Set __attrs_base_of_slotted__ for unused base classes

Author: hynek

src/attr/_make.py

@@ -12,6 +12,7 @@
 import sys
 import types
 import unicodedata
+import weakref
 
 from collections.abc import Callable, Mapping
 from functools import cached_property
@@ -836,6 +837,7 @@ def build_class(self):
         self._eval_snippets()
         if self._slots is True:
             cls = self._create_slots_class()
+            self._cls.__attrs_base_of_slotted__ = weakref.ref(cls)
         else:
             cls = self._patch_original_class()
             if PY_3_10_PLUS:

tests/test_slots.py

@@ -104,6 +104,20 @@ def test_slots_being_used():
     assert attr.asdict(slot_instance) == attr.asdict(non_slot_instance)
 
 
+def test_slots_base_of_slotted():
+    """
+    The (hopefully gc'ed) temporary base class of a slotted class contains a
+    reference to the slotted class.
+    """
+
+    class Base:
+        pass
+
+    Slotted = attr.s(slots=True)(Base)
+
+    assert Slotted is Base.__attrs_base_of_slotted__()
+
+
 def test_basic_attr_funcs():
     """
     Comparison, `__eq__`, `__hash__`, `__repr__`, `attrs.asdict` work.
@@ -755,7 +769,7 @@ def f(self):
     assert "__dict__" not in dir(A)
 
 
-def test_slots_cached_property_works_on_frozen_isntances():
+def test_slots_cached_property_works_on_frozen_instances():
     """
     Infers type of cached property.
     """