Add exported functions to preserve pkg/flag compatibility

flag.go

@@ -160,7 +160,7 @@ type FlagSet struct {
 	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
+	output            io.Writer // nil means stderr; use Output() accessor
 	interspersed      bool      // allow interspersed option/non-option args
 	normalizeNameFunc func(f *FlagSet, name string) NormalizedName
 
@@ -255,13 +255,20 @@ func (f *FlagSet) normalizeFlagName(name string) NormalizedName {
 	return n(f, name)
 }
 
-func (f *FlagSet) out() io.Writer {
+// 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
+}
+
 // SetOutput sets the destination for usage and error messages.
 // If output is nil, os.Stderr is used.
 func (f *FlagSet) SetOutput(output io.Writer) {
@@ -358,7 +365,7 @@ func (f *FlagSet) ShorthandLookup(name string) *Flag {
 	}
 	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)
+		fmt.Fprintf(f.Output(), msg)
 		panic(msg)
 	}
 	c := name[0]
@@ -482,7 +489,7 @@ func (f *FlagSet) Set(name, value string) error {
 	}
 
 	if flag.Deprecated != "" {
-		fmt.Fprintf(f.out(), "Flag --%s has been deprecated, %s\n", flag.Name, flag.Deprecated)
+		fmt.Fprintf(f.Output(), "Flag --%s has been deprecated, %s\n", flag.Name, flag.Deprecated)
 	}
 	return nil
 }
@@ -523,7 +530,7 @@ func Set(name, value string) error {
 // otherwise, the default values of all defined flags in the set.
 func (f *FlagSet) PrintDefaults() {
 	usages := f.FlagUsages()
-	fmt.Fprint(f.out(), usages)
+	fmt.Fprint(f.Output(), usages)
 }
 
 // defaultIsZeroValue returns true if the default value for this flag represents
@@ -758,7 +765,7 @@ func 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)
+	fmt.Fprintf(f.Output(), "Usage of %s:\n", f.name)
 	f.PrintDefaults()
 }
 
@@ -844,7 +851,7 @@ func (f *FlagSet) AddFlag(flag *Flag) {
 	_, alreadyThere := f.formal[normalizedFlagName]
 	if alreadyThere {
 		msg := fmt.Sprintf("%s flag redefined: %s", f.name, flag.Name)
-		fmt.Fprintln(f.out(), msg)
+		fmt.Fprintln(f.Output(), msg)
 		panic(msg) // Happens only if flags are declared with identical names
 	}
 	if f.formal == nil {
@@ -860,7 +867,7 @@ func (f *FlagSet) AddFlag(flag *Flag) {
 	}
 	if len(flag.Shorthand) > 1 {
 		msg := fmt.Sprintf("%q shorthand is more than one ASCII character", flag.Shorthand)
-		fmt.Fprintf(f.out(), msg)
+		fmt.Fprintf(f.Output(), msg)
 		panic(msg)
 	}
 	if f.shorthands == nil {
@@ -870,7 +877,7 @@ func (f *FlagSet) AddFlag(flag *Flag) {
 	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)
+		fmt.Fprintf(f.Output(), msg)
 		panic(msg)
 	}
 	f.shorthands[c] = flag
@@ -909,7 +916,7 @@ func VarP(value Value, name, shorthand, usage string) {
 func (f *FlagSet) failf(format string, a ...interface{}) error {
 	err := fmt.Errorf(format, a...)
 	if f.errorHandling != ContinueOnError {
-		fmt.Fprintln(f.out(), err)
+		fmt.Fprintln(f.Output(), err)
 		f.usage()
 	}
 	return err
@@ -1060,7 +1067,7 @@ func (f *FlagSet) parseSingleShortArg(shorthands string, args []string, fn parse
 	}
 
 	if flag.ShorthandDeprecated != "" {
-		fmt.Fprintf(f.out(), "Flag shorthand -%s has been deprecated, %s\n", flag.Shorthand, flag.ShorthandDeprecated)
+		fmt.Fprintf(f.Output(), "Flag shorthand -%s has been deprecated, %s\n", flag.Shorthand, flag.ShorthandDeprecated)
 	}
 
 	err = fn(flag, value)

flag_test.go

@@ -159,6 +159,16 @@ func TestAnnotation(t *testing.T) {
 	}
 }
 
+func TestName(t *testing.T) {
+	flagSetName := "bob"
+	f := NewFlagSet(flagSetName, ContinueOnError)
+
+	givenName := f.Name()
+	if givenName != flagSetName {
+		t.Errorf("Unexpected result when retrieving a FlagSet's name: expected %s, but found %s", flagSetName, givenName)
+	}
+}
+
 func testParse(f *FlagSet, t *testing.T) {
 	if f.Parsed() {
 		t.Error("f.Parse() = true before Parse")
@@ -854,6 +864,17 @@ func TestSetOutput(t *testing.T) {
 	}
 }
 
+func TestOutput(t *testing.T) {
+	var flags FlagSet
+	var buf bytes.Buffer
+	expect := "an example string"
+	flags.SetOutput(&buf)
+	fmt.Fprint(flags.Output(), expect)
+	if out := buf.String(); !strings.Contains(out, expect) {
+		t.Errorf("expected output %q; got %q", expect, 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) {