Update dependencies (#2007)

* Update dependencies

14 files changed, 5291 insertions, 0 deletions

diff --git a/vendor/golang.org/x/tools/internal/gcimporter/bexport.go b/vendor/golang.org/x/tools/internal/gcimporter/bexport.go
new file mode 100644
index 00000000..30582ed6
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/bexport.go
@@ -0,0 +1,852 @@
+// 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/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
+
+// 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 IMPLEMENTED 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 !token.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() != "_" && !token.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 token.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 != "" && !token.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/internal/gcimporter/bimport.go b/vendor/golang.org/x/tools/internal/gcimporter/bimport.go
new file mode 100644
index 00000000..b85de014
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/bimport.go
@@ -0,0 +1,1053 @@
+// 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]*fileInfo),
+		},
+	}
+	defer p.fake.setLines() // set lines for files in fset
+
+	// 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]*fileInfo
+}
+
+type fileInfo struct {
+	file     *token.File
+	lastline int
+}
+
+const maxlines = 64 * 1024
+
+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. We delay calling token.File.SetLines until all
+	// positions have been calculated (by way of fakeFileSet.setLines), so that
+	// we can avoid setting unnecessary lines. See also golang/go#46586.
+	f := s.files[file]
+	if f == nil {
+		f = &fileInfo{file: s.fset.AddFile(file, -1, maxlines)}
+		s.files[file] = f
+	}
+	if line > maxlines {
+		line = 1
+	}
+	if line > f.lastline {
+		f.lastline = line
+	}
+
+	// Return a fake position assuming that f.file consists only of newlines.
+	return token.Pos(f.file.Base() + line - 1)
+}
+
+func (s *fakeFileSet) setLines() {
+	fakeLinesOnce.Do(func() {
+		fakeLines = make([]int, maxlines)
+		for i := range fakeLines {
+			fakeLines[i] = i
+		}
+	})
+	for _, f := range s.files {
+		f.file.SetLines(fakeLines[:f.lastline])
+	}
+}
+
+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/internal/gcimporter/exportdata.go b/vendor/golang.org/x/tools/internal/gcimporter/exportdata.go
new file mode 100644
index 00000000..f6437feb
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/exportdata.go
@@ -0,0 +1,99 @@
+// 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 int64, 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]))
+	length, err := strconv.Atoi(s)
+	size = int64(length)
+	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 "$$B".
+// The size result is the length of the export data in bytes, or -1 if not known.
+func FindExportData(r *bufio.Reader) (hdr string, size int64, err error) {
+	// Read first line to make sure this is an object file.
+	line, err := r.ReadSlice('\n')
+	if err != nil {
+		err = fmt.Errorf("can't find export data (%v)", err)
+		return
+	}
+
+	if string(line) == "!<arch>\n" {
+		// Archive file. Scan to __.PKGDEF.
+		var name string
+		if name, size, err = readGopackHeader(r); err != nil {
+			return
+		}
+
+		// First entry should be __.PKGDEF.
+		if name != "__.PKGDEF" {
+			err = fmt.Errorf("go archive is missing __.PKGDEF")
+			return
+		}
+
+		// Read first line of __.PKGDEF data, so that line
+		// is once again the first line of the input.
+		if line, err = r.ReadSlice('\n'); err != nil {
+			err = fmt.Errorf("can't find export data (%v)", err)
+			return
+		}
+		size -= int64(len(line))
+	}
+
+	// Now at __.PKGDEF in archive or still at beginning of file.
+	// Either way, line should begin with "go object ".
+	if !strings.HasPrefix(string(line), "go object ") {
+		err = fmt.Errorf("not a Go object file")
+		return
+	}
+
+	// Skip over object header to export data.
+	// Begins after first line starting with $$.
+	for line[0] != '$' {
+		if line, err = r.ReadSlice('\n'); err != nil {
+			err = fmt.Errorf("can't find export data (%v)", err)
+			return
+		}
+		size -= int64(len(line))
+	}
+	hdr = string(line)
+	if size < 0 {
+		size = -1
+	}
+
+	return
+}
diff --git a/vendor/golang.org/x/tools/internal/gcimporter/gcimporter.go b/vendor/golang.org/x/tools/internal/gcimporter/gcimporter.go
new file mode 100644
index 00000000..0372fb3a
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/gcimporter.go
@@ -0,0 +1,265 @@
+// 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 reduced copy of $GOROOT/src/go/internal/gcimporter/gcimporter.go.
+
+// 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/internal/gcimporter"
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"go/build"
+	"go/token"
+	"go/types"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"sync"
+)
+
+const (
+	// Enable debug during development: it adds some additional checks, and
+	// prevents errors from being recovered.
+	debug = false
+
+	// If trace is set, debugging output is printed to std out.
+	trace = false
+)
+
+var exportMap sync.Map // package dir → func() (string, bool)
+
+// lookupGorootExport returns the location of the export data
+// (normally found in the build cache, but located in GOROOT/pkg
+// in prior Go releases) for the package located in pkgDir.
+//
+// (We use the package's directory instead of its import path
+// mainly to simplify handling of the packages in src/vendor
+// and cmd/vendor.)
+func lookupGorootExport(pkgDir string) (string, bool) {
+	f, ok := exportMap.Load(pkgDir)
+	if !ok {
+		var (
+			listOnce   sync.Once
+			exportPath string
+		)
+		f, _ = exportMap.LoadOrStore(pkgDir, func() (string, bool) {
+			listOnce.Do(func() {
+				cmd := exec.Command("go", "list", "-export", "-f", "{{.Export}}", pkgDir)
+				cmd.Dir = build.Default.GOROOT
+				var output []byte
+				output, err := cmd.Output()
+				if err != nil {
+					return
+				}
+
+				exports := strings.Split(string(bytes.TrimSpace(output)), "\n")
+				if len(exports) != 1 {
+					return
+				}
+
+				exportPath = exports[0]
+			})
+
+			return exportPath, exportPath != ""
+		})
+	}
+
+	return f.(func() (string, bool))()
+}
+
+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 == "" {
+			var ok bool
+			if bp.Goroot && bp.Dir != "" {
+				filename, ok = lookupGorootExport(bp.Dir)
+			}
+			if !ok {
+				id = path // make sure we have an id to print in error message
+				return
+			}
+		} else {
+			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)
+		}
+	}
+
+	if filename != "" {
+		if f, err := os.Stat(filename); err == nil && !f.IsDir() {
+			return
+		}
+	}
+
+	// try extensions
+	for _, ext := range pkgExts {
+		filename = noext + ext
+		if f, err := os.Stat(filename); err == nil && !f.IsDir() {
+			return
+		}
+	}
+
+	filename = "" // not found
+	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
+	var size int64
+	buf := bufio.NewReader(rc)
+	if hdr, size, err = FindExportData(buf); err != nil {
+		return
+	}
+
+	switch hdr {
+	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 {
+			switch data[0] {
+			case 'i':
+				_, pkg, err := IImportData(fset, packages, data[1:], id)
+				return pkg, err
+
+			case 'v', 'c', 'd':
+				_, pkg, err := BImportData(fset, packages, data, id)
+				return pkg, err
+
+			case 'u':
+				_, pkg, err := UImportData(fset, packages, data[1:size], id)
+				return pkg, err
+
+			default:
+				l := len(data)
+				if l > 10 {
+					l = 10
+				}
+				return nil, fmt.Errorf("unexpected export data with prefix %q for path %s", string(data[:l]), id)
+			}
+		}
+
+	default:
+		err = fmt.Errorf("unknown export data header: %q", hdr)
+	}
+
+	return
+}
+
+func deref(typ types.Type) types.Type {
+	if p, _ := typ.(*types.Pointer); p != nil {
+		return p.Elem()
+	}
+	return typ
+}
+
+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/internal/gcimporter/iexport.go b/vendor/golang.org/x/tools/internal/gcimporter/iexport.go
new file mode 100644
index 00000000..ba53cdcd
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/iexport.go
@@ -0,0 +1,1180 @@
+// 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"
+	"fmt"
+	"go/constant"
+	"go/token"
+	"go/types"
+	"io"
+	"math/big"
+	"reflect"
+	"sort"
+	"strconv"
+	"strings"
+
+	"golang.org/x/tools/internal/tokeninternal"
+	"golang.org/x/tools/internal/typeparams"
+)
+
+// IExportShallow encodes "shallow" export data for the specified package.
