1 files changed, 76 insertions, 0 deletions
diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 045f2a3b4d..bf038bf143 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -2695,6 +2695,82 @@ class ProtocolTests(BaseTestCase):
         with self.assertRaises(TypeError):
             issubclass(D, PNonCall)
 
+    def test_no_weird_caching_with_issubclass_after_isinstance(self):
+        @runtime_checkable
+        class Spam(Protocol):
+            x: int
+
+        class Eggs:
+            def __init__(self) -> None:
+                self.x = 42
+
+        self.assertIsInstance(Eggs(), Spam)
+
+        # gh-104555: If we didn't override ABCMeta.__subclasscheck__ in _ProtocolMeta,
+        # TypeError wouldn't be raised here,
+        # as the cached result of the isinstance() check immediately above
+        # would mean the issubclass() call would short-circuit
+        # before we got to the "raise TypeError" line
+        with self.assertRaises(TypeError):
+            issubclass(Eggs, Spam)
+
+    def test_no_weird_caching_with_issubclass_after_isinstance_2(self):
+        @runtime_checkable
+        class Spam(Protocol):
+            x: int
+
+        class Eggs: ...
+
+        self.assertNotIsInstance(Eggs(), Spam)
+
+        # gh-104555: If we didn't override ABCMeta.__subclasscheck__ in _ProtocolMeta,
+        # TypeError wouldn't be raised here,
+        # as the cached result of the isinstance() check immediately above
+        # would mean the issubclass() call would short-circuit
+        # before we got to the "raise TypeError" line
+        with self.assertRaises(TypeError):
+            issubclass(Eggs, Spam)
+
+    def test_no_weird_caching_with_issubclass_after_isinstance_3(self):
+        @runtime_checkable
+        class Spam(Protocol):
+            x: int
+
+        class Eggs:
+            def __getattr__(self, attr):
+                if attr == "x":
+                    return 42
+                raise AttributeError(attr)
+
+        self.assertNotIsInstance(Eggs(), Spam)
+
+        # gh-104555: If we didn't override ABCMeta.__subclasscheck__ in _ProtocolMeta,
+        # TypeError wouldn't be raised here,
+        # as the cached result of the isinstance() check immediately above
+        # would mean the issubclass() call would short-circuit
+        # before we got to the "raise TypeError" line
+        with self.assertRaises(TypeError):
+            issubclass(Eggs, Spam)
+
+    def test_no_weird_caching_with_issubclass_after_isinstance_pep695(self):
+        @runtime_checkable
+        class Spam[T](Protocol):
+            x: T
+
+        class Eggs[T]:
+            def __init__(self, x: T) -> None:
+                self.x = x
+
+        self.assertIsInstance(Eggs(42), Spam)
+
+        # gh-104555: If we didn't override ABCMeta.__subclasscheck__ in _ProtocolMeta,
+        # TypeError wouldn't be raised here,
+        # as the cached result of the isinstance() check immediately above
+        # would mean the issubclass() call would short-circuit
+        # before we got to the "raise TypeError" line
+        with self.assertRaises(TypeError):
+            issubclass(Eggs, Spam)
+
     def test_protocols_isinstance(self):
         T = TypeVar('T')