Provide motivation and clarity on Ubuntu version selection

[ysangkok]

As @liskin notes, the source still specifies bionic as the default, but it doesn't seem to be true.

In the source it seems that Xenial and Bionic are valid options: https://github.com/haskell-CI/haskell-ci/blob/5e5b27d74f90e73905c4f56f4aefe521f97879f0/src/HaskellCI/Config/Ubuntu.hs

Ok, bionic might not be the default, but it is still supported, right? I run

# oldproj is 'tested-with: GHC ==8.0.2'
$ haskell-ci-0.19.20240702 github oldproj.cabal --distribution bionic
*ERROR* bionicdistribution is not supported

This error message is different from if I specify some garbage string. So bionic is recognized but not supported? But not usable? If the point of recognizing it is to provide a better error message, it might make sense to make Haskell-CI link to @hasufell's comment on the github thread so that the user understands why Haskell-CI refuses to use Bionic and Xenial.

I saw this comment saying that the runsOn version isn't that important. But now that GitHub broke Haskell-CI with people using Ubuntu Bionic, it does seem kinda important. I don't understand the value in setting the default to 20.04 (Focal) now. Because if Haskell-CI now sets the Ubuntu to version Focal, I get the impression from the breakage of Bionic that those CI plans with Focal will get invalid earlier than if Haskell-CI used Ubuntu 24.04 (Noble). If Haskell-CI generated CI plans with Noble, those plans would stay valid for longer. That would provide a better user experience since people wouldn't need to upgrade Haskell-CI as soon as they otherwise would.

[phadej]

This issue makes me reconsider whether to publish haskell-ci on Hackage at all.

Many people use the master version, and I suggest you should too if you run into some problems with the version you have.

[endgame]

See also #739

Having it on Hackage makes it readily available in nixpkgs, which I find quite useful. How often does it change and need a new release?

[phadej]

How often does it change and need a new release?

https://github.com/haskell-CI/haskell-ci/commits/master/ looks like every other week at least