1 files changed, 54 insertions, 0 deletions
diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index 5ac1022207..a62488d447 100644
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -2569,3 +2569,57 @@ func TestUnmarshalMaxDepth(t *testing.T) {
 		}
 	}
 }
+
+func TestUnmarshalMapPointerElem(t *testing.T) {
+	type S struct{ Unchanged, Changed int }
+	input := []byte(`{"S":{"Changed":5}}`)
+	want := S{1, 5}
+
+	// First, a map with struct pointer elements. The key-value pair exists,
+	// so reuse the existing value.
+	s := &S{1, 2}
+	ptrMap := map[string]*S{"S": s}
+	if err := Unmarshal(input, &ptrMap); err != nil {
+		t.Fatal(err)
+	}
+	if s != ptrMap["S"] {
+		t.Fatal("struct pointer element in map was completely replaced")
+	}
+	if got := *s; got != want {
+		t.Fatalf("want %#v, got %#v", want, got)
+	}
+
+	// Second, a map with struct elements. The key-value pair exists, but
+	// the value isn't addresable, so make a copy and use that.
+	s = &S{1, 2}
+	strMap := map[string]S{"S": *s}
+	if err := Unmarshal(input, &strMap); err != nil {
+		t.Fatal(err)
+	}
+	if *s == strMap["S"] {
+		t.Fatal("struct element in map wasn't copied")
+	}
+	if got := strMap["S"]; got != want {
+		t.Fatalf("want %#v, got %#v", want, got)
+	}
+
+	// Finally, check the cases where the key-value pair exists, but the
+	// value is zero.
+	want = S{0, 5}
+
+	ptrMap = map[string]*S{"S": nil}
+	if err := Unmarshal(input, &ptrMap); err != nil {
+		t.Fatal(err)
+	}
+	if got := *ptrMap["S"]; got != want {
+		t.Fatalf("want %#v, got %#v", want, got)
+	}
+
+	strMap = map[string]S{"S": {}}
+	if err := Unmarshal(input, &strMap); err != nil {
+		t.Fatal(err)
+	}
+	if got := strMap["S"]; got != want {
+		t.Fatalf("want %#v, got %#v", want, got)
+	}
+}