[herd] Expose herd as a dune library

[fsestini]

This PR implements step 4 of the plan documented in issue #1782: it makes herd available as a dune library, herd_core, so that other OCaml tools in the repository can depend on its internals directly.

Note that the broader plan to make herd's core code properly library-like and client-agnostic is still work in progress. In other words, this PR does not claim to provide a polished or stable API, nor does it address all remaining issues and TODOs described in the aforementioned issue #1782.

That said, the API that herd does currently offer (mainly through its modules ParseTest and Top_herd) is already useful enough for other internal tools to take advantage of it. See, for example, my upcoming tool litmus2desc (#1903), which runs herd directly in OCaml via the herd_core library added here.

Since the proposed herd_core library is intended for internal use only (at least of now), I think it is reasonable to expose it now as an incremental step, while continuing the remaining refactoring work tracked in #1782.

Let me know your thoughts.

PS: This PR also updates herd/rc11.ml to use explicit namespacing for record field accessors. Adding the module to the wrapped herd_core library made the compiler report warnings 40 and 42 for various record accesses. The PR only adds explicit module names to those field accesses, it does not change any of the logic. As an aside, rc11.ml does not currently appear to be used anywhere in herd.

[HadrienRenaud]

Hi @fsestini, this looks good to me, I don't see any negative to this.

By curiosity, did you notice a difference in compilation time (from clean or just with small edits)?

[fsestini]

Hi @fsestini, this looks good to me, I don't see any negative to this.

By curiosity, did you notice a difference in compilation time (from clean or just with small edits)?

Thanks @HadrienRenaud . I did not felt a noticeable difference as I was developing, but did not measure it. I've now run a simple time measurement, both from clean. The difference seems mostly noise:

This PR:
dune build herd/herd.exe  136.25s user 26.95s system 509% cpu 32.016 total

master:
dune build herd/herd.exe  134.48s user 26.46s system 490% cpu 32.804 total

[psafont]

Are there any plans on having more opam metadata files on the top level? it might be worth adding (package herdtools7) if that's the case

[fsestini]

Are there any plans on having more opam metadata files on the top level? it might be worth adding (package herdtools7) if that's the case

Added: 92904d8

[relokin]

This is more of a question than a concern. Shouldn't lexConf_herd be part of the library? For example www also needs it. Is there any herd interface that wouldn't need it?

[fsestini]

Yes, you're right.

[relokin]

LGTM, thanks Filippo!