[3.13] gh-123935: Fix typo in _get_slots in dataclasses.py (GH-123941) (#123991)

gh-123935: Fix typo in `_get_slots` in `dataclasses.py` (GH-123941)
(cherry picked from commit ac918ccad7)

Co-authored-by: sobolevn <mail@sobolevn.me>

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):

Lib/test/test_dataclasses/__init__.py

@@ -3707,6 +3707,25 @@ class TestSlots(unittest.TestCase):
         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.

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__``.