Add vendor files for spf13/viper

1 files changed, 1157 insertions, 0 deletions

diff --git a/vendor/github.com/spf13/pflag/flag.go b/vendor/github.com/spf13/pflag/flag.go
new file mode 100644
index 00000000..28538c07
--- /dev/null
+++ b/vendor/github.com/spf13/pflag/flag.go
@@ -0,0 +1,1157 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package pflag is a drop-in replacement for Go's flag package, implementing
+POSIX/GNU-style --flags.
+
+pflag is compatible with the GNU extensions to the POSIX recommendations
+for command-line options. See
+http://www.gnu.org/software/libc/manual/html_node/Argument-Syntax.html
+
+Usage:
+
+pflag is a drop-in replacement of Go's native flag package. If you import
+pflag under the name "flag" then all code should continue to function
+with no changes.
+
+	import flag "github.com/spf13/pflag"
+
+There is one exception to this: if you directly instantiate the Flag struct
+there is one more field "Shorthand" that you will need to set.
+Most code never instantiates this struct directly, and instead uses
+functions such as String(), BoolVar(), and Var(), and is therefore
+unaffected.
+
+Define flags using flag.String(), Bool(), Int(), etc.
+
+This declares an integer flag, -flagname, stored in the pointer ip, with type *int.
+	var ip = flag.Int("flagname", 1234, "help message for flagname")
+If you like, you can bind the flag to a variable using the Var() functions.
+	var flagvar int
+	func init() {
+		flag.IntVar(&flagvar, "flagname", 1234, "help message for flagname")
+	}
+Or you can create custom flags that satisfy the Value interface (with
+pointer receivers) and couple them to flag parsing by
+	flag.Var(&flagVal, "name", "help message for flagname")
+For such flags, the default value is just the initial value of the variable.
+
+After all flags are defined, call
+	flag.Parse()
+to parse the command line into the defined flags.
+
+Flags may then be used directly. If you're using the flags themselves,
+they are all pointers; if you bind to variables, they're values.
+	fmt.Println("ip has value ", *ip)
+	fmt.Println("flagvar has value ", flagvar)
+
+After parsing, the arguments after the flag are available as the
+slice flag.Args() or individually as flag.Arg(i).
+The arguments are indexed from 0 through flag.NArg()-1.
+
+The pflag package also defines some new functions that are not in flag,
+that give one-letter shorthands for flags. You can use these by appending
+'P' to the name of any function that defines a flag.
+	var ip = flag.IntP("flagname", "f", 1234, "help message")
+	var flagvar bool
+	func init() {
+		flag.BoolVarP("boolname", "b", true, "help message")
+	}
+	flag.VarP(&flagVar, "varname", "v", 1234, "help message")
+Shorthand letters can be used with single dashes on the command line.
+Boolean shorthand flags can be combined with other shorthand flags.
+
+Command line flag syntax:
+	--flag    // boolean flags only
+	--flag=x
+
+Unlike the flag package, a single dash before an option means something
+different than a double dash. Single dashes signify a series of shorthand
+letters for flags. All but the last shorthand letter must be boolean flags.
+	// boolean flags
+	-f
+	-abc
+	// non-boolean flags
+	-n 1234
+	-Ifile
+	// mixed
+	-abcs "hello"
+	-abcn1234
+
+Flag parsing stops after the terminator "--". Unlike the flag package,
+flags can be interspersed with arguments anywhere on the command line
+before this terminator.
+
+Integer flags accept 1234, 0664, 0x1234 and may be negative.
+Boolean flags (in their long form) accept 1, 0, t, f, true, false,
+TRUE, FALSE, True, False.
+Duration flags accept any input valid for time.ParseDuration.
+
+The default set of command-line flags is controlled by
+top-level functions.  The FlagSet type allows one to define
+independent sets of flags, such as to implement subcommands
+in a command-line interface. The methods of FlagSet are
+analogous to the top-level functions for the command-line
+flag set.
+*/
+package pflag
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"sort"
+	"strings"
+)
+
+// ErrHelp is the error returned if the flag -help is invoked but no such flag is defined.
+var ErrHelp = errors.New("pflag: help requested")
+
+// ErrorHandling defines how to handle flag parsing errors.
+type ErrorHandling int
+
+const (
+	// ContinueOnError will return an err from Parse() if an error is found
+	ContinueOnError ErrorHandling = iota
+	// ExitOnError will call os.Exit(2) if an error is found when parsing
+	ExitOnError
+	// PanicOnError will panic() if an error is found when parsing flags
+	PanicOnError
+)
+
+// NormalizedName is a flag name that has been normalized according to rules
+// for the FlagSet (e.g. making '-' and '_' equivalent).
+type NormalizedName string
+
+// A FlagSet represents a set of defined flags.
+type FlagSet struct {
+	// Usage is the function called when an error occurs while parsing flags.
+	// The field is a function (not a method) that may be changed to point to
+	// a custom error handler.
