ToSlash(query) {
+			if len(response.Packages[0].GoFiles) == 0 {
+				filename := filepath.Join(pattern, filepath.Base(query)) // avoid recomputing abspath
+				// TODO(matloob): check if the file is outside of a root dir?
+				for path := range state.cfg.Overlay {
+					if path == filename {
+						response.Packages[0].Errors = nil
+						response.Packages[0].GoFiles = []string{path}
+						response.Packages[0].CompiledGoFiles = []string{path}
+					}
+				}
+			}
+		}
+	}
+	return response, nil
+}
+
+// Fields must match go list;
+// see $GOROOT/src/cmd/go/internal/load/pkg.go.
+type jsonPackage struct {
+	ImportPath        string
+	Dir               string
+	Name              string
+	Export            string
+	GoFiles           []string
+	CompiledGoFiles   []string
+	IgnoredGoFiles    []string
+	IgnoredOtherFiles []string
+	CFiles            []string
+	CgoFiles          []string
+	CXXFiles          []string
+	MFiles            []string
+	HFiles            []string
+	FFiles            []string
+	SFiles            []string
+	SwigFiles         []string
+	SwigCXXFiles      []string
+	SysoFiles         []string
+	Imports           []string
+	ImportMap         map[string]string
+	Deps              []string
+	Module            *Module
+	TestGoFiles       []string
+	TestImports       []string
+	XTestGoFiles      []string
+	XTestImports      []string
+	ForTest           string // q in a "p [q.test]" package, else ""
+	DepOnly           bool
+
+	Error      *packagesinternal.PackageError
+	DepsErrors []*packagesinternal.PackageError
+}
+
+type jsonPackageError struct {
+	ImportStack []string
+	Pos         string
+	Err         string
+}
+
+func otherFiles(p *jsonPackage) [][]string {
+	return [][]string{p.CFiles, p.CXXFiles, p.MFiles, p.HFiles, p.FFiles, p.SFiles, p.SwigFiles, p.SwigCXXFiles, p.SysoFiles}
+}
+
+// createDriverResponse uses the "go list" command to expand the pattern
+// words and return a response for the specified packages.
+func (state *golistState) createDriverResponse(words ...string) (*driverResponse, error) {
+	// go list uses the following identifiers in ImportPath and Imports:
+	//
+	// 	"p"			-- importable package or main (command)
+	// 	"q.test"		-- q's test executable
+	// 	"p [q.test]"		-- variant of p as built for q's test executable
+	// 	"q_test [q.test]"	-- q's external test package
+	//
+	// The packages p that are built differently for a test q.test
+	// are q itself, plus any helpers used by the external test q_test,
+	// typically including "testing" and all its dependencies.
+
+	// Run "go list" for complete
+	// information on the specified packages.
+	buf, err := state.invokeGo("list", golistargs(state.cfg, words)...)
+	if err != nil {
+		return nil, err
+	}
+	seen := make(map[string]*jsonPackage)
+	pkgs := make(map[string]*Package)
+	additionalErrors := make(map[string][]Error)
+	// Decode the JSON and convert it to Package form.
+	var response driverResponse
+	for dec := json.NewDecoder(buf); dec.More(); {
+		p := new(jsonPackage)
+		if err := dec.Decode(p); err != nil {
+			return nil, fmt.Errorf("JSON decoding failed: %v", err)
+		}
+
+		if p.ImportPath == "" {
+			// The documentation for go list says that “[e]rroneous packages will have
+			// a non-empty ImportPath”. If for some reason it comes back empty, we
+			// prefer to error out rather than silently discarding data or handing
+			// back a package without any way to refer to it.
+			if p.Error != nil {
+				return nil, Error{
+					Pos: p.Error.Pos,
+					Msg: p.Error.Err,
+				}
+			}
+			return nil, fmt.Errorf("package missing import path: %+v", p)
+		}
+
+		// Work around https://golang.org/issue/33157:
+		// go list -e, when given an absolute path, will find the package contained at
+		// that directory. But when no package exists there, it will return a fake package
+		// with an error and the ImportPath set to the absolute path provided to go list.
+		// Try to convert that absolute path to what its package path would be if it's
+		// contained in a known module or GOPATH entry. This will allow the package to be
+		// properly "reclaimed" when overlays are processed.
+		if filepath.IsAbs(p.ImportPath) && p.Error != nil {
+			pkgPath, ok, err := state.getPkgPath(p.ImportPath)
+			if err != nil {
+				return nil, err
+			}
+			if ok {
+				p.ImportPath = pkgPath
+			}
+		}
+
+		if old, found := seen[p.ImportPath]; found {
+			// If one version of the package has an error, and the other doesn't, assume
+			// that this is a case where go list is reporting a fake dependency variant
+			// of the imported package: When a package tries to invalidly import another
+			// package, go list emits a variant of the imported package (with the same
+			// import path, but with an error on it, and the package will have a
+			// DepError set on it). An example of when this can happen is for imports of
+			// main packages: main packages can not be imported, but they may be
+			// separately matched and listed by another pattern.
+			// See golang.org/issue/36188 for more details.
+
+			// The plan is that eventually, hopefully in Go 1.15, the error will be
+			// reported on the importing package rather than the duplicate "fake"
+			// version of the imported package. Once all supported versions of Go
+			// have the new behavior this logic can be deleted.
+			// TODO(matloob): delete the workaround logic once all supported versions of
+			// Go return the errors on the proper package.
+
+			// There should be exactly one version of a package that doesn't have an
+			// error.
+			if old.Error == nil && p.Error == nil {
+				if !reflect.DeepEqual(p, old) {
+					return nil, fmt.Errorf("internal error: go list gives conflicting information for package %v", p.ImportPath)
+				}
+				continue
+			}
+
+			// Determine if this package's error needs to be bubbled up.
+			// This is a hack, and we expect for go list to eventually set the error
+			// on the package.
+			if old.Error != nil {
+				var errkind string
+				if strings.Contains(old.Error.Err, "not an importable package") {
+					errkind = "not an importable package"
+				} else if strings.Contains(old.Error.Err, "use of internal package") && strings.Contains(old.Error.Err, "not allowed") {
+					errkind = "use of internal package not allowed"
+				}
+				if errkind != "" {
+					if len(old.Error.ImportStack) < 1 {
+						return nil, fmt.Errorf(`internal error: go list gave a %q error with empty import stack`, errkind)
+					}
+					importingPkg := old.Error.ImportStack[len(old.Error.ImportStack)-1]
+					if importingPkg == old.ImportPath {
+						// Using an older version of Go which put this package itself on top of import
+						// stack, instead of the importer. Look for importer in second from top
+						// position.
+						if len(old.Error.ImportStack) < 2 {
+							return nil, fmt.Errorf(`internal error: go list gave a %q error with an import stack without importing package`, errkind)
+						}
+						importingPkg = old.Error.ImportStack[len(old.Error.ImportStack)-2]
+					}
+					additionalErrors[importingPkg] = append(additionalErrors[importingPkg], Error{
+						Pos:  old.Error.Pos,
+						Msg:  old.Error.Err,
+						Kind: ListError,
+					})
+				}
+			}
+
+			// Make sure that if there's a version of the package without an error,
+			// that's the one reported to the user.
+			if old.Error == nil {
+				continue
+			}
+
+			// This package will replace the old one at the end of the loop.
+		}
+		seen[p.ImportPath] = p
+
+		pkg := &Package{
+			Name:            p.Name,
+			ID:              p.ImportPath,
+			GoFiles:         absJoin(p.Dir, p.GoFiles, p.CgoFiles),
+			CompiledGoFiles: absJoin(p.Dir, p.CompiledGoFiles),
+			OtherFiles:      absJoin(p.Dir, otherFiles(p)...),
+			IgnoredFiles:    absJoin(p.Dir, p.IgnoredGoFiles, p.IgnoredOtherFiles),
+			forTest:         p.ForTest,
+			depsErrors:      p.DepsErrors,
+			Module:          p.Module,
+		}
+
+		if (state.cfg.Mode&typecheckCgo) != 0 && len(p.CgoFiles) != 0 {
+			if len(p.CompiledGoFiles) > len(p.GoFiles) {
+				// We need the cgo definitions, which are in the first
+				// CompiledGoFile after the non-cgo ones. This is a hack but there
+				// isn't currently a better way to find it. We also need the pure
+				// Go files and unprocessed cgo files, all of which are already
+				// in pkg.GoFiles.
+				cgoTypes := p.CompiledGoFiles[len(p.GoFiles)]
+				pkg.CompiledGoFiles = append([]string{cgoTypes}, pkg.GoFiles...)
+			} else {
+				// golang/go#38990: go list silently fails to do cgo processing
+				pkg.CompiledGoFiles = nil
+				pkg.Errors = append(pkg.Errors, Error{
+					Msg:  "go list failed to return CompiledGoFiles. This may indicate failure to perform cgo processing; try building at the command line. See https://golang.org/issue/38990.",
+					Kind: ListError,
+				})
+			}
+		}
+
+		// Work around https://golang.org/issue/28749:
+		// cmd/go puts assembly, C, and C++ files in CompiledGoFiles.
+		// Filter out any elements of CompiledGoFiles that are also in OtherFiles.
+		// We have to keep this workaround in place until go1.12 is a distant memory.
+		if len(pkg.OtherFiles) > 0 {
+			other := make(map[string]bool, len(pkg.OtherFiles))
+			for _, f := range pkg.OtherFiles {
+				other[f] = true
+			}
+
+			out := pkg.CompiledGoFiles[:0]
+			for _, f := range pkg.CompiledGoFiles {
+				if other[f] {
+					continue
+				}
+				out = append(out, f)
+			}
+			pkg.CompiledGoFiles = out
+		}
+
+		// Extract the PkgPath from the package's ID.
+		if i := strings.IndexByte(pkg.ID, ' '); i >= 0 {
+			pkg.PkgPath = pkg.ID[:i]
+		} else {
+			pkg.PkgPath = pkg.ID
+		}
+
+		if pkg.PkgPath == "unsafe" {
+			pkg.GoFiles = nil // ignore fake unsafe.go file
+		}
+
+		// Assume go list emits only absolute paths for Dir.
+		if p.Dir != "" && !filepath.IsAbs(p.Dir) {
+			log.Fatalf("internal error: go list returned non-absolute Package.Dir: %s", p.Dir)
+		}
+
+		if p.Export != "" && !filepath.IsAbs(p.Export) {
+			pkg.ExportFile = filepath.Join(p.Dir, p.Export)
+		} else {
+			pkg.ExportFile = p.Export
+		}
+
+		// imports
+		//
+		// Imports contains the IDs of all imported packages.
+		// ImportsMap records (path, ID) only where they differ.
+		ids := make(map[string]bool)
+		for _, id := range p.Imports {
+			ids[id] = true
+		}
+		pkg.Imports = make(map[string]*Package)
+		for path, id := range p.ImportMap {
+			pkg.Imports[path] = &Package{ID: id} // non-identity import
+			delete(ids, id)
+		}
+		for id := range ids {
+			if id == "C" {
+				continue
+			}
+
+			pkg.Imports[id] = &Package{ID: id} // identity import
+		}
+		if !p.DepOnly {
+			response.Roots = append(response.Roots, pkg.ID)
+		}
+
+		// Work around for pre-go.1.11 versions of go list.
+		// TODO(matloob): they should be handled by the fallback.
+		// Can we delete this?
+		if len(pkg.CompiledGoFiles) == 0 {
+			pkg.CompiledGoFiles = pkg.GoFiles
+		}
+
+		// Temporary work-around for golang/go#39986. Parse filenames out of
+		// error messages. This happens if there are unrecoverable syntax
+		// errors in the source, so we can't match on a specific error message.
+		if err := p.Error; err != nil && state.shouldAddFilenameFromError(p) {
+			addFilenameFromPos := func(pos string) bool {
+				split := strings.Split(pos, ":")
+				if len(split) < 1 {
+					return false
+				}
+				filename := strings.TrimSpace(split[0])
+				if filename == "" {
+					return false
+				}
+				if !filepath.IsAbs(filename) {
+					filename = filepath.Join(state.cfg.Dir, filename)
+				}
+				info, _ := os.Stat(filename)
+				if info == nil {
+					return false
+				}
+				pkg.CompiledGoFiles = append(pkg.CompiledGoFiles, filename)
+				pkg.GoFiles = append(pkg.GoFiles, filename)
+				return true
+			}
+			found := addFilenameFromPos(err.Pos)
+			// In some cases, go list only reports the error position in the
+			// error text, not the error position. One such case is when the
+			// file's package name is a keyword (see golang.org/issue/39763).
+			if !found {
+				addFilenameFromPos(err.Err)
+			}
+		}
+
+		if p.Error != nil {
+			msg := strings.TrimSpace(p.Error.Err) // Trim to work around golang.org/issue/32363.
+			// Address golang.org/issue/35964 by appending import stack to error message.
+			if msg == "import cycle not allowed" && len(p.Error.ImportStack) != 0 {
+				msg += fmt.Sprintf(": import stack: %v", p.Error.ImportStack)
+			}
+			pkg.Errors = append(pkg.Errors, Error{
+				Pos:  p.Error.Pos,
+				Msg:  msg,
+				Kind: ListError,
+			})
+		}
+
+		pkgs[pkg.ID] = pkg
+	}
+
+	for id, errs := range additionalErrors {
+		if p, ok := pkgs[id]; ok {
+			p.Errors = append(p.Errors, errs...)
+		}
+	}
+	for _, pkg := range pkgs {
+		response.Packages = append(response.Packages, pkg)
+	}
+	sort.Slice(response.Packages, func(i, j int) bool { return response.Packages[i].ID < response.Packages[j].ID })
+
+	return &response, nil
+}
+
+func (state *golistState) shouldAddFilenameFromError(p *jsonPackage) bool {
+	if len(p.GoFiles) > 0 || len(p.CompiledGoFiles) > 0 {
+		return false
+	}
+
+	goV, err := state.getGoVersion()
+	if err != nil {
+		return false
+	}
+
+	// On Go 1.14 and earlier, only add filenames from errors if the import stack is empty.
+	// The import stack behaves differently for these versions than newer Go versions.
+	if goV < 15 {
+		return len(p.Error.ImportStack) == 0
+	}
+
+	// On Go 1.15 and later, only parse filenames out of error if there's no import stack,
+	// or the current package is at the top of the import stack. This is not guaranteed
+	// to work perfectly, but should avoid some cases where files in errors don't belong to this
+	// package.
+	return len(p.Error.ImportStack) == 0 || p.Error.ImportStack[len(p.Error.ImportStack)-1] == p.ImportPath
+}
+
+func (state *golistState) getGoVersion() (int, error) {
+	state.goVersionOnce.Do(func() {
+		state.goVersion, state.goVersionError = gocommand.GoVersion(state.ctx, state.cfgInvocation(), state.cfg.gocmdRunner)
+	})
+	return state.goVersion, state.goVersionError
+}
+
+// getPkgPath finds the package path of a directory if it's relative to a root
+// directory.
+func (state *golistState) getPkgPath(dir string) (string, bool, error) {
+	absDir, err := filepath.Abs(dir)
+	if err != nil {
+		return "", false, err
+	}
+	roots, err := state.determineRootDirs()
+	if err != nil {
+		return "", false, err
+	}
+
+	for rdir, rpath := range roots {
+		// Make sure that the directory is in the module,
+		// to avoid creating a path relative to another module.
+		if !strings.HasPrefix(absDir, rdir) {
+			continue
+		}
+		// TODO(matloob): This doesn't properly handle symlinks.
+		r, err := filepath.Rel(rdir, dir)
+		if err != nil {
+			continue
+		}
+		if rpath != "" {
+			// We choose only one root even though the directory even it can belong in multiple modules
+			// or GOPATH entries. This is okay because we only need to work with absolute dirs when a
+			// file is missing from disk, for instance when gopls calls go/packages in an overlay.
+			// Once the file is saved, gopls, or the next invocation of the tool will get the correct
+			// result straight from golist.
+			// TODO(matloob): Implement module tiebreaking?
+			return path.Join(rpath, filepath.ToSlash(r)), true, nil
+		}
+		return filepath.ToSlash(r), true, nil
+	}
+	return "", false, nil
+}
+
+// absJoin absolutizes and flattens the lists of files.
+func absJoin(dir string, fileses ...[]string) (res []string) {
+	for _, files := range fileses {
+		for _, file := range files {
+			if !filepath.IsAbs(file) {
+				file = filepath.Join(dir, file)
+			}
+			res = append(res, file)
+		}
+	}
+	return res
+}
+
+func golistargs(cfg *Config, words []string) []string {
+	const findFlags = NeedImports | NeedTypes | NeedSyntax | NeedTypesInfo
+	fullargs := []string{
+		"-e", "-json",
+		fmt.Sprintf("-compiled=%t", cfg.Mode&(NeedCompiledGoFiles|NeedSyntax|NeedTypes|NeedTypesInfo|NeedTypesSizes) != 0),
+		fmt.Sprintf("-test=%t", cfg.Tests),
+		fmt.Sprintf("-export=%t", usesExportData(cfg)),
+		fmt.Sprintf("-deps=%t", cfg.Mode&NeedImports != 0),
+		// go list doesn't let you pass -test and -find together,
+		// probably because you'd just get the TestMain.
+		fmt.Sprintf("-find=%t", !cfg.Tests && cfg.Mode&findFlags == 0),
+	}
+	fullargs = append(fullargs, cfg.BuildFlags...)
+	fullargs = append(fullargs, "--")
+	fullargs = append(fullargs, words...)
+	return fullargs
+}
+
+// cfgInvocation returns an Invocation that reflects cfg's settings.
+func (state *golistState) cfgInvocation() gocommand.Invocation {
+	cfg := state.cfg
+	return gocommand.Invocation{
+		BuildFlags: cfg.BuildFlags,
+		ModFile:    cfg.modFile,
+		ModFlag:    cfg.modFlag,
+		CleanEnv:   cfg.Env != nil,
+		Env:        cfg.Env,
+		Logf:       cfg.Logf,
+		WorkingDir: cfg.Dir,
+	}
+}
+
+// invokeGo returns the stdout of a go command invocation.
+func (state *golistState) invokeGo(verb string, args ...string) (*bytes.Buffer, error) {
+	cfg := state.cfg
+
+	inv := state.cfgInvocation()
+
+	// For Go versions 1.16 and above, `go list` accepts overlays directly via
+	// the -overlay flag. Set it, if it's available.
+	//
+	// The check for "list" is not necessarily required, but we should avoid
+	// getting the go version if possible.
+	if verb == "list" {
+		goVersion, err := state.getGoVersion()
+		if err != nil {
+			return nil, err
+		}
+		if goVersion >= 16 {
+			filename, cleanup, err := state.writeOverlays()
+			if err != nil {
+				return nil, err
+			}
+			defer cleanup()
+			inv.Overlay = filename
+		}
+	}
+	inv.Verb = verb
+	inv.Args = args
+	gocmdRunner := cfg.gocmdRunner
+	if gocmdRunner == nil {
+		gocmdRunner = &gocommand.Runner{}
+	}
+	stdout, stderr, friendlyErr, err := gocmdRunner.RunRaw(cfg.Context, inv)
+	if err != nil {
+		// Check for 'go' executable not being found.
+		if ee, ok := err.(*exec.Error); ok && ee.Err == exec.ErrNotFound {
+			return nil, fmt.Errorf("'go list' driver requires 'go', but %s", exec.ErrNotFound)
+		}
+
+		exitErr, ok := err.(*exec.ExitError)
+		if !ok {
+			// Catastrophic error:
+			// - context cancellation
+			return nil, xerrors.Errorf("couldn't run 'go': %w", err)
+		}
+
+		// Old go version?
+		if strings.Contains(stderr.String(), "flag provided but not defined") {
+			return nil, goTooOldError{fmt.Errorf("unsupported version of go: %s: %s", exitErr, stderr)}
+		}
+
+		// Related to #24854
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "unexpected directory layout") {
+			return nil, friendlyErr
+		}
+
+		// Is there an error running the C compiler in cgo? This will be reported in the "Error" field
+		// and should be suppressed by go list -e.
+		//
+		// This condition is not perfect yet because the error message can include other error messages than runtime/cgo.
+		isPkgPathRune := func(r rune) bool {
+			// From https://golang.org/ref/spec#Import_declarations:
+			//    Implementation restriction: A compiler may restrict ImportPaths to non-empty strings
+			//    using only characters belonging to Unicode's L, M, N, P, and S general categories
+			//    (the Graphic characters without spaces) and may also exclude the
+			//    characters !"#$%&'()*,:;<=>?[\]^`{|} and the Unicode replacement character U+FFFD.
+			return unicode.IsOneOf([]*unicode.RangeTable{unicode.L, unicode.M, unicode.N, unicode.P, unicode.S}, r) &&
+				!strings.ContainsRune("!\"#$%&'()*,:;<=>?[\\]^`{|}\uFFFD", r)
+		}
+		// golang/go#36770: Handle case where cmd/go prints module download messages before the error.
+		msg := stderr.String()
+		for strings.HasPrefix(msg, "go: downloading") {
+			msg = msg[strings.IndexRune(msg, '\n')+1:]
+		}
+		if len(stderr.String()) > 0 && strings.HasPrefix(stderr.String(), "# ") {
+			msg := msg[len("# "):]
+			if strings.HasPrefix(strings.TrimLeftFunc(msg, isPkgPathRune), "\n") {
+				return stdout, nil
+			}
+			// Treat pkg-config errors as a special case (golang.org/issue/36770).
+			if strings.HasPrefix(msg, "pkg-config") {
+				return stdout, nil
+			}
+		}
+
+		// This error only appears in stderr. See golang.org/cl/166398 for a fix in go list to show
+		// the error in the Err section of stdout in case -e option is provided.
+		// This fix is provided for backwards compatibility.
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "named files must be .go files") {
+			output := fmt.Sprintf(`{"ImportPath": "command-line-arguments","Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				strings.Trim(stderr.String(), "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
+		// Similar to the previous error, but currently lacks a fix in Go.
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "named files must all be in one directory") {
+			output := fmt.Sprintf(`{"ImportPath": "command-line-arguments","Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				strings.Trim(stderr.String(), "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
+		// Backwards compatibility for Go 1.11 because 1.12 and 1.13 put the directory in the ImportPath.
+		// If the package doesn't exist, put the absolute path of the directory into the error message,
+		// as Go 1.13 list does.
+		const noSuchDirectory = "no such directory"
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), noSuchDirectory) {
+			errstr := stderr.String()
+			abspath := strings.TrimSpace(errstr[strings.Index(errstr, noSuchDirectory)+len(noSuchDirectory):])
+			output := fmt.Sprintf(`{"ImportPath": %q,"Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				abspath, strings.Trim(stderr.String(), "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
+		// Workaround for #29280: go list -e has incorrect behavior when an ad-hoc package doesn't exist.
+		// Note that the error message we look for in this case is different that the one looked for above.
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "no such file or directory") {
+			output := fmt.Sprintf(`{"ImportPath": "command-line-arguments","Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				strings.Trim(stderr.String(), "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
+		// Workaround for #34273. go list -e with GO111MODULE=on has incorrect behavior when listing a
+		// directory outside any module.
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "outside available modules") {
+			output := fmt.Sprintf(`{"ImportPath": %q,"Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				// TODO(matloob): command-line-arguments isn't correct here.
+				"command-line-arguments", strings.Trim(stderr.String(), "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
+		// Another variation of the previous error
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "outside module root") {
+			output := fmt.Sprintf(`{"ImportPath": %q,"Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				// TODO(matloob): command-line-arguments isn't correct here.
+				"command-line-arguments", strings.Trim(stderr.String(), "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
+		// Workaround for an instance of golang.org/issue/26755: go list -e  will return a non-zero exit
+		// status if there's a dependency on a package that doesn't exist. But it should return
+		// a zero exit status and set an error on that package.
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "no Go files in") {
+			// Don't clobber stdout if `go list` actually returned something.
+			if len(stdout.String()) > 0 {
+				return stdout, nil
+			}
+			// try to extract package name from string
+			stderrStr := stderr.String()
+			var importPath string
+			colon := strings.Index(stderrStr, ":")
+			if colon > 0 && strings.HasPrefix(stderrStr, "go build ") {
+				importPath = stderrStr[len("go build "):colon]
+			}
+			output := fmt.Sprintf(`{"ImportPath": %q,"Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				importPath, strings.Trim(stderrStr, "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
+		// Export mode entails a build.
+		// If that build fails, errors appear on stderr
+		// (despite the -e flag) and the Export field is blank.
+		// Do not fail in that case.
+		// The same is true if an ad-hoc package given to go list doesn't exist.
+		// TODO(matloob): Remove these once we can depend on go list to exit with a zero status with -e even when
+		// packages don't exist or a build fails.
+		if !usesExportData(cfg) && !containsGoFile(args) {
+			return nil, friendlyErr
+		}
+	}
+	return stdout, nil
+}
+
+// OverlayJSON is the format overlay files are expected to be in.
+// The Replace map maps from overlaid paths to replacement paths:
+// the Go command will forward all reads trying to open
+// each overlaid path to its replacement path, or consider the overlaid
+// path not to exist if the replacement path is empty.
+//
+// From golang/go#39958.
+type OverlayJSON struct {
+	Replace map[string]string `json:"replace,omitempty"`
+}
+
+// writeOverlays writes out files for go list's -overlay flag, as described
+// above.
+func (state *golistState) writeOverlays() (filename string, cleanup func(), err error) {
+	// Do nothing if there are no overlays in the config.
+	if len(state.cfg.Overlay) == 0 {
+		return "", func() {}, nil
+	}
+	dir, err := ioutil.TempDir("", "gopackages-*")
+	if err != nil {
+		return "", nil, err
+	}
+	// The caller must clean up this directory, unless this function returns an
+	// error.
+	cleanup = func() {
+		os.RemoveAll(dir)
+	}
+	defer func() {
+		if err != nil {
+			cleanup()
+		}
+	}()
+	overlays := map[string]string{}
+	for k, v := range state.cfg.Overlay {
+		// Create a unique filename for the overlaid files, to avoid
+		// creating nested directories.
+		noSeparator := strings.Join(strings.Split(filepath.ToSlash(k), "/"), "")
+		f, err := ioutil.TempFile(dir, fmt.Sprintf("*-%s", noSeparator))
+		if err != nil {
+			return "", func() {}, err
+		}
+		if _, err := f.Write(v); err != nil {
+			return "", func() {}, err
+		}
+		if err := f.Close(); err != nil {
+			return "", func() {}, err
+		}
+		overlays[k] = f.Name()
+	}
+	b, err := json.Marshal(OverlayJSON{Replace: overlays})
+	if err != nil {
+		return "", func() {}, err
+	}
+	// Write out the overlay file that contains the filepath mappings.
+	filename = filepath.Join(dir, "overlay.json")
+	if err := ioutil.WriteFile(filename, b, 0665); err != nil {
+		return "", func() {}, err
+	}
+	return filename, cleanup, nil
+}
+
+func containsGoFile(s []string) bool {
+	for _, f := range s {
+		if strings.HasSuffix(f, ".go") {
+			return true
+		}
+	}
+	return false
+}
+
+func cmdDebugStr(cmd *exec.Cmd) string {
+	env := make(map[string]string)
+	for _, kv := range cmd.Env {
+		split := strings.SplitN(kv, "=", 2)
+		k, v := split[0], split[1]
+		env[k] = v
+	}
+
+	var args []string
+	for _, arg := range cmd.Args {
+		quoted := strconv.Quote(arg)
+		if quoted[1:len(quoted)-1] != arg || strings.Contains(arg, " ") {
+			args = append(args, quoted)
+		} else {
+			args = append(args, arg)
+		}
+	}
+	return fmt.Sprintf("GOROOT=%v GOPATH=%v GO111MODULE=%v GOPROXY=%v PWD=%v %v", env["GOROOT"], env["GOPATH"], env["GO111MODULE"], env["GOPROXY"], env["PWD"], strings.Join(args, " "))
+}
diff --git a/vendor/golang.org/x/tools/go/packages/golist_overlay.go b/vendor/golang.org/x/tools/go/packages/golist_overlay.go
new file mode 100644
index 00000000..9576b472
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/packages/golist_overlay.go
@@ -0,0 +1,575 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packages
+
+import (
+	"encoding/json"
+	"fmt"
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+
+	"golang.org/x/tools/internal/gocommand"
+)
+
+// processGolistOverlay provides rudimentary support for adding
+// files that don't exist on disk to an overlay. The results can be
+// sometimes incorrect.
