decode: fix pointers and fix null into string

Fixes bug #1133337.

R=jameinel
CC=
https://codereview.appspot.com/8019043

decode.go

@@ -308,8 +308,10 @@ func (d *decoder) scalar(n *node, out reflect.Value) (good bool) {
 	}
 	switch out.Kind() {
 	case reflect.String:
-		out.SetString(n.value)
-		good = true
+		if resolved != nil {
+			out.SetString(n.value)
+			good = true
+		}
 	case reflect.Interface:
 		if resolved == nil {
 			out.Set(reflect.Zero(out.Type()))
@@ -360,6 +362,13 @@ func (d *decoder) scalar(n *node, out reflect.Value) (good bool) {
 		case nil:
 			out.Set(reflect.Zero(out.Type()))
 			good = true
+		default:
+			if out.Type().Elem() == reflect.TypeOf(resolved) {
+				elem := reflect.New(out.Type().Elem())
+				elem.Elem().Set(reflect.ValueOf(resolved))
+				out.Set(elem)
+				good = true
+			}
 		}
 	}
 	return good

decode_test.go

@@ -23,8 +23,7 @@ var unmarshalTests = []struct {
 	{"v: 10", map[string]interface{}{"v": 10}},
 	{"v: 0b10", map[string]interface{}{"v": 2}},
 	{"v: 0xA", map[string]interface{}{"v": 10}},
-	{"v: 4294967296", map[string]interface{}{"v": int64(4294967296)}},
-	{"v: 4294967296", map[string]int64{"v": int64(4294967296)}},
+	{"v: 4294967296", map[string]int64{"v": 4294967296}},
 	{"v: 0.1", map[string]interface{}{"v": 0.1}},
 	{"v: .1", map[string]interface{}{"v": 0.1}},
 	{"v: .Inf", map[string]interface{}{"v": math.Inf(+1)}},
@@ -122,6 +121,10 @@ var unmarshalTests = []struct {
 			}
 		}{struct{ C int }{1}, struct{ C int }{1}}},
 	{"a: &a [1, 2]\nb: *a", &struct{ B []int }{[]int{1, 2}}},
+
+	// BUG #1133337
+	{"foo: ''", map[string]*string{"foo": new(string)}},
+	{"foo: null", map[string]string{}},
 }
 
 func (s *S) TestUnmarshal(c *C) {

goyaml.go

@@ -59,7 +59,7 @@ type Getter interface {
 // If an internal pointer within a struct is not initialized, goyaml
 // will initialize it if necessary for unmarshalling the provided data,
 // but the struct provided as out must not be a nil pointer.
-// 
+//
 // The type of the decoded values and the type of out will be considered,
 // and Unmarshal() will do the best possible job to unmarshal values
 // appropriately.  It is NOT considered an error, though, to skip values
@@ -83,7 +83,7 @@ type Getter interface {
 //     }
 //     var T t
 //     goyaml.Unmarshal([]byte("a: 1\nb: 2"), &t)
-// 
+//
 func Unmarshal(in []byte, out interface{}) (err error) {
 	defer handleErr(&err)
 	d := newDecoder()