+//
+// No promises are made about the encoding other than that it can be
+// decoded by the same version of IIExportShallow. If you plan to save
+// export data in the file system, be sure to include a cryptographic
+// digest of the executable in the key to avoid version skew.
+func IExportShallow(fset *token.FileSet, pkg *types.Package) ([]byte, error) {
+	// In principle this operation can only fail if out.Write fails,
+	// but that's impossible for bytes.Buffer---and as a matter of
+	// fact iexportCommon doesn't even check for I/O errors.
+	// TODO(adonovan): handle I/O errors properly.
+	// TODO(adonovan): use byte slices throughout, avoiding copying.
+	const bundle, shallow = false, true
+	var out bytes.Buffer
+	err := iexportCommon(&out, fset, bundle, shallow, iexportVersion, []*types.Package{pkg})
+	return out.Bytes(), err
+}
+
+// IImportShallow decodes "shallow" types.Package data encoded by IExportShallow
+// in the same executable. This function cannot import data from
+// cmd/compile or gcexportdata.Write.
+func IImportShallow(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string, insert InsertType) (*types.Package, error) {
+	const bundle = false
+	pkgs, err := iimportCommon(fset, imports, data, bundle, path, insert)
+	if err != nil {
+		return nil, err
+	}
+	return pkgs[0], nil
+}
+
+// InsertType is the type of a function that creates a types.TypeName
+// object for a named type and inserts it into the scope of the
+// specified Package.
+type InsertType = func(pkg *types.Package, name string)
+
+// 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 {
+	const bundle, shallow = false, false
+	return iexportCommon(out, fset, bundle, shallow, iexportVersion, []*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 {
+	const bundle, shallow = true, false
+	return iexportCommon(out, fset, bundle, shallow, iexportVersion, pkgs)
+}
+
+func iexportCommon(out io.Writer, fset *token.FileSet, bundle, shallow bool, version int, 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,
+		version:     version,
+		shallow:     shallow,
+		allPkgs:     map[*types.Package]bool{},
+		stringIndex: map[string]uint64{},
+		declIndex:   map[types.Object]uint64{},
+		tparamNames: map[types.Object]string{},
+		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 token.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())
+	}
+
+	// Produce index of offset of each file record in files.
+	var files intWriter
+	var fileOffset []uint64 // fileOffset[i] is offset in files of file encoded as i
+	if p.shallow {
+		fileOffset = make([]uint64, len(p.fileInfos))
+		for i, info := range p.fileInfos {
+			fileOffset[i] = uint64(files.Len())
+			p.encodeFile(&files, info.file, info.needed)
+		}
+	}
+
+	// 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(uint64(p.version))
+	hdr.uint64(uint64(p.strings.Len()))
+	if p.shallow {
+		hdr.uint64(uint64(files.Len()))
+		hdr.uint64(uint64(len(fileOffset)))
+		for _, offset := range fileOffset {
+			hdr.uint64(offset)
+		}
+	}
+	hdr.uint64(dataLen)
+
+	// Flush output.
+	io.Copy(out, &hdr)
+	io.Copy(out, &p.strings)
+	if p.shallow {
+		io.Copy(out, &files)
+	}
+	io.Copy(out, &p.data0)
+
+	return nil
+}
+
+// encodeFile writes to w a representation of the file sufficient to
+// faithfully restore position information about all needed offsets.
+// Mutates the needed array.
+func (p *iexporter) encodeFile(w *intWriter, file *token.File, needed []uint64) {
+	_ = needed[0] // precondition: needed is non-empty
+
+	w.uint64(p.stringOff(file.Name()))
+
+	size := uint64(file.Size())
+	w.uint64(size)
+
+	// Sort the set of needed offsets. Duplicates are harmless.
+	sort.Slice(needed, func(i, j int) bool { return needed[i] < needed[j] })
+
+	lines := tokeninternal.GetLines(file) // byte offset of each line start
+	w.uint64(uint64(len(lines)))
+
+	// Rather than record the entire array of line start offsets,
+	// we save only a sparse list of (index, offset) pairs for
+	// the start of each line that contains a needed position.
+	var sparse [][2]int // (index, offset) pairs
+outer:
+	for i, lineStart := range lines {
+		lineEnd := size
+		if i < len(lines)-1 {
+			lineEnd = uint64(lines[i+1])
+		}
+		// Does this line contains a needed offset?
+		if needed[0] < lineEnd {
+			sparse = append(sparse, [2]int{i, lineStart})
+			for needed[0] < lineEnd {
+				needed = needed[1:]
+				if len(needed) == 0 {
+					break outer
+				}
+			}
+		}
+	}
+
+	// Delta-encode the columns.
+	w.uint64(uint64(len(sparse)))
+	var prev [2]int
+	for _, pair := range sparse {
+		w.uint64(uint64(pair[0] - prev[0]))
+		w.uint64(uint64(pair[1] - prev[1]))
+		prev = pair
+	}
+}
+
+// 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) {
+	type pkgObj struct {
+		obj  types.Object
+		name string // qualified name; differs from obj.Name for type params
+	}
+	// Build a map from packages to objects from that package.
+	pkgObjs := map[*types.Package][]pkgObj{}
+
+	// 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 {
+		name := w.p.exportName(obj)
+		pkgObjs[obj.Pkg()] = append(pkgObjs[obj.Pkg()], pkgObj{obj, name})
+	}
+
+	var pkgs []*types.Package
+	for pkg, objs := range pkgObjs {
+		pkgs = append(pkgs, pkg)
+
+		sort.Slice(objs, func(i, j int) bool {
+			return objs[i].name < objs[j].name
+		})
+	}
+
+	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(obj.name)
+			w.uint64(index[obj.obj])
+		}
+	}
+}
+
+// exportName returns the 'exported' name of an object. It differs from
+// obj.Name() only for type parameters (see tparamExportName for details).
+func (p *iexporter) exportName(obj types.Object) (res string) {
+	if name := p.tparamNames[obj]; name != "" {
+		return name
+	}
+	return obj.Name()
+}
+
+type iexporter struct {
+	fset    *token.FileSet
+	out     *bytes.Buffer
+	version int
+
+	shallow  bool           // don't put types from other packages in the index
+	localpkg *types.Package // (nil in bundle mode)
+
+	// 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
+
+	// In shallow mode, object positions are encoded as (file, offset).
+	// Each file is recorded as a line-number table.
+	// Only the lines of needed positions are saved faithfully.
+	fileInfo  map[*token.File]uint64 // value is index in fileInfos
+	fileInfos []*filePositions
+
+	data0       intWriter
+	declIndex   map[types.Object]uint64
+	tparamNames map[types.Object]string // typeparam->exported name
+	typIndex    map[types.Type]uint64
+
+	indent int // for tracing support
+}
+
+type filePositions struct {
+	file   *token.File
+	needed []uint64 // unordered list of needed file offsets
+}
+
+func (p *iexporter) trace(format string, args ...interface{}) {
+	if !trace {
+		// Call sites should also be guarded, but having this check here allows
+		// easily enabling/disabling debug trace statements.
