bpo-38008: Move builtin protocol whitelist to mapping instead of list (GH-15647)

Fixes https://bugs.python.org/issue38008 (cherry picked from commit 692a0dc) Co-authored-by: Divij Rajkumar <drajkuma1@gmail.com>

Author: miss-islington

Lib/test/test_typing.py

@@ -1381,6 +1381,14 @@ def close(self):
  self.assertIsSubclass(B, Custom)
  self.assertNotIsSubclass(A, Custom)
 
+ def test_builtin_protocol_whitelist(self):
+ with self.assertRaises(TypeError):
+ class CustomProtocol(TestCase, Protocol):
+ pass
+
+ class CustomContextManager(typing.ContextManager, Protocol):
+ pass
+
 class GenericTests(BaseTestCase):
 
  def test_basics(self):

Lib/typing.py

@@ -989,10 +989,13 @@ def _allow_reckless_class_cheks():
  return True
 
 
-_PROTO_WHITELIST = ['Callable', 'Awaitable',
- 'Iterable', 'Iterator', 'AsyncIterable', 'AsyncIterator',
- 'Hashable', 'Sized', 'Container', 'Collection', 'Reversible',
- 'ContextManager', 'AsyncContextManager']
+_PROTO_WHITELIST = {
+ 'collections.abc': [
+ 'Callable', 'Awaitable', 'Iterable', 'Iterator', 'AsyncIterable',
+ 'Hashable', 'Sized', 'Container', 'Collection', 'Reversible',
+ ],
+ 'contextlib': ['AbstractContextManager', 'AbstractAsyncContextManager'],
+}
 
 
 class _ProtocolMeta(ABCMeta):
@@ -1105,7 +1108,8 @@ def _proto_hook(other):
  # ... otherwise check consistency of bases, and prohibit instantiation.
  for base in cls.__bases__:
  if not (base in (object, Generic) or
- base.__module__ == 'collections.abc' and base.__name__ in _PROTO_WHITELIST or
+ base.__module__ in _PROTO_WHITELIST and
+ base.__name__ in _PROTO_WHITELIST[base.__module__] or
  issubclass(base, Generic) and base._is_protocol):
  raise TypeError('Protocols can only inherit from other'
  ' protocols, got %r' % base)

Misc/NEWS.d/next/Library/2019-09-12-10-47-34.bpo-38008.sH74Iy.rst

@@ -0,0 +1,3 @@
+Fix parent class check in protocols to correctly identify the module that
+provides a builtin protocol, instead of assuming they all come from the
+:mod:`collections.abc` module