encoding/json: check for exported fields in embedded structs

Addresses issue #12367.

Must be checked in before CL 14010.

Change-Id: I7233c3a62d4f55d0ac7e8a87df5fc4ee7beb7207
Reviewed-on: https://go-review.googlesource.com/14011Reviewed-by: Russ Cox <rsc@golang.org>

src/encoding/json/decode_test.go

@@ -118,6 +118,7 @@ type Top struct {
 	Loop
 	Embed0p // has Point with X, Y, used
 	Embed0q // has Point with Z, used
+	embed   // contains exported field
 }
 
 type Embed0 struct {
@@ -148,6 +149,10 @@ type Embed0q struct {
 	Point
 }
 
+type embed struct {
+	Q int
+}
+
 type Loop struct {
 	Loop1 int `json:",omitempty"`
 	Loop2 int `json:",omitempty"`
@@ -331,7 +336,8 @@ var unmarshalTests = []unmarshalTest{
 			"Loop2": 14,
 			"X": 15,
 			"Y": 16,
-			"Z": 17
+			"Z": 17,
+			"Q": 18
 		}`,
 		ptr: new(Top),
 		out: Top{
@@ -361,6 +367,9 @@ var unmarshalTests = []unmarshalTest{
 			Embed0q: Embed0q{
 				Point: Point{Z: 17},
 			},
+			embed: embed{
+				Q: 18,
+			},
 		},
 	},
 	{
@@ -507,12 +516,15 @@ func TestMarshalEmbeds(t *testing.T) {
 		Embed0q: Embed0q{
 			Point: Point{Z: 17},
 		},
+		embed: embed{
+			Q: 18,
+		},
 	}
 	b, err := Marshal(top)
 	if err != nil {
 		t.Fatal(err)
 	}
-	want := "{\"Level0\":1,\"Level1b\":2,\"Level1c\":3,\"Level1a\":5,\"LEVEL1B\":6,\"e\":{\"Level1a\":8,\"Level1b\":9,\"Level1c\":10,\"Level1d\":11,\"x\":12},\"Loop1\":13,\"Loop2\":14,\"X\":15,\"Y\":16,\"Z\":17}"
+	want := "{\"Level0\":1,\"Level1b\":2,\"Level1c\":3,\"Level1a\":5,\"LEVEL1B\":6,\"e\":{\"Level1a\":8,\"Level1b\":9,\"Level1c\":10,\"Level1d\":11,\"x\":12},\"Loop1\":13,\"Loop2\":14,\"X\":15,\"Y\":16,\"Z\":17,\"Q\":18}"
 	if string(b) != want {
 		t.Errorf("Wrong marshal result.\n got: %q\nwant: %q", b, want)
 	}

src/encoding/json/encode.go

@@ -1021,7 +1021,7 @@ func typeFields(t reflect.Type) []field {
 			// Scan f.typ for fields to include.
 			for i := 0; i < f.typ.NumField(); i++ {
 				sf := f.typ.Field(i)
-				if sf.PkgPath != "" { // unexported
+				if sf.PkgPath != "" && !sf.Anonymous { // unexported
 					continue
 				}
 				tag := sf.Tag.Get("json")