Initial commit: Go 1.23 release state

src/flag/example_flagset_test.go

@@ -0,0 +1,57 @@
+// Copyright 2023 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_test
+
+import (
+	"flag"
+	"fmt"
+	"time"
+)
+
+func ExampleFlagSet() {
+
+	start := func(args []string) {
+		// A real program (not an example) would use flag.ExitOnError.
+		fs := flag.NewFlagSet("start", flag.ContinueOnError)
+		addr := fs.String("addr", ":8080", "`address` to listen on")
+		if err := fs.Parse(args); err != nil {
+			fmt.Printf("error: %s", err)
+			return
+		}
+		fmt.Printf("starting server on %s\n", *addr)
+	}
+
+	stop := func(args []string) {
+		fs := flag.NewFlagSet("stop", flag.ContinueOnError)
+		timeout := fs.Duration("timeout", time.Second, "stop timeout duration")
+		if err := fs.Parse(args); err != nil {
+			fmt.Printf("error: %s", err)
+			return
+		}
+		fmt.Printf("stopping server (timeout=%v)\n", *timeout)
+	}
+
+	main := func(args []string) {
+		subArgs := args[2:] // Drop program name and command.
+		switch args[1] {
+		case "start":
+			start(subArgs)
+		case "stop":
+			stop(subArgs)
+		default:
+			fmt.Printf("error: unknown command - %q\n", args[1])
+			// In a real program (not an example) print to os.Stderr and exit the program with non-zero value.
+		}
+	}
+
+	main([]string{"httpd", "start", "-addr", ":9999"})
+	main([]string{"httpd", "stop"})
+	main([]string{"http", "start", "-log-level", "verbose"})
+
+	// Output:
+	// starting server on :9999
+	// stopping server (timeout=1s)
+	// error: flag provided but not defined: -log-level
+}

src/flag/example_func_test.go

@@ -0,0 +1,57 @@
+// Copyright 2020 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_test
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"net"
+	"os"
+)
+
+func ExampleFunc() {
+	fs := flag.NewFlagSet("ExampleFunc", flag.ContinueOnError)
+	fs.SetOutput(os.Stdout)
+	var ip net.IP
+	fs.Func("ip", "`IP address` to parse", func(s string) error {
+		ip = net.ParseIP(s)
+		if ip == nil {
+			return errors.New("could not parse IP")
+		}
+		return nil
+	})
+	fs.Parse([]string{"-ip", "127.0.0.1"})
+	fmt.Printf("{ip: %v, loopback: %t}\n\n", ip, ip.IsLoopback())
+
+	// 256 is not a valid IPv4 component
+	fs.Parse([]string{"-ip", "256.0.0.1"})
+	fmt.Printf("{ip: %v, loopback: %t}\n\n", ip, ip.IsLoopback())
+
+	// Output:
+	// {ip: 127.0.0.1, loopback: true}
+	//
+	// invalid value "256.0.0.1" for flag -ip: could not parse IP
+	// Usage of ExampleFunc:
+	//   -ip IP address
+	//     	IP address to parse
+	// {ip: <nil>, loopback: false}
+}
+
+func ExampleBoolFunc() {
+	fs := flag.NewFlagSet("ExampleBoolFunc", flag.ContinueOnError)
+	fs.SetOutput(os.Stdout)
+
+	fs.BoolFunc("log", "logs a dummy message", func(s string) error {
+		fmt.Println("dummy message:", s)
+		return nil
+	})
+	fs.Parse([]string{"-log"})
+	fs.Parse([]string{"-log=0"})
+
+	// Output:
+	// dummy message: true
+	// dummy message: 0
+}

src/flag/example_test.go

@@ -0,0 +1,85 @@
+// Copyright 2012 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.
+
+// These examples demonstrate more intricate uses of the flag package.
+package flag_test
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"strings"
+	"time"
+)
+
+// Example 1: A single string flag called "species" with default value "gopher".
+var species = flag.String("species", "gopher", "the species we are studying")
+
+// Example 2: Two flags sharing a variable, so we can have a shorthand.
+// The order of initialization is undefined, so make sure both use the
+// same default value. They must be set up with an init function.
+var gopherType string
+
+func init() {
+	const (
+		defaultGopher = "pocket"
+		usage         = "the variety of gopher"
+	)
+	flag.StringVar(&gopherType, "gopher_type", defaultGopher, usage)
+	flag.StringVar(&gopherType, "g", defaultGopher, usage+" (shorthand)")
+}
+
+// Example 3: A user-defined flag type, a slice of durations.
+type interval []time.Duration
+
+// String is the method to format the flag's value, part of the flag.Value interface.
+// The String method's output will be used in diagnostics.
+func (i *interval) String() string {
+	return fmt.Sprint(*i)
+}
+
+// Set is the method to set the flag value, part of the flag.Value interface.
+// Set's argument is a string to be parsed to set the flag.
+// It's a comma-separated list, so we split it.
