Inheriting class with __slots__ defined

• Are you reporting a bug, or opening a feature request?

Feature request

• Please insert below the code you are checking with mypy.

class Base():
    __slots__: List[str] = ['foo', 'bar']
    if TYPE_CHECKING:
        foo: int
        bar: int

class Derived(Base):
    __slots__: List[str] = ['bar']

• What is the actual behavior/output?

Success: no issues found in 1 source file

• What is the behavior/output you expect?

I believe it would be nice if mypy generated an error on __slots__ declaration in Derived class because 'bar' slot was already declared in Base class.

• What are the versions of mypy and Python you are using?

Python 3.8.0, mypy 0.761

Inizia riproducendo con mypy l'esempio fornito di Base e Derived con slots. Traccia la gestione di slots da parte del type checker tra le classi ereditate, quindi verifica che uno slot ereditato duplicato produca una diagnostica, mentre le dichiarazioni di slot valide continuino a essere accettate.