+		return
+	}
+	fmt.Printf(strings.Repeat("..", p.indent)+format+"\n", args...)
+}
+
+// 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
+}
+
+// fileIndexAndOffset returns the index of the token.File and the byte offset of pos within it.
+func (p *iexporter) fileIndexAndOffset(file *token.File, pos token.Pos) (uint64, uint64) {
+	index, ok := p.fileInfo[file]
+	if !ok {
+		index = uint64(len(p.fileInfo))
+		p.fileInfos = append(p.fileInfos, &filePositions{file: file})
+		if p.fileInfo == nil {
+			p.fileInfo = make(map[*token.File]uint64)
+		}
+		p.fileInfo[file] = index
+	}
+	// Record each needed offset.
+	info := p.fileInfos[index]
+	offset := uint64(file.Offset(pos))
+	info.needed = append(info.needed, offset)
+
+	return index, offset
+}
+
+// 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.
+	// Caller should not ask us to do export it.
+	if obj.Pkg() == types.Unsafe {
+		panic("cannot export package unsafe")
+	}
+
+	// Shallow export data: don't index decls from other packages.
+	if p.shallow && obj.Pkg() != p.localpkg {
+		return
+	}
+
+	if _, ok := p.declIndex[obj]; ok {
+		return
+	}
+
+	p.declIndex[obj] = ^uint64(0) // mark obj 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) {
+	if trace {
+		p.trace("exporting decl %v (%T)", obj, obj)
+		p.indent++
+		defer func() {
+			p.indent--
+			p.trace("=> %s", obj)
+		}()
+	}
+	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 {
+			// We shouldn't see methods in the package scope,
+			// but the type checker may repair "func () F() {}"
+			// to "func (Invalid) F()" and then treat it like "func F()",
+			// so allow that. See golang/go#57729.
+			if sig.Recv().Type() != types.Typ[types.Invalid] {
+				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 where they are used.
+		//
+		// While importing the type parameters, tparamList computes and records
+		// their export name, so that it can be later used when writing the index.
+		if tparams := typeparams.ForSignature(sig); tparams.Len() > 0 {
+			w.tparamList(obj.Name(), 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())
+			constraint := tparam.Constraint()
+			if p.version >= iexportVersionGo1_18 {
+				implicit := false
+				if iface, _ := constraint.(*types.Interface); iface != nil {
+					implicit = typeparams.IsImplicit(iface)
+				}
+				w.bool(implicit)
+			}
+			w.typ(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 {
+			// While importing the type parameters, tparamList computes and records
+			// their export name, so that it can be later used when writing the index.
+			w.tparamList(obj.Name(), 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)
+
+			// Receiver type parameters are type arguments of the receiver type, so
+			// their name must be qualified before exporting recv.
+			if rparams := typeparams.RecvTypeParams(sig); rparams.Len() > 0 {
+				prefix := obj.Name() + "." + m.Name()
+				for i := 0; i < rparams.Len(); i++ {
+					rparam := rparams.At(i)
+					name := tparamExportName(prefix, rparam)
+					w.p.tparamNames[rparam.Obj()] = name
+				}
+			}
+			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 w.p.shallow {
+		w.posV2(pos)
+	} else if w.p.version >= iexportVersionPosCol {
+		w.posV1(pos)
+	} else {
+		w.posV0(pos)
+	}
+}
+
+// posV2 encoding (used only in shallow mode) records positions as
+// (file, offset), where file is the index in the token.File table
+// (which records the file name and newline offsets) and offset is a
+// byte offset. It effectively ignores //line directives.
+func (w *exportWriter) posV2(pos token.Pos) {
+	if pos == token.NoPos {
+		w.uint64(0)
+		return
+	}
+	file := w.p.fset.File(pos) // fset must be non-nil
+	index, offset := w.p.fileIndexAndOffset(file, pos)
+	w.uint64(1 + index)
+	w.uint64(offset)
+}
+
+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) qualifiedType(obj *types.TypeName) {
+	name := w.p.exportName(obj)
+
+	// Ensure any referenced declarations are written out too.
+	w.p.pushDecl(obj)
+	w.string(name)
+	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) {
+	if trace {
+		w.p.trace("exporting type %s (%T)", t, t)
+		w.p.indent++
+		defer func() {
+			w.p.indent--
+			w.p.trace("=> %s", t)
+		}()
+	}
+	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.qualifiedType(t.Obj())
+
+	case *typeparams.TypeParam:
+		w.startType(typeParamType)
+		w.qualifiedType(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)
+		n := t.NumFields()
+		if n > 0 {
+			w.setPkg(t.Field(0).Pkg(), true) // qualifying package for field objects
+		} else {
+			w.setPkg(pkg, true)
+		}
+		w.uint64(uint64(n))
+		for i := 0; i < n; i++ {
+			f := t.Field(i)
+			w.pos(f.Pos())
+			w.string(f.Name()) // unexported fields implicitly qualified by prior setPkg
+			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(prefix string, list *typeparams.TypeParamList, pkg *types.Package) {
+	ll := uint64(list.Len())
+	w.uint64(ll)
+	for i := 0; i < list.Len(); i++ {
+		tparam := list.At(i)
+		// Set the type parameter exportName before exporting its type.
+		exportName := tparamExportName(prefix, tparam)
+		w.p.tparamNames[tparam.Obj()] = exportName
+		w.typ(list.At(i), pkg)
+	}
+}
+
+const blankMarker = "$"
+
+// tparamExportName returns the 'exported' name of a type parameter, which
+// differs from its actual object name: it is prefixed with a qualifier, and
+// blank type parameter names are disambiguated by their index in the type
+// parameter list.
+func tparamExportName(prefix string, tparam *typeparams.TypeParam) string {
+	assert(prefix != "")
+	name := tparam.Obj().Name()
+	if name == "_" {
+		name = blankMarker + strconv.Itoa(tparam.Index())
+	}
+	return prefix + "." + name
+}
+
+// tparamName returns the real name of a type parameter, after stripping its
+// qualifying prefix and reverting blank-name encoding. See tparamExportName
+// for details.
+func tparamName(exportName string) string {
+	// Remove the "path" from the type param name that makes it unique.
+	ix := strings.LastIndex(exportName, ".")
+	if ix < 0 {
+		errorf("malformed type parameter export name %s: missing prefix", exportName)
+	}
+	name := exportName[ix+1:]
+	if strings.HasPrefix(name, blankMarker) {
+		return "_"
+	}
+	return name
+}
+
+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)
+	if w.p.version >= iexportVersionGo1_18 {
+		w.int64(int64(v.Kind()))
+	}
+
+	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 := obj.Name()
+	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/internal/gcimporter/iimport.go b/vendor/golang.org/x/tools/internal/gcimporter/iimport.go
new file mode 100644
index 00000000..448f903e
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/iimport.go
@@ -0,0 +1,976 @@
+// 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"
+	"math/big"
+	"sort"
+	"strings"
+
+	"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
+	iexportVersionGo1_18   = 2
+	iexportVersionGenerics = 2
+
+	iexportVersionCurrent = 2
+)
+
+type ident struct {
+	pkg  *types.Package
+	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, nil)
+	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, "", nil)
+}
+
+func iimportCommon(fset *token.FileSet, imports map[string]*types.Package, data []byte, bundle bool, path string, insert InsertType) (pkgs []*types.Package, err error) {
+	const currentVersion = iexportVersionCurrent
+	version := int64(-1)
+	if !debug {
+		defer func() {
+			if e := recover(); e != nil {
+				if bundle {
+					err = fmt.Errorf("%v", e)
+				} else 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 iexportVersionGo1_18, iexportVersionPosCol, iexportVersionGo1_11:
+	default:
+		if version > iexportVersionGo1_18 {
+			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())
+	var fLen int64
+	var fileOffset []uint64
+	if insert != nil {
+		// Shallow mode uses a different position encoding.
