gob: must register basic types to store them in interfaces.

Fixes #1230.

R=rsc
CC=golang-dev
https://golang.org/cl/2750041

src/pkg/gob/codec_test.go

@@ -1195,6 +1195,51 @@ func TestInterface(t *testing.T) {
 
 }
 
+// A struct with all basic types, stored in interfaces.
+type BasicInterfaceItem struct {
+	Int, Int8, Int16, Int32, Int64      interface{}
+	Uint, Uint8, Uint16, Uint32, Uint64 interface{}
+	Float, Float32, Float64             interface{}
+	Complex, Complex64, Complex128      interface{}
+	Bool                                interface{}
+	String                              interface{}
+	Bytes                               interface{}
+}
+
+func TestInterfaceBasic(t *testing.T) {
+	b := new(bytes.Buffer)
+	item1 := &BasicInterfaceItem{
+		int(1), int8(1), int16(1), int32(1), int64(1),
+		uint(1), uint8(1), uint16(1), uint32(1), uint64(1),
+		float(1), float32(1), float64(1),
+		complex(0i), complex64(0i), complex128(0i),
+		true,
+		"hello",
+		[]byte("sailor"),
+	}
+	// Register the types.
+	err := NewEncoder(b).Encode(item1)
+	if err != nil {
+		t.Error("expected no encode error; got", err)
+	}
+
+	item2 := &BasicInterfaceItem{}
+	err = NewDecoder(b).Decode(&item2)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if !reflect.DeepEqual(item1, item2) {
+		t.Errorf("encode expected %v got %v", item1, item2)
+	}
+	// Hand check a couple for correct types.
+	if v, ok := item2.Bool.(bool); !ok || !v {
+		t.Error("boolean should be true")
+	}
+	if v, ok := item2.String.(string); !ok || v != item1.String.(string) {
+		t.Errorf("string should be %v is %v", item1.String, v)
+	}
+}
+
 func TestIgnoreInterface(t *testing.T) {
 	iVal := Int(3)
 	fVal := Float(5)

src/pkg/gob/type.go

@@ -132,6 +132,7 @@ func init() {
 		panic(fmt.Sprintln("nextId too large:", nextId))
 	}
 	nextId = firstUserId
+	registerBasics()
 }
 
 // Array type
@@ -498,3 +499,25 @@ func Register(value interface{}) {
 
 	RegisterName(name, value)
 }
+
+func registerBasics() {
+	Register(int(0))
+	Register(int8(0))
+	Register(int16(0))
+	Register(int32(0))
+	Register(int64(0))
+	Register(uint(0))
+	Register(uint8(0))
+	Register(uint16(0))
+	Register(uint32(0))
+	Register(uint64(0))
+	Register(float(0))
+	Register(float32(0))
+	Register(float64(0))
+	Register(complex(0i))
+	Register(complex64(0i))
+	Register(complex128(0i))
+	Register(false)
+	Register("")
+	Register([]byte(nil))
+}