disable field type pointer-wrapping for Marshal*

This makes the ,omitempty tag work correctly.

genmethod.go

@@ -25,15 +25,17 @@ var (
 type marshalMethod struct {
 	mtyp        *marshalerType
 	scope       *funcScope
+	isUnmarshal bool
 	// cached identifiers for map, slice conversions
 	iterKey, iterVal Var
 }
 
-func newMarshalMethod(mtyp *marshalerType) *marshalMethod {
+func newMarshalMethod(mtyp *marshalerType, isUnmarshal bool) *marshalMethod {
 	s := newFuncScope(mtyp.scope)
 	return &marshalMethod{
 		mtyp:        mtyp,
 		scope:       newFuncScope(mtyp.scope),
+		isUnmarshal: isUnmarshal,
 		iterKey:     Name(s.newIdent("k")),
 		iterVal:     Name(s.newIdent("v")),
 	}
@@ -47,8 +49,8 @@ func writeFunction(w io.Writer, fs *token.FileSet, fn Function) {
 // genUnmarshalJSON generates the UnmarshalJSON method.
 func genUnmarshalJSON(mtyp *marshalerType) Function {
 	var (
-		m        = newMarshalMethod(mtyp)
+		m        = newMarshalMethod(mtyp, true)
-		recv     = m.receiver(true)
+		recv     = m.receiver()
 		input    = Name(m.scope.newIdent("input"))
 		intertyp = m.intermediateType(m.scope.newIdent(m.mtyp.orig.Obj().Name() + "JSON"))
 		dec      = Name(m.scope.newIdent("dec"))
@@ -79,8 +81,8 @@ func genUnmarshalJSON(mtyp *marshalerType) Function {
 // genMarshalJSON generates the MarshalJSON method.
 func genMarshalJSON(mtyp *marshalerType) Function {
 	var (
-		m        = newMarshalMethod(mtyp)
+		m        = newMarshalMethod(mtyp, false)
-		recv     = m.receiver(false)
+		recv     = m.receiver()
 		intertyp = m.intermediateType(m.scope.newIdent(m.mtyp.orig.Obj().Name() + "JSON"))
 		enc      = Name(m.scope.newIdent("enc"))
 		json     = Name(m.scope.parent.packageName("encoding/json"))
@@ -107,8 +109,8 @@ func genMarshalJSON(mtyp *marshalerType) Function {
 // genUnmarshalYAML generates the UnmarshalYAML method.
 func genUnmarshalYAML(mtyp *marshalerType) Function {
 	var (
-		m         = newMarshalMethod(mtyp)
+		m         = newMarshalMethod(mtyp, true)
-		recv      = m.receiver(true)
+		recv      = m.receiver()
 		unmarshal = Name(m.scope.newIdent("unmarshal"))
 		intertyp  = m.intermediateType(m.scope.newIdent(m.mtyp.orig.Obj().Name() + "YAML"))
 		dec       = Name(m.scope.newIdent("dec"))
@@ -135,8 +137,8 @@ func genUnmarshalYAML(mtyp *marshalerType) Function {
 // genMarshalYAML generates the MarshalYAML method.
 func genMarshalYAML(mtyp *marshalerType) Function {
 	var (
-		m        = newMarshalMethod(mtyp)
+		m        = newMarshalMethod(mtyp, false)
-		recv     = m.receiver(false)
+		recv     = m.receiver()
 		intertyp = m.intermediateType(m.scope.newIdent(m.mtyp.orig.Obj().Name() + "YAML"))
 		enc      = Name(m.scope.newIdent("enc"))
 	)
@@ -154,10 +156,10 @@ func genMarshalYAML(mtyp *marshalerType) Function {
 	return fn
 }
 
