Issue 1294232: Fix errors in metaclass calculation affecting some cases of metaclass inheritance. Patch by Daniel Urban.
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 6258167..9c50b88 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -35,9 +35,10 @@
static PyObject *
builtin___build_class__(PyObject *self, PyObject *args, PyObject *kwds)
{
- PyObject *func, *name, *bases, *mkw, *meta, *prep, *ns, *cell;
+ PyObject *func, *name, *bases, *mkw, *meta, *winner, *prep, *ns, *cell;
PyObject *cls = NULL;
Py_ssize_t nargs, nbases;
+ int isclass;
assert(args != NULL);
if (!PyTuple_Check(args)) {
@@ -82,17 +83,42 @@
Py_DECREF(bases);
return NULL;
}
+ /* metaclass is explicitly given, check if it's indeed a class */
+ isclass = PyType_Check(meta);
}
}
if (meta == NULL) {
- if (PyTuple_GET_SIZE(bases) == 0)
+ /* if there are no bases, use type: */
+ if (PyTuple_GET_SIZE(bases) == 0) {
meta = (PyObject *) (&PyType_Type);
+ }
+ /* else get the type of the first base */
else {
PyObject *base0 = PyTuple_GET_ITEM(bases, 0);
meta = (PyObject *) (base0->ob_type);
}
Py_INCREF(meta);
+ isclass = 1; /* meta is really a class */
}
+ if (isclass) {
+ /* meta is really a class, so check for a more derived
+ metaclass, or possible metaclass conflicts: */
+ winner = (PyObject *)_PyType_CalculateMetaclass((PyTypeObject *)meta,
+ bases);
+ if (winner == NULL) {
+ Py_DECREF(meta);
+ Py_XDECREF(mkw);
+ Py_DECREF(bases);
+ return NULL;
+ }
+ if (winner != meta) {
+ Py_DECREF(meta);
+ meta = winner;
+ Py_INCREF(meta);
+ }
+ }
+ /* else: meta is not a class, so we cannot do the metaclass
+ calculation, so we will use the explicitly given object as it is */
prep = PyObject_GetAttrString(meta, "__prepare__");
if (prep == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError)) {