+		fLen = int64(r.uint64())
+		fileOffset = make([]uint64, r.uint64())
+		for i := range fileOffset {
+			fileOffset[i] = r.uint64()
+		}
+	}
+	dLen := int64(r.uint64())
+
+	whence, _ := r.Seek(0, io.SeekCurrent)
+	stringData := data[whence : whence+sLen]
+	fileData := data[whence+sLen : whence+sLen+fLen]
+	declData := data[whence+sLen+fLen : whence+sLen+fLen+dLen]
+	r.Seek(sLen+fLen+dLen, io.SeekCurrent)
+
+	p := iimporter{
+		version: int(version),
+		ipath:   path,
+		insert:  insert,
+
+		stringData:  stringData,
+		stringCache: make(map[uint64]string),
+		fileOffset:  fileOffset,
+		fileData:    fileData,
+		fileCache:   make([]*token.File, len(fileOffset)),
+		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.
+		tparamIndex: make(map[ident]types.Type),
+
+		fake: fakeFileSet{
+			fset:  fset,
+			files: make(map[string]*fileInfo),
+		},
+	}
+	defer p.fake.setLines() // set lines for files in fset
+
+	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)
+		}
+		if i == 0 && !bundle {
+			p.localpkg = pkg
+		}
+
+		p.pkgCache[pkgPathOff] = pkg
+
+		// Read index for package.
+		nameIndex := make(map[string]uint64)
+		nSyms := r.uint64()
+		// In shallow mode we don't expect an index for other packages.
+		assert(nSyms == 0 || p.localpkg == pkg || p.insert == nil)
+		for ; 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()
+	}
+
+	// SetConstraint can't be called if the constraint type is not yet complete.
+	// When type params are created in the 'P' case of (*importReader).obj(),
+	// the associated constraint type may not be complete due to recursion.
+	// Therefore, we defer calling SetConstraint there, and call it here instead
+	// after all types are complete.
+	for _, d := range p.later {
+		typeparams.SetTypeParamConstraint(d.t, d.constraint)
+	}
+
+	for _, typ := range p.interfaceList {
+		typ.Complete()
+	}
+
+	return pkgs, nil
+}
+
+type setConstraintArgs struct {
+	t          *typeparams.TypeParam
+	constraint types.Type
+}
+
+type iimporter struct {
+	version int
+	ipath   string
+
+	localpkg *types.Package
+	insert   func(pkg *types.Package, name string) // "shallow" mode only
+
+	stringData  []byte
+	stringCache map[uint64]string
+	fileOffset  []uint64 // fileOffset[i] is offset in fileData for info about file encoded as i
+	fileData    []byte
+	fileCache   []*token.File // memoized decoding of file encoded as i
+	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
+
+	// Arguments for calls to SetConstraint that are deferred due to recursive types
+	later []setConstraintArgs
+
+	indent int // for tracing support
+}
+
+func (p *iimporter) trace(format string, args ...interface{}) {
+	if !trace {
+		// Call sites should also be guarded, but having this check here allows
+		// easily enabling/disabling debug trace statements.
+		return
+	}
+	fmt.Printf(strings.Repeat("..", p.indent)+format+"\n", args...)
+}
+
+func (p *iimporter) doDecl(pkg *types.Package, name string) {
+	if debug {
+		p.trace("import decl %s", name)
+		p.indent++
+		defer func() {
+			p.indent--
+			p.trace("=> %s", name)
+		}()
+	}
+	// 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 {
+		// In "shallow" mode, call back to the application to
+		// find the object and insert it into the package scope.
+		if p.insert != nil {
+			assert(pkg != p.localpkg)
+			p.insert(pkg, name) // "can't fail"
+			return
+		}
+		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) fileAt(index uint64) *token.File {
+	file := p.fileCache[index]
+	if file == nil {
+		off := p.fileOffset[index]
+		file = p.decodeFile(intReader{bytes.NewReader(p.fileData[off:]), p.ipath})
+		p.fileCache[index] = file
+	}
+	return file
+}
+
+func (p *iimporter) decodeFile(rd intReader) *token.File {
+	filename := p.stringAt(rd.uint64())
+	size := int(rd.uint64())
+	file := p.fake.fset.AddFile(filename, -1, size)
+
+	// SetLines requires a nondecreasing sequence.
+	// Because it is common for clients to derive the interval
+	// [start, start+len(name)] from a start position, and we
+	// want to ensure that the end offset is on the same line,
+	// we fill in the gaps of the sparse encoding with values
+	// that strictly increase by the largest possible amount.
+	// This allows us to avoid having to record the actual end
+	// offset of each needed line.
+
+	lines := make([]int, int(rd.uint64()))
+	var index, offset int
+	for i, n := 0, int(rd.uint64()); i < n; i++ {
+		index += int(rd.uint64())
+		offset += int(rd.uint64())
+		lines[index] = offset
+
+		// Ensure monotonicity between points.
+		for j := index - 1; j > 0 && lines[j] == 0; j-- {
+			lines[j] = lines[j+1] - 1
+		}
+	}
+
+	// Ensure monotonicity after last point.
+	for j := len(lines) - 1; j > 0 && lines[j] == 0; j-- {
+		size--
+		lines[j] = size
+	}
+
+	if !file.SetLines(lines) {
+		errorf("SetLines failed: %d", lines) // can't happen
+	}
+	return file
+}
+
+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 && canReuse(base, 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 canReuse(base, t) {
+		p.typCache[off] = t
+	}
+	return t
+}
+
+// canReuse reports whether the type rhs on the RHS of the declaration for def
+// may be re-used.
+//
+// Specifically, if def is non-nil and rhs is an interface type with methods, it
+// may not be re-used because we have a convention of setting the receiver type
+// for interface methods to def.
+func canReuse(def *types.Named, rhs types.Type) bool {
+	if def == nil {
+		return true
+	}
+	iface, _ := rhs.(*types.Interface)
+	if iface == nil {
+		return true
+	}
+	// Don't use iface.Empty() here as iface may not be complete.
+	return iface.NumEmbeddeds() == 0 && iface.NumExplicitMethods() == 0
+}
+
+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, nil, 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()
+
+				// 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).
+				base := baseType(recv.Type())
+				assert(base != nil)
+				targs := typeparams.NamedTypeArgs(base)
+				var rparams []*typeparams.TypeParam
+				if targs.Len() > 0 {
+					rparams = make([]*typeparams.TypeParam, targs.Len())
+					for i := range rparams {
+						rparams[i] = targs.At(i).(*typeparams.TypeParam)
+					}
+				}
+				msig := r.signature(recv, rparams, nil)
+
+				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.version < iexportVersionGenerics {
+			errorf("unexpected type param type")
+		}
+		name0 := tparamName(name)
+		tn := types.NewTypeName(pos, r.currPkg, name0, nil)
+		t := typeparams.NewTypeParam(tn, nil)
+
+		// 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}
+		r.p.tparamIndex[id] = t
+		var implicit bool
+		if r.p.version >= iexportVersionGo1_18 {
+			implicit = r.bool()
+		}
+		constraint := r.typ()
+		if implicit {
+			iface, _ := constraint.(*types.Interface)
+			if iface == nil {
+				errorf("non-interface constraint marked implicit")
+			}
+			typeparams.MarkImplicit(iface)
+		}
+		// The constraint type may not be complete, if we
+		// are in the middle of a type recursion involving type
+		// constraints. So, we defer SetConstraint until we have
+		// completely set up all types in ImportData.
