Switch to ocaml-opam/opam-repository-mingw

[dra27]

fdopen/opam-repository-mingw has not been receiving updates since November last year, following its previously announced deprecation.

opam 2.2 will add some required additional support for depext support on Windows and we (opam devs) expect to update opam-repository's compiler packages as part of this so that ocaml/opam-repository can be used without needing opam-repository-mingw, however we're suffering from a slight race condition for the next month or so with existing CI workflows still using fdopen/opam-repository-mingw and wanting to add ocaml/opam-repository in order to get new versions of packages which already work. Workflows which want new releases have been adding ocaml/opam-repository:

  opam-repositories: |
    opam-repository-mingw: https://github.com/fdopen/opam-repository-mingw.git
    default: https://github.com/ocaml/opam-repository.git

This has been causing some problems, the first of which was fixed in #647. The other problem is not in setup-ocaml but with opam-repository-mingw itself, which occurs when constraints in existing packages have to be updated because of new releases in opam-repository.

In order to deal with this, opam-repository-mingw has been forked to ocaml-opam/opam-repository-mingw solely for the purpose of applying constraint changes to it, and adding the missing 4.x compiler.

This is intended solely to bridge the gap between requiring both opam-repository-mingw, which is necessary at the moment while the compiler packages are being stabilised and an opam 2.2 capable of reliably using them isn't ready.

With this PR, default workflows will be unaffected, but other workflows can now use:

  opam-repositories: |
    opam-repository-mingw: https://github.com/ocaml-opam/opam-repository-mingw.git
    default: https://github.com/ocaml/opam-repository.git

[dra27]

This PR is a draft, because it's still being discussed and because updates to the infrastructure blog and ocaml.org to support it are also being drafted.

[dra27]

Cross-referencing ocaml-opam/opam-repository-mingw#4; this is ready to go.

[smorimoto]

Looks good to me!

[smorimoto]

@dra27 ocaml-variants.4.14.1+msvc64c doesn't seem to exist on sunset branch, but is it really enough to select the package without the "c" suffix (+msvc64)?

[dra27]

@smorimoto - it does exist? https://github.com/ocaml-opam/opam-repository-mingw/tree/sunset/packages/ocaml-variants/ocaml-variants.4.14.1+msvc64c ?

For the 4.14.1 packages, the "c" and non-"c" packages are identical. For all the previous releases, the "c" packages install much faster.

[smorimoto]

I misread the error. It's just that ocaml.4.14.1 is missing.
https://github.com/ocaml-opam/opam-repository-mingw/tree/sunset/packages/ocaml

[dra27]

Whoops! 😱 See ocaml-opam/opam-repository-mingw#5!

[smorimoto]

I'm a little relieved to know that even you make small slips 🙃