1 files changed, 78 insertions, 19 deletions
diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index 27ceee471a..34b7ec6d97 100644
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -195,11 +195,6 @@ type embed struct {
 	Q int
 }
 
-type Issue21357 struct {
-	*embed
-	R int
-}
-
 type Loop struct {
 	Loop1 int `json:",omitempty"`
 	Loop2 int `json:",omitempty"`
@@ -871,20 +866,6 @@ var unmarshalTests = []unmarshalTest{
 		err: fmt.Errorf("json: unknown field \"extra\""),
 		disallowUnknownFields: true,
 	},
-
-	// Issue 21357.
-	// Ignore any embedded fields that are pointers to unexported structs.
-	{
-		in:  `{"Q":1,"R":2}`,
-		ptr: new(Issue21357),
-		out: Issue21357{R: 2},
-	},
-	{
-		in:  `{"Q":1,"R":2}`,
-		ptr: new(Issue21357),
-		err: fmt.Errorf("json: unknown field \"Q\""),
-		disallowUnknownFields: true,
-	},
 }
 
 func TestMarshal(t *testing.T) {
@@ -2107,3 +2088,81 @@ func TestInvalidStringOption(t *testing.T) {
 		t.Fatalf("Unmarshal: %v", err)
 	}
 }
+
+// Test unmarshal behavior with regards to embedded pointers to unexported structs.
+// If unallocated, this returns an error because unmarshal cannot set the field.
+// Issue 21357.
+func TestUnmarshalEmbeddedPointerUnexported(t *testing.T) {
+	type (
+		embed1 struct{ Q int }
+		embed2 struct{ Q int }
+		embed3 struct {
+			Q int64 `json:",string"`
+		}
+		S1 struct {
+			*embed1
+			R int
+		}
+		S2 struct {
+			*embed1
+			Q int
+		}
+		S3 struct {
+			embed1
+			R int
+		}
+		S4 struct {
+			*embed1
+			embed2
+		}
+		S5 struct {
+			*embed3
+			R int
+		}
+	)
+
+	tests := []struct {
+		in  string
+		ptr interface{}
+		out interface{}
+		err error
+	}{{
+		// Error since we cannot set S1.embed1, but still able to set S1.R.
+		in:  `{"R":2,"Q":1}`,
+		ptr: new(S1),
+		out: &S1{R: 2},
+		err: fmt.Errorf("json: cannot set embedded pointer to unexported struct: json.embed1"),
+	}, {
+		// The top level Q field takes precedence.
+		in:  `{"Q":1}`,
+		ptr: new(S2),
+		out: &S2{Q: 1},
+	}, {
+		// No issue with non-pointer variant.
+		in:  `{"R":2,"Q":1}`,
+		ptr: new(S3),
+		out: &S3{embed1: embed1{Q: 1}, R: 2},
+	}, {
+		// No error since both embedded structs have field R, which annihilate each other.
+		// Thus, no attempt is made at setting S4.embed1.
+		in:  `{"R":2}`,
+		ptr: new(S4),
+		out: new(S4),
+	}, {
+		// Error since we cannot set S5.embed1, but still able to set S5.R.
+		in:  `{"R":2,"Q":1}`,
+		ptr: new(S5),
+		out: &S5{R: 2},
+		err: fmt.Errorf("json: cannot set embedded pointer to unexported struct: json.embed3"),
+	}}
+
+	for i, tt := range tests {
+		err := Unmarshal([]byte(tt.in), tt.ptr)
+		if !reflect.DeepEqual(err, tt.err) {
+			t.Errorf("#%d: %v, want %v", i, err, tt.err)
+		}
+		if !reflect.DeepEqual(tt.ptr, tt.out) {
+			t.Errorf("#%d: mismatch\ngot:  %#+v\nwant: %#+v", i, tt.ptr, tt.out)
+		}
+	}
+}