+	Usage func()
+
+	// SortFlags is used to indicate, if user wants to have sorted flags in
+	// help/usage messages.
+	SortFlags bool
+
+	name              string
+	parsed            bool
+	actual            map[NormalizedName]*Flag
+	orderedActual     []*Flag
+	sortedActual      []*Flag
+	formal            map[NormalizedName]*Flag
+	orderedFormal     []*Flag
+	sortedFormal      []*Flag
+	shorthands        map[byte]*Flag
+	args              []string // arguments after flags
+	argsLenAtDash     int      // len(args) when a '--' was located when parsing, or -1 if no --
+	errorHandling     ErrorHandling
+	output            io.Writer // nil means stderr; use out() accessor
+	interspersed      bool      // allow interspersed option/non-option args
+	normalizeNameFunc func(f *FlagSet, name string) NormalizedName
+}
+
+// A Flag represents the state of a flag.
+type Flag struct {
+	Name                string              // name as it appears on command line
+	Shorthand           string              // one-letter abbreviated flag
+	Usage               string              // help message
+	Value               Value               // value as set
+	DefValue            string              // default value (as text); for usage message
+	Changed             bool                // If the user set the value (or if left to default)
+	NoOptDefVal         string              // default value (as text); if the flag is on the command line without any options
+	Deprecated          string              // If this flag is deprecated, this string is the new or now thing to use
+	Hidden              bool                // used by cobra.Command to allow flags to be hidden from help/usage text
+	ShorthandDeprecated string              // If the shorthand of this flag is deprecated, this string is the new or now thing to use
+	Annotations         map[string][]string // used by cobra.Command bash autocomple code
+}
+
+// Value is the interface to the dynamic value stored in a flag.
+// (The default value is represented as a string.)
+type Value interface {
+	String() string
+	Set(string) error
+	Type() string
+}
+
+// sortFlags returns the flags as a slice in lexicographical sorted order.
+func sortFlags(flags map[NormalizedName]*Flag) []*Flag {
+	list := make(sort.StringSlice, len(flags))
+	i := 0
+	for k := range flags {
+		list[i] = string(k)
+		i++
+	}
+	list.Sort()
+	result := make([]*Flag, len(list))
+	for i, name := range list {
+		result[i] = flags[NormalizedName(name)]
+	}
+	return result
+}
+
+// SetNormalizeFunc allows you to add a function which can translate flag names.
+// Flags added to the FlagSet will be translated and then when anything tries to
+// look up the flag that will also be translated. So it would be possible to create
+// a flag named "getURL" and have it translated to "geturl".  A user could then pass
+// "--getUrl" which may also be translated to "geturl" and everything will work.
+func (f *FlagSet) SetNormalizeFunc(n func(f *FlagSet, name string) NormalizedName) {
+	f.normalizeNameFunc = n
+	f.sortedFormal = f.sortedFormal[:0]
+	for fname, flag := range f.formal {
+		nname := f.normalizeFlagName(flag.Name)
+		if fname == nname {
+			continue
+		}
+		flag.Name = string(nname)
+		delete(f.formal, fname)
+		f.formal[nname] = flag
+		if _, set := f.actual[fname]; set {
+			delete(f.actual, fname)
+			f.actual[nname] = flag
+		}
+	}
+}
+
+// GetNormalizeFunc returns the previously set NormalizeFunc of a function which
+// does no translation, if not set previously.
+func (f *FlagSet) GetNormalizeFunc() func(f *FlagSet, name string) NormalizedName {
+	if f.normalizeNameFunc != nil {
+		return f.normalizeNameFunc
+	}
+	return func(f *FlagSet, name string) NormalizedName { return NormalizedName(name) }
+}
+
+func (f *FlagSet) normalizeFlagName(name string) NormalizedName {
+	n := f.GetNormalizeFunc()
+	return n(f, name)
+}
+
+func (f *FlagSet) out() io.Writer {
+	if f.output == nil {
+		return os.Stderr
+	}
+	return f.output
+}
+
+// SetOutput sets the destination for usage and error messages.
+// If output is nil, os.Stderr is used.
+func (f *FlagSet) SetOutput(output io.Writer) {
+	f.output = output
+}
+
+// VisitAll visits the flags in lexicographical order or
+// in primordial order if f.SortFlags is false, calling fn for each.
+// It visits all flags, even those not set.
+func (f *FlagSet) VisitAll(fn func(*Flag)) {
+	if len(f.formal) == 0 {
+		return
+	}
+
+	var flags []*Flag
+	if f.SortFlags {
+		if len(f.formal) != len(f.sortedFormal) {
+			f.sortedFormal = sortFlags(f.formal)
+		}
+		flags = f.sortedFormal
+	} else {
+		flags = f.orderedFormal
+	}
+
+	for _, flag := range flags {
+		fn(flag)
+	}
+}
+
+// HasFlags returns a bool to indicate if the FlagSet has any flags definied.
