From 261d26ed4536b8a6593f82aa6a2c3a1d7c9664d4 Mon Sep 17 00:00:00 2001
From: Hynek Schlawack <hs@ox.cx>
Date: Tue, 27 Jun 2023 07:12:37 +0200
Subject: [PATCH] Demonstrate init subclass workaround

---
 tests/test_init_subclass.py | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/tests/test_init_subclass.py b/tests/test_init_subclass.py
index ffd36108..cff4e948 100644
--- a/tests/test_init_subclass.py
+++ b/tests/test_init_subclass.py
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: MIT
 
 """
-Tests for `__init_subclass__` related tests.
+Tests for `__init_subclass__` related functionality.
 """
 
 import attr
@@ -41,3 +41,26 @@ def test_init_subclass_attrs():
         pass
 
     assert "foo" == Attrs().param
+
+
+def test_init_subclass_slots_workaround():
+    """
+    `__init_subclass__` works with modern APIs if care is taken around classes
+    existing twice.
+    """
+    subs = {}
+
+    @attr.define
+    class Base:
+        def __init_subclass__(cls):
+            subs[cls.__qualname__] = cls
+
+    @attr.define
+    class Sub1(Base):
+        x: int
+
+    @attr.define
+    class Sub2(Base):
+        y: int
+
+    assert (Sub1, Sub2) == tuple(subs.values())