k3s/vendor/github.com/rancher/spur/flag/flag.go

// 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 flag implements command-line flag parsing.

	Usage

	Define flags using flag.String(), Bool(), Int(), etc.

	This declares an integer flag, -n, stored in the pointer nFlag, with type *int:
		import "flag"
		var nFlag = flag.Int("n", 1234, "help message for flag n")
	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 following the flags are available as the
	slice flag.Args() or individually as flag.Arg(i).
	The arguments are indexed from 0 through flag.NArg()-1.

	Command line flag syntax

	The following forms are permitted:

		-flag
		-flag=x
		-flag x  // non-boolean flags only
	One or two minus signs may be used; they are equivalent.
	The last form is not permitted for boolean flags because the
	meaning of the command
		cmd -x *
	where * is a Unix shell wildcard, will change if there is a file
	called 0, false, etc. You must use the -flag=false form to turn
	off a boolean flag.

	Flag parsing stops just before the first non-flag argument
	("-" is a non-flag argument) or after the terminator "--".

	Integer flags accept 1234, 0664, 0x1234 and may be negative.
	Boolean flags may be:
		1, 0, t, f, 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 flag

import (
	"errors"
	"fmt"
	"io"
	"os"
	"reflect"
	"sort"
	"strings"

	"github.com/rancher/spur/generic"
)

// ErrHelp is the error returned if the -help or -h flag is invoked
// but no such flag is defined.
var ErrHelp = errors.New("flag: help requested")

// Value is the interface to the dynamic value stored in a flag.
// (The default value is represented as a string.)
//
// If a Value has an IsBoolFlag() bool method returning true,
// the command-line parser makes -name equivalent to -name=true
// rather than using the next command-line argument.
//
// Set is called once, in command line order, for each flag present.
// The flag package may call the String method with a zero-valued receiver,
// such as a nil pointer.
type Value interface {
	String() string
	Set(interface{}) error
}

// Getter is an interface that allows the contents of a Value to be retrieved.
// It wraps the Value interface, rather than being part of it, because it
// appeared after Go 1 and its compatibility rules. All Value types provided
// by this package satisfy the Getter interface.
type Getter interface {
	Value
	Get() interface{}
}

// BoolFlag is an interface for determining if the value of a flag is needed.
type BoolFlag interface {
	IsBoolFlag() bool
}

// IsBoolValue returns true for data types which don't require a flag value
func IsBoolValue(value interface{}) bool {
	if v, ok := value.(BoolFlag); ok {
		return v.IsBoolFlag()
	}
	var t reflect.Type
	if v, ok := value.(Getter); ok {
		t = generic.ElemTypeOf(v.Get())
	} else {
		t = generic.ElemTypeOf(value)
	}
	return t != nil && t.String() == "bool"
}

// ErrorHandling defines how FlagSet.Parse behaves if the parse fails.
type ErrorHandling int

// These constants cause FlagSet.Parse to behave as described if the parse fails.
const (
	ContinueOnError ErrorHandling = iota // Return a descriptive error.
	ExitOnError                          // Call os.Exit(2) or for -h/-help Exit(0).
	PanicOnError                         // Call panic with a descriptive error.
)

// A FlagSet represents a set of defined flags. The zero value of a FlagSet
// has no name and has ContinueOnError error handling.
//
// Flag names must be unique within a FlagSet. An attempt to define a flag whose
// name is already in use will cause a panic.
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. What happens after Usage is called depends
	// on the ErrorHandling setting; for the command line, this defaults
	// to ExitOnError, which exits the program after calling Usage.
	Usage func()

	name          string
	parsed        bool
	actual        map[string]*Flag
	formal        map[string]*Flag
	args          []string // arguments after flags
	errorHandling ErrorHandling
	output        io.Writer // nil means stderr; use Output() accessor
}

// A Flag represents the state of a flag.
type Flag struct {
	Name     string // name as it appears on command line
	Usage    string // help message
	Value    Value  // value as set
	DefValue string // default value (as text); for usage message
}

// sortFlags returns the flags as a slice in lexicographical sorted order.
func sortFlags(flags map[string]*Flag) []*Flag {
	result := make([]*Flag, len(flags))
	i := 0
	for _, f := range flags {
		result[i] = f
		i++
	}
	sort.Slice(result, func(i, j int) bool {
		return result[i].Name < result[j].Name
	})
	return result
}

const invalidValueTemplate = "invalid value %q for flag -%s: %v"

func (f *FlagSet) addActual(name string, flag *Flag) {
	if f.actual == nil {
		f.actual = make(map[string]*Flag)
	}
	f.actual[name] = flag
}

// Output returns the destination for usage and error messages. os.Stderr is returned if
// output was not set or was set to nil.
func (f *FlagSet) Output() io.Writer {
	if f.output == nil {
		return os.Stderr
	}
	return f.output
}

// Name returns the name of the flag set.
func (f *FlagSet) Name() string {
	return f.name
}

