coverage combine can fail complaining about missing files

[ssbarnea]

Describe the bug
(WIP):
coverage==7.2.3

To Reproduce
How can we reproduce the problem? Please be specific. Don't link to a failing CI job. Answer the questions below:

1. What version of Python are you using?: 3.11
2. What version of coverage.py shows the problem? The output of coverage debug sys is helpful.
3. What versions of what packages do you have installed? The output of pip freeze is helpful.
4. 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.
5. What commands did you run?

py: commands[2]> sh -c 'coverage combine -a -q --data-file=.coverage .tox/.coverage.*'
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.35703.363167-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.46376.762932-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.46844.059134' doesn't seem to be a coverage data file: 
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.47064.452252' doesn't seem to be a coverage data file: 
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.47341.075353' doesn't seem to be a coverage data file: 
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.48144.272428-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.48380.995178-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.54852.820997-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.55378.251736' doesn't seem to be a coverage data file: 
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.56278.178380-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.56447.276199-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.59807.597105' doesn't seem to be a coverage data file: 
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.73574.478229' doesn't seem to be a coverage data file: 
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.76121.299390-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.76270.743970-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.76283.235127-journal': file is not a database
  data._warn(str(exc))
/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.76588.477104-journal': file is not a database
  data._warn(str(exc))
Traceback (most recent call last):
  File "/Users/ssbarnea/c/a/ansible-lint/.tox/py/bin/coverage", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/cmdline.py", line 974, in main
    status = CoverageScript().command_line(argv)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/cmdline.py", line 690, in command_line
    self.coverage.combine(data_paths, strict=True, keep=bool(options.keep))
  File "/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/control.py", line 807, in combine
    combine_parallel_data(
  File "/Users/ssbarnea/c/a/ansible-lint/.tox/py/lib/python3.11/site-packages/coverage/data.py", line 148, in combine_parallel_data
    with open(f, "rb") as fobj:
         ^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: '/Users/ssbarnea/c/a/ansible-lint/.tox/.coverage.py.m1.77285.627909-journal'
py: exit 1 (7.07 seconds) /Users/ssbarnea/c/a/ansible-lint> sh -c 'coverage combine -a -q --data-file=.coverage .tox/.coverage.*' pid=15473

Expected behavior
No failure.

Additional context

Based on my tests, its seems that some .coverage...-journal leftover files from incomplete coverage runs can cause this failures.

In order to improve the UX, I would recommend changing coverage behavior to ignore these leftover files or even to remove them if found. In my particular case I added an extra rm step to my tox file. WDYT?

[nedbat]

Hmm, I wonder why there is a *-journal file lying around? That sounds like a race condition of some sort. Do you know what is causing that? We could ignore those files, but it seems like a warning signal of some kind.

[ssbarnea]

apressing ctrl-c during previous test run? Maybe we could include a cleanup before starting?

[nedbat]

#1567 is the same problem, with a fix, but I wish I understood the cause better.

[ssbarnea]

@nedbat While I was not able to reproduce the same error, I discovered something new. Apparently, on macos in particular the total reported coverage is lower (random between two runs). See https://github.com/ansible/ansible-lint/actions/runs/5014693902/jobs/8989285980?pr=3462 -- job failed on macos-py311 due to coverage being 88 instead of minimum of 93. It happened at least twice in the last couple of days and alway on the macos one.

I wonder if some of the recent changes or this bug might have anything to do about it.

I do not remember seeing this bug before switching to 7.2.5 and it never happened locally, only on GHA.

[felippemr]

I think have a similar issue. When I split tests using circle ci and run coverage for each split group individualy, coveragepy complains with:

/usr/lib/python3.9/site-packages/coverage/data.py:166: CoverageWarning: Couldn't use data file 'coverage_2.xml': file is not a database
  data._warn(str(exc))
Couldn't combine data file coverage_2.xml: Couldn't use data file 'coverage_2.xml': file is not a database

I have many files prefixed with coverage_ and the number that comes after it is the split group.

[nedbat]

This is fixed in 7c25ba0, and journal file writing is disabled on 3.12 in 8624ce9.