+func (i *interval) Set(value string) error {
+	// If we wanted to allow the flag to be set multiple times,
+	// accumulating values, we would delete this if statement.
+	// That would permit usages such as
+	//	-deltaT 10s -deltaT 15s
+	// and other combinations.
+	if len(*i) > 0 {
+		return errors.New("interval flag already set")
+	}
+	for _, dt := range strings.Split(value, ",") {
+		duration, err := time.ParseDuration(dt)
+		if err != nil {
+			return err
+		}
+		*i = append(*i, duration)
+	}
+	return nil
+}
+
+// Define a flag to accumulate durations. Because it has a special type,
+// we need to use the Var function and therefore create the flag during
+// init.
+
+var intervalFlag interval
+
+func init() {
+	// Tie the command-line flag to the intervalFlag variable and
+	// set a usage message.
+	flag.Var(&intervalFlag, "deltaT", "comma-separated list of intervals to use between events")
+}
+
+func Example() {
+	// All the interesting pieces are with the variables declared above, but
+	// to enable the flag package to see the flags defined there, one must
+	// execute, typically at the start of main (not init!):
+	//	flag.Parse()
+	// We don't call it here because this code is a function called "Example"
+	// that is part of the testing suite for the package, which has already
+	// parsed the flags. When viewed at pkg.go.dev, however, the function is
+	// renamed to "main" and it could be run as a standalone example.
+}

src/flag/example_textvar_test.go

@@ -0,0 +1,35 @@
+// 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.
+
+package flag_test
+
+import (
+	"flag"
+	"fmt"
+	"net"
+	"os"
+)
+
+func ExampleTextVar() {
+	fs := flag.NewFlagSet("ExampleTextVar", flag.ContinueOnError)
+	fs.SetOutput(os.Stdout)
+	var ip net.IP
+	fs.TextVar(&ip, "ip", net.IPv4(192, 168, 0, 100), "`IP address` to parse")
+	fs.Parse([]string{"-ip", "127.0.0.1"})
+	fmt.Printf("{ip: %v}\n\n", ip)
+
+	// 256 is not a valid IPv4 component
+	ip = nil
+	fs.Parse([]string{"-ip", "256.0.0.1"})
+	fmt.Printf("{ip: %v}\n\n", ip)
+
+	// Output:
+	// {ip: 127.0.0.1}
+	//
+	// invalid value "256.0.0.1" for flag -ip: invalid IP address: 256.0.0.1
+	// Usage of ExampleTextVar:
+	//   -ip IP address
+	//     	IP address to parse (default 192.168.0.100)
+	// {ip: <nil>}
+}

src/flag/example_value_test.go

@@ -0,0 +1,44 @@
+// 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.
+
+package flag_test
+
+import (
+	"flag"
+	"fmt"
+	"net/url"
+)
+
+type URLValue struct {
+	URL *url.URL
+}
+
+func (v URLValue) String() string {
+	if v.URL != nil {
+		return v.URL.String()
+	}
+	return ""
+}
+
+func (v URLValue) Set(s string) error {
+	if u, err := url.Parse(s); err != nil {
+		return err
+	} else {
+		*v.URL = *u
+	}
+	return nil
+}
+
+var u = &url.URL{}
+
+func ExampleValue() {
+	fs := flag.NewFlagSet("ExampleValue", flag.ExitOnError)
+	fs.Var(&URLValue{u}, "url", "URL to parse")
+
+	fs.Parse([]string{"-url", "https://golang.org/pkg/flag/"})
+	fmt.Printf(`{scheme: %q, host: %q, path: %q}`, u.Scheme, u.Host, u.Path)
+
+	// Output:
+	// {scheme: "https", host: "golang.org", path: "/pkg/flag/"}
+}

src/flag/export_test.go

@@ -0,0 +1,24 @@
+// Copyright 2010 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
+
+import (
+	"io"
+	"os"
+)
+
+// Additional routines compiled into the package only during testing.
+
+var DefaultUsage = Usage
+
+// ResetForTesting clears all flag state and sets the usage function as directed.
+// After calling ResetForTesting, parse errors in flag handling will not
+// exit the program.
