run --append doesn't create coverage file

[nedbat]

Originally reported by Mattijs Ugen (Bitbucket: akaidiot, GitHub: akaidiot)

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We're using something like coverage run --append --source module_name py.test tests-folder/ to run unit tests with coverage. For multi-python support, this line is run with both python2.7 and python3.4 from tox. Tox makes sure COVERAGE_FILE is set to a location that suits our build env.

This has worked great for a while, but today our versionless dependency on coverage broke this, complaining with the following error twice (for both used python versions):

Couldn't combine from non-existent path 'coverage/file'

The folder exists (file name is fictional), coverage.py 3.x created the file if it didn't exist, 4.0 breaks when it doesn't. Touching the file beforehand doesn't help; an empty file is an invalid coverage data file.

Command coverage html subsequently fails because there's no data to report.

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I'm not too familiar with the current issues and sources for coverage.py, it could have something to do with #220, but I can't currently find an issue that is identical to our problem right now :)

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• Bitbucket: https://bitbucket.org/ned/coveragepy/issue/392

[nedbat]

A definite regression, thanks for the bug report. This will be fixed shortly.

[nedbat]

Fixed in 8e9fd5121aae (bb)

[nedbat]

Original comment by Mattijs Ugen (Bitbucket: akaidiot, GitHub: akaidiot)

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Took some effort to insert the current master into our build, but I can confirm this fixes our issue; thank you sir :)