+// TODO(matloob): Handle unsupported cases, including the following:
+// - determining the correct package to add given a new import path
+func (state *golistState) processGolistOverlay(response *responseDeduper) (modifiedPkgs, needPkgs []string, err error) {
+	havePkgs := make(map[string]string) // importPath -> non-test package ID
+	needPkgsSet := make(map[string]bool)
+	modifiedPkgsSet := make(map[string]bool)
+
+	pkgOfDir := make(map[string][]*Package)
+	for _, pkg := range response.dr.Packages {
+		// This is an approximation of import path to id. This can be
+		// wrong for tests, vendored packages, and a number of other cases.
+		havePkgs[pkg.PkgPath] = pkg.ID
+		dir, err := commonDir(pkg.GoFiles)
+		if err != nil {
+			return nil, nil, err
+		}
+		if dir != "" {
+			pkgOfDir[dir] = append(pkgOfDir[dir], pkg)
+		}
+	}
+
+	// If no new imports are added, it is safe to avoid loading any needPkgs.
+	// Otherwise, it's hard to tell which package is actually being loaded
+	// (due to vendoring) and whether any modified package will show up
+	// in the transitive set of dependencies (because new imports are added,
+	// potentially modifying the transitive set of dependencies).
+	var overlayAddsImports bool
+
+	// If both a package and its test package are created by the overlay, we
+	// need the real package first. Process all non-test files before test
+	// files, and make the whole process deterministic while we're at it.
+	var overlayFiles []string
+	for opath := range state.cfg.Overlay {
+		overlayFiles = append(overlayFiles, opath)
+	}
+	sort.Slice(overlayFiles, func(i, j int) bool {
+		iTest := strings.HasSuffix(overlayFiles[i], "_test.go")
+		jTest := strings.HasSuffix(overlayFiles[j], "_test.go")
+		if iTest != jTest {
+			return !iTest // non-tests are before tests.
+		}
+		return overlayFiles[i] < overlayFiles[j]
+	})
+	for _, opath := range overlayFiles {
+		contents := state.cfg.Overlay[opath]
+		base := filepath.Base(opath)
+		dir := filepath.Dir(opath)
+		var pkg *Package           // if opath belongs to both a package and its test variant, this will be the test variant
+		var testVariantOf *Package // if opath is a test file, this is the package it is testing
+		var fileExists bool
+		isTestFile := strings.HasSuffix(opath, "_test.go")
+		pkgName, ok := extractPackageName(opath, contents)
+		if !ok {
+			// Don't bother adding a file that doesn't even have a parsable package statement
+			// to the overlay.
+			continue
+		}
+		// If all the overlay files belong to a different package, change the
+		// package name to that package.
+		maybeFixPackageName(pkgName, isTestFile, pkgOfDir[dir])
+	nextPackage:
+		for _, p := range response.dr.Packages {
+			if pkgName != p.Name && p.ID != "command-line-arguments" {
+				continue
+			}
+			for _, f := range p.GoFiles {
+				if !sameFile(filepath.Dir(f), dir) {
+					continue
+				}
+				// Make sure to capture information on the package's test variant, if needed.
+				if isTestFile && !hasTestFiles(p) {
+					// TODO(matloob): Are there packages other than the 'production' variant
+					// of a package that this can match? This shouldn't match the test main package
+					// because the file is generated in another directory.
+					testVariantOf = p
+					continue nextPackage
+				} else if !isTestFile && hasTestFiles(p) {
+					// We're examining a test variant, but the overlaid file is
+					// a non-test file. Because the overlay implementation
+					// (currently) only adds a file to one package, skip this
+					// package, so that we can add the file to the production
+					// variant of the package. (https://golang.org/issue/36857
+					// tracks handling overlays on both the production and test
+					// variant of a package).
+					continue nextPackage
+				}
+				if pkg != nil && p != pkg && pkg.PkgPath == p.PkgPath {
+					// We have already seen the production version of the
+					// for which p is a test variant.
+					if hasTestFiles(p) {
+						testVariantOf = pkg
+					}
+				}
+				pkg = p
+				if filepath.Base(f) == base {
+					fileExists = true
+				}
+			}
+		}
+		// The overlay could have included an entirely new package or an
+		// ad-hoc package. An ad-hoc package is one that we have manually
+		// constructed from inadequate `go list` results for a file= query.
+		// It will have the ID command-line-arguments.
+		if pkg == nil || pkg.ID == "command-line-arguments" {
+			// Try to find the module or gopath dir the file is contained in.
+			// Then for modules, add the module opath to the beginning.
+			pkgPath, ok, err := state.getPkgPath(dir)
+			if err != nil {
+				return nil, nil, err
+			}
+			if !ok {
+				break
+			}
+			var forTest string // only set for x tests
+			isXTest := strings.HasSuffix(pkgName, "_test")
+			if isXTest {
+				forTest = pkgPath
+				pkgPath += "_test"
+			}
+			id := pkgPath
+			if isTestFile {
+				if isXTest {
+					id = fmt.Sprintf("%s [%s.test]", pkgPath, forTest)
+				} else {
+					id = fmt.Sprintf("%s [%s.test]", pkgPath, pkgPath)
+				}
+			}
+			if pkg != nil {
+				// TODO(rstambler): We should change the package's path and ID
+				// here. The only issue is that this messes with the roots.
+			} else {
+				// Try to reclaim a package with the same ID, if it exists in the response.
+				for _, p := range response.dr.Packages {
+					if reclaimPackage(p, id, opath, contents) {
+						pkg = p
+						break
+					}
+				}
+				// Otherwise, create a new package.
+				if pkg == nil {
+					pkg = &Package{
+						PkgPath: pkgPath,
+						ID:      id,
+						Name:    pkgName,
+						Imports: make(map[string]*Package),
+					}
+					response.addPackage(pkg)
+					havePkgs[pkg.PkgPath] = id
+					// Add the production package's sources for a test variant.
+					if isTestFile && !isXTest && testVariantOf != nil {
+						pkg.GoFiles = append(pkg.GoFiles, testVariantOf.GoFiles...)
+						pkg.CompiledGoFiles = append(pkg.CompiledGoFiles, testVariantOf.CompiledGoFiles...)
+						// Add the package under test and its imports to the test variant.
+						pkg.forTest = testVariantOf.PkgPath
+						for k, v := range testVariantOf.Imports {
+							pkg.Imports[k] = &Package{ID: v.ID}
+						}
+					}
+					if isXTest {
+						pkg.forTest = forTest
+					}
+				}
+			}
+		}
+		if !fileExists {
+			pkg.GoFiles = append(pkg.GoFiles, opath)
+			// TODO(matloob): Adding the file to CompiledGoFiles can exhibit the wrong behavior
+			// if the file will be ignored due to its build tags.
+			pkg.CompiledGoFiles = append(pkg.CompiledGoFiles, opath)
+			modifiedPkgsSet[pkg.ID] = true
+		}
+		imports, err := extractImports(opath, contents)
+		if err != nil {
+			// Let the parser or type checker report errors later.
+			continue
+		}
+		for _, imp := range imports {
+			// TODO(rstambler): If the package is an x test and the import has
+			// a test variant, make sure to replace it.
+			if _, found := pkg.Imports[imp]; found {
+				continue
+			}
+			overlayAddsImports = true
+			id, ok := havePkgs[imp]
+			if !ok {
+				var err error
+				id, err = state.resolveImport(dir, imp)
+				if err != nil {
+					return nil, nil, err
+				}
+			}
+			pkg.Imports[imp] = &Package{ID: id}
+			// Add dependencies to the non-test variant version of this package as well.
+			if testVariantOf != nil {
+				testVariantOf.Imports[imp] = &Package{ID: id}
+			}
+		}
+	}
+
+	// toPkgPath guesses the package path given the id.
+	toPkgPath := func(sourceDir, id string) (string, error) {
+		if i := strings.IndexByte(id, ' '); i >= 0 {
+			return state.resolveImport(sourceDir, id[:i])
+		}
+		return state.resolveImport(sourceDir, id)
+	}
+
+	// Now that new packages have been created, do another pass to determine
+	// the new set of missing packages.
+	for _, pkg := range response.dr.Packages {
+		for _, imp := range pkg.Imports {
+			if len(pkg.GoFiles) == 0 {
+				return nil, nil, fmt.Errorf("cannot resolve imports for package %q with no Go files", pkg.PkgPath)
+			}
+			pkgPath, err := toPkgPath(filepath.Dir(pkg.GoFiles[0]), imp.ID)
+			if err != nil {
+				return nil, nil, err
+			}
+			if _, ok := havePkgs[pkgPath]; !ok {
+				needPkgsSet[pkgPath] = true
+			}
+		}
+	}
+
+	if overlayAddsImports {
+		needPkgs = make([]string, 0, len(needPkgsSet))
+		for pkg := range needPkgsSet {
+			needPkgs = append(needPkgs, pkg)
+		}
+	}
+	modifiedPkgs = make([]string, 0, len(modifiedPkgsSet))
+	for pkg := range modifiedPkgsSet {
+		modifiedPkgs = append(modifiedPkgs, pkg)
+	}
+	return modifiedPkgs, needPkgs, err
+}
+
+// resolveImport finds the ID of a package given its import path.
+// In particular, it will find the right vendored copy when in GOPATH mode.
+func (state *golistState) resolveImport(sourceDir, importPath string) (string, error) {
+	env, err := state.getEnv()
+	if err != nil {
+		return "", err
+	}
+	if env["GOMOD"] != "" {
+		return importPath, nil
+	}
+
+	searchDir := sourceDir
+	for {
+		vendorDir := filepath.Join(searchDir, "vendor")
+		exists, ok := state.vendorDirs[vendorDir]
+		if !ok {
+			info, err := os.Stat(vendorDir)
+			exists = err == nil && info.IsDir()
+			state.vendorDirs[vendorDir] = exists
+		}
+
+		if exists {
+			vendoredPath := filepath.Join(vendorDir, importPath)
+			if info, err := os.Stat(vendoredPath); err == nil && info.IsDir() {
+				// We should probably check for .go files here, but shame on anyone who fools us.
+				path, ok, err := state.getPkgPath(vendoredPath)
+				if err != nil {
+					return "", err
+				}
+				if ok {
+					return path, nil
+				}
+			}
+		}
+
+		// We know we've hit the top of the filesystem when we Dir / and get /,
+		// or C:\ and get C:\, etc.
+		next := filepath.Dir(searchDir)
+		if next == searchDir {
+			break
+		}
+		searchDir = next
+	}
+	return importPath, nil
+}
+
+func hasTestFiles(p *Package) bool {
+	for _, f := range p.GoFiles {
+		if strings.HasSuffix(f, "_test.go") {
+			return true
+		}
+	}
+	return false
+}
+
+// determineRootDirs returns a mapping from absolute directories that could
+// contain code to their corresponding import path prefixes.
+func (state *golistState) determineRootDirs() (map[string]string, error) {
+	env, err := state.getEnv()
+	if err != nil {
+		return nil, err
+	}
+	if env["GOMOD"] != "" {
+		state.rootsOnce.Do(func() {
+			state.rootDirs, state.rootDirsError = state.determineRootDirsModules()
+		})
+	} else {
+		state.rootsOnce.Do(func() {
+			state.rootDirs, state.rootDirsError = state.determineRootDirsGOPATH()
+		})
+	}
+	return state.rootDirs, state.rootDirsError
+}
+
+func (state *golistState) determineRootDirsModules() (map[string]string, error) {
+	// List all of the modules--the first will be the directory for the main
+	// module. Any replaced modules will also need to be treated as roots.
+	// Editing files in the module cache isn't a great idea, so we don't
+	// plan to ever support that.
+	out, err := state.invokeGo("list", "-m", "-json", "all")
+	if err != nil {
+		// 'go list all' will fail if we're outside of a module and
+		// GO111MODULE=on. Try falling back without 'all'.
+		var innerErr error
+		out, innerErr = state.invokeGo("list", "-m", "-json")
+		if innerErr != nil {
+			return nil, err
+		}
+	}
+	roots := map[string]string{}
+	modules := map[string]string{}
+	var i int
+	for dec := json.NewDecoder(out); dec.More(); {
+		mod := new(gocommand.ModuleJSON)
+		if err := dec.Decode(mod); err != nil {
+			return nil, err
+		}
+		if mod.Dir != "" && mod.Path != "" {
+			// This is a valid module; add it to the map.
+			absDir, err := filepath.Abs(mod.Dir)
+			if err != nil {
+				return nil, err
+			}
+			modules[absDir] = mod.Path
+			// The first result is the main module.
+			if i == 0 || mod.Replace != nil && mod.Replace.Path != "" {
+				roots[absDir] = mod.Path
+			}
+		}
+		i++
+	}
+	return roots, nil
+}
+
+func (state *golistState) determineRootDirsGOPATH() (map[string]string, error) {
+	m := map[string]string{}
+	for _, dir := range filepath.SplitList(state.mustGetEnv()["GOPATH"]) {
+		absDir, err := filepath.Abs(dir)
+		if err != nil {
+			return nil, err
+		}
+		m[filepath.Join(absDir, "src")] = ""
+	}
+	return m, nil
+}
+
+func extractImports(filename string, contents []byte) ([]string, error) {
+	f, err := parser.ParseFile(token.NewFileSet(), filename, contents, parser.ImportsOnly) // TODO(matloob): reuse fileset?
+	if err != nil {
+		return nil, err
+	}
+	var res []string
+	for _, imp := range f.Imports {
+		quotedPath := imp.Path.Value
+		path, err := strconv.Unquote(quotedPath)
+		if err != nil {
+			return nil, err
+		}
+		res = append(res, path)
+	}
+	return res, nil
+}
+
+// reclaimPackage attempts to reuse a package that failed to load in an overlay.
+//
+// If the package has errors and has no Name, GoFiles, or Imports,
+// then it's possible that it doesn't yet exist on disk.
+func reclaimPackage(pkg *Package, id string, filename string, contents []byte) bool {
+	// TODO(rstambler): Check the message of the actual error?
+	// It differs between $GOPATH and module mode.
+	if pkg.ID != id {
+		return false
+	}
+	if len(pkg.Errors) != 1 {
+		return false
+	}
+	if pkg.Name != "" || pkg.ExportFile != "" {
+		return false
+	}
+	if len(pkg.GoFiles) > 0 || len(pkg.CompiledGoFiles) > 0 || len(pkg.OtherFiles) > 0 {
+		return false
+	}
+	if len(pkg.Imports) > 0 {
+		return false
+	}
+	pkgName, ok := extractPackageName(filename, contents)
+	if !ok {
+		return false
+	}
+	pkg.Name = pkgName
+	pkg.Errors = nil
+	return true
+}
+
+func extractPackageName(filename string, contents []byte) (string, bool) {
+	// TODO(rstambler): Check the message of the actual error?
+	// It differs between $GOPATH and module mode.
+	f, err := parser.ParseFile(token.NewFileSet(), filename, contents, parser.PackageClauseOnly) // TODO(matloob): reuse fileset?
+	if err != nil {
+		return "", false
+	}
+	return f.Name.Name, true
+}
+
+// commonDir returns the directory that all files are in, "" if files is empty,
+// or an error if they aren't in the same directory.
+func commonDir(files []string) (string, error) {
+	seen := make(map[string]bool)
+	for _, f := range files {
+		seen[filepath.Dir(f)] = true
+	}
+	if len(seen) > 1 {
+		return "", fmt.Errorf("files (%v) are in more than one directory: %v", files, seen)
+	}
+	for k := range seen {
+		// seen has only one element; return it.
+		return k, nil
+	}
+	return "", nil // no files
+}
+
+// It is possible that the files in the disk directory dir have a different package
+// name from newName, which is deduced from the overlays. If they all have a different
+// package name, and they all have the same package name, then that name becomes
+// the package name.
+// It returns true if it changes the package name, false otherwise.
+func maybeFixPackageName(newName string, isTestFile bool, pkgsOfDir []*Package) {
+	names := make(map[string]int)
+	for _, p := range pkgsOfDir {
+		names[p.Name]++
+	}
+	if len(names) != 1 {
+		// some files are in different packages
+		return
+	}
+	var oldName string
+	for k := range names {
+		oldName = k
+	}
+	if newName == oldName {
+		return
+	}
+	// We might have a case where all of the package names in the directory are
+	// the same, but the overlay file is for an x test, which belongs to its
+	// own package. If the x test does not yet exist on disk, we may not yet
+	// have its package name on disk, but we should not rename the packages.
+	//
+	// We use a heuristic to determine if this file belongs to an x test:
+	// The test file should have a package name whose package name has a _test
+	// suffix or looks like "newName_test".
+	maybeXTest := strings.HasPrefix(oldName+"_test", newName) || strings.HasSuffix(newName, "_test")
+	if isTestFile && maybeXTest {
+		return
+	}
+	for _, p := range pkgsOfDir {
+		p.Name = newName
+	}
+}
+
+// This function is copy-pasted from
+// https://github.com/golang/go/blob/9706f510a5e2754595d716bd64be8375997311fb/src/cmd/go/internal/search/search.go#L360.
+// It should be deleted when we remove support for overlays from go/packages.
+//
+// NOTE: This does not handle any ./... or ./ style queries, as this function
+// doesn't know the working directory.
+//
+// matchPattern(pattern)(name) reports whether
+// name matches pattern. Pattern is a limited glob
+// pattern in which '...' means 'any string' and there
+// is no other special syntax.
+// Unfortunately, there are two special cases. Quoting "go help packages":
+//
+// First, /... at the end of the pattern can match an empty string,
+// so that net/... matches both net and packages in its subdirectories, like net/http.
+// Second, any slash-separated pattern element containing a wildcard never
+// participates in a match of the "vendor" element in the path of a vendored
+// package, so that ./... does not match packages in subdirectories of
+// ./vendor or ./mycode/vendor, but ./vendor/... and ./mycode/vendor/... do.
+// Note, however, that a directory named vendor that itself contains code
+// is not a vendored package: cmd/vendor would be a command named vendor,
+// and the pattern cmd/... matches it.
+func matchPattern(pattern string) func(name string) bool {
+	// Convert pattern to regular expression.
+	// The strategy for the trailing /... is to nest it in an explicit ? expression.
+	// The strategy for the vendor exclusion is to change the unmatchable
+	// vendor strings to a disallowed code point (vendorChar) and to use
+	// "(anything but that codepoint)*" as the implementation of the ... wildcard.
+	// This is a bit complicated but the obvious alternative,
+	// namely a hand-written search like in most shell glob matchers,
+	// is too easy to make accidentally exponential.
+	// Using package regexp guarantees linear-time matching.
+
+	const vendorChar = "\x00"
+
+	if strings.Contains(pattern, vendorChar) {
+		return func(name string) bool { return false }
+	}
+
+	re := regexp.QuoteMeta(pattern)
+	re = replaceVendor(re, vendorChar)
+	switch {
+	case strings.HasSuffix(re, `/`+vendorChar+`/\.\.\.`):
+		re = strings.TrimSuffix(re, `/`+vendorChar+`/\.\.\.`) + `(/vendor|/` + vendorChar + `/\.\.\.)`
+	case re == vendorChar+`/\.\.\.`:
+		re = `(/vendor|/` + vendorChar + `/\.\.\.)`
+	case strings.HasSuffix(re, `/\.\.\.`):
+		re = strings.TrimSuffix(re, `/\.\.\.`) + `(/\.\.\.)?`
+	}
+	re = strings.ReplaceAll(re, `\.\.\.`, `[^`+vendorChar+`]*`)
+
+	reg := regexp.MustCompile(`^` + re + `$`)
+
+	return func(name string) bool {
+		if strings.Contains(name, vendorChar) {
+			return false
+		}
+		return reg.MatchString(replaceVendor(name, vendorChar))
+	}
+}
+
+// replaceVendor returns the result of replacing
+// non-trailing vendor path elements in x with repl.
+func replaceVendor(x, repl string) string {
+	if !strings.Contains(x, "vendor") {
+		return x
+	}
+	elem := strings.Split(x, "/")
+	for i := 0; i < len(elem)-1; i++ {
+		if elem[i] == "vendor" {
+			elem[i] = repl
+		}
+	}
+	return strings.Join(elem, "/")
+}
diff --git a/vendor/golang.org/x/tools/go/packages/loadmode_string.go b/vendor/golang.org/x/tools/go/packages/loadmode_string.go
new file mode 100644
index 00000000..7ea37e7e
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/packages/loadmode_string.go
@@ -0,0 +1,57 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packages
+
+import (
+	"fmt"
+	"strings"
+)
+
+var allModes = []LoadMode{
+	NeedName,
+	NeedFiles,
+	NeedCompiledGoFiles,
+	NeedImports,
+	NeedDeps,
+	NeedExportsFile,
+	NeedTypes,
+	NeedSyntax,
+	NeedTypesInfo,
+	NeedTypesSizes,
+}
+
+var modeStrings = []string{
+	"NeedName",
+	"NeedFiles",
+	"NeedCompiledGoFiles",
+	"NeedImports",
+	"NeedDeps",
+	"NeedExportsFile",
+	"NeedTypes",
+	"NeedSyntax",
+	"NeedTypesInfo",
+	"NeedTypesSizes",
+}
+
+func (mod LoadMode) String() string {
+	m := mod
+	if m == 0 {
+		return "LoadMode(0)"
+	}
+	var out []string
+	for i, x := range allModes {
+		if x > m {
+			break
+		}
+		if (m & x) != 0 {
+			out = append(out, modeStrings[i])
+			m = m ^ x
+		}
+	}
+	if m != 0 {
+		out = append(out, "Unknown")
+	}
+	return fmt.Sprintf("LoadMode(%s)", strings.Join(out, "|"))
+}
diff --git a/vendor/golang.org/x/tools/go/packages/packages.go b/vendor/golang.org/x/tools/go/packages/packages.go
new file mode 100644
index 00000000..8a1a2d68
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/packages/packages.go
@@ -0,0 +1,1239 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packages
+
+// See doc.go for package documentation and implementation notes.
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/scanner"
+	"go/token"
+	"go/types"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/tools/go/gcexportdata"
+	"golang.org/x/tools/internal/gocommand"
+	"golang.org/x/tools/internal/packagesinternal"
+	"golang.org/x/tools/internal/typesinternal"
+)
+
+// A LoadMode controls the amount of detail to return when loading.
+// The bits below can be combined to specify which fields should be
+// filled in the result packages.
+// The zero value is a special case, equivalent to combining
+// the NeedName, NeedFiles, and NeedCompiledGoFiles bits.
+// ID and Errors (if present) will always be filled.
+// Load may return more information than requested.
+type LoadMode int
+
+// TODO(matloob): When a V2 of go/packages is released, rename NeedExportsFile to
+// NeedExportFile to make it consistent with the Package field it's adding.
+
+const (
+	// NeedName adds Name and PkgPath.
+	NeedName LoadMode = 1 << iota
+
+	// NeedFiles adds GoFiles and OtherFiles.
+	NeedFiles
+
+	// NeedCompiledGoFiles adds CompiledGoFiles.
+	NeedCompiledGoFiles
+
+	// NeedImports adds Imports. If NeedDeps is not set, the Imports field will contain
+	// "placeholder" Packages with only the ID set.
+	NeedImports
+
+	// NeedDeps adds the fields requested by the LoadMode in the packages in Imports.
+	NeedDeps
+
+	// NeedExportsFile adds ExportFile.
+	NeedExportsFile
+
+	// NeedTypes adds Types, Fset, and IllTyped.
+	NeedTypes
+
+	// NeedSyntax adds Syntax.
+	NeedSyntax
+
+	// NeedTypesInfo adds TypesInfo.
+	NeedTypesInfo
+
+	// NeedTypesSizes adds TypesSizes.
+	NeedTypesSizes
+
+	// typecheckCgo enables full support for type checking cgo. Requires Go 1.15+.
+	// Modifies CompiledGoFiles and Types, and has no effect on its own.
+	typecheckCgo
+
+	// NeedModule adds Module.
+	NeedModule
+)
+
+const (
+	// Deprecated: LoadFiles exists for historical compatibility
+	// and should not be used. Please directly specify the needed fields using the Need values.
+	LoadFiles = NeedName | NeedFiles | NeedCompiledGoFiles
+
+	// Deprecated: LoadImports exists for historical compatibility
+	// and should not be used. Please directly specify the needed fields using the Need values.
+	LoadImports = LoadFiles | NeedImports
+
+	// Deprecated: LoadTypes exists for historical compatibility
+	// and should not be used. Please directly specify the needed fields using the Need values.
+	LoadTypes = LoadImports | NeedTypes | NeedTypesSizes
+
+	// Deprecated: LoadSyntax exists for historical compatibility
+	// and should not be used. Please directly specify the needed fields using the Need values.
+	LoadSyntax = LoadTypes | NeedSyntax | NeedTypesInfo
+
+	// Deprecated: LoadAllSyntax exists for historical compatibility
+	// and should not be used. Please directly specify the needed fields using the Need values.
+	LoadAllSyntax = LoadSyntax | NeedDeps
+)
+
+// A Config specifies details about how packages should be loaded.
+// The zero value is a valid configuration.
+// Calls to Load do not modify this struct.
+type Config struct {
+	// Mode controls the level of information returned for each package.
+	Mode LoadMode
+
+	// Context specifies the context for the load operation.
+	// If the context is cancelled, the loader may stop early
+	// and return an ErrCancelled error.
+	// If Context is nil, the load cannot be cancelled.
+	Context context.Context
+
+	// Logf is the logger for the config.
+	// If the user provides a logger, debug logging is enabled.
+	// If the GOPACKAGESDEBUG environment variable is set to true,
+	// but the logger is nil, default to log.Printf.
+	Logf func(format string, args ...interface{})
+
+	// Dir is the directory in which to run the build system's query tool
+	// that provides information about the packages.
+	// If Dir is empty, the tool is run in the current directory.
+	Dir string
+
+	// Env is the environment to use when invoking the build system's query tool.
+	// If Env is nil, the current environment is used.
+	// As in os/exec's Cmd, only the last value in the slice for
+	// each environment key is used. To specify the setting of only
+	// a few variables, append to the current environment, as in:
+	//
+	//	opt.Env = append(os.Environ(), "GOOS=plan9", "GOARCH=386")
+	//
+	Env []string
+
+	// gocmdRunner guards go command calls from concurrency errors.
+	gocmdRunner *gocommand.Runner
+
+	// BuildFlags is a list of command-line flags to be passed through to
+	// the build system's query tool.
+	BuildFlags []string
+
+	// modFile will be used for -modfile in go command invocations.
+	modFile string
+
+	// modFlag will be used for -modfile in go command invocations.
+	modFlag string
+
+	// Fset provides source position information for syntax trees and types.
+	// If Fset is nil, Load will use a new fileset, but preserve Fset's value.
+	Fset *token.FileSet
+
+	// ParseFile is called to read and parse each file
+	// when preparing a package's type-checked syntax tree.
+	// It must be safe to call ParseFile simultaneously from multiple goroutines.