+		r.p.later = append(r.p.later, setConstraintArgs{t: t, constraint: constraint})
+
+	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()
+	if r.p.version >= iexportVersionGo1_18 {
+		// TODO: add support for using the kind.
+		_ = constant.Kind(r.int64())
+	}
+
+	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:
+		var x big.Int
+		r.mpint(&x, b)
+		val = constant.Make(&x)
+
+	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(x *big.Int, typ *types.Basic) {
+	signed, maxBytes := intSize(typ)
+
+	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
+			}
+		}
+		x.SetInt64(v)
+		return
+	}
+
+	v := -n
+	if signed {
+		v = -(n &^ 1) >> 1
+	}
+	if v < 1 || uint(v) > maxBytes {
+		errorf("weird decoding: %v, %v => %v", n, signed, v)
+	}
+	b := make([]byte, v)
+	io.ReadFull(&r.declReader, b)
+	x.SetBytes(b)
+	if signed && n&1 != 0 {
+		x.Neg(x)
+	}
+}
+
+func (r *importReader) mpfloat(typ *types.Basic) constant.Value {
+	var mant big.Int
+	r.mpint(&mant, typ)
+	var f big.Float
+	f.SetInt(&mant)
+	if f.Sign() != 0 {
+		f.SetMantExp(&f, int(r.int64()))
+	}
+	return constant.Make(&f)
+}
+
+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.insert != nil { // shallow mode
+		return r.posv2()
+	}
+	if r.p.version >= 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) posv2() token.Pos {
+	file := r.uint64()
+	if file == 0 {
+		return token.NoPos
+	}
+	tf := r.p.fileAt(file - 1)
+	return tf.Pos(int(r.uint64()))
+}
+
+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) (res types.Type) {
+	k := r.kind()
+	if debug {
+		r.p.trace("importing type %d (base: %s)", k, base)
+		r.p.indent++
+		defer func() {
+			r.p.indent--
+			r.p.trace("=> %s", res)
+		}()
+	}
+	switch 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, nil, 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, nil, nil)
+			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.version < iexportVersionGenerics {
+			errorf("unexpected type param type")
+		}
+		pkg, name := r.qualifiedIdent()
+		id := ident{pkg, 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.version < 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.version < 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, rparams []*typeparams.TypeParam, tparams []*typeparams.TypeParam) *types.Signature {
+	params := r.paramList()
+	results := r.paramList()
+	variadic := params.Len() > 0 && r.bool()
+	return typeparams.NewSignatureType(recv, rparams, tparams, 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
+}
diff --git a/vendor/golang.org/x/tools/internal/gcimporter/newInterface10.go b/vendor/golang.org/x/tools/internal/gcimporter/newInterface10.go
new file mode 100644
index 00000000..8b163e3d
--- /dev/null
+++ b/vendor/golang.org/x/tools/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/internal/gcimporter/newInterface11.go b/vendor/golang.org/x/tools/internal/gcimporter/newInterface11.go
new file mode 100644
index 00000000..49984f40
--- /dev/null
+++ b/vendor/golang.org/x/tools/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/internal/gcimporter/support_go117.go b/vendor/golang.org/x/tools/internal/gcimporter/support_go117.go
new file mode 100644
index 00000000..d892273e
--- /dev/null
+++ b/vendor/golang.org/x/tools/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 !go1.18
+// +build !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/internal/gcimporter/support_go118.go b/vendor/golang.org/x/tools/internal/gcimporter/support_go118.go
new file mode 100644
index 00000000..edbe6ea7
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/support_go118.go
@@ -0,0 +1,37 @@
+// 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 go1.18
+// +build 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(),
+
+		// any
+		types.Universe.Lookup("any").Type(),
+	}
+}
+
+// See cmd/compile/internal/types.SplitVargenSuffix.
+func splitVargenSuffix(name string) (base, suffix string) {
+	i := len(name)
+	for i > 0 && name[i-1] >= '0' && name[i-1] <= '9' {
+		i--
+	}
+	const dot = "·"
+	if i >= len(dot) && name[i-len(dot):i] == dot {
+		i -= len(dot)
+		return name[:i], name[i:]
+	}
+	return name, ""
+}
diff --git a/vendor/golang.org/x/tools/internal/gcimporter/unified_no.go b/vendor/golang.org/x/tools/internal/gcimporter/unified_no.go
new file mode 100644
index 00000000..286bf445
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/unified_no.go
@@ -0,0 +1,10 @@
+// Copyright 2022 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 !(go1.18 && goexperiment.unified)
+// +build !go1.18 !goexperiment.unified
+
+package gcimporter
+
+const unifiedIR = false
diff --git a/vendor/golang.org/x/tools/internal/gcimporter/unified_yes.go b/vendor/golang.org/x/tools/internal/gcimporter/unified_yes.go
new file mode 100644
index 00000000..b5d69ffb
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/unified_yes.go
@@ -0,0 +1,10 @@
+// Copyright 2022 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 go1.18 && goexperiment.unified
+// +build go1.18,goexperiment.unified
+
+package gcimporter
+
+const unifiedIR = true
diff --git a/vendor/golang.org/x/tools/internal/gcimporter/ureader_no.go b/vendor/golang.org/x/tools/internal/gcimporter/ureader_no.go
new file mode 100644
index 00000000..8eb20729
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/ureader_no.go
@@ -0,0 +1,19 @@
+// Copyright 2022 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 !go1.18
+// +build !go1.18
+
+package gcimporter
+
+import (
+	"fmt"
+	"go/token"
+	"go/types"
+)
+
+func UImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (_ int, pkg *types.Package, err error) {
+	err = fmt.Errorf("go/tools compiled with a Go version earlier than 1.18 cannot read unified IR export data")
+	return
+}
diff --git a/vendor/golang.org/x/tools/internal/gcimporter/ureader_yes.go b/vendor/golang.org/x/tools/internal/gcimporter/ureader_yes.go
new file mode 100644
index 00000000..b285a11c
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gcimporter/ureader_yes.go
@@ -0,0 +1,738 @@
+// 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.
+
+// Derived from go/internal/gcimporter/ureader.go
+
+//go:build go1.18
+// +build go1.18
+
+package gcimporter
+
+import (
+	"go/token"
+	"go/types"
+	"strings"
+
+	"golang.org/x/tools/internal/pkgbits"
+)
+
+// A pkgReader holds the shared state for reading a unified IR package
+// description.
+type pkgReader struct {
+	pkgbits.PkgDecoder
+
+	fake fakeFileSet
+
+	ctxt    *types.Context
+	imports map[string]*types.Package // previously imported packages, indexed by path
+
+	// lazily initialized arrays corresponding to the unified IR
+	// PosBase, Pkg, and Type sections, respectively.
+	posBases []string // position bases (i.e., file names)
+	pkgs     []*types.Package
+	typs     []types.Type
+
+	// laterFns holds functions that need to be invoked at the end of
+	// import reading.
+	laterFns []func()
+	// laterFors is used in case of 'type A B' to ensure that B is processed before A.
+	laterFors map[types.Type]int
+
+	// ifaces holds a list of constructed Interfaces, which need to have
+	// Complete called after importing is done.
+	ifaces []*types.Interface
+}
+
+// later adds a function to be invoked at the end of import reading.
