Better diagnostic for use of unbound ParamSpec

[second-ed]

Summary

ty not identifying when the first arg of a Callable is ParamSpec when within a bound TypeVar

The first argument to Callable must be either a list of types, ParamSpec, Concatenate, or ...

Playground

main.py

from collections.abc import Callable
from typing import ParamSpec, TypeVar

P = ParamSpec("P")
C = TypeVar("C", bound=Callable[P, object])

causes ty to complain:

The first argument to `Callable` must be either a list of types, ParamSpec, Concatenate, or `...` (invalid-type-form)

Version

No response

[AlexWaygood]

Thanks for the report! I think ty is correct to issue a diagnostic here, since P is unbound in this context. However, the diagnostic message is not great right now. It would be better for us to say "P is unbound" or "TypeVar bound cannot be generic" rather than "The first argument to Callable must be either a list of types, ParamSpec, Concatenate, or ...".

[ratijas]

Not sure if this is the same underlying issue, but looks similar enough, so I'll throw in my five cents.

This wrapper makes ty unhappy, because it thinks the task is somehow a coroutine of Unknown return type, rather than R:

import asyncio
import functools
import typing as t

P = t.ParamSpec("P")
R = t.TypeVar("R")


def make_sync(func: t.Callable[P, t.Awaitable[R]]) -> t.Callable[P, R]:
    """
    Wrap an async function so it can be called synchronously.

    See: https://github.com/pallets/click/issues/2033
    """

    @functools.wraps(func)
    def wrapper(*args: P.args, **kwargs: P.kwargs) -> R:
        task = func(*args, **kwargs)
        return asyncio.run(task)

    return wrapper

Argument to function `run` is incorrect: Expected `Coroutine[Any, Any, Unknown]`, found `Awaitable[R@make_sync]`ty[invalid-argument-type](https://ty.dev/rules#invalid-argument-type)

Other than that, VS Code plugin Pylance, when hovered, correctly reports task in a popup as (variable) task: Awaitable[R@make_sync]

[dhruvmanila]

@ratijas I think your issue is different but it seems more an issue in typeshed instead because with 3.14 the docs says that both asyncio.run and asyncio.Runner.run can accept any awaitable object (https://docs.python.org/3.14/library/asyncio-runner.html#asyncio.run) but the PR (python/typeshed#15046) only updated asyncio.Runner.run. I think we need to update typeshed here.

Edit: I've opened python/typeshed#15807