encoding/xml: reject > chain with non-element

Fixes #5033.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/7764044

src/pkg/encoding/xml/marshal.go

@@ -301,7 +301,7 @@ func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
 	s := parentStack{printer: p}
 	for i := range tinfo.fields {
 		finfo := &tinfo.fields[i]
-		if finfo.flags&(fAttr) != 0 {
+		if finfo.flags&fAttr != 0 {
 			continue
 		}
 		vf := finfo.value(val)

src/pkg/encoding/xml/marshal_test.go

@@ -272,6 +272,10 @@ type EmbedInt struct {
 	MyInt
 }
 
+type Strings struct {
+	X []string `xml:"A>B,omitempty"`
+}
+
 // Unless explicitly stated as such (or *Plain), all of the
 // tests below are two-way tests. When introducing new tests,
 // please try to make them two-way as well to ensure that
@@ -802,6 +806,11 @@ var marshalTests = []struct {
 			MyInt: 42,
 		},
 	},
+	// Test omitempty with parent chain; see golang.org/issue/4168.
+	{
+		ExpectXML: `<Strings><A></A></Strings>`,
+		Value:     &Strings{},
+	},
 }
 
 func TestMarshal(t *testing.T) {
@@ -824,6 +833,10 @@ func TestMarshal(t *testing.T) {
 	}
 }
 
+type AttrParent struct {
+	X string `xml:"X>Y,attr"`
+}
+
 var marshalErrorTests = []struct {
 	Value interface{}
 	Err   string
@@ -851,6 +864,11 @@ var marshalErrorTests = []struct {
 		Value: &Domain{Comment: []byte("f--bar")},
 		Err:   `xml: comments must not contain "--"`,
 	},
+	// Reject parent chain with attr, never worked; see golang.org/issue/5033.
+	{
+		Value: &AttrParent{},
+		Err:   `xml: X>Y chain not valid with attr flag`,
+	},
 }
 
 var marshalIndentTests = []struct {
@@ -873,8 +891,12 @@ var marshalIndentTests = []struct {
 
 func TestMarshalErrors(t *testing.T) {
 	for idx, test := range marshalErrorTests {
-		_, err := Marshal(test.Value)
-		if err == nil || err.Error() != test.Err {
+		data, err := Marshal(test.Value)
+		if err == nil {
+			t.Errorf("#%d: marshal(%#v) = [success] %q, want error %v", idx, test.Value, data, test.Err)
+			continue
+		}
+		if err.Error() != test.Err {
 			t.Errorf("#%d: marshal(%#v) = [error] %v, want %v", idx, test.Value, err, test.Err)
 		}
 		if test.Kind != reflect.Invalid {

src/pkg/encoding/xml/typeinfo.go

@@ -192,16 +192,19 @@ func structFieldInfo(typ reflect.Type, f *reflect.StructField) (*fieldInfo, erro
 	}
 
 	// Prepare field name and parents.
-	tokens = strings.Split(tag, ">")
-	if tokens[0] == "" {
-		tokens[0] = f.Name
+	parents := strings.Split(tag, ">")
+	if parents[0] == "" {
+		parents[0] = f.Name
 	}
-	if tokens[len(tokens)-1] == "" {
+	if parents[len(parents)-1] == "" {
 		return nil, fmt.Errorf("xml: trailing '>' in field %s of type %s", f.Name, typ)
 	}
-	finfo.name = tokens[len(tokens)-1]
-	if len(tokens) > 1 {
-		finfo.parents = tokens[:len(tokens)-1]
+	finfo.name = parents[len(parents)-1]
+	if len(parents) > 1 {
+		if (finfo.flags & fElement) == 0 {
+			return nil, fmt.Errorf("xml: %s chain not valid with %s flag", tag, strings.Join(tokens[1:], ","))
+		}
+		finfo.parents = parents[:len(parents)-1]
 	}
 
 	// If the field type has an XMLName field, the names must match