+func (f *FlagSet) HasFlags() bool {
+	return len(f.formal) > 0
+}
+
+// HasAvailableFlags returns a bool to indicate if the FlagSet has any flags
+// definied that are not hidden or deprecated.
+func (f *FlagSet) HasAvailableFlags() bool {
+	for _, flag := range f.formal {
+		if !flag.Hidden && len(flag.Deprecated) == 0 {
+			return true
+		}
+	}
+	return false
+}
+
+// VisitAll visits the command-line flags in lexicographical order or
+// in primordial order if f.SortFlags is false, calling fn for each.
+// It visits all flags, even those not set.
+func VisitAll(fn func(*Flag)) {
+	CommandLine.VisitAll(fn)
+}
+
+// Visit visits the flags in lexicographical order or
+// in primordial order if f.SortFlags is false, calling fn for each.
+// It visits only those flags that have been set.
+func (f *FlagSet) Visit(fn func(*Flag)) {
+	if len(f.actual) == 0 {
+		return
+	}
+
+	var flags []*Flag
+	if f.SortFlags {
+		if len(f.actual) != len(f.sortedActual) {
+			f.sortedActual = sortFlags(f.actual)
+		}
+		flags = f.sortedActual
+	} else {
+		flags = f.orderedActual
+	}
+
+	for _, flag := range flags {
+		fn(flag)
+	}
+}
+
+// Visit visits the command-line flags in lexicographical order or
+// in primordial order if f.SortFlags is false, calling fn for each.
+// It visits only those flags that have been set.
+func Visit(fn func(*Flag)) {
+	CommandLine.Visit(fn)
+}
+
+// Lookup returns the Flag structure of the named flag, returning nil if none exists.
+func (f *FlagSet) Lookup(name string) *Flag {
+	return f.lookup(f.normalizeFlagName(name))
+}
+
+// ShorthandLookup returns the Flag structure of the short handed flag,
+// returning nil if none exists.
+// It panics, if len(name) > 1.
+func (f *FlagSet) ShorthandLookup(name string) *Flag {
+	if name == "" {
+		return nil
+	}
+	if len(name) > 1 {
+		msg := fmt.Sprintf("can not look up shorthand which is more than one ASCII character: %q", name)
+		fmt.Fprintf(f.out(), msg)
+		panic(msg)
+	}
+	c := name[0]
+	return f.shorthands[c]
+}
+
+// lookup returns the Flag structure of the named flag, returning nil if none exists.
+func (f *FlagSet) lookup(name NormalizedName) *Flag {
+	return f.formal[name]
+}
+
+// func to return a given type for a given flag name
+func (f *FlagSet) getFlagType(name string, ftype string, convFunc func(sval string) (interface{}, error)) (interface{}, error) {
+	flag := f.Lookup(name)
+	if flag == nil {
+		err := fmt.Errorf("flag accessed but not defined: %s", name)
+		return nil, err
+	}
+
+	if flag.Value.Type() != ftype {
+		err := fmt.Errorf("trying to get %s value of flag of type %s", ftype, flag.Value.Type())
+		return nil, err
+	}
+
+	sval := flag.Value.String()
+	result, err := convFunc(sval)
+	if err != nil {
+		return nil, err
+	}
+	return result, nil
+}
+
+// ArgsLenAtDash will return the length of f.Args at the moment when a -- was
+// found during arg parsing. This allows your program to know which args were
+// before the -- and which came after.
+func (f *FlagSet) ArgsLenAtDash() int {
+	return f.argsLenAtDash
+}
+
+// MarkDeprecated indicated that a flag is deprecated in your program. It will
+// continue to function but will not show up in help or usage messages. Using
+// this flag will also print the given usageMessage.
+func (f *FlagSet) MarkDeprecated(name string, usageMessage string) error {
+	flag := f.Lookup(name)
+	if flag == nil {
+		return fmt.Errorf("flag %q does not exist", name)
+	}
+	if usageMessage == "" {
+		return fmt.Errorf("deprecated message for flag %q must be set", name)
+	}
+	flag.Deprecated = usageMessage
+	return nil
+}
+
+// MarkShorthandDeprecated will mark the shorthand of a flag deprecated in your
+// program. It will continue to function but will not show up in help or usage
+// messages. Using this flag will also print the given usageMessage.
+func (f *FlagSet) MarkShorthandDeprecated(name string, usageMessage string) error {
+	flag := f.Lookup(name)
+	if flag == nil {
+		return fmt.Errorf("flag %q does not exist", name)
+	}
+	if usageMessage == "" {
+		return fmt.Errorf("deprecated message for flag %q must be set", name)
+	}
+	flag.ShorthandDeprecated = usageMessage
+	return nil
+}
+
+// MarkHidden sets a flag to 'hidden' in your program. It will continue to
+// function but will not show up in help or usage messages.
