TRIO100 false positive with an async CM (already fixed in flake8-trio - ruff is out of date)

[mikenerone]

Ruff 0.2.1

The following snippet illustrates a TRIO100 false positive when the scope contains an async context manager. Note that this bug is already fixed in flake8-trio (in python-trio/flake8-async/pull/176 I think). It's probably worth checking whether ruff needs to port other more recent fixes, as well.

from collections.abc import AsyncGenerator
from contextlib import asynccontextmanager

import trio

@asynccontextmanager
async def a_cm_can_start_a_nursery() -> AsyncGenerator[None]:
    async with trio.open_nursery() as nursery:
        nursery.start_soon(trio.sleep_forever)
        yield

async def main() -> None:
    # ↓↓↓↓↓ TRIO100 A `with trio.CancelScope(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
    with trio.CancelScope() as cancel_scope:
        async with a_cm_can_start_a_nursery():
            try:
                pass # Pretend there's some real logic.
            finally:
                # Body exiting. For all I know, the CM has nursery like this one does. If so, I need it cancelled.
                cancel_scope.cancel()

trio.run(main)

The above is a valid case for a cancel scope with no explicit awaits in the body. Without the cancel(), this hangs forever instead of exiting.

Note: if I put an async for in the try:, it's even more obvious that this yields, but TRIO100 still triggers.

[charliermarsh]

Thanks, will fix this tonight.

[mikenerone]

@charliermarsh I missed #9855. It looks like you may have already fixed this in main.

[charliermarsh]

Wow, yeah, I fixed it this week and didn't even remember!

[charliermarsh]

Will be included in the next release.