+	// If ParseFile is nil, the loader will uses parser.ParseFile.
+	//
+	// ParseFile should parse the source from src and use filename only for
+	// recording position information.
+	//
+	// An application may supply a custom implementation of ParseFile
+	// to change the effective file contents or the behavior of the parser,
+	// or to modify the syntax tree. For example, selectively eliminating
+	// unwanted function bodies can significantly accelerate type checking.
+	ParseFile func(fset *token.FileSet, filename string, src []byte) (*ast.File, error)
+
+	// If Tests is set, the loader includes not just the packages
+	// matching a particular pattern but also any related test packages,
+	// including test-only variants of the package and the test executable.
+	//
+	// For example, when using the go command, loading "fmt" with Tests=true
+	// returns four packages, with IDs "fmt" (the standard package),
+	// "fmt [fmt.test]" (the package as compiled for the test),
+	// "fmt_test" (the test functions from source files in package fmt_test),
+	// and "fmt.test" (the test binary).
+	//
+	// In build systems with explicit names for tests,
+	// setting Tests may have no effect.
+	Tests bool
+
+	// Overlay provides a mapping of absolute file paths to file contents.
+	// If the file with the given path already exists, the parser will use the
+	// alternative file contents provided by the map.
+	//
+	// Overlays provide incomplete support for when a given file doesn't
+	// already exist on disk. See the package doc above for more details.
+	Overlay map[string][]byte
+}
+
+// driver is the type for functions that query the build system for the
+// packages named by the patterns.
+type driver func(cfg *Config, patterns ...string) (*driverResponse, error)
+
+// driverResponse contains the results for a driver query.
+type driverResponse struct {
+	// NotHandled is returned if the request can't be handled by the current
+	// driver. If an external driver returns a response with NotHandled, the
+	// rest of the driverResponse is ignored, and go/packages will fallback
+	// to the next driver. If go/packages is extended in the future to support
+	// lists of multiple drivers, go/packages will fall back to the next driver.
+	NotHandled bool
+
+	// Sizes, if not nil, is the types.Sizes to use when type checking.
+	Sizes *types.StdSizes
+
+	// Roots is the set of package IDs that make up the root packages.
+	// We have to encode this separately because when we encode a single package
+	// we cannot know if it is one of the roots as that requires knowledge of the
+	// graph it is part of.
+	Roots []string `json:",omitempty"`
+
+	// Packages is the full set of packages in the graph.
+	// The packages are not connected into a graph.
+	// The Imports if populated will be stubs that only have their ID set.
+	// Imports will be connected and then type and syntax information added in a
+	// later pass (see refine).
+	Packages []*Package
+}
+
+// Load loads and returns the Go packages named by the given patterns.
+//
+// Config specifies loading options;
+// nil behaves the same as an empty Config.
+//
+// Load returns an error if any of the patterns was invalid
+// as defined by the underlying build system.
+// It may return an empty list of packages without an error,
+// for instance for an empty expansion of a valid wildcard.
+// Errors associated with a particular package are recorded in the
+// corresponding Package's Errors list, and do not cause Load to
+// return an error. Clients may need to handle such errors before
+// proceeding with further analysis. The PrintErrors function is
+// provided for convenient display of all errors.
+func Load(cfg *Config, patterns ...string) ([]*Package, error) {
+	l := newLoader(cfg)
+	response, err := defaultDriver(&l.Config, patterns...)
+	if err != nil {
+		return nil, err
+	}
+	l.sizes = response.Sizes
+	return l.refine(response.Roots, response.Packages...)
+}
+
+// defaultDriver is a driver that implements go/packages' fallback behavior.
+// It will try to request to an external driver, if one exists. If there's
+// no external driver, or the driver returns a response with NotHandled set,
+// defaultDriver will fall back to the go list driver.
+func defaultDriver(cfg *Config, patterns ...string) (*driverResponse, error) {
+	driver := findExternalDriver(cfg)
+	if driver == nil {
+		driver = goListDriver
+	}
+	response, err := driver(cfg, patterns...)
+	if err != nil {
+		return response, err
+	} else if response.NotHandled {
+		return goListDriver(cfg, patterns...)
+	}
+	return response, nil
+}
+
+// A Package describes a loaded Go package.
+type Package struct {
+	// ID is a unique identifier for a package,
+	// in a syntax provided by the underlying build system.
+	//
+	// Because the syntax varies based on the build system,
+	// clients should treat IDs as opaque and not attempt to
+	// interpret them.
+	ID string
+
+	// Name is the package name as it appears in the package source code.
+	Name string
+
+	// PkgPath is the package path as used by the go/types package.
+	PkgPath string
+
+	// Errors contains any errors encountered querying the metadata
+	// of the package, or while parsing or type-checking its files.
+	Errors []Error
+
+	// GoFiles lists the absolute file paths of the package's Go source files.
+	GoFiles []string
+
+	// CompiledGoFiles lists the absolute file paths of the package's source
+	// files that are suitable for type checking.
+	// This may differ from GoFiles if files are processed before compilation.
+	CompiledGoFiles []string
+
+	// OtherFiles lists the absolute file paths of the package's non-Go source files,
+	// including assembly, C, C++, Fortran, Objective-C, SWIG, and so on.
+	OtherFiles []string
+
+	// IgnoredFiles lists source files that are not part of the package
+	// using the current build configuration but that might be part of
+	// the package using other build configurations.
+	IgnoredFiles []string
+
+	// ExportFile is the absolute path to a file containing type
+	// information for the package as provided by the build system.
+	ExportFile string
+
+	// Imports maps import paths appearing in the package's Go source files
+	// to corresponding loaded Packages.
+	Imports map[string]*Package
+
+	// Types provides type information for the package.
+	// The NeedTypes LoadMode bit sets this field for packages matching the
+	// patterns; type information for dependencies may be missing or incomplete,
+	// unless NeedDeps and NeedImports are also set.
+	Types *types.Package
+
+	// Fset provides position information for Types, TypesInfo, and Syntax.
+	// It is set only when Types is set.
+	Fset *token.FileSet
+
+	// IllTyped indicates whether the package or any dependency contains errors.
+	// It is set only when Types is set.
+	IllTyped bool
+
+	// Syntax is the package's syntax trees, for the files listed in CompiledGoFiles.
+	//
+	// The NeedSyntax LoadMode bit populates this field for packages matching the patterns.
+	// If NeedDeps and NeedImports are also set, this field will also be populated
+	// for dependencies.
+	Syntax []*ast.File
+
+	// TypesInfo provides type information about the package's syntax trees.
+	// It is set only when Syntax is set.
+	TypesInfo *types.Info
+
+	// TypesSizes provides the effective size function for types in TypesInfo.
+	TypesSizes types.Sizes
+
+	// forTest is the package under test, if any.
+	forTest string
+
+	// depsErrors is the DepsErrors field from the go list response, if any.
+	depsErrors []*packagesinternal.PackageError
+
+	// module is the module information for the package if it exists.
+	Module *Module
+}
+
+// Module provides module information for a package.
+type Module struct {
+	Path      string       // module path
+	Version   string       // module version
+	Replace   *Module      // replaced by this module
+	Time      *time.Time   // time version was created
+	Main      bool         // is this the main module?
+	Indirect  bool         // is this module only an indirect dependency of main module?
+	Dir       string       // directory holding files for this module, if any
+	GoMod     string       // path to go.mod file used when loading this module, if any
+	GoVersion string       // go version used in module
+	Error     *ModuleError // error loading module
+}
+
+// ModuleError holds errors loading a module.
+type ModuleError struct {
+	Err string // the error itself
+}
+
+func init() {
+	packagesinternal.GetForTest = func(p interface{}) string {
+		return p.(*Package).forTest
+	}
+	packagesinternal.GetDepsErrors = func(p interface{}) []*packagesinternal.PackageError {
+		return p.(*Package).depsErrors
+	}
+	packagesinternal.GetGoCmdRunner = func(config interface{}) *gocommand.Runner {
+		return config.(*Config).gocmdRunner
+	}
+	packagesinternal.SetGoCmdRunner = func(config interface{}, runner *gocommand.Runner) {
+		config.(*Config).gocmdRunner = runner
+	}
+	packagesinternal.SetModFile = func(config interface{}, value string) {
+		config.(*Config).modFile = value
+	}
+	packagesinternal.SetModFlag = func(config interface{}, value string) {
+		config.(*Config).modFlag = value
+	}
+	packagesinternal.TypecheckCgo = int(typecheckCgo)
+}
+
+// An Error describes a problem with a package's metadata, syntax, or types.
+type Error struct {
+	Pos  string // "file:line:col" or "file:line" or "" or "-"
+	Msg  string
+	Kind ErrorKind
+}
+
+// ErrorKind describes the source of the error, allowing the user to
+// differentiate between errors generated by the driver, the parser, or the
+// type-checker.
+type ErrorKind int
+
+const (
+	UnknownError ErrorKind = iota
+	ListError
+	ParseError
+	TypeError
+)
+
+func (err Error) Error() string {
+	pos := err.Pos
+	if pos == "" {
+		pos = "-" // like token.Position{}.String()
+	}
+	return pos + ": " + err.Msg
+}
+
+// flatPackage is the JSON form of Package
+// It drops all the type and syntax fields, and transforms the Imports
+//
+// TODO(adonovan): identify this struct with Package, effectively
+// publishing the JSON protocol.
+type flatPackage struct {
+	ID              string
+	Name            string            `json:",omitempty"`
+	PkgPath         string            `json:",omitempty"`
+	Errors          []Error           `json:",omitempty"`
+	GoFiles         []string          `json:",omitempty"`
+	CompiledGoFiles []string          `json:",omitempty"`
+	OtherFiles      []string          `json:",omitempty"`
+	IgnoredFiles    []string          `json:",omitempty"`
+	ExportFile      string            `json:",omitempty"`
+	Imports         map[string]string `json:",omitempty"`
+}
+
+// MarshalJSON returns the Package in its JSON form.
+// For the most part, the structure fields are written out unmodified, and
+// the type and syntax fields are skipped.
+// The imports are written out as just a map of path to package id.
+// The errors are written using a custom type that tries to preserve the
+// structure of error types we know about.
+//
+// This method exists to enable support for additional build systems.  It is
+// not intended for use by clients of the API and we may change the format.
+func (p *Package) MarshalJSON() ([]byte, error) {
+	flat := &flatPackage{
+		ID:              p.ID,
+		Name:            p.Name,
+		PkgPath:         p.PkgPath,
+		Errors:          p.Errors,
+		GoFiles:         p.GoFiles,
+		CompiledGoFiles: p.CompiledGoFiles,
+		OtherFiles:      p.OtherFiles,
+		IgnoredFiles:    p.IgnoredFiles,
+		ExportFile:      p.ExportFile,
+	}
+	if len(p.Imports) > 0 {
+		flat.Imports = make(map[string]string, len(p.Imports))
+		for path, ipkg := range p.Imports {
+			flat.Imports[path] = ipkg.ID
+		}
+	}
+	return json.Marshal(flat)
+}
+
+// UnmarshalJSON reads in a Package from its JSON format.
+// See MarshalJSON for details about the format accepted.
+func (p *Package) UnmarshalJSON(b []byte) error {
+	flat := &flatPackage{}
+	if err := json.Unmarshal(b, &flat); err != nil {
+		return err
+	}
+	*p = Package{
+		ID:              flat.ID,
+		Name:            flat.Name,
+		PkgPath:         flat.PkgPath,
+		Errors:          flat.Errors,
+		GoFiles:         flat.GoFiles,
+		CompiledGoFiles: flat.CompiledGoFiles,
+		OtherFiles:      flat.OtherFiles,
+		ExportFile:      flat.ExportFile,
+	}
+	if len(flat.Imports) > 0 {
+		p.Imports = make(map[string]*Package, len(flat.Imports))
+		for path, id := range flat.Imports {
+			p.Imports[path] = &Package{ID: id}
+		}
+	}
+	return nil
+}
+
+func (p *Package) String() string { return p.ID }
+
+// loaderPackage augments Package with state used during the loading phase
+type loaderPackage struct {
+	*Package
+	importErrors map[string]error // maps each bad import to its error
+	loadOnce     sync.Once
+	color        uint8 // for cycle detection
+	needsrc      bool  // load from source (Mode >= LoadTypes)
+	needtypes    bool  // type information is either requested or depended on
+	initial      bool  // package was matched by a pattern
+}
+
+// loader holds the working state of a single call to load.
+type loader struct {
+	pkgs map[string]*loaderPackage
+	Config
+	sizes        types.Sizes
+	parseCache   map[string]*parseValue
+	parseCacheMu sync.Mutex
+	exportMu     sync.Mutex // enforces mutual exclusion of exportdata operations
+
+	// Config.Mode contains the implied mode (see impliedLoadMode).
+	// Implied mode contains all the fields we need the data for.
+	// In requestedMode there are the actually requested fields.
+	// We'll zero them out before returning packages to the user.
+	// This makes it easier for us to get the conditions where
+	// we need certain modes right.
+	requestedMode LoadMode
+}
+
+type parseValue struct {
+	f     *ast.File
+	err   error
+	ready chan struct{}
+}
+
+func newLoader(cfg *Config) *loader {
+	ld := &loader{
+		parseCache: map[string]*parseValue{},
+	}
+	if cfg != nil {
+		ld.Config = *cfg
+		// If the user has provided a logger, use it.
+		ld.Config.Logf = cfg.Logf
+	}
+	if ld.Config.Logf == nil {
+		// If the GOPACKAGESDEBUG environment variable is set to true,
+		// but the user has not provided a logger, default to log.Printf.
+		if debug {
+			ld.Config.Logf = log.Printf
+		} else {
+			ld.Config.Logf = func(format string, args ...interface{}) {}
+		}
+	}
+	if ld.Config.Mode == 0 {
+		ld.Config.Mode = NeedName | NeedFiles | NeedCompiledGoFiles // Preserve zero behavior of Mode for backwards compatibility.
+	}
+	if ld.Config.Env == nil {
+		ld.Config.Env = os.Environ()
+	}
+	if ld.Config.gocmdRunner == nil {
+		ld.Config.gocmdRunner = &gocommand.Runner{}
+	}
+	if ld.Context == nil {
+		ld.Context = context.Background()
+	}
+	if ld.Dir == "" {
+		if dir, err := os.Getwd(); err == nil {
+			ld.Dir = dir
+		}
+	}
+
+	// Save the actually requested fields. We'll zero them out before returning packages to the user.
+	ld.requestedMode = ld.Mode
+	ld.Mode = impliedLoadMode(ld.Mode)
+
+	if ld.Mode&NeedTypes != 0 || ld.Mode&NeedSyntax != 0 {
+		if ld.Fset == nil {
+			ld.Fset = token.NewFileSet()
+		}
+
+		// ParseFile is required even in LoadTypes mode
+		// because we load source if export data is missing.
+		if ld.ParseFile == nil {
+			ld.ParseFile = func(fset *token.FileSet, filename string, src []byte) (*ast.File, error) {
+				const mode = parser.AllErrors | parser.ParseComments
+				return parser.ParseFile(fset, filename, src, mode)
+			}
+		}
+	}
+
+	return ld
+}
+
+// refine connects the supplied packages into a graph and then adds type and
+// and syntax information as requested by the LoadMode.
+func (ld *loader) refine(roots []string, list ...*Package) ([]*Package, error) {
+	rootMap := make(map[string]int, len(roots))
+	for i, root := range roots {
+		rootMap[root] = i
+	}
+	ld.pkgs = make(map[string]*loaderPackage)
+	// first pass, fixup and build the map and roots
+	var initial = make([]*loaderPackage, len(roots))
+	for _, pkg := range list {
+		rootIndex := -1
+		if i, found := rootMap[pkg.ID]; found {
+			rootIndex = i
+		}
+
+		// Overlays can invalidate export data.
+		// TODO(matloob): make this check fine-grained based on dependencies on overlaid files
+		exportDataInvalid := len(ld.Overlay) > 0 || pkg.ExportFile == "" && pkg.PkgPath != "unsafe"
+		// This package needs type information if the caller requested types and the package is
+		// either a root, or it's a non-root and the user requested dependencies ...
+		needtypes := (ld.Mode&NeedTypes|NeedTypesInfo != 0 && (rootIndex >= 0 || ld.Mode&NeedDeps != 0))
+		// This package needs source if the call requested source (or types info, which implies source)
+		// and the package is either a root, or itas a non- root and the user requested dependencies...
+		needsrc := ((ld.Mode&(NeedSyntax|NeedTypesInfo) != 0 && (rootIndex >= 0 || ld.Mode&NeedDeps != 0)) ||
+			// ... or if we need types and the exportData is invalid. We fall back to (incompletely)
+			// typechecking packages from source if they fail to compile.
+			(ld.Mode&NeedTypes|NeedTypesInfo != 0 && exportDataInvalid)) && pkg.PkgPath != "unsafe"
+		lpkg := &loaderPackage{
+			Package:   pkg,
+			needtypes: needtypes,
+			needsrc:   needsrc,
+		}
+		ld.pkgs[lpkg.ID] = lpkg
+		if rootIndex >= 0 {
+			initial[rootIndex] = lpkg
+			lpkg.initial = true
+		}
+	}
+	for i, root := range roots {
+		if initial[i] == nil {
+			return nil, fmt.Errorf("root package %v is missing", root)
+		}
+	}
+
+	// Materialize the import graph.
+
+	const (
+		white = 0 // new
+		grey  = 1 // in progress
+		black = 2 // complete
+	)
+
+	// visit traverses the import graph, depth-first,
+	// and materializes the graph as Packages.Imports.
+	//
+	// Valid imports are saved in the Packages.Import map.
+	// Invalid imports (cycles and missing nodes) are saved in the importErrors map.
+	// Thus, even in the presence of both kinds of errors, the Import graph remains a DAG.
+	//
+	// visit returns whether the package needs src or has a transitive
+	// dependency on a package that does. These are the only packages
+	// for which we load source code.
+	var stack []*loaderPackage
+	var visit func(lpkg *loaderPackage) bool
+	var srcPkgs []*loaderPackage
+	visit = func(lpkg *loaderPackage) bool {
+		switch lpkg.color {
+		case black:
+			return lpkg.needsrc
+		case grey:
+			panic("internal error: grey node")
+		}
+		lpkg.color = grey
+		stack = append(stack, lpkg) // push
+		stubs := lpkg.Imports       // the structure form has only stubs with the ID in the Imports
+		// If NeedImports isn't set, the imports fields will all be zeroed out.
+		if ld.Mode&NeedImports != 0 {
+			lpkg.Imports = make(map[string]*Package, len(stubs))
+			for importPath, ipkg := range stubs {
+				var importErr error
+				imp := ld.pkgs[ipkg.ID]
+				if imp == nil {
+					// (includes package "C" when DisableCgo)
+					importErr = fmt.Errorf("missing package: %q", ipkg.ID)
+				} else if imp.color == grey {
+					importErr = fmt.Errorf("import cycle: %s", stack)
+				}
+				if importErr != nil {
+					if lpkg.importErrors == nil {
+						lpkg.importErrors = make(map[string]error)
+					}
+					lpkg.importErrors[importPath] = importErr
+					continue
+				}
+
+				if visit(imp) {
+					lpkg.needsrc = true
+				}
+				lpkg.Imports[importPath] = imp.Package
+			}
+		}
+		if lpkg.needsrc {
+			srcPkgs = append(srcPkgs, lpkg)
+		}
+		if ld.Mode&NeedTypesSizes != 0 {
+			lpkg.TypesSizes = ld.sizes
+		}
+		stack = stack[:len(stack)-1] // pop
+		lpkg.color = black
+
+		return lpkg.needsrc
+	}
+
+	if ld.Mode&NeedImports == 0 {
+		// We do this to drop the stub import packages that we are not even going to try to resolve.
+		for _, lpkg := range initial {
+			lpkg.Imports = nil
+		}
+	} else {
+		// For each initial package, create its import DAG.
+		for _, lpkg := range initial {
+			visit(lpkg)
+		}
+	}
+	if ld.Mode&NeedImports != 0 && ld.Mode&NeedTypes != 0 {
+		for _, lpkg := range srcPkgs {
+			// Complete type information is required for the
+			// immediate dependencies of each source package.
+			for _, ipkg := range lpkg.Imports {
+				imp := ld.pkgs[ipkg.ID]
+				imp.needtypes = true
+			}
+		}
+	}
+	// Load type data and syntax if needed, starting at
+	// the initial packages (roots of the import DAG).
+	if ld.Mode&NeedTypes != 0 || ld.Mode&NeedSyntax != 0 {
+		var wg sync.WaitGroup
+		for _, lpkg := range initial {
+			wg.Add(1)
+			go func(lpkg *loaderPackage) {
+				ld.loadRecursive(lpkg)
+				wg.Done()
+			}(lpkg)
+		}
+		wg.Wait()
+	}
+
+	result := make([]*Package, len(initial))
+	for i, lpkg := range initial {
+		result[i] = lpkg.Package
+	}
+	for i := range ld.pkgs {
+		// Clear all unrequested fields,
+		// to catch programs that use more than they request.
+		if ld.requestedMode&NeedName == 0 {
+			ld.pkgs[i].Name = ""
+			ld.pkgs[i].PkgPath = ""
+		}
+		if ld.requestedMode&NeedFiles == 0 {
+			ld.pkgs[i].GoFiles = nil
+			ld.pkgs[i].OtherFiles = nil
+			ld.pkgs[i].IgnoredFiles = nil
+		}
+		if ld.requestedMode&NeedCompiledGoFiles == 0 {
+			ld.pkgs[i].CompiledGoFiles = nil
+		}
+		if ld.requestedMode&NeedImports == 0 {
+			ld.pkgs[i].Imports = nil
+		}
+		if ld.requestedMode&NeedExportsFile == 0 {
+			ld.pkgs[i].ExportFile = ""
+		}
+		if ld.requestedMode&NeedTypes == 0 {
+			ld.pkgs[i].Types = nil
+			ld.pkgs[i].Fset = nil
+			ld.pkgs[i].IllTyped = false
+		}
+		if ld.requestedMode&NeedSyntax == 0 {
+			ld.pkgs[i].Syntax = nil
+		}
+		if ld.requestedMode&NeedTypesInfo == 0 {
+			ld.pkgs[i].TypesInfo = nil
+		}
+		if ld.requestedMode&NeedTypesSizes == 0 {
+			ld.pkgs[i].TypesSizes = nil
+		}
+		if ld.requestedMode&NeedModule == 0 {
+			ld.pkgs[i].Module = nil
+		}
+	}
+
+	return result, nil
+}
+
+// loadRecursive loads the specified package and its dependencies,
+// recursively, in parallel, in topological order.
+// It is atomic and idempotent.
+// Precondition: ld.Mode&NeedTypes.
+func (ld *loader) loadRecursive(lpkg *loaderPackage) {
+	lpkg.loadOnce.Do(func() {
+		// Load the direct dependencies, in parallel.
+		var wg sync.WaitGroup
+		for _, ipkg := range lpkg.Imports {
+			imp := ld.pkgs[ipkg.ID]
+			wg.Add(1)
+			go func(imp *loaderPackage) {
+				ld.loadRecursive(imp)
+				wg.Done()
+			}(imp)
+		}
+		wg.Wait()
+		ld.loadPackage(lpkg)
+	})
+}
+
+// loadPackage loads the specified package.
+// It must be called only once per Package,
+// after immediate dependencies are loaded.
+// Precondition: ld.Mode & NeedTypes.
+func (ld *loader) loadPackage(lpkg *loaderPackage) {
+	if lpkg.PkgPath == "unsafe" {
+		// Fill in the blanks to avoid surprises.
+		lpkg.Types = types.Unsafe
+		lpkg.Fset = ld.Fset
+		lpkg.Syntax = []*ast.File{}
+		lpkg.TypesInfo = new(types.Info)
+		lpkg.TypesSizes = ld.sizes
+		return
+	}
+
+	// Call NewPackage directly with explicit name.
+	// This avoids skew between golist and go/types when the files'
+	// package declarations are inconsistent.
+	lpkg.Types = types.NewPackage(lpkg.PkgPath, lpkg.Name)
+	lpkg.Fset = ld.Fset
+
+	// Subtle: we populate all Types fields with an empty Package
+	// before loading export data so that export data processing
+	// never has to create a types.Package for an indirect dependency,
+	// which would then require that such created packages be explicitly
+	// inserted back into the Import graph as a final step after export data loading.
+	// The Diamond test exercises this case.
+	if !lpkg.needtypes && !lpkg.needsrc {
+		return
+	}
+	if !lpkg.needsrc {
+		ld.loadFromExportData(lpkg)
+		return // not a source package, don't get syntax trees
+	}
+
+	appendError := func(err error) {
+		// Convert various error types into the one true Error.
+		var errs []Error
+		switch err := err.(type) {
+		case Error:
+			// from driver
+			errs = append(errs, err)
+
+		case *os.PathError:
+			// from parser
+			errs = append(errs, Error{
+				Pos:  err.Path + ":1",
+				Msg:  err.Err.Error(),
+				Kind: ParseError,
+			})
+
+		case scanner.ErrorList:
+			// from parser
+			for _, err := range err {
+				errs = append(errs, Error{
+					Pos:  err.Pos.String(),
+					Msg:  err.Msg,
+					Kind: ParseError,
+				})
+			}
+
+		case types.Error:
+			// from type checker
+			errs = append(errs, Error{
+				Pos:  err.Fset.Position(err.Pos).String(),
+				Msg:  err.Msg,
+				Kind: TypeError,
+			})
+
+		default:
+			// unexpected impoverished error from parser?
+			errs = append(errs, Error{
+				Pos:  "-",
+				Msg:  err.Error(),
+				Kind: UnknownError,
+			})
+
+			// If you see this error message, please file a bug.
+			log.Printf("internal error: error %q (%T) without position", err, err)
+		}
+
+		lpkg.Errors = append(lpkg.Errors, errs...)
+	}
+
+	if ld.Config.Mode&NeedTypes != 0 && len(lpkg.CompiledGoFiles) == 0 && lpkg.ExportFile != "" {
+		// The config requested loading sources and types, but sources are missing.
+		// Add an error to the package and fall back to loading from export data.
+		appendError(Error{"-", fmt.Sprintf("sources missing for package %s", lpkg.ID), ParseError})
+		ld.loadFromExportData(lpkg)
+		return // can't get syntax trees for this package
+	}
+
+	files, errs := ld.parseFiles(lpkg.CompiledGoFiles)
+	for _, err := range errs {
+		appendError(err)
+	}
+
+	lpkg.Syntax = files
+	if ld.Config.Mode&NeedTypes == 0 {
+		return
+	}
+
+	lpkg.TypesInfo = &types.Info{
+		Types:      make(map[ast.Expr]types.TypeAndValue),
+		Defs:       make(map[*ast.Ident]types.Object),
+		Uses:       make(map[*ast.Ident]types.Object),
+		Implicits:  make(map[ast.Node]types.Object),
+		Scopes:     make(map[ast.Node]*types.Scope),
+		Selections: make(map[*ast.SelectorExpr]*types.Selection),
+	}
+	lpkg.TypesSizes = ld.sizes
+
+	importer := importerFunc(func(path string) (*types.Package, error) {
+		if path == "unsafe" {
+			return types.Unsafe, nil
+		}
+
+		// The imports map is keyed by import path.
+		ipkg := lpkg.Imports[path]
+		if ipkg == nil {
+			if err := lpkg.importErrors[path]; err != nil {
+				return nil, err
+			}
+			// There was skew between the metadata and the
+			// import declarations, likely due to an edit
+			// race, or because the ParseFile feature was
+			// used to supply alternative file contents.
