Add the utility.

Also use it in _bz2.

Author: ZeroIntensity

Include/cpython/object.h

@@ -491,3 +491,7 @@ PyAPI_FUNC(int) PyUnstable_TryIncRef(PyObject *);
 PyAPI_FUNC(void) PyUnstable_EnableTryIncRef(PyObject *);
 
 PyAPI_FUNC(int) PyUnstable_Object_IsUniquelyReferenced(PyObject *);
+
+/* Utility for the tp_traverse slot of mutable heap types that have no other
+ * references. */
+PyAPI_FUNC(int) _PyObject_VisitType(PyObject *op, visitproc visit, void *arg);

Modules/_bz2module.c

@@ -391,13 +391,6 @@ BZ2Compressor_dealloc(PyObject *op)
     Py_DECREF(tp);
 }
 
-static int
-BZ2Compressor_traverse(PyObject *self, visitproc visit, void *arg)
-{
-    Py_VISIT(Py_TYPE(self));
-    return 0;
-}
-
 static PyMethodDef BZ2Compressor_methods[] = {
     _BZ2_BZ2COMPRESSOR_COMPRESS_METHODDEF
     _BZ2_BZ2COMPRESSOR_FLUSH_METHODDEF
@@ -409,7 +402,7 @@ static PyType_Slot bz2_compressor_type_slots[] = {
     {Py_tp_methods, BZ2Compressor_methods},
     {Py_tp_new, _bz2_BZ2Compressor},
     {Py_tp_doc, (char *)_bz2_BZ2Compressor__doc__},
-    {Py_tp_traverse, BZ2Compressor_traverse},
+    {Py_tp_traverse, _PyObject_VisitType},
     {0, 0}
 };
 
@@ -703,13 +696,6 @@ BZ2Decompressor_dealloc(PyObject *op)
     Py_DECREF(tp);
 }
 
-static int
-BZ2Decompressor_traverse(PyObject *self, visitproc visit, void *arg)
-{
-    Py_VISIT(Py_TYPE(self));
-    return 0;
-}
-
 static PyMethodDef BZ2Decompressor_methods[] = {
     _BZ2_BZ2DECOMPRESSOR_DECOMPRESS_METHODDEF
     {NULL}
@@ -740,7 +726,7 @@ static PyType_Slot bz2_decompressor_type_slots[] = {
     {Py_tp_doc, (char *)_bz2_BZ2Decompressor__doc__},
     {Py_tp_members, BZ2Decompressor_members},
     {Py_tp_new, _bz2_BZ2Decompressor},
-    {Py_tp_traverse, BZ2Decompressor_traverse},
+    {Py_tp_traverse, _PyObject_VisitType},
     {0, 0}
 };
 

Objects/object.c

@@ -3384,3 +3384,10 @@ PyUnstable_Object_IsUniquelyReferenced(PyObject *op)
     assert(op != NULL);
     return _PyObject_IsUniquelyReferenced(op);
 }
+
+int _PyObject_VisitType(PyObject *op, visitproc visit, void *arg)
+{
+    assert(op != NULL);
+    Py_VISIT(Py_TYPE(op));
+    return 0;
+}