+func ResetForTesting(usage func()) {
+	CommandLine = NewFlagSet(os.Args[0], ContinueOnError)
+	CommandLine.SetOutput(io.Discard)
+	CommandLine.Usage = commandLineUsage
+	Usage = usage
+}

src/flag/flag_test.go

@@ -0,0 +1,858 @@
+// 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_test
+
+import (
+	"bytes"
+	. "flag"
+	"fmt"
+	"internal/testenv"
+	"io"
+	"os"
+	"os/exec"
+	"regexp"
+	"runtime"
+	"slices"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+)
+
+func boolString(s string) string {
+	if s == "0" {
+		return "false"
+	}
+	return "true"
+}
+
+func TestEverything(t *testing.T) {
+	ResetForTesting(nil)
+	Bool("test_bool", false, "bool value")
+	Int("test_int", 0, "int value")
+	Int64("test_int64", 0, "int64 value")
+	Uint("test_uint", 0, "uint value")
+	Uint64("test_uint64", 0, "uint64 value")
+	String("test_string", "0", "string value")
+	Float64("test_float64", 0, "float64 value")
+	Duration("test_duration", 0, "time.Duration value")
+	Func("test_func", "func value", func(string) error { return nil })
+	BoolFunc("test_boolfunc", "func", func(string) error { return nil })
+
+	m := make(map[string]*Flag)
+	desired := "0"
+	visitor := func(f *Flag) {
+		if len(f.Name) > 5 && f.Name[0:5] == "test_" {
+			m[f.Name] = f
+			ok := false
+			switch {
+			case f.Value.String() == desired:
+				ok = true
+			case f.Name == "test_bool" && f.Value.String() == boolString(desired):
+				ok = true
+			case f.Name == "test_duration" && f.Value.String() == desired+"s":
+				ok = true
+			case f.Name == "test_func" && f.Value.String() == "":
+				ok = true
+			case f.Name == "test_boolfunc" && f.Value.String() == "":
+				ok = true
+			}
+			if !ok {
+				t.Error("Visit: bad value", f.Value.String(), "for", f.Name)
+			}
+		}
+	}
+	VisitAll(visitor)
+	if len(m) != 10 {
+		t.Error("VisitAll misses some flags")
+		for k, v := range m {
+			t.Log(k, *v)
+		}
+	}
+	m = make(map[string]*Flag)
+	Visit(visitor)
+	if len(m) != 0 {
+		t.Errorf("Visit sees unset flags")
+		for k, v := range m {
+			t.Log(k, *v)
+		}
+	}
+	// Now set all flags
+	Set("test_bool", "true")
+	Set("test_int", "1")
+	Set("test_int64", "1")
+	Set("test_uint", "1")
+	Set("test_uint64", "1")
+	Set("test_string", "1")
+	Set("test_float64", "1")
+	Set("test_duration", "1s")
+	Set("test_func", "1")
+	Set("test_boolfunc", "")
+	desired = "1"
+	Visit(visitor)
+	if len(m) != 10 {
+		t.Error("Visit fails after set")
+		for k, v := range m {
+			t.Log(k, *v)
+		}
+	}
+	// Now test they're visited in sort order.
+	var flagNames []string
+	Visit(func(f *Flag) { flagNames = append(flagNames, f.Name) })
+	if !slices.IsSorted(flagNames) {
+		t.Errorf("flag names not sorted: %v", flagNames)
+	}
+}
+
+func TestGet(t *testing.T) {
+	ResetForTesting(nil)
+	Bool("test_bool", true, "bool value")
+	Int("test_int", 1, "int value")
+	Int64("test_int64", 2, "int64 value")
+	Uint("test_uint", 3, "uint value")
+	Uint64("test_uint64", 4, "uint64 value")
+	String("test_string", "5", "string value")
+	Float64("test_float64", 6, "float64 value")
+	Duration("test_duration", 7, "time.Duration value")
+
+	visitor := func(f *Flag) {
+		if len(f.Name) > 5 && f.Name[0:5] == "test_" {
+			g, ok := f.Value.(Getter)
+			if !ok {
+				t.Errorf("Visit: value does not satisfy Getter: %T", f.Value)
+				return
+			}
+			switch f.Name {
+			case "test_bool":
+				ok = g.Get() == true
+			case "test_int":
+				ok = g.Get() == int(1)
+			case "test_int64":
+				ok = g.Get() == int64(2)
+			case "test_uint":
+				ok = g.Get() == uint(3)
+			case "test_uint64":
+				ok = g.Get() == uint64(4)
+			case "test_string":
+				ok = g.Get() == "5"
+			case "test_float64":
+				ok = g.Get() == float64(6)
+			case "test_duration":
+				ok = g.Get() == time.Duration(7)
+			}
+			if !ok {
+				t.Errorf("Visit: bad value %T(%v) for %s", g.Get(), g.Get(), f.Name)
+			}
+		}
+	}
+	VisitAll(visitor)
+}
+
+func TestUsage(t *testing.T) {
+	called := false
+	ResetForTesting(func() { called = true })
+	if CommandLine.Parse([]string{"-x"}) == nil {
+		t.Error("parse did not fail for unknown flag")
+	}
+	if !called {
+		t.Error("did not call Usage for unknown flag")
+	}
+}
+
+func testParse(f *FlagSet, t *testing.T) {
+	if f.Parsed() {
+		t.Error("f.Parse() = true before Parse")
+	}
+	boolFlag := f.Bool("bool", false, "bool value")