+			return nil, fmt.Errorf("no metadata for %s", path)
+		}
+
+		if ipkg.Types != nil && ipkg.Types.Complete() {
+			return ipkg.Types, nil
+		}
+		log.Fatalf("internal error: package %q without types was imported from %q", path, lpkg)
+		panic("unreachable")
+	})
+
+	// type-check
+	tc := &types.Config{
+		Importer: importer,
+
+		// Type-check bodies of functions only in non-initial packages.
+		// Example: for import graph A->B->C and initial packages {A,C},
+		// we can ignore function bodies in B.
+		IgnoreFuncBodies: ld.Mode&NeedDeps == 0 && !lpkg.initial,
+
+		Error: appendError,
+		Sizes: ld.sizes,
+	}
+	if (ld.Mode & typecheckCgo) != 0 {
+		if !typesinternal.SetUsesCgo(tc) {
+			appendError(Error{
+				Msg:  "typecheckCgo requires Go 1.15+",
+				Kind: ListError,
+			})
+			return
+		}
+	}
+	types.NewChecker(tc, ld.Fset, lpkg.Types, lpkg.TypesInfo).Files(lpkg.Syntax)
+
+	lpkg.importErrors = nil // no longer needed
+
+	// If !Cgo, the type-checker uses FakeImportC mode, so
+	// it doesn't invoke the importer for import "C",
+	// nor report an error for the import,
+	// or for any undefined C.f reference.
+	// We must detect this explicitly and correctly
+	// mark the package as IllTyped (by reporting an error).
+	// TODO(adonovan): if these errors are annoying,
+	// we could just set IllTyped quietly.
+	if tc.FakeImportC {
+	outer:
+		for _, f := range lpkg.Syntax {
+			for _, imp := range f.Imports {
+				if imp.Path.Value == `"C"` {
+					err := types.Error{Fset: ld.Fset, Pos: imp.Pos(), Msg: `import "C" ignored`}
+					appendError(err)
+					break outer
+				}
+			}
+		}
+	}
+
+	// Record accumulated errors.
+	illTyped := len(lpkg.Errors) > 0
+	if !illTyped {
+		for _, imp := range lpkg.Imports {
+			if imp.IllTyped {
+				illTyped = true
+				break
+			}
+		}
+	}
+	lpkg.IllTyped = illTyped
+}
+
+// An importFunc is an implementation of the single-method
+// types.Importer interface based on a function value.
+type importerFunc func(path string) (*types.Package, error)
+
+func (f importerFunc) Import(path string) (*types.Package, error) { return f(path) }
+
+// We use a counting semaphore to limit
+// the number of parallel I/O calls per process.
+var ioLimit = make(chan bool, 20)
+
+func (ld *loader) parseFile(filename string) (*ast.File, error) {
+	ld.parseCacheMu.Lock()
+	v, ok := ld.parseCache[filename]
+	if ok {
+		// cache hit
+		ld.parseCacheMu.Unlock()
+		<-v.ready
+	} else {
+		// cache miss
+		v = &parseValue{ready: make(chan struct{})}
+		ld.parseCache[filename] = v
+		ld.parseCacheMu.Unlock()
+
+		var src []byte
+		for f, contents := range ld.Config.Overlay {
+			if sameFile(f, filename) {
+				src = contents
+			}
+		}
+		var err error
+		if src == nil {
+			ioLimit <- true // wait
+			src, err = ioutil.ReadFile(filename)
+			<-ioLimit // signal
+		}
+		if err != nil {
+			v.err = err
+		} else {
+			v.f, v.err = ld.ParseFile(ld.Fset, filename, src)
+		}
+
+		close(v.ready)
+	}
+	return v.f, v.err
+}
+
+// parseFiles reads and parses the Go source files and returns the ASTs
+// of the ones that could be at least partially parsed, along with a
+// list of I/O and parse errors encountered.
+//
+// Because files are scanned in parallel, the token.Pos
+// positions of the resulting ast.Files are not ordered.
+//
+func (ld *loader) parseFiles(filenames []string) ([]*ast.File, []error) {
+	var wg sync.WaitGroup
+	n := len(filenames)
+	parsed := make([]*ast.File, n)
+	errors := make([]error, n)
+	for i, file := range filenames {
+		if ld.Config.Context.Err() != nil {
+			parsed[i] = nil
+			errors[i] = ld.Config.Context.Err()
+			continue
+		}
+		wg.Add(1)
+		go func(i int, filename string) {
+			parsed[i], errors[i] = ld.parseFile(filename)
+			wg.Done()
+		}(i, file)
+	}
+	wg.Wait()
+
+	// Eliminate nils, preserving order.
+	var o int
+	for _, f := range parsed {
+		if f != nil {
+			parsed[o] = f
+			o++
+		}
+	}
+	parsed = parsed[:o]
+
+	o = 0
+	for _, err := range errors {
+		if err != nil {
+			errors[o] = err
+			o++
+		}
+	}
+	errors = errors[:o]
+
+	return parsed, errors
+}
+
+// sameFile returns true if x and y have the same basename and denote
+// the same file.
+//
+func sameFile(x, y string) bool {
+	if x == y {
+		// It could be the case that y doesn't exist.
+		// For instance, it may be an overlay file that
+		// hasn't been written to disk. To handle that case
+		// let x == y through. (We added the exact absolute path
+		// string to the CompiledGoFiles list, so the unwritten
+		// overlay case implies x==y.)
+		return true
+	}
+	if strings.EqualFold(filepath.Base(x), filepath.Base(y)) { // (optimisation)
+		if xi, err := os.Stat(x); err == nil {
+			if yi, err := os.Stat(y); err == nil {
+				return os.SameFile(xi, yi)
+			}
+		}
+	}
+	return false
+}
+
+// loadFromExportData returns type information for the specified
+// package, loading it from an export data file on the first request.
+func (ld *loader) loadFromExportData(lpkg *loaderPackage) (*types.Package, error) {
+	if lpkg.PkgPath == "" {
+		log.Fatalf("internal error: Package %s has no PkgPath", lpkg)
+	}
+
+	// Because gcexportdata.Read has the potential to create or
+	// modify the types.Package for each node in the transitive
+	// closure of dependencies of lpkg, all exportdata operations
+	// must be sequential. (Finer-grained locking would require
+	// changes to the gcexportdata API.)
+	//
+	// The exportMu lock guards the Package.Pkg field and the
+	// types.Package it points to, for each Package in the graph.
+	//
+	// Not all accesses to Package.Pkg need to be protected by exportMu:
+	// graph ordering ensures that direct dependencies of source
+	// packages are fully loaded before the importer reads their Pkg field.
+	ld.exportMu.Lock()
+	defer ld.exportMu.Unlock()
+
+	if tpkg := lpkg.Types; tpkg != nil && tpkg.Complete() {
+		return tpkg, nil // cache hit
+	}
+
+	lpkg.IllTyped = true // fail safe
+
+	if lpkg.ExportFile == "" {
+		// Errors while building export data will have been printed to stderr.
+		return nil, fmt.Errorf("no export data file")
+	}
+	f, err := os.Open(lpkg.ExportFile)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	// Read gc export data.
+	//
+	// We don't currently support gccgo export data because all
+	// underlying workspaces use the gc toolchain. (Even build
+	// systems that support gccgo don't use it for workspace
+	// queries.)
+	r, err := gcexportdata.NewReader(f)
+	if err != nil {
+		return nil, fmt.Errorf("reading %s: %v", lpkg.ExportFile, err)
+	}
+
+	// Build the view.
+	//
+	// The gcexportdata machinery has no concept of package ID.
+	// It identifies packages by their PkgPath, which although not
+	// globally unique is unique within the scope of one invocation
+	// of the linker, type-checker, or gcexportdata.
+	//
+	// So, we must build a PkgPath-keyed view of the global
+	// (conceptually ID-keyed) cache of packages and pass it to
+	// gcexportdata. The view must contain every existing
+	// package that might possibly be mentioned by the
+	// current package---its transitive closure.
+	//
+	// In loadPackage, we unconditionally create a types.Package for
+	// each dependency so that export data loading does not
+	// create new ones.
+	//
+	// TODO(adonovan): it would be simpler and more efficient
+	// if the export data machinery invoked a callback to
+	// get-or-create a package instead of a map.
+	//
+	view := make(map[string]*types.Package) // view seen by gcexportdata
+	seen := make(map[*loaderPackage]bool)   // all visited packages
+	var visit func(pkgs map[string]*Package)
+	visit = func(pkgs map[string]*Package) {
+		for _, p := range pkgs {
+			lpkg := ld.pkgs[p.ID]
+			if !seen[lpkg] {
+				seen[lpkg] = true
+				view[lpkg.PkgPath] = lpkg.Types
+				visit(lpkg.Imports)
+			}
+		}
+	}
+	visit(lpkg.Imports)
+
+	viewLen := len(view) + 1 // adding the self package
+	// Parse the export data.
+	// (May modify incomplete packages in view but not create new ones.)
+	tpkg, err := gcexportdata.Read(r, ld.Fset, view, lpkg.PkgPath)
+	if err != nil {
+		return nil, fmt.Errorf("reading %s: %v", lpkg.ExportFile, err)
+	}
+	if viewLen != len(view) {
+		log.Fatalf("Unexpected package creation during export data loading")
+	}
+
+	lpkg.Types = tpkg
+	lpkg.IllTyped = false
+
+	return tpkg, nil
+}
+
+// impliedLoadMode returns loadMode with its dependencies.
+func impliedLoadMode(loadMode LoadMode) LoadMode {
+	if loadMode&NeedTypesInfo != 0 && loadMode&NeedImports == 0 {
+		// If NeedTypesInfo, go/packages needs to do typechecking itself so it can
+		// associate type info with the AST. To do so, we need the export data
+		// for dependencies, which means we need to ask for the direct dependencies.
+		// NeedImports is used to ask for the direct dependencies.
+		loadMode |= NeedImports
+	}
+
+	if loadMode&NeedDeps != 0 && loadMode&NeedImports == 0 {
+		// With NeedDeps we need to load at least direct dependencies.
+		// NeedImports is used to ask for the direct dependencies.
+		loadMode |= NeedImports
+	}
+
+	return loadMode
+}
+
+func usesExportData(cfg *Config) bool {
+	return cfg.Mode&NeedExportsFile != 0 || cfg.Mode&NeedTypes != 0 && cfg.Mode&NeedDeps == 0
+}
diff --git a/vendor/golang.org/x/tools/go/packages/visit.go b/vendor/golang.org/x/tools/go/packages/visit.go
new file mode 100644
index 00000000..a1dcc40b
--- /dev/null
+++ b/vendor/golang.org/x/tools/go/packages/visit.go
@@ -0,0 +1,59 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packages
+
+import (
+	"fmt"
+	"os"
+	"sort"
+)
+
+// Visit visits all the packages in the import graph whose roots are
+// pkgs, calling the optional pre function the first time each package
+// is encountered (preorder), and the optional post function after a
+// package's dependencies have been visited (postorder).
+// The boolean result of pre(pkg) determines whether
+// the imports of package pkg are visited.
+func Visit(pkgs []*Package, pre func(*Package) bool, post func(*Package)) {
+	seen := make(map[*Package]bool)
+	var visit func(*Package)
+	visit = func(pkg *Package) {
+		if !seen[pkg] {
+			seen[pkg] = true
+
+			if pre == nil || pre(pkg) {
+				paths := make([]string, 0, len(pkg.Imports))
+				for path := range pkg.Imports {
+					paths = append(paths, path)
+				}
+				sort.Strings(paths) // Imports is a map, this makes visit stable
+				for _, path := range paths {
+					visit(pkg.Imports[path])
+				}
+			}
+
+			if post != nil {
+				post(pkg)
+			}
+		}
+	}
+	for _, pkg := range pkgs {
+		visit(pkg)
+	}
+}
+
+// PrintErrors prints to os.Stderr the accumulated errors of all
+// packages in the import graph rooted at pkgs, dependencies first.
+// PrintErrors returns the number of errors printed.
+func PrintErrors(pkgs []*Package) int {
+	var n int
+	Visit(pkgs, nil, func(pkg *Package) {
+		for _, err := range pkg.Errors {
+			fmt.Fprintln(os.Stderr, err)
+			n++
+		}
+	})
+	return n
+}
diff --git a/vendor/golang.org/x/tools/internal/event/core/event.go b/vendor/golang.org/x/tools/internal/event/core/event.go
new file mode 100644
index 00000000..a6cf0e64
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/core/event.go
@@ -0,0 +1,85 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package core provides support for event based telemetry.
+package core
+
+import (
+	"fmt"
+	"time"
+
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Event holds the information about an event of note that occurred.
+type Event struct {
+	at time.Time
+
+	// As events are often on the stack, storing the first few labels directly
+	// in the event can avoid an allocation at all for the very common cases of
+	// simple events.
+	// The length needs to be large enough to cope with the majority of events
+	// but no so large as to cause undue stack pressure.
+	// A log message with two values will use 3 labels (one for each value and
+	// one for the message itself).
+
+	static  [3]label.Label // inline storage for the first few labels
+	dynamic []label.Label  // dynamically sized storage for remaining labels
+}
+
+// eventLabelMap implements label.Map for a the labels of an Event.
+type eventLabelMap struct {
+	event Event
+}
+
+func (ev Event) At() time.Time { return ev.at }
+
+func (ev Event) Format(f fmt.State, r rune) {
+	if !ev.at.IsZero() {
+		fmt.Fprint(f, ev.at.Format("2006/01/02 15:04:05 "))
+	}
+	for index := 0; ev.Valid(index); index++ {
+		if l := ev.Label(index); l.Valid() {
+			fmt.Fprintf(f, "\n\t%v", l)
+		}
+	}
+}
+
+func (ev Event) Valid(index int) bool {
+	return index >= 0 && index < len(ev.static)+len(ev.dynamic)
+}
+
+func (ev Event) Label(index int) label.Label {
+	if index < len(ev.static) {
+		return ev.static[index]
+	}
+	return ev.dynamic[index-len(ev.static)]
+}
+
+func (ev Event) Find(key label.Key) label.Label {
+	for _, l := range ev.static {
+		if l.Key() == key {
+			return l
+		}
+	}
+	for _, l := range ev.dynamic {
+		if l.Key() == key {
+			return l
+		}
+	}
+	return label.Label{}
+}
+
+func MakeEvent(static [3]label.Label, labels []label.Label) Event {
+	return Event{
+		static:  static,
+		dynamic: labels,
+	}
+}
+
+// CloneEvent event returns a copy of the event with the time adjusted to at.
+func CloneEvent(ev Event, at time.Time) Event {
+	ev.at = at
+	return ev
+}
diff --git a/vendor/golang.org/x/tools/internal/event/core/export.go b/vendor/golang.org/x/tools/internal/event/core/export.go
new file mode 100644
index 00000000..05f3a9a5
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/core/export.go
@@ -0,0 +1,70 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package core
+
+import (
+	"context"
+	"sync/atomic"
+	"time"
+	"unsafe"
+
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Exporter is a function that handles events.
+// It may return a modified context and event.
+type Exporter func(context.Context, Event, label.Map) context.Context
+
+var (
+	exporter unsafe.Pointer
+)
+
+// SetExporter sets the global exporter function that handles all events.
+// The exporter is called synchronously from the event call site, so it should
+// return quickly so as not to hold up user code.
+func SetExporter(e Exporter) {
+	p := unsafe.Pointer(&e)
+	if e == nil {
+		// &e is always valid, and so p is always valid, but for the early abort
+		// of ProcessEvent to be efficient it needs to make the nil check on the
+		// pointer without having to dereference it, so we make the nil function
+		// also a nil pointer
+		p = nil
+	}
+	atomic.StorePointer(&exporter, p)
+}
+
+// deliver is called to deliver an event to the supplied exporter.
+// it will fill in the time.
+func deliver(ctx context.Context, exporter Exporter, ev Event) context.Context {
+	// add the current time to the event
+	ev.at = time.Now()
+	// hand the event off to the current exporter
+	return exporter(ctx, ev, ev)
+}
+
+// Export is called to deliver an event to the global exporter if set.
+func Export(ctx context.Context, ev Event) context.Context {
+	// get the global exporter and abort early if there is not one
+	exporterPtr := (*Exporter)(atomic.LoadPointer(&exporter))
+	if exporterPtr == nil {
+		return ctx
+	}
+	return deliver(ctx, *exporterPtr, ev)
+}
+
+// ExportPair is called to deliver a start event to the supplied exporter.
+// It also returns a function that will deliver the end event to the same
+// exporter.
+// It will fill in the time.
+func ExportPair(ctx context.Context, begin, end Event) (context.Context, func()) {
+	// get the global exporter and abort early if there is not one
+	exporterPtr := (*Exporter)(atomic.LoadPointer(&exporter))
+	if exporterPtr == nil {
+		return ctx, func() {}
+	}
+	ctx = deliver(ctx, *exporterPtr, begin)
+	return ctx, func() { deliver(ctx, *exporterPtr, end) }
+}
diff --git a/vendor/golang.org/x/tools/internal/event/core/fast.go b/vendor/golang.org/x/tools/internal/event/core/fast.go
new file mode 100644
index 00000000..06c1d461
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/core/fast.go
@@ -0,0 +1,77 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package core
+
+import (
+	"context"
+
+	"golang.org/x/tools/internal/event/keys"
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Log1 takes a message and one label delivers a log event to the exporter.
+// It is a customized version of Print that is faster and does no allocation.
+func Log1(ctx context.Context, message string, t1 label.Label) {
+	Export(ctx, MakeEvent([3]label.Label{
+		keys.Msg.Of(message),
+		t1,
+	}, nil))
+}
+
+// Log2 takes a message and two labels and delivers a log event to the exporter.
+// It is a customized version of Print that is faster and does no allocation.
+func Log2(ctx context.Context, message string, t1 label.Label, t2 label.Label) {
+	Export(ctx, MakeEvent([3]label.Label{
+		keys.Msg.Of(message),
+		t1,
+		t2,
+	}, nil))
+}
+
+// Metric1 sends a label event to the exporter with the supplied labels.
+func Metric1(ctx context.Context, t1 label.Label) context.Context {
+	return Export(ctx, MakeEvent([3]label.Label{
+		keys.Metric.New(),
+		t1,
+	}, nil))
+}
+
+// Metric2 sends a label event to the exporter with the supplied labels.
+func Metric2(ctx context.Context, t1, t2 label.Label) context.Context {
+	return Export(ctx, MakeEvent([3]label.Label{
+		keys.Metric.New(),
+		t1,
+		t2,
+	}, nil))
+}
+
+// Start1 sends a span start event with the supplied label list to the exporter.
+// It also returns a function that will end the span, which should normally be
+// deferred.
+func Start1(ctx context.Context, name string, t1 label.Label) (context.Context, func()) {
+	return ExportPair(ctx,
+		MakeEvent([3]label.Label{
+			keys.Start.Of(name),
+			t1,
+		}, nil),
+		MakeEvent([3]label.Label{
+			keys.End.New(),
+		}, nil))
+}
+
+// Start2 sends a span start event with the supplied label list to the exporter.
+// It also returns a function that will end the span, which should normally be
+// deferred.
+func Start2(ctx context.Context, name string, t1, t2 label.Label) (context.Context, func()) {
+	return ExportPair(ctx,
+		MakeEvent([3]label.Label{
+			keys.Start.Of(name),
+			t1,
+			t2,
+		}, nil),
+		MakeEvent([3]label.Label{
+			keys.End.New(),
+		}, nil))
+}
diff --git a/vendor/golang.org/x/tools/internal/event/doc.go b/vendor/golang.org/x/tools/internal/event/doc.go
new file mode 100644
index 00000000..5dc6e6ba
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/doc.go
@@ -0,0 +1,7 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package event provides a set of packages that cover the main
+// concepts of telemetry in an implementation agnostic way.
+package event
diff --git a/vendor/golang.org/x/tools/internal/event/event.go b/vendor/golang.org/x/tools/internal/event/event.go
new file mode 100644
index 00000000..4d55e577
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/event.go
@@ -0,0 +1,127 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package event
+
+import (
+	"context"
+
+	"golang.org/x/tools/internal/event/core"
+	"golang.org/x/tools/internal/event/keys"
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Exporter is a function that handles events.
+// It may return a modified context and event.
+type Exporter func(context.Context, core.Event, label.Map) context.Context
+
+// SetExporter sets the global exporter function that handles all events.
+// The exporter is called synchronously from the event call site, so it should
+// return quickly so as not to hold up user code.
+func SetExporter(e Exporter) {
+	core.SetExporter(core.Exporter(e))
+}
+
+// Log takes a message and a label list and combines them into a single event
+// before delivering them to the exporter.
+func Log(ctx context.Context, message string, labels ...label.Label) {
+	core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Msg.Of(message),
+	}, labels))
+}
+
+// IsLog returns true if the event was built by the Log function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsLog(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Msg
+}
+
+// Error takes a message and a label list and combines them into a single event
+// before delivering them to the exporter. It captures the error in the
+// delivered event.
+func Error(ctx context.Context, message string, err error, labels ...label.Label) {
+	core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Msg.Of(message),
+		keys.Err.Of(err),
+	}, labels))
+}
+
+// IsError returns true if the event was built by the Error function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsError(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Msg &&
+		ev.Label(1).Key() == keys.Err
+}
+
+// Metric sends a label event to the exporter with the supplied labels.
+func Metric(ctx context.Context, labels ...label.Label) {
+	core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Metric.New(),
+	}, labels))
+}
+
+// IsMetric returns true if the event was built by the Metric function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsMetric(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Metric
+}
+
+// Label sends a label event to the exporter with the supplied labels.
+func Label(ctx context.Context, labels ...label.Label) context.Context {
+	return core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Label.New(),
+	}, labels))
+}
+
+// IsLabel returns true if the event was built by the Label function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsLabel(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Label
+}
+
+// Start sends a span start event with the supplied label list to the exporter.
+// It also returns a function that will end the span, which should normally be
+// deferred.
+func Start(ctx context.Context, name string, labels ...label.Label) (context.Context, func()) {
+	return core.ExportPair(ctx,
+		core.MakeEvent([3]label.Label{
+			keys.Start.Of(name),
+		}, labels),
+		core.MakeEvent([3]label.Label{
+			keys.End.New(),
+		}, nil))
+}
+
+// IsStart returns true if the event was built by the Start function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsStart(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Start
+}
+
+// IsEnd returns true if the event was built by the End function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsEnd(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.End
+}
+
+// Detach returns a context without an associated span.
+// This allows the creation of spans that are not children of the current span.
+func Detach(ctx context.Context) context.Context {
+	return core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Detach.New(),
+	}, nil))
+}
+
+// IsDetach returns true if the event was built by the Detach function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsDetach(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Detach
+}
diff --git a/vendor/golang.org/x/tools/internal/event/keys/keys.go b/vendor/golang.org/x/tools/internal/event/keys/keys.go
new file mode 100644
index 00000000..a02206e3
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/keys/keys.go
@@ -0,0 +1,564 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package keys
+
+import (
+	"fmt"
+	"io"
+	"math"
+	"strconv"
+
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Value represents a key for untyped values.
+type Value struct {
+	name        string
+	description string
+}
+
+// New creates a new Key for untyped values.
+func New(name, description string) *Value {
+	return &Value{name: name, description: description}
+}
+
+func (k *Value) Name() string        { return k.name }
+func (k *Value) Description() string { return k.description }
+
+func (k *Value) Format(w io.Writer, buf []byte, l label.Label) {
+	fmt.Fprint(w, k.From(l))
+}
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Value) Get(lm label.Map) interface{} {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return nil
+}
+
+// From can be used to get a value from a Label.
+func (k *Value) From(t label.Label) interface{} { return t.UnpackValue() }
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Value) Of(value interface{}) label.Label { return label.OfValue(k, value) }
+
+// Tag represents a key for tagging labels that have no value.
+// These are used when the existence of the label is the entire information it
+// carries, such as marking events to be of a specific kind, or from a specific
+// package.
+type Tag struct {
+	name        string
+	description string
+}
+
+// NewTag creates a new Key for tagging labels.
+func NewTag(name, description string) *Tag {
+	return &Tag{name: name, description: description}
+}
+
+func (k *Tag) Name() string        { return k.name }
+func (k *Tag) Description() string { return k.description }
+
+func (k *Tag) Format(w io.Writer, buf []byte, l label.Label) {}
+
+// New creates a new Label with this key.
+func (k *Tag) New() label.Label { return label.OfValue(k, nil) }
+
+// Int represents a key
+type Int struct {
+	name        string
+	description string
+}
+
+// NewInt creates a new Key for int values.
+func NewInt(name, description string) *Int {
+	return &Int{name: name, description: description}
+}
+
+func (k *Int) Name() string        { return k.name }
+func (k *Int) Description() string { return k.description }
+
+func (k *Int) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, int64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int) Of(v int) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int) Get(lm label.Map) int {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int) From(t label.Label) int { return int(t.Unpack64()) }
+
+// Int8 represents a key
+type Int8 struct {
+	name        string
+	description string
+}
+
+// NewInt8 creates a new Key for int8 values.
+func NewInt8(name, description string) *Int8 {
+	return &Int8{name: name, description: description}
+}
+
+func (k *Int8) Name() string        { return k.name }
+func (k *Int8) Description() string { return k.description }
+
+func (k *Int8) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, int64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int8) Of(v int8) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int8) Get(lm label.Map) int8 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int8) From(t label.Label) int8 { return int8(t.Unpack64()) }
+
+// Int16 represents a key
+type Int16 struct {
+	name        string
+	description string
+}
+
+// NewInt16 creates a new Key for int16 values.
+func NewInt16(name, description string) *Int16 {
+	return &Int16{name: name, description: description}
+}
+
+func (k *Int16) Name() string        { return k.name }
+func (k *Int16) Description() string { return k.description }
+
+func (k *Int16) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, int64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int16) Of(v int16) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int16) Get(lm label.Map) int16 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int16) From(t label.Label) int16 { return int16(t.Unpack64()) }
+
+// Int32 represents a key
+type Int32 struct {
+	name        string
+	description string
+}
+
+// NewInt32 creates a new Key for int32 values.
+func NewInt32(name, description string) *Int32 {
+	return &Int32{name: name, description: description}
+}
+
+func (k *Int32) Name() string        { return k.name }
+func (k *Int32) Description() string { return k.description }
+
+func (k *Int32) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, int64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int32) Of(v int32) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int32) Get(lm label.Map) int32 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int32) From(t label.Label) int32 { return int32(t.Unpack64()) }
+
+// Int64 represents a key
+type Int64 struct {
+	name        string
+	description string
+}
+
+// NewInt64 creates a new Key for int64 values.
+func NewInt64(name, description string) *Int64 {
+	return &Int64{name: name, description: description}
+}
+
+func (k *Int64) Name() string        { return k.name }
+func (k *Int64) Description() string { return k.description }
+
+func (k *Int64) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, k.From(l), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int64) Of(v int64) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int64) Get(lm label.Map) int64 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int64) From(t label.Label) int64 { return int64(t.Unpack64()) }
+
+// UInt represents a key
+type UInt struct {
+	name        string
+	description string
+}
+
+// NewUInt creates a new Key for uint values.
+func NewUInt(name, description string) *UInt {
+	return &UInt{name: name, description: description}
+}
+
+func (k *UInt) Name() string        { return k.name }
+func (k *UInt) Description() string { return k.description }
+
+func (k *UInt) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, uint64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt) Of(v uint) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt) Get(lm label.Map) uint {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt) From(t label.Label) uint { return uint(t.Unpack64()) }
+
+// UInt8 represents a key
+type UInt8 struct {
+	name        string
+	description string
+}
+
+// NewUInt8 creates a new Key for uint8 values.