+func (pr *pkgReader) later(fn func()) {
+	pr.laterFns = append(pr.laterFns, fn)
+}
+
+// See cmd/compile/internal/noder.derivedInfo.
+type derivedInfo struct {
+	idx    pkgbits.Index
+	needed bool
+}
+
+// See cmd/compile/internal/noder.typeInfo.
+type typeInfo struct {
+	idx     pkgbits.Index
+	derived bool
+}
+
+func UImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (_ int, pkg *types.Package, err error) {
+	s := string(data)
+	s = s[:strings.LastIndex(s, "\n$$\n")]
+	input := pkgbits.NewPkgDecoder(path, s)
+	pkg = readUnifiedPackage(fset, nil, imports, input)
+	return
+}
+
+// laterFor adds a function to be invoked at the end of import reading, and records the type that function is finishing.
+func (pr *pkgReader) laterFor(t types.Type, fn func()) {
+	if pr.laterFors == nil {
+		pr.laterFors = make(map[types.Type]int)
+	}
+	pr.laterFors[t] = len(pr.laterFns)
+	pr.laterFns = append(pr.laterFns, fn)
+}
+
+// readUnifiedPackage reads a package description from the given
+// unified IR export data decoder.
+func readUnifiedPackage(fset *token.FileSet, ctxt *types.Context, imports map[string]*types.Package, input pkgbits.PkgDecoder) *types.Package {
+	pr := pkgReader{
+		PkgDecoder: input,
+
+		fake: fakeFileSet{
+			fset:  fset,
+			files: make(map[string]*fileInfo),
+		},
+
+		ctxt:    ctxt,
+		imports: imports,
+
+		posBases: make([]string, input.NumElems(pkgbits.RelocPosBase)),
+		pkgs:     make([]*types.Package, input.NumElems(pkgbits.RelocPkg)),
+		typs:     make([]types.Type, input.NumElems(pkgbits.RelocType)),
+	}
+	defer pr.fake.setLines()
+
+	r := pr.newReader(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)
+	pkg := r.pkg()
+	r.Bool() // has init
+
+	for i, n := 0, r.Len(); i < n; i++ {
+		// As if r.obj(), but avoiding the Scope.Lookup call,
+		// to avoid eager loading of imports.
+		r.Sync(pkgbits.SyncObject)
+		assert(!r.Bool())
+		r.p.objIdx(r.Reloc(pkgbits.RelocObj))
+		assert(r.Len() == 0)
+	}
+
+	r.Sync(pkgbits.SyncEOF)
+
+	for _, fn := range pr.laterFns {
+		fn()
+	}
+
+	for _, iface := range pr.ifaces {
+		iface.Complete()
+	}
+
+	pkg.MarkComplete()
+	return pkg
+}
+
+// A reader holds the state for reading a single unified IR element
+// within a package.
+type reader struct {
+	pkgbits.Decoder
+
+	p *pkgReader
+
+	dict *readerDict
+}
+
+// A readerDict holds the state for type parameters that parameterize
+// the current unified IR element.
+type readerDict struct {
+	// bounds is a slice of typeInfos corresponding to the underlying
+	// bounds of the element's type parameters.
+	bounds []typeInfo
+
+	// tparams is a slice of the constructed TypeParams for the element.
+	tparams []*types.TypeParam
+
+	// devived is a slice of types derived from tparams, which may be
+	// instantiated while reading the current element.
+	derived      []derivedInfo
+	derivedTypes []types.Type // lazily instantiated from derived
+}
+
+func (pr *pkgReader) newReader(k pkgbits.RelocKind, idx pkgbits.Index, marker pkgbits.SyncMarker) *reader {
+	return &reader{
+		Decoder: pr.NewDecoder(k, idx, marker),
+		p:       pr,
+	}
+}
+
+func (pr *pkgReader) tempReader(k pkgbits.RelocKind, idx pkgbits.Index, marker pkgbits.SyncMarker) *reader {
+	return &reader{
+		Decoder: pr.TempDecoder(k, idx, marker),
+		p:       pr,
+	}
+}
+
+func (pr *pkgReader) retireReader(r *reader) {
+	pr.RetireDecoder(&r.Decoder)
+}
+
+// @@@ Positions
+
+func (r *reader) pos() token.Pos {
+	r.Sync(pkgbits.SyncPos)
+	if !r.Bool() {
+		return token.NoPos
+	}
+
+	// TODO(mdempsky): Delta encoding.
+	posBase := r.posBase()
+	line := r.Uint()
+	col := r.Uint()
+	return r.p.fake.pos(posBase, int(line), int(col))
+}
+
+func (r *reader) posBase() string {
+	return r.p.posBaseIdx(r.Reloc(pkgbits.RelocPosBase))
+}
+
+func (pr *pkgReader) posBaseIdx(idx pkgbits.Index) string {
+	if b := pr.posBases[idx]; b != "" {
+		return b
+	}
+
+	var filename string
+	{
+		r := pr.tempReader(pkgbits.RelocPosBase, idx, pkgbits.SyncPosBase)
+
+		// Within types2, position bases have a lot more details (e.g.,
+		// keeping track of where //line directives appeared exactly).
+		//
+		// For go/types, we just track the file name.
+
+		filename = r.String()
+
+		if r.Bool() { // file base
+			// Was: "b = token.NewTrimmedFileBase(filename, true)"
+		} else { // line base
+			pos := r.pos()
+			line := r.Uint()
+			col := r.Uint()
+
+			// Was: "b = token.NewLineBase(pos, filename, true, line, col)"
+			_, _, _ = pos, line, col
+		}
+		pr.retireReader(r)
+	}
+	b := filename
+	pr.posBases[idx] = b
+	return b
+}
+
+// @@@ Packages
+
+func (r *reader) pkg() *types.Package {
+	r.Sync(pkgbits.SyncPkg)
+	return r.p.pkgIdx(r.Reloc(pkgbits.RelocPkg))
+}
+
+func (pr *pkgReader) pkgIdx(idx pkgbits.Index) *types.Package {
+	// TODO(mdempsky): Consider using some non-nil pointer to indicate
+	// the universe scope, so we don't need to keep re-reading it.
+	if pkg := pr.pkgs[idx]; pkg != nil {
+		return pkg
+	}
+
+	pkg := pr.newReader(pkgbits.RelocPkg, idx, pkgbits.SyncPkgDef).doPkg()
+	pr.pkgs[idx] = pkg
+	return pkg
+}
+
+func (r *reader) doPkg() *types.Package {
+	path := r.String()
+	switch path {
+	case "":
+		path = r.p.PkgPath()
+	case "builtin":
+		return nil // universe
+	case "unsafe":
+		return types.Unsafe
+	}
+
+	if pkg := r.p.imports[path]; pkg != nil {
+		return pkg
+	}
+
+	name := r.String()
+
+	pkg := types.NewPackage(path, name)
+	r.p.imports[path] = pkg
+
+	imports := make([]*types.Package, r.Len())
+	for i := range imports {
+		imports[i] = r.pkg()
+	}
+	pkg.SetImports(flattenImports(imports))
+
+	return pkg
+}
+
+// flattenImports returns the transitive closure of all imported
+// packages rooted from pkgs.
+func flattenImports(pkgs []*types.Package) []*types.Package {
+	var res []*types.Package
+	seen := make(map[*types.Package]struct{})
+	for _, pkg := range pkgs {
+		if _, ok := seen[pkg]; ok {
+			continue
+		}
+		seen[pkg] = struct{}{}
+		res = append(res, pkg)
+
+		// pkg.Imports() is already flattened.
