encoder: Fix class wrt protocol version

- we can use STACK_GLOBAL only if protocol >= 4.
- for earlier protocols we have to use text-based GLOBAL.

encode.go

@@ -406,7 +406,7 @@ func (e *Encoder) encodeMap(m reflect.Value) error {
 }
 
 func (e *Encoder) encodeCall(v *Call) error {
-	err := e.emitf("%c%s\n%s\n", opGlobal, v.Callable.Module, v.Callable.Name)
+	err := e.encodeClass(&v.Callable)
 	if err != nil {
 		return err
 	}
@@ -418,11 +418,22 @@ func (e *Encoder) encodeCall(v *Call) error {
 }
 
 func (e *Encoder) encodeClass(v *Class) error {
-	err := e.emitf("%c'%s'\n%c'%s'\n", opString, v.Module, opString, v.Name)
+	// PEP 3154: Protocol 4 forbids use of the GLOBAL opcode and replaces
+	// it with STACK_GLOBAL.
+	if e.config.Protocol >= 4 {
+		err := e.encodeString(v.Module)
+		if err != nil {
+			return err
+		}
+		err = e.encodeString(v.Name)
 		if err != nil {
 			return err
 		}
 		return e.emit(opStackGlobal)
+	}
+
+	// else use GLOBAL opcode from protocol 0
+	return e.emitf("%c%s\n%s\n", opGlobal, v.Module, v.Name)
 }
 
 var errP0PersIDStringLineOnly = errors.New(`protocol 0: persistent ID must be string without \n`)

ogorek_test.go

@@ -287,10 +287,16 @@ var tests = []TestEntry{
 		I("(dp0\nS'a'\np1\nS'1'\np2\nsS'b'\np3\nS'2'\np4\ns.")),
 
 	X("foo.bar  # global", Class{Module: "foo", Name: "bar"},
+		P0123("cfoo\nbar\n."),              // GLOBAL
+		P4_("\x8c\x03foo\x8c\x03bar\x93."), // SHORT_BINUNICODE + STACK_GLOBAL
 		I("S'foo'\nS'bar'\n\x93.")),        // STRING + STACK_GLOBAL
 
 	X(`foo.bar("bing")  # global + reduce`, Call{Callable: Class{Module: "foo", Name: "bar"}, Args: []interface{}{"bing"}},
-		I("cfoo\nbar\nS'bing'\n\x85R.")), // GLOBAL + STRING + TUPLE1 + REDUCE
+		P0("cfoo\nbar\n(S\"bing\"\ntR."),                     // GLOBAL + MARK + STRING + TUPLE + REDUCE
+		P1("cfoo\nbar\n(U\x04bingtR."),                       // GLOBAL + MARK + SHORT_BINSTRING + TUPLE + REDUCE
+		P2("cfoo\nbar\nU\x04bing\x85R."),                     // GLOBAL + SHORT_BINSTRING + TUPLE1 + REDUCE
+		P3("cfoo\nbar\nX\x04\x00\x00\x00bing\x85R."),         // GLOBAL + BINUNICODE + TUPLE1 + REDUCE
+		P4_("\x8c\x03foo\x8c\x03bar\x93\x8c\x04bing\x85R.")), // SHORT_BINUNICODE + STACK_GLOBAL + TUPLE1 + REDUCE
 
 	X(`persref("abc")`, Ref{"abc"},
 		P0("Pabc\n."),                // PERSID