Fix structuring of attrs class that inherit from typing/collections.abc generic type aliases (#655)

* [test_converter_inheritance] test inheriting from generic collections.abc types still works

This reproduces issue #654: AttributeError: type object 'Iterable' has no attribute '__parameters__'

* [_generics] handle parametrized types from collections.abc without __parameters__ attributes

Reverts 2fe721e

Author: anthrotype

HISTORY.md

@@ -11,6 +11,11 @@ The third number is for emergencies when we need to start branches for older rel
 
 Our backwards-compatibility policy can be found [here](https://github.com/python-attrs/cattrs/blob/main/.github/SECURITY.md).
 
+## 25.1.1 (UNRELEASED)
+
+- Fixed `AttributeError: no attribute '__parameters__'` while structuring attrs classes that inherit from parametrized generic aliases from `collections.abc`.
+  ([#654](https://github.com/python-attrs/cattrs/issues/654) [#655](https://github.com/python-attrs/cattrs/pull/655))
+
 ## 25.1.0 (2025-05-31)
 
 - **Potentially breaking**: The converters raise {class}`StructureHandlerNotFoundError` more eagerly (on hook creation, instead of on hook use).

src/cattrs/gen/_generics.py

@@ -36,7 +36,14 @@ def generate_mapping(cl: type, old_mapping: dict[str, type] = {}) -> dict[str, t
     origin = get_origin(cl)
 
     if origin is not None:
-        parameters = origin.__parameters__
+        # To handle the cases where classes in the typing module are using
+        # the GenericAlias structure but aren't a Generic and hence
+        # end up in this function but do not have an `__parameters__`
+        # attribute. These classes are interface types, for example
+        # `typing.Hashable`.
+        parameters = getattr(get_origin(cl), "__parameters__", None)
+        if parameters is None:
+            return dict(old_mapping)
 
         for p, t in zip(parameters, get_args(cl)):
             if isinstance(t, TypeVar):

tests/test_converter_inheritance.py

@@ -41,7 +41,7 @@ class B(A):
     assert converter.structure({"i": 1}, B) == B(2)
 
 
-@pytest.mark.parametrize("typing_cls", [Hashable, Iterable, Reversible])
+@pytest.mark.parametrize("typing_cls", [Hashable, Iterable, Reversible, Iterable[int]])
 def test_inherit_typing(converter: BaseConverter, typing_cls):
     """Stuff from typing.* resolves to runtime to collections.abc.*.
 
@@ -67,7 +67,12 @@ def __reversed__(self):
 
 @pytest.mark.parametrize(
     "collections_abc_cls",
-    [collections.abc.Hashable, collections.abc.Iterable, collections.abc.Reversible],
+    [
+        collections.abc.Hashable,
+        collections.abc.Iterable,
+        collections.abc.Reversible,
+        collections.abc.Iterable[int],
+    ],
 )
 def test_inherit_collections_abc(converter: BaseConverter, collections_abc_cls):
     """As extension of test_inherit_typing, check if collections.abc.* work."""