Haskell updates: GHC 9 and Stackage 19

[Lars-Dominik Braun <lars@6xq.net>]

Hi everyone,

it’s time to update our Haskell environment – again. GHC 9.0 has been
out for a while and Stackage updated its LTS distribution to version 19
recently, providing a new set of packages for GHC 9.0.

Additionally there some issues/patches regarding haskell-build-system
and the importer, which we should address in this cycle:

- build: haskell-build-system: Support packages w. multiple libraries
  https://issues.guix.gnu.org/54729
  (applied to wip-haskell, fixes https://issues.guix.gnu.org/52152)
- build-system: haskell: Add ‘package-with-explicit-haskell’ procedure
  https://issues.guix.gnu.org/51655
  (probably a world rebuild including Python, maybe core-updates?)
- import: hackage: `elif` conditionals not supported
  https://issues.guix.gnu.org/54752
  (needs patch)
- guix import hackage does not support build-tools and build-tool-depends stanzas
  https://issues.guix.gnu.org/49320
  (?)

Are there any other issues that need to be adressed that require a
world rebuild?

To ease the update it would also be very nice if the importer could
update the entire package definition, including inputs and arguments
(#:cabal-revision, in particular). Is that somehow possible? I will not
be able to perform the upgrade if it is not possible. The amount of
manual work required is too much for me.

Thanks,
Lars