gh-95196: Disable incorrect pickling of the C implemented classmethod descriptors (GH-96383)

Author: serhiy-storchaka

Lib/test/pickletester.py

@@ -2776,6 +2776,15 @@ def pie(self):
                     unpickled = self.loads(self.dumps(method, proto))
                     self.assertEqual(method(obj), unpickled(obj))
 
+        descriptors = (
+            PyMethodsTest.__dict__['cheese'],  # static method descriptor
+            PyMethodsTest.__dict__['wine'],  # class method descriptor
+        )
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            for descr in descriptors:
+                with self.subTest(proto=proto, descr=descr):
+                    self.assertRaises(TypeError, self.dumps, descr, proto)
+
     def test_c_methods(self):
         global Subclass
         class Subclass(tuple):
@@ -2811,6 +2820,15 @@ class Nested(str):
                     unpickled = self.loads(self.dumps(method, proto))
                     self.assertEqual(method(*args), unpickled(*args))
 
+        descriptors = (
+            bytearray.__dict__['maketrans'],  # built-in static method descriptor
+            dict.__dict__['fromkeys'],  # built-in class method descriptor
+        )
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            for descr in descriptors:
+                with self.subTest(proto=proto, descr=descr):
+                    self.assertRaises(TypeError, self.dumps, descr, proto)
+
     def test_compat_pickle(self):
         tests = [
             (range(1, 7), '__builtin__', 'xrange'),

Misc/NEWS.d/next/Core and Builtins/2022-08-29-13-06-58.gh-issue-95196.eGRR4b.rst

@@ -0,0 +1 @@
+Disable incorrect pickling of the C implemented classmethod descriptors.

Objects/descrobject.c

@@ -776,7 +776,7 @@ PyTypeObject PyClassMethodDescr_Type = {
     0,                                          /* tp_weaklistoffset */
     0,                                          /* tp_iter */
     0,                                          /* tp_iternext */
-    descr_methods,                              /* tp_methods */
+    0,                                          /* tp_methods */
     descr_members,                              /* tp_members */
     method_getset,                              /* tp_getset */
     0,                                          /* tp_base */