Iteration exhaustion branch of asynchronous for loop is shown as missing

[manueljacob]

import asyncio

async def async_gen():
    yield 1

async def async_test():
    a = None
    async for i in async_gen():
        print(i)

asyncio.run(async_test())

I’ve run coverage run --branch script.py with Python 3.9.2 + coverage 5.5 and from Git commit 40c87e0.

I would expect that no line or branch is shown as missing, however branch 8->exit is shown as missing.

Similarly, when using the following script, branch 8->11 is shown as missing, although running the script fails at line 11.

import asyncio

async def async_gen():
    yield 1

async def async_test():
    a = None
    async for i in async_gen():
        print(i)
    else:
        zzz

asyncio.run(async_test())

When removing the a = None line or running on PyPy3.7 v7.3.4, no line or branch is shown as missing.

Also, with the following synchronous version, no line or branch is shown as missing:

def sync_gen():
    yield 1

def sync_test():
    a = None
    for i in sync_gen():
        print(i)

sync_test()

[jorants]

Came across the same problem when using coverage on beanie which uses a lot of async for loops. Might be related to #1176

[nedbat]

I added a test for this on a branch, and it seems to do the right things for these Python versions: 3.7.10, 3.8.10, and 3.10.0b3.
It doesn't trace correctly on Python 3.9.5.
So this seems like a problem in Python 3.9. Can you confirm?

[jorants]

I tried the same tests from beanie on 3.8 and there it does seem to work correctly, i can not easily test the others right now.

[nedbat]

I've reported this against CPython https://bugs.python.org/issue44621.

[nedbat]

This CPython bug has been fixed in 3.9.7.