encoding/xml: allow embedded non-structs

The old code just assumed that the only thing
you can embed is a struct. Not true.

Fixes #3803.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/7743043

src/pkg/encoding/xml/marshal_test.go

@@ -266,6 +266,12 @@ type Plain struct {
 	V interface{}
 }
 
+type MyInt int
+
+type EmbedInt struct {
+	MyInt
+}
+
 // 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
@@ -790,6 +796,12 @@ var marshalTests = []struct {
 		},
 		UnmarshalOnly: true,
 	},
+	{
+		ExpectXML: `<EmbedInt><MyInt>42</MyInt></EmbedInt>`,
+		Value: &EmbedInt{
+			MyInt: 42,
+		},
+	},
 }
 
 func TestMarshal(t *testing.T) {

src/pkg/encoding/xml/typeinfo.go

@@ -70,20 +70,19 @@ func getTypeInfo(typ reflect.Type) (*typeInfo, error) {
 				if t.Kind() == reflect.Ptr {
 					t = t.Elem()
 				}
-				if t.Kind() != reflect.Struct {
-					continue
-				}
-				inner, err := getTypeInfo(t)
-				if err != nil {
-					return nil, err
-				}
-				for _, finfo := range inner.fields {
-					finfo.idx = append([]int{i}, finfo.idx...)
-					if err := addFieldInfo(typ, tinfo, &finfo); err != nil {
+				if t.Kind() == reflect.Struct {
+					inner, err := getTypeInfo(t)
+					if err != nil {
 						return nil, err
 					}
+					for _, finfo := range inner.fields {
+						finfo.idx = append([]int{i}, finfo.idx...)
+						if err := addFieldInfo(typ, tinfo, &finfo); err != nil {
+							return nil, err
+						}
+					}
+					continue
 				}
-				continue
 			}
 
 			finfo, err := structFieldInfo(typ, &f)