pythongh-112903: Fix MRO resolution for GenericAlias types

Author: sobolevn

Lib/test/test_typing.py

@@ -4886,6 +4886,20 @@ class B(Generic[S]): ...
         class C(List[int], B): ...
         self.assertEqual(C.__mro__, (C, list, B, Generic, object))
 
+    def test_multiple_inheritance_gh112903(self):
+        # https://github.com/python/cpython/issues/112903
+        K = TypeVar("K")
+        V = TypeVar("V")
+
+        class BaseMap(typing.Mapping[K, V]): ...
+        class MutableMap(BaseMap[K, V], typing.MutableMapping[K, V]): ...
+        # This should not raise:
+        class MyMap1(Dict[K, V], MutableMap[K, V]): ...
+        class MyMap2(MutableMap[K, V], Dict[K, V]): ...
+
+        self.assertIn(Generic, MyMap1.__mro__)
+        self.assertIn(Generic, MyMap2.__mro__)
+
     def test_init_subclass_super_called(self):
         class FinalException(Exception):
             pass

Lib/typing.py

@@ -1137,7 +1137,10 @@ def __mro_entries__(self, bases):
             res.append(self.__origin__)
         i = bases.index(self)
         for b in bases[i+1:]:
-            if isinstance(b, _BaseGenericAlias) or issubclass(b, Generic):
+            if (
+                isinstance(b, (_BaseGenericAlias, GenericAlias))
+                or issubclass(b, Generic)
+            ):
                 break
         else:
             res.append(Generic)

Misc/NEWS.d/next/Library/2023-12-09-23-19-14.gh-issue-112903.qusnMI.rst

@@ -0,0 +1 @@
+Fix MRO resolution issue for generic aliases in 3.13