[3.11] gh-103171: Revert undocumented behaviour change for runtime-checkable protocols decorated with @final (#105445)

Lib/test/test_typing.py

@@ -3349,6 +3349,71 @@ class ProtocolTests(BaseTestCase):
 
         Foo()  # Previously triggered RecursionError
 
+    def test_empty_protocol_decorated_with_final(self):
+        @final
+        @runtime_checkable
+        class EmptyProtocol(Protocol): ...
+
+        self.assertIsSubclass(object, EmptyProtocol)
+        self.assertIsInstance(object(), EmptyProtocol)
+
+    def test_protocol_decorated_with_final_callable_members(self):
+        @final
+        @runtime_checkable
+        class ProtocolWithMethod(Protocol):
+            def startswith(self, string: str) -> bool: ...
+
+        self.assertIsSubclass(str, ProtocolWithMethod)
+        self.assertNotIsSubclass(int, ProtocolWithMethod)
+        self.assertIsInstance('foo', ProtocolWithMethod)
+        self.assertNotIsInstance(42, ProtocolWithMethod)
+
+    def test_protocol_decorated_with_final_noncallable_members(self):
+        @final
+        @runtime_checkable
+        class ProtocolWithNonCallableMember(Protocol):
+            x: int
+
+        class Foo:
+            x = 42
+
+        only_callable_members_please = (
+            r"Protocols with non-method members don't support issubclass()"
+        )
+
+        with self.assertRaisesRegex(TypeError, only_callable_members_please):
+            issubclass(Foo, ProtocolWithNonCallableMember)
+
+        with self.assertRaisesRegex(TypeError, only_callable_members_please):
+            issubclass(int, ProtocolWithNonCallableMember)
+
+        self.assertIsInstance(Foo(), ProtocolWithNonCallableMember)
+        self.assertNotIsInstance(42, ProtocolWithNonCallableMember)
+
+    def test_protocol_decorated_with_final_mixed_members(self):
+        @final
+        @runtime_checkable
+        class ProtocolWithMixedMembers(Protocol):
+            x: int
+            def method(self) -> None: ...
+
+        class Foo:
+            x = 42
+            def method(self) -> None: ...
+
+        only_callable_members_please = (
+            r"Protocols with non-method members don't support issubclass()"
+        )
+
+        with self.assertRaisesRegex(TypeError, only_callable_members_please):
+            issubclass(Foo, ProtocolWithMixedMembers)
+
+        with self.assertRaisesRegex(TypeError, only_callable_members_please):
+            issubclass(int, ProtocolWithMixedMembers)
+
+        self.assertIsInstance(Foo(), ProtocolWithMixedMembers)
+        self.assertNotIsInstance(42, ProtocolWithMixedMembers)
+
 
 class GenericTests(BaseTestCase):