ci: test suite failing in main branch

There is a test failure in the main branch.

tests/unit/contentproviders/test_git.py test test_submodule_clone fails because its the first to request the fixture repo_with_submodule, which in turn fails to setup.

https://github.com/jupyterhub/repo2docker/blob/e0d5b9bb63a7908b4edd9e6b6d5ca51d47fd9aaf/tests/conftest.py#L124-L157

I’m not sure whats going on yet, help resolving this greatly appreciated as it distracts review of PRs.

[minrk]

For the most part, I’ve found that git clone --recursive successfully clones any repo, whether it’s got submodules or not. I’m not aware of anything not working in repo2docker, and the failure here is only because we set up an unrealistic repo with local-file references in submodules, which is insecure. “Real” submodules should still work fine, I think.

[betatim]

Unrelated to the CI failure, but related to “can we remove submodule support?”: In my opinion submodules are only useful for a very niche set of use-cases, but are used a lot more often than that. They bring a whole host of subtle challenges with them, for users and for repo2docker maintainers. I think we started out with “no submodule support” because of that, but then added it because people who need/want submodules were vocal about it. And I think even with the status quo there are submodule use-cases that don’t work properly in repo2docker?!

Maybe this bit of history is useful in deciding what to do about sub-module support in the future.