// ErrorHandling returns the error handling behavior of the flag set.
func (f *FlagSet) ErrorHandling() ErrorHandling {
	return f.errorHandling
}

// 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, calling fn for each.
// It visits all flags, even those not set.
func (f *FlagSet) VisitAll(fn func(*Flag)) {
	for _, flag := range sortFlags(f.formal) {
		fn(flag)
	}
}

// VisitAll visits the command-line flags in lexicographical order, 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, calling fn for each.
// It visits only those flags that have been set.
func (f *FlagSet) Visit(fn func(*Flag)) {
	for _, flag := range sortFlags(f.actual) {
		fn(flag)
	}
}

// NeedsVisit marks the named flags for visit.
func (f *FlagSet) NeedsVisit(names ...string) {
	for _, name := range names {
		if flag := f.Lookup(name); flag != nil {
			f.addActual(name, flag)
		}
	}
}

// Visit visits the command-line flags in lexicographical order, 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.formal[name]
}

// Lookup returns the Flag structure of the named command-line flag,
// returning nil if none exists.
func Lookup(name string) *Flag {
	return CommandLine.formal[name]
}

// Set sets the value of the named flag.
func (f *FlagSet) Set(name string, value interface{}) error {
	flag, ok := f.formal[name]
	if !ok {
		return fmt.Errorf("no such flag -%v", name)
	}
	err := flag.Value.Set(value)
	if err != nil {
		return fmt.Errorf(invalidValueTemplate, value, name, err)
	}
	f.addActual(name, flag)
	return nil
}

// Set sets the value of the named command-line flag.
func Set(name string, value interface{}) error {
	return CommandLine.Set(name, value)
}

// isZeroValue determines whether the string represents the zero
// value for a flag.
func isZeroValue(flag *Flag, value string) bool {
	// Build a zero value of the flag's Value type, and see if the
	// result of calling its String method equals the value passed in.
	if val, ok := flag.Value.(Getter); ok {
		if s, ok := generic.ToString(generic.Zero(val.Get())); ok {
			return value == s
		}
	}
	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.
		}
	}
	// No explicit name, so use type if we can find one.
	name = "value"
	if v, ok := flag.Value.(Getter); ok {
		name = generic.TypeOf(v.Get()).String()
	}
	if IsBoolValue(flag.Value) {
		name = ""
	}
	return
}

// PrintDefaults prints, to standard error unless configured otherwise, the
// default values of all defined command-line flags in the set. See the
// documentation for the global function PrintDefaults for more information.
func (f *FlagSet) PrintDefaults() {
	f.VisitAll(func(flag *Flag) {
		s := fmt.Sprintf("  -%s", flag.Name) // Two spaces before -; see next two comments.
		name, usage := UnquoteUsage(flag)
		if len(name) > 0 {
			s += " " + name
		}
		// Boolean flags of one ASCII letter are so common we
		// treat them specially, putting their usage on the same line.
		if len(s) <= 4 { // space, space, '-', 'x'.
			s += "\t"
		} else {
			// Four spaces before the tab triggers good alignment
			// for both 4- and 8-space tab stops.
			s += "\n    \t"
		}
		s += strings.ReplaceAll(usage, "\n", "\n    \t")

		if !isZeroValue(flag, flag.DefValue) {
			if v, ok := flag.Value.(Getter); ok && generic.TypeOf(v.Get()).String() == "string" {
				// put quotes on the value
				s += fmt.Sprintf(" (default %q)", flag.DefValue)
			} else {
				s += fmt.Sprintf(" (default %v)", flag.DefValue)
			}
		}
		fmt.Fprint(f.Output(), s, "\n")
	})
}

// PrintDefaults prints, to standard error unless configured otherwise,
// a usage message showing the default settings of all defined
// command-line flags.
// For an integer valued flag x, the default output has the form
//	-x int
//		usage-message-for-x (default 7)
// The usage message will appear on a separate line for anything but
// a bool flag with a one-byte name. For bool flags, the type is
// omitted and if the flag name is one byte the usage message appears
// on the same line. The parenthetical default is omitted if the
// default is the zero value for the type. The listed type, here int,
// can be changed by placing a back-quoted name in the flag's usage
// string; the first such item in the message is taken to be a parameter
// name to show in the message and the back quotes are stripped from
// the message when displayed. For instance, given
//	flag.String("I", "", "search `directory` for include files")
// the output will be
//	-I directory
//		search directory for include files.
//
// To change the destination for flag messages, call CommandLine.SetOutput.
func PrintDefaults() {
	CommandLine.PrintDefaults()
}

