support for cborgen struct field tags

gen.go

@@ -75,6 +75,7 @@ var _ = sort.Sort
 
 type Field struct {
 	Name    string
+	MapKey  string
 	Pointer bool
 	Type    reflect.Type
 	Pkg     string
@@ -194,8 +195,15 @@ func ParseTypeInfo(i interface{}) (*GenTypeInfo, error) {
 			pointer = true
 		}
 
+		mapk := f.Name
+		tagval := f.Tag.Get("cborgen")
+		if tagval != "" {
+			mapk = tagval
+		}
+
 		out.Fields = append(out.Fields, Field{
 			Name:    f.Name,
+			MapKey:  mapk,
 			Pointer: pointer,
 			Type:    ft,
 			Pkg:     pkg,
@@ -1129,7 +1137,7 @@ 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.MapKey + `"`,
 		}); err != nil {
 			return err
 		}
@@ -1224,7 +1232,7 @@ 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 "{{ .MapKey }}":
 `)
 		if err != nil {
 			return err

testgen/main.go

@@ -22,6 +22,7 @@ func main() {
 		types.NeedScratchForMap{},
 		types.SimpleStructV1{},
 		types.SimpleStructV2{},
+		types.RenamedFields{},
 	); err != nil {
 		panic(err)
 	}

testing/types.go

@@ -45,12 +45,12 @@ type SimpleTypeTree struct {
 }
 
 type SimpleStructV1 struct {
-	OldStr string
-	OldBytes []byte
-	OldNum uint64
-	OldPtr *cid.Cid
-	OldMap map[string]SimpleTypeOne
-	OldArray []SimpleTypeOne
+	OldStr    string
+	OldBytes  []byte
+	OldNum    uint64
+	OldPtr    *cid.Cid
+	OldMap    map[string]SimpleTypeOne
+	OldArray  []SimpleTypeOne
 	OldStruct SimpleTypeOne
 }
 
@@ -99,3 +99,8 @@ type ThingWithSomeTime struct {
 type NeedScratchForMap struct {
 	Thing bool
 }
+
+type RenamedFields struct {
+	Foo int64  `cborgen:"foo"`
+	Bar string `cborgen:"beep"`
+}