Mypy does not correctly understand MemberDescriptors for objects with slots.

Bug Report

When a Python object uses slots, MemberDescriptors are created for each attribute defined as a slot.

Mypy incorrectly interprets these fields as the type of the slotted value, rather than as a member descriptor.

To Reproduce

class TestObject(object):
   __slots__ = ["a", "b"]
   a: int
   b: str

   def __init__(self, a: int, b: str) -> None:
      self.a = a
      self.b = b

def test() -> None:
   x = TestObject(5, "hi")
   reveal_type(TestObject.a)
   reveal_type(TestObject.b)
   reveal_type(x.a)
   reveal_type(x.b)

Expected Behavior

Here is what the types actually are based on the python repl.

>>> TestObject
<class '__main__.TestObject'>
>>> x = TestObject(10, "hi")
>>> type(TestObject.a)
<class 'member_descriptor'>
>>> type(TestObject.b)
<class 'member_descriptor'>
>>> type(x.a)
<class 'int'>
>>> type(x.b)
<class 'str'>

Actual Behavior

Mypy output:
12: note: Revealed type is 'builtins.int'
13: note: Revealed type is 'builtins.str'
14: note: Revealed type is 'builtins.int'
15: note: Revealed type is 'builtins.str'

Your Environment

Python 3.8.1
mypy 0.782

Beginne mit der bereitgestellten Reproduktion von slots und MemberDescriptor und verfolge dann, wie mypy die für Klassenattribute im Vergleich zu Instanzattributen aufgedeckten Typen bestimmt. Bestätige die Korrektur, indem du prüfst, dass TestObject.a und TestObject.b als Member-Deskriptoren gemeldet werden, während x.a und x.b int und str bleiben.