Status of old ghcs ci job

[jneira]

• Will be restored by Post remove ci templates #8000
• It is somehwat fragile: it needs a specific container with ubuntu xenial, a specific flavour for ghcs (-dyn)
• You cant use haskell-action+ghcup nor the default checkout gha
• We should decide when we will drop support for older ones progresively (re Overhaul CI to use ghcup and not a mixture of obsolete sources of GHC, etc. #7798)

[jneira]

We should decide when we will drop support for older ones progresively

That decission should depend of a agreement about a support window for ghcs at runtime, as that job tests old ghcs at runtime. Afaics i dont see any explicit policy of such support.

We have a limited support window for ghc versions used to build Cabal and cabal-install in the readme:

• https://github.com/haskell/cabal/blob/master/CONTRIBUTING.md#conventions
• The original rfc was RFC: Dropping build support for GHC < 8 #7531

Discussion about restoring the old ghcs job in the pr which removed it temporary:

• Avoid templating GitHub Actions workflow #7952 (comment)

//cc @emilypi @Mikolaj @fgaz