+		for _, pkg := range pkg.Imports() {
+			if _, ok := seen[pkg]; ok {
+				continue
+			}
+			seen[pkg] = struct{}{}
+			res = append(res, pkg)
+		}
+	}
+	return res
+}
+
+// @@@ Types
+
+func (r *reader) typ() types.Type {
+	return r.p.typIdx(r.typInfo(), r.dict)
+}
+
+func (r *reader) typInfo() typeInfo {
+	r.Sync(pkgbits.SyncType)
+	if r.Bool() {
+		return typeInfo{idx: pkgbits.Index(r.Len()), derived: true}
+	}
+	return typeInfo{idx: r.Reloc(pkgbits.RelocType), derived: false}
+}
+
+func (pr *pkgReader) typIdx(info typeInfo, dict *readerDict) types.Type {
+	idx := info.idx
+	var where *types.Type
+	if info.derived {
+		where = &dict.derivedTypes[idx]
+		idx = dict.derived[idx].idx
+	} else {
+		where = &pr.typs[idx]
+	}
+
+	if typ := *where; typ != nil {
+		return typ
+	}
+
+	var typ types.Type
+	{
+		r := pr.tempReader(pkgbits.RelocType, idx, pkgbits.SyncTypeIdx)
+		r.dict = dict
+
+		typ = r.doTyp()
+		assert(typ != nil)
+		pr.retireReader(r)
+	}
+	// See comment in pkgReader.typIdx explaining how this happens.
+	if prev := *where; prev != nil {
+		return prev
+	}
+
+	*where = typ
+	return typ
+}
+
+func (r *reader) doTyp() (res types.Type) {
+	switch tag := pkgbits.CodeType(r.Code(pkgbits.SyncType)); tag {
+	default:
+		errorf("unhandled type tag: %v", tag)
+		panic("unreachable")
+
+	case pkgbits.TypeBasic:
+		return types.Typ[r.Len()]
+
+	case pkgbits.TypeNamed:
+		obj, targs := r.obj()
+		name := obj.(*types.TypeName)
+		if len(targs) != 0 {
+			t, _ := types.Instantiate(r.p.ctxt, name.Type(), targs, false)
+			return t
+		}
+		return name.Type()
+
+	case pkgbits.TypeTypeParam:
+		return r.dict.tparams[r.Len()]
+
+	case pkgbits.TypeArray:
+		len := int64(r.Uint64())
+		return types.NewArray(r.typ(), len)
+	case pkgbits.TypeChan:
+		dir := types.ChanDir(r.Len())
+		return types.NewChan(dir, r.typ())
+	case pkgbits.TypeMap:
+		return types.NewMap(r.typ(), r.typ())
+	case pkgbits.TypePointer:
+		return types.NewPointer(r.typ())
+	case pkgbits.TypeSignature:
+		return r.signature(nil, nil, nil)
+	case pkgbits.TypeSlice:
+		return types.NewSlice(r.typ())
+	case pkgbits.TypeStruct:
+		return r.structType()
+	case pkgbits.TypeInterface:
+		return r.interfaceType()
+	case pkgbits.TypeUnion:
+		return r.unionType()
+	}
+}
+
+func (r *reader) structType() *types.Struct {
+	fields := make([]*types.Var, r.Len())
+	var tags []string
+	for i := range fields {
+		pos := r.pos()
+		pkg, name := r.selector()
+		ftyp := r.typ()
+		tag := r.String()
+		embedded := r.Bool()
+
+		fields[i] = types.NewField(pos, pkg, name, ftyp, embedded)
+		if tag != "" {
+			for len(tags) < i {
+				tags = append(tags, "")
+			}
+			tags = append(tags, tag)
+		}
+	}
+	return types.NewStruct(fields, tags)
+}
+
+func (r *reader) unionType() *types.Union {
+	terms := make([]*types.Term, r.Len())
+	for i := range terms {
+		terms[i] = types.NewTerm(r.Bool(), r.typ())
+	}
+	return types.NewUnion(terms)
+}
+
+func (r *reader) interfaceType() *types.Interface {
+	methods := make([]*types.Func, r.Len())
+	embeddeds := make([]types.Type, r.Len())
+	implicit := len(methods) == 0 && len(embeddeds) == 1 && r.Bool()
+
+	for i := range methods {
+		pos := r.pos()
+		pkg, name := r.selector()
+		mtyp := r.signature(nil, nil, nil)
+		methods[i] = types.NewFunc(pos, pkg, name, mtyp)
+	}
+
+	for i := range embeddeds {
+		embeddeds[i] = r.typ()
+	}
+
+	iface := types.NewInterfaceType(methods, embeddeds)
+	if implicit {
+		iface.MarkImplicit()
+	}
+
+	// We need to call iface.Complete(), but if there are any embedded
+	// defined types, then we may not have set their underlying
+	// interface type yet. So we need to defer calling Complete until
+	// after we've called SetUnderlying everywhere.
+	//
+	// TODO(mdempsky): After CL 424876 lands, it should be safe to call
+	// iface.Complete() immediately.
+	r.p.ifaces = append(r.p.ifaces, iface)
+
+	return iface
+}
+
+func (r *reader) signature(recv *types.Var, rtparams, tparams []*types.TypeParam) *types.Signature {
+	r.Sync(pkgbits.SyncSignature)
+
+	params := r.params()
+	results := r.params()
+	variadic := r.Bool()
+
+	return types.NewSignatureType(recv, rtparams, tparams, params, results, variadic)
+}
+
+func (r *reader) params() *types.Tuple {
+	r.Sync(pkgbits.SyncParams)
+
+	params := make([]*types.Var, r.Len())
+	for i := range params {
+		params[i] = r.param()
+	}
+
+	return types.NewTuple(params...)
+}
+
+func (r *reader) param() *types.Var {
+	r.Sync(pkgbits.SyncParam)
+
+	pos := r.pos()
+	pkg, name := r.localIdent()
+	typ := r.typ()
+
+	return types.NewParam(pos, pkg, name, typ)
+}
+
+// @@@ Objects
+
+func (r *reader) obj() (types.Object, []types.Type) {
+	r.Sync(pkgbits.SyncObject)
+
+	assert(!r.Bool())
+
+	pkg, name := r.p.objIdx(r.Reloc(pkgbits.RelocObj))
+	obj := pkgScope(pkg).Lookup(name)
+
+	targs := make([]types.Type, r.Len())
+	for i := range targs {
+		targs[i] = r.typ()
+	}
+
+	return obj, targs
+}
+
+func (pr *pkgReader) objIdx(idx pkgbits.Index) (*types.Package, string) {
+
+	var objPkg *types.Package
+	var objName string
+	var tag pkgbits.CodeObj
+	{
+		rname := pr.tempReader(pkgbits.RelocName, idx, pkgbits.SyncObject1)
+
+		objPkg, objName = rname.qualifiedIdent()
+		assert(objName != "")
+
+		tag = pkgbits.CodeObj(rname.Code(pkgbits.SyncCodeObj))
+		pr.retireReader(rname)
+	}
+
+	if tag == pkgbits.ObjStub {
+		assert(objPkg == nil || objPkg == types.Unsafe)
+		return objPkg, objName
+	}
+
+	// Ignore local types promoted to global scope (#55110).