+func NewUInt8(name, description string) *UInt8 {
+	return &UInt8{name: name, description: description}
+}
+
+func (k *UInt8) Name() string        { return k.name }
+func (k *UInt8) Description() string { return k.description }
+
+func (k *UInt8) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, uint64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt8) Of(v uint8) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt8) Get(lm label.Map) uint8 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt8) From(t label.Label) uint8 { return uint8(t.Unpack64()) }
+
+// UInt16 represents a key
+type UInt16 struct {
+	name        string
+	description string
+}
+
+// NewUInt16 creates a new Key for uint16 values.
+func NewUInt16(name, description string) *UInt16 {
+	return &UInt16{name: name, description: description}
+}
+
+func (k *UInt16) Name() string        { return k.name }
+func (k *UInt16) Description() string { return k.description }
+
+func (k *UInt16) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, uint64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt16) Of(v uint16) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt16) Get(lm label.Map) uint16 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt16) From(t label.Label) uint16 { return uint16(t.Unpack64()) }
+
+// UInt32 represents a key
+type UInt32 struct {
+	name        string
+	description string
+}
+
+// NewUInt32 creates a new Key for uint32 values.
+func NewUInt32(name, description string) *UInt32 {
+	return &UInt32{name: name, description: description}
+}
+
+func (k *UInt32) Name() string        { return k.name }
+func (k *UInt32) Description() string { return k.description }
+
+func (k *UInt32) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, uint64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt32) Of(v uint32) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt32) Get(lm label.Map) uint32 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt32) From(t label.Label) uint32 { return uint32(t.Unpack64()) }
+
+// UInt64 represents a key
+type UInt64 struct {
+	name        string
+	description string
+}
+
+// NewUInt64 creates a new Key for uint64 values.
+func NewUInt64(name, description string) *UInt64 {
+	return &UInt64{name: name, description: description}
+}
+
+func (k *UInt64) Name() string        { return k.name }
+func (k *UInt64) Description() string { return k.description }
+
+func (k *UInt64) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, k.From(l), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt64) Of(v uint64) label.Label { return label.Of64(k, v) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt64) Get(lm label.Map) uint64 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt64) From(t label.Label) uint64 { return t.Unpack64() }
+
+// Float32 represents a key
+type Float32 struct {
+	name        string
+	description string
+}
+
+// NewFloat32 creates a new Key for float32 values.
+func NewFloat32(name, description string) *Float32 {
+	return &Float32{name: name, description: description}
+}
+
+func (k *Float32) Name() string        { return k.name }
+func (k *Float32) Description() string { return k.description }
+
+func (k *Float32) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendFloat(buf, float64(k.From(l)), 'E', -1, 32))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Float32) Of(v float32) label.Label {
+	return label.Of64(k, uint64(math.Float32bits(v)))
+}
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Float32) Get(lm label.Map) float32 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Float32) From(t label.Label) float32 {
+	return math.Float32frombits(uint32(t.Unpack64()))
+}
+
+// Float64 represents a key
+type Float64 struct {
+	name        string
+	description string
+}
+
+// NewFloat64 creates a new Key for int64 values.
+func NewFloat64(name, description string) *Float64 {
+	return &Float64{name: name, description: description}
+}
+
+func (k *Float64) Name() string        { return k.name }
+func (k *Float64) Description() string { return k.description }
+
+func (k *Float64) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendFloat(buf, k.From(l), 'E', -1, 64))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Float64) Of(v float64) label.Label {
+	return label.Of64(k, math.Float64bits(v))
+}
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Float64) Get(lm label.Map) float64 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Float64) From(t label.Label) float64 {
+	return math.Float64frombits(t.Unpack64())
+}
+
+// String represents a key
+type String struct {
+	name        string
+	description string
+}
+
+// NewString creates a new Key for int64 values.
+func NewString(name, description string) *String {
+	return &String{name: name, description: description}
+}
+
+func (k *String) Name() string        { return k.name }
+func (k *String) Description() string { return k.description }
+
+func (k *String) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendQuote(buf, k.From(l)))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *String) Of(v string) label.Label { return label.OfString(k, v) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *String) Get(lm label.Map) string {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return ""
+}
+
+// From can be used to get a value from a Label.
+func (k *String) From(t label.Label) string { return t.UnpackString() }
+
+// Boolean represents a key
+type Boolean struct {
+	name        string
+	description string
+}
+
+// NewBoolean creates a new Key for bool values.
+func NewBoolean(name, description string) *Boolean {
+	return &Boolean{name: name, description: description}
+}
+
+func (k *Boolean) Name() string        { return k.name }
+func (k *Boolean) Description() string { return k.description }
+
+func (k *Boolean) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendBool(buf, k.From(l)))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Boolean) Of(v bool) label.Label {
+	if v {
+		return label.Of64(k, 1)
+	}
+	return label.Of64(k, 0)
+}
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Boolean) Get(lm label.Map) bool {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return false
+}
+
+// From can be used to get a value from a Label.
+func (k *Boolean) From(t label.Label) bool { return t.Unpack64() > 0 }
+
+// Error represents a key
+type Error struct {
+	name        string
+	description string
+}
+
+// NewError creates a new Key for int64 values.
+func NewError(name, description string) *Error {
+	return &Error{name: name, description: description}
+}
+
+func (k *Error) Name() string        { return k.name }
+func (k *Error) Description() string { return k.description }
+
+func (k *Error) Format(w io.Writer, buf []byte, l label.Label) {
+	io.WriteString(w, k.From(l).Error())
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Error) Of(v error) label.Label { return label.OfValue(k, v) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Error) Get(lm label.Map) error {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return nil
+}
+
+// From can be used to get a value from a Label.
+func (k *Error) From(t label.Label) error {
+	err, _ := t.UnpackValue().(error)
+	return err
+}
diff --git a/vendor/golang.org/x/tools/internal/event/keys/standard.go b/vendor/golang.org/x/tools/internal/event/keys/standard.go
new file mode 100644
index 00000000..7e958665
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/keys/standard.go
@@ -0,0 +1,22 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package keys
+
+var (
+	// Msg is a key used to add message strings to label lists.
+	Msg = NewString("message", "a readable message")
+	// Label is a key used to indicate an event adds labels to the context.
+	Label = NewTag("label", "a label context marker")
+	// Start is used for things like traces that have a name.
+	Start = NewString("start", "span start")
+	// Metric is a key used to indicate an event records metrics.
+	End = NewTag("end", "a span end marker")
+	// Metric is a key used to indicate an event records metrics.
+	Detach = NewTag("detach", "a span detach marker")
+	// Err is a key used to add error values to label lists.
+	Err = NewError("error", "an error that occurred")
+	// Metric is a key used to indicate an event records metrics.
+	Metric = NewTag("metric", "a metric event marker")
+)
diff --git a/vendor/golang.org/x/tools/internal/event/label/label.go b/vendor/golang.org/x/tools/internal/event/label/label.go
new file mode 100644
index 00000000..0f526e1f
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/label/label.go
@@ -0,0 +1,215 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package label
+
+import (
+	"fmt"
+	"io"
+	"reflect"
+	"unsafe"
+)
+
+// Key is used as the identity of a Label.
+// Keys are intended to be compared by pointer only, the name should be unique
+// for communicating with external systems, but it is not required or enforced.
+type Key interface {
+	// Name returns the key name.
+	Name() string
+	// Description returns a string that can be used to describe the value.
+	Description() string
+
+	// Format is used in formatting to append the value of the label to the
+	// supplied buffer.
+	// The formatter may use the supplied buf as a scratch area to avoid
+	// allocations.
+	Format(w io.Writer, buf []byte, l Label)
+}
+
+// Label holds a key and value pair.
+// It is normally used when passing around lists of labels.
+type Label struct {
+	key     Key
+	packed  uint64
+	untyped interface{}
+}
+
+// Map is the interface to a collection of Labels indexed by key.
+type Map interface {
+	// Find returns the label that matches the supplied key.
+	Find(key Key) Label
+}
+
+// List is the interface to something that provides an iterable
+// list of labels.
+// Iteration should start from 0 and continue until Valid returns false.
+type List interface {
+	// Valid returns true if the index is within range for the list.
+	// It does not imply the label at that index will itself be valid.
+	Valid(index int) bool
+	// Label returns the label at the given index.
+	Label(index int) Label
+}
+
+// list implements LabelList for a list of Labels.
+type list struct {
+	labels []Label
+}
+
+// filter wraps a LabelList filtering out specific labels.
+type filter struct {
+	keys       []Key
+	underlying List
+}
+
+// listMap implements LabelMap for a simple list of labels.
+type listMap struct {
+	labels []Label
+}
+
+// mapChain implements LabelMap for a list of underlying LabelMap.
+type mapChain struct {
+	maps []Map
+}
+
+// OfValue creates a new label from the key and value.
+// This method is for implementing new key types, label creation should
+// normally be done with the Of method of the key.
+func OfValue(k Key, value interface{}) Label { return Label{key: k, untyped: value} }
+
+// UnpackValue assumes the label was built using LabelOfValue and returns the value
+// that was passed to that constructor.
+// This method is for implementing new key types, for type safety normal
+// access should be done with the From method of the key.
+func (t Label) UnpackValue() interface{} { return t.untyped }
+
+// Of64 creates a new label from a key and a uint64. This is often
+// used for non uint64 values that can be packed into a uint64.
+// This method is for implementing new key types, label creation should
+// normally be done with the Of method of the key.
+func Of64(k Key, v uint64) Label { return Label{key: k, packed: v} }
+
+// Unpack64 assumes the label was built using LabelOf64 and returns the value that
+// was passed to that constructor.
+// This method is for implementing new key types, for type safety normal
+// access should be done with the From method of the key.
+func (t Label) Unpack64() uint64 { return t.packed }
+
+type stringptr unsafe.Pointer
+
+// OfString creates a new label from a key and a string.
+// This method is for implementing new key types, label creation should
+// normally be done with the Of method of the key.
+func OfString(k Key, v string) Label {
+	hdr := (*reflect.StringHeader)(unsafe.Pointer(&v))
+	return Label{
+		key:     k,
+		packed:  uint64(hdr.Len),
+		untyped: stringptr(hdr.Data),
+	}
+}
+
+// UnpackString assumes the label was built using LabelOfString and returns the
+// value that was passed to that constructor.
+// This method is for implementing new key types, for type safety normal
+// access should be done with the From method of the key.
+func (t Label) UnpackString() string {
+	var v string
+	hdr := (*reflect.StringHeader)(unsafe.Pointer(&v))
+	hdr.Data = uintptr(t.untyped.(stringptr))
+	hdr.Len = int(t.packed)
+	return v
+}
+
+// Valid returns true if the Label is a valid one (it has a key).
+func (t Label) Valid() bool { return t.key != nil }
+
+// Key returns the key of this Label.
+func (t Label) Key() Key { return t.key }
+
+// Format is used for debug printing of labels.
+func (t Label) Format(f fmt.State, r rune) {
+	if !t.Valid() {
+		io.WriteString(f, `nil`)
+		return
+	}
+	io.WriteString(f, t.Key().Name())
+	io.WriteString(f, "=")
+	var buf [128]byte
+	t.Key().Format(f, buf[:0], t)
+}
+
+func (l *list) Valid(index int) bool {
+	return index >= 0 && index < len(l.labels)
+}
+
+func (l *list) Label(index int) Label {
+	return l.labels[index]
+}
+
+func (f *filter) Valid(index int) bool {
+	return f.underlying.Valid(index)
+}
+
+func (f *filter) Label(index int) Label {
+	l := f.underlying.Label(index)
+	for _, f := range f.keys {
+		if l.Key() == f {
+			return Label{}
+		}
+	}
+	return l
+}
+
+func (lm listMap) Find(key Key) Label {
+	for _, l := range lm.labels {
+		if l.Key() == key {
+			return l
+		}
+	}
+	return Label{}
+}
+
+func (c mapChain) Find(key Key) Label {
+	for _, src := range c.maps {
+		l := src.Find(key)
+		if l.Valid() {
+			return l
+		}
+	}
+	return Label{}
+}
+
+var emptyList = &list{}
+
+func NewList(labels ...Label) List {
+	if len(labels) == 0 {
+		return emptyList
+	}
+	return &list{labels: labels}
+}
+
+func Filter(l List, keys ...Key) List {
+	if len(keys) == 0 {
+		return l
+	}
+	return &filter{keys: keys, underlying: l}
+}
+
+func NewMap(labels ...Label) Map {
+	return listMap{labels: labels}
+}
+
+func MergeMaps(srcs ...Map) Map {
+	var nonNil []Map
+	for _, src := range srcs {
+		if src != nil {
+			nonNil = append(nonNil, src)
+		}
+	}
+	if len(nonNil) == 1 {
+		return nonNil[0]
+	}
+	return mapChain{maps: nonNil}
+}
diff --git a/vendor/golang.org/x/tools/internal/gocommand/invoke.go b/vendor/golang.org/x/tools/internal/gocommand/invoke.go
new file mode 100644
index 00000000..8659a0c5
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gocommand/invoke.go
@@ -0,0 +1,273 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package gocommand is a helper for calling the go command.
+package gocommand
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	exec "golang.org/x/sys/execabs"
+	"io"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/tools/internal/event"
+)
+
+// An Runner will run go command invocations and serialize
+// them if it sees a concurrency error.
+type Runner struct {
+	// once guards the runner initialization.
+	once sync.Once
+
+	// inFlight tracks available workers.
+	inFlight chan struct{}
+
+	// serialized guards the ability to run a go command serially,
+	// to avoid deadlocks when claiming workers.
+	serialized chan struct{}
+}
+
+const maxInFlight = 10
+
+func (runner *Runner) initialize() {
+	runner.once.Do(func() {
+		runner.inFlight = make(chan struct{}, maxInFlight)
+		runner.serialized = make(chan struct{}, 1)
+	})
+}
+
+// 1.13: go: updates to go.mod needed, but contents have changed
+// 1.14: go: updating go.mod: existing contents have changed since last read
+var modConcurrencyError = regexp.MustCompile(`go:.*go.mod.*contents have changed`)
+
+// Run is a convenience wrapper around RunRaw.
+// It returns only stdout and a "friendly" error.
+func (runner *Runner) Run(ctx context.Context, inv Invocation) (*bytes.Buffer, error) {
+	stdout, _, friendly, _ := runner.RunRaw(ctx, inv)
+	return stdout, friendly
+}
+
+// RunPiped runs the invocation serially, always waiting for any concurrent
+// invocations to complete first.
+func (runner *Runner) RunPiped(ctx context.Context, inv Invocation, stdout, stderr io.Writer) error {
+	_, err := runner.runPiped(ctx, inv, stdout, stderr)
+	return err
+}
+
+// RunRaw runs the invocation, serializing requests only if they fight over
+// go.mod changes.
+func (runner *Runner) RunRaw(ctx context.Context, inv Invocation) (*bytes.Buffer, *bytes.Buffer, error, error) {
+	// Make sure the runner is always initialized.
+	runner.initialize()
+
+	// First, try to run the go command concurrently.
+	stdout, stderr, friendlyErr, err := runner.runConcurrent(ctx, inv)
+
+	// If we encounter a load concurrency error, we need to retry serially.
+	if friendlyErr == nil || !modConcurrencyError.MatchString(friendlyErr.Error()) {
+		return stdout, stderr, friendlyErr, err
+	}
+	event.Error(ctx, "Load concurrency error, will retry serially", err)
+
+	// Run serially by calling runPiped.
+	stdout.Reset()
+	stderr.Reset()
+	friendlyErr, err = runner.runPiped(ctx, inv, stdout, stderr)
+	return stdout, stderr, friendlyErr, err
+}
+
+func (runner *Runner) runConcurrent(ctx context.Context, inv Invocation) (*bytes.Buffer, *bytes.Buffer, error, error) {
+	// Wait for 1 worker to become available.
+	select {
+	case <-ctx.Done():
+		return nil, nil, nil, ctx.Err()
+	case runner.inFlight <- struct{}{}:
+		defer func() { <-runner.inFlight }()
+	}
+
+	stdout, stderr := &bytes.Buffer{}, &bytes.Buffer{}
+	friendlyErr, err := inv.runWithFriendlyError(ctx, stdout, stderr)
+	return stdout, stderr, friendlyErr, err
+}
+
+func (runner *Runner) runPiped(ctx context.Context, inv Invocation, stdout, stderr io.Writer) (error, error) {
+	// Make sure the runner is always initialized.
+	runner.initialize()
+
+	// Acquire the serialization lock. This avoids deadlocks between two
+	// runPiped commands.
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case runner.serialized <- struct{}{}:
+		defer func() { <-runner.serialized }()
+	}
+
+	// Wait for all in-progress go commands to return before proceeding,
+	// to avoid load concurrency errors.
+	for i := 0; i < maxInFlight; i++ {
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case runner.inFlight <- struct{}{}:
+			// Make sure we always "return" any workers we took.
+			defer func() { <-runner.inFlight }()
+		}
+	}
+
+	return inv.runWithFriendlyError(ctx, stdout, stderr)
+}
+
+// An Invocation represents a call to the go command.
+type Invocation struct {
+	Verb       string
+	Args       []string
+	BuildFlags []string
+	ModFlag    string
+	ModFile    string
+	Overlay    string
+	// If CleanEnv is set, the invocation will run only with the environment
+	// in Env, not starting with os.Environ.
+	CleanEnv   bool
+	Env        []string
+	WorkingDir string
+	Logf       func(format string, args ...interface{})
+}
+
+func (i *Invocation) runWithFriendlyError(ctx context.Context, stdout, stderr io.Writer) (friendlyError error, rawError error) {
+	rawError = i.run(ctx, stdout, stderr)
+	if rawError != nil {
+		friendlyError = rawError
+		// Check for 'go' executable not being found.
+		if ee, ok := rawError.(*exec.Error); ok && ee.Err == exec.ErrNotFound {
+			friendlyError = fmt.Errorf("go command required, not found: %v", ee)
+		}
+		if ctx.Err() != nil {
+			friendlyError = ctx.Err()
+		}
+		friendlyError = fmt.Errorf("err: %v: stderr: %s", friendlyError, stderr)
+	}
+	return
+}
+
+func (i *Invocation) run(ctx context.Context, stdout, stderr io.Writer) error {
+	log := i.Logf
+	if log == nil {
+		log = func(string, ...interface{}) {}
+	}
+
+	goArgs := []string{i.Verb}
+
+	appendModFile := func() {
+		if i.ModFile != "" {
+			goArgs = append(goArgs, "-modfile="+i.ModFile)
+		}
+	}
+	appendModFlag := func() {
+		if i.ModFlag != "" {
+			goArgs = append(goArgs, "-mod="+i.ModFlag)
+		}
+	}
+	appendOverlayFlag := func() {
+		if i.Overlay != "" {
+			goArgs = append(goArgs, "-overlay="+i.Overlay)
+		}
+	}
+
+	switch i.Verb {
+	case "env", "version":
+		goArgs = append(goArgs, i.Args...)
+	case "mod":
+		// mod needs the sub-verb before flags.
+		goArgs = append(goArgs, i.Args[0])
+		appendModFile()
+		goArgs = append(goArgs, i.Args[1:]...)
+	case "get":
+		goArgs = append(goArgs, i.BuildFlags...)
+		appendModFile()
+		goArgs = append(goArgs, i.Args...)
+
+	default: // notably list and build.
+		goArgs = append(goArgs, i.BuildFlags...)
+		appendModFile()
+		appendModFlag()
+		appendOverlayFlag()
+		goArgs = append(goArgs, i.Args...)
+	}
+	cmd := exec.Command("go", goArgs...)
+	cmd.Stdout = stdout
+	cmd.Stderr = stderr
+	// On darwin the cwd gets resolved to the real path, which breaks anything that
+	// expects the working directory to keep the original path, including the
+	// go command when dealing with modules.
+	// The Go stdlib has a special feature where if the cwd and the PWD are the
+	// same node then it trusts the PWD, so by setting it in the env for the child
+	// process we fix up all the paths returned by the go command.
+	if !i.CleanEnv {
+		cmd.Env = os.Environ()
+	}
+	cmd.Env = append(cmd.Env, i.Env...)
+	if i.WorkingDir != "" {
+		cmd.Env = append(cmd.Env, "PWD="+i.WorkingDir)
+		cmd.Dir = i.WorkingDir
+	}
+	defer func(start time.Time) { log("%s for %v", time.Since(start), cmdDebugStr(cmd)) }(time.Now())
+
+	return runCmdContext(ctx, cmd)
+}
+
+// runCmdContext is like exec.CommandContext except it sends os.Interrupt
+// before os.Kill.
+func runCmdContext(ctx context.Context, cmd *exec.Cmd) error {
+	if err := cmd.Start(); err != nil {
+		return err
+	}
+	resChan := make(chan error, 1)
+	go func() {
+		resChan <- cmd.Wait()
+	}()
+
+	select {
+	case err := <-resChan:
+		return err
+	case <-ctx.Done():
+	}
+	// Cancelled. Interrupt and see if it ends voluntarily.
+	cmd.Process.Signal(os.Interrupt)
+	select {
+	case err := <-resChan:
+		return err
+	case <-time.After(time.Second):
+	}
+	// Didn't shut down in response to interrupt. Kill it hard.
+	cmd.Process.Kill()
+	return <-resChan
+}
+
+func cmdDebugStr(cmd *exec.Cmd) string {
+	env := make(map[string]string)
+	for _, kv := range cmd.Env {
+		split := strings.SplitN(kv, "=", 2)
+		k, v := split[0], split[1]
+		env[k] = v
+	}
+
+	var args []string
+	for _, arg := range cmd.Args {
+		quoted := strconv.Quote(arg)
+		if quoted[1:len(quoted)-1] != arg || strings.Contains(arg, " ") {
+			args = append(args, quoted)
+		} else {
+			args = append(args, arg)
+		}
+	}
+	return fmt.Sprintf("GOROOT=%v GOPATH=%v GO111MODULE=%v GOPROXY=%v PWD=%v %v", env["GOROOT"], env["GOPATH"], env["GO111MODULE"], env["GOPROXY"], env["PWD"], strings.Join(args, " "))
+}
diff --git a/vendor/golang.org/x/tools/internal/gocommand/vendor.go b/vendor/golang.org/x/tools/internal/gocommand/vendor.go
new file mode 100644
index 00000000..5e75bd6d
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gocommand/vendor.go
@@ -0,0 +1,107 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gocommand
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"time"
+
+	"golang.org/x/mod/semver"
+)
+
+// ModuleJSON holds information about a module.
+type ModuleJSON struct {
+	Path      string      // module path
+	Version   string      // module version
+	Versions  []string    // available module versions (with -versions)
+	Replace   *ModuleJSON // replaced by this module
+	Time      *time.Time  // time version was created
+	Update    *ModuleJSON // available update, if any (with -u)
+	Main      bool        // is this the main module?
+	Indirect  bool        // is this module only an indirect dependency of main module?
+	Dir       string      // directory holding files for this module, if any
+	GoMod     string      // path to go.mod file used when loading this module, if any
+	GoVersion string      // go version used in module
+}
+
+var modFlagRegexp = regexp.MustCompile(`-mod[ =](\w+)`)
+
+// VendorEnabled reports whether vendoring is enabled. It takes a *Runner to execute Go commands
+// with the supplied context.Context and Invocation. The Invocation can contain pre-defined fields,
+// of which only Verb and Args are modified to run the appropriate Go command.
+// Inspired by setDefaultBuildMod in modload/init.go
+func VendorEnabled(ctx context.Context, inv Invocation, r *Runner) (*ModuleJSON, bool, error) {
+	mainMod, go114, err := getMainModuleAnd114(ctx, inv, r)
+	if err != nil {
+		return nil, false, err
+	}
+
+	// We check the GOFLAGS to see if there is anything overridden or not.
+	inv.Verb = "env"
+	inv.Args = []string{"GOFLAGS"}
+	stdout, err := r.Run(ctx, inv)
+	if err != nil {
+		return nil, false, err
+	}
+	goflags := string(bytes.TrimSpace(stdout.Bytes()))
+	matches := modFlagRegexp.FindStringSubmatch(goflags)
+	var modFlag string
+	if len(matches) != 0 {
+		modFlag = matches[1]
+	}
+	if modFlag != "" {
+		// Don't override an explicit '-mod=' argument.
+		return mainMod, modFlag == "vendor", nil
+	}
+	if mainMod == nil || !go114 {
+		return mainMod, false, nil
+	}
+	// Check 1.14's automatic vendor mode.
+	if fi, err := os.Stat(filepath.Join(mainMod.Dir, "vendor")); err == nil && fi.IsDir() {
+		if mainMod.GoVersion != "" && semver.Compare("v"+mainMod.GoVersion, "v1.14") >= 0 {
+			// The Go version is at least 1.14, and a vendor directory exists.
+			// Set -mod=vendor by default.
+			return mainMod, true, nil
+		}
+	}
+	return mainMod, false, nil
+}
+
+// getMainModuleAnd114 gets the main module's information and whether the
+// go command in use is 1.14+. This is the information needed to figure out
+// if vendoring should be enabled.
+func getMainModuleAnd114(ctx context.Context, inv Invocation, r *Runner) (*ModuleJSON, bool, error) {
+	const format = `{{.Path}}
+{{.Dir}}
+{{.GoMod}}
+{{.GoVersion}}
+{{range context.ReleaseTags}}{{if eq . "go1.14"}}{{.}}{{end}}{{end}}
+`
+	inv.Verb = "list"
+	inv.Args = []string{"-m", "-f", format}
+	stdout, err := r.Run(ctx, inv)
+	if err != nil {
+		return nil, false, err
+	}
+
+	lines := strings.Split(stdout.String(), "\n")
+	if len(lines) < 5 {
+		return nil, false, fmt.Errorf("unexpected stdout: %q", stdout.String())
+	}
+	mod := &ModuleJSON{
+		Path:      lines[0],
+		Dir:       lines[1],
+		GoMod:     lines[2],
+		GoVersion: lines[3],
+		Main:      true,
+	}
+	return mod, lines[4] == "go1.14", nil
+}
diff --git a/vendor/golang.org/x/tools/internal/gocommand/version.go b/vendor/golang.org/x/tools/internal/gocommand/version.go
new file mode 100644
index 00000000..71304368
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gocommand/version.go
@@ -0,0 +1,51 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gocommand
+
+import (
+	"context"
+	"fmt"
+	"strings"
+)
+
+// GoVersion checks the go version by running "go list" with modules off.
+// It returns the X in Go 1.X.
+func GoVersion(ctx context.Context, inv Invocation, r *Runner) (int, error) {
+	inv.Verb = "list"
+	inv.Args = []string{"-e", "-f", `{{context.ReleaseTags}}`, `--`, `unsafe`}
+	inv.Env = append(append([]string{}, inv.Env...), "GO111MODULE=off")
+	// Unset any unneeded flags, and remove them from BuildFlags, if they're
+	// present.
+	inv.ModFile = ""
+	inv.ModFlag = ""
+	var buildFlags []string
+	for _, flag := range inv.BuildFlags {
+		// Flags can be prefixed by one or two dashes.
+		f := strings.TrimPrefix(strings.TrimPrefix(flag, "-"), "-")
+		if strings.HasPrefix(f, "mod=") || strings.HasPrefix(f, "modfile=") {
+			continue
+		}
+		buildFlags = append(buildFlags, flag)
+	}
+	inv.BuildFlags = buildFlags
+	stdoutBytes, err := r.Run(ctx, inv)
+	if err != nil {
+		return 0, err
+	}
+	stdout := stdoutBytes.String()
+	if len(stdout) < 3 {
+		return 0, fmt.Errorf("bad ReleaseTags output: %q", stdout)
+	}
+	// Split up "[go1.1 go1.15]"
+	tags := strings.Fields(stdout[1 : len(stdout)-2])
+	for i := len(tags) - 1; i >= 0; i-- {
+		var version int
+		if _, err := fmt.Sscanf(tags[i], "go1.%d", &version); err != nil {
+			continue
+		}
+		return version, nil
+	}
+	return 0, fmt.Errorf("no parseable ReleaseTags in %v", tags)
+}
diff --git a/vendor/golang.org/x/tools/internal/packagesinternal/packages.go b/vendor/golang.org/x/tools/internal/packagesinternal/packages.go
new file mode 100644
index 00000000..9702094c
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/packagesinternal/packages.go
@@ -0,0 +1,28 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package packagesinternal exposes internal-only fields from go/packages.
