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1. Implement  support for enums pointers.
2. Add various enum test cases.

context.go

@@ -889,7 +889,11 @@ func checkEnum(value *Value, target reflect.Value) error {
 
 	case reflect.Map, reflect.Struct:
 		return errors.Errorf("enum can only be applied to a slice or value")
-
+	case reflect.Ptr:
+		if target.IsNil() {
+			return nil
+		}
+		return checkEnum(value, target.Elem())
 	default:
 		enumSlice := value.EnumSlice()
 		v := fmt.Sprintf("%v", target)

kong_test.go

@@ -1704,3 +1704,44 @@ func TestUnsupportedPtr(t *testing.T) {
 	require.Error(t, err)
 	require.Equal(t, "--f: cannot find mapper for kong_test.Foo", err.Error())
 }
+
+func TestEnumPtr(t *testing.T) {
+	var cli struct {
+		X *string `enum:"A,B,C" default:"C"`
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{"--x=A"})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.NotNil(t, cli.X)
+	require.Equal(t, "A", *cli.X)
+}
+
+func TestEnumPtrOmitted(t *testing.T) {
+	var cli struct {
+		X *string `enum:"A,B,C" default:"C"`
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.NotNil(t, cli.X)
+	require.Equal(t, "C", *cli.X)
+}
+
+func TestEnumPtrOmittedNoDefault(t *testing.T) {
+	var cli struct {
+		X *string `enum:"A,B,C"`
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.Nil(t, cli.X)
+}

tag.go

@@ -230,7 +230,7 @@ func hydrateTag(t *Tag, typ reflect.Type) error { // nolint: gocyclo
 	}
 	t.PlaceHolder = t.Get("placeholder")
 	t.Enum = t.Get("enum")
-	scalarType := (typ == nil || !(typ.Kind() == reflect.Slice || typ.Kind() == reflect.Map))
+	scalarType := (typ == nil || !(typ.Kind() == reflect.Slice || typ.Kind() == reflect.Map || typ.Kind() == reflect.Ptr))
 	if t.Enum != "" && !(t.Required || t.HasDefault) && scalarType {
 		return fmt.Errorf("enum value is only valid if it is either required or has a valid default value")
 	}