don't reset all fields in Unmarshal*

This preserves decoding into a struct with pre-filled, possibly
unexported fields.

genmethod.go

@@ -54,7 +54,6 @@ func genUnmarshalJSON(mtyp *marshalerType) Function {
 		input    = Name(m.scope.newIdent("input"))
 		intertyp = m.intermediateType(m.scope.newIdent(m.mtyp.orig.Obj().Name() + "JSON"))
 		dec      = Name(m.scope.newIdent("dec"))
-		conv     = Name(m.scope.newIdent("x"))
 		json     = Name(m.scope.parent.packageName("encoding/json"))
 	)
 	fn := Function{
@@ -69,11 +68,9 @@ func genUnmarshalJSON(mtyp *marshalerType) Function {
 				Func:   Dotted{Receiver: json, Name: "Unmarshal"},
 				Params: []Expression{input, AddressOf{Value: dec}},
 			}),
-			Declare{Name: conv.Name, TypeName: m.mtyp.name},
 		},
 	}
-	fn.Body = append(fn.Body, m.unmarshalConversions(dec, conv, "json")...)
-	fn.Body = append(fn.Body, Assign{Lhs: Star{Value: Name(recv.Name)}, Rhs: conv})
+	fn.Body = append(fn.Body, m.unmarshalConversions(dec, Name(recv.Name), "json")...)
 	fn.Body = append(fn.Body, Return{Values: []Expression{NIL}})
 	return fn
 }
@@ -123,7 +120,6 @@ func genUnmarshalLikeYAML(mtyp *marshalerType, name string) Function {
 		unmarshal = Name(m.scope.newIdent("unmarshal"))
 		intertyp  = m.intermediateType(m.scope.newIdent(m.mtyp.orig.Obj().Name() + name))
 		dec       = Name(m.scope.newIdent("dec"))
-		conv      = Name(m.scope.newIdent("x"))
 		tag       = strings.ToLower(name)
 	)
 	fn := Function{
@@ -135,11 +131,9 @@ func genUnmarshalLikeYAML(mtyp *marshalerType, name string) Function {
 			declStmt{intertyp},
 			Declare{Name: dec.Name, TypeName: intertyp.Name},
 			errCheck(CallFunction{Func: unmarshal, Params: []Expression{AddressOf{Value: dec}}}),
-			Declare{Name: conv.Name, TypeName: m.mtyp.name},
 		},
 	}
-	fn.Body = append(fn.Body, m.unmarshalConversions(dec, conv, tag)...)
-	fn.Body = append(fn.Body, Assign{Lhs: Star{Value: Name(recv.Name)}, Rhs: conv})
+	fn.Body = append(fn.Body, m.unmarshalConversions(dec, Name(recv.Name), tag)...)
 	fn.Body = append(fn.Body, Return{Values: []Expression{NIL}})
 	return fn
 }

internal/tests/mapconv/output.go

@@ -106,30 +106,28 @@ func (x *X) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if err := unmarshal(&dec); err != nil {
 		return err
 	}
-	var x0 X
 	if dec.Map == nil {
 		return errors.New("missing required field 'map' for X")
 	}
-	x0.Map = make(map[string]int, len(dec.Map))
+	x.Map = make(map[string]int, len(dec.Map))
 	for k, v := range dec.Map {
-		x0.Map[string(k)] = int(v)
+		x.Map[string(k)] = int(v)
 	}
 	if dec.Named == nil {
 		return errors.New("missing required field 'named' for X")
 	}
-	x0.Named = make(namedMap, len(dec.Named))
+	x.Named = make(namedMap, len(dec.Named))
 	for k, v := range dec.Named {
-		x0.Named[string(k)] = int(v)
+		x.Named[string(k)] = int(v)
 	}
 	if dec.NoConv == nil {
 		return errors.New("missing required field 'noConv' for X")
 	}
-	x0.NoConv = dec.NoConv
+	x.NoConv = dec.NoConv
 	if dec.NoConvNamed == nil {
 		return errors.New("missing required field 'noConvNamed' for X")
 	}
-	x0.NoConvNamed = dec.NoConvNamed
-	*x = x0
+	x.NoConvNamed = dec.NoConvNamed
 	return nil
 }
 
@@ -169,29 +167,27 @@ func (x *X) UnmarshalTOML(unmarshal func(interface{}) error) error {
 	if err := unmarshal(&dec); err != nil {
 		return err
 	}
-	var x0 X
 	if dec.Map == nil {
 		return errors.New("missing required field 'map' for X")
 	}
-	x0.Map = make(map[string]int, len(dec.Map))
+	x.Map = make(map[string]int, len(dec.Map))
 	for k, v := range dec.Map {
-		x0.Map[string(k)] = int(v)
+		x.Map[string(k)] = int(v)
 	}
 	if dec.Named == nil {
 		return errors.New("missing required field 'named' for X")
 	}
-	x0.Named = make(namedMap, len(dec.Named))
+	x.Named = make(namedMap, len(dec.Named))
 	for k, v := range dec.Named {
-		x0.Named[string(k)] = int(v)
+		x.Named[string(k)] = int(v)
 	}
 	if dec.NoConv == nil {
 		return errors.New("missing required field 'noConv' for X")
 	}
-	x0.NoConv = dec.NoConv
+	x.NoConv = dec.NoConv
 	if dec.NoConvNamed == nil {
 		return errors.New("missing required field 'noConvNamed' for X")
 	}
-	x0.NoConvNamed = dec.NoConvNamed
-	*x = x0
+	x.NoConvNamed = dec.NoConvNamed
 	return nil
 }

