Don't show empty slices as flag default values in help

Author: FollowTheProcess

command_test.go

@@ -600,6 +600,8 @@ func TestHelp(t *testing.T) {
 				cli.SubCommands(sub1, sub2),
 				cli.Flag(new(bool), "delete", 'd', false, "Delete something"),
 				cli.Flag(new(int), "count", cli.NoShortHand, -1, "Count something"),
+				cli.Flag(new([]string), "things", cli.NoShortHand, nil, "Names of things"),
+				cli.Flag(new([]string), "more", cli.NoShortHand, []string{"one", "two"}, "Names of things with a default"),
 			},
 			wantErr: false,
 		},

internal/flag/flag.go

@@ -107,7 +107,7 @@ func New[T Flaggable](p *T, name string, short rune, value T, usage string) (Fla
 
 	// If the default value is not the zero value for the type, it is treated as
 	// significant and shown to the user
-	if !isZero(value) {
+	if !isZeroIsh(value) {
 		// \t so that defaults get aligned by tabwriter when the command
 		// dumps the flags
 		usage += fmt.Sprintf("\t[default: %v]", value)
@@ -905,8 +905,16 @@ func formatStringSlice(slice []string) string {
 	return s.String()
 }
 
-// isZero reports whether value is the zero value for it's type.
-func isZero[T Flaggable](value T) bool {
+// isZeroIsh reports whether value is the zero value (ish) for it's type.
+//
+// "ish" means that empty slices will return true from isZeroIsh despite their official
+// zero value being nil. The primary use of isZeroIsh is to determine whether or not
+// a default value is worth displaying to the user in the help text, and an empty slice
+// is probably not.
+func isZeroIsh[T Flaggable](value T) bool { //nolint:cyclop // Not much else we can do here
+	// Note: all the slice values ([]T) are in their own separate branches because if you
+	// combine them, the resulting value in the body of the case block is 'any' and
+	// you cannot do len(any)
 	switch typ := any(value).(type) {
 	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, uintptr, float32, float64:
 		return typ == 0
@@ -916,8 +924,34 @@ func isZero[T Flaggable](value T) bool {
 		return typ == ""
 	case bool:
 		return !typ
-	case []byte, net.IP, []int, []int8, []int16, []int32, []int64, []uint, []uint16, []uint32, []uint64, []float32, []float64, []string:
-		return typ == nil
+	case []byte:
+		return len(typ) == 0
+	case net.IP:
+		return len(typ) == 0
+	case []int:
+		return len(typ) == 0
+	case []int8:
+		return len(typ) == 0
+	case []int16:
+		return len(typ) == 0
+	case []int32:
+		return len(typ) == 0
+	case []int64:
+		return len(typ) == 0
+	case []uint:
+		return len(typ) == 0
+	case []uint16:
+		return len(typ) == 0
+	case []uint32:
+		return len(typ) == 0
+	case []uint64:
+		return len(typ) == 0
+	case []float32:
+		return len(typ) == 0
+	case []float64:
+		return len(typ) == 0
+	case []string:
+		return len(typ) == 0
 	case time.Time:
 		var zero time.Time
 		return typ.Equal(zero)

testdata/snapshots/TestHelp/with_subcommands_and_flags.snap.txt

@@ -11,9 +11,11 @@ Commands:
 
 Options:
 
-  N/A  --count    int   Count something  [default: -1]
-  -d   --delete   bool  Delete something
-  -h   --help     bool  Show help for test
-  -V   --version  bool  Show version info for test
+  N/A  --count    int       Count something  [default: -1]
+  -d   --delete   bool      Delete something
+  -h   --help     bool      Show help for test
+  N/A  --more     []string  Names of things with a default  [default: [one two]]
+  N/A  --things   []string  Names of things
+  -V   --version  bool      Show version info for test
 
 Use "test [command] -h/--help" for more information about a command.