Support GHC nightlies obtained via ghcup

[Bodigrim]

It would be great to be able to add a job testing GHC HEAD, presumably using a new ghcup feature to download nightlies: https://www.haskell.org/ghcup/guide/#nightlies

[phadej]

Apparently allow-failure doesn't work on GHA. Why did I think it does. Well, I'm not going to add GHC nightly support then yet, it should be possible to mark it as fallible.

actions/runner#2347

[phadej]

Wait, continue-on-error: ${{ matrix.experimental }} may work. Let me try that.

[phadej]

The action is marked as passing: https://github.com/haskell-CI/haskell-ci/actions/runs/5754864293, but the PR&commit are not #671

That is silly, and there is issue https://github.com/orgs/community/discussions/15452 about it.

[phadej]

This is also blocked on haskell/ghcup-metadata#149 (comment)

I totally agree artifacts from the nightly pipeline are not a thing anybody should rely on.

though in haskell-ci usage we would ever grab only the latest, which is hopefully nor purged too early. But apparently it happened at least once, that nightly pipeline was unstable enough, so the latest successful one was purged.

In other words, until GHC folks themself explicitly says (e.g. somewhere in GHC wiki) that the nighties can be used for (automated) testing (which I think they did, so I'm getting mixed messages), only then I'll reconsider using nightlies.

Until then I close this issue, as this is blocked indefinitely for now.

[hasufell]

Yes, nightlies have been a failure. GHC developers have not been able to provide a reliable infrastructure for them.

[chreekat]

so I'm getting mixed messages...

@phadej I should specify that my opinions I've shared here on this ticket only represent my personal views. :P I was unhappy with GHC Nightlies as soon as I heard about how they were implemented.

I've tried to improve the situation by better clarifying their (lack of) reliability. See https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-Status#2-ghc-nightlies.

Dashboard with status: https://grafana.gitlab.haskell.org/d/ab109e66-a8a1-4ae9-b976-40e2dfe281ab/availabilitie-of-ghc-nightlies-via-ghcup?orgId=2&from=1681980144490&to=1697791344490&refresh=1d