+package packagesinternal
+
+import (
+	"golang.org/x/tools/internal/gocommand"
+)
+
+var GetForTest = func(p interface{}) string { return "" }
+var GetDepsErrors = func(p interface{}) []*PackageError { return nil }
+
+type PackageError struct {
+	ImportStack []string // shortest path from package named on command line to this one
+	Pos         string   // position of error (if present, file:line:col)
+	Err         string   // the error itself
+}
+
+var GetGoCmdRunner = func(config interface{}) *gocommand.Runner { return nil }
+
+var SetGoCmdRunner = func(config interface{}, runner *gocommand.Runner) {}
+
+var TypecheckCgo int
+
+var SetModFlag = func(config interface{}, value string) {}
+var SetModFile = func(config interface{}, value string) {}
diff --git a/vendor/golang.org/x/tools/internal/typeparams/common.go b/vendor/golang.org/x/tools/internal/typeparams/common.go
new file mode 100644
index 00000000..9fc6b4be
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/common.go
@@ -0,0 +1,25 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package typeparams provides functions to work indirectly with type parameter
+// data stored in go/ast and go/types objects, while these API are guarded by a
+// build constraint.
+//
+// This package exists to make it easier for tools to work with generic code,
+// while also compiling against older Go versions.
+package typeparams
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+// A IndexExprData holds data from both ast.IndexExpr and the new
+// ast.MultiIndexExpr, which was introduced in Go 1.18.
+type IndexExprData struct {
+	X       ast.Expr   // expression
+	Lbrack  token.Pos  // position of "["
+	Indices []ast.Expr // index expressions
+	Rbrack  token.Pos  // position of "]"
+}
diff --git a/vendor/golang.org/x/tools/internal/typeparams/enabled_go117.go b/vendor/golang.org/x/tools/internal/typeparams/enabled_go117.go
new file mode 100644
index 00000000..72d010e5
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/enabled_go117.go
@@ -0,0 +1,12 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !typeparams || !go1.18
+// +build !typeparams !go1.18
+
+package typeparams
+
+// Enabled reports whether type parameters are enabled in the current build
+// environment.
+const Enabled = false
diff --git a/vendor/golang.org/x/tools/internal/typeparams/enabled_go118.go b/vendor/golang.org/x/tools/internal/typeparams/enabled_go118.go
new file mode 100644
index 00000000..642fc8ee
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/enabled_go118.go
@@ -0,0 +1,15 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build typeparams && go1.18
+// +build typeparams,go1.18
+
+package typeparams
+
+// Note: this constant is in a separate file as this is the only acceptable
+// diff between the <1.18 API of this package and the 1.18 API.
+
+// Enabled reports whether type parameters are enabled in the current build
+// environment.
+const Enabled = true
diff --git a/vendor/golang.org/x/tools/internal/typeparams/typeparams_go117.go b/vendor/golang.org/x/tools/internal/typeparams/typeparams_go117.go
new file mode 100644
index 00000000..12817af8
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/typeparams_go117.go
@@ -0,0 +1,177 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !typeparams || !go1.18
+// +build !typeparams !go1.18
+
+package typeparams
+
+import (
+	"go/ast"
+	"go/types"
+)
+
+func unsupported() {
+	panic("type parameters are unsupported at this go version")
+}
+
+// GetIndexExprData extracts data from *ast.IndexExpr nodes.
+// For other nodes, GetIndexExprData returns nil.
+func GetIndexExprData(n ast.Node) *IndexExprData {
+	if e, _ := n.(*ast.IndexExpr); e != nil {
+		return &IndexExprData{
+			X:       e.X,
+			Lbrack:  e.Lbrack,
+			Indices: []ast.Expr{e.Index},
+			Rbrack:  e.Rbrack,
+		}
+	}
+	return nil
+}
+
+// ForTypeSpec returns an empty field list, as type parameters on not supported
+// at this Go version.
+func ForTypeSpec(*ast.TypeSpec) *ast.FieldList {
+	return nil
+}
+
+// ForFuncType returns an empty field list, as type parameters are not
+// supported at this Go version.
+func ForFuncType(*ast.FuncType) *ast.FieldList {
+	return nil
+}
+
+// TypeParam is a placeholder type, as type parameters are not supported at
+// this Go version. Its methods panic on use.
+type TypeParam struct{ types.Type }
+
+func (*TypeParam) Constraint() types.Type { unsupported(); return nil }
+func (*TypeParam) Obj() *types.TypeName   { unsupported(); return nil }
+
+// TypeParamList is a placeholder for an empty type parameter list.
+type TypeParamList struct{}
+
+func (*TypeParamList) Len() int          { return 0 }
+func (*TypeParamList) At(int) *TypeParam { unsupported(); return nil }
+
+// TypeList is a placeholder for an empty type list.
+type TypeList struct{}
+
+func (*TypeList) Len() int          { return 0 }
+func (*TypeList) At(int) types.Type { unsupported(); return nil }
+
+// NewTypeParam is unsupported at this Go version, and panics.
+func NewTypeParam(name *types.TypeName, constraint types.Type) *TypeParam {
+	unsupported()
+	return nil
+}
+
+// SetTypeParamConstraint is unsupported at this Go version, and panics.
+func SetTypeParamConstraint(tparam *TypeParam, constraint types.Type) {
+	unsupported()
+}
+
+// ForSignature returns an empty slice.
+func ForSignature(*types.Signature) *TypeParamList {
+	return nil
+}
+
+// SetForSignature panics if tparams is non-empty.
+func SetForSignature(_ *types.Signature, tparams []*TypeParam) {
+	if len(tparams) > 0 {
+		unsupported()
+	}
+}
+
+// RecvTypeParams returns a nil slice.
+func RecvTypeParams(sig *types.Signature) *TypeParamList {
+	return nil
+}
+
+// SetRecvTypeParams panics if rparams is non-empty.
+func SetRecvTypeParams(sig *types.Signature, rparams []*TypeParam) {
+	if len(rparams) > 0 {
+		unsupported()
+	}
+}
+
+// IsComparable returns false, as no interfaces are type-restricted at this Go
+// version.
+func IsComparable(*types.Interface) bool {
+	return false
+}
+
+// IsConstraint returns false, as no interfaces are type-restricted at this Go
+// version.
+func IsConstraint(*types.Interface) bool {
+	return false
+}
+
+// ForNamed returns an empty type parameter list, as type parameters are not
+// supported at this Go version.
+func ForNamed(*types.Named) *TypeParamList {
+	return nil
+}
+
+// SetForNamed panics if tparams is non-empty.
+func SetForNamed(_ *types.Named, tparams []*TypeParam) {
+	if len(tparams) > 0 {
+		unsupported()
+	}
+}
+
+// NamedTypeArgs returns nil.
+func NamedTypeArgs(*types.Named) *TypeList {
+	return nil
+}
+
+// NamedTypeOrigin is the identity method at this Go version.
+func NamedTypeOrigin(named *types.Named) types.Type {
+	return named
+}
+
+// Term is a placeholder type, as type parameters are not supported at this Go
+// version. Its methods panic on use.
+type Term struct{}
+
+func (*Term) Tilde() bool            { unsupported(); return false }
+func (*Term) Type() types.Type       { unsupported(); return nil }
+func (*Term) String() string         { unsupported(); return "" }
+func (*Term) Underlying() types.Type { unsupported(); return nil }
+
+// NewTerm is unsupported at this Go version, and panics.
+func NewTerm(tilde bool, typ types.Type) *Term {
+	unsupported()
+	return nil
+}
+
+// Union is a placeholder type, as type parameters are not supported at this Go
+// version. Its methods panic on use.
+type Union struct{ types.Type }
+
+func (*Union) Len() int         { return 0 }
+func (*Union) Term(i int) *Term { unsupported(); return nil }
+
+// NewUnion is unsupported at this Go version, and panics.
+func NewUnion(terms []*Term) *Union {
+	unsupported()
+	return nil
+}
+
+// InitInstanceInfo is a noop at this Go version.
+func InitInstanceInfo(*types.Info) {}
+
+// GetInstance returns nothing, as type parameters are not supported at this Go
+// version.
+func GetInstance(*types.Info, *ast.Ident) (*TypeList, types.Type) { return nil, nil }
+
+// Environment is a placeholder type, as type parameters are not supported at
+// this Go version.
+type Environment struct{}
+
+// Instantiate is unsupported on this Go version, and panics.
+func Instantiate(env *Environment, typ types.Type, targs []types.Type, validate bool) (types.Type, error) {
+	unsupported()
+	return nil, nil
+}
diff --git a/vendor/golang.org/x/tools/internal/typeparams/typeparams_go118.go b/vendor/golang.org/x/tools/internal/typeparams/typeparams_go118.go
new file mode 100644
index 00000000..8ab17b77
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/typeparams_go118.go
@@ -0,0 +1,165 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build typeparams && go1.18
+// +build typeparams,go1.18
+
+package typeparams
+
+import (
+	"go/ast"
+	"go/types"
+)
+
+// GetIndexExprData extracts data from AST nodes that represent index
+// expressions.
+//
+// For an ast.IndexExpr, the resulting IndexExprData will have exactly one
+// index expression. For an ast.IndexListExpr (go1.18+), it may have a
+// variable number of index expressions.
+//
+// For nodes that don't represent index expressions, GetIndexExprData returns
+// nil.
+func GetIndexExprData(n ast.Node) *IndexExprData {
+	switch e := n.(type) {
+	case *ast.IndexExpr:
+		return &IndexExprData{
+			X:       e.X,
+			Lbrack:  e.Lbrack,
+			Indices: []ast.Expr{e.Index},
+			Rbrack:  e.Rbrack,
+		}
+	case *ast.IndexListExpr:
+		return (*IndexExprData)(e)
+	}
+	return nil
+}
+
+// ForTypeSpec returns n.TypeParams.
+func ForTypeSpec(n *ast.TypeSpec) *ast.FieldList {
+	if n == nil {
+		return nil
+	}
+	return n.TypeParams
+}
+
+// ForFuncType returns n.TypeParams.
+func ForFuncType(n *ast.FuncType) *ast.FieldList {
+	if n == nil {
+		return nil
+	}
+	return n.TypeParams
+}
+
+// TypeParam is an alias for types.TypeParam
+type TypeParam = types.TypeParam
+
+// TypeParamList is an alias for types.TypeParamList
+type TypeParamList = types.TypeParamList
+
+// TypeList is an alias for types.TypeList
+type TypeList = types.TypeList
+
+// NewTypeParam calls types.NewTypeParam.
+func NewTypeParam(name *types.TypeName, constraint types.Type) *TypeParam {
+	return types.NewTypeParam(name, constraint)
+}
+
+// SetTypeParamConstraint calls tparam.SetConstraint(constraint).
+func SetTypeParamConstraint(tparam *TypeParam, constraint types.Type) {
+	tparam.SetConstraint(constraint)
+}
+
+// ForSignature returns sig.TypeParams()
+func ForSignature(sig *types.Signature) *TypeParamList {
+	return sig.TypeParams()
+}
+
+// SetForSignature calls sig.SetTypeParams(tparams)
+func SetForSignature(sig *types.Signature, tparams []*TypeParam) {
+	sig.SetTypeParams(tparams)
+}
+
+// RecvTypeParams returns sig.RecvTypeParams().
+func RecvTypeParams(sig *types.Signature) *TypeParamList {
+	return sig.RecvTypeParams()
+}
+
+// SetRecvTypeParams calls sig.SetRecvTypeParams(rparams).
+func SetRecvTypeParams(sig *types.Signature, rparams []*TypeParam) {
+	sig.SetRecvTypeParams(rparams)
+}
+
+// IsComparable calls iface.IsComparable().
+func IsComparable(iface *types.Interface) bool {
+	return iface.IsComparable()
+}
+
+// IsConstraint calls iface.IsConstraint().
+func IsConstraint(iface *types.Interface) bool {
+	return iface.IsConstraint()
+}
+
+// ForNamed extracts the (possibly empty) type parameter object list from
+// named.
+func ForNamed(named *types.Named) *TypeParamList {
+	return named.TypeParams()
+}
+
+// SetForNamed sets the type params tparams on n. Each tparam must be of
+// dynamic type *types.TypeParam.
+func SetForNamed(n *types.Named, tparams []*TypeParam) {
+	n.SetTypeParams(tparams)
+}
+
+// NamedTypeArgs returns named.TypeArgs().
+func NamedTypeArgs(named *types.Named) *TypeList {
+	return named.TypeArgs()
+}
+
+// NamedTypeOrigin returns named.Orig().
+func NamedTypeOrigin(named *types.Named) types.Type {
+	return named.Origin()
+}
+
+// Term is an alias for types.Term.
+type Term = types.Term
+
+// NewTerm calls types.NewTerm.
+func NewTerm(tilde bool, typ types.Type) *Term {
+	return types.NewTerm(tilde, typ)
+}
+
+// Union is an alias for types.Union
+type Union = types.Union
+
+// NewUnion calls types.NewUnion.
+func NewUnion(terms []*Term) *Union {
+	return types.NewUnion(terms)
+}
+
+// InitInstanceInfo initializes info to record information about type and
+// function instances.
+func InitInstanceInfo(info *types.Info) {
+	info.Instances = make(map[*ast.Ident]types.Instance)
+}
+
+// GetInstance extracts information about the instantiation occurring at the
+// identifier id. id should be the identifier denoting a parameterized type or
+// function in an instantiation expression or function call.
+func GetInstance(info *types.Info, id *ast.Ident) (*TypeList, types.Type) {
+	if info.Instances != nil {
+		inf := info.Instances[id]
+		return inf.TypeArgs, inf.Type
+	}
+	return nil, nil
+}
+
+// Environment is an alias for types.Environment.
+type Environment = types.Environment
+
+// Instantiate calls types.Instantiate.
+func Instantiate(env *Environment, typ types.Type, targs []types.Type, validate bool) (types.Type, error) {
+	return types.Instantiate(env, typ, targs, validate)
+}
diff --git a/vendor/golang.org/x/tools/internal/typesinternal/errorcode.go b/vendor/golang.org/x/tools/internal/typesinternal/errorcode.go
new file mode 100644
index 00000000..fa2834e2
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typesinternal/errorcode.go
@@ -0,0 +1,1368 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typesinternal
+
+//go:generate stringer -type=ErrorCode
+
+type ErrorCode int
+
+// This file defines the error codes that can be produced during type-checking.
+// Collectively, these codes provide an identifier that may be used to
+// implement special handling for certain types of errors.
+//
+// Error codes should be fine-grained enough that the exact nature of the error
+// can be easily determined, but coarse enough that they are not an
+// implementation detail of the type checking algorithm. As a rule-of-thumb,
+// errors should be considered equivalent if there is a theoretical refactoring
+// of the type checker in which they are emitted in exactly one place. For
+// example, the type checker emits different error messages for "too many
+// arguments" and "too few arguments", but one can imagine an alternative type
+// checker where this check instead just emits a single "wrong number of
+// arguments", so these errors should have the same code.
+//
+// Error code names should be as brief as possible while retaining accuracy and
+// distinctiveness. In most cases names should start with an adjective
+// describing the nature of the error (e.g. "invalid", "unused", "misplaced"),
+// and end with a noun identifying the relevant language object. For example,
+// "DuplicateDecl" or "InvalidSliceExpr". For brevity, naming follows the
+// convention that "bad" implies a problem with syntax, and "invalid" implies a
+// problem with types.
+
+const (
+	_ ErrorCode = iota
+
+	// Test is reserved for errors that only apply while in self-test mode.
+	Test
+
+	/* package names */
+
+	// BlankPkgName occurs when a package name is the blank identifier "_".
+	//
+	// Per the spec:
+	//  "The PackageName must not be the blank identifier."
+	BlankPkgName
+
+	// MismatchedPkgName occurs when a file's package name doesn't match the
+	// package name already established by other files.
+	MismatchedPkgName
+
+	// InvalidPkgUse occurs when a package identifier is used outside of a
+	// selector expression.
+	//
+	// Example:
+	//  import "fmt"
+	//
+	//  var _ = fmt
+	InvalidPkgUse
+
+	/* imports */
+
+	// BadImportPath occurs when an import path is not valid.
+	BadImportPath
+
+	// BrokenImport occurs when importing a package fails.
+	//
+	// Example:
+	//  import "amissingpackage"
+	BrokenImport
+
+	// ImportCRenamed occurs when the special import "C" is renamed. "C" is a
+	// pseudo-package, and must not be renamed.
+	//
+	// Example:
+	//  import _ "C"
+	ImportCRenamed
+
+	// UnusedImport occurs when an import is unused.
+	//
+	// Example:
+	//  import "fmt"
+	//
+	//  func main() {}
+	UnusedImport
+
+	/* initialization */
+
+	// InvalidInitCycle occurs when an invalid cycle is detected within the
+	// initialization graph.
+	//
+	// Example:
+	//  var x int = f()
+	//
+	//  func f() int { return x }
+	InvalidInitCycle
+
+	/* decls */
+
+	// DuplicateDecl occurs when an identifier is declared multiple times.
+	//
+	// Example:
+	//  var x = 1
+	//  var x = 2
+	DuplicateDecl
+
+	// InvalidDeclCycle occurs when a declaration cycle is not valid.
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  type T struct {
+	//  	a [n]int
+	//  }
+	//
+	//  var n = unsafe.Sizeof(T{})
+	InvalidDeclCycle
+
+	// InvalidTypeCycle occurs when a cycle in type definitions results in a
+	// type that is not well-defined.
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  type T [unsafe.Sizeof(T{})]int
+	InvalidTypeCycle
+
+	/* decls > const */
+
+	// InvalidConstInit occurs when a const declaration has a non-constant
+	// initializer.
+	//
+	// Example:
+	//  var x int
+	//  const _ = x
+	InvalidConstInit
+
+	// InvalidConstVal occurs when a const value cannot be converted to its
+	// target type.
+	//
+	// TODO(findleyr): this error code and example are not very clear. Consider
+	// removing it.
+	//
+	// Example:
+	//  const _ = 1 << "hello"
+	InvalidConstVal
+
+	// InvalidConstType occurs when the underlying type in a const declaration
+	// is not a valid constant type.
+	//
+	// Example:
+	//  const c *int = 4
+	InvalidConstType
+
+	/* decls > var (+ other variable assignment codes) */
+
+	// UntypedNil occurs when the predeclared (untyped) value nil is used to
+	// initialize a variable declared without an explicit type.
+	//
+	// Example:
+	//  var x = nil
+	UntypedNil
+
+	// WrongAssignCount occurs when the number of values on the right-hand side
+	// of an assignment or or initialization expression does not match the number
+	// of variables on the left-hand side.
+	//
+	// Example:
+	//  var x = 1, 2
+	WrongAssignCount
+
+	// UnassignableOperand occurs when the left-hand side of an assignment is
+	// not assignable.
+	//
+	// Example:
+	//  func f() {
+	//  	const c = 1
+	//  	c = 2
+	//  }
+	UnassignableOperand
+
+	// NoNewVar occurs when a short variable declaration (':=') does not declare
+	// new variables.
+	//
+	// Example:
+	//  func f() {
+	//  	x := 1
+	//  	x := 2
+	//  }
+	NoNewVar
+
+	// MultiValAssignOp occurs when an assignment operation (+=, *=, etc) does
+	// not have single-valued left-hand or right-hand side.
+	//
+	// Per the spec:
+	//  "In assignment operations, both the left- and right-hand expression lists
+	//  must contain exactly one single-valued expression"
+	//
+	// Example:
+	//  func f() int {
+	//  	x, y := 1, 2
+	//  	x, y += 1
+	//  	return x + y
+	//  }
+	MultiValAssignOp
+
+	// InvalidIfaceAssign occurs when a value of type T is used as an
+	// interface, but T does not implement a method of the expected interface.
+	//
+	// Example:
+	//  type I interface {
+	//  	f()
+	//  }
+	//
+	//  type T int
+	//
+	//  var x I = T(1)
+	InvalidIfaceAssign
+
+	// InvalidChanAssign occurs when a chan assignment is invalid.
+	//
+	// Per the spec, a value x is assignable to a channel type T if:
+	//  "x is a bidirectional channel value, T is a channel type, x's type V and
+	//  T have identical element types, and at least one of V or T is not a
+	//  defined type."
+	//
+	// Example:
+	//  type T1 chan int
+	//  type T2 chan int
+	//
+	//  var x T1
+	//  // Invalid assignment because both types are named
+	//  var _ T2 = x
+	InvalidChanAssign
+
+	// IncompatibleAssign occurs when the type of the right-hand side expression
+	// in an assignment cannot be assigned to the type of the variable being
+	// assigned.
+	//
+	// Example:
+	//  var x []int
+	//  var _ int = x
+	IncompatibleAssign
+
+	// UnaddressableFieldAssign occurs when trying to assign to a struct field
+	// in a map value.
+	//
+	// Example:
+	//  func f() {
+	//  	m := make(map[string]struct{i int})
+	//  	m["foo"].i = 42
+	//  }
+	UnaddressableFieldAssign
+
+	/* decls > type (+ other type expression codes) */
+
+	// NotAType occurs when the identifier used as the underlying type in a type
+	// declaration or the right-hand side of a type alias does not denote a type.
+	//
+	// Example:
+	//  var S = 2
+	//
+	//  type T S
+	NotAType
+
+	// InvalidArrayLen occurs when an array length is not a constant value.
+	//
+	// Example:
+	//  var n = 3
+	//  var _ = [n]int{}
+	InvalidArrayLen
+
+	// BlankIfaceMethod occurs when a method name is '_'.
+	//
+	// Per the spec:
+	//  "The name of each explicitly specified method must be unique and not
+	//  blank."
+	//
+	// Example:
+	//  type T interface {
+	//  	_(int)
+	//  }
+	BlankIfaceMethod
+
+	// IncomparableMapKey occurs when a map key type does not support the == and
+	// != operators.
+	//
+	// Per the spec:
+	//  "The comparison operators == and != must be fully defined for operands of
+	//  the key type; thus the key type must not be a function, map, or slice."
+	//
+	// Example:
+	//  var x map[T]int
+	//
+	//  type T []int
+	IncomparableMapKey
+
+	// InvalidIfaceEmbed occurs when a non-interface type is embedded in an
+	// interface.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  func (T) m()
+	//
+	//  type I interface {
+	//  	T
+	//  }
+	InvalidIfaceEmbed
+
+	// InvalidPtrEmbed occurs when an embedded field is of the pointer form *T,
+	// and T itself is itself a pointer, an unsafe.Pointer, or an interface.
+	//
+	// Per the spec:
+	//  "An embedded field must be specified as a type name T or as a pointer to
+	//  a non-interface type name *T, and T itself may not be a pointer type."
+	//
+	// Example:
+	//  type T *int
+	//
+	//  type S struct {
+	//  	*T
+	//  }
+	InvalidPtrEmbed
+
+	/* decls > func and method */
+
+	// BadRecv occurs when a method declaration does not have exactly one
+	// receiver parameter.
+	//
+	// Example:
+	//  func () _() {}
+	BadRecv
+
+	// InvalidRecv occurs when a receiver type expression is not of the form T
+	// or *T, or T is a pointer type.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  func (**T) m() {}
+	InvalidRecv
+
+	// DuplicateFieldAndMethod occurs when an identifier appears as both a field
+	// and method name.
+	//
+	// Example:
+	//  type T struct {
+	//  	m int
+	//  }
+	//
+	//  func (T) m() {}
+	DuplicateFieldAndMethod
+
+	// DuplicateMethod occurs when two methods on the same receiver type have
+	// the same name.
+	//
+	// Example:
+	//  type T struct {}
+	//  func (T) m() {}
+	//  func (T) m(i int) int { return i }
+	DuplicateMethod
+
+	/* decls > special */
+
+	// InvalidBlank occurs when a blank identifier is used as a value or type.
+	//
+	// Per the spec:
+	//  "The blank identifier may appear as an operand only on the left-hand side
+	//  of an assignment."
+	//
+	// Example:
+	//  var x = _
+	InvalidBlank
+
+	// InvalidIota occurs when the predeclared identifier iota is used outside
+	// of a constant declaration.
+	//
+	// Example:
+	//  var x = iota
+	InvalidIota
+
+	// MissingInitBody occurs when an init function is missing its body.
+	//
+	// Example:
+	//  func init()
+	MissingInitBody
+
+	// InvalidInitSig occurs when an init function declares parameters or
+	// results.
+	//
+	// Example:
+	//  func init() int { return 1 }
+	InvalidInitSig
+
+	// InvalidInitDecl occurs when init is declared as anything other than a
+	// function.
+	//
+	// Example:
+	//  var init = 1
+	InvalidInitDecl
+
+	// InvalidMainDecl occurs when main is declared as anything other than a
+	// function, in a main package.
+	InvalidMainDecl
+
+	/* exprs */
+
+	// TooManyValues occurs when a function returns too many values for the
+	// expression context in which it is used.
+	//
+	// Example:
+	//  func ReturnTwo() (int, int) {
+	//  	return 1, 2
+	//  }
+	//
+	//  var x = ReturnTwo()
+	TooManyValues
+
+	// NotAnExpr occurs when a type expression is used where a value expression
+	// is expected.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  func f() {
+	//  	T
+	//  }
+	NotAnExpr
+
+	/* exprs > const */
+
+	// TruncatedFloat occurs when a float constant is truncated to an integer
+	// value.
+	//
+	// Example:
+	//  var _ int = 98.6
+	TruncatedFloat
+
+	// NumericOverflow occurs when a numeric constant overflows its target type.
+	//
+	// Example:
+	//  var x int8 = 1000
+	NumericOverflow
+
+	/* exprs > operation */
+
+	// UndefinedOp occurs when an operator is not defined for the type(s) used
+	// in an operation.
+	//
+	// Example:
+	//  var c = "a" - "b"
+	UndefinedOp
+
+	// MismatchedTypes occurs when operand types are incompatible in a binary
+	// operation.
+	//
+	// Example:
+	//  var a = "hello"
+	//  var b = 1
+	//  var c = a - b
+	MismatchedTypes
+
+	// DivByZero occurs when a division operation is provable at compile
+	// time to be a division by zero.
+	//
+	// Example:
+	//  const divisor = 0
+	//  var x int = 1/divisor
+	DivByZero
+
+	// NonNumericIncDec occurs when an increment or decrement operator is
+	// applied to a non-numeric value.
+	//
+	// Example:
+	//  func f() {
+	//  	var c = "c"
+	//  	c++
+	//  }
+	NonNumericIncDec
+
+	/* exprs > ptr */
+
+	// UnaddressableOperand occurs when the & operator is applied to an
+	// unaddressable expression.
+	//
+	// Example:
+	//  var x = &1
+	UnaddressableOperand
+
+	// InvalidIndirection occurs when a non-pointer value is indirected via the
+	// '*' operator.
+	//
+	// Example:
+	//  var x int
+	//  var y = *x
+	InvalidIndirection
+
+	/* exprs > [] */
+
+	// NonIndexableOperand occurs when an index operation is applied to a value
+	// that cannot be indexed.
+	//
+	// Example:
+	//  var x = 1
+	//  var y = x[1]
+	NonIndexableOperand
+
+	// InvalidIndex occurs when an index argument is not of integer type,
+	// negative, or out-of-bounds.
