gh-105834: Add tests for calling issubclass() between two protocols

Lib/test/test_typing.py

@@ -2759,6 +2759,54 @@ def x(self): ...
  with self.assertRaisesRegex(TypeError, only_classes_allowed):
  issubclass(1, BadPG)
 
+ def test_implicit_issubclass_between_two_protocols(self):
+ @runtime_checkable
+ class CallableMembersProto(Protocol):
+ def meth(self): ...
+
+ # All the below protocols should be considered "subclasses"
+ # of CallableMembersProto at runtime,
+ # even though none of them explicitly subclass CallableMembersProto
+
+ class IdenticalProto(Protocol):
+ def meth(self): ...
+
+ class SupersetProto(Protocol):
+ def meth(self): ...
+ def meth2(self): ...
+
+ class NonCallableMembersProto(Protocol):
+ meth: Callable[[], None]
+
+ class NonCallableMembersSupersetProto(Protocol):
+ meth: Callable[[], None]
+ meth2: Callable[[str, int], bool]
+
+ class MixedMembersProto1(Protocol):
+ meth: Callable[[], None]
+ def meth2(self): ...
+
+ class MixedMembersProto2(Protocol):
+ def meth(self): ...
+ meth2: Callable[[str, int], bool]
+
+ for proto in (
+ IdenticalProto, SupersetProto, NonCallableMembersProto,
+ NonCallableMembersSupersetProto, MixedMembersProto1, MixedMembersProto2
+ ):
+ with self.subTest(proto=proto.__name__):
+ self.assertIsSubclass(proto, CallableMembersProto)
+
+ # These two shouldn't be considered subclasses of CallableMembersProto, however,
+ # since they don't have the `meth` protocol member
+
+ class EmptyProtocol(Protocol): ...
+ class UnrelatedProtocol(Protocol):
+ def wut(self): ...
+
+ self.assertNotIsSubclass(EmptyProtocol, CallableMembersProto)
+ self.assertNotIsSubclass(UnrelatedProtocol, CallableMembersProto)
+
  def test_isinstance_checks_not_at_whim_of_gc(self):
  self.addCleanup(gc.enable)
  gc.disable()