-func (m *marshalMethod) receiver(pointer bool) Receiver {
+func (m *marshalMethod) receiver() Receiver {
 	letter := strings.ToLower(m.mtyp.name[:1])
 	r := Receiver{Name: m.scope.newIdent(letter), Type: Name(m.mtyp.name)}
-	if pointer {
+	if m.isUnmarshal {
 		r.Type = Star{Value: r.Type}
 	}
 	return r
@@ -166,9 +168,13 @@ func (m *marshalMethod) receiver(pointer bool) Receiver {
 func (m *marshalMethod) intermediateType(name string) Struct {
 	s := Struct{Name: name}
 	for _, f := range m.mtyp.Fields {
+		typ := f.typ
+		if m.isUnmarshal {
+			typ = ensureNilCheckable(typ)
+		}
 		s.Fields = append(s.Fields, Field{
 			Name:     f.name,
-			TypeName: types.TypeString(f.typ, m.mtyp.scope.qualify),
+			TypeName: types.TypeString(typ, m.mtyp.scope.qualify),
 			Tag:      f.tag,
 		})
 	}
@@ -179,10 +185,11 @@ func (m *marshalMethod) unmarshalConversions(from, to Var, format string) (s []S
 	for _, f := range m.mtyp.Fields {
 		accessFrom := Dotted{Receiver: from, Name: f.name}
 		accessTo := Dotted{Receiver: to, Name: f.name}
+		typ := ensureNilCheckable(f.typ)
 		if f.isOptional(format) {
 			s = append(s, If{
 				Condition: NotEqual{Lhs: accessFrom, Rhs: NIL},
-				Body:      m.convert(accessFrom, accessTo, f.typ, f.origTyp),
+				Body:      m.convert(accessFrom, accessTo, typ, f.origTyp),
 			})
 		} else {
 			err := fmt.Sprintf("missing required field '%s' for %s", f.encodedName(format), m.mtyp.name)
@@ -200,7 +207,7 @@ func (m *marshalMethod) unmarshalConversions(from, to Var, format string) (s []S
 					},
 				},
 			})
-			s = append(s, m.convert(accessFrom, accessTo, f.typ, f.origTyp)...)
+			s = append(s, m.convert(accessFrom, accessTo, typ, f.origTyp)...)
 		}
 	}
 	return s

internal/tests/nameclash/output.go

@@ -11,18 +11,18 @@ import (
 
 func (y Y) MarshalJSON() ([]byte, error) {
 	type YJSON0 struct {
-		Foo    *json0.Foo   `optional:"true"`
+		Foo    json0.Foo   `optional:"true"`
-		Foo2   *json0.Foo   `optional:"true"`
+		Foo2   json0.Foo   `optional:"true"`
-		Bar    *errors0.Foo `optional:"true"`
+		Bar    errors0.Foo `optional:"true"`
-		Gazonk *YJSON       `optional:"true"`
+		Gazonk YJSON       `optional:"true"`
-		Over   *enc         `optional:"true"`
+		Over   enc         `optional:"true"`
 	}
 	var enc0 YJSON0
-	enc0.Foo = &y.Foo
+	enc0.Foo = y.Foo
-	enc0.Foo2 = &y.Foo2
+	enc0.Foo2 = y.Foo2
-	enc0.Bar = &y.Bar
+	enc0.Bar = y.Bar
-	enc0.Gazonk = &y.Gazonk
+	enc0.Gazonk = y.Gazonk
-	enc0.Over = (*enc)(&y.Over)
+	enc0.Over = enc(y.Over)
 	return json.Marshal(&enc0)
 }
 
@@ -60,18 +60,18 @@ func (y *Y) UnmarshalJSON(input []byte) error {
 
 func (y Y) MarshalYAML() (interface{}, error) {
 	type YYAML struct {
-		Foo    *json0.Foo   `optional:"true"`
+		Foo    json0.Foo   `optional:"true"`
-		Foo2   *json0.Foo   `optional:"true"`
+		Foo2   json0.Foo   `optional:"true"`
-		Bar    *errors0.Foo `optional:"true"`
+		Bar    errors0.Foo `optional:"true"`
-		Gazonk *YJSON       `optional:"true"`
+		Gazonk YJSON       `optional:"true"`
-		Over   *enc         `optional:"true"`
+		Over   enc         `optional:"true"`
 	}
 	var enc0 YYAML
-	enc0.Foo = &y.Foo
+	enc0.Foo = y.Foo
-	enc0.Foo2 = &y.Foo2
+	enc0.Foo2 = y.Foo2
-	enc0.Bar = &y.Bar
+	enc0.Bar = y.Bar
-	enc0.Gazonk = &y.Gazonk
+	enc0.Gazonk = y.Gazonk
-	enc0.Over = (*enc)(&y.Over)
+	enc0.Over = enc(y.Over)
 	return &enc0, nil
 }
 

