Rename fields when generating map encodings

gen.go

@@ -69,10 +69,11 @@ var _ = xerrors.Errorf
 }
 
 type Field struct {
-	Name    string
-	Pointer bool
-	Type    reflect.Type
-	Pkg     string
+	Name       string
+	Serialized string
+	Pointer    bool
+	Type       reflect.Type
+	Pkg        string
 
 	IterLabel string
 }
@@ -189,11 +190,16 @@ func ParseTypeInfo(i interface{}) (*GenTypeInfo, error) {
 			pointer = true
 		}
 
+		serialized, hasSerialized := f.Tag.Lookup("json")
+		if !hasSerialized {
+			serialized = f.Name
+		}
 		out.Fields = append(out.Fields, Field{
-			Name:    f.Name,
-			Pointer: pointer,
-			Type:    ft,
-			Pkg:     pkg,
+			Name:       f.Name,
+			Serialized: serialized,
+			Pointer:    pointer,
+			Type:       ft,
+			Pkg:        pkg,
 		})
 	}
 
@@ -1124,7 +1130,7 @@ func emitCborMarshalStructMap(w io.Writer, gti *GenTypeInfo) error {
 		fmt.Fprintf(w, "\n\t// t.%s (%s) (%s)", f.Name, f.Type, f.Type.Kind())
 
 		if err := emitCborMarshalStringField(w, Field{
-			Name: `"` + f.Name + `"`,
+			Name: `"` + f.Serialized + `"`,
 		}); err != nil {
 			return err
 		}
@@ -1219,7 +1225,7 @@ func (t *{{ .Name}}) UnmarshalCBOR(r io.Reader) error {
 		fmt.Fprintf(w, "// t.%s (%s) (%s)", f.Name, f.Type, f.Type.Kind())
 
 		err := doTemplate(w, f, `
-		case "{{ .Name }}":
+		case "{{ .Serialized }}":
 `)
 		if err != nil {
 			return err

testgen/main.go

@@ -20,6 +20,7 @@ func main() {
 	if err := cbg.WriteMapEncodersToFile("testing/cbor_map_gen.go", "testing",
 		types.SimpleTypeTree{},
 		types.NeedScratchForMap{},
+		types.MapWithRenames{},
 	); err != nil {
 		panic(err)
 	}

testing/roundtrip_test.go

@@ -43,6 +43,10 @@ func TestNeedScratchForMap(t *testing.T) {
 	testTypeRoundtrips(t, reflect.TypeOf(NeedScratchForMap{}))
 }
 
+func TestMapWithRenames(t *testing.T) {
+	testTypeRoundtrips(t, reflect.TypeOf(MapWithRenames{}))
+}
+
 func testValueRoundtrip(t *testing.T, obj cbg.CBORMarshaler, nobj cbg.CBORUnmarshaler) {
 
 	buf := new(bytes.Buffer)

testing/types.go

@@ -65,3 +65,9 @@ type ThingWithSomeTime struct {
 type NeedScratchForMap struct {
 	Thing bool
 }
+
+type MapWithRenames struct {
+	String string `json:"s"`
+	Int    uint64 `json:"i"`
+	Bytes  []byte `json:"b"`
+}