+func (f *FlagSet) MarkHidden(name string) error {
+	flag := f.Lookup(name)
+	if flag == nil {
+		return fmt.Errorf("flag %q does not exist", name)
+	}
+	flag.Hidden = true
+	return nil
+}
+
+// Lookup returns the Flag structure of the named command-line flag,
+// returning nil if none exists.
+func Lookup(name string) *Flag {
+	return CommandLine.Lookup(name)
+}
+
+// ShorthandLookup returns the Flag structure of the short handed flag,
+// returning nil if none exists.
+func ShorthandLookup(name string) *Flag {
+	return CommandLine.ShorthandLookup(name)
+}
+
+// Set sets the value of the named flag.
+func (f *FlagSet) Set(name, value string) error {
+	normalName := f.normalizeFlagName(name)
+	flag, ok := f.formal[normalName]
+	if !ok {
+		return fmt.Errorf("no such flag -%v", name)
+	}
+
+	err := flag.Value.Set(value)
+	if err != nil {
+		var flagName string
+		if flag.Shorthand != "" && flag.ShorthandDeprecated == "" {
+			flagName = fmt.Sprintf("-%s, --%s", flag.Shorthand, flag.Name)
+		} else {
+			flagName = fmt.Sprintf("--%s", flag.Name)
+		}
+		return fmt.Errorf("invalid argument %q for %q flag: %v", value, flagName, err)
+	}
+
+	if !flag.Changed {
+		if f.actual == nil {
+			f.actual = make(map[NormalizedName]*Flag)
+		}
+		f.actual[normalName] = flag
+		f.orderedActual = append(f.orderedActual, flag)
+
+		flag.Changed = true
+	}
+
+	if flag.Deprecated != "" {
+		fmt.Fprintf(f.out(), "Flag --%s has been deprecated, %s\n", flag.Name, flag.Deprecated)
+	}
+	return nil
+}
+
+// SetAnnotation allows one to set arbitrary annotations on a flag in the FlagSet.
+// This is sometimes used by spf13/cobra programs which want to generate additional
+// bash completion information.
+func (f *FlagSet) SetAnnotation(name, key string, values []string) error {
+	normalName := f.normalizeFlagName(name)
+	flag, ok := f.formal[normalName]
+	if !ok {
+		return fmt.Errorf("no such flag -%v", name)
+	}
+	if flag.Annotations == nil {
+		flag.Annotations = map[string][]string{}
+	}
+	flag.Annotations[key] = values
+	return nil
+}
+
+// Changed returns true if the flag was explicitly set during Parse() and false
+// otherwise
+func (f *FlagSet) Changed(name string) bool {
+	flag := f.Lookup(name)
+	// If a flag doesn't exist, it wasn't changed....
+	if flag == nil {
+		return false
+	}
+	return flag.Changed
+}
+
+// Set sets the value of the named command-line flag.
+func Set(name, value string) error {
+	return CommandLine.Set(name, value)
+}
+
+// PrintDefaults prints, to standard error unless configured
+// otherwise, the default values of all defined flags in the set.
+func (f *FlagSet) PrintDefaults() {
+	usages := f.FlagUsages()
+	fmt.Fprint(f.out(), usages)
+}
+
+// defaultIsZeroValue returns true if the default value for this flag represents
+// a zero value.
+func (f *Flag) defaultIsZeroValue() bool {
+	switch f.Value.(type) {
+	case boolFlag:
+		return f.DefValue == "false"
+	case *durationValue:
+		// Beginning in Go 1.7, duration zero values are "0s"
+		return f.DefValue == "0" || f.DefValue == "0s"
+	case *intValue, *int8Value, *int32Value, *int64Value, *uintValue, *uint8Value, *uint16Value, *uint32Value, *uint64Value, *countValue, *float32Value, *float64Value:
+		return f.DefValue == "0"
+	case *stringValue:
+		return f.DefValue == ""
+	case *ipValue, *ipMaskValue, *ipNetValue:
+		return f.DefValue == "<nil>"
+	case *intSliceValue, *stringSliceValue, *stringArrayValue:
+		return f.DefValue == "[]"
+	default:
+		switch f.Value.String() {
+		case "false":
+			return true
+		case "<nil>":
+			return true
+		case "":
+			return true
+		case "0":
+			return true
+		}
+		return false
+	}
+}
+
+// UnquoteUsage extracts a back-quoted name from the usage
+// string for a flag and returns it and the un-quoted usage.
+// Given "a `name` to show" it returns ("name", "a name to show").
+// If there are no back quotes, the name is an educated guess of the
+// type of the flag's value, or the empty string if the flag is boolean.
+func UnquoteUsage(flag *Flag) (name string, usage string) {
+	// Look for a back-quoted name, but avoid the strings package.
+	usage = flag.Usage
+	for i := 0; i < len(usage); i++ {
+		if usage[i] == '`' {
+			for j := i + 1; j < len(usage); j++ {
+				if usage[j] == '`' {
+					name = usage[i+1 : j]
+					usage = usage[:i] + name + usage[j+1:]
+					return name, usage
+				}
+			}
+			break // Only one back quote; use type name.
