Allow specifying a StringSlice destination for StringSliceFlag

flag_string_slice.go

@@ -71,6 +71,7 @@ type StringSliceFlag struct {
 	Value       *StringSlice
 	DefaultText string
 	HasBeenSet  bool
+	Destination *StringSlice
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -117,20 +118,33 @@ func (f *StringSliceFlag) GetValue() string {
 func (f *StringSliceFlag) Apply(set *flag.FlagSet) error {
 	if val, ok := flagFromEnvOrFile(f.EnvVars, f.FilePath); ok {
 		f.Value = &StringSlice{}
+		destination := f.Value
+		if f.Destination != nil {
+			destination = f.Destination
+		}
 
 		for _, s := range strings.Split(val, ",") {
-			if err := f.Value.Set(strings.TrimSpace(s)); err != nil {
+			if err := destination.Set(strings.TrimSpace(s)); err != nil {
 				return fmt.Errorf("could not parse %q as string value for flag %s: %s", val, f.Name, err)
 			}
 		}
 
+		// Set this to false so that we reset the slice if we then set values from
+		// flags that have already been set by the environment.
+		destination.hasBeenSet = false
 		f.HasBeenSet = true
 	}
 
 	for _, name := range f.Names() {
 		if f.Value == nil {
 			f.Value = &StringSlice{}
 		}
+
+		if f.Destination != nil {
+			set.Var(f.Destination, name, f.Usage)
+			continue
+		}
+
 		set.Var(f.Value, name, f.Usage)
 	}
 

flag_test.go

@@ -59,7 +59,7 @@ func TestFlagsFromEnv(t *testing.T) {
 
 	newSetStringSlice := func(defaults ...string) StringSlice {
 		s := NewStringSlice(defaults...)
-		s.hasBeenSet = true
+		s.hasBeenSet = false
 		return *s
 	}
 
@@ -917,6 +917,47 @@ func TestParseMultiStringSliceWithDefaults(t *testing.T) {
 	}).Run([]string{"run", "-s", "10", "-s", "20"})
 }
 
+func TestParseMultiStringSliceWithDestination(t *testing.T) {
+	dest := &StringSlice{}
+	_ = (&App{
+		Flags: []Flag{
+			&StringSliceFlag{Name: "serve", Aliases: []string{"s"}, Destination: dest},
+		},
+		Action: func(ctx *Context) error {
+			expected := []string{"10", "20"}
+			if !reflect.DeepEqual(dest.slice, expected) {
+				t.Errorf("main name not set: %v != %v", expected, ctx.StringSlice("serve"))
+			}
+			if !reflect.DeepEqual(dest.slice, expected) {
+				t.Errorf("short name not set: %v != %v", expected, ctx.StringSlice("s"))
+			}
+			return nil
+		},
+	}).Run([]string{"run", "-s", "10", "-s", "20"})
+}
+
+func TestParseMultiStringSliceWithDestinationAndEnv(t *testing.T) {
+	os.Clearenv()
+	_ = os.Setenv("APP_INTERVALS", "20,30,40")
+
+	dest := &StringSlice{}
+	_ = (&App{
+		Flags: []Flag{
+			&StringSliceFlag{Name: "serve", Aliases: []string{"s"}, Destination: dest, EnvVars: []string{"APP_INTERVALS"}},
+		},
+		Action: func(ctx *Context) error {
+			expected := []string{"10", "20"}
+			if !reflect.DeepEqual(dest.slice, expected) {
+				t.Errorf("main name not set: %v != %v", expected, ctx.StringSlice("serve"))
+			}
+			if !reflect.DeepEqual(dest.slice, expected) {
+				t.Errorf("short name not set: %v != %v", expected, ctx.StringSlice("s"))
+			}
+			return nil
+		},
+	}).Run([]string{"run", "-s", "10", "-s", "20"})
+}
+
 func TestParseMultiStringSliceWithDefaultsUnset(t *testing.T) {
 	_ = (&App{
 		Flags: []Flag{
@@ -1014,6 +1055,27 @@ func TestParseMultiStringSliceFromEnvCascadeWithDefaults(t *testing.T) {
 	}).Run([]string{"run"})
 }
 
+func TestParseMultiStringSliceFromEnvWithDestination(t *testing.T) {
+	os.Clearenv()
+	_ = os.Setenv("APP_INTERVALS", "20,30,40")
+
+	dest := &StringSlice{}
+	_ = (&App{
+		Flags: []Flag{
+			&StringSliceFlag{Name: "intervals", Aliases: []string{"i"}, Destination: dest, EnvVars: []string{"APP_INTERVALS"}},
+		},
+		Action: func(ctx *Context) error {
+			if !reflect.DeepEqual(dest.slice, []string{"20", "30", "40"}) {
+				t.Errorf("main name not set from env")
+			}
+			if !reflect.DeepEqual(dest.slice, []string{"20", "30", "40"}) {
+				t.Errorf("short name not set from env")
+			}
+			return nil
+		},
+	}).Run([]string{"run"})
+}
+
 func TestParseMultiInt(t *testing.T) {
 	_ = (&App{
 		Flags: []Flag{