frame_traverse(): Use the standard Py_VISIT macro.

Py_VISIT:  cast the `op` argument to PyObject* when calling
`visit()`.  Else the caller has to pay too much attention to
this silly detail (e.g., frame_traverse needs to traverse
`struct _frame *` and `PyCodeObject *` pointers too).

Include/objimpl.h

@@ -303,13 +303,13 @@ PyAPI_FUNC(void) PyObject_GC_Del(void *);
  * "visit" and "arg".  This is intended to keep tp_traverse functions
  * looking as much alike as possible.
  */
-#define Py_VISIT(op)					\
-        do { 						\
-                if (op) {				\
-                        int vret = visit((op), arg);	\
-                        if (vret)			\
-                                return vret;		\
-                }					\
+#define Py_VISIT(op)							\
+        do { 								\
+                if (op) {						\
+                        int vret = visit((PyObject *)(op), arg);	\
+                        if (vret)					\
+                                return vret;				\
+                }							\
         } while (0)
 
 /* This is here for the sake of backwards compatibility.  Extensions that

Objects/frameobject.c

@@ -422,30 +422,28 @@ static int
 frame_traverse(PyFrameObject *f, visitproc visit, void *arg)
 {
 	PyObject **fastlocals, **p;
-	int i, err, slots;
-#define VISIT(o) if (o) {if ((err = visit((PyObject *)(o), arg))) return err;}
-
-	VISIT(f->f_back);
-	VISIT(f->f_code);
-	VISIT(f->f_builtins);
-	VISIT(f->f_globals);
-	VISIT(f->f_locals);
-	VISIT(f->f_trace);
-	VISIT(f->f_exc_type);
-	VISIT(f->f_exc_value);
-	VISIT(f->f_exc_traceback);
+	int i, slots;
+
+	Py_VISIT(f->f_back);
+	Py_VISIT(f->f_code);
+	Py_VISIT(f->f_builtins);
+	Py_VISIT(f->f_globals);
+	Py_VISIT(f->f_locals);
+	Py_VISIT(f->f_trace);
+	Py_VISIT(f->f_exc_type);
+	Py_VISIT(f->f_exc_value);
+	Py_VISIT(f->f_exc_traceback);
 
 	/* locals */
 	slots = f->f_nlocals + f->f_ncells + f->f_nfreevars;
 	fastlocals = f->f_localsplus;
-	for (i = slots; --i >= 0; ++fastlocals) {
-		VISIT(*fastlocals);
-	}
+	for (i = slots; --i >= 0; ++fastlocals)
+		Py_VISIT(*fastlocals);
 
 	/* stack */
 	if (f->f_stacktop != NULL) {
 		for (p = f->f_valuestack; p < f->f_stacktop; p++)
-			VISIT(*p);
+			Py_VISIT(*p);
 	}
 	return 0;
 }