gh-106403: Restore weakref support for TypeVar and friends (#106418)

Author: JelleZijlstra

Diff for: Lib/test/test_type_params.py

@@ -3,6 +3,7 @@
 import types
 import unittest
 import pickle
+import weakref
 from test.support import requires_working_socket, check_syntax_error, run_code
 
 from typing import Generic, Sequence, TypeVar, TypeVarTuple, ParamSpec, get_args
@@ -921,3 +922,33 @@ def test_pickling_classes(self):
                     # These instances are not equal,
                     # but class check is good enough:
                     self.assertIsInstance(pickle.loads(pickled), real_class)
+
+
+class TypeParamsWeakRefTest(unittest.TestCase):
+    def test_weakrefs(self):
+        T = TypeVar('T')
+        P = ParamSpec('P')
+        class OldStyle(Generic[T]):
+            pass
+
+        class NewStyle[T]:
+            pass
+
+        cases = [
+            T,
+            TypeVar('T', bound=int),
+            P,
+            P.args,
+            P.kwargs,
+            TypeVarTuple('Ts'),
+            OldStyle,
+            OldStyle[int],
+            OldStyle(),
+            NewStyle,
+            NewStyle[int],
+            NewStyle(),
+            Generic[T],
+        ]
+        for case in cases:
+            with self.subTest(case=case):
+                weakref.ref(case)

Diff for: Misc/NEWS.d/next/Library/2023-07-04-07-25-30.gh-issue-106403.GmefbV.rst

@@ -0,0 +1,4 @@
+Instances of :class:`typing.TypeVar`, :class:`typing.ParamSpec`,
+:class:`typing.ParamSpecArgs`, :class:`typing.ParamSpecKwargs`, and
+:class:`typing.TypeVarTuple` once again support weak references, fixing a
+regression introduced in Python 3.12.0 beta 1. Patch by Jelle Zijlstra.

Diff for: Objects/typevarobject.c

@@ -500,7 +500,7 @@ PyType_Spec typevar_spec = {
     .name = "typing.TypeVar",
     .basicsize = sizeof(typevarobject),
     .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_IMMUTABLETYPE
-        | Py_TPFLAGS_MANAGED_DICT,
+        | Py_TPFLAGS_MANAGED_DICT | Py_TPFLAGS_MANAGED_WEAKREF,
     .slots = typevar_slots,
 };
 
@@ -647,7 +647,8 @@ static PyType_Slot paramspecargs_slots[] = {
 PyType_Spec paramspecargs_spec = {
     .name = "typing.ParamSpecArgs",
     .basicsize = sizeof(paramspecattrobject),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_IMMUTABLETYPE,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_IMMUTABLETYPE
+        | Py_TPFLAGS_MANAGED_WEAKREF,
     .slots = paramspecargs_slots,
 };
 
@@ -726,7 +727,8 @@ static PyType_Slot paramspeckwargs_slots[] = {
 PyType_Spec paramspeckwargs_spec = {
     .name = "typing.ParamSpecKwargs",
     .basicsize = sizeof(paramspecattrobject),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_IMMUTABLETYPE,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_IMMUTABLETYPE
+        | Py_TPFLAGS_MANAGED_WEAKREF,
     .slots = paramspeckwargs_slots,
 };
 
@@ -1007,7 +1009,7 @@ PyType_Spec paramspec_spec = {
     .name = "typing.ParamSpec",
     .basicsize = sizeof(paramspecobject),
     .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_IMMUTABLETYPE
-        | Py_TPFLAGS_MANAGED_DICT,
+        | Py_TPFLAGS_MANAGED_DICT | Py_TPFLAGS_MANAGED_WEAKREF,
     .slots = paramspec_slots,
 };
 
@@ -1228,7 +1230,7 @@ PyType_Spec typevartuple_spec = {
     .name = "typing.TypeVarTuple",
     .basicsize = sizeof(typevartupleobject),
     .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_IMMUTABLETYPE | Py_TPFLAGS_MANAGED_DICT
-        | Py_TPFLAGS_HAVE_GC,
+        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_MANAGED_WEAKREF,
     .slots = typevartuple_slots,
 };