Fixed _get_slots bug, according to issue gh-105866

Lib/dataclasses.py

@@ -1172,8 +1172,10 @@ def _dataclass_setstate(self, state):
 
 def _get_slots(cls):
     match cls.__dict__.get('__slots__'):
+        # A class which does not define __slots__ at all is equivalent
+        # to a class defining __slots__ = ('__dict__', '__weakref__')
         case None:
-            return
+            yield from ('__dict__', '__weakref__')
         case str(slot):
             yield slot
         # Slots may be any iterable, but we cannot handle an iterator

Misc/NEWS.d/next/Library/2023-06-16-19-17-06.gh-issue-105866.0NBveV.rst

@@ -0,0 +1 @@
+Fixed `_get_slots` bug which caused error when defining dataclasses with slots and a weakref_slot.