[Nix-dev] Hydra: hashes change?

[Peter Simons]

Hi Vladimír,

 > I noticed that builders now often complain that hashes of some path
 > have changed, e.g.: https://hydra.nixos.org/build/6151693

I believe that this is an issue with GHC, not with Hydra. GHC cannot
guarantee that two identical builds of itself yield identical results:

  http://ghc.haskell.org/trac/ghc/ticket/4012

I'm not sure what happened exactly, but the fact that the only packages
to exhibit these issue are Haskell packages seems like a strong
indication that the bug mentioned above is at work. Maybe two build
slaves ended up building GHC 7.6.3 independently from each other, and
now we have two mutually incompatible GHC binaries lying around on the
Hydra cluster?

Take care,
Peter