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flag_parse.go
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flag_parse.go
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// SPDX-License-Identifier: Apache-2.0
// Copyright 2023 The Prime Citizens
package cli
import (
"strings"
"time"
"unicode/utf8"
)
type (
// ParseErrorHandleFunc handles the parseErr when parsing args[posErrArg].
//
// Return nil to ignore the parseErr and continue parsing.
ParseErrorHandleFunc = func(opts *ParseOptions, args []string, posErrArg int, parseErr error) (err error)
)
// ParseOptions are options for flag parsing.
type ParseOptions struct {
// StartTime is assumed to be the time of parsing start.
StartTime time.Time
// HandleParseError is the function to handle flag parsing errors.
HandleParseError ParseErrorHandleFunc
// PosArgsBuf is the buffer used by ParseFlags{,LowLevel} for appending
// positional args.
PosArgsBuf []string
// HelpArgs are arg values can initiate help request.
//
// - HelpArgs = nil, is equivalent to HelpArgs = []string{"--help", "-h", "help"}.
// - HelpArgs = []string{} will disable the help system.
// - otherwise, use the supplied HelpArgs to match args.
HelpArgs []string
// Extra custom data.
Extra any
}
// IsHelpArg returns true if x is supposed to be an arg requesting help.
func (c *ParseOptions) IsHelpArg(x string) bool {
if c == nil || c.HelpArgs == nil {
switch x {
case "--help", "-h", "help":
return true
}
} else {
for _, cmd := range c.HelpArgs {
if cmd == x {
return true
}
}
}
return false
}
// ParseFlags parses args with options, where args are usually the os.Args[1:].
//
// Return value posArgs are positional args, dashArgs are args after the first
// dash (`--`).
//
// Known limitations:
//
// - Flags allow implicit value cannot accept valid standalone value prefixed
// with hyphen (`-`) due to ambiguity.
// e.g. `--foo -1` where flag `foo` is of type IntSum.
// To workaround, use `--foo=-1`.
//
// - Standalone dash (`--`) can never become flag value or positional
// arg.
// To workaround for flag value, use `--flag=--`.
// There is no workaround to make `--` as a posArg.
func ParseFlags(args []string, flags FlagFinder, opts *ParseOptions) (posArgs, dashArgs []string, err error) {
if opts != nil {
posArgs = opts.PosArgsBuf
}
_, posDash, _, posArgs, _, err := ParseFlagsLowLevel(
args, flags, opts,
0, // offset
true, // appendPosArgs
false, // stopAtFirstPosArg
true, // setFlags
posArgs, // posArgsBuf
)
if posDash >= 0 {
dashArgs = args[posDash+1:]
}
return
}
// ParseFlagsLowLevel is the low-level version of ParseFlags with more
// options for flag parsing control.
//
// If appendPosArgs is false, this function doesn't append positional args to
// posArgs, so the return value posArgs will be exactly the same a posArgsBuf.
//
// If stopAtFirstPosArg is true, this function returns on reaching the first
// positional arg (before the dash), that arg is not added to nParsed.
//
// If len(opts.HelpArgs) > 0, this function returns on reaching the first flag
// that matches any of help flags, in which case, the return value helpArgAt
// is expected to be greater or equal to zero, and args[helpArgAt] is the arg
// triggered this return.
//
// If setFlagValue is false, this function calls Flag.Decode() with set = false.
//
// The return value nParsed is the count of args parsed, which includes the
// bad flag on error return (in which case there are nParsed-1 known good
// args).
//
// The return value posDash is the index into args, when posDash >= 0,
// args[posDash] = "--" and args[posDash+1:] is dashArgs.
func ParseFlagsLowLevel(
args []string,
flags FlagFinder,
opts *ParseOptions,
offset int,
appendPosArgs bool,
stopAtFirstPosArg bool,
setFlagValue bool,
posArgsBuf []string,
) (
nParsed int,
posDash int,
foundPosArg bool,
posArgs []string,
helpArgAt int,
err error,
) {
posArgs = posArgsBuf
posDash = -1
helpArgAt = -1
i := offset
for ; i < len(args); i++ {
arg := args[i]
szArg := len(arg)
if szArg == 0 || arg[0] != '-' || szArg == 1 /* '-' */ {
foundPosArg = true
if appendPosArgs {
posArgs = append(posArgs, arg)
}
if isHelpArg := opts.IsHelpArg(arg); isHelpArg || stopAtFirstPosArg {
if isHelpArg {
helpArgAt = i
}
// DO NOT include the pos arg (this one).
nParsed = i - offset
return
}
continue
}
var shiftNext bool
if arg[1] == '-' {
if szArg == 2 {
// dash
nParsed = len(args)
posDash = i
return
}
if opts.IsHelpArg(arg) {
helpArgAt = i
if _, ok := flags.FindFlag(arg[2:]); ok {
// there is real help flag, parse it as application may expect
// its value getting set.
shiftNext, err = parseLongFlag(flags, opts, args, i, setFlagValue)
} else {
// TODO: the help flag is a pseudo flag.
}
nParsed = i + 1 - offset
return
}
shiftNext, err = parseLongFlag(flags, opts, args, i, setFlagValue)
} else {
if opts.IsHelpArg(arg) {
helpArgAt = i
if _, ok := flags.FindFlag(arg[1:]); ok {
// there is real help flag, parse it as application may expect
// its value getting set.
//
// TODO: should we only parse the help flag instead of the whole shorthand cluster?
shiftNext, err = parseShortFlags(flags, opts, args, i, setFlagValue)
} else {
// TODO: the help flag is a pseudo flag.
