Be able to choose GHC to use, especially when working with Stackage snapshots?

[thomasjm]

This is a follow-up from the discussion on #1301.

I'd like to be able to set up dev environments using haskell.nix, but I would really like to use the vanilla GHC builds from Nixpkgs rather than the patched ones provided here.

This would be especially useful because haskell.nix seems to be the only tool around that reliably builds packages from Stackage snapshots. (Nixpkgs itself has about 5% of Stackage packages broken at the moment.) For example, I'd love to be able to build expressions like the following, but using a vanilla GHC.

haskell-nix.snapshots."lts-19.13".ghcWithPackages (ps: with ps; [aeson ...])

Is it possible to do this at the moment, or could it be made possible? I saw that there's a module option ghc.package which looks promising, but it's not clear to me whether I can use that with snapshots.XXX.ghcWithPackages. Thanks!

[shlevy]

@hamishmack Is there any particular blocker to this? Do our patches to GHC's build affect the resulting package's interfaces to the packaging system or are they just ways to ensure we can build it?