ci: add basic windows CI

[zimbatm]

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[zimbatm]

@pjeby it looks like direnv has more Unixism (see rc_test.go). What is the recommended way to deal with paths in a cross-platform manner?

[pjeby]

Well, for that test you could just delete the tests and the function they're testing, which is what I did in my WIP because the rootDir function is no longer used anywhere AFAICT. 😉

[zimbatm]

good point. any ideas why the rest of the tests are failing?

[pjeby]

The eachDir test is failing because / yields E:\ and E: as parents. (Well, at least on my machine, where the tests are running on E:.) It's a more-or-less reasonable outcome (though the meaning of E: and E:\ are subtly different). I've basically just been skipping that test while figuring out more important stuff.

I'll go ahead and tell you that there are a bunch of shallow failures of this sort elsewhere, like the use of cd -P making paths look wrong when you compare them even though they're actually equivalent. I've got workarounds for some of them, and a few commented out that just aren't going to pass (the empty-var ones) and I also have the symlink-changed test commented out for now as well.

These changes are all in my work tree for the attempt at fixing PATH, which I need to clean out and rebase now that so many other things are in.

[zimbatm]

Ok, it might make sense to pick my commits into your branch then. I will close this PR.