[Nix-dev] Our Haskell setup no longer works with GHC HEAD/soon 7.10

[Peter Simons]

Hi Mateusz,

 > If you build the existing (outdated) GHC HEAD expression from nixpkgs
 > then you'll find that GHC itself works fine. The problem is that it no
 > longer works for packages.

the haskell-ng branch of my repository [1] has full support for GHC 7.9.x
and beyond.

Our current cabal builder generates a package database file the way it
used to be done with GHC 6.10. We do this precisely so that the builder
works with that older compiler version, and all newer GHCs up to and
including 7.8.3 dealt with that database file just fine. It appears that
7.9.x dropped support for those database files, though. The newest
compiler expects the package database to come in the form of a
"packages.conf.d/*.conf"-style directory. Alas, the new builder uses this
approach and thus works fine with the current GHC HEAD snapshot.

I also bumped the snapshot version in the haskell-ng branch and I'll port
those updates back to 'master' soon. I probably won't port the changes to
the Cabal builder back to 'master', though. Instead, I'd rather move
forward finalizing the new code, which is much nicer, IMHO.

So, to cut a long story short: if you want to mess with ghc-HEAD, you need
the haskell-ng branch. By the time 7.10.x comes out, though, our 'master'
branch will support it just fine.

Best regards,
Peter

[1] https://github.com/peti/nixpkgs