Jruby build is broken. This is an attempt to fix it.

Well, "fix" is one way to put it... 😆

I think the root cause here is that our code is not really thread safe, and that's why JRuby (which is much more concurrent than the evil-GIL-threaded MRI) triggers these errors.

I think we should work on fixing this; I don't think disabling CI on JRuby is the right way forward. (I looked briefly at the code in base.rb right now, and couldn't find any immediate non-threadsafe part.)

The error:

Error: test_git_init_bare(TestThreadSafety): Git::GitExecuteError: git '--git-dir=/tmp/d20180328-6779-88i76v/.git' init '--bare'  2>&1:fatal: GIT_WORK_TREE (or --work-tree=<directory>) not allowed without specifying GIT_DIR (or --git-dir=<directory>)

...indicates that something goes wrong; it does specify the --git-dir but git still complains about this.

I read this SO thread but I couldn't see the GIT_WORK_TREE variable being set on the Travis machines.

I completely agree that we need to fix Jruby, but we also need to get the huge backlog of PRs merged in, and a temperament master build really won't help.

That I can agree with.

I suggest we take it out of the build on master, and spin up a branch along side which automatically merges master, but has jruby enabled, so that we can see what's going on.

The easiest way for now is probably to allow JRuby to fail: https://docs.travis-ci.com/user/customizing-the-build/#Rows-that-are-Allowed-to-Fail

If we do it like that, I think I can live with it for the time being; we will still see it if we look closely, but it won't mark everything as red on GitHub. Thanks for the effort btw!

I wasn't aware of the allow failures functionality! I've implemented that- I agree its much neater.

I've also raised issue #358 to track the fixing of jruby and added it to the top of the backlog.