Re-enable Appveyor CI

[craigfe]

Fix #963.

Currently a draft as there are no changes... The name of this branch should trigger Appveyor CI on master so we can se what problems currently exist.

[craigfe]

The CI jobs have now been queued for 30 minutes without starting.... Not a good start 😕

[samoht]

Still no sign of appveyor :-/ Maybe faster to add windows workers to the CI :p

[craigfe]

Passed after ~3 hours (with 45 minutes of actual CI time). That suggests that #963 might have fixed itself, but I'm not sure I want to add a 3 hour CI loop to the repository.

What does everyone else think?

[samoht]

A ~3h feedback loop is way too long. I'm thinking of ditching Travis support out instead to only keep the fast feedback loop.

Is there anything that Travis is doing here that ocaml-ci is not doing yet?

[craigfe]

Is there anything that Travis is doing here that ocaml-ci is not doing yet?

Yes. ocaml-ci does not install packages and run tests separately for each package as Travis does. This means that Travis ends up catching quite a lot of Opam metadata bugs that we would otherwise only find out about during the release: e.g. #1064.

[craigfe]

Closing this as it doesn't seem likely that we'll be re-adding AppVeyor any time soon. We can purge it completely once OCaml-CI has Windows support.