Simplify slot field detection

Author: hynek

src/attr/_make.py

@@ -2113,15 +2113,12 @@ def validate(inst):
             v(inst, a, getattr(inst, a.name))
 
 
-def _is_slot_cls(cls):
-    return "__slots__" in cls.__dict__
-
-
 def _is_slot_attr(a_name, base_attr_map):
     """
     Check if the attribute name comes from a slot class.
     """
-    return a_name in base_attr_map and _is_slot_cls(base_attr_map[a_name])
+    cls = base_attr_map.get(a_name)
+    return cls and "__slots__" in cls.__dict__
 
 
 def _make_init(

tests/test_dunders.py

@@ -20,7 +20,6 @@
     NOTHING,
     Factory,
     _add_repr,
-    _is_slot_cls,
     _make_init,
     fields,
     make_class,
@@ -98,7 +97,7 @@ def _add_init(cls, frozen):
         ),
         getattr(cls, "__attrs_post_init__", False),
         frozen,
-        _is_slot_cls(cls),
+        "__slots__" in cls.__dict__,
         cache_hash=False,
         base_attr_map={},
         is_exc=False,