+	bool2Flag := f.Bool("bool2", false, "bool2 value")
+	intFlag := f.Int("int", 0, "int value")
+	int64Flag := f.Int64("int64", 0, "int64 value")
+	uintFlag := f.Uint("uint", 0, "uint value")
+	uint64Flag := f.Uint64("uint64", 0, "uint64 value")
+	stringFlag := f.String("string", "0", "string value")
+	float64Flag := f.Float64("float64", 0, "float64 value")
+	durationFlag := f.Duration("duration", 5*time.Second, "time.Duration value")
+	extra := "one-extra-argument"
+	args := []string{
+		"-bool",
+		"-bool2=true",
+		"--int", "22",
+		"--int64", "0x23",
+		"-uint", "24",
+		"--uint64", "25",
+		"-string", "hello",
+		"-float64", "2718e28",
+		"-duration", "2m",
+		extra,
+	}
+	if err := f.Parse(args); err != nil {
+		t.Fatal(err)
+	}
+	if !f.Parsed() {
+		t.Error("f.Parse() = false after Parse")
+	}
+	if *boolFlag != true {
+		t.Error("bool flag should be true, is ", *boolFlag)
+	}
+	if *bool2Flag != true {
+		t.Error("bool2 flag should be true, is ", *bool2Flag)
+	}
+	if *intFlag != 22 {
+		t.Error("int flag should be 22, is ", *intFlag)
+	}
+	if *int64Flag != 0x23 {
+		t.Error("int64 flag should be 0x23, is ", *int64Flag)
+	}
+	if *uintFlag != 24 {
+		t.Error("uint flag should be 24, is ", *uintFlag)
+	}
+	if *uint64Flag != 25 {
+		t.Error("uint64 flag should be 25, is ", *uint64Flag)
+	}
+	if *stringFlag != "hello" {
+		t.Error("string flag should be `hello`, is ", *stringFlag)
+	}
+	if *float64Flag != 2718e28 {
+		t.Error("float64 flag should be 2718e28, is ", *float64Flag)
+	}
+	if *durationFlag != 2*time.Minute {
+		t.Error("duration flag should be 2m, is ", *durationFlag)
+	}
+	if len(f.Args()) != 1 {
+		t.Error("expected one argument, got", len(f.Args()))
+	} else if f.Args()[0] != extra {
+		t.Errorf("expected argument %q got %q", extra, f.Args()[0])
+	}
+}
+
+func TestParse(t *testing.T) {
+	ResetForTesting(func() { t.Error("bad parse") })
+	testParse(CommandLine, t)
+}
+
+func TestFlagSetParse(t *testing.T) {
+	testParse(NewFlagSet("test", ContinueOnError), t)
+}
+
+// Declare a user-defined flag type.
+type flagVar []string
+
+func (f *flagVar) String() string {
+	return fmt.Sprint([]string(*f))
+}
+
+func (f *flagVar) Set(value string) error {
+	*f = append(*f, value)
+	return nil
+}
+
+func TestUserDefined(t *testing.T) {
+	var flags FlagSet
+	flags.Init("test", ContinueOnError)
+	flags.SetOutput(io.Discard)
+	var v flagVar
+	flags.Var(&v, "v", "usage")
+	if err := flags.Parse([]string{"-v", "1", "-v", "2", "-v=3"}); err != nil {
+		t.Error(err)
+	}
+	if len(v) != 3 {
+		t.Fatal("expected 3 args; got ", len(v))
+	}
+	expect := "[1 2 3]"
+	if v.String() != expect {
+		t.Errorf("expected value %q got %q", expect, v.String())
+	}
+}
+
+func TestUserDefinedFunc(t *testing.T) {
+	flags := NewFlagSet("test", ContinueOnError)
+	flags.SetOutput(io.Discard)
+	var ss []string
+	flags.Func("v", "usage", func(s string) error {
+		ss = append(ss, s)
+		return nil
+	})
+	if err := flags.Parse([]string{"-v", "1", "-v", "2", "-v=3"}); err != nil {
+		t.Error(err)
+	}
+	if len(ss) != 3 {
+		t.Fatal("expected 3 args; got ", len(ss))
+	}
+	expect := "[1 2 3]"
+	if got := fmt.Sprint(ss); got != expect {
+		t.Errorf("expected value %q got %q", expect, got)
+	}
+	// test usage
+	var buf strings.Builder
+	flags.SetOutput(&buf)
+	flags.Parse([]string{"-h"})
+	if usage := buf.String(); !strings.Contains(usage, "usage") {
+		t.Errorf("usage string not included: %q", usage)
+	}
+	// test Func error
+	flags = NewFlagSet("test", ContinueOnError)
+	flags.SetOutput(io.Discard)
+	flags.Func("v", "usage", func(s string) error {
+		return fmt.Errorf("test error")
+	})
+	// flag not set, so no error
+	if err := flags.Parse(nil); err != nil {
+		t.Error(err)
+	}
+	// flag set, expect error
+	if err := flags.Parse([]string{"-v", "1"}); err == nil {
+		t.Error("expected error; got none")
+	} else if errMsg := err.Error(); !strings.Contains(errMsg, "test error") {
+		t.Errorf(`error should contain "test error"; got %q`, errMsg)
+	}
+}
+
+func TestUserDefinedForCommandLine(t *testing.T) {
+	const help = "HELP"
+	var result string
+	ResetForTesting(func() { result = help })
+	Usage()
+	if result != help {
+		t.Fatalf("got %q; expected %q", result, help)
+	}
+}
+
+// Declare a user-defined boolean flag type.