+		}
+	}
+
+	name = flag.Value.Type()
+	switch name {
+	case "bool":
+		name = ""
+	case "float64":
+		name = "float"
+	case "int64":
+		name = "int"
+	case "uint64":
+		name = "uint"
+	case "stringSlice":
+		name = "strings"
+	case "intSlice":
+		name = "ints"
+	case "uintSlice":
+		name = "uints"
+	case "boolSlice":
+		name = "bools"
+	}
+
+	return
+}
+
+// Splits the string `s` on whitespace into an initial substring up to
+// `i` runes in length and the remainder. Will go `slop` over `i` if
+// that encompasses the entire string (which allows the caller to
+// avoid short orphan words on the final line).
+func wrapN(i, slop int, s string) (string, string) {
+	if i+slop > len(s) {
+		return s, ""
+	}
+
+	w := strings.LastIndexAny(s[:i], " \t")
+	if w <= 0 {
+		return s, ""
+	}
+
+	return s[:w], s[w+1:]
+}
+
+// Wraps the string `s` to a maximum width `w` with leading indent
+// `i`. The first line is not indented (this is assumed to be done by
+// caller). Pass `w` == 0 to do no wrapping
+func wrap(i, w int, s string) string {
+	if w == 0 {
+		return s
+	}
+
+	// space between indent i and end of line width w into which
+	// we should wrap the text.
+	wrap := w - i
+
+	var r, l string
+
+	// Not enough space for sensible wrapping. Wrap as a block on
+	// the next line instead.
+	if wrap < 24 {
+		i = 16
+		wrap = w - i
+		r += "\n" + strings.Repeat(" ", i)
+	}
+	// If still not enough space then don't even try to wrap.
+	if wrap < 24 {
+		return s
+	}
+
+	// Try to avoid short orphan words on the final line, by
+	// allowing wrapN to go a bit over if that would fit in the
+	// remainder of the line.
+	slop := 5
+	wrap = wrap - slop
+
+	// Handle first line, which is indented by the caller (or the
+	// special case above)
+	l, s = wrapN(wrap, slop, s)
+	r = r + l
+
+	// Now wrap the rest
+	for s != "" {
+		var t string
+
+		t, s = wrapN(wrap, slop, s)
+		r = r + "\n" + strings.Repeat(" ", i) + t
+	}
+
+	return r
+
+}
+
+// FlagUsagesWrapped returns a string containing the usage information
+// for all flags in the FlagSet. Wrapped to `cols` columns (0 for no
+// wrapping)
+func (f *FlagSet) FlagUsagesWrapped(cols int) string {
+	buf := new(bytes.Buffer)
+
+	lines := make([]string, 0, len(f.formal))
+
+	maxlen := 0
+	f.VisitAll(func(flag *Flag) {
+		if flag.Deprecated != "" || flag.Hidden {
+			return
+		}
+
+		line := ""
+		if flag.Shorthand != "" && flag.ShorthandDeprecated == "" {
+			line = fmt.Sprintf("  -%s, --%s", flag.Shorthand, flag.Name)
+		} else {
+			line = fmt.Sprintf("      --%s", flag.Name)
+		}
+
+		varname, usage := UnquoteUsage(flag)
+		if varname != "" {
+			line += " " + varname
+		}
+		if flag.NoOptDefVal != "" {
+			switch flag.Value.Type() {
+			case "string":
+				line += fmt.Sprintf("[=\"%s\"]", flag.NoOptDefVal)
+			case "bool":
+				if flag.NoOptDefVal != "true" {
+					line += fmt.Sprintf("[=%s]", flag.NoOptDefVal)
+				}
+			case "count":
+				if flag.NoOptDefVal != "+1" {
+					line += fmt.Sprintf("[=%s]", flag.NoOptDefVal)
+				}
+			default:
+				line += fmt.Sprintf("[=%s]", flag.NoOptDefVal)
+			}
+		}
+
+		// This special character will be replaced with spacing once the
+		// correct alignment is calculated
+		line += "\x00"
+		if len(line) > maxlen {
+			maxlen = len(line)
+		}
+
+		line += usage
+		if !flag.defaultIsZeroValue() {
+			if flag.Value.Type() == "string" {
+				line += fmt.Sprintf(" (default %q)", flag.DefValue)
+			} else {
+				line += fmt.Sprintf(" (default %s)", flag.DefValue)
+			}
+		}
+
+		lines = append(lines, line)
+	})
+
+	for _, line := range lines {
+		sidx := strings.Index(line, "\x00")
+		spacing := strings.Repeat(" ", maxlen-sidx)
+		// maxlen + 2 comes from + 1 for the \x00 and + 1 for the (deliberate) off-by-one in maxlen-sidx
+		fmt.Fprintln(buf, line[:sidx], spacing, wrap(maxlen+2, cols, line[sidx+1:]))
+	}
+
+	return buf.String()
+}
+
+// FlagUsages returns a string containing the usage information for all flags in
+// the FlagSet
+func (f *FlagSet) FlagUsages() string {
+	return f.FlagUsagesWrapped(0)
+}
+
+// PrintDefaults prints to standard error the default values of all defined command-line flags.
