conf-postgresql - update depexts package name for macos + homebrew (#23912)

[haochenx]

• this should fix conf-postgres depext needs to be updated for homebrew #23912.

[haochenx]

It seems that postgres installation via brew itself was successful, but since the installed packages (namely, postgresql@15) is a so called "keg-only" formula, binaries that come with the package are not exposed and the detection command (namely, pg_config) fails.

I'll investigate into options to work around this.

Log:

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
[ERROR] The compilation of conf-postgresql.1 failed at "pg_config".

#=== ERROR while compiling conf-postgresql.1 ==================================#
# context              2.1.5 | macos/x86_64 | ocaml-base-compiler.4.14.1 | pinned
# path                 ~/.opam/4.14.1/.opam-switch/build/conf-postgresql.1
# command              ~/.opam/opam-init/hooks/sandbox.sh build pg_config
# exit-code            10
# env-file             ~/.opam/log/conf-postgresql-90902-0cb162.env
# output-file          ~/.opam/log/conf-postgresql-90902-0cb162.out
### output ###
# [ERROR] Command not found: pg_config

[haochenx]

To "link" keg-only formulas, one can run brew link postgresql@15.

But I have no idea how to achieve that in the opam file.
@avsm @mseri @kit-ty-kate could you provide some advice?

[kit-ty-kate]

Sorry for the delay.

The behaviour by homebrew is a bit annoying to map in opam but we could do a couple of things:

• Mirror what we did for conf-libssl (https://github.com/ocaml/opam-repository/blob/9faf3dbf816f376733b73f3ed8832c4213db4a02/packages/conf-libssl/conf-libssl.4/files/homebrew.sh) and copy the binaries and libraries in the opam switch. However i feel a bit icky doing this for this package (it's fine for libssl as it is a central package and not much needs to be done anyway) because it's fairly brittle and not the best to maintain.
• Ignore the failures in CI as there isn't that many packages that rely on postgresql in opam and display a post-message inviting the user to call brew link manually

We could also try to bake this behaviour in opam as a more long term solution. Could you open a ticket in the opam bugtracker to at least get the conversation started? https://github.com/ocaml/opam/issues

For now i think we could go with the second solution with a message looking like that? What do you think?

[kit-ty-kate]

Thanks!

[haochenx]

Many thanks @kit-ty-kate! I have created the issue in ocaml/opam to kick off the discussion as advised.