+type boolFlagVar struct {
+	count int
+}
+
+func (b *boolFlagVar) String() string {
+	return fmt.Sprintf("%d", b.count)
+}
+
+func (b *boolFlagVar) Set(value string) error {
+	if value == "true" {
+		b.count++
+	}
+	return nil
+}
+
+func (b *boolFlagVar) IsBoolFlag() bool {
+	return b.count < 4
+}
+
+func TestUserDefinedBool(t *testing.T) {
+	var flags FlagSet
+	flags.Init("test", ContinueOnError)
+	flags.SetOutput(io.Discard)
+	var b boolFlagVar
+	var err error
+	flags.Var(&b, "b", "usage")
+	if err = flags.Parse([]string{"-b", "-b", "-b", "-b=true", "-b=false", "-b", "barg", "-b"}); err != nil {
+		if b.count < 4 {
+			t.Error(err)
+		}
+	}
+
+	if b.count != 4 {
+		t.Errorf("want: %d; got: %d", 4, b.count)
+	}
+
+	if err == nil {
+		t.Error("expected error; got none")
+	}
+}
+
+func TestUserDefinedBoolUsage(t *testing.T) {
+	var flags FlagSet
+	flags.Init("test", ContinueOnError)
+	var buf bytes.Buffer
+	flags.SetOutput(&buf)
+	var b boolFlagVar
+	flags.Var(&b, "b", "X")
+	b.count = 0
+	// b.IsBoolFlag() will return true and usage will look boolean.
+	flags.PrintDefaults()
+	got := buf.String()
+	want := "  -b\tX\n"
+	if got != want {
+		t.Errorf("false: want %q; got %q", want, got)
+	}
+	b.count = 4
+	// b.IsBoolFlag() will return false and usage will look non-boolean.
+	flags.PrintDefaults()
+	got = buf.String()
+	want = "  -b\tX\n  -b value\n    \tX\n"
+	if got != want {
+		t.Errorf("false: want %q; got %q", want, got)
+	}
+}
+
+func TestSetOutput(t *testing.T) {
+	var flags FlagSet
+	var buf strings.Builder
+	flags.SetOutput(&buf)
+	flags.Init("test", ContinueOnError)
+	flags.Parse([]string{"-unknown"})
+	if out := buf.String(); !strings.Contains(out, "-unknown") {
+		t.Logf("expected output mentioning unknown; got %q", out)
+	}
+}
+
+// This tests that one can reset the flags. This still works but not well, and is
+// superseded by FlagSet.
+func TestChangingArgs(t *testing.T) {
+	ResetForTesting(func() { t.Fatal("bad parse") })
+	oldArgs := os.Args
+	defer func() { os.Args = oldArgs }()
+	os.Args = []string{"cmd", "-before", "subcmd", "-after", "args"}
+	before := Bool("before", false, "")
+	if err := CommandLine.Parse(os.Args[1:]); err != nil {
+		t.Fatal(err)
+	}
+	cmd := Arg(0)
+	os.Args = Args()
+	after := Bool("after", false, "")
+	Parse()
+	args := Args()
+
+	if !*before || cmd != "subcmd" || !*after || len(args) != 1 || args[0] != "args" {
+		t.Fatalf("expected true subcmd true [args] got %v %v %v %v", *before, cmd, *after, args)
+	}
+}
+
+// Test that -help invokes the usage message and returns ErrHelp.
+func TestHelp(t *testing.T) {
+	var helpCalled = false
+	fs := NewFlagSet("help test", ContinueOnError)
+	fs.Usage = func() { helpCalled = true }
+	var flag bool
+	fs.BoolVar(&flag, "flag", false, "regular flag")
+	// Regular flag invocation should work
+	err := fs.Parse([]string{"-flag=true"})
+	if err != nil {
+		t.Fatal("expected no error; got ", err)
+	}
+	if !flag {
+		t.Error("flag was not set by -flag")
+	}
+	if helpCalled {
+		t.Error("help called for regular flag")
+		helpCalled = false // reset for next test
+	}
+	// Help flag should work as expected.
+	err = fs.Parse([]string{"-help"})
+	if err == nil {
+		t.Fatal("error expected")
+	}
+	if err != ErrHelp {
+		t.Fatal("expected ErrHelp; got ", err)
+	}
+	if !helpCalled {
+		t.Fatal("help was not called")
+	}
+	// If we define a help flag, that should override.
