encoding/xml: Makes XML Marshaler take into account XMLName field from anonymous field

Fixes #7614.

LGTM=rsc
R=golang-codereviews, r, rsc, dan.kortschak, applezinc
CC=golang-codereviews
https://golang.org/cl/79210044

src/pkg/encoding/xml/marshal_test.go

@@ -314,6 +314,31 @@ type MarshalerStruct struct {
 	Foo MyMarshalerAttrTest `xml:",attr"`
 }
 
+type InnerStruct struct {
+	XMLName Name `xml:"testns outer"`
+}
+
+type OuterStruct struct {
+	InnerStruct
+	IntAttr int `xml:"int,attr"`
+}
+
+type OuterNamedStruct struct {
+	InnerStruct
+	XMLName Name `xml:"outerns test"`
+	IntAttr int  `xml:"int,attr"`
+}
+
+type OuterNamedOrderedStruct struct {
+	XMLName Name `xml:"outerns test"`
+	InnerStruct
+	IntAttr int `xml:"int,attr"`
+}
+
+type OuterOuterStruct struct {
+	OuterStruct
+}
+
 func ifaceptr(x interface{}) interface{} {
 	return &x
 }
@@ -883,6 +908,22 @@ var marshalTests = []struct {
 		ExpectXML: `<MarshalerStruct Foo="hello world"></MarshalerStruct>`,
 		Value:     &MarshalerStruct{},
 	},
+	{
+		ExpectXML: `<outer xmlns="testns" int="10"></outer>`,
+		Value:     &OuterStruct{IntAttr: 10},
+	},
+	{
+		ExpectXML: `<test xmlns="outerns" int="10"></test>`,
+		Value:     &OuterNamedStruct{XMLName: Name{Space: "outerns", Local: "test"}, IntAttr: 10},
+	},
+	{
+		ExpectXML: `<test xmlns="outerns" int="10"></test>`,
+		Value:     &OuterNamedOrderedStruct{XMLName: Name{Space: "outerns", Local: "test"}, IntAttr: 10},
+	},
+	{
+		ExpectXML: `<outer xmlns="testns" int="10"></outer>`,
+		Value:     &OuterOuterStruct{OuterStruct{IntAttr: 10}},
+	},
 }
 
 func TestMarshal(t *testing.T) {

src/pkg/encoding/xml/typeinfo.go

@@ -75,6 +75,9 @@ func getTypeInfo(typ reflect.Type) (*typeInfo, error) {
 					if err != nil {
 						return nil, err
 					}
+					if tinfo.xmlname == nil {
+						tinfo.xmlname = inner.xmlname
+					}
 					for _, finfo := range inner.fields {
 						finfo.idx = append([]int{i}, finfo.idx...)
 						if err := addFieldInfo(typ, tinfo, &finfo); err != nil {