Merging issue 280 with master changes

README.md

@@ -384,6 +384,20 @@ var CLI struct {
 
 For flags, multiple key+value pairs should be separated by `mapsep:"rune"` tag (defaults to `;`) eg. `--set="key1=value1;key2=value2"`.
 
+## Pointers
+
+Pointers work like the underlying type, except that you can differentiate between the presence of the zero value and no value being supplied.
+
+For example:
+
+```go
+var CLI struct {
+	Foo *int
+}
+```
+
+Would produce a nil value for `Foo` if no `--foo` argument is supplied, but would have a pointer to the value 0 if the argument `--foo=0` was supplied.
+
 ## Nested data structure
 
 Kong support a nested data structure as well with `embed:""`. You can combine `embed:""` with `prefix:""`:
@@ -628,4 +642,4 @@ See the [section on hooks](#hooks-beforeresolve-beforeapply-afterapply-and-the-b
 
 ### Other options
 
-The full set of options can be found [here](https://godoc.org/github.com/alecthomas/kong#Option).
+The full set of options can be found [here](https://godoc.org/github.com/alecthomas/kong#Option).

context.go

@@ -661,6 +661,22 @@ func (c *Context) Apply() (string, error) {
 	return strings.Join(path, " "), nil
 }
 
+func flipBoolValue(value reflect.Value) error {
+	if value.Kind() == reflect.Bool {
+		value.SetBool(!value.Bool())
+		return nil
+	}
+
+	if value.Kind() == reflect.Ptr {
+		if !value.IsNil() {
+			return flipBoolValue(value.Elem())
+		}
+		return nil
+	}
+
+	return fmt.Errorf("cannot negate a value of %s", value.Type().String())
+}
+
 func (c *Context) parseFlag(flags []*Flag, match string) (err error) {
 	candidates := []string{}
 	for _, flag := range flags {
@@ -689,7 +705,10 @@ func (c *Context) parseFlag(flags []*Flag, match string) (err error) {
 		}
 		if flag.Negated {
 			value := c.getValue(flag.Value)
-			value.SetBool(!value.Bool())
+			err := flipBoolValue(value)
+			if err != nil {
+				return err
+			}
 			flag.Value.Apply(value)
 		}
 		c.Path = append(c.Path, &Path{Flag: flag})
@@ -889,6 +908,11 @@ func checkEnum(value *Value, target reflect.Value) error {
 	case reflect.Map, reflect.Struct:
 		return errors.New("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

@@ -1542,3 +1542,234 @@ func TestPassthroughCmdOnlyStringArgs(t *testing.T) {
 	_, err := kong.New(&cli)
 	require.EqualError(t, err, "<anonymous struct>.Command: passthrough command command [<args> ...] must contain exactly one positional argument of []string type")
 }
+
+func TestStringPointer(t *testing.T) {
+	var cli struct {
+		Foo *string
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{"--foo", "wtf"})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.NotNil(t, cli.Foo)
+	require.Equal(t, "wtf", *cli.Foo)
+}
+
+func TestStringPointerNoValue(t *testing.T) {
+	var cli struct {
+		Foo *string
+	}
+	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.Foo)
+}
+
+func TestStringPointerDefault(t *testing.T) {
+	var cli struct {
+		Foo *string `default:"stuff"`
+	}
+	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.Foo)
+	require.Equal(t, "stuff", *cli.Foo)
+}
+
+func TestStringPointerAliasNoValue(t *testing.T) {
+	type Foo string
+	var cli struct {
+		F *Foo
+	}
+	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.F)
+}
+
+func TestStringPointerAlias(t *testing.T) {
+	type Foo string
+	var cli struct {
+		F *Foo
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{"--f=value"})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.NotNil(t, cli.F)
+	require.Equal(t, Foo("value"), *cli.F)
+}
+
+func TestStringPointerEmptyValue(t *testing.T) {
+	var cli struct {
+		F *string
+		G *string
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{"--f", "", "--g="})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.NotNil(t, cli.F)
+	require.NotNil(t, cli.G)
+	require.Equal(t, "", *cli.F)
+	require.Equal(t, "", *cli.G)
+}
+
+func TestIntPtr(t *testing.T) {
+	var cli struct {
+		F *int
+		G *int
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{"--f=6"})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.NotNil(t, cli.F)
+	require.Nil(t, cli.G)
+	require.Equal(t, 6, *cli.F)
+}
+
+func TestBoolPtr(t *testing.T) {
+	var cli struct {
+		X *bool
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{"--x"})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.NotNil(t, cli.X)
+	require.Equal(t, true, *cli.X)
+}
+
+func TestBoolPtrFalse(t *testing.T) {
+	var cli struct {
+		X *bool
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{"--x=false"})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.NotNil(t, cli.X)
+	require.Equal(t, false, *cli.X)
+}
+
+func TestBoolPtrNegated(t *testing.T) {
+	var cli struct {
+		X *bool `negatable:""`
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{"--no-x"})
+	require.NoError(t, err)
+	require.NotNil(t, ctx)
+	require.NotNil(t, cli.X)
+	require.Equal(t, false, *cli.X)
+}
+
+func TestNilNegatableBoolPtr(t *testing.T) {
+	var cli struct {
+		X *bool `negatable:""`
+	}
+	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)
+}
+
+func TestBoolPtrNil(t *testing.T) {
+	var cli struct {
+		X *bool
+	}
+	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)
+}
+
+func TestUnsupportedPtr(t *testing.T) {
+	//nolint:structcheck,unused
+	type Foo struct {
+		x int
+		y int
+	}
+
+	var cli struct {
+		F *Foo
+	}
+	k, err := kong.New(&cli)
+	require.NoError(t, err)
+	require.NotNil(t, k)
+	ctx, err := k.Parse([]string{"--f=whatever"})
+	require.Nil(t, ctx)
+	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)
+}

