changes for more restricted reflect.SetValue

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/4423043

src/cmd/gofmt/rewrite.go

@@ -276,21 +276,21 @@ func subst(m map[string]reflect.Value, pattern reflect.Value, pos reflect.Value)
 		return v
 
 	case reflect.Struct:
-		v := reflect.Zero(p.Type())
+		v := reflect.New(p.Type()).Elem()
 		for i := 0; i < p.NumField(); i++ {
 			v.Field(i).Set(subst(m, p.Field(i), pos))
 		}
 		return v
 
 	case reflect.Ptr:
-		v := reflect.Zero(p.Type())
+		v := reflect.New(p.Type()).Elem()
 		if elem := p.Elem(); elem.IsValid() {
 			v.Set(subst(m, elem, pos).Addr())
 		}
 		return v
 
 	case reflect.Interface:
-		v := reflect.Zero(p.Type())
+		v := reflect.New(p.Type()).Elem()
 		if elem := p.Elem(); elem.IsValid() {
 			v.Set(subst(m, elem, pos))
 		}

src/pkg/asn1/asn1_test.go

@@ -267,11 +267,6 @@ func TestParseFieldParameters(t *testing.T) {
 	}
 }
 
-type unmarshalTest struct {
-	in  []byte
-	out interface{}
-}
-
 type TestObjectIdentifierStruct struct {
 	OID ObjectIdentifier
 }
@@ -290,7 +285,10 @@ type TestElementsAfterString struct {
 	A, B int
 }
 
-var unmarshalTestData []unmarshalTest = []unmarshalTest{
+var unmarshalTestData = []struct {
+	in  []byte
+	out interface{}
+}{
 	{[]byte{0x02, 0x01, 0x42}, newInt(0x42)},
 	{[]byte{0x30, 0x08, 0x06, 0x06, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d}, &TestObjectIdentifierStruct{[]int{1, 2, 840, 113549}}},
 	{[]byte{0x03, 0x04, 0x06, 0x6e, 0x5d, 0xc0}, &BitString{[]byte{110, 93, 192}, 18}},
@@ -309,9 +307,7 @@ var unmarshalTestData []unmarshalTest = []unmarshalTest{
 
 func TestUnmarshal(t *testing.T) {
 	for i, test := range unmarshalTestData {
-		pv := reflect.Zero(reflect.NewValue(test.out).Type())
-		zv := reflect.Zero(pv.Type().Elem())
-		pv.Set(zv.Addr())
+		pv := reflect.New(reflect.Typeof(test.out).Elem())
 		val := pv.Interface()
 		_, err := Unmarshal(test.in, val)
 		if err != nil {

src/pkg/gob/codec_test.go

@@ -999,7 +999,6 @@ type Bad0 struct {
 	C  float64
 }
 
-
 func TestInvalidField(t *testing.T) {
 	var bad0 Bad0
 	bad0.CH = make(chan int)