+	if _, suffix := splitVargenSuffix(objName); suffix != "" {
+		return objPkg, objName
+	}
+
+	if objPkg.Scope().Lookup(objName) == nil {
+		dict := pr.objDictIdx(idx)
+
+		r := pr.newReader(pkgbits.RelocObj, idx, pkgbits.SyncObject1)
+		r.dict = dict
+
+		declare := func(obj types.Object) {
+			objPkg.Scope().Insert(obj)
+		}
+
+		switch tag {
+		default:
+			panic("weird")
+
+		case pkgbits.ObjAlias:
+			pos := r.pos()
+			typ := r.typ()
+			declare(types.NewTypeName(pos, objPkg, objName, typ))
+
+		case pkgbits.ObjConst:
+			pos := r.pos()
+			typ := r.typ()
+			val := r.Value()
+			declare(types.NewConst(pos, objPkg, objName, typ, val))
+
+		case pkgbits.ObjFunc:
+			pos := r.pos()
+			tparams := r.typeParamNames()
+			sig := r.signature(nil, nil, tparams)
+			declare(types.NewFunc(pos, objPkg, objName, sig))
+
+		case pkgbits.ObjType:
+			pos := r.pos()
+
+			obj := types.NewTypeName(pos, objPkg, objName, nil)
+			named := types.NewNamed(obj, nil, nil)
+			declare(obj)
+
+			named.SetTypeParams(r.typeParamNames())
+
+			setUnderlying := func(underlying types.Type) {
+				// If the underlying type is an interface, we need to
+				// duplicate its methods so we can replace the receiver
+				// parameter's type (#49906).
+				if iface, ok := underlying.(*types.Interface); ok && iface.NumExplicitMethods() != 0 {
+					methods := make([]*types.Func, iface.NumExplicitMethods())
+					for i := range methods {
+						fn := iface.ExplicitMethod(i)
+						sig := fn.Type().(*types.Signature)
+
+						recv := types.NewVar(fn.Pos(), fn.Pkg(), "", named)
+						methods[i] = types.NewFunc(fn.Pos(), fn.Pkg(), fn.Name(), types.NewSignature(recv, sig.Params(), sig.Results(), sig.Variadic()))
+					}
+
+					embeds := make([]types.Type, iface.NumEmbeddeds())
+					for i := range embeds {
+						embeds[i] = iface.EmbeddedType(i)
+					}
+
+					newIface := types.NewInterfaceType(methods, embeds)
+					r.p.ifaces = append(r.p.ifaces, newIface)
+					underlying = newIface
+				}
+
+				named.SetUnderlying(underlying)
+			}
+
+			// Since go.dev/cl/455279, we can assume rhs.Underlying() will
+			// always be non-nil. However, to temporarily support users of
+			// older snapshot releases, we continue to fallback to the old
+			// behavior for now.
+			//
+			// TODO(mdempsky): Remove fallback code and simplify after
+			// allowing time for snapshot users to upgrade.
+			rhs := r.typ()
+			if underlying := rhs.Underlying(); underlying != nil {
+				setUnderlying(underlying)
+			} else {
+				pk := r.p
+				pk.laterFor(named, func() {
+					// First be sure that the rhs is initialized, if it needs to be initialized.
+					delete(pk.laterFors, named) // prevent cycles
+					if i, ok := pk.laterFors[rhs]; ok {
+						f := pk.laterFns[i]
+						pk.laterFns[i] = func() {} // function is running now, so replace it with a no-op
+						f()                        // initialize RHS
+					}
+					setUnderlying(rhs.Underlying())
+				})
+			}
+
+			for i, n := 0, r.Len(); i < n; i++ {
+				named.AddMethod(r.method())
+			}
+
+		case pkgbits.ObjVar:
+			pos := r.pos()
+			typ := r.typ()
+			declare(types.NewVar(pos, objPkg, objName, typ))
+		}
+	}
+
+	return objPkg, objName
+}
+
+func (pr *pkgReader) objDictIdx(idx pkgbits.Index) *readerDict {
+
+	var dict readerDict
+
+	{
+		r := pr.tempReader(pkgbits.RelocObjDict, idx, pkgbits.SyncObject1)
+		if implicits := r.Len(); implicits != 0 {
+			errorf("unexpected object with %v implicit type parameter(s)", implicits)
+		}
+
+		dict.bounds = make([]typeInfo, r.Len())
+		for i := range dict.bounds {
+			dict.bounds[i] = r.typInfo()
+		}
+
+		dict.derived = make([]derivedInfo, r.Len())
+		dict.derivedTypes = make([]types.Type, len(dict.derived))
+		for i := range dict.derived {
+			dict.derived[i] = derivedInfo{r.Reloc(pkgbits.RelocType), r.Bool()}
+		}
+
+		pr.retireReader(r)
+	}
+	// function references follow, but reader doesn't need those
+
+	return &dict
+}
+
+func (r *reader) typeParamNames() []*types.TypeParam {
+	r.Sync(pkgbits.SyncTypeParamNames)
+
+	// Note: This code assumes it only processes objects without
+	// implement type parameters. This is currently fine, because
+	// reader is only used to read in exported declarations, which are
+	// always package scoped.
+
+	if len(r.dict.bounds) == 0 {
+		return nil
+	}
+
+	// Careful: Type parameter lists may have cycles. To allow for this,
+	// we construct the type parameter list in two passes: first we
+	// create all the TypeNames and TypeParams, then we construct and
+	// set the bound type.
+
+	r.dict.tparams = make([]*types.TypeParam, len(r.dict.bounds))
+	for i := range r.dict.bounds {
+		pos := r.pos()
+		pkg, name := r.localIdent()
+
+		tname := types.NewTypeName(pos, pkg, name, nil)
+		r.dict.tparams[i] = types.NewTypeParam(tname, nil)
+	}
+
+	typs := make([]types.Type, len(r.dict.bounds))
+	for i, bound := range r.dict.bounds {
+		typs[i] = r.p.typIdx(bound, r.dict)
+	}
+
+	// TODO(mdempsky): This is subtle, elaborate further.
+	//
+	// We have to save tparams outside of the closure, because
+	// typeParamNames() can be called multiple times with the same
+	// dictionary instance.
+	//
+	// Also, this needs to happen later to make sure SetUnderlying has
+	// been called.
+	//
+	// TODO(mdempsky): Is it safe to have a single "later" slice or do
+	// we need to have multiple passes? See comments on CL 386002 and
+	// go.dev/issue/52104.
+	tparams := r.dict.tparams
+	r.p.later(func() {
+		for i, typ := range typs {
+			tparams[i].SetConstraint(typ)
+		}
+	})
+
+	return r.dict.tparams
+}
+
+func (r *reader) method() *types.Func {
+	r.Sync(pkgbits.SyncMethod)
+	pos := r.pos()
+	pkg, name := r.selector()
+
+	rparams := r.typeParamNames()
+	sig := r.signature(r.param(), rparams, nil)
+
+	_ = r.pos() // TODO(mdempsky): Remove; this is a hacker for linker.go.
+	return types.NewFunc(pos, pkg, name, sig)
+}
+
+func (r *reader) qualifiedIdent() (*types.Package, string) { return r.ident(pkgbits.SyncSym) }
+func (r *reader) localIdent() (*types.Package, string)     { return r.ident(pkgbits.SyncLocalIdent) }
+func (r *reader) selector() (*types.Package, string)       { return r.ident(pkgbits.SyncSelector) }
+
+func (r *reader) ident(marker pkgbits.SyncMarker) (*types.Package, string) {
+	r.Sync(marker)
+	return r.pkg(), r.String()
+}
+
+// pkgScope returns pkg.Scope().
+// If pkg is nil, it returns types.Universe instead.
+//
+// TODO(mdempsky): Remove after x/tools can depend on Go 1.19.
+func pkgScope(pkg *types.Package) *types.Scope {
+	if pkg != nil {
+		return pkg.Scope()
+	}
+	return types.Universe
+}