}
nParsed = i + 1 - offset
return
}
// match shorthand, here we don't check the flag length
// as it may contain multiple shorthand flags (e.g. `-vvv`)
shiftNext, err = parseShortFlags(flags, opts, args, i, setFlagValue)
}
if err != nil {
if opts == nil || opts.HandleParseError == nil { // no error handler
nParsed = i + 1 - offset
return
}
err = opts.HandleParseError(opts, args, i, err)
if err != nil {
nParsed = i + 1 - offset
return
}
// error ignored
}
if shiftNext {
i++
}
}
nParsed = i - offset
return
}
func parseLongFlag(
flags FlagFinder,
opts *ParseOptions,
args []string, // args[i] is the long flag with dash prefix
i int,
set bool,
) (shiftNext bool, err error) {
name, value, hasValue := strings.Cut(args[i][2:], "=")
// name MUST not be empty
if len(name) == 0 {
// defensive check, should never happen as the caller always checks the size.
panic("unexpected empty arg name")
}
f, ok := flags.FindFlag(name)
if !ok {
return false, &ErrFlagUndefined{
Name: name,
At: i,
}
}
if hasValue {
// --foo=bar case
err = f.Decode(opts, name, value, set)
if err != nil {
return false, &ErrFlagValueInvalid{
Name: name,
Value: value,
NameAt: i,
ValueAt: i,
}
}
return false, nil
}
// --foo case
if i == len(args)-1 || args[i+1] == "--" /* never use standalone dash as value */ {
// when not having arg value, it MUST be an implicit arg
goto TryImplied
}
value = args[i+1]
if err = f.Decode(opts, name, value, false /* set = false for checking */); err == nil {
// can consume next arg
if strings.HasPrefix(value, "-") {
if _, ok = f.ImplyValue(); ok {
return true, &ErrAmbiguousArgs{
Name: name,
Value: value,
At: i,
}
}
}
if set {
return true, f.Decode(opts, name, value, true)
}
return true, nil
}
// cannot consume next arg, try implied value.
TryImplied:
if value, ok = f.ImplyValue(); ok {
err = f.Decode(opts, name, value, set)
if err != nil {
return false, &ErrFlagValueInvalid{
Name: name,
Value: value,
NameAt: i,
ValueAt: -1,
Reason: err,
}
}
return false, nil
}
// no implied value
if i == len(args)-1 || args[i+1] == "--" {
return false, &ErrFlagValueMissing{Name: name, At: i}
}
return false, &ErrFlagValueInvalid{
Name: name,
Value: args[i+1],
NameAt: i,
ValueAt: i + 1,
Reason: err,
}
}
func parseShortFlags(
flags FlagFinder,
opts *ParseOptions,
args []string, // args[i] is the shorthand (cluster) with hyphen prefix
i int,
set bool,
) (shiftNext bool, err error) {
var (
offset int
width int
sz int
f Flag
name string
value string
hasValue bool
ok bool
)
s, value, hasValue := strings.Cut(args[i][1:], "=")
for sz = len(s); offset < sz; {
_, width = utf8.DecodeRuneInString(s[offset:])
name = s[offset : offset+width]
f, ok = flags.FindFlag(name)
if !ok {
return false, &ErrFlagUndefined{
Name: name,
At: i,
}
}
offset += width
if offset == sz { // reaching the last shorthand
if hasValue {
err = f.Decode(opts, name, value, set)
if err != nil {
return false, &ErrFlagValueInvalid{
Name: name,
Value: value,
NameAt: i,
ValueAt: i,
Reason: err,
}
}
return false, nil
}
if i == len(args)-1 || args[i+1] == "--" /* never use standalone dash as value */ {
goto TryImplied
}
value = args[i+1]
if err = f.Decode(opts, name, value, false /* set = false for checking */); err == nil {
// can consume the next arg.
if strings.HasPrefix(value, "-") {
if _, ok = f.ImplyValue(); ok {
return true, &ErrAmbiguousArgs{
Name: name,
Value: value,
At: i,
}
}
}
if set {
err = f.Decode(opts, name, value, true)
if err != nil {
return true, &ErrFlagValueInvalid{
Name: name,
Value: value,
NameAt: i,
ValueAt: i + 1,
}
}
return true, nil
}
return true, nil
}
// cannot consume the next arg, try implied value
TryImplied:
if value, ok = f.ImplyValue(); ok {
err = f.Decode(opts, name, value, set)
if err != nil {
return false, &ErrFlagValueInvalid{
Name: name,
Value: value,
NameAt: i,
ValueAt: -1,
Reason: err,
}
}
return false, nil
}
// bad
if i == len(args)-1 || args[i+1] == "--" {
return false, &ErrFlagValueMissing{Name: name, At: i}
}
return false, &ErrFlagValueInvalid{
Name: name,
Value: args[i+1],
NameAt: i,
ValueAt: i + 1,
}
}
// not the last shorthand
//
// flags in between prefer implicit value.
if impliedValue, ok := f.ImplyValue(); ok {
if err := f.Decode(opts, name, impliedValue, set); err != nil {
return false, err
}
continue
}
// flag not having implicit value
// treate remaining value in s as arg value
// e.g. given `-t` == `--type`, then `-tfile` == `--type file`
//
// but reject `-abcd=file` because we are not `d`, and assigning
// explicit value to `c` is not intuitive.
if hasValue {
return false, &ErrShorthandOfExplicitFlagInMiddle{
Shorthand: name,
ShorthandCluster: s,
Value: value,
}
}
err = f.Decode(opts, name, s[offset:], set)
if err != nil {
return false, &ErrFlagValueInvalid{
Name: "",
Value: s[offset:],
NameAt: i,
ValueAt: i,
Reason: err,
}
}
return false, nil
}
return false, nil
}