+func PrintDefaults() {
+	CommandLine.PrintDefaults()
+}
+
+// defaultUsage is the default function to print a usage message.
+func defaultUsage(f *FlagSet) {
+	fmt.Fprintf(f.out(), "Usage of %s:\n", f.name)
+	f.PrintDefaults()
+}
+
+// NOTE: Usage is not just defaultUsage(CommandLine)
+// because it serves (via godoc flag Usage) as the example
+// for how to write your own usage function.
+
+// Usage prints to standard error a usage message documenting all defined command-line flags.
+// The function is a variable that may be changed to point to a custom function.
+// By default it prints a simple header and calls PrintDefaults; for details about the
+// format of the output and how to control it, see the documentation for PrintDefaults.
+var Usage = func() {
+	fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
+	PrintDefaults()
+}
+
+// NFlag returns the number of flags that have been set.
+func (f *FlagSet) NFlag() int { return len(f.actual) }
+
+// NFlag returns the number of command-line flags that have been set.
+func NFlag() int { return len(CommandLine.actual) }
+
+// Arg returns the i'th argument.  Arg(0) is the first remaining argument
+// after flags have been processed.
+func (f *FlagSet) Arg(i int) string {
+	if i < 0 || i >= len(f.args) {
+		return ""
+	}
+	return f.args[i]
+}
+
+// Arg returns the i'th command-line argument.  Arg(0) is the first remaining argument
+// after flags have been processed.
+func Arg(i int) string {
+	return CommandLine.Arg(i)
+}
+
+// NArg is the number of arguments remaining after flags have been processed.
+func (f *FlagSet) NArg() int { return len(f.args) }
+
+// NArg is the number of arguments remaining after flags have been processed.
+func NArg() int { return len(CommandLine.args) }
+
+// Args returns the non-flag arguments.
+func (f *FlagSet) Args() []string { return f.args }
+
+// Args returns the non-flag command-line arguments.
+func Args() []string { return CommandLine.args }
+
+// Var defines a flag with the specified name and usage string. The type and
+// value of the flag are represented by the first argument, of type Value, which
+// typically holds a user-defined implementation of Value. For instance, the
+// caller could create a flag that turns a comma-separated string into a slice
+// of strings by giving the slice the methods of Value; in particular, Set would
+// decompose the comma-separated string into the slice.
+func (f *FlagSet) Var(value Value, name string, usage string) {
+	f.VarP(value, name, "", usage)
+}
+
+// VarPF is like VarP, but returns the flag created
+func (f *FlagSet) VarPF(value Value, name, shorthand, usage string) *Flag {
+	// Remember the default value as a string; it won't change.
+	flag := &Flag{
+		Name:      name,
+		Shorthand: shorthand,
+		Usage:     usage,
+		Value:     value,
+		DefValue:  value.String(),
+	}
+	f.AddFlag(flag)
+	return flag
+}
+
+// VarP is like Var, but accepts a shorthand letter that can be used after a single dash.
+func (f *FlagSet) VarP(value Value, name, shorthand, usage string) {
+	f.VarPF(value, name, shorthand, usage)
+}
+
+// AddFlag will add the flag to the FlagSet
+func (f *FlagSet) AddFlag(flag *Flag) {
+	normalizedFlagName := f.normalizeFlagName(flag.Name)
+
+	_, alreadyThere := f.formal[normalizedFlagName]
+	if alreadyThere {
+		msg := fmt.Sprintf("%s flag redefined: %s", f.name, flag.Name)
+		fmt.Fprintln(f.out(), msg)
+		panic(msg) // Happens only if flags are declared with identical names
+	}
+	if f.formal == nil {
+		f.formal = make(map[NormalizedName]*Flag)
+	}
+
+	flag.Name = string(normalizedFlagName)
+	f.formal[normalizedFlagName] = flag
+	f.orderedFormal = append(f.orderedFormal, flag)
+
+	if flag.Shorthand == "" {
+		return
+	}
+	if len(flag.Shorthand) > 1 {
+		msg := fmt.Sprintf("%q shorthand is more than one ASCII character", flag.Shorthand)
+		fmt.Fprintf(f.out(), msg)
+		panic(msg)
+	}
+	if f.shorthands == nil {
+		f.shorthands = make(map[byte]*Flag)
+	}
+	c := flag.Shorthand[0]
+	used, alreadyThere := f.shorthands[c]
+	if alreadyThere {
+		msg := fmt.Sprintf("unable to redefine %q shorthand in %q flagset: it's already used for %q flag", c, f.name, used.Name)
+		fmt.Fprintf(f.out(), msg)
+		panic(msg)
+	}
+	f.shorthands[c] = flag
+}
+
+// AddFlagSet adds one FlagSet to another. If a flag is already present in f
+// the flag from newSet will be ignored.
