feature: have a `menhir.ocamlbuild` ocamlfind package that `-use-menhir` relies on

[gasche]

I'm a bit frustrated with the state of menhir support in ocamlbuild: there are many more options in the tool than there were when it was first implemented, and some of them require non-trivial choices from the build system point of view (in particular the way .messages files are updated). I would be happy to provide a separate menhir plugin for ocamlbuild, but this seems to conflict with the -use-menhir option that is supposed to already do the job.

An idea I had not considered before is to indeed separate the plugin as a menhir.ocamlbuild plugin (distributed separately from menhir itself, and separately from ocamlbuild), but have hardcoded support for it in plugin.ml that makes sure to link this plugin whenever -use-menhir is passed, or give an error message if the plugin is not installed (we could also just do the minimal service of changing the command name to menhir, and emitting a warning instead of an error, to limit breakage among users that don't know about ocamlfind/opam). We would have two different codepaths for this linking depending on whether -use-ocamlfind is used, but I think it should be fine.

I think that this could achieve minimal disruption for most users, while simplifying and improving our relation with respect to Menhir-side changes.

[dbuenzli]

I think your plan is overly complex. Make the plugin, advertise it and deprecate -use-menhir at the same time. Then kill the -use-menhir in the subsequent version.

[whitequark]

I agree with @dbuenzli, assuming the plugin still works in old ocamlbuild versions there is no downside to kicking these rules out of ocamlbuild.

[disteph]

I'm just adding my +1 in support of this wishlist item. Is it possible, with use-menhir or with a new alternative for it, to let the menhir invocation (on Ocamlbuild's command-line or in the _tags file) accept a string of menhir options that would be blindly passed to the menhir call, so that Menhir can keep on evolving without having to update Ocamlbuild's Menhir tags?