Drop support for GHC 7.x and hvr/ppa install method

[andreasabel]

I'd say the time is ripe now for dropping installation support for GHC 7.

• Stop using ppa:hvr/ghc haskell/actions#133

[MaximilianAlgehed]

We still try to support old versions of GHC running on ubuntu 20.04 in QuickCheck and I'm working on trying to migrate our CI to haskell-actions/setup instead of the current haskell-ci generated CI script. However, this would make it impossible for me to do so.

[andreasabel]

Thanks for the feedback, @MaximilianAlgehed.
There is no rush in dropping GHC 7 now.
Do you have a policy how long you want to support GHC 7? (GHC 8.0 was released in May 2016, so that is becoming 8 years soon.)

At some point, GHA will pull the plug on ubuntu-20.04, and that will be the end for the ppa:hvr/ghc install method. If they follow the same schedule as for 18.04, brownouts could already start in Fall 2024: https://github.blog/changelog/2022-08-09-github-actions-the-ubuntu-18-04-actions-runner-image-is-being-deprecated-and-will-be-removed-by-12-1-22/

[MaximilianAlgehed]

I think @nick8325 is best positioned to decide when / if to drop ghc 7 support. If we are forced to migrate away from ubuntu-20.04 I don't think we have the option to maintain ghc 7 support in any meaningful way in ci. However, we do still support hugs so it would be sad to have to drop ghc 7 support so soon.

One option when we loose ppa:hvr/ghc is to "simply" download and install from haskell.org - assuming that executable keeps working with newer versions of e.g. lib-c. Would it be an option for haskell-actions/setup to support an install method like that?

[andreasabel]

Would it be an option for haskell-actions/setup to support an install method like that?

I think binary installs should be handled by ghcup; I do see not point in duplicating this feature here. Maybe you could add a release channel to ghcup that handles legacy GHCs on certain machines. (E.g. macOS only properly supports GHC 7.10 and up.)