src/pkg/gob/decode.go

@@ -581,7 +581,7 @@ func (dec *Decoder) decodeArray(atyp reflect.Type, state *decoderState, p uintpt
 // unlike the other items we can't use a pointer directly.
 func decodeIntoValue(state *decoderState, op decOp, indir int, v reflect.Value, ovfl os.ErrorString) reflect.Value {
 	instr := &decInstr{op, 0, indir, 0, ovfl}
-	up := unsafe.Pointer(v.UnsafeAddr())
+	up := unsafe.Pointer(unsafeAddr(v))
 	if indir > 1 {
 		up = decIndirect(up, indir)
 	}
@@ -608,8 +608,8 @@ func (dec *Decoder) decodeMap(mtyp reflect.Type, state *decoderState, p uintptr,
 	v := reflect.NewValue(unsafe.Unreflect(mtyp, unsafe.Pointer(p)))
 	n := int(state.decodeUint())
 	for i := 0; i < n; i++ {
-		key := decodeIntoValue(state, keyOp, keyIndir, reflect.Zero(mtyp.Key()), ovfl)
-		elem := decodeIntoValue(state, elemOp, elemIndir, reflect.Zero(mtyp.Elem()), ovfl)
+		key := decodeIntoValue(state, keyOp, keyIndir, allocValue(mtyp.Key()), ovfl)
+		elem := decodeIntoValue(state, elemOp, elemIndir, allocValue(mtyp.Elem()), ovfl)
 		v.SetMapIndex(key, elem)
 	}
 }
@@ -686,8 +686,8 @@ func setInterfaceValue(ivalue reflect.Value, value reflect.Value) {
 // Interfaces are encoded as the name of a concrete type followed by a value.
 // If the name is empty, the value is nil and no value is sent.
 func (dec *Decoder) decodeInterface(ityp reflect.Type, state *decoderState, p uintptr, indir int) {
-	// Create an interface reflect.Value.  We need one even for the nil case.
-	ivalue := reflect.Zero(ityp)
+	// Create a writable interface reflect.Value.  We need one even for the nil case.
+	ivalue := allocValue(ityp)
 	// Read the name of the concrete type.
 	b := make([]byte, state.decodeUint())
 	state.b.Read(b)
@@ -712,7 +712,7 @@ func (dec *Decoder) decodeInterface(ityp reflect.Type, state *decoderState, p ui
 	// in case we want to ignore the value by skipping it completely).
 	state.decodeUint()
 	// Read the concrete value.
-	value := reflect.Zero(typ)
+	value := allocValue(typ)
 	dec.decodeValue(concreteId, value)
 	if dec.err != nil {
 		error(dec.err)
@@ -1209,9 +1209,9 @@ func (dec *Decoder) decodeValue(wireId typeId, val reflect.Value) {
 			name := base.Name()
 			errorf("gob: type mismatch: no fields matched compiling decoder for %s", name)
 		}
-		dec.decodeStruct(engine, ut, uintptr(val.UnsafeAddr()), ut.indir)
+		dec.decodeStruct(engine, ut, uintptr(unsafeAddr(val)), ut.indir)
 	} else {
-		dec.decodeSingle(engine, ut, uintptr(val.UnsafeAddr()))
+		dec.decodeSingle(engine, ut, uintptr(unsafeAddr(val)))
 	}
 }
 
@@ -1256,3 +1256,26 @@ func init() {
 	}
 	decOpTable[reflect.Uintptr] = uop
 }
+
+// Gob assumes it can call UnsafeAddr on any Value
+// in order to get a pointer it can copy data from.
+// Values that have just been created and do not point
+// into existing structs or slices cannot be addressed,
+// so simulate it by returning a pointer to a copy.
+// Each call allocates once.
+func unsafeAddr(v reflect.Value) uintptr {
+	if v.CanAddr() {
+		return v.UnsafeAddr()
+	}
+	x := reflect.New(v.Type()).Elem()
+	x.Set(v)
+	return x.UnsafeAddr()
+}
+
+// Gob depends on being able to take the address
+// of zeroed Values it creates, so use this wrapper instead
+// of the standard reflect.Zero.
+// Each call allocates once.
+func allocValue(t reflect.Type) reflect.Value {
+	return reflect.New(t).Elem()
+}

src/pkg/gob/decoder.go

@@ -171,12 +171,18 @@ func (dec *Decoder) Decode(e interface{}) os.Error {
 	return dec.DecodeValue(value)
 }
 
-// DecodeValue reads the next value from the connection and stores
-// it in the data represented by the reflection value.
-// The value must be the correct type for the next
-// data item received, or it may be nil, which means the
-// value will be discarded.
-func (dec *Decoder) DecodeValue(value reflect.Value) os.Error {
+// DecodeValue reads the next value from the connection.
+// If v is the zero reflect.Value (v.Kind() == Invalid), DecodeValue discards the value.
+// Otherwise, it stores the value into v.  In that case, v must represent
+// a non-nil pointer to data or be an assignable reflect.Value (v.CanSet())
+func (dec *Decoder) DecodeValue(v reflect.Value) os.Error {
+	if v.IsValid() {
+		if v.Kind() == reflect.Ptr && !v.IsNil() {
+			// That's okay, we'll store through the pointer.
+		} else if !v.CanSet() {
+			return os.ErrorString("gob: DecodeValue of unassignable value")
+		}
+	}
 	// Make sure we're single-threaded through here.
 	dec.mutex.Lock()
 	defer dec.mutex.Unlock()
@@ -185,7 +191,7 @@ func (dec *Decoder) DecodeValue(value reflect.Value) os.Error {
 	dec.err = nil
 	id := dec.decodeTypeSequence(false)
 	if dec.err == nil {
-		dec.decodeValue(id, value)
+		dec.decodeValue(id, v)
 	}
 	return dec.err
 }

