[autodoc] Fix subclassing a MockObject together with typing.Generic

CHANGES.rst

@@ -116,6 +116,9 @@ Bugs fixed
 * #10785: Autodoc: Allow type aliases defined in the project to be properly
   cross-referenced when used as type annotations. This makes it possible
   for objects documented as ``:py:data:`` to be hyperlinked in function signatures.
+* #12797: Fix
+  ``TypeError: Some type variables (...) are not listed in Generic[...]``
+  when inheriting from both Generic and autodoc mocked class.
 
 Testing
 -------

sphinx/ext/autodoc/mock.py

@@ -29,6 +29,8 @@ class _MockObject:
     __name__ = ''
     __sphinx_mock__ = True
     __sphinx_decorator_args__: tuple[Any, ...] = ()
+    # Attributes listed here should not be mocked and rather raise an Attribute error:
+    __sphinx_empty_attrs__: set[str] = {'__typing_subst__'}
 
     def __new__(cls, *args: Any, **kwargs: Any) -> Any:  # NoQA: ARG004
         if len(args) == 3 and isinstance(args[1], tuple):
@@ -63,6 +65,8 @@ def __getitem__(self, key: Any) -> _MockObject:
         return _make_subclass(str(key), self.__display_name__, self.__class__)()
 
     def __getattr__(self, key: str) -> _MockObject:
+        if key in self.__sphinx_empty_attrs__:
+            raise AttributeError
         return _make_subclass(key, self.__display_name__, self.__class__)()
 
     def __call__(self, *args: Any, **kwargs: Any) -> Any:

tests/test_extensions/test_ext_autodoc_mock.py

@@ -5,7 +5,7 @@
 import abc
 import sys
 from importlib import import_module
-from typing import TypeVar
+from typing import Generic, TypeVar
 
 import pytest
 
@@ -57,6 +57,28 @@ class SubClass2(mock.SomeClass[T]):
     assert SubClass2.__doc__ == 'docstring of SubClass'
     assert isinstance(obj2, SubClass2)
 
+    # test subclass with typing.Generic
+    # Creating this class would raise an error on Python3.11+
+    # as mock objects are detected as typevars if hasattr(__typing_subst__) is True.
+
+    assert not hasattr(mock.SomeClass, '__typing_subst__')
+    S = TypeVar('S')
+
+    class GenericClass(mock.SomeClass, Generic[T, S]):
+        """docstring of GenericSubclass"""
+
+    obj3 = GenericClass()
+    assert isinstance(obj3, _MockObject)
+    assert isinstance(obj3.some_attr, _MockObject)
+    assert isinstance(obj3.some_method(), _MockObject)
+    assert isinstance(obj3.attr1.attr2, _MockObject)
+    assert isinstance(obj3.attr1.attr2.meth(), _MockObject)
+
+    # check that Generic Subscriptions still works
+
+    class GenericSubclass(GenericClass[mock.MockedClass, S]):
+        """docstring of GenericSubclass"""
+
 
 def test_mock() -> None:
     modname = 'sphinx.unknown'