Protocols don't support descriptors

[ilevkivskyi]

Consider this code:

class Descr:
    def __get__(self, inst: Any, owner: Any) -> int: ...

class Proto(Protocol):
    x: int

class C:
    x = Descr()

a: Proto = C()

I think it should be allowed. This can be done by simply re-using the logic in analyze_member_access in checkmember.py, see also #5136.

[bryanforbes]

This will be fixed when #3832 is complete

[ilevkivskyi]

This appeared again in dropbox/sqlalchemy-stubs#134

[ckarnell]

Can you tell me exactly where in the code the duplication is happening WRT Protocols, so I can try to piece together some understanding and look into fixing it? I'm looking myself but it's not immediately obvious, and I'm unfamiliar with the codebase.

[ilevkivskyi]

Just to set realistic expectations: it is unlikely anyone beyond core team can fix this. But anyway, the problematic logic duplication is between is_protocol_implementation()/find_member() in subtypes.py and analyze_instance_member_access() in checkmember.py.

[ckarnell]

Got it, makes sense. I might take a peek anyway just out of curiosity.

[sobolevn]

This was raised once again in django-stubs repo: typeddjango/django-stubs#651