can't encode array or slice - catch in sendType rather than failing in Encode

R=rsc
DELTA=38  (33 added, 3 deleted, 2 changed)
OCL=34101
CL=34104

src/pkg/gob/encoder.go

@@ -241,22 +241,30 @@ func (enc *Encoder) sendType(origt reflect.Type) {
 
 	// We only send structs - everything else is basic or an error
 	switch t := rt.(type) {
-	case *reflect.StructType:
+	case *reflect.StructType:	// TODO: when compiler handles type lists, can fold these
 		break;	// we handle these
 	case *reflect.ChanType:
 		enc.badType(rt);
 		return;
-	case *reflect.MapType:
-		enc.badType(rt);
-		return;
 	case *reflect.FuncType:
 		enc.badType(rt);
 		return;
+	case *reflect.MapType:
+		enc.badType(rt);
+		return;
 	case *reflect.InterfaceType:
 		enc.badType(rt);
 		return;
+	// Array and slice types are not sent, only their element types.
+	// If we see one here it's user error.
+	case *reflect.ArrayType:
+		enc.badType(rt);
+		return;
+	case *reflect.SliceType:
+		enc.badType(rt);
+		return;
 	default:
-		return;	// basic, array, etc; not a type to be sent.
+		return;	// basic, not a type to be sent.
 	}
 
 	// Have we already sent this type?  This time we ask about the base type.

src/pkg/gob/encoder_test.go

@@ -243,3 +243,25 @@ func TestBadData(t *testing.T) {
 	corruptDataCheck("\x7Fhi", io.ErrUnexpectedEOF, t);
 	corruptDataCheck("\x03now is the time for all good men", errBadType, t);
 }
+
+// Types not supported by the Encoder (only structs work at the top level).
+// Basic types work implicitly.
+var unsupportedValues = []interface{} {
+	[]int{ 1, 2, 3 },
+	[3]int{ 1, 2, 3 },
+	make(chan int),
+	func(a int) bool { return true },
+	make(map[string] int),
+	new(interface{}),
+}
+
+func TestUnsupported(t *testing.T) {
+	var b bytes.Buffer;
+	enc := NewEncoder(&b);
+	for _, v := range unsupportedValues {
+		err := enc.Encode(v);
+		if err == nil {
+			t.Errorf("expected error for %T; got none", v)
+		}
+	}
+}