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Branch coverage missing in `async for` loop w/ `break` (CPython 3.10.2)
Describe the bug
When an async for loop contains a conditional break (or return) from the loop, it manifests as missing branch coverage under CPython 3.10.2. The branch is correctly covered under CPython 3.8.x.
To Reproduce How can we reproduce the problem? Please be specific. Don't link to a failing CI job. Answer the questions below:
-
What version of Python are you using? CPython 3.10.2
-
What version of coverage.py shows the problem? The output of
coverage debug sysis helpful.coverage_version: 6.3.1 -
What versions of what packages do you have installed? The output of
pip freezeis helpful. Onlycoverage. -
What code shows the problem? Give us a specific commit of a specific repo that we can check out. If you've already worked around the problem, please provide a commit before that fix. Suppose there are two files in a directory,
test.pyand.coveragerc, respectively:
import asyncio
class CoverMe:
def __init__(self, number):
self._number = number
async def _async_range(self):
for n in range(self._number):
yield n
async def do_something(self):
accumulated = 0
async for n in self._async_range():
accumulated += n
if accumulated > 10:
break
return accumulated
async def main():
print(await CoverMe(1).do_something())
print(await CoverMe(3).do_something())
print(await CoverMe(10).do_something())
if __name__ == '__main__':
asyncio.run(main())
[run]
branch = True
[report]
show_missing = True
What commands did you run? Inside the same directory with the two described files, run the following commands:
$ coverage erase
$ coverage run test.py
0
3
15
$ coverage report
Name Stmts Miss Branch BrPart Cover Missing
-----------------------------------------------------
test.py 20 0 10 2 93% 16->14, 28->exit
-----------------------------------------------------
TOTAL 20 0 10 2 93%
Expected behavior Repeating the same steps on CPython 3.8.x yields:
Name Stmts Miss Branch BrPart Cover Missing
-----------------------------------------------------
test.py 20 0 10 1 97% 28->exit
-----------------------------------------------------
TOTAL 20 0 10 1 97%
... which illustrates that I didn't bother to try importing this module as opposed to running as the main script. But the branch is now covered as expected.
I am also seeing this with async with statements, when they contain a branch within the block. On Python 3.10.2 and coverage 6.3.2
I think this is a CPython bug. I've written a report here: https://github.com/python/cpython/issues/93061
I think this is a CPython bug. I've written a report here: python/cpython#93061
The fix is on CPython 3.11 and 3.10. There's no backport for 3.8.