+	//
+	// Example:
+	//  var s = [...]int{1,2,3}
+	//  var x = s[5]
+	//
+	// Example:
+	//  var s = []int{1,2,3}
+	//  var _ = s[-1]
+	//
+	// Example:
+	//  var s = []int{1,2,3}
+	//  var i string
+	//  var _ = s[i]
+	InvalidIndex
+
+	// SwappedSliceIndices occurs when constant indices in a slice expression
+	// are decreasing in value.
+	//
+	// Example:
+	//  var _ = []int{1,2,3}[2:1]
+	SwappedSliceIndices
+
+	/* operators > slice */
+
+	// NonSliceableOperand occurs when a slice operation is applied to a value
+	// whose type is not sliceable, or is unaddressable.
+	//
+	// Example:
+	//  var x = [...]int{1, 2, 3}[:1]
+	//
+	// Example:
+	//  var x = 1
+	//  var y = 1[:1]
+	NonSliceableOperand
+
+	// InvalidSliceExpr occurs when a three-index slice expression (a[x:y:z]) is
+	// applied to a string.
+	//
+	// Example:
+	//  var s = "hello"
+	//  var x = s[1:2:3]
+	InvalidSliceExpr
+
+	/* exprs > shift */
+
+	// InvalidShiftCount occurs when the right-hand side of a shift operation is
+	// either non-integer, negative, or too large.
+	//
+	// Example:
+	//  var (
+	//  	x string
+	//  	y int = 1 << x
+	//  )
+	InvalidShiftCount
+
+	// InvalidShiftOperand occurs when the shifted operand is not an integer.
+	//
+	// Example:
+	//  var s = "hello"
+	//  var x = s << 2
+	InvalidShiftOperand
+
+	/* exprs > chan */
+
+	// InvalidReceive occurs when there is a channel receive from a value that
+	// is either not a channel, or is a send-only channel.
+	//
+	// Example:
+	//  func f() {
+	//  	var x = 1
+	//  	<-x
+	//  }
+	InvalidReceive
+
+	// InvalidSend occurs when there is a channel send to a value that is not a
+	// channel, or is a receive-only channel.
+	//
+	// Example:
+	//  func f() {
+	//  	var x = 1
+	//  	x <- "hello!"
+	//  }
+	InvalidSend
+
+	/* exprs > literal */
+
+	// DuplicateLitKey occurs when an index is duplicated in a slice, array, or
+	// map literal.
+	//
+	// Example:
+	//  var _ = []int{0:1, 0:2}
+	//
+	// Example:
+	//  var _ = map[string]int{"a": 1, "a": 2}
+	DuplicateLitKey
+
+	// MissingLitKey occurs when a map literal is missing a key expression.
+	//
+	// Example:
+	//  var _ = map[string]int{1}
+	MissingLitKey
+
+	// InvalidLitIndex occurs when the key in a key-value element of a slice or
+	// array literal is not an integer constant.
+	//
+	// Example:
+	//  var i = 0
+	//  var x = []string{i: "world"}
+	InvalidLitIndex
+
+	// OversizeArrayLit occurs when an array literal exceeds its length.
+	//
+	// Example:
+	//  var _ = [2]int{1,2,3}
+	OversizeArrayLit
+
+	// MixedStructLit occurs when a struct literal contains a mix of positional
+	// and named elements.
+	//
+	// Example:
+	//  var _ = struct{i, j int}{i: 1, 2}
+	MixedStructLit
+
+	// InvalidStructLit occurs when a positional struct literal has an incorrect
+	// number of values.
+	//
+	// Example:
+	//  var _ = struct{i, j int}{1,2,3}
+	InvalidStructLit
+
+	// MissingLitField occurs when a struct literal refers to a field that does
+	// not exist on the struct type.
+	//
+	// Example:
+	//  var _ = struct{i int}{j: 2}
+	MissingLitField
+
+	// DuplicateLitField occurs when a struct literal contains duplicated
+	// fields.
+	//
+	// Example:
+	//  var _ = struct{i int}{i: 1, i: 2}
+	DuplicateLitField
+
+	// UnexportedLitField occurs when a positional struct literal implicitly
+	// assigns an unexported field of an imported type.
+	UnexportedLitField
+
+	// InvalidLitField occurs when a field name is not a valid identifier.
+	//
+	// Example:
+	//  var _ = struct{i int}{1: 1}
+	InvalidLitField
+
+	// UntypedLit occurs when a composite literal omits a required type
+	// identifier.
+	//
+	// Example:
+	//  type outer struct{
+	//  	inner struct { i int }
+	//  }
+	//
+	//  var _ = outer{inner: {1}}
+	UntypedLit
+
+	// InvalidLit occurs when a composite literal expression does not match its
+	// type.
+	//
+	// Example:
+	//  type P *struct{
+	//  	x int
+	//  }
+	//  var _ = P {}
+	InvalidLit
+
+	/* exprs > selector */
+
+	// AmbiguousSelector occurs when a selector is ambiguous.
+	//
+	// Example:
+	//  type E1 struct { i int }
+	//  type E2 struct { i int }
+	//  type T struct { E1; E2 }
+	//
+	//  var x T
+	//  var _ = x.i
+	AmbiguousSelector
+
+	// UndeclaredImportedName occurs when a package-qualified identifier is
+	// undeclared by the imported package.
+	//
+	// Example:
+	//  import "go/types"
+	//
+	//  var _ = types.NotAnActualIdentifier
+	UndeclaredImportedName
+
+	// UnexportedName occurs when a selector refers to an unexported identifier
+	// of an imported package.
+	//
+	// Example:
+	//  import "reflect"
+	//
+	//  type _ reflect.flag
+	UnexportedName
+
+	// UndeclaredName occurs when an identifier is not declared in the current
+	// scope.
+	//
+	// Example:
+	//  var x T
+	UndeclaredName
+
+	// MissingFieldOrMethod occurs when a selector references a field or method
+	// that does not exist.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  var x = T{}.f
+	MissingFieldOrMethod
+
+	/* exprs > ... */
+
+	// BadDotDotDotSyntax occurs when a "..." occurs in a context where it is
+	// not valid.
+	//
+	// Example:
+	//  var _ = map[int][...]int{0: {}}
+	BadDotDotDotSyntax
+
+	// NonVariadicDotDotDot occurs when a "..." is used on the final argument to
+	// a non-variadic function.
+	//
+	// Example:
+	//  func printArgs(s []string) {
+	//  	for _, a := range s {
+	//  		println(a)
+	//  	}
+	//  }
+	//
+	//  func f() {
+	//  	s := []string{"a", "b", "c"}
+	//  	printArgs(s...)
+	//  }
+	NonVariadicDotDotDot
+
+	// MisplacedDotDotDot occurs when a "..." is used somewhere other than the
+	// final argument to a function call.
+	//
+	// Example:
+	//  func printArgs(args ...int) {
+	//  	for _, a := range args {
+	//  		println(a)
+	//  	}
+	//  }
+	//
+	//  func f() {
+	//  	a := []int{1,2,3}
+	//  	printArgs(0, a...)
+	//  }
+	MisplacedDotDotDot
+
+	// InvalidDotDotDotOperand occurs when a "..." operator is applied to a
+	// single-valued operand.
+	//
+	// Example:
+	//  func printArgs(args ...int) {
+	//  	for _, a := range args {
+	//  		println(a)
+	//  	}
+	//  }
+	//
+	//  func f() {
+	//  	a := 1
+	//  	printArgs(a...)
+	//  }
+	//
+	// Example:
+	//  func args() (int, int) {
+	//  	return 1, 2
+	//  }
+	//
+	//  func printArgs(args ...int) {
+	//  	for _, a := range args {
+	//  		println(a)
+	//  	}
+	//  }
+	//
+	//  func g() {
+	//  	printArgs(args()...)
+	//  }
+	InvalidDotDotDotOperand
+
+	// InvalidDotDotDot occurs when a "..." is used in a non-variadic built-in
+	// function.
+	//
+	// Example:
+	//  var s = []int{1, 2, 3}
+	//  var l = len(s...)
+	InvalidDotDotDot
+
+	/* exprs > built-in */
+
+	// UncalledBuiltin occurs when a built-in function is used as a
+	// function-valued expression, instead of being called.
+	//
+	// Per the spec:
+	//  "The built-in functions do not have standard Go types, so they can only
+	//  appear in call expressions; they cannot be used as function values."
+	//
+	// Example:
+	//  var _ = copy
+	UncalledBuiltin
+
+	// InvalidAppend occurs when append is called with a first argument that is
+	// not a slice.
+	//
+	// Example:
+	//  var _ = append(1, 2)
+	InvalidAppend
+
+	// InvalidCap occurs when an argument to the cap built-in function is not of
+	// supported type.
+	//
+	// See https://golang.org/ref/spec#Lengthand_capacity for information on
+	// which underlying types are supported as arguments to cap and len.
+	//
+	// Example:
+	//  var s = 2
+	//  var x = cap(s)
+	InvalidCap
+
+	// InvalidClose occurs when close(...) is called with an argument that is
+	// not of channel type, or that is a receive-only channel.
+	//
+	// Example:
+	//  func f() {
+	//  	var x int
+	//  	close(x)
+	//  }
+	InvalidClose
+
+	// InvalidCopy occurs when the arguments are not of slice type or do not
+	// have compatible type.
+	//
+	// See https://golang.org/ref/spec#Appendingand_copying_slices for more
+	// information on the type requirements for the copy built-in.
+	//
+	// Example:
+	//  func f() {
+	//  	var x []int
+	//  	y := []int64{1,2,3}
+	//  	copy(x, y)
+	//  }
+	InvalidCopy
+
+	// InvalidComplex occurs when the complex built-in function is called with
+	// arguments with incompatible types.
+	//
+	// Example:
+	//  var _ = complex(float32(1), float64(2))
+	InvalidComplex
+
+	// InvalidDelete occurs when the delete built-in function is called with a
+	// first argument that is not a map.
+	//
+	// Example:
+	//  func f() {
+	//  	m := "hello"
+	//  	delete(m, "e")
+	//  }
+	InvalidDelete
+
+	// InvalidImag occurs when the imag built-in function is called with an
+	// argument that does not have complex type.
+	//
+	// Example:
+	//  var _ = imag(int(1))
+	InvalidImag
+
+	// InvalidLen occurs when an argument to the len built-in function is not of
+	// supported type.
+	//
+	// See https://golang.org/ref/spec#Lengthand_capacity for information on
+	// which underlying types are supported as arguments to cap and len.
+	//
+	// Example:
+	//  var s = 2
+	//  var x = len(s)
+	InvalidLen
+
+	// SwappedMakeArgs occurs when make is called with three arguments, and its
+	// length argument is larger than its capacity argument.
+	//
+	// Example:
+	//  var x = make([]int, 3, 2)
+	SwappedMakeArgs
+
+	// InvalidMake occurs when make is called with an unsupported type argument.
+	//
+	// See https://golang.org/ref/spec#Makingslices_maps_and_channels for
+	// information on the types that may be created using make.
+	//
+	// Example:
+	//  var x = make(int)
+	InvalidMake
+
+	// InvalidReal occurs when the real built-in function is called with an
+	// argument that does not have complex type.
+	//
+	// Example:
+	//  var _ = real(int(1))
+	InvalidReal
+
+	/* exprs > assertion */
+
+	// InvalidAssert occurs when a type assertion is applied to a
+	// value that is not of interface type.
+	//
+	// Example:
+	//  var x = 1
+	//  var _ = x.(float64)
+	InvalidAssert
+
+	// ImpossibleAssert occurs for a type assertion x.(T) when the value x of
+	// interface cannot have dynamic type T, due to a missing or mismatching
+	// method on T.
+	//
+	// Example:
+	//  type T int
+	//
+	//  func (t *T) m() int { return int(*t) }
+	//
+	//  type I interface { m() int }
+	//
+	//  var x I
+	//  var _ = x.(T)
+	ImpossibleAssert
+
+	/* exprs > conversion */
+
+	// InvalidConversion occurs when the argument type cannot be converted to the
+	// target.
+	//
+	// See https://golang.org/ref/spec#Conversions for the rules of
+	// convertibility.
+	//
+	// Example:
+	//  var x float64
+	//  var _ = string(x)
+	InvalidConversion
+
+	// InvalidUntypedConversion occurs when an there is no valid implicit
+	// conversion from an untyped value satisfying the type constraints of the
+	// context in which it is used.
+	//
+	// Example:
+	//  var _ = 1 + ""
+	InvalidUntypedConversion
+
+	/* offsetof */
+
+	// BadOffsetofSyntax occurs when unsafe.Offsetof is called with an argument
+	// that is not a selector expression.
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  var x int
+	//  var _ = unsafe.Offsetof(x)
+	BadOffsetofSyntax
+
+	// InvalidOffsetof occurs when unsafe.Offsetof is called with a method
+	// selector, rather than a field selector, or when the field is embedded via
+	// a pointer.
+	//
+	// Per the spec:
+	//
+	//  "If f is an embedded field, it must be reachable without pointer
+	//  indirections through fields of the struct. "
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  type T struct { f int }
+	//  type S struct { *T }
+	//  var s S
+	//  var _ = unsafe.Offsetof(s.f)
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  type S struct{}
+	//
+	//  func (S) m() {}
+	//
+	//  var s S
+	//  var _ = unsafe.Offsetof(s.m)
+	InvalidOffsetof
+
+	/* control flow > scope */
+
+	// UnusedExpr occurs when a side-effect free expression is used as a
+	// statement. Such a statement has no effect.
+	//
+	// Example:
+	//  func f(i int) {
+	//  	i*i
+	//  }
+	UnusedExpr
+
+	// UnusedVar occurs when a variable is declared but unused.
+	//
+	// Example:
+	//  func f() {
+	//  	x := 1
+	//  }
+	UnusedVar
+
+	// MissingReturn occurs when a function with results is missing a return
+	// statement.
+	//
+	// Example:
+	//  func f() int {}
+	MissingReturn
+
+	// WrongResultCount occurs when a return statement returns an incorrect
+	// number of values.
+	//
+	// Example:
+	//  func ReturnOne() int {
+	//  	return 1, 2
+	//  }
+	WrongResultCount
+
+	// OutOfScopeResult occurs when the name of a value implicitly returned by
+	// an empty return statement is shadowed in a nested scope.
+	//
+	// Example:
+	//  func factor(n int) (i int) {
+	//  	for i := 2; i < n; i++ {
+	//  		if n%i == 0 {
+	//  			return
+	//  		}
+	//  	}
+	//  	return 0
+	//  }
+	OutOfScopeResult
+
+	/* control flow > if */
+
+	// InvalidCond occurs when an if condition is not a boolean expression.
+	//
+	// Example:
+	//  func checkReturn(i int) {
+	//  	if i {
+	//  		panic("non-zero return")
+	//  	}
+	//  }
+	InvalidCond
+
+	/* control flow > for */
+
+	// InvalidPostDecl occurs when there is a declaration in a for-loop post
+	// statement.
+	//
+	// Example:
+	//  func f() {
+	//  	for i := 0; i < 10; j := 0 {}
+	//  }
+	InvalidPostDecl
+
+	// InvalidChanRange occurs when a send-only channel used in a range
+	// expression.
+	//
+	// Example:
+	//  func sum(c chan<- int) {
+	//  	s := 0
+	//  	for i := range c {
+	//  		s += i
+	//  	}
+	//  }
+	InvalidChanRange
+
+	// InvalidIterVar occurs when two iteration variables are used while ranging
+	// over a channel.
+	//
+	// Example:
+	//  func f(c chan int) {
+	//  	for k, v := range c {
+	//  		println(k, v)
+	//  	}
+	//  }
+	InvalidIterVar
+
+	// InvalidRangeExpr occurs when the type of a range expression is not array,
+	// slice, string, map, or channel.
+	//
+	// Example:
+	//  func f(i int) {
+	//  	for j := range i {
+	//  		println(j)
+	//  	}
+	//  }
+	InvalidRangeExpr
+
+	/* control flow > switch */
+
+	// MisplacedBreak occurs when a break statement is not within a for, switch,
+	// or select statement of the innermost function definition.
+	//
+	// Example:
+	//  func f() {
+	//  	break
+	//  }
+	MisplacedBreak
+
+	// MisplacedContinue occurs when a continue statement is not within a for
+	// loop of the innermost function definition.
+	//
+	// Example:
+	//  func sumeven(n int) int {
+	//  	proceed := func() {
+	//  		continue
+	//  	}
+	//  	sum := 0
+	//  	for i := 1; i <= n; i++ {
+	//  		if i % 2 != 0 {
+	//  			proceed()
+	//  		}
+	//  		sum += i
+	//  	}
+	//  	return sum
+	//  }
+	MisplacedContinue
+
+	// MisplacedFallthrough occurs when a fallthrough statement is not within an
+	// expression switch.
+	//
+	// Example:
+	//  func typename(i interface{}) string {
+	//  	switch i.(type) {
+	//  	case int64:
+	//  		fallthrough
+	//  	case int:
+	//  		return "int"
+	//  	}
+	//  	return "unsupported"
+	//  }
+	MisplacedFallthrough
+
+	// DuplicateCase occurs when a type or expression switch has duplicate
+	// cases.
+	//
+	// Example:
+	//  func printInt(i int) {
+	//  	switch i {
+	//  	case 1:
+	//  		println("one")
+	//  	case 1:
+	//  		println("One")
+	//  	}
+	//  }
+	DuplicateCase
+
+	// DuplicateDefault occurs when a type or expression switch has multiple
+	// default clauses.
+	//
+	// Example:
+	//  func printInt(i int) {
+	//  	switch i {
+	//  	case 1:
+	//  		println("one")
+	//  	default:
+	//  		println("One")
+	//  	default:
+	//  		println("1")
+	//  	}
+	//  }
+	DuplicateDefault
+
+	// BadTypeKeyword occurs when a .(type) expression is used anywhere other
+	// than a type switch.
+	//
+	// Example:
+	//  type I interface {
+	//  	m()
+	//  }
+	//  var t I
+	//  var _ = t.(type)
+	BadTypeKeyword
+
+	// InvalidTypeSwitch occurs when .(type) is used on an expression that is
+	// not of interface type.
+	//
+	// Example:
+	//  func f(i int) {
+	//  	switch x := i.(type) {}
+	//  }
+	InvalidTypeSwitch
+
+	// InvalidExprSwitch occurs when a switch expression is not comparable.
+	//
+	// Example:
+	//  func _() {
+	//  	var a struct{ _ func() }
+	//  	switch a /* ERROR cannot switch on a */ {
+	//  	}
+	//  }
+	InvalidExprSwitch
+
+	/* control flow > select */
+
+	// InvalidSelectCase occurs when a select case is not a channel send or
+	// receive.
+	//
+	// Example:
+	//  func checkChan(c <-chan int) bool {
+	//  	select {
+	//  	case c:
+	//  		return true
+	//  	default:
+	//  		return false
+	//  	}
+	//  }
+	InvalidSelectCase
+
+	/* control flow > labels and jumps */
+
+	// UndeclaredLabel occurs when an undeclared label is jumped to.
+	//
+	// Example:
+	//  func f() {
+	//  	goto L
+	//  }
+	UndeclaredLabel
+
+	// DuplicateLabel occurs when a label is declared more than once.
+	//
+	// Example:
+	//  func f() int {
+	//  L:
+	//  L:
+	//  	return 1
+	//  }
+	DuplicateLabel
+
+	// MisplacedLabel occurs when a break or continue label is not on a for,
+	// switch, or select statement.
+	//
+	// Example:
+	//  func f() {
+	//  L:
+	//  	a := []int{1,2,3}
+	//  	for _, e := range a {
+	//  		if e > 10 {
+	//  			break L
+	//  		}
+	//  		println(a)
+	//  	}
+	//  }
+	MisplacedLabel
+
+	// UnusedLabel occurs when a label is declared but not used.
+	//
+	// Example:
+	//  func f() {
+	//  L:
+	//  }
+	UnusedLabel
+
+	// JumpOverDecl occurs when a label jumps over a variable declaration.
+	//
+	// Example:
+	//  func f() int {
+	//  	goto L
+	//  	x := 2
+	//  L:
+	//  	x++
+	//  	return x
+	//  }
+	JumpOverDecl
+
+	// JumpIntoBlock occurs when a forward jump goes to a label inside a nested
+	// block.
+	//
+	// Example:
+	//  func f(x int) {
+	//  	goto L
+	//  	if x > 0 {
+	//  	L:
+	//  		print("inside block")
+	//  	}
+	// }
+	JumpIntoBlock
+
+	/* control flow > calls */
+
+	// InvalidMethodExpr occurs when a pointer method is called but the argument
+	// is not addressable.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  func (*T) m() int { return 1 }
+	//
+	//  var _ = T.m(T{})
+	InvalidMethodExpr
+
+	// WrongArgCount occurs when too few or too many arguments are passed by a
+	// function call.
+	//
+	// Example:
+	//  func f(i int) {}
+	//  var x = f()
+	WrongArgCount
+
+	// InvalidCall occurs when an expression is called that is not of function
+	// type.
+	//
+	// Example:
+	//  var x = "x"
+	//  var y = x()
+	InvalidCall
+
+	/* control flow > suspended */
+
+	// UnusedResults occurs when a restricted expression-only built-in function
+	// is suspended via go or defer. Such a suspension discards the results of
+	// these side-effect free built-in functions, and therefore is ineffectual.
+	//
+	// Example:
+	//  func f(a []int) int {
+	//  	defer len(a)
+	//  	return i
+	//  }
+	UnusedResults
+
+	// InvalidDefer occurs when a deferred expression is not a function call,
+	// for example if the expression is a type conversion.
+	//
+	// Example:
+	//  func f(i int) int {
+	//  	defer int32(i)
+	//  	return i
+	//  }
+	InvalidDefer
+
+	// InvalidGo occurs when a go expression is not a function call, for example
+	// if the expression is a type conversion.
+	//
+	// Example:
+	//  func f(i int) int {
+	//  	go int32(i)
+	//  	return i
+	//  }
+	InvalidGo
+)
diff --git a/vendor/golang.org/x/tools/internal/typesinternal/errorcode_string.go b/vendor/golang.org/x/tools/internal/typesinternal/errorcode_string.go
new file mode 100644
index 00000000..3e5842a5
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typesinternal/errorcode_string.go
@@ -0,0 +1,153 @@
+// Code generated by "stringer -type=ErrorCode"; DO NOT EDIT.
+
+package typesinternal
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[Test-1]
+	_ = x[BlankPkgName-2]
+	_ = x[MismatchedPkgName-3]
+	_ = x[InvalidPkgUse-4]
+	_ = x[BadImportPath-5]
+	_ = x[BrokenImport-6]
+	_ = x[ImportCRenamed-7]
+	_ = x[UnusedImport-8]
+	_ = x[InvalidInitCycle-9]
+	_ = x[DuplicateDecl-10]
+	_ = x[InvalidDeclCycle-11]
+	_ = x[InvalidTypeCycle-12]
+	_ = x[InvalidConstInit-13]
+	_ = x[InvalidConstVal-14]
+	_ = x[InvalidConstType-15]
+	_ = x[UntypedNil-16]
+	_ = x[WrongAssignCount-17]
+	_ = x[UnassignableOperand-18]
+	_ = x[NoNewVar-19]
+	_ = x[MultiValAssignOp-20]
+	_ = x[InvalidIfaceAssign-21]
+	_ = x[InvalidChanAssign-22]
+	_ = x[IncompatibleAssign-23]
+	_ = x[UnaddressableFieldAssign-24]
+	_ = x[NotAType-25]
+	_ = x[InvalidArrayLen-26]
+	_ = x[BlankIfaceMethod-27]
+	_ = x[IncomparableMapKey-28]
+	_ = x[InvalidIfaceEmbed-29]
+	_ = x[InvalidPtrEmbed-30]
+	_ = x[BadRecv-31]
+	_ = x[InvalidRecv-32]
+	_ = x[DuplicateFieldAndMethod-33]
+	_ = x[DuplicateMethod-34]
+	_ = x[InvalidBlank-35]
+	_ = x[InvalidIota-36]
+	_ = x[MissingInitBody-37]
+	_ = x[InvalidInitSig-38]
+	_ = x[InvalidInitDecl-39]
+	_ = x[InvalidMainDecl-40]
+	_ = x[TooManyValues-41]
+	_ = x[NotAnExpr-42]
+	_ = x[TruncatedFloat-43]
+	_ = x[NumericOverflow-44]
+	_ = x[UndefinedOp-45]
+	_ = x[MismatchedTypes-46]
+	_ = x[DivByZero-47]
+	_ = x[NonNumericIncDec-48]
+	_ = x[UnaddressableOperand-49]
+	_ = x[InvalidIndirection-50]
+	_ = x[NonIndexableOperand-51]
+	_ = x[InvalidIndex-52]
+	_ = x[SwappedSliceIndices-53]
+	_ = x[NonSliceableOperand-54]
+	_ = x[InvalidSliceExpr-55]
+	_ = x[InvalidShiftCount-56]
+	_ = x[InvalidShiftOperand-57]
+	_ = x[InvalidReceive-58]
+	_ = x[InvalidSend-59]
+	_ = x[DuplicateLitKey-60]
+	_ = x[MissingLitKey-61]
+	_ = x[InvalidLitIndex-62]
+	_ = x[OversizeArrayLit-63]
+	_ = x[MixedStructLit-64]
+	_ = x[InvalidStructLit-65]
+	_ = x[MissingLitField-66]
+	_ = x[DuplicateLitField-67]
+	_ = x[UnexportedLitField-68]
+	_ = x[InvalidLitField-69]
+	_ = x[UntypedLit-70]
+	_ = x[InvalidLit-71]
+	_ = x[AmbiguousSelector-72]
+	_ = x[UndeclaredImportedName-73]
+	_ = x[UnexportedName-74]
+	_ = x[UndeclaredName-75]
+	_ = x[MissingFieldOrMethod-76]
+	_ = x[BadDotDotDotSyntax-77]
+	_ = x[NonVariadicDotDotDot-78]
+	_ = x[MisplacedDotDotDot-79]
+	_ = x[InvalidDotDotDotOperand-80]
+	_ = x[InvalidDotDotDot-81]
+	_ = x[UncalledBuiltin-82]
+	_ = x[InvalidAppend-83]
+	_ = x[InvalidCap-84]
+	_ = x[InvalidClose-85]
+	_ = x[InvalidCopy-86]
+	_ = x[InvalidComplex-87]
+	_ = x[InvalidDelete-88]
+	_ = x[InvalidImag-89]
+	_ = x[InvalidLen-90]
+	_ = x[SwappedMakeArgs-91]
+	_ = x[InvalidMake-92]
+	_ = x[InvalidReal-93]
+	_ = x[InvalidAssert-94]
+	_ = x[ImpossibleAssert-95]
+	_ = x[InvalidConversion-96]
+	_ = x[InvalidUntypedConversion-97]
+	_ = x[BadOffsetofSyntax-98]
+	_ = x[InvalidOffsetof-99]
+	_ = x[UnusedExpr-100]
+	_ = x[UnusedVar-101]
+	_ = x[MissingReturn-102]
+	_ = x[WrongResultCount-103]
+	_ = x[OutOfScopeResult-104]
+	_ = x[InvalidCond-105]
+	_ = x[InvalidPostDecl-106]
+	_ = x[InvalidChanRange-107]
+	_ = x[InvalidIterVar-108]
+	_ = x[InvalidRangeExpr-109]
+	_ = x[MisplacedBreak-110]
+	_ = x[MisplacedContinue-111]
+	_ = x[MisplacedFallthrough-112]
+	_ = x[DuplicateCase-113]
+	_ = x[DuplicateDefault-114]
+	_ = x[BadTypeKeyword-115]
+	_ = x[InvalidTypeSwitch-116]
+	_ = x[InvalidExprSwitch-117]
+	_ = x[InvalidSelectCase-118]
+	_ = x[UndeclaredLabel-119]
+	_ = x[DuplicateLabel-120]
+	_ = x[MisplacedLabel-121]
+	_ = x[UnusedLabel-122]
+	_ = x[JumpOverDecl-123]
+	_ = x[JumpIntoBlock-124]
+	_ = x[InvalidMethodExpr-125]
+	_ = x[WrongArgCount-126]
+	_ = x[InvalidCall-127]
+	_ = x[UnusedResults-128]
+	_ = x[InvalidDefer-129]
+	_ = x[InvalidGo-130]
+}
+
+const _ErrorCode_name = "TestBlankPkgNameMismatchedPkgNameInvalidPkgUseBadImportPathBrokenImportImportCRenamedUnusedImportInvalidInitCycleDuplicateDeclInvalidDeclCycleInvalidTypeCycleInvalidConstInitInvalidConstValInvalidConstTypeUntypedNilWrongAssignCountUnassignableOperandNoNewVarMultiValAssignOpInvalidIfaceAssignInvalidChanAssignIncompatibleAssignUnaddressableFieldAssignNotATypeInvalidArrayLenBlankIfaceMethodIncomparableMapKeyInvalidIfaceEmbedInvalidPtrEmbedBadRecvInvalidRecvDuplicateFieldAndMethodDuplicateMethodInvalidBlankInvalidIotaMissingInitBodyInvalidInitSigInvalidInitDeclInvalidMainDeclTooManyValuesNotAnExprTruncatedFloatNumericOverflowUndefinedOpMismatchedTypesDivByZeroNonNumericIncDecUnaddressableOperandInvalidIndirectionNonIndexableOperandInvalidIndexSwappedSliceIndicesNonSliceableOperandInvalidSliceExprInvalidShiftCountInvalidShiftOperandInvalidReceiveInvalidSendDuplicateLitKeyMissingLitKeyInvalidLitIndexOversizeArrayLitMixedStructLitInvalidStructLitMissingLitFieldDuplicateLitFieldUnexportedLitFieldInvalidLitFieldUntypedLitInvalidLitAmbiguousSelectorUndeclaredImportedNameUnexportedNameUndeclaredNameMissingFieldOrMethodBadDotDotDotSyntaxNonVariadicDotDotDotMisplacedDotDotDotInvalidDotDotDotOperandInvalidDotDotDotUncalledBuiltinInvalidAppendInvalidCapInvalidCloseInvalidCopyInvalidComplexInvalidDeleteInvalidImagInvalidLenSwappedMakeArgsInvalidMakeInvalidRealInvalidAssertImpossibleAssertInvalidConversionInvalidUntypedConversionBadOffsetofSyntaxInvalidOffsetofUnusedExprUnusedVarMissingReturnWrongResultCountOutOfScopeResultInvalidCondInvalidPostDeclInvalidChanRangeInvalidIterVarInvalidRangeExprMisplacedBreakMisplacedContinueMisplacedFallthroughDuplicateCaseDuplicateDefaultBadTypeKeywordInvalidTypeSwitchInvalidExprSwitchInvalidSelectCaseUndeclaredLabelDuplicateLabelMisplacedLabelUnusedLabelJumpOverDeclJumpIntoBlockInvalidMethodExprWrongArgCountInvalidCallUnusedResultsInvalidDeferInvalidGo"
+
+var _ErrorCode_index = [...]uint16{0, 4, 16, 33, 46, 59, 71, 85, 97, 113, 126, 142, 158, 174, 189, 205, 215, 231, 250, 258, 274, 292, 309, 327, 351, 359, 374, 390, 408, 425, 440, 447, 458, 481, 496, 508, 519, 534, 548, 563, 578, 591, 600, 614, 629, 640, 655, 664, 680, 700, 718, 737, 749, 768, 787, 803, 820, 839, 853, 864, 879, 892, 907, 923, 937, 953, 968, 985, 1003, 1018, 1028, 1038, 1055, 1077, 1091, 1105, 1125, 1143, 1163, 1181, 1204, 1220, 1235, 1248, 1258, 1270, 1281, 1295, 1308, 1319, 1329, 1344, 1355, 1366, 1379, 1395, 1412, 1436, 1453, 1468, 1478, 1487, 1500, 1516, 1532, 1543, 1558, 1574, 1588, 1604, 1618, 1635, 1655, 1668, 1684, 1698, 1715, 1732, 1749, 1764, 1778, 1792, 1803, 1815, 1828, 1845, 1858, 1869, 1882, 1894, 1903}
+
+func (i ErrorCode) String() string {
+	i -= 1
+	if i < 0 || i >= ErrorCode(len(_ErrorCode_index)-1) {
+		return "ErrorCode(" + strconv.FormatInt(int64(i+1), 10) + ")"
+	}
+	return _ErrorCode_name[_ErrorCode_index[i]:_ErrorCode_index[i+1]]
+}
diff --git a/vendor/golang.org/x/tools/internal/typesinternal/types.go b/vendor/golang.org/x/tools/internal/typesinternal/types.go
new file mode 100644
index 00000000..7c77c2fb
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typesinternal/types.go
@@ -0,0 +1,50 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package typesinternal provides access to internal go/types APIs that are not
+// yet exported.
