reflect: implement Set(nil), SetValue(nil) for PtrValue and MapValue

R=r
CC=golang-dev
https://golang.org/cl/823048

src/pkg/reflect/all_test.go

@@ -350,6 +350,26 @@ func TestPtrPointTo(t *testing.T) {
 	}
 }
 
+func TestPtrSetNil(t *testing.T) {
+	var i int32 = 1234
+	ip := &i
+	vip := NewValue(&ip)
+	vip.(*PtrValue).Elem().(*PtrValue).Set(nil)
+	if ip != nil {
+		t.Errorf("got non-nil (%d), want nil", *ip)
+	}
+}
+
+func TestMapSetNil(t *testing.T) {
+	m := make(map[string]int)
+	vm := NewValue(&m)
+	vm.(*PtrValue).Elem().(*MapValue).Set(nil)
+	if m != nil {
+		t.Errorf("got non-nil (%p), want nil", m)
+	}
+}
+
+
 func TestAll(t *testing.T) {
 	testType(t, 1, Typeof((int8)(0)), "int8")
 	testType(t, 2, Typeof((*int8)(nil)).(*PtrType).Elem(), "int8")
@@ -838,6 +858,12 @@ func TestMap(t *testing.T) {
 	if ok {
 		t.Errorf("newm[\"a\"] = %d after delete", v)
 	}
+
+	mv = NewValue(&m).(*PtrValue).Elem().(*MapValue)
+	mv.Set(nil)
+	if m != nil {
+		t.Errorf("mv.Set(nil) failed")
+	}
 }
 
 func TestChan(t *testing.T) {

src/pkg/reflect/value.go

@@ -1038,12 +1038,22 @@ func (v *MapValue) Set(x *MapValue) {
 	if !v.canSet {
 		panic(cannotSet)
 	}
+	if x == nil {
+		*(**uintptr)(v.addr) = nil
+		return
+	}
 	typesMustMatch(v.typ, x.typ)
 	*(*uintptr)(v.addr) = *(*uintptr)(x.addr)
 }
 
 // Set sets v to the value x.
-func (v *MapValue) SetValue(x Value) { v.Set(x.(*MapValue)) }
+func (v *MapValue) SetValue(x Value) {
+	if x == nil {
+		v.Set(nil)
+		return
+	}
+	v.Set(x.(*MapValue))
+}
 
 // Get returns the uintptr value of v.
 // It is mainly useful for printing.
@@ -1146,6 +1156,10 @@ func (v *PtrValue) Get() uintptr { return *(*uintptr)(v.addr) }
 // Set assigns x to v.
 // The new value x must have the same type as v.
 func (v *PtrValue) Set(x *PtrValue) {
+	if x == nil {
+		*(**uintptr)(v.addr) = nil
+		return
+	}
 	if !v.canSet {
 		panic(cannotSet)
 	}
@@ -1156,7 +1170,13 @@ func (v *PtrValue) Set(x *PtrValue) {
 }
 
 // Set sets v to the value x.
-func (v *PtrValue) SetValue(x Value) { v.Set(x.(*PtrValue)) }
+func (v *PtrValue) SetValue(x Value) {
+	if x == nil {
+		v.Set(nil)
+		return
+	}
+	v.Set(x.(*PtrValue))
+}
 
 // PointTo changes v to point to x.
 func (v *PtrValue) PointTo(x Value) {