Rewrite gen_link_flags in OCaml

[Halbaroth]

As we noticed yesterday, Dune does not call an appropriate shell with the stanza (run ...) on
Windows. I tried (run bash ...) but I ran into issues with absolute and relative paths. Another solution consists in using
the stanza (enabled_if ...) to prevent Dune from calling the script on Windows. This solution is ugly because the mini-language for actions in Dune is really limited.

Finally, I rewrite the simple script in OCaml. This solution works fine!

I tested the workflow here: https://github.com/Halbaroth/alt-ergo/actions/runs/10162591930

[bclement-ocp]

This is not a request to use it (I think the script is simple enough this way) but did you look at https://dune.readthedocs.io/en/stable/dune-libs.html#configurator ? I believe it is supposed to provide facilities to do this sort of things.

[bclement-ocp]

There should be no need to promote this executable, let's not clutter the source directory.

[bclement-ocp]

I believe this is not needed and you can just use ./gen_link_flags.exe (or %{bin:gen_link_flags}) in the run command below

[Halbaroth]

My first attempt was:

(executable
  (name gen_link_flags)
  (libraries unix fmt stdcompat)
  (modules gen_link_flags))

(rule
 (with-stdout-to link_flags.dune
  (run %{bin:gen_link_flags} %{env:LINK_MODE=dynamic} %{ocaml-config:system})))

But it does not work. It works if I add public_name and package in the executable stanza. I do not want to distribute this script. This is the only workaround I found to call gen_link_flags without shipping it in an opam package. I also add until-clean for this purpose.

[bclement-ocp]

Right, %{bin} scope is for installed executable — the following should work with no promotion tho:

(executable
  (name gen_link_flags)
  (libraries unix fmt stdcompat)
  (modules gen_link_flags))

(rule
 (with-stdout-to link_flags.dune
  (run ./gen_link_flags.exe %{env:LINK_MODE=dynamic} %{ocaml-config:system})))

[bclement-ocp]

It doesn't look like we use cmdliner, it should not be a dependency.

[Halbaroth]

I wrote a previous version with cmdliner but it was a bit over-engineering. I forgot to remove the dependency.