From 29f35a9795a9732433b4f8b52bc872d6d2eedfeb Mon Sep 17 00:00:00 2001
From: Nikita Sobolev <mail@sobolevn.me>
Date: Tue, 14 Mar 2023 00:42:05 +0300
Subject: [PATCH] gh-102069: Fix `__weakref__` descriptor generation for custom
 dataclasses (#102075)

---
 Lib/dataclasses.py                                |  3 +++
 Lib/test/test_dataclasses.py                      | 15 +++++++++++----
 ...2023-02-20-16-47-56.gh-issue-102069.FS7f1j.rst |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2023-02-20-16-47-56.gh-issue-102069.FS7f1j.rst

diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 7c3285cf440a397..82b08fc017884f5 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -1189,6 +1189,9 @@ def _add_slots(cls, is_frozen, weakref_slot):
     # Remove __dict__ itself.
     cls_dict.pop('__dict__', None)
 
+    # Clear existing `__weakref__` descriptor, it belongs to a previous type:
+    cls_dict.pop('__weakref__', None)  # gh-102069
+
     # And finally create the class.
     qualname = getattr(cls, '__qualname__', None)
     cls = type(cls)(cls.__name__, cls.__bases__, cls_dict)
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 46d4e0fedad2f27..46f33043c270714 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -3175,6 +3175,8 @@ class A:
         with self.assertRaisesRegex(TypeError,
                                     "cannot create weak reference"):
             weakref.ref(a)
+        with self.assertRaises(AttributeError):
+            a.__weakref__
 
     def test_slots_weakref(self):
         @dataclass(slots=True, weakref_slot=True)
@@ -3183,7 +3185,9 @@ class A:
 
         self.assertIn("__weakref__", A.__slots__)
         a = A(1)
-        weakref.ref(a)
+        a_ref = weakref.ref(a)
+
+        self.assertIs(a.__weakref__, a_ref)
 
     def test_slots_weakref_base_str(self):
         class Base:
@@ -3249,7 +3253,8 @@ class A(Base):
         self.assertIn("__weakref__", Base.__slots__)
         self.assertNotIn("__weakref__", A.__slots__)
         a = A(1)
-        weakref.ref(a)
+        a_ref = weakref.ref(a)
+        self.assertIs(a.__weakref__, a_ref)
 
     def test_weakref_slot_subclass_no_weakref_slot(self):
         @dataclass(slots=True, weakref_slot=True)
@@ -3265,7 +3270,8 @@ class A(Base):
         self.assertIn("__weakref__", Base.__slots__)
         self.assertNotIn("__weakref__", A.__slots__)
         a = A(1)
-        weakref.ref(a)
+        a_ref = weakref.ref(a)
+        self.assertIs(a.__weakref__, a_ref)
 
     def test_weakref_slot_normal_base_weakref_slot(self):
         class Base:
@@ -3280,7 +3286,8 @@ class A(Base):
         self.assertIn("__weakref__", Base.__slots__)
         self.assertNotIn("__weakref__", A.__slots__)
         a = A(1)
-        weakref.ref(a)
+        a_ref = weakref.ref(a)
+        self.assertIs(a.__weakref__, a_ref)
 
 
 class TestDescriptors(unittest.TestCase):
diff --git a/Misc/NEWS.d/next/Library/2023-02-20-16-47-56.gh-issue-102069.FS7f1j.rst b/Misc/NEWS.d/next/Library/2023-02-20-16-47-56.gh-issue-102069.FS7f1j.rst
new file mode 100644
index 000000000000000..04c87e515cca939
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-02-20-16-47-56.gh-issue-102069.FS7f1j.rst
@@ -0,0 +1 @@
+Fix ``__weakref__`` descriptor generation for custom dataclasses.