Test packages on the full range of supported OCaml versions

[craigfe]

Test packages on the full range of supported OCaml versions

[talex5]

This might be easier:

If a package's opam file contains an explicit constraint on the version of OCaml then:

• Exclude it from non-matching versions
• Force it to be included for matching versions (complain if not)

[craigfe]

If a package's opam file contains an explicit constraint on the version of OCaml then:

* Exclude it from non-matching versions

* Force it to be included for matching versions (complain if not)

I'm not sure I like the idea of adding artificial constraints in .opam files purely to signal intention to the CI – it's not easy to check when / if it's possible to relax those constraints – but it's definitely easier to implement and clearly better than the prior approach of replicating this info in config files. I'd be happy with this as a solution 🙂

[dra27]

Given the potential for stopping testing a version without realising it, might it be an idea to be stronger and actually require a version constraint on ocaml?

[dra27]

So if you have no constraint on OCaml, then your package should be testing on all supported versions, and either the lint or analyse phases will fail if packages aren’t installable in a given version

[talex5]

Given the potential for stopping testing a version without realising it, might it be an idea to be stronger and actually require a version constraint on ocaml?

Yes, I've been wondering about that too.

My only concern is that sometimes a package is temporarily uninstallable on a new compiler release due to missing dependencies (e.g. Lwt not available on OCaml 4.12). We don't want to encourage people to go around adding ocaml < 4.12 constraints everywhere while that's being fixed.

But for lower bounds at least it seems fine. So if I say ocaml >= 4.02 then it must work with 4.02.

[avsm]

This is also an issue for Lwt now, since lwt_ppx is 4.04 only, but the rest of the opam packages should build on 4.02 but aren't being tested.