1 files changed, 122 insertions, 0 deletions
diff --git a/src/cmd/go/internal/cmdflag/flag.go b/src/cmd/go/internal/cmdflag/flag.go
new file mode 100644
index 0000000..86e33ea
--- /dev/null
+++ b/src/cmd/go/internal/cmdflag/flag.go
@@ -0,0 +1,122 @@
+// Copyright 2017 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 cmdflag handles flag processing common to several go tools.
+package cmdflag
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"strings"
+)
+
+// The flag handling part of go commands such as test is large and distracting.
+// We can't use the standard flag package because some of the flags from
+// our command line are for us, and some are for the binary we're running,
+// and some are for both.
+
+// ErrFlagTerminator indicates the distinguished token "--", which causes the
+// flag package to treat all subsequent arguments as non-flags.
+var ErrFlagTerminator = errors.New("flag terminator")
+
+// A FlagNotDefinedError indicates a flag-like argument that does not correspond
+// to any registered flag in a FlagSet.
+type FlagNotDefinedError struct {
+	RawArg   string // the original argument, like --foo or -foo=value
+	Name     string
+	HasValue bool   // is this the -foo=value or --foo=value form?
+	Value    string // only provided if HasValue is true
+}
+
+func (e FlagNotDefinedError) Error() string {
+	return fmt.Sprintf("flag provided but not defined: -%s", e.Name)
+}
+
+// A NonFlagError indicates an argument that is not a syntactically-valid flag.
+type NonFlagError struct {
+	RawArg string
+}
+
+func (e NonFlagError) Error() string {
+	return fmt.Sprintf("not a flag: %q", e.RawArg)
+}
+
+// ParseOne sees if args[0] is present in the given flag set and if so,
+// sets its value and returns the flag along with the remaining (unused) arguments.
+//
+// ParseOne always returns either a non-nil Flag or a non-nil error,
+// and always consumes at least one argument (even on error).
+//
+// Unlike (*flag.FlagSet).Parse, ParseOne does not log its own errors.
+func ParseOne(fs *flag.FlagSet, args []string) (f *flag.Flag, remainingArgs []string, err error) {
+	// This function is loosely derived from (*flag.FlagSet).parseOne.
+
+	raw, args := args[0], args[1:]
+	arg := raw
+	if strings.HasPrefix(arg, "--") {
+		if arg == "--" {
+			return nil, args, ErrFlagTerminator
+		}
+		arg = arg[1:] // reduce two minuses to one
+	}
+
+	switch arg {
+	case "-?", "-h", "-help":
+		return nil, args, flag.ErrHelp
+	}
+	if len(arg) < 2 || arg[0] != '-' || arg[1] == '-' || arg[1] == '=' {
+		return nil, args, NonFlagError{RawArg: raw}
+	}
+
+	name, value, hasValue := strings.Cut(arg[1:], "=")
+
+	f = fs.Lookup(name)
+	if f == nil {
+		return nil, args, FlagNotDefinedError{
+			RawArg:   raw,
+			Name:     name,
+			HasValue: hasValue,
+			Value:    value,
+		}
+	}
+
+	// Use fs.Set instead of f.Value.Set below so that any subsequent call to
+	// fs.Visit will correctly visit the flags that have been set.
+
+	failf := func(format string, a ...any) (*flag.Flag, []string, error) {
+		return f, args, fmt.Errorf(format, a...)
+	}
+
+	if fv, ok := f.Value.(boolFlag); ok && fv.IsBoolFlag() { // special case: doesn't need an arg
+		if hasValue {
+			if err := fs.Set(name, value); err != nil {
+				return failf("invalid boolean value %q for -%s: %v", value, name, err)
+			}
+		} else {
+			if err := fs.Set(name, "true"); err != nil {
+				return failf("invalid boolean flag %s: %v", name, err)
+			}
+		}
+	} else {
+		// It must have a value, which might be the next argument.
+		if !hasValue && len(args) > 0 {
+			// value is the next arg
+			hasValue = true
+			value, args = args[0], args[1:]
+		}
+		if !hasValue {
+			return failf("flag needs an argument: -%s", name)
+		}
+		if err := fs.Set(name, value); err != nil {
+			return failf("invalid value %q for flag -%s: %v", value, name, err)
+		}
+	}
+
+	return f, args, nil
+}
+
+type boolFlag interface {
+	IsBoolFlag() bool
+}