I am unhappy about turning this back on for all projects. I have not seen this coverage failure in other c-code projects. I wonder if there's a specific reason why the coverage data is not found (or not written).

Perhaps there is something just weird about persistent? tox -re coverage works on the master of BTrees (which has that commit applied) and on the config-with-c-code-template-4eec7859 branch of zope.i18nmessageid (which applies it).

I'll try to spend some time on that tomorrow. There has to be a way to get this working for persistent without usedevelop. It works for other similar packages as well.

A little research has shown that this is not a common issue for c-code projects. It affected persistent because that uses custom coverage configurations that don't work (anymore). This is fixed in zopefoundation/persistent@149c88e. The test failures on Windows are unrelated, those come from yet another setuptools incompatibility and I will fix that within the configuration template.

@dataflake Thanks for figuring that out! I broke my brain on it yesterday.

@dataflake I spoke a little too soon: tox -re coverage still fails the same way in persistent on master after the change you applied in 149c88e.