Allow ocaml/opam-repository to be added to a opam-repositories without hash errors

[dra27]

Currently if you add ocaml/opam-repository to the opam-repositories field, e.g.

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

The installation of the compiler will fail with:

 #=== ERROR while compiling ocaml-config.3 =====================================#
  Bad hash for D:/.opam/repo/default/packages/ocaml-config/ocaml-config.3/files/gen_ocaml_config.ml.in

This is something which is already fixed in opam 2.1 (see ocaml/opam#3882). The proposed fix here works around the problem with the opam 2.0.10 binary from OCaml for Windows.

The problem is that the initial clone of the repository is checked out using Windows line-endings, which causes the hashing problem. The mechanism opam uses to update repositories means this would not happen on subsequent opam update instructions. The workaround here is that setup-ocaml ensures that core.autocrlf is temporarily set to input while adding the repositories (it then restores whatever setting either the runner or workflow had specified afterwards).

This shim can be removed once setup-ocaml adopts opam 2.2 for the Windows runners.

[smorimoto]

@dra27 I think it would be much better for us in the future if you could leave an explicit comment about removing shim once opam 2.2 is available. (You and I both input so many things into our brains every day that we could easily pass this up...)

[dra27]

I added a comment in the code, and I've put a post-release step on opam 2.2's release checklist

[smorimoto]

Thank you so much 🙂