Type is incompatible with Callable when using Concatenate

[ringohoffman]

Bug Report

As expected, a class A can be typed as Type[A] or Callable[P, A], where P is a ParamSpec.

Using Concatenate then, you should also be able to bind A to Callable[Concatenate[<type>, P], A], where <type> is the type of A's first constructor parameter, but mypy currently errors when you attempt this.

To Reproduce

gist: https://gist.github.com/mypy-play/1cab71a52f3d7f3a4e9045e6e68eabe0 mypy-playground: https://mypy-play.net/?mypy=latest&python=3.10&gist=1cab71a52f3d7f3a4e9045e6e68eabe0

from __future__ import annotations

from typing import Callable, Concatenate, ParamSpec

P = ParamSpec("P")


class A:
    def __init__(self, a_param_1: str) -> None:
        ...

    @classmethod
    def add_params(cls: Callable[P, A]) -> Callable[Concatenate[float, P], A]:
        def new_constructor(i: float, *args: P.args, **kwargs: P.kwargs) -> A:
            return cls(*args, **kwargs)
        return new_constructor
    
    @classmethod
    def remove_params(cls: Callable[Concatenate[str, P], A]) -> Callable[P, A]:
        def new_constructor(*args: P.args, **kwargs: P.kwargs) -> A:
            return cls("my_special_str", *args, **kwargs)
        return new_constructor

A.add_params()  # OK
A.remove_params()  # [misc] mypy(error): Invalid self argument "Type[A]" to attribute function "remove_params" with type "Callable[[Callable[[str, **P], A]], Callable[P, A]]"

Expected Behavior

No error should be raised.

Actual Behavior

error: Invalid self argument "Type[A]" to attribute function "remove_params" with type "Callable[[Callable[[str, **P], A]], Callable[P, A]]"  [misc]

Your Environment

• Mypy version used: mypy 0.991 (compiled: yes)
• Python version used: 3.10.6

[ringohoffman]

The difference in behavior between add_params and remove_params seems to come from this line in check_self_arg :

if subtypes.is_subtype(dispatched_arg_type, erase_typevars(erase_to_bound(selfarg))):

name	selfarg	dispatched_arg_type	subtypes.is_subtype(...)
add_params	def (*P.args, **P.kwargs) -> A	def (a_param_1: builtins.str) -> A	True from are_trivial_parameters(...) in are_parameters_compatible
remove_params	def (builtins.str, *P.args, **P.kwargs) -> A	def (a_param_1: builtins.str) -> A	False from not allow_partial_overlap in are_parameters_compatible

In the case of remove_params, by setting is_callable_compatible(allow_partial_overlap=right.from_concatenate or left.from_concatenate) in visit_callable_type, we can progress a little further into are_parameters_compatible... however we then return False from the condition in "Phase 2":

if (
    right_by_name is not None
    and right_by_pos is not None
    and right_by_name != right_by_pos
    and (right_by_pos.required or right_by_name.required)
    and strict_concatenate_check
):
    return False

right_by_name	right_by_pos
FormalArgument(name='a_param_1', pos=None, typ=Any, required=False)	FormalArgument(name=None, pos=0, typ=builtins.str, required=True)

I feel like if def (a_param_1: builtins.str) -> A is considered a subtype of def (*P.args, **P.kwargs) -> A, then it should also be a subtype of def (builtins.str, *P.args, **P.kwargs) -> A, since this seems to be how Concatenate works in similar constructions:

from typing import ParamSpec, TypeVar

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


def decorator(f: Callable[Concatenate[str, P], T]) -> Callable[P, T]:
    def new_func(*args: P.args, **kwargs: P.kwargs) -> T:
        return f("my_special_str", *args, **kwargs)
    return new_func


@decorator  # OK
def foo(foo_param_1: str) -> None:
    ...

@A5rocks @cdce8p @JukkaL Does my reasoning and proposed change seem sound? What change related to the "Phase 2" condition should be made s.t. the subtype check passes?