Run CI on Windows

[aantron]

Right now, it's not clear how to install this package ssl on a GitHub Actions Windows runner. This should be addressed and maintained in this repo for all downstream users. At the moment, it's not clear which version of SSL is even being linked against by
the environment created by setup-ocaml in GHA. For example, windows-latest at the moment appears to be windows-2022, with software list here, which includes OpenSSL 1.1.1w. Yet trying to build ssl on it fails with the issue in #155, so I suspect some other SSL from the setup-ocaml (Cygwin?) environment is at play. We encountered this in various forms during aantron/dream#337, but it really should be solved upstream, perhaps by having this repo's GHA .yml file be an example.

If the CI build for this PR fails on Windows, what would it take to get it to work?

Long-term, this repo probably doesn't need a full (OS x OCaml) build matrix, but just to include: one row for testing on Windows on a certain OCaml version.

[anmonteiro]

I think you still need something like runs-on: ${{ matrix.setup.os }}

[aantron]

@anmonteiro Could you take over this? The Windows build on 4.05 failed, but I don't think that's important -- we'd basically like to see the 4.14 and 5.x builds working in some way, 4.05 might have too much bitrot and it would be fine from Dream's point of view to just include: those in the matrix.

The actual 4.14 and 5.x builds were canceled, presumably by 4.05, but I also see a nix_build failure, which, I think, is outside the scope of this PR.

[aantron]

I've also opened ocaml/setup-ocaml#856 so that the setup-ocaml maintainers might comment on the environment this is all running in.

[anmonteiro]

I can try but I’m not sure how far I’ll get, since I don’t have access to a windows machine (or enough interest to spend significant time on it)

[anmonteiro]

@aantron you can now see the windows failure in CI:

[ERROR] depext is not a known command or plugin (package opam-depext.1.2.3 does not have the 'plugin' flag set).

I have no idea what this means or how to solve it since I don't use opam

[anmonteiro]

The failure now seems to reproduce what you reported. It would be interesting to understand how to get a newer libssl on windows.

[aantron]

Great, thank you! I left a comment about that in setup-ocaml. I'd wait for a response to that, and once that's clarified, we can merge this PR in this repo so that it also keeps checking that ssl is still installable in GHA, which should help everybody downstream.

[aantron]

Overextending. I would suggest merging this PR in this repo :) Thanks again!

[anmonteiro]

I'd be happy to merge this PR once we can get the build to be green