bpo-43977: Properly update the tp_flags of existing subclasses when their parents are registered (GH-26864)

(cherry picked from commit ca2009d72a)

Co-authored-by: Brandt Bucher <brandt@python.org>

Lib/test/test_patma.py

@@ -24,7 +24,43 @@ class TestCompiler(unittest.TestCase):
 
 class TestInheritance(unittest.TestCase):
 
-    def test_multiple_inheritance(self):
+    @staticmethod
+    def check_sequence_then_mapping(x):
+        match x:
+            case [*_]:
+                return "seq"
+            case {}:
+                return "map"
+
+    @staticmethod
+    def check_mapping_then_sequence(x):
+        match x:
+            case {}:
+                return "map"
+            case [*_]:
+                return "seq"
+
+    def test_multiple_inheritance_mapping(self):
+        class C:
+            pass
+        class M1(collections.UserDict, collections.abc.Sequence):
+            pass
+        class M2(C, collections.UserDict, collections.abc.Sequence):
+            pass
+        class M3(collections.UserDict, C, list):
+            pass
+        class M4(dict, collections.abc.Sequence, C):
+            pass
+        self.assertEqual(self.check_sequence_then_mapping(M1()), "map")
+        self.assertEqual(self.check_sequence_then_mapping(M2()), "map")
+        self.assertEqual(self.check_sequence_then_mapping(M3()), "map")
+        self.assertEqual(self.check_sequence_then_mapping(M4()), "map")
+        self.assertEqual(self.check_mapping_then_sequence(M1()), "map")
+        self.assertEqual(self.check_mapping_then_sequence(M2()), "map")
+        self.assertEqual(self.check_mapping_then_sequence(M3()), "map")
+        self.assertEqual(self.check_mapping_then_sequence(M4()), "map")
+
+    def test_multiple_inheritance_sequence(self):
         class C:
             pass
         class S1(collections.UserList, collections.abc.Mapping):
@@ -35,32 +71,60 @@ class TestInheritance(unittest.TestCase):
             pass
         class S4(collections.UserList, dict, C):
             pass
-        class M1(collections.UserDict, collections.abc.Sequence):
+        self.assertEqual(self.check_sequence_then_mapping(S1()), "seq")
+        self.assertEqual(self.check_sequence_then_mapping(S2()), "seq")
+        self.assertEqual(self.check_sequence_then_mapping(S3()), "seq")
+        self.assertEqual(self.check_sequence_then_mapping(S4()), "seq")
+        self.assertEqual(self.check_mapping_then_sequence(S1()), "seq")
+        self.assertEqual(self.check_mapping_then_sequence(S2()), "seq")
+        self.assertEqual(self.check_mapping_then_sequence(S3()), "seq")
+        self.assertEqual(self.check_mapping_then_sequence(S4()), "seq")
+
+    def test_late_registration_mapping(self):
+        class Parent:
             pass
-        class M2(C, collections.UserDict, collections.abc.Sequence):
+        class ChildPre(Parent):
             pass
-        class M3(collections.UserDict, C, list):
+        class GrandchildPre(ChildPre):
             pass
-        class M4(dict, collections.abc.Sequence, C):
+        collections.abc.Mapping.register(Parent)
+        class ChildPost(Parent):
             pass
-        def f(x):
-            match x:
-                case []:
-                    return "seq"
-                case {}:
-                    return "map"
-        def g(x):
-            match x:
-                case {}:
-                    return "map"
-                case []:
-                    return "seq"
-        for Seq in (S1, S2, S3, S4):
-            self.assertEqual(f(Seq()), "seq")
-            self.assertEqual(g(Seq()), "seq")
-        for Map in (M1, M2, M3, M4):
-            self.assertEqual(f(Map()), "map")
-            self.assertEqual(g(Map()), "map")
+        class GrandchildPost(ChildPost):
+            pass
+        self.assertEqual(self.check_sequence_then_mapping(Parent()), "map")
+        self.assertEqual(self.check_sequence_then_mapping(ChildPre()), "map")
+        self.assertEqual(self.check_sequence_then_mapping(GrandchildPre()), "map")
+        self.assertEqual(self.check_sequence_then_mapping(ChildPost()), "map")
+        self.assertEqual(self.check_sequence_then_mapping(GrandchildPost()), "map")
+        self.assertEqual(self.check_mapping_then_sequence(Parent()), "map")
+        self.assertEqual(self.check_mapping_then_sequence(ChildPre()), "map")
+        self.assertEqual(self.check_mapping_then_sequence(GrandchildPre()), "map")
+        self.assertEqual(self.check_mapping_then_sequence(ChildPost()), "map")
+        self.assertEqual(self.check_mapping_then_sequence(GrandchildPost()), "map")
+
+    def test_late_registration_sequence(self):
+        class Parent:
+            pass
+        class ChildPre(Parent):
+            pass
+        class GrandchildPre(ChildPre):
+            pass
+        collections.abc.Sequence.register(Parent)
+        class ChildPost(Parent):
+            pass
+        class GrandchildPost(ChildPost):
+            pass
+        self.assertEqual(self.check_sequence_then_mapping(Parent()), "seq")
+        self.assertEqual(self.check_sequence_then_mapping(ChildPre()), "seq")
+        self.assertEqual(self.check_sequence_then_mapping(GrandchildPre()), "seq")
+        self.assertEqual(self.check_sequence_then_mapping(ChildPost()), "seq")
+        self.assertEqual(self.check_sequence_then_mapping(GrandchildPost()), "seq")
+        self.assertEqual(self.check_mapping_then_sequence(Parent()), "seq")
+        self.assertEqual(self.check_mapping_then_sequence(ChildPre()), "seq")
+        self.assertEqual(self.check_mapping_then_sequence(GrandchildPre()), "seq")
+        self.assertEqual(self.check_mapping_then_sequence(ChildPost()), "seq")
+        self.assertEqual(self.check_mapping_then_sequence(GrandchildPost()), "seq")
 
 
 class TestPatma(unittest.TestCase):