[Nix-dev] Haskell build failures (was: Zero Hydra Failures (ZHF) project)

[Daniel Bergey]

On 2014-08-08 at 15:41, Mateusz Kowalczyk <fuuzetsu at fuuzetsu.co.uk> wrote:
> On 08/08/2014 02:35 PM, Eelco Dolstra wrote:
>> Note the huge number of Haskell and Python packages.
>
> The problem with Haskell jobs as far as I can tell is that we often
> remove old versions of packages when ‘updating’. Consider something like
> QuickCheck 1.x: we update its dependencies in nixpkgs and the package
> now becomes forever broken because we haven't kept the old version of
> things and told QC to use that. QC 1.x is old so it's not reasonable to
> go back and make it work with new dependencies: upstream won't do it and
> everyone will probably use QC 2.x. If there are packages depending on
> 1.x then they should be updated instead.

From my random sample of broken Haskell packages this morning, I think
there's another problem.  Nix includes several versions of GHC, and
one of the few cases where we include multiple versions of a Haskell
library is when that library ships with GHC or Haskell Platform.  Eg, 10
versions of HTTP, 9 versions of GLUT.

We end up telling Hydra to build every version of the library against
every version of GHC, when what we actually want is to pick a library
version based on the GHC version.  (With maybe some overlap.)

I'd like to spend some time pinning down which versions work together.
Can someone point me at an example that specifies these conditions?

Thanks,
Daniel
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