From 883f1bdbe3b65eaea571f59922d6c725500844ef Mon Sep 17 00:00:00 2001
From: sobolevn <mail@sobolevn.me>
Date: Thu, 12 Sep 2024 10:29:06 +0300
Subject: [PATCH] gh-123935: Fix typo in `_get_slots` in `dataclasses.py`
 (GH-123941) (cherry picked from commit
 ac918ccad707ab2d7dbb78a4796a7b8a874f334c)

Co-authored-by: sobolevn <mail@sobolevn.me>
---
 Lib/dataclasses.py                            |  2 +-
 Lib/test/test_dataclasses/__init__.py         | 19 +++++++++++++++++++
 ...-09-11-13-33-19.gh-issue-123935.fRZ_56.rst |  2 ++
 3 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2024-09-11-13-33-19.gh-issue-123935.fRZ_56.rst

diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 74011b7e28b9f3..7883ce78e57d50 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -1206,7 +1206,7 @@ def _get_slots(cls):
             slots = []
             if getattr(cls, '__weakrefoffset__', -1) != 0:
                 slots.append('__weakref__')
-            if getattr(cls, '__dictrefoffset__', -1) != 0:
+            if getattr(cls, '__dictoffset__', -1) != 0:
                 slots.append('__dict__')
             yield from slots
         case str(slot):
diff --git a/Lib/test/test_dataclasses/__init__.py b/Lib/test/test_dataclasses/__init__.py
index 260e0d74917181..87353b665ddb85 100644
--- a/Lib/test/test_dataclasses/__init__.py
+++ b/Lib/test/test_dataclasses/__init__.py
@@ -3664,6 +3664,25 @@ class A(WithDictSlot): ...
         self.assertEqual(A().__dict__, {})
         A()
 
+    @support.cpython_only
+    def test_dataclass_slot_dict_ctype(self):
+        # https://github.com/python/cpython/issues/123935
+        from test.support import import_helper
+        # Skips test if `_testcapi` is not present:
+        _testcapi = import_helper.import_module('_testcapi')
+
+        @dataclass(slots=True)
+        class HasDictOffset(_testcapi.HeapCTypeWithDict):
+            __dict__: dict = {}
+        self.assertNotEqual(_testcapi.HeapCTypeWithDict.__dictoffset__, 0)
+        self.assertEqual(HasDictOffset.__slots__, ())
+
+        @dataclass(slots=True)
+        class DoesNotHaveDictOffset(_testcapi.HeapCTypeWithWeakref):
+            __dict__: dict = {}
+        self.assertEqual(_testcapi.HeapCTypeWithWeakref.__dictoffset__, 0)
+        self.assertEqual(DoesNotHaveDictOffset.__slots__, ('__dict__',))
+
     @support.cpython_only
     def test_slots_with_wrong_init_subclass(self):
         # TODO: This test is for a kinda-buggy behavior.
diff --git a/Misc/NEWS.d/next/Library/2024-09-11-13-33-19.gh-issue-123935.fRZ_56.rst b/Misc/NEWS.d/next/Library/2024-09-11-13-33-19.gh-issue-123935.fRZ_56.rst
new file mode 100644
index 00000000000000..de720c3714c6ff
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-09-11-13-33-19.gh-issue-123935.fRZ_56.rst
@@ -0,0 +1,2 @@
+Fix parent slots detection for dataclasses that inherit from classes with
+``__dictoffset__``.