// defaultUsage is the default function to print a usage message.
func (f *FlagSet) defaultUsage() {
	if f.name == "" {
		fmt.Fprintf(f.Output(), "Usage:\n")
	} else {
		fmt.Fprintf(f.Output(), "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 a usage message documenting all defined command-line flags
// to CommandLine's output, which by default is os.Stderr.
// It is called when an error occurs while parsing 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.
// Custom usage functions may choose to exit the program; by default exiting
// happens anyway as the command line's error handling strategy is set to
// ExitOnError.
var Usage = func() {
	fmt.Fprintf(CommandLine.Output(), "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. Arg returns an empty string if the
// requested element does not exist.
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. Arg returns an empty string if the
// requested element does not exist.
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) {
	// Remember the default value as a string; it won't change.
	flag := &Flag{name, usage, value, value.String()}
	_, alreadythere := f.formal[name]
	if alreadythere {
		var msg string
		if f.name == "" {
			msg = fmt.Sprintf("flag redefined: %s", name)
		} else {
			msg = fmt.Sprintf("%s flag redefined: %s", f.name, name)
		}
		fmt.Fprintln(f.Output(), msg)
		panic(msg) // Happens only if flags are declared with identical names
	}
	if f.formal == nil {
		f.formal = make(map[string]*Flag)
	}
	f.formal[name] = 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.Var(value, name, 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...)
	fmt.Fprintln(f.Output(), err)
	f.usage()
	return err
}

// usage calls the Usage method for the flag set if one is specified,
// or the appropriate default usage function otherwise.
func (f *FlagSet) usage() {
	if f.Usage == nil {
		f.defaultUsage()
	} else {
		f.Usage()
	}
}

// parseOne parses one flag. It reports whether a flag was seen.
func (f *FlagSet) parseOne() (bool, error) {
	if len(f.args) == 0 {
		return false, nil
	}
	s := f.args[0]
	if len(s) < 2 || s[0] != '-' {
		return false, nil
	}
	numMinuses := 1
	if s[1] == '-' {
		numMinuses++
		if len(s) == 2 { // "--" terminates the flags
			f.args = f.args[1:]
			return false, nil
		}
	}
	name := s[numMinuses:]
	if len(name) == 0 || name[0] == '-' || name[0] == '=' {
		return false, f.failf("bad flag syntax: %s", s)
	}

	// it's a flag. does it have an argument?
	f.args = f.args[1:]
	hasValue := false
	value := ""
	for i := 1; i < len(name); i++ { // equals cannot be first
		if name[i] == '=' {
			value = name[i+1:]
			hasValue = true
			name = name[0:i]
			break
		}
	}
	m := f.formal
	flag, alreadythere := m[name] // BUG
	if !alreadythere {
		if name == "help" || name == "h" { // special case for nice help message.
			f.usage()
			return false, ErrHelp
		}
		return false, f.failf("flag provided but not defined: -%s", name)
	}

	if IsBoolValue(flag.Value) { // special case: doesn't need an arg
		if hasValue {
			if err := flag.Value.Set(value); err != nil {
				return false, f.failf(invalidValueTemplate, value, name, err)
			}
		} else {
			if err := flag.Value.Set("true"); err != nil {
				return false, f.failf("invalid boolean flag %s: %v", name, err)
			}
		}
	} else {
		// It must have a value, which might be the next argument.
		if !hasValue && len(f.args) > 0 {
			// value is the next arg
			hasValue = true
			value, f.args = f.args[0], f.args[1:]
		}
		if !hasValue {
			return false, f.failf("flag needs an argument: -%s", name)
		}
		if err := flag.Value.Set(value); err != nil {
			return false, f.failf(invalidValueTemplate, value, name, err)
		}
	}
	if f.actual == nil {
		f.actual = make(map[string]*Flag)
	}
	f.actual[name] = flag
	return true, nil
}

// 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 or -h were set but not defined.
func (f *FlagSet) Parse(arguments []string) error {
	f.parsed = true
	f.args = arguments
	for {
		seen, err := f.parseOne()
		if seen {
			continue
		}
		if err == nil {
			break
		}
		switch f.errorHandling {
		case ContinueOnError:
			return err
		case ExitOnError:
			if err == ErrHelp {
				os.Exit(0)
			}
			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:])
}

// Parsed reports whether 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.
// The top-level functions such as BoolVar, Arg, and so on are wrappers for the
// methods of CommandLine.
var CommandLine = NewFlagSet(os.Args[0], ExitOnError)

func init() {
	// Override generic FlagSet default Usage with call to global Usage.
	// Note: This is not CommandLine.Usage = Usage,
	// because we want any eventual call to use any updated value of Usage,
	// not the value it has when this line is run.
	CommandLine.Usage = commandLineUsage
}

func commandLineUsage() {
	Usage()
}

// NewFlagSet returns a new, empty flag set with the specified name and
// error handling property. If the name is not empty, it will be printed
// in the default usage message and in error messages.
func NewFlagSet(name string, errorHandling ErrorHandling) *FlagSet {
	f := &FlagSet{
		name:          name,
		errorHandling: errorHandling,
	}
	f.Usage = f.defaultUsage
	return f
}

// 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
}