Issue 1294232: Fix errors in metaclass calculation affecting some cases of metaclass inheritance. Patch by Daniel Urban.

1 files changed, 41 insertions, 20 deletions

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 856a4a5..9f62401 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -1912,6 +1912,42 @@ PyType_GetFlags(PyTypeObject *type)
     return type->tp_flags;
 }
 
+/* Determine the most derived metatype. */
+PyTypeObject *
+_PyType_CalculateMetaclass(PyTypeObject *metatype, PyObject *bases)
+{
+    Py_ssize_t i, nbases;
+    PyTypeObject *winner;
+    PyObject *tmp;
+    PyTypeObject *tmptype;
+
+    /* Determine the proper metatype to deal with this,
+       and check for metatype conflicts while we're at it.
+       Note that if some other metatype wins to contract,
+       it's possible that its instances are not types. */
+
+    nbases = PyTuple_GET_SIZE(bases);
+    winner = metatype;
+    for (i = 0; i < nbases; i++) {
+        tmp = PyTuple_GET_ITEM(bases, i);
+        tmptype = Py_TYPE(tmp);
+        if (PyType_IsSubtype(winner, tmptype))
+            continue;
+        if (PyType_IsSubtype(tmptype, winner)) {
+            winner = tmptype;
+            continue;
+        }
+        /* else: */
+        PyErr_SetString(PyExc_TypeError,
+                        "metaclass conflict: "
+                        "the metaclass of a derived class "
+                        "must be a (non-strict) subclass "
+                        "of the metaclasses of all its bases");
+        return NULL;
+    }
+    return winner;
+}
+
 static PyObject *
 type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
 {
@@ -1955,28 +1991,12 @@ type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
                                      &PyDict_Type, &dict))
         return NULL;
 
-    /* Determine the proper metatype to deal with this,
-       and check for metatype conflicts while we're at it.
-       Note that if some other metatype wins to contract,
-       it's possible that its instances are not types. */
-    nbases = PyTuple_GET_SIZE(bases);
-    winner = metatype;
-    for (i = 0; i < nbases; i++) {
-        tmp = PyTuple_GET_ITEM(bases, i);
-        tmptype = Py_TYPE(tmp);
-        if (PyType_IsSubtype(winner, tmptype))
-            continue;
-        if (PyType_IsSubtype(tmptype, winner)) {
-            winner = tmptype;
-            continue;
-        }
-        PyErr_SetString(PyExc_TypeError,
-                        "metaclass conflict: "
-                        "the metaclass of a derived class "
-                        "must be a (non-strict) subclass "
-                        "of the metaclasses of all its bases");
+    /* Determine the proper metatype to deal with this: */
+    winner = _PyType_CalculateMetaclass(metatype, bases);
+    if (winner == NULL) {
         return NULL;
     }
+
     if (winner != metatype) {
         if (winner->tp_new != type_new) /* Pass it to the winner */
             return winner->tp_new(winner, args, kwds);
@@ -1984,6 +2004,7 @@ type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
     }
 
     /* Adjust for empty tuple bases */
+    nbases = PyTuple_GET_SIZE(bases);
     if (nbases == 0) {
         bases = PyTuple_Pack(1, &PyBaseObject_Type);
         if (bases == NULL)