deprecation warnings for issubclass() too, why not

Author: AlexWaygood

Lib/test/test_typing.py

@@ -7510,6 +7510,10 @@ def test_bytestring(self):
             self.assertIsInstance(b'', ByteString)
         with self.assertWarns(DeprecationWarning):
             self.assertIsInstance(bytearray(b''), ByteString)
+        with self.assertWarns(DeprecationWarning):
+            self.assertIsSubclass(bytes, ByteString)
+        with self.assertWarns(DeprecationWarning):
+            self.assertIsSubclass(bytearray, ByteString)
         with self.assertWarns(DeprecationWarning):
             class Foo(ByteString): ...
         with self.assertWarns(DeprecationWarning):

Lib/typing.py

@@ -3806,6 +3806,13 @@ def __instancecheck__(self, inst):
                 )
                 return super().__instancecheck__(inst)
 
+            def __subclasscheck__(self, cls):
+                import warnings
+                warnings._deprecated(
+                    f"{self.__module__}.{self._name}", remove=self._removal_version
+                )
+                return super().__subclasscheck__(cls)
+
         with warnings.catch_warnings(
             action="ignore", category=DeprecationWarning
         ):