Incremental mode bug for nested ParamSpecs

[ringohoffman]

Bug Report

This bug only occurs on the second run when using incremental mode. When using nested ParamSpecs, the outer ParamSpec (M below) is erroneously equal to the inner ParamSpec (P below).

Notably, pyright handles this correctly.

To Reproduce

from __future__ import annotations

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


class ABase:
    ...


class ADerived(ABase):
    def __init__(self, a_param_1: float) -> None:
        super().__init__()
        self.a_1 = a_param_1


M = ParamSpec("M")
P = ParamSpec("P")
R = TypeVar("R", bound=ABase)


class B(Generic[P, R]):
    def __init__(
        self,
        a_class: Callable[P, R],
        b_param_1: str,
        *args: P.args,
        **kwargs: P.kwargs,
    ) -> None:
        self.a = a_class(*args, **kwargs)
        self.b_1 = b_param_1

    @classmethod
    def build(
        cls: Callable[Concatenate[Callable[P, R], M], B[P, R]], 
        a_class: Callable[P, R]
    ) -> Callable[M, B[P, R]]:

        def new_constructor(
            *args: M.args,
            **kwargs: M.kwargs,
        ) -> B[P, R]:
            return cls(a_class, *args, **kwargs)

        return new_constructor


BADerived = B.build(ADerived)

reveal_type(BADerived)  # note): Revealed type is "def (a_param_1: builtins.float) -> B[[a_param_1: builtins.float], ADerived]"

b_a_derived_1 = B(ADerived, "my_str", 1.0)  # OK
b_a_derived_2 = BADerived(  # [call-arg] error: Too many arguments
    "my_str", 1.0  # [arg-type] error: Argument 1 has incompatible type "str"; expected "float"
)

Expected Behavior

I expect the signature of BADerived to include b_param_1, like this:

mypy_nested_paramspec.py:49: note: Revealed type is "def (b_param_1: builtins.str, a_param_1: builtins.float) -> mypy_nested_paramspec.B[[a_param_1: builtins.float], ADerived]"

I also expect that calls to BADerived with the correct parameter count and types do not raise any errors.

Actual Behavior

mypy_nested_paramspec.py:49: note: Revealed type is "def (a_param_1: builtins.float) -> mypy_nested_paramspec.B[[a_param_1: builtins.float], mypy_nested_paramspec.ADerived]"
mypy_nested_paramspec.py:52: error: Too many arguments  [call-arg]
mypy_nested_paramspec.py:53: error: Argument 1 has incompatible type "str"; expected "float"  [arg-type]

Your Environment

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

[ringohoffman]

BTW if anyone can advise ... I am also at a loss to annotate BADerived and solve my var-annotated error:

main.py:53: error: Need type annotation for "BADerived"  [var-annotated]

[ilevkivskyi]

On current master I see the same behaviour with cold and warm cache, so removing the incremental label. The behavior however is still weird: it is different whether I call BADerived = B.build(ADerived) in the same or in a different file. In one case I get

first.py:47: error: Need type annotation for "BADerived"  [var-annotated]
first.py:49: note: Revealed type is "def (*Any, **Any) -> first.B[[a_param_1: builtins.float], first.ADerived]"

In other case I get

second.py:7: note: Revealed type is "def (*Never, **Never) -> first.B[[a_param_1: builtins.float], first.ADerived]"