[Nix-dev] Haskell build failures

[Peter Simons]

Hi guys,

I've modified hackage4nix [1] to use the following policy for our
Haskell packages in Nix:

 | hackage4nix: disable Hydra builds for all "old" Haskell packages
 |
 | Old means that we have a newer version in Nixpkgs already. If there
 | is a reason for the old package to still exist, i.e. because some
 | other package is still referring to it, then Hydra will still build
 | the package as a dependency, but we won't want to build old packages
 | on their own right.

This change reduced the number of Hydra errors greatly. Further efforts
are necessary, though: see my other message from a few minutes ago.

Best regards,
Peter

[1] https://github.com/NixOS/cabal2nix/commit/e82ffbf303150c9121c426f6ff4c9d8fe41470dc