internal/tests/nameclash/output.go

@@ -87,23 +87,21 @@ func (y *Y) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if err := unmarshal(&dec); err != nil {
 		return err
 	}
-	var x Y
 	if dec.Foo != nil {
-		x.Foo = *dec.Foo
+		y.Foo = *dec.Foo
 	}
 	if dec.Foo2 != nil {
-		x.Foo2 = *dec.Foo2
+		y.Foo2 = *dec.Foo2
 	}
 	if dec.Bar != nil {
-		x.Bar = *dec.Bar
+		y.Bar = *dec.Bar
 	}
 	if dec.Gazonk != nil {
-		x.Gazonk = *dec.Gazonk
+		y.Gazonk = *dec.Gazonk
 	}
 	if dec.Over != nil {
-		x.Over = int(*dec.Over)
+		y.Over = int(*dec.Over)
 	}
-	*y = x
 	return nil
 }
 
@@ -136,22 +134,20 @@ func (y *Y) UnmarshalTOML(unmarshal func(interface{}) error) error {
 	if err := unmarshal(&dec); err != nil {
 		return err
 	}
-	var x Y
 	if dec.Foo != nil {
-		x.Foo = *dec.Foo
+		y.Foo = *dec.Foo
 	}
 	if dec.Foo2 != nil {
-		x.Foo2 = *dec.Foo2
+		y.Foo2 = *dec.Foo2
 	}
 	if dec.Bar != nil {
-		x.Bar = *dec.Bar
+		y.Bar = *dec.Bar
 	}
 	if dec.Gazonk != nil {
-		x.Gazonk = *dec.Gazonk
+		y.Gazonk = *dec.Gazonk
 	}
 	if dec.Over != nil {
-		x.Over = int(*dec.Over)
+		y.Over = int(*dec.Over)
 	}
-	*y = x
 	return nil
 }

internal/tests/omitempty/output.go

@@ -50,12 +50,10 @@ func (x *X) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	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
+	x.Int = int(*dec.Int)
 	return nil
 }
 
@@ -76,11 +74,9 @@ func (x *X) UnmarshalTOML(unmarshal func(interface{}) error) error {
 	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
+	x.Int = int(*dec.Int)
 	return nil
 }

internal/tests/sliceconv/output.go

@@ -116,34 +116,32 @@ func (x *X) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if err := unmarshal(&dec); err != nil {
 		return err
 	}
-	var x0 X
 	if dec.Slice == nil {
 		return errors.New("missing required field 'slice' for X")
 	}
-	x0.Slice = make([]int, len(dec.Slice))
+	x.Slice = make([]int, len(dec.Slice))
 	for k, v := range dec.Slice {
-		x0.Slice[k] = int(v)
+		x.Slice[k] = int(v)
 	}
 	if dec.Named == nil {
 		return errors.New("missing required field 'named' for X")
 	}
-	x0.Named = make(namedSlice, len(dec.Named))
+	x.Named = make(namedSlice, len(dec.Named))
 	for k, v := range dec.Named {
-		x0.Named[k] = int(v)
+		x.Named[k] = int(v)
 	}
 	if dec.ByteString == nil {
 		return errors.New("missing required field 'byteString' for X")
 	}
-	x0.ByteString = string(dec.ByteString)
+	x.ByteString = string(dec.ByteString)
 	if dec.NoConv == nil {
 		return errors.New("missing required field 'noConv' for X")
 	}
-	x0.NoConv = dec.NoConv
+	x.NoConv = dec.NoConv
 	if dec.NoConvNamed == nil {
 		return errors.New("missing required field 'noConvNamed' for X")
 	}
-	x0.NoConvNamed = dec.NoConvNamed
-	*x = x0
+	x.NoConvNamed = dec.NoConvNamed
 	return nil
 }
 
@@ -186,33 +184,31 @@ func (x *X) UnmarshalTOML(unmarshal func(interface{}) error) error {
 	if err := unmarshal(&dec); err != nil {
 		return err
 	}
-	var x0 X
 	if dec.Slice == nil {
 		return errors.New("missing required field 'slice' for X")
 	}
-	x0.Slice = make([]int, len(dec.Slice))
+	x.Slice = make([]int, len(dec.Slice))
 	for k, v := range dec.Slice {
-		x0.Slice[k] = int(v)
+		x.Slice[k] = int(v)
 	}
 	if dec.Named == nil {
 		return errors.New("missing required field 'named' for X")
 	}
-	x0.Named = make(namedSlice, len(dec.Named))
+	x.Named = make(namedSlice, len(dec.Named))
 	for k, v := range dec.Named {
-		x0.Named[k] = int(v)
+		x.Named[k] = int(v)
 	}
 	if dec.ByteString == nil {
 		return errors.New("missing required field 'byteString' for X")
 	}
-	x0.ByteString = string(dec.ByteString)
+	x.ByteString = string(dec.ByteString)
 	if dec.NoConv == nil {
 		return errors.New("missing required field 'noConv' for X")
 	}
-	x0.NoConv = dec.NoConv
+	x.NoConv = dec.NoConv
 	if dec.NoConvNamed == nil {
 		return errors.New("missing required field 'noConvNamed' for X")
 	}
-	x0.NoConvNamed = dec.NoConvNamed
-	*x = x0
+	x.NoConvNamed = dec.NoConvNamed
 	return nil
 }