mark packages as broken

[avsm]

Discussed with @AltGr the possibility of repository triagers marking a package as broken, with a reason and a constraint. e..g broken : "needs newer clang" {os = "darwin"}

CI can use this to triage and move on - right now we need to block on doing a fix which is sometimes difficult on the spot and/or simply not possible (if a depext is missing).

I could imagine something around:

• making broken packages not installable by default
• having a flag to allow forcing the broken package to install (e.g. for pinning/testing a fix)
• listing broken packages (so we can ask people to help fix them)

This would help us design a workflow for making it easier for external contributors to give us fixes for problems, and also for CI to semi-automatically mark packages as known-broken. The CI could also verify that broken packages are in fact still broken.

[hannesm]

(I appreciate an explicit broken: marker, and used available: [ ocaml-version = "0" ] to mark packages uninstallable (e.g. some mirage-net-xen versions which have security issues, https://github.com/ocaml/opam-repository/blob/master/packages/mirage-net-xen/mirage-net-xen.1.1.1/opam#L18 -- this works fine with earlier opam (at least 1.2))

[AltGr]

available: false would have worked too :)
Or even available: broken, abusing the handling of undefined variables... That way you would get:

Your request can't be satisfied:
  - unmet availability conditions: broken

Even available: !(broken-needs-newer-clang & os = "darwin") would work.

DISCLAIMER: I am not advising the above, just saying that it's possible. And the main point here is easier triaging and automated handling, which this hack would clearly not help with. A broken: field seems a good idea.