False negative when inferring paramspec for a class constructor #2587
Description
Summary
The following playground link emits no errors:
from typing import Generic, ParamSpec, Protocol
P = ParamSpec("P")
class ParentClass:
pass
class MyProto(Protocol, Generic[P]):
def __call__(self, *args: P.args, **kwargs: P.kwargs) -> ParentClass: ...
class MyType(ParentClass):
def __init__(self, x: int):
pass
def create(p: MyProto[P], *args: P.args, **kwargs: P.kwargs):
pass
create(MyType)https://play.ty.dev/8273c9c2-da7f-4432-982d-71bba5c60dbe
However, this code is not sound.
To typecheck this method, P must be inferred empty:
def create(p: MyProto[P], *args: P.args, **kwargs: P.kwargs):
pass
create(MyType)Hence, the function must accept no parameters except self:
class MyProto(Protocol, Generic[P]):
def __call__(self, *args: P.args, **kwargs: P.kwargs) -> ParentClass: ...However, MyType is defined as follows:
class MyType(ParentClass):
def __init__(self, x: int):
passSo it cannot be called with no parameters. (This is not about self being considered a parameter - the result is the same regardless of how many parameters __init__ wants here.)
Version
0.0.13