Propagate error to the caller in json.Marshal. Fixes issue 445.

R=rsc, imkrasin
CC=golang-dev
https://golang.org/cl/179125

src/pkg/json/struct.go

@@ -366,11 +366,9 @@ func writeStruct(w io.Writer, val *reflect.StructValue) os.Error {
 	for i := 0; i < val.NumField(); i++ {
 		fieldValue := val.Field(i)
 		fmt.Fprintf(w, "%q:", typ.Field(i).Name)
-
 		if err := writeValue(w, fieldValue); err != nil {
 			return err
 		}
-
 		if i < val.NumField()-1 {
 			fmt.Fprint(w, ",")
 		}
@@ -398,14 +396,19 @@ func writeValue(w io.Writer, val reflect.Value) (err os.Error) {
 	case *reflect.StructValue:
 		err = writeStruct(w, v)
 	case *reflect.ChanValue,
-		*reflect.PtrValue,
 		*reflect.UnsafePointerValue:
 		err = &MarshalError{val.Type()}
 	case *reflect.InterfaceValue:
 		if v.IsNil() {
 			fmt.Fprint(w, "null")
 		} else {
-			err = &MarshalError{val.Type()}
+			err = writeValue(w, v.Elem())
+		}
+	case *reflect.PtrValue:
+		if v.IsNil() {
+			fmt.Fprint(w, "null")
+		} else {
+			err = writeValue(w, v.Elem())
 		}
 	default:
 		value := val.(reflect.Value)

src/pkg/json/struct_test.go

@@ -175,6 +175,12 @@ type marshalTest struct {
 	out string
 }
 
+type MTE string
+
+type OneField struct {
+	a int
+}
+
 var marshalTests = []marshalTest{
 	// basic string
 	marshalTest{nil, "null"},
@@ -201,6 +207,9 @@ var marshalTests = []marshalTest{
 		`{"a":1,"b":"hello"}`,
 	},
 	marshalTest{map[string][]int{"3": []int{1, 2, 3}}, `{"3":[1,2,3]}`},
+	marshalTest{map[string]*MTE{"hi": nil}, `{"hi":null}`},
+	marshalTest{map[string]interface{}{"hi": 3}, `{"hi":3}`},
+	marshalTest{&OneField{3}, `{"a":3}`},
 }
 
 func TestMarshal(t *testing.T) {
@@ -224,11 +233,14 @@ type marshalErrorTest struct {
 	error string
 }
 
-type MTE string
+type ChanVal struct {
+	C chan int
+}
 
 var marshalErrorTests = []marshalErrorTest{
 	marshalErrorTest{map[chan int]string{make(chan int): "one"}, "json cannot encode value of type map[chan int] string"},
-	marshalErrorTest{map[string]*MTE{"hi": nil}, "json cannot encode value of type *json.MTE"},
+	marshalErrorTest{make(chan int, 100), "json cannot encode value of type chan int"},
+	marshalErrorTest{new(ChanVal), "json cannot encode value of type chan int"},
 }
 
 func TestMarshalError(t *testing.T) {