src/pkg/gob/encode.go

@@ -402,7 +402,7 @@ func encodeReflectValue(state *encoderState, v reflect.Value, op encOp, indir in
 	if !v.IsValid() {
 		errorf("gob: encodeReflectValue: nil element")
 	}
-	op(nil, state, unsafe.Pointer(v.UnsafeAddr()))
+	op(nil, state, unsafe.Pointer(unsafeAddr(v)))
 }
 
 // encodeMap encodes a map as unsigned count followed by key:value pairs.
@@ -695,8 +695,8 @@ func (enc *Encoder) encode(b *bytes.Buffer, value reflect.Value, ut *userTypeInf
 		value = reflect.Indirect(value)
 	}
 	if !ut.isGobEncoder && value.Type().Kind() == reflect.Struct {
-		enc.encodeStruct(b, engine, value.UnsafeAddr())
+		enc.encodeStruct(b, engine, unsafeAddr(value))
 	} else {
-		enc.encodeSingle(b, engine, value.UnsafeAddr())
+		enc.encodeSingle(b, engine, unsafeAddr(value))
 	}
 }

src/pkg/gob/encoder_test.go

@@ -170,7 +170,7 @@ func TestTypeToPtrType(t *testing.T) {
 		A int
 	}
 	t0 := Type0{7}
-	t0p := (*Type0)(nil)
+	t0p := new(Type0)
 	if err := encAndDec(t0, t0p); err != nil {
 		t.Error(err)
 	}

src/pkg/json/decode.go

@@ -124,8 +124,7 @@ func (d *decodeState) unmarshal(v interface{}) (err os.Error) {
 
 	rv := reflect.NewValue(v)
 	pv := rv
-	if pv.Kind() != reflect.Ptr ||
-		pv.IsNil() {
+	if pv.Kind() != reflect.Ptr || pv.IsNil() {
 		return &InvalidUnmarshalError{reflect.Typeof(v)}
 	}
 
@@ -267,17 +266,17 @@ func (d *decodeState) indirect(v reflect.Value, wantptr bool) (Unmarshaler, refl
 			v = iv.Elem()
 			continue
 		}
+
 		pv := v
 		if pv.Kind() != reflect.Ptr {
 			break
 		}
 
-		if pv.Elem().Kind() != reflect.Ptr &&
-			wantptr && !isUnmarshaler {
+		if pv.Elem().Kind() != reflect.Ptr && wantptr && pv.CanSet() && !isUnmarshaler {
 			return nil, pv
 		}
 		if pv.IsNil() {
-			pv.Set(reflect.Zero(pv.Type().Elem()).Addr())
+			pv.Set(reflect.New(pv.Type().Elem()))
 		}
 		if isUnmarshaler {
 			// Using v.Interface().(Unmarshaler)
@@ -443,6 +442,8 @@ func (d *decodeState) object(v reflect.Value) {
 		return
 	}
 
+	var mapElem reflect.Value
+
 	for {
 		// Read opening " of string key or closing }.
 		op := d.scanWhile(scanSkipSpace)
@@ -466,7 +467,13 @@ func (d *decodeState) object(v reflect.Value) {
 		// Figure out field corresponding to key.
 		var subv reflect.Value
 		if mv.IsValid() {
-			subv = reflect.Zero(mv.Type().Elem())
+			elemType := mv.Type().Elem()
+			if !mapElem.IsValid() {
+				mapElem = reflect.New(elemType).Elem()
+			} else {
+				mapElem.Set(reflect.Zero(elemType))
+			}
+			subv = mapElem
 		} else {
 			var f reflect.StructField
 			var ok bool

