From 0939d820fd0f62f020d6d8a03d09c4f7e808dff5 Mon Sep 17 00:00:00 2001
From: sobolevn <mail@sobolevn.me>
Date: Mon, 26 Aug 2024 18:38:09 +0300
Subject: [PATCH 1/2] gh-91126: Docs and tests for slotted dataclasses with
 `__init_subclass__`

---
 Doc/library/dataclasses.rst           | 18 +++++++++++++----
 Lib/test/test_dataclasses/__init__.py | 28 +++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/Doc/library/dataclasses.rst b/Doc/library/dataclasses.rst
index fcb5e8bad295a0..3d9a2173a25a0e 100644
--- a/Doc/library/dataclasses.rst
+++ b/Doc/library/dataclasses.rst
@@ -185,10 +185,20 @@ Module contents
    - *slots*: If true (the default is ``False``), :attr:`~object.__slots__` attribute
      will be generated and new class will be returned instead of the original one.
      If :attr:`!__slots__` is already defined in the class, then :exc:`TypeError`
-     is raised. Calling no-arg :func:`super` in dataclasses using ``slots=True`` will result in
-     the following exception being raised:
-     ``TypeError: super(type, obj): obj must be an instance or subtype of type``.
-     The two-arg :func:`super` is a valid workaround. See :gh:`90562` for full details.
+     is raised.
+
+    .. warning::
+        Calling no-arg :func:`super` in dataclasses using ``slots=True``
+        will result in the following exception being raised:
+        ``TypeError: super(type, obj): obj must be an instance or subtype of type``.
+        The two-arg :func:`super` is a valid workaround.
+        See :gh:`90562` for full details.
+
+    .. warning::
+       Having a base class with :meth:`~object.__init_subclass__` with parameters
+       when using ``slots=True`` will result in a :exc:`TypeError`.
+       Either use ``__init_subclass__`` with no parameters or use default values.
+       See :gh:`91126` for full details.
 
     .. versionadded:: 3.10
 
diff --git a/Lib/test/test_dataclasses/__init__.py b/Lib/test/test_dataclasses/__init__.py
index b93c99d8c90bf3..6b62021ea075f4 100644
--- a/Lib/test/test_dataclasses/__init__.py
+++ b/Lib/test/test_dataclasses/__init__.py
@@ -3664,6 +3664,34 @@ class A(WithDictSlot): ...
         self.assertEqual(A().__dict__, {})
         A()
 
+    def test_slots_with_wrong_init_subclass(self):
+        class WrongSuper:
+            def __init_subclass__(cls, arg):
+                pass
+
+        with self.assertRaisesRegex(
+            TypeError,
+            "missing 1 required positional argument: 'arg'",
+        ):
+            @dataclass(slots=True)
+            class WithWrongSuper(WrongSuper, arg=1):
+                pass
+
+    def test_slots_with_correct_init_subclass(self):
+        class CorrectSuper:
+            args = []
+            def __init_subclass__(cls, arg="default"):
+                cls.args.append(arg)
+
+        @dataclass(slots=True)
+        class WithCorrectSuper(CorrectSuper):
+            pass
+
+        # __init_subclass__ is called twice: once for `WithCorrectSuper`
+        # and once for `WithCorrectSuper__slots__` new class
+        # that we create internally.
+        self.assertEqual(CorrectSuper.args, ["default", "default"])
+
 
 class TestDescriptors(unittest.TestCase):
     def test_set_name(self):

From c5ac01613548345070fca054f9b41dc3afc42455 Mon Sep 17 00:00:00 2001
From: sobolevn <mail@sobolevn.me>
Date: Mon, 26 Aug 2024 22:07:28 +0300
Subject: [PATCH 2/2] Address review

---
 Doc/library/dataclasses.rst           | 5 +++--
 Lib/test/test_dataclasses/__init__.py | 6 +++++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/Doc/library/dataclasses.rst b/Doc/library/dataclasses.rst
index 3d9a2173a25a0e..db1e6af530bdeb 100644
--- a/Doc/library/dataclasses.rst
+++ b/Doc/library/dataclasses.rst
@@ -195,9 +195,10 @@ Module contents
         See :gh:`90562` for full details.
 
     .. warning::
-       Having a base class with :meth:`~object.__init_subclass__` with parameters
+       Passing parameters to a base class :meth:`~object.__init_subclass__`
        when using ``slots=True`` will result in a :exc:`TypeError`.
-       Either use ``__init_subclass__`` with no parameters or use default values.
+       Either use ``__init_subclass__`` with no parameters
+       or use default values as a workaround.
        See :gh:`91126` for full details.
 
     .. versionadded:: 3.10
diff --git a/Lib/test/test_dataclasses/__init__.py b/Lib/test/test_dataclasses/__init__.py
index 6b62021ea075f4..da696ad961cfd7 100644
--- a/Lib/test/test_dataclasses/__init__.py
+++ b/Lib/test/test_dataclasses/__init__.py
@@ -3664,7 +3664,12 @@ class A(WithDictSlot): ...
         self.assertEqual(A().__dict__, {})
         A()
 
+    @support.cpython_only
     def test_slots_with_wrong_init_subclass(self):
+        # TODO: This test is for a kinda-buggy behavior.
+        # Ideally, it should be fixed and `__init_subclass__`
+        # should be fully supported in the future versions.
+        # See https://github.com/python/cpython/issues/91126
         class WrongSuper:
             def __init_subclass__(cls, arg):
                 pass
@@ -3677,7 +3682,6 @@ def __init_subclass__(cls, arg):
             class WithWrongSuper(WrongSuper, arg=1):
                 pass
 
-    def test_slots_with_correct_init_subclass(self):
         class CorrectSuper:
             args = []
             def __init_subclass__(cls, arg="default"):