+func (f *FlagSet) AddFlagSet(newSet *FlagSet) {
+	if newSet == nil {
+		return
+	}
+	newSet.VisitAll(func(flag *Flag) {
+		if f.Lookup(flag.Name) == nil {
+			f.AddFlag(flag)
+		}
+	})
+}
+
+// Var defines a flag with the specified name and usage string. The type and
+// value of the flag are represented by the first argument, of type Value, which
+// typically holds a user-defined implementation of Value. For instance, the
+// caller could create a flag that turns a comma-separated string into a slice
+// of strings by giving the slice the methods of Value; in particular, Set would
+// decompose the comma-separated string into the slice.
+func Var(value Value, name string, usage string) {
+	CommandLine.VarP(value, name, "", usage)
+}
+
+// VarP is like Var, but accepts a shorthand letter that can be used after a single dash.
+func VarP(value Value, name, shorthand, usage string) {
+	CommandLine.VarP(value, name, shorthand, usage)
+}
+
+// failf prints to standard error a formatted error and usage message and
+// returns the error.
+func (f *FlagSet) failf(format string, a ...interface{}) error {
+	err := fmt.Errorf(format, a...)
+	if f.errorHandling != ContinueOnError {
+		fmt.Fprintln(f.out(), err)
+		f.usage()
+	}
+	return err
+}
+
+// usage calls the Usage method for the flag set, or the usage function if
+// the flag set is CommandLine.
+func (f *FlagSet) usage() {
+	if f == CommandLine {
+		Usage()
+	} else if f.Usage == nil {
+		defaultUsage(f)
+	} else {
+		f.Usage()
+	}
+}
+
+func (f *FlagSet) parseLongArg(s string, args []string, fn parseFunc) (a []string, err error) {
+	a = args
+	name := s[2:]
+	if len(name) == 0 || name[0] == '-' || name[0] == '=' {
+		err = f.failf("bad flag syntax: %s", s)
+		return
+	}
+
+	split := strings.SplitN(name, "=", 2)
+	name = split[0]
+	flag, exists := f.formal[f.normalizeFlagName(name)]
+	if !exists {
+		if name == "help" { // special case for nice help message.
+			f.usage()
+			return a, ErrHelp
+		}
+		err = f.failf("unknown flag: --%s", name)
+		return
+	}
+
+	var value string
+	if len(split) == 2 {
+		// '--flag=arg'
+		value = split[1]
+	} else if flag.NoOptDefVal != "" {
+		// '--flag' (arg was optional)
+		value = flag.NoOptDefVal
+	} else if len(a) > 0 {
+		// '--flag arg'
+		value = a[0]
+		a = a[1:]
+	} else {
+		// '--flag' (arg was required)
+		err = f.failf("flag needs an argument: %s", s)
+		return
+	}
+
+	err = fn(flag, value)
+	if err != nil {
+		f.failf(err.Error())
+	}
+	return
+}
+
+func (f *FlagSet) parseSingleShortArg(shorthands string, args []string, fn parseFunc) (outShorts string, outArgs []string, err error) {
+	if strings.HasPrefix(shorthands, "test.") {
+		return
+	}
+
+	outArgs = args
+	outShorts = shorthands[1:]
+	c := shorthands[0]
+
+	flag, exists := f.shorthands[c]
+	if !exists {
+		if c == 'h' { // special case for nice help message.
+			f.usage()
+			err = ErrHelp
+			return
+		}
+		err = f.failf("unknown shorthand flag: %q in -%s", c, shorthands)
+		return
+	}
+
+	var value string
+	if len(shorthands) > 2 && shorthands[1] == '=' {
+		// '-f=arg'
+		value = shorthands[2:]
+		outShorts = ""
+	} else if flag.NoOptDefVal != "" {
+		// '-f' (arg was optional)
+		value = flag.NoOptDefVal
+	} else if len(shorthands) > 1 {
+		// '-farg'
+		value = shorthands[1:]
+		outShorts = ""
+	} else if len(args) > 0 {
+		// '-f arg'
+		value = args[0]
+		outArgs = args[1:]
+	} else {
+		// '-f' (arg was required)
+		err = f.failf("flag needs an argument: %q in -%s", c, shorthands)
+		return
+	}
+
+	if flag.ShorthandDeprecated != "" {
+		fmt.Fprintf(f.out(), "Flag shorthand -%s has been deprecated, %s\n", flag.Shorthand, flag.ShorthandDeprecated)
+	}
+
+	err = fn(flag, value)
+	if err != nil {
+		f.failf(err.Error())
+	}
+	return
+}
+
+func (f *FlagSet) parseShortArg(s string, args []string, fn parseFunc) (a []string, err error) {
+	a = args
+	shorthands := s[1:]
+
+	// "shorthands" can be a series of shorthand letters of flags (e.g. "-vvv").
