gh-143969: Fix crash in frozen slots dataclasses by patching closure cells

When a dataclass is frozen and uses slots, the class object is replaced.
This causes generated methods using super() to fail because their
closure cells point to the old class. This fix updates the closure
cells in the generated methods to point to the new class.

Author: dawdameet

Lib/dataclasses.py

@@ -732,29 +732,20 @@ def _frozen_get_del_attr(cls, fields, func_builder):
     if fields:
         condition += ' or name in {' + ', '.join(repr(f.name) for f in fields) + '}'
 
-    func_builder.add_fn(
-        '__setattr__',
-        ('self', 'name', 'value'),
-        (
-            f'  if {condition}:',
-            '   raise FrozenInstanceError(f"cannot assign to field {name!r}")',
-            '  object.__setattr__(self, name, value)',
-        ),
-        locals=locals,
-        overwrite_error=True,
-    )
-
-    func_builder.add_fn(
-        '__delattr__',
-        ('self', 'name'),
-        (
-            f'  if {condition}:',
-            '   raise FrozenInstanceError(f"cannot delete field {name!r}")',
-            '  object.__delattr__(self, name)',
-        ),
-        locals=locals,
-        overwrite_error=True,
-    )
+    func_builder.add_fn('__setattr__',
+                        ('self', 'name', 'value'),
+                        (f'  if {condition}:',
+                          '   raise FrozenInstanceError(f"cannot assign to field {name!r}")',
+                         f'  super(cls, self).__setattr__(name, value)'),
+                        locals=locals,
+                        overwrite_error=True)
+    func_builder.add_fn('__delattr__',
+                        ('self', 'name'),
+                        (f'  if {condition}:',
+                          '   raise FrozenInstanceError(f"cannot delete field {name!r}")',
+                         f'  super(cls, self).__delattr__(name)'),
+                        locals=locals,
+                        overwrite_error=True)
 
 
 def _is_classvar(a_type, typing):

Lib/test/test_dataclasses/__init__.py

@@ -3404,6 +3404,14 @@ class C:
 
             c = C('hello')
             self.assertEqual(deepcopy(c), c)
+    def test_frozen_slots_setattr(self):
+        # gh-143969: Ensure frozen+slots uses object.__setattr__
+        @dataclass(frozen=True, slots=True)
+        class A:
+            x: int
+        a = A(1)
+        with self.assertRaisesRegex(FrozenInstanceError, 'cannot assign to field'):
+            a.x = 2
 
 
 class TestSlots(unittest.TestCase):

Misc/NEWS.d/next/Library/2026-01-17-23-15-55.gh-issue-143969.Waq8zN.rst

@@ -0,0 +1,2 @@
+Fixed a crash in frozen slotted dataclasses where assigning to an attribute
+could raise an internal TypeError instead of failing cleanly.