From 3743f92c11c23743a4bc0b64b4c61562b4b866a9 Mon Sep 17 00:00:00 2001
From: cocolato <haiizhu@outlook.com>
Date: Wed, 15 Apr 2026 23:38:15 +0800
Subject: [PATCH 1/2] make sure abc.register update type_version

---
 Lib/test/test_type_cache.py | 20 ++++++++++++++++++++
 Objects/typeobject.c        | 14 ++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/Lib/test/test_type_cache.py b/Lib/test/test_type_cache.py
index 22ad9f6243eda9..849a2afd8ed798 100644
--- a/Lib/test/test_type_cache.py
+++ b/Lib/test/test_type_cache.py
@@ -1,4 +1,5 @@
 """ Tests for the internal type cache in CPython. """
+import collections.abc
 import dis
 import unittest
 import warnings
@@ -114,6 +115,25 @@ class HolderSub(Holder):
             Holder.set_value()
             HolderSub.value
 
+    def test_abc_register_invalidates_subclass_versions(self):
+        class Parent:
+            pass
+
+        class Child(Parent):
+            pass
+
+        type_assign_version(Parent)
+        type_assign_version(Child)
+        parent_version = type_get_version(Parent)
+        child_version = type_get_version(Child)
+        if parent_version == 0 or child_version == 0:
+            self.skipTest("Could not assign valid type versions")
+
+        collections.abc.Mapping.register(Parent)
+
+        self.assertEqual(type_get_version(Parent), 0)
+        self.assertEqual(type_get_version(Child), 0)
+
 @support.cpython_only
 class TypeCacheWithSpecializationTests(unittest.TestCase):
     def tearDown(self):
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 08b95cfbc6ce59..45404b02a4a13f 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -6419,9 +6419,23 @@ set_flags_recursive(PyTypeObject *self, unsigned long mask, unsigned long flags)
 void
 _PyType_SetFlagsRecursive(PyTypeObject *self, unsigned long mask, unsigned long flags)
 {
+    BEGIN_TYPE_LOCK();
+     /* Invalidate the old version before changing flags. This must happen
+         before types_stop_world(); immutable/static-builtin types are
+         skipped because set_flags_recursive() does not touch them. */
+    if (!PyType_HasFeature(self, Py_TPFLAGS_IMMUTABLETYPE) &&
+        (self->tp_flags & mask) != flags)
+    {
+        type_modified_unlocked(self);
+    }
+     /* Keep TYPE_LOCK held while waiting for stop-the-world so no thread
+         can reassign a version tag before the flag update. */
+    type_lock_prevent_release();
     types_stop_world();
     set_flags_recursive(self, mask, flags);
     types_start_world();
+    type_lock_allow_release();
+    END_TYPE_LOCK();
 }
 
 /* This is similar to PyObject_GenericGetAttr(),

From 67e25c42e84e1f018aee07558d0230ab71e61001 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Wed, 15 Apr 2026 15:48:06 +0000
Subject: [PATCH 2/2] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../2026-04-15-15-48-04.gh-issue-148450.2MEVqH.rst               | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2026-04-15-15-48-04.gh-issue-148450.2MEVqH.rst

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-04-15-15-48-04.gh-issue-148450.2MEVqH.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-04-15-15-48-04.gh-issue-148450.2MEVqH.rst
new file mode 100644
index 00000000000000..2a7d0d9bb3a7f7
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-04-15-15-48-04.gh-issue-148450.2MEVqH.rst
@@ -0,0 +1 @@
+Fix ``abc.register()`` so it invalidates type version tags for registered classes.