internal/tests/omitempty/input.go

@@ -0,0 +1,17 @@
+// Copyright 2017 Felix Lange <fjl@twurst.com>.
+// Use of this source code is governed by the MIT license,
+// which can be found in the LICENSE file.
+
+//go:generate gencodec -type X -field-override Xo -formats json,yaml -out output.go
+
+package omitempty
+
+type replacedInt int
+
+type X struct {
+	Int int `json:",omitempty"`
+}
+
+type Xo struct {
+	Int replacedInt
+}

internal/tests/omitempty/input_test.go

@@ -0,0 +1,21 @@
+// Copyright 2017 Felix Lange <fjl@twurst.com>.
+// Use of this source code is governed by the MIT license,
+// which can be found in the LICENSE file.
+
+package omitempty
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestOmitemptyJSON(t *testing.T) {
+	want := `{}`
+	out, err := json.Marshal(new(X))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(out) != want {
+		t.Fatalf("got %#q, want %#q", string(out), want)
+	}
+}

internal/tests/omitempty/output.go

@@ -0,0 +1,60 @@
+// Code generated by github.com/fjl/gencodec. DO NOT EDIT.
+
+package omitempty
+
+import (
+	"encoding/json"
+	"errors"
+)
+
+func (x X) MarshalJSON() ([]byte, error) {
+	type XJSON struct {
+		Int replacedInt `json:",omitempty"`
+	}
+	var enc XJSON
+	enc.Int = replacedInt(x.Int)
+	return json.Marshal(&enc)
+}
+
+func (x *X) UnmarshalJSON(input []byte) error {
+	type XJSON struct {
+		Int *replacedInt `json:",omitempty"`
+	}
+	var dec XJSON
+	if err := json.Unmarshal(input, &dec); err != nil {
+		return err
+	}
+	var x0 X
+	if dec.Int == nil {
+		return errors.New("missing required field 'int' for X")
+	}
+	x0.Int = int(*dec.Int)
+	*x = x0
+	return nil
+}
+
+func (x X) MarshalYAML() (interface{}, error) {
+	type XYAML struct {
+		Int replacedInt `json:",omitempty"`
+	}
+	var enc XYAML
+	enc.Int = replacedInt(x.Int)
+	return &enc, nil
+}
+
+func (x *X) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	type XYAML struct {
+		Int *replacedInt `json:",omitempty"`
+	}
+	var dec XYAML
+	if err := unmarshal(&dec); err != nil {
+		return err
+	}
+	var x0 X
+	if dec.Int == nil {
+		return errors.New("missing required field 'int' for X")
+	}
+	x0.Int = int(*dec.Int)
+	*x = x0
+	return nil
+}

main.go

@@ -284,7 +284,7 @@ func newMarshalerType(fs *token.FileSet, imp types.Importer, typ *types.Named) *
 		}
 		mf := &marshalerField{
 			name:    f.Name(),
-			typ:     ensureNilCheckable(f.Type()),
+			typ:     f.Type(),
 			origTyp: f.Type(),
 			tag:     styp.Tag(i),
 		}
@@ -312,7 +312,7 @@ func (mtyp *marshalerType) loadOverrides(otypename string, otyp *types.Struct) e
 		if err := checkConvertible(of.Type(), f.origTyp); err != nil {
 			return fmt.Errorf("%v: invalid field override: %v", mtyp.fs.Position(of.Pos()), err)
 		}
-		f.typ = ensureNilCheckable(of.Type())
+		f.typ = of.Type()
 	}
 	mtyp.scope.addReferences(otyp)
 	return nil

main_test.go

@@ -29,6 +29,10 @@ func TestNameClash(t *testing.T) {
 	runGoldenTest(t, Config{Dir: "nameclash", Type: "Y", FieldOverride: "Yo", Formats: AllFormats})
 }
 
+func TestOmitempty(t *testing.T) {
+	runGoldenTest(t, Config{Dir: "omitempty", Type: "X", FieldOverride: "Xo", Formats: AllFormats})
+}
+
 func runGoldenTest(t *testing.T, cfg Config) {
 	cfg.Dir = filepath.Join("internal", "tests", cfg.Dir)
 	want, err := ioutil.ReadFile(filepath.Join(cfg.Dir, "output.go"))