+	var help bool
+	fs.BoolVar(&help, "help", false, "help flag")
+	helpCalled = false
+	err = fs.Parse([]string{"-help"})
+	if err != nil {
+		t.Fatal("expected no error for defined -help; got ", err)
+	}
+	if helpCalled {
+		t.Fatal("help was called; should not have been for defined help flag")
+	}
+}
+
+// zeroPanicker is a flag.Value whose String method panics if its dontPanic
+// field is false.
+type zeroPanicker struct {
+	dontPanic bool
+	v         string
+}
+
+func (f *zeroPanicker) Set(s string) error {
+	f.v = s
+	return nil
+}
+
+func (f *zeroPanicker) String() string {
+	if !f.dontPanic {
+		panic("panic!")
+	}
+	return f.v
+}
+
+const defaultOutput = `  -A	for bootstrapping, allow 'any' type
+  -Alongflagname
+    	disable bounds checking
+  -C	a boolean defaulting to true (default true)
+  -D path
+    	set relative path for local imports
+  -E string
+    	issue 23543 (default "0")
+  -F number
+    	a non-zero number (default 2.7)
+  -G float
+    	a float that defaults to zero
+  -M string
+    	a multiline
+    	help
+    	string
+  -N int
+    	a non-zero int (default 27)
+  -O	a flag
+    	multiline help string (default true)
+  -V list
+    	a list of strings (default [a b])
+  -Z int
+    	an int that defaults to zero
+  -ZP0 value
+    	a flag whose String method panics when it is zero
+  -ZP1 value
+    	a flag whose String method panics when it is zero
+  -maxT timeout
+    	set timeout for dial
+
+panic calling String method on zero flag_test.zeroPanicker for flag ZP0: panic!
+panic calling String method on zero flag_test.zeroPanicker for flag ZP1: panic!
+`
+
+func TestPrintDefaults(t *testing.T) {
+	fs := NewFlagSet("print defaults test", ContinueOnError)
+	var buf strings.Builder
+	fs.SetOutput(&buf)
+	fs.Bool("A", false, "for bootstrapping, allow 'any' type")
+	fs.Bool("Alongflagname", false, "disable bounds checking")
+	fs.Bool("C", true, "a boolean defaulting to true")
+	fs.String("D", "", "set relative `path` for local imports")
+	fs.String("E", "0", "issue 23543")
+	fs.Float64("F", 2.7, "a non-zero `number`")
+	fs.Float64("G", 0, "a float that defaults to zero")
+	fs.String("M", "", "a multiline\nhelp\nstring")
+	fs.Int("N", 27, "a non-zero int")
+	fs.Bool("O", true, "a flag\nmultiline help string")
+	fs.Var(&flagVar{"a", "b"}, "V", "a `list` of strings")
+	fs.Int("Z", 0, "an int that defaults to zero")
+	fs.Var(&zeroPanicker{true, ""}, "ZP0", "a flag whose String method panics when it is zero")
+	fs.Var(&zeroPanicker{true, "something"}, "ZP1", "a flag whose String method panics when it is zero")
+	fs.Duration("maxT", 0, "set `timeout` for dial")
+	fs.PrintDefaults()
+	got := buf.String()
+	if got != defaultOutput {
+		t.Errorf("got:\n%q\nwant:\n%q", got, defaultOutput)
+	}
+}
+
+// Issue 19230: validate range of Int and Uint flag values.
+func TestIntFlagOverflow(t *testing.T) {
+	if strconv.IntSize != 32 {
+		return
+	}
+	ResetForTesting(nil)
+	Int("i", 0, "")
+	Uint("u", 0, "")
+	if err := Set("i", "2147483648"); err == nil {
+		t.Error("unexpected success setting Int")
+	}
+	if err := Set("u", "4294967296"); err == nil {
+		t.Error("unexpected success setting Uint")
+	}
+}
+
+// Issue 20998: Usage should respect CommandLine.output.
