Fix incompatibility with OCaml 5.4

[xavierleroy]

The type of long idents changed in OCaml 5.4. Instead of building long idents by hand, use the Longident.unflatten API, which has been available since OCaml 4.06.

Fixes: #45

[xavierleroy]

CI failure is an OPAM failure:

[ERROR] Undefined filter variable with-dev in dependencies of dream-inertia.0.0.1

Huh?

[kit-ty-kate]

This is an issue in opam-repository. I've reported it upstream in ocaml/opam-repository#27955 and it'll be fixed at some point.

However your CI system uses --strict which isn't made for this kind of use and can break easily. I've opened a PR to fix this in #47 which uses opam lint instead to check that the opam file is well formed.

[kit-ty-kate]

I believe the CI can be relaunched. I'm happy to handle the release on opam-repository once a tag is available for me to use if you don't have the time for that.

[xavierleroy]

This PR doesn't work, because the Longident module is hidden in the toplevel, so loading num_top fails. I'm not seeing an obvious workaround at this point.

[xavierleroy]

I took inspiration from ZArith and used ugly string evals. It seems to work and should be compatible with all OCaml versions. The code definitely needs a review, if only to agree that there are no better ways to go about this.

[Octachron]

Another option would be to update the type of install_printer to take as an argument a type of longident with locations: Octachron/ocaml@8dcd3d8 . With this changes and type-directed disambiguation, num doesn't need to be patched, and I expect this would be the same for toplevel scripts that install printers.

Otherwise, going through Toplevel.parse_toplevel_phrase seems like the simplest path to use the Longident module without referring to it explicitly. Going through eval is not strictly necessary through:

let parse_longident s =
  let install = Format.asprintf "#install_printer %s;;" s in
  let l = Lexing.from_string install in
  match !Toploop.parse_toplevel_phrase l with
  | Parsetree.Ptop_dir { pdir_arg=Some ({pdira_desc=Pdir_ident id}); _ } -> id
  | _ -> assert false

I am not sure if this is a less hackish solution however.

[xavierleroy]

For reference: Sherlocode shows 10 uses of dir_install_printer (https://sherlocode.com/?q=Topdirs.dir_install_printer). I suspect several of these uses are broken by the change to the longident type.

My gut feeling is that there's no point in adding locations to each component of a longident and that it is still time to revert this change in OCaml 5.4. Otherwise, I'm sort of OK with the proposed fix to Num, based on string eval, and I'll let others deal with the other failures.

[Octachron]

Looking at those ten users:

• 3 uses Longident.parse and are unaffected by the change
• 1 uses compiler-libs heavily and need to patched for each new version any way
• 1 is a copy of num
• 2 are broken by the change (one even segfault due to the change!), but the corresponding libraries are no longer distributed as far as I can see.

[xavierleroy]

Thanks for looking at these other uses of dir_install_printer.

In accordance with @Octachron , I'm going to merge the current PR and make a release of Num, so as to unblock the OPAM packages for OCaml 5.4.