mapper.go

@@ -274,7 +274,8 @@ func (r *Registry) RegisterDefaults() *Registry {
 		RegisterName("path", pathMapper(r)).
 		RegisterName("existingfile", existingFileMapper(r)).
 		RegisterName("existingdir", existingDirMapper(r)).
-		RegisterName("counter", counterMapper())
+		RegisterName("counter", counterMapper()).
+		RegisterKind(reflect.Ptr, ptrMapper(r))
 }
 
 type boolMapper struct{}
@@ -653,6 +654,22 @@ func existingDirMapper(r *Registry) MapperFunc {
 	}
 }
 
+func ptrMapper(r *Registry) MapperFunc {
+	return func(ctx *DecodeContext, target reflect.Value) error {
+		elem := reflect.New(target.Type().Elem()).Elem()
+		nestedMapper := r.ForValue(elem)
+		if nestedMapper == nil {
+			return fmt.Errorf("cannot find mapper for %v", target.Type().Elem().String())
+		}
+		err := nestedMapper.Decode(ctx, elem)
+		if err != nil {
+			return err
+		}
+		target.Set(elem.Addr())
+		return nil
+	}
+}
+
 func counterMapper() MapperFunc {
 	return func(ctx *DecodeContext, target reflect.Value) error {
 		if ctx.Scan.Peek().Type == FlagValueToken {

tag.go

@@ -169,9 +169,11 @@ func parseTag(parent reflect.Value, ft reflect.StructField) (*Tag, error) {
 func hydrateTag(t *Tag, typ reflect.Type) error { // nolint: gocyclo
 	var typeName string
 	var isBool bool
+	var isBoolPtr bool
 	if typ != nil {
 		typeName = typ.Name()
 		isBool = typ.Kind() == reflect.Bool
+		isBoolPtr = typ.Kind() == reflect.Ptr && typ.Elem().Kind() == reflect.Bool
 	}
 	var err error
 	t.Cmd = t.Has("cmd")
@@ -212,7 +214,7 @@ func hydrateTag(t *Tag, typ reflect.Type) error { // nolint: gocyclo
 	t.EnvPrefix = t.Get("envprefix")
 	t.Embed = t.Has("embed")
 	negatable := t.Has("negatable")
-	if negatable && !isBool {
+	if negatable && !isBool && !isBoolPtr {
 		return fmt.Errorf("negatable can only be set on booleans")
 	}
 	t.Negatable = negatable
@@ -230,7 +232,7 @@ 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")
 	}