+func TestUsageOutput(t *testing.T) {
+	ResetForTesting(DefaultUsage)
+	var buf strings.Builder
+	CommandLine.SetOutput(&buf)
+	defer func(old []string) { os.Args = old }(os.Args)
+	os.Args = []string{"app", "-i=1", "-unknown"}
+	Parse()
+	const want = "flag provided but not defined: -i\nUsage of app:\n"
+	if got := buf.String(); got != want {
+		t.Errorf("output = %q; want %q", got, want)
+	}
+}
+
+func TestGetters(t *testing.T) {
+	expectedName := "flag set"
+	expectedErrorHandling := ContinueOnError
+	expectedOutput := io.Writer(os.Stderr)
+	fs := NewFlagSet(expectedName, expectedErrorHandling)
+
+	if fs.Name() != expectedName {
+		t.Errorf("unexpected name: got %s, expected %s", fs.Name(), expectedName)
+	}
+	if fs.ErrorHandling() != expectedErrorHandling {
+		t.Errorf("unexpected ErrorHandling: got %d, expected %d", fs.ErrorHandling(), expectedErrorHandling)
+	}
+	if fs.Output() != expectedOutput {
+		t.Errorf("unexpected output: got %#v, expected %#v", fs.Output(), expectedOutput)
+	}
+
+	expectedName = "gopher"
+	expectedErrorHandling = ExitOnError
+	expectedOutput = os.Stdout
+	fs.Init(expectedName, expectedErrorHandling)
+	fs.SetOutput(expectedOutput)
+
+	if fs.Name() != expectedName {
+		t.Errorf("unexpected name: got %s, expected %s", fs.Name(), expectedName)
+	}
+	if fs.ErrorHandling() != expectedErrorHandling {
+		t.Errorf("unexpected ErrorHandling: got %d, expected %d", fs.ErrorHandling(), expectedErrorHandling)
+	}
+	if fs.Output() != expectedOutput {
+		t.Errorf("unexpected output: got %v, expected %v", fs.Output(), expectedOutput)
+	}
+}
+
+func TestParseError(t *testing.T) {
+	for _, typ := range []string{"bool", "int", "int64", "uint", "uint64", "float64", "duration"} {
+		fs := NewFlagSet("parse error test", ContinueOnError)
+		fs.SetOutput(io.Discard)
+		_ = fs.Bool("bool", false, "")
+		_ = fs.Int("int", 0, "")
+		_ = fs.Int64("int64", 0, "")
+		_ = fs.Uint("uint", 0, "")
+		_ = fs.Uint64("uint64", 0, "")
+		_ = fs.Float64("float64", 0, "")
+		_ = fs.Duration("duration", 0, "")
+		// Strings cannot give errors.
+		args := []string{"-" + typ + "=x"}
+		err := fs.Parse(args) // x is not a valid setting for any flag.
+		if err == nil {
+			t.Errorf("Parse(%q)=%v; expected parse error", args, err)
+			continue
+		}
+		if !strings.Contains(err.Error(), "invalid") || !strings.Contains(err.Error(), "parse error") {
+			t.Errorf("Parse(%q)=%v; expected parse error", args, err)
+		}
+	}
+}
+
+func TestRangeError(t *testing.T) {
+	bad := []string{
+		"-int=123456789012345678901",
+		"-int64=123456789012345678901",
+		"-uint=123456789012345678901",
+		"-uint64=123456789012345678901",
+		"-float64=1e1000",
+	}
+	for _, arg := range bad {
+		fs := NewFlagSet("parse error test", ContinueOnError)
+		fs.SetOutput(io.Discard)
+		_ = fs.Int("int", 0, "")
+		_ = fs.Int64("int64", 0, "")
+		_ = fs.Uint("uint", 0, "")
+		_ = fs.Uint64("uint64", 0, "")
+		_ = fs.Float64("float64", 0, "")
+		// Strings cannot give errors, and bools and durations do not return strconv.NumError.
+		err := fs.Parse([]string{arg})
+		if err == nil {
+			t.Errorf("Parse(%q)=%v; expected range error", arg, err)
+			continue
+		}
+		if !strings.Contains(err.Error(), "invalid") || !strings.Contains(err.Error(), "value out of range") {
+			t.Errorf("Parse(%q)=%v; expected range error", arg, err)
+		}
+	}
+}
+
+func TestExitCode(t *testing.T) {
+	testenv.MustHaveExec(t)
+
+	magic := 123
+	if os.Getenv("GO_CHILD_FLAG") != "" {
+		fs := NewFlagSet("test", ExitOnError)
+		if os.Getenv("GO_CHILD_FLAG_HANDLE") != "" {
+			var b bool
+			fs.BoolVar(&b, os.Getenv("GO_CHILD_FLAG_HANDLE"), false, "")
+		}
+		fs.Parse([]string{os.Getenv("GO_CHILD_FLAG")})
+		os.Exit(magic)
+	}
+
+	tests := []struct {
+		flag       string
+		flagHandle string
+		expectExit int
+	}{
+		{
+			flag:       "-h",
+			expectExit: 0,
+		},
+		{
+			flag:       "-help",
+			expectExit: 0,
+		},
+		{
+			flag:       "-undefined",
+			expectExit: 2,
+		},
+		{
+			flag:       "-h",
+			flagHandle: "h",
+			expectExit: magic,
+		},
+		{
+			flag:       "-help",
+			flagHandle: "help",
+			expectExit: magic,
+		},
+	}
+
+	for _, test := range tests {
+		cmd := exec.Command(os.Args[0], "-test.run=^TestExitCode$")
+		cmd.Env = append(
+			os.Environ(),
+			"GO_CHILD_FLAG="+test.flag,
+			"GO_CHILD_FLAG_HANDLE="+test.flagHandle,
+		)
+		cmd.Run()
+		got := cmd.ProcessState.ExitCode()
+		// ExitCode is either 0 or 1 on Plan 9.
