fix: map keys being string type definitions

Co-authored-by: Marcela Campo <mcampo@pivotal.io>

marshal_test.go

@@ -203,6 +203,12 @@ var _ = Describe("Marshal", func() {
 				mn := map[int]interface{}{4: 3}
 				expectToFail(struct{ M map[int]interface{} }{M: mn}, `maps must only have string keys for "map[int]interface {}" at field "M" (type "map[int]interface {}")`)
 			})
+
+			It("marshals a map with keys that are string type definitions", func() {
+				type stringy string
+				me := map[stringy]string{"foo": "hello"}
+				expectToMarshal(struct{ M map[stringy]string }{M: me}, `{"M":{"foo": "hello"}}`)
+			})
 		})
 
 		It("marshals a json.Marshaler", func() {

unmarshal.go

@@ -188,7 +188,7 @@ func unmarshalIntoSlice(ctx context.Context, target reflect.Value, found bool, s
 func unmarshalIntoMap(ctx context.Context, target reflect.Value, found bool, source interface{}) error {
 	targetType := underlyingType(target)
 
-	if targetType.Key() != reflect.TypeOf("") {
+	if targetType.Key().Kind() != reflect.String {
 		return newUnsupportedKeyTypeError(ctx, targetType.Key())
 	}
 
@@ -210,7 +210,7 @@ func unmarshalIntoMap(ctx context.Context, target reflect.Value, found bool, sou
 			return err
 		}
 
-		m.SetMapIndex(reflect.ValueOf(k), targetValue)
+		m.SetMapIndex(reflect.ValueOf(k).Convert(targetType.Key()), targetValue)
 	}
 
 	return nil

unmarshal_test.go

@@ -400,10 +400,17 @@ var _ = Describe("Unmarshal", func() {
 				})
 			})
 
-			It("rejects an map field that does not have string keys", func() {
+			It("rejects a map field that does not have string keys", func() {
 				var s struct{ S map[int]string }
 				expectToFail(&s, `{}`, `maps must only have string keys for "int" at field "S" (type "map[int]string")`)
 			})
+
+			It("unmarshals a map with keys that are string type definitions", func() {
+				type stringy string
+				var s struct{ S map[stringy]string }
+				unmarshal(&s, `{"S": { "data": "some-data" } }`)
+				Expect(s.S).To(Equal(map[stringy]string{"data": "some-data"}))
+			})
 		})
 
 		It("unmarshals into json.Unmarshaler field", func() {