More-helpful typing errors with Generics and Callables

Feature

Taking into consideration the following code (using mypy==1.4.1), the error messages are not very useful in debugging the problem. I have included the Pyright error message for comparison:

"""A test pipeline"""
from __future__ import annotations

from typing import Callable, Generic, TypeVar

from pydantic import BaseModel

from filter_base.filters.base_filter import BaseFilter

ModelT = TypeVar("ModelT", bound=BaseModel)


class TestFilter(BaseFilter, Generic[ModelT]):
    """A filter for loading a JSON file."""

    def __init__(self, model_type: type[ModelT]):
        """Test filter."""
        self.model_type: type[ModelT] = model_type

    def output(self) -> ModelT:
        """Output the loaded model"""
        return self.model_type()

    def input(self, obj: ModelT) -> None:
        """Input the model"""
        pass


T = TypeVar("T")


def connect(
    connect_signal: Callable[[], T],
    connect_slot: Callable[[T], None],
) -> None:
    """Connect a signal to a slot"""

    # TODO: this is a bit silly - we're just immedicately calling the signal/slot
    # however - it'll do for the purposes of type checking
    connect_slot(connect_signal())


class SimpleModel(BaseModel):
    """A simple model"""

    a: int
    b: str


class SimpleModel2(BaseModel):
    """A simple model"""

    c: int
    d: str


def main() -> None:
    a = TestFilter(SimpleModel)
    b = TestFilter(SimpleModel2)

    connect(a.output, b.input)

The diagnostics from mypy and Pyright are as follows (error is on the final line of code):

Diagnostics:
1. mypy: Cannot infer type argument 1 of "connect" [misc]
2. Pyright: Argument of type "(obj: SimpleModel2) -> None" cannot be assigned to parameter "connect_slot" of type "(T@connect) -> None" in function "connect"
     Type "(obj: SimpleModel2) -> None" cannot be assigned to type "(SimpleModel) -> None"
       Parameter 1: type "SimpleModel" cannot be assigned to type "SimpleModel2"
         "SimpleModel" is incompatible with "SimpleModel2" [reportGeneralTypeIssues]

Pitch

Having the error messages of mypy more in-line with Pyright's reporting would mean that it is not essential to use Pyright's typechecking system when developing these sorts of generic systems.

Commencez par reproduire l’exemple Python fourni avec mypy 1.4.1 et comparez son diagnostic final avec la sortie de Pyright affichée dans l’issue. Le travail est terminé lorsque mypy explique l’argument Generic Callable incompatible avec des détails de type tout aussi exploitables ; l’issue n’indique aucun fichier source ni test à cibler.