+	for len(shorthands) > 0 {
+		shorthands, a, err = f.parseSingleShortArg(shorthands, args, fn)
+		if err != nil {
+			return
+		}
+	}
+
+	return
+}
+
+func (f *FlagSet) parseArgs(args []string, fn parseFunc) (err error) {
+	for len(args) > 0 {
+		s := args[0]
+		args = args[1:]
+		if len(s) == 0 || s[0] != '-' || len(s) == 1 {
+			if !f.interspersed {
+				f.args = append(f.args, s)
+				f.args = append(f.args, args...)
+				return nil
+			}
+			f.args = append(f.args, s)
+			continue
+		}
+
+		if s[1] == '-' {
+			if len(s) == 2 { // "--" terminates the flags
+				f.argsLenAtDash = len(f.args)
+				f.args = append(f.args, args...)
+				break
+			}
+			args, err = f.parseLongArg(s, args, fn)
+		} else {
+			args, err = f.parseShortArg(s, args, fn)
+		}
+		if err != nil {
+			return
+		}
+	}
+	return
+}
+
+// Parse parses flag definitions from the argument list, which should not
+// include the command name.  Must be called after all flags in the FlagSet
+// are defined and before flags are accessed by the program.
+// The return value will be ErrHelp if -help was set but not defined.
+func (f *FlagSet) Parse(arguments []string) error {
+	f.parsed = true
+
+	if len(arguments) < 0 {
+		return nil
+	}
+
+	f.args = make([]string, 0, len(arguments))
+
+	set := func(flag *Flag, value string) error {
+		return f.Set(flag.Name, value)
+	}
+
+	err := f.parseArgs(arguments, set)
+	if err != nil {
+		switch f.errorHandling {
+		case ContinueOnError:
+			return err
+		case ExitOnError:
+			fmt.Println(err)
+			os.Exit(2)
+		case PanicOnError:
+			panic(err)
+		}
+	}
+	return nil
+}
+
+type parseFunc func(flag *Flag, value string) error
+
+// ParseAll parses flag definitions from the argument list, which should not
+// include the command name. The arguments for fn are flag and value. Must be
+// called after all flags in the FlagSet are defined and before flags are
+// accessed by the program. The return value will be ErrHelp if -help was set
+// but not defined.
+func (f *FlagSet) ParseAll(arguments []string, fn func(flag *Flag, value string) error) error {
+	f.parsed = true
+	f.args = make([]string, 0, len(arguments))
+
+	err := f.parseArgs(arguments, fn)
+	if err != nil {
+		switch f.errorHandling {
+		case ContinueOnError:
+			return err
+		case ExitOnError:
+			os.Exit(2)
+		case PanicOnError:
+			panic(err)
+		}
+	}
+	return nil
+}
+
+// Parsed reports whether f.Parse has been called.
+func (f *FlagSet) Parsed() bool {
+	return f.parsed
+}
+
+// Parse parses the command-line flags from os.Args[1:].  Must be called
+// after all flags are defined and before flags are accessed by the program.
+func Parse() {
+	// Ignore errors; CommandLine is set for ExitOnError.
+	CommandLine.Parse(os.Args[1:])
+}
+
+// ParseAll parses the command-line flags from os.Args[1:] and called fn for each.
+// The arguments for fn are flag and value. Must be called after all flags are
+// defined and before flags are accessed by the program.
+func ParseAll(fn func(flag *Flag, value string) error) {
+	// Ignore errors; CommandLine is set for ExitOnError.
+	CommandLine.ParseAll(os.Args[1:], fn)
+}
+
+// SetInterspersed sets whether to support interspersed option/non-option arguments.
+func SetInterspersed(interspersed bool) {
+	CommandLine.SetInterspersed(interspersed)
+}
+
+// Parsed returns true if the command-line flags have been parsed.
+func Parsed() bool {
+	return CommandLine.Parsed()
+}
+
+// CommandLine is the default set of command-line flags, parsed from os.Args.
+var CommandLine = NewFlagSet(os.Args[0], ExitOnError)
+
+// NewFlagSet returns a new, empty flag set with the specified name,
+// error handling property and SortFlags set to true.
+func NewFlagSet(name string, errorHandling ErrorHandling) *FlagSet {
+	f := &FlagSet{
+		name:          name,
+		errorHandling: errorHandling,
+		argsLenAtDash: -1,
+		interspersed:  true,
+		SortFlags:     true,
+	}
+	return f
+}
+
+// SetInterspersed sets whether to support interspersed option/non-option arguments.
+func (f *FlagSet) SetInterspersed(interspersed bool) {
+	f.interspersed = interspersed
+}
+
+// Init sets the name and error handling property for a flag set.
+// By default, the zero FlagSet uses an empty name and the
+// ContinueOnError error handling policy.
+func (f *FlagSet) Init(name string, errorHandling ErrorHandling) {
+	f.name = name
+	f.errorHandling = errorHandling
+	f.argsLenAtDash = -1
+}