Test with ocaml-system

[kit-ty-kate]

Reopening a separate issue after #43 (comment) was closed

this feature is still desirable

[shonfeder]

Thanks! It would help us with prioritization if you could give a nut-shelled account of why we need this in the CI and how it would show up in the CI results. As it is, there are like 6 years worth of discussions across different PRs and issues to try comb through, and afaict none of them give a concise statement of how this work is meant to benefit opam repo's CI, at least not one that is clear to me given my limited context. Thanks in advance!

Something that would really help with prioritization is a remark on the impact of NOT having this feature in place currently.

[kit-ty-kate]

ocaml-system is one of the default OCaml compiler that people will encounter in the wild. People that simply install ocaml and opam through their system package manager will get it.

The limitations of ocaml-system (the installation of OCaml being split between /usr/... and the opamroot) are well known but not tested at all anywhere. So it seems reasonable to test it. The typical issues can in build-system themselves where they look at /usr/... for packages instead of the opamroot, or if the ocaml-system package itself if the substitute for the ocaml binary (which is a script in this context) gets broken.

[samoht]

Related to this, I've recently hit that bug locally recently:

#=== ERROR while installing zarith.1.14 =======================================#
# context     2.2.0 | macos/arm64 |  | [https://opam.ocaml.org#f302b6aaf01995b706f9b5a0a8fc2e6bb299eae8](https://opam.ocaml.org/#f302b6aaf01995b706f9b5a0a8fc2e6bb299eae8)
# path        ~/git/tagit/_opam/.opam-switch/build/zarith.1.14
# command     ~/.opam/opam-init/hooks/sandbox.sh install make install
# exit-code   2
# env-file    ~/.opam/log/zarith-29532-6d2ce3.env
# output-file ~/.opam/log/zarith-29532-6d2ce3.out
### output ###
# [...]
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/z.cmx
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/zarith_version.cmx
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/zarith.cmxa
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/z.mli
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/zarith_top.cma
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/big_int_Z.cmi
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/q.cmi
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/z.cmi
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/libzarith.a
# Installed /Users/samoht/git/tagit/_opam/lib/zarith/zarith.cma
# ocamlfind: /Users/samoht/.opam/default/lib/ocaml/ld.conf: Operation not permitted
# make: *** [install] Error 2

The ocamlfind installation runes used to be racy so the build/install steps were split at one point in the opam file of the projects that continues to use ocamlfind install (which I suspect Zarith do).