TRIO100 false positive with an async CM (already fixed in flake8-trio - ruff is out of date) #9934
Description
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.