using a decorator on an overloaded function where the decorator uses `Concatenate` causes false positive "Overloaded function implementation does not accept all possible arguments" error

[DetachHead]

from typing import Callable, Concatenate, TypeVar, overload, ParamSpec

T = TypeVar("T")
P = ParamSpec("P")
R = TypeVar("R")


def foo(fn: Callable[Concatenate[T, P], R]) -> Callable[Concatenate[T, P], R]:
    return fn


class Foo:
    @overload
    def bar(self, a: str) -> str: ...
    @overload
    def bar(self, a: int) -> int: ...

    # error: Overloaded function implementation does not accept all possible arguments of signature 1
    # error: Overloaded function implementation does not accept all possible arguments of signature 2
    @foo
    def bar(self, a: object) -> object: ...

playground

[ilevkivskyi]

This is because foo() destroys the argument name for the first argument. Internally, I see the inferred type for implementation is

def (__main__.Foo, a: builtins.object) -> builtins.object

so it cannot accept call like Foo.bar(self=Foo(), a=1). This seems way too pedantic however.

[DetachHead]

imo self should be implicitly positional only. i can't think of a case where you'd want to specify it as a keyword argument

[erictraut]

imo self should be implicitly positional only

There was a discussion about this in the typing forum. The general consensus was aligned with this viewpoint, and this is what I've implemented in pyright, but this hasn't yet been formally incorporated into the typing spec. You're welcome to add your input to the discussion thread.