+		if runtime.GOOS == "plan9" && test.expectExit != 0 {
+			test.expectExit = 1
+		}
+		if got != test.expectExit {
+			t.Errorf("unexpected exit code for test case %+v \n: got %d, expect %d",
+				test, got, test.expectExit)
+		}
+	}
+}
+
+func mustPanic(t *testing.T, testName string, expected string, f func()) {
+	t.Helper()
+	defer func() {
+		switch msg := recover().(type) {
+		case nil:
+			t.Errorf("%s\n: expected panic(%q), but did not panic", testName, expected)
+		case string:
+			if ok, _ := regexp.MatchString(expected, msg); !ok {
+				t.Errorf("%s\n: expected panic(%q), but got panic(%q)", testName, expected, msg)
+			}
+		default:
+			t.Errorf("%s\n: expected panic(%q), but got panic(%T%v)", testName, expected, msg, msg)
+		}
+	}()
+	f()
+}
+
+func TestInvalidFlags(t *testing.T) {
+	tests := []struct {
+		flag     string
+		errorMsg string
+	}{
+		{
+			flag:     "-foo",
+			errorMsg: "flag \"-foo\" begins with -",
+		},
+		{
+			flag:     "foo=bar",
+			errorMsg: "flag \"foo=bar\" contains =",
+		},
+	}
+
+	for _, test := range tests {
+		testName := fmt.Sprintf("FlagSet.Var(&v, %q, \"\")", test.flag)
+
+		fs := NewFlagSet("", ContinueOnError)
+		buf := &strings.Builder{}
+		fs.SetOutput(buf)
+
+		mustPanic(t, testName, test.errorMsg, func() {
+			var v flagVar
+			fs.Var(&v, test.flag, "")
+		})
+		if msg := test.errorMsg + "\n"; msg != buf.String() {
+			t.Errorf("%s\n: unexpected output: expected %q, bug got %q", testName, msg, buf)
+		}
+	}
+}
+
+func TestRedefinedFlags(t *testing.T) {
+	tests := []struct {
+		flagSetName string
+		errorMsg    string
+	}{
+		{
+			flagSetName: "",
+			errorMsg:    "flag redefined: foo",
+		},
+		{
+			flagSetName: "fs",
+			errorMsg:    "fs flag redefined: foo",
+		},
+	}
+
+	for _, test := range tests {
+		testName := fmt.Sprintf("flag redefined in FlagSet(%q)", test.flagSetName)
+
+		fs := NewFlagSet(test.flagSetName, ContinueOnError)
+		buf := &strings.Builder{}
+		fs.SetOutput(buf)
+
+		var v flagVar
+		fs.Var(&v, "foo", "")
+
+		mustPanic(t, testName, test.errorMsg, func() {
+			fs.Var(&v, "foo", "")
+		})
+		if msg := test.errorMsg + "\n"; msg != buf.String() {
+			t.Errorf("%s\n: unexpected output: expected %q, bug got %q", testName, msg, buf)
+		}
+	}
+}
+
+func TestUserDefinedBoolFunc(t *testing.T) {
+	flags := NewFlagSet("test", ContinueOnError)
+	flags.SetOutput(io.Discard)
+	var ss []string
+	flags.BoolFunc("v", "usage", func(s string) error {
+		ss = append(ss, s)
+		return nil
+	})
+	if err := flags.Parse([]string{"-v", "", "-v", "1", "-v=2"}); err != nil {
+		t.Error(err)
+	}
+	if len(ss) != 1 {
+		t.Fatalf("got %d args; want 1 arg", len(ss))
+	}
+	want := "[true]"
+	if got := fmt.Sprint(ss); got != want {
+		t.Errorf("got %q; want %q", got, want)
+	}
+	// test usage
+	var buf strings.Builder
+	flags.SetOutput(&buf)
+	flags.Parse([]string{"-h"})
+	if usage := buf.String(); !strings.Contains(usage, "usage") {
+		t.Errorf("usage string not included: %q", usage)
+	}
+	// test BoolFunc error
+	flags = NewFlagSet("test", ContinueOnError)
+	flags.SetOutput(io.Discard)
+	flags.BoolFunc("v", "usage", func(s string) error {
+		return fmt.Errorf("test error")
+	})
+	// flag not set, so no error
+	if err := flags.Parse(nil); err != nil {
+		t.Error(err)
+	}
+	// flag set, expect error
+	if err := flags.Parse([]string{"-v", ""}); err == nil {
+		t.Error("got err == nil; want err != nil")
+	} else if errMsg := err.Error(); !strings.Contains(errMsg, "test error") {
+		t.Errorf(`got %q; error should contain "test error"`, errMsg)
+	}
+}
+
+func TestDefineAfterSet(t *testing.T) {
+	flags := NewFlagSet("test", ContinueOnError)
+	// Set by itself doesn't panic.
+	flags.Set("myFlag", "value")
+
+	// Define-after-set panics.
+	mustPanic(t, "DefineAfterSet", "flag myFlag set at .*/flag_test.go:.* before being defined", func() {
+		_ = flags.String("myFlag", "default", "usage")
+	})
+}