+package typesinternal
+
+import (
+	"go/token"
+	"go/types"
+	"reflect"
+	"unsafe"
+)
+
+func SetUsesCgo(conf *types.Config) bool {
+	v := reflect.ValueOf(conf).Elem()
+
+	f := v.FieldByName("go115UsesCgo")
+	if !f.IsValid() {
+		f = v.FieldByName("UsesCgo")
+		if !f.IsValid() {
+			return false
+		}
+	}
+
+	addr := unsafe.Pointer(f.UnsafeAddr())
+	*(*bool)(addr) = true
+
+	return true
+}
+
+// ReadGo116ErrorData extracts additional information from types.Error values
+// generated by Go version 1.16 and later: the error code, start position, and
+// end position. If all positions are valid, start <= err.Pos <= end.
+//
+// If the data could not be read, the final result parameter will be false.
+func ReadGo116ErrorData(err types.Error) (code ErrorCode, start, end token.Pos, ok bool) {
+	var data [3]int
+	// By coincidence all of these fields are ints, which simplifies things.
+	v := reflect.ValueOf(err)
+	for i, name := range []string{"go116code", "go116start", "go116end"} {
+		f := v.FieldByName(name)
+		if !f.IsValid() {
+			return 0, 0, 0, false
+		}
+		data[i] = int(f.Int())
+	}
+	return ErrorCode(data[0]), token.Pos(data[1]), token.Pos(data[2]), true
+}
diff --git a/vendor/golang.org/x/xerrors/LICENSE b/vendor/golang.org/x/xerrors/LICENSE
new file mode 100644
index 00000000..e4a47e17
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2019 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/vendor/golang.org/x/xerrors/PATENTS b/vendor/golang.org/x/xerrors/PATENTS
new file mode 100644
index 00000000..73309904
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/PATENTS
@@ -0,0 +1,22 @@
+Additional IP Rights Grant (Patents)
+
+"This implementation" means the copyrightable works distributed by
+Google as part of the Go project.
+
+Google hereby grants to You a perpetual, worldwide, non-exclusive,
+no-charge, royalty-free, irrevocable (except as stated in this section)
+patent license to make, have made, use, offer to sell, sell, import,
+transfer and otherwise run, modify and propagate the contents of this
+implementation of Go, where such license applies only to those patent
+claims, both currently owned or controlled by Google and acquired in
+the future, licensable by Google that are necessarily infringed by this
+implementation of Go.  This grant does not include claims that would be
+infringed only as a consequence of further modification of this
+implementation.  If you or your agent or exclusive licensee institute or
+order or agree to the institution of patent litigation against any
+entity (including a cross-claim or counterclaim in a lawsuit) alleging
+that this implementation of Go or any code incorporated within this
+implementation of Go constitutes direct or contributory patent
+infringement, or inducement of patent infringement, then any patent
+rights granted to you under this License for this implementation of Go
+shall terminate as of the date such litigation is filed.
diff --git a/vendor/golang.org/x/xerrors/README b/vendor/golang.org/x/xerrors/README
new file mode 100644
index 00000000..aac7867a
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/README
@@ -0,0 +1,2 @@
+This repository holds the transition packages for the new Go 1.13 error values.
+See golang.org/design/29934-error-values.
diff --git a/vendor/golang.org/x/xerrors/adaptor.go b/vendor/golang.org/x/xerrors/adaptor.go
new file mode 100644
index 00000000..4317f248
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/adaptor.go
@@ -0,0 +1,193 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package xerrors
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"reflect"
+	"strconv"
+)
+
+// FormatError calls the FormatError method of f with an errors.Printer
+// configured according to s and verb, and writes the result to s.
+func FormatError(f Formatter, s fmt.State, verb rune) {
+	// Assuming this function is only called from the Format method, and given
+	// that FormatError takes precedence over Format, it cannot be called from
+	// any package that supports errors.Formatter. It is therefore safe to
+	// disregard that State may be a specific printer implementation and use one
+	// of our choice instead.
+
+	// limitations: does not support printing error as Go struct.
+
+	var (
+		sep    = " " // separator before next error
+		p      = &state{State: s}
+		direct = true
+	)
+
+	var err error = f
+
+	switch verb {
+	// Note that this switch must match the preference order
+	// for ordinary string printing (%#v before %+v, and so on).
+
+	case 'v':
+		if s.Flag('#') {
+			if stringer, ok := err.(fmt.GoStringer); ok {
+				io.WriteString(&p.buf, stringer.GoString())
+				goto exit
+			}
+			// proceed as if it were %v
+		} else if s.Flag('+') {
+			p.printDetail = true
+			sep = "\n  - "
+		}
+	case 's':
+	case 'q', 'x', 'X':
+		// Use an intermediate buffer in the rare cases that precision,
+		// truncation, or one of the alternative verbs (q, x, and X) are
+		// specified.
+		direct = false
+
+	default:
+		p.buf.WriteString("%!")
+		p.buf.WriteRune(verb)
+		p.buf.WriteByte('(')
+		switch {
+		case err != nil:
+			p.buf.WriteString(reflect.TypeOf(f).String())
+		default:
+			p.buf.WriteString("<nil>")
+		}
+		p.buf.WriteByte(')')
+		io.Copy(s, &p.buf)
+		return
+	}
+
+loop:
+	for {
+		switch v := err.(type) {
+		case Formatter:
+			err = v.FormatError((*printer)(p))
+		case fmt.Formatter:
+			v.Format(p, 'v')
+			break loop
+		default:
+			io.WriteString(&p.buf, v.Error())
+			break loop
+		}
+		if err == nil {
+			break
+		}
+		if p.needColon || !p.printDetail {
+			p.buf.WriteByte(':')
+			p.needColon = false
+		}
+		p.buf.WriteString(sep)
+		p.inDetail = false
+		p.needNewline = false
+	}
+
+exit:
+	width, okW := s.Width()
+	prec, okP := s.Precision()
+
+	if !direct || (okW && width > 0) || okP {
+		// Construct format string from State s.
+		format := []byte{'%'}
+		if s.Flag('-') {
+			format = append(format, '-')
+		}
+		if s.Flag('+') {
+			format = append(format, '+')
+		}
+		if s.Flag(' ') {
+			format = append(format, ' ')
+		}
+		if okW {
+			format = strconv.AppendInt(format, int64(width), 10)
+		}
+		if okP {
+			format = append(format, '.')
+			format = strconv.AppendInt(format, int64(prec), 10)
+		}
+		format = append(format, string(verb)...)
+		fmt.Fprintf(s, string(format), p.buf.String())
+	} else {
+		io.Copy(s, &p.buf)
+	}
+}
+
+var detailSep = []byte("\n    ")
+
+// state tracks error printing state. It implements fmt.State.
+type state struct {
+	fmt.State
+	buf bytes.Buffer
+
+	printDetail bool
+	inDetail    bool
+	needColon   bool
+	needNewline bool
+}
+
+func (s *state) Write(b []byte) (n int, err error) {
+	if s.printDetail {
+		if len(b) == 0 {
+			return 0, nil
+		}
+		if s.inDetail && s.needColon {
+			s.needNewline = true
+			if b[0] == '\n' {
+				b = b[1:]
+			}
+		}
+		k := 0
+		for i, c := range b {
+			if s.needNewline {
+				if s.inDetail && s.needColon {
+					s.buf.WriteByte(':')
+					s.needColon = false
+				}
+				s.buf.Write(detailSep)
+				s.needNewline = false
+			}
+			if c == '\n' {
+				s.buf.Write(b[k:i])
+				k = i + 1
+				s.needNewline = true
+			}
+		}
+		s.buf.Write(b[k:])
+		if !s.inDetail {
+			s.needColon = true
+		}
+	} else if !s.inDetail {
+		s.buf.Write(b)
+	}
+	return len(b), nil
+}
+
+// printer wraps a state to implement an xerrors.Printer.
+type printer state
+
+func (s *printer) Print(args ...interface{}) {
+	if !s.inDetail || s.printDetail {
+		fmt.Fprint((*state)(s), args...)
+	}
+}
+
+func (s *printer) Printf(format string, args ...interface{}) {
+	if !s.inDetail || s.printDetail {
+		fmt.Fprintf((*state)(s), format, args...)
+	}
+}
+
+func (s *printer) Detail() bool {
+	s.inDetail = true
+	return s.printDetail
+}
diff --git a/vendor/golang.org/x/xerrors/codereview.cfg b/vendor/golang.org/x/xerrors/codereview.cfg
new file mode 100644
index 00000000..3f8b14b6
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/codereview.cfg
@@ -0,0 +1 @@
+issuerepo: golang/go
diff --git a/vendor/golang.org/x/xerrors/doc.go b/vendor/golang.org/x/xerrors/doc.go
new file mode 100644
index 00000000..eef99d9d
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/doc.go
@@ -0,0 +1,22 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package xerrors implements functions to manipulate errors.
+//
+// This package is based on the Go 2 proposal for error values:
+//   https://golang.org/design/29934-error-values
+//
+// These functions were incorporated into the standard library's errors package
+// in Go 1.13:
+// - Is
+// - As
+// - Unwrap
+//
+// Also, Errorf's %w verb was incorporated into fmt.Errorf.
+//
+// Use this package to get equivalent behavior in all supported Go versions.
+//
+// No other features of this package were included in Go 1.13, and at present
+// there are no plans to include any of them.
+package xerrors // import "golang.org/x/xerrors"
diff --git a/vendor/golang.org/x/xerrors/errors.go b/vendor/golang.org/x/xerrors/errors.go
new file mode 100644
index 00000000..e88d3772
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/errors.go
@@ -0,0 +1,33 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package xerrors
+
+import "fmt"
+
+// errorString is a trivial implementation of error.
+type errorString struct {
+	s     string
+	frame Frame
+}
+
+// New returns an error that formats as the given text.
+//
+// The returned error contains a Frame set to the caller's location and
+// implements Formatter to show this information when printed with details.
+func New(text string) error {
+	return &errorString{text, Caller(1)}
+}
+
+func (e *errorString) Error() string {
+	return e.s
+}
+
+func (e *errorString) Format(s fmt.State, v rune) { FormatError(e, s, v) }
+
+func (e *errorString) FormatError(p Printer) (next error) {
+	p.Print(e.s)
+	e.frame.Format(p)
+	return nil
+}
diff --git a/vendor/golang.org/x/xerrors/fmt.go b/vendor/golang.org/x/xerrors/fmt.go
new file mode 100644
index 00000000..829862dd
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/fmt.go
@@ -0,0 +1,187 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package xerrors
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+
+	"golang.org/x/xerrors/internal"
+)
+
+const percentBangString = "%!"
+
+// Errorf formats according to a format specifier and returns the string as a
+// value that satisfies error.
+//
+// The returned error includes the file and line number of the caller when
+// formatted with additional detail enabled. If the last argument is an error
+// the returned error's Format method will return it if the format string ends
+// with ": %s", ": %v", or ": %w". If the last argument is an error and the
+// format string ends with ": %w", the returned error implements an Unwrap
+// method returning it.
+//
+// If the format specifier includes a %w verb with an error operand in a
+// position other than at the end, the returned error will still implement an
+// Unwrap method returning the operand, but the error's Format method will not
+// return the wrapped error.
+//
+// It is invalid to include more than one %w verb or to supply it with an
+// operand that does not implement the error interface. The %w verb is otherwise
+// a synonym for %v.
+func Errorf(format string, a ...interface{}) error {
+	format = formatPlusW(format)
+	// Support a ": %[wsv]" suffix, which works well with xerrors.Formatter.
+	wrap := strings.HasSuffix(format, ": %w")
+	idx, format2, ok := parsePercentW(format)
+	percentWElsewhere := !wrap && idx >= 0
+	if !percentWElsewhere && (wrap || strings.HasSuffix(format, ": %s") || strings.HasSuffix(format, ": %v")) {
+		err := errorAt(a, len(a)-1)
+		if err == nil {
+			return &noWrapError{fmt.Sprintf(format, a...), nil, Caller(1)}
+		}
+		// TODO: this is not entirely correct. The error value could be
+		// printed elsewhere in format if it mixes numbered with unnumbered
+		// substitutions. With relatively small changes to doPrintf we can
+		// have it optionally ignore extra arguments and pass the argument
+		// list in its entirety.
+		msg := fmt.Sprintf(format[:len(format)-len(": %s")], a[:len(a)-1]...)
+		frame := Frame{}
+		if internal.EnableTrace {
+			frame = Caller(1)
+		}
+		if wrap {
+			return &wrapError{msg, err, frame}
+		}
+		return &noWrapError{msg, err, frame}
+	}
+	// Support %w anywhere.
+	// TODO: don't repeat the wrapped error's message when %w occurs in the middle.
+	msg := fmt.Sprintf(format2, a...)
+	if idx < 0 {
+		return &noWrapError{msg, nil, Caller(1)}
+	}
+	err := errorAt(a, idx)
+	if !ok || err == nil {
+		// Too many %ws or argument of %w is not an error. Approximate the Go
+		// 1.13 fmt.Errorf message.
+		return &noWrapError{fmt.Sprintf("%sw(%s)", percentBangString, msg), nil, Caller(1)}
+	}
+	frame := Frame{}
+	if internal.EnableTrace {
+		frame = Caller(1)
+	}
+	return &wrapError{msg, err, frame}
+}
+
+func errorAt(args []interface{}, i int) error {
+	if i < 0 || i >= len(args) {
+		return nil
+	}
+	err, ok := args[i].(error)
+	if !ok {
+		return nil
+	}
+	return err
+}
+
+// formatPlusW is used to avoid the vet check that will barf at %w.
+func formatPlusW(s string) string {
+	return s
+}
+
+// Return the index of the only %w in format, or -1 if none.
+// Also return a rewritten format string with %w replaced by %v, and
+// false if there is more than one %w.
+// TODO: handle "%[N]w".
+func parsePercentW(format string) (idx int, newFormat string, ok bool) {
+	// Loosely copied from golang.org/x/tools/go/analysis/passes/printf/printf.go.
+	idx = -1
+	ok = true
+	n := 0
+	sz := 0
+	var isW bool
+	for i := 0; i < len(format); i += sz {
+		if format[i] != '%' {
+			sz = 1
+			continue
+		}
+		// "%%" is not a format directive.
+		if i+1 < len(format) && format[i+1] == '%' {
+			sz = 2
+			continue
+		}
+		sz, isW = parsePrintfVerb(format[i:])
+		if isW {
+			if idx >= 0 {
+				ok = false
+			} else {
+				idx = n
+			}
+			// "Replace" the last character, the 'w', with a 'v'.
+			p := i + sz - 1
+			format = format[:p] + "v" + format[p+1:]
+		}
+		n++
+	}
+	return idx, format, ok
+}
+
+// Parse the printf verb starting with a % at s[0].
+// Return how many bytes it occupies and whether the verb is 'w'.
+func parsePrintfVerb(s string) (int, bool) {
+	// Assume only that the directive is a sequence of non-letters followed by a single letter.
+	sz := 0
+	var r rune
+	for i := 1; i < len(s); i += sz {
+		r, sz = utf8.DecodeRuneInString(s[i:])
+		if unicode.IsLetter(r) {
+			return i + sz, r == 'w'
+		}
+	}
+	return len(s), false
+}
+
+type noWrapError struct {
+	msg   string
+	err   error
+	frame Frame
+}
+
+func (e *noWrapError) Error() string {
+	return fmt.Sprint(e)
+}
+
+func (e *noWrapError) Format(s fmt.State, v rune) { FormatError(e, s, v) }
+
+func (e *noWrapError) FormatError(p Printer) (next error) {
+	p.Print(e.msg)
+	e.frame.Format(p)
+	return e.err
+}
+
+type wrapError struct {
+	msg   string
+	err   error
+	frame Frame
+}
+
+func (e *wrapError) Error() string {
+	return fmt.Sprint(e)
+}
+
+func (e *wrapError) Format(s fmt.State, v rune) { FormatError(e, s, v) }
+
+func (e *wrapError) FormatError(p Printer) (next error) {
+	p.Print(e.msg)
+	e.frame.Format(p)
+	return e.err
+}
+
+func (e *wrapError) Unwrap() error {
+	return e.err
+}
diff --git a/vendor/golang.org/x/xerrors/format.go b/vendor/golang.org/x/xerrors/format.go
new file mode 100644
index 00000000..1bc9c26b
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/format.go
@@ -0,0 +1,34 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package xerrors
+
+// A Formatter formats error messages.
+type Formatter interface {
+	error
+
+	// FormatError prints the receiver's first error and returns the next error in
+	// the error chain, if any.
+	FormatError(p Printer) (next error)
+}
+
+// A Printer formats error messages.
+//
+// The most common implementation of Printer is the one provided by package fmt
+// during Printf (as of Go 1.13). Localization packages such as golang.org/x/text/message
+// typically provide their own implementations.
+type Printer interface {
+	// Print appends args to the message output.
+	Print(args ...interface{})
+
+	// Printf writes a formatted string.
+	Printf(format string, args ...interface{})
+
+	// Detail reports whether error detail is requested.
+	// After the first call to Detail, all text written to the Printer
+	// is formatted as additional detail, or ignored when
+	// detail has not been requested.
+	// If Detail returns false, the caller can avoid printing the detail at all.
+	Detail() bool
+}
diff --git a/vendor/golang.org/x/xerrors/frame.go b/vendor/golang.org/x/xerrors/frame.go
new file mode 100644
index 00000000..0de628ec
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/frame.go
@@ -0,0 +1,56 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package xerrors
+
+import (
+	"runtime"
+)
+
+// A Frame contains part of a call stack.
+type Frame struct {
+	// Make room for three PCs: the one we were asked for, what it called,
+	// and possibly a PC for skipPleaseUseCallersFrames. See:
+	// https://go.googlesource.com/go/+/032678e0fb/src/runtime/extern.go#169
+	frames [3]uintptr
+}
+
+// Caller returns a Frame that describes a frame on the caller's stack.
+// The argument skip is the number of frames to skip over.
+// Caller(0) returns the frame for the caller of Caller.
+func Caller(skip int) Frame {
+	var s Frame
+	runtime.Callers(skip+1, s.frames[:])
+	return s
+}
+
+// location reports the file, line, and function of a frame.
+//
+// The returned function may be "" even if file and line are not.
+func (f Frame) location() (function, file string, line int) {
+	frames := runtime.CallersFrames(f.frames[:])
+	if _, ok := frames.Next(); !ok {
+		return "", "", 0
+	}
+	fr, ok := frames.Next()
+	if !ok {
+		return "", "", 0
+	}
+	return fr.Function, fr.File, fr.Line
+}
+
+// Format prints the stack as error detail.
+// It should be called from an error's Format implementation
+// after printing any other error detail.
+func (f Frame) Format(p Printer) {
+	if p.Detail() {
+		function, file, line := f.location()
+		if function != "" {
+			p.Printf("%s\n    ", function)
+		}
+		if file != "" {
+			p.Printf("%s:%d\n", file, line)
+		}
+	}
+}
diff --git a/vendor/golang.org/x/xerrors/internal/internal.go b/vendor/golang.org/x/xerrors/internal/internal.go
new file mode 100644
index 00000000..89f4eca5
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/internal/internal.go
@@ -0,0 +1,8 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package internal
+
+// EnableTrace indicates whether stack information should be recorded in errors.
+var EnableTrace = true
diff --git a/vendor/golang.org/x/xerrors/wrap.go b/vendor/golang.org/x/xerrors/wrap.go
new file mode 100644
index 00000000..9a3b5103
--- /dev/null
+++ b/vendor/golang.org/x/xerrors/wrap.go
@@ -0,0 +1,106 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package xerrors
+
+import (
+	"reflect"
+)
+
+// A Wrapper provides context around another error.
+type Wrapper interface {
+	// Unwrap returns the next error in the error chain.
+	// If there is no next error, Unwrap returns nil.
+	Unwrap() error
+}
+
+// Opaque returns an error with the same error formatting as err
+// but that does not match err and cannot be unwrapped.
+func Opaque(err error) error {
+	return noWrapper{err}
+}
+
+type noWrapper struct {
+	error
+}
+
+func (e noWrapper) FormatError(p Printer) (next error) {
+	if f, ok := e.error.(Formatter); ok {
+		return f.FormatError(p)
+	}
+	p.Print(e.error)
+	return nil
+}
+
+// Unwrap returns the result of calling the Unwrap method on err, if err implements
+// Unwrap. Otherwise, Unwrap returns nil.
+func Unwrap(err error) error {
+	u, ok := err.(Wrapper)
+	if !ok {
+		return nil
+	}
+	return u.Unwrap()
+}
+
+// Is reports whether any error in err's chain matches target.
+//
+// An error is considered to match a target if it is equal to that target or if
+// it implements a method Is(error) bool such that Is(target) returns true.
+func Is(err, target error) bool {
+	if target == nil {
+		return err == target
+	}
+
+	isComparable := reflect.TypeOf(target).Comparable()
+	for {
+		if isComparable && err == target {
+			return true
+		}
+		if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(target) {
+			return true
+		}
+		// TODO: consider supporing target.Is(err). This would allow
+		// user-definable predicates, but also may allow for coping with sloppy
+		// APIs, thereby making it easier to get away with them.
+		if err = Unwrap(err); err == nil {
+			return false
+		}
+	}
+}
+
+// As finds the first error in err's chain that matches the type to which target
+// points, and if so, sets the target to its value and returns true. An error
+// matches a type if it is assignable to the target type, or if it has a method
+// As(interface{}) bool such that As(target) returns true. As will panic if target
+// is not a non-nil pointer to a type which implements error or is of interface type.
+//
+// The As method should set the target to its value and return true if err
+// matches the type to which target points.
+func As(err error, target interface{}) bool {
+	if target == nil {
+		panic("errors: target cannot be nil")
+	}
+	val := reflect.ValueOf(target)
+	typ := val.Type()
+	if typ.Kind() != reflect.Ptr || val.IsNil() {
+		panic("errors: target must be a non-nil pointer")
+	}
+	if e := typ.Elem(); e.Kind() != reflect.Interface && !e.Implements(errorType) {
+		panic("errors: *target must be interface or implement error")
+	}
+	targetType := typ.Elem()
+	for err != nil {
+		if reflect.TypeOf(err).AssignableTo(targetType) {
+			val.Elem().Set(reflect.ValueOf(err))
+			return true
+		}
+		if x, ok := err.(interface{ As(interface{}) bool }); ok && x.As(target) {
+			return true
+		}
+		err = Unwrap(err)
+	}
+	return false
+}
+
+var errorType = reflect.TypeOf((*error)(nil)).Elem()