src/pkg/json/decode_test.go

@@ -138,8 +138,7 @@ func TestUnmarshal(t *testing.T) {
 			continue
 		}
 		// v = new(right-type)
-		v := reflect.NewValue(tt.ptr)
-		v.Set(reflect.Zero(v.Type().Elem()).Addr())
+		v := reflect.New(reflect.Typeof(tt.ptr).Elem())
 		if err := Unmarshal([]byte(in), v.Interface()); !reflect.DeepEqual(err, tt.err) {
 			t.Errorf("#%d: %v want %v", i, err, tt.err)
 			continue

src/pkg/netchan/export.go

@@ -221,7 +221,7 @@ func (client *expClient) serveSend(hdr header) {
 		return
 	}
 	// Create a new value for each received item.
-	val := reflect.Zero(nch.ch.Type().Elem())
+	val := reflect.New(nch.ch.Type().Elem()).Elem()
 	if err := client.decode(val); err != nil {
 		expLog("value decode:", err, "; type ", nch.ch.Type())
 		return

src/pkg/netchan/import.go

@@ -133,7 +133,7 @@ func (imp *Importer) run() {
 		ackHdr.SeqNum = hdr.SeqNum
 		imp.encode(ackHdr, payAck, nil)
 		// Create a new value for each received item.
-		value := reflect.Zero(nch.ch.Type().Elem())
+		value := reflect.New(nch.ch.Type().Elem()).Elem()
 		if e := imp.decode(value); e != nil {
 			impLog("importer value decode:", e)
 			return

src/pkg/rpc/server.go

@@ -297,12 +297,6 @@ type InvalidRequest struct{}
 
 var invalidRequest = InvalidRequest{}
 
-func _new(t reflect.Type) reflect.Value {
-	v := reflect.Zero(t)
-	v.Set(reflect.Zero(t.Elem()).Addr())
-	return v
-}
-
 func (server *Server) sendResponse(sending *sync.Mutex, req *Request, reply interface{}, codec ServerCodec, errmsg string) {
 	resp := server.getResponse()
 	// Encode the response header
@@ -411,8 +405,8 @@ func (server *Server) ServeCodec(codec ServerCodec) {
 		}
 
 		// Decode the argument value.
-		argv := _new(mtype.ArgType)
-		replyv := _new(mtype.ReplyType)
+		argv := reflect.New(mtype.ArgType.Elem())
+		replyv := reflect.New(mtype.ReplyType.Elem())
 		err = codec.ReadRequestBody(argv.Interface())
 		if err != nil {
 			if err == os.EOF || err == io.ErrUnexpectedEOF {

src/pkg/testing/quick/quick.go

@@ -107,8 +107,8 @@ func Value(t reflect.Type, rand *rand.Rand) (value reflect.Value, ok bool) {
 		if !ok {
 			return reflect.Value{}, false
 		}
-		p := reflect.Zero(concrete)
-		p.Set(v.Addr())
+		p := reflect.New(concrete.Elem())
+		p.Elem().Set(v)
 		return p, true
 	case reflect.Slice:
 		numElems := rand.Intn(complexSize)
@@ -129,7 +129,7 @@ func Value(t reflect.Type, rand *rand.Rand) (value reflect.Value, ok bool) {
 		}
 		return reflect.NewValue(string(codePoints)), true
 	case reflect.Struct:
-		s := reflect.Zero(t)
+		s := reflect.New(t).Elem()
 		for i := 0; i < s.NumField(); i++ {
 			v, ok := Value(concrete.Field(i).Type, rand)
 			if !ok {

src/pkg/xml/read_test.go

@@ -288,9 +288,7 @@ var pathTests = []interface{}{
 
 func TestUnmarshalPaths(t *testing.T) {
 	for _, pt := range pathTests {
-		p := reflect.Zero(reflect.NewValue(pt).Type())
-		p.Set(reflect.Zero(p.Type().Elem()).Addr())
-		v := p.Interface()
+		v := reflect.New(reflect.Typeof(pt).Elem()).Interface()
 		if err := Unmarshal(StringReader(pathTestString), v); err != nil {
 			t.Fatalf("Unmarshal: %s", err)
 		}