[3.13] gh-119004: fix a crash in equality testing between OrderedDict (GH-121329) (#124507)

gh-119004: fix a crash in equality testing between `OrderedDict` (GH-121329)
(cherry picked from commit 38a887dc3e)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Lib/test/test_ordered_dict.py

@@ -2,7 +2,9 @@ import builtins
 import contextlib
 import copy
 import gc
+import operator
 import pickle
+import re
 from random import randrange, shuffle
 import struct
 import sys
@@ -740,11 +742,44 @@ class OrderedDictTests:
         # when it's mutated and returned from __next__:
         self.assertTrue(gc.is_tracked(next(it)))
 
+
+class _TriggerSideEffectOnEqual:
+    count = 0   # number of calls to __eq__
+    trigger = 1 # count value when to trigger side effect
+
+    def __eq__(self, other):
+        if self.__class__.count == self.__class__.trigger:
+            self.side_effect()
+        self.__class__.count += 1
+        return True
+
+    def __hash__(self):
+        # all instances represent the same key
+        return -1
+
+    def side_effect(self):
+        raise NotImplementedError
+
 class PurePythonOrderedDictTests(OrderedDictTests, unittest.TestCase):
 
     module = py_coll
     OrderedDict = py_coll.OrderedDict
 
+    def test_issue119004_attribute_error(self):
+        class Key(_TriggerSideEffectOnEqual):
+            def side_effect(self):
+                del dict1[TODEL]
+
+        TODEL = Key()
+        dict1 = self.OrderedDict(dict.fromkeys((0, TODEL, 4.2)))
+        dict2 = self.OrderedDict(dict.fromkeys((0, Key(), 4.2)))
+        # This causes an AttributeError due to the linked list being changed
+        msg = re.escape("'NoneType' object has no attribute 'key'")
+        self.assertRaisesRegex(AttributeError, msg, operator.eq, dict1, dict2)
+        self.assertEqual(Key.count, 2)
+        self.assertDictEqual(dict1, dict.fromkeys((0, 4.2)))
+        self.assertDictEqual(dict2, dict.fromkeys((0, Key(), 4.2)))
+
 
 class CPythonBuiltinDictTests(unittest.TestCase):
     """Builtin dict preserves insertion order.
@@ -765,8 +800,85 @@ for method in (
 del method
 
 
+class CPythonOrderedDictSideEffects:
+
+    def check_runtime_error_issue119004(self, dict1, dict2):
+        msg = re.escape("OrderedDict mutated during iteration")
+        self.assertRaisesRegex(RuntimeError, msg, operator.eq, dict1, dict2)
+
+    def test_issue119004_change_size_by_clear(self):
+        class Key(_TriggerSideEffectOnEqual):
+            def side_effect(self):
+                dict1.clear()
+
+        dict1 = self.OrderedDict(dict.fromkeys((0, Key(), 4.2)))
+        dict2 = self.OrderedDict(dict.fromkeys((0, Key(), 4.2)))
+        self.check_runtime_error_issue119004(dict1, dict2)
+        self.assertEqual(Key.count, 2)
+        self.assertDictEqual(dict1, {})
+        self.assertDictEqual(dict2, dict.fromkeys((0, Key(), 4.2)))
+
+    def test_issue119004_change_size_by_delete_key(self):
+        class Key(_TriggerSideEffectOnEqual):
+            def side_effect(self):
+                del dict1[TODEL]
+
+        TODEL = Key()
+        dict1 = self.OrderedDict(dict.fromkeys((0, TODEL, 4.2)))
+        dict2 = self.OrderedDict(dict.fromkeys((0, Key(), 4.2)))
+        self.check_runtime_error_issue119004(dict1, dict2)
+        self.assertEqual(Key.count, 2)
+        self.assertDictEqual(dict1, dict.fromkeys((0, 4.2)))
+        self.assertDictEqual(dict2, dict.fromkeys((0, Key(), 4.2)))
+
+    def test_issue119004_change_linked_list_by_clear(self):
+        class Key(_TriggerSideEffectOnEqual):
+            def side_effect(self):
+                dict1.clear()
+                dict1['a'] = dict1['b'] = 'c'
+
+        dict1 = self.OrderedDict(dict.fromkeys((0, Key(), 4.2)))
+        dict2 = self.OrderedDict(dict.fromkeys((0, Key(), 4.2)))
+        self.check_runtime_error_issue119004(dict1, dict2)
+        self.assertEqual(Key.count, 2)
+        self.assertDictEqual(dict1, dict.fromkeys(('a', 'b'), 'c'))
+        self.assertDictEqual(dict2, dict.fromkeys((0, Key(), 4.2)))
+
+    def test_issue119004_change_linked_list_by_delete_key(self):
+        class Key(_TriggerSideEffectOnEqual):
+            def side_effect(self):
+                del dict1[TODEL]
+                dict1['a'] = 'c'
+
+        TODEL = Key()
+        dict1 = self.OrderedDict(dict.fromkeys((0, TODEL, 4.2)))
+        dict2 = self.OrderedDict(dict.fromkeys((0, Key(), 4.2)))
+        self.check_runtime_error_issue119004(dict1, dict2)
+        self.assertEqual(Key.count, 2)
+        self.assertDictEqual(dict1, {0: None, 'a': 'c', 4.2: None})
+        self.assertDictEqual(dict2, dict.fromkeys((0, Key(), 4.2)))
+
+    def test_issue119004_change_size_by_delete_key_in_dict_eq(self):
+        class Key(_TriggerSideEffectOnEqual):
+            trigger = 0
+            def side_effect(self):
+                del dict1[TODEL]
+
+        TODEL = Key()
+        dict1 = self.OrderedDict(dict.fromkeys((0, TODEL, 4.2)))
+        dict2 = self.OrderedDict(dict.fromkeys((0, Key(), 4.2)))
+        self.assertEqual(Key.count, 0)
+        # the side effect is in dict.__eq__ and modifies the length
+        self.assertNotEqual(dict1, dict2)
+        self.assertEqual(Key.count, 2)
+        self.assertDictEqual(dict1, dict.fromkeys((0, 4.2)))
+        self.assertDictEqual(dict2, dict.fromkeys((0, Key(), 4.2)))
+
+
 @unittest.skipUnless(c_coll, 'requires the C version of the collections module')
-class CPythonOrderedDictTests(OrderedDictTests, unittest.TestCase):
+class CPythonOrderedDictTests(OrderedDictTests,
+                              CPythonOrderedDictSideEffects,
+                              unittest.TestCase):
 
     module = c_coll
     OrderedDict = c_coll.OrderedDict