[Haskell-cafe] GHC update from 7.8.4 to 7.10.1 breaks 1, 500 packages in NixOS

[Erik Hesselink]

Hi Peter,

Useful information! Do you have any way to list only packages that
actually fail to build, as opposed to also listing packages where the
dependencies fail to build?

Erik

On Tue, Mar 31, 2015 at 1:14 PM, Peter Simons <simons at cryp.to> wrote:
> Hi guys,
>
> the Nixpkgs distribution [1] contains all of Hackage -- 7,898 packages at
> the time of this writing --, and we regularly build these packages with
> GHC 7.8.4 in our CI environment [2] running NixOS Linux. About 3,000 of
> these builds are disabled outright, because we know they won't succeed
> anyway (i.e. they have dependencies we cannot fulfill), but the remaining
> 5,000 packages compile successfully most of the time.
>
> Now, a few days ago, we created a separate build job [2] that compiles the
> same package set with GHC 7.10.1, and the result is interesting: with the
> newer compiler, approximately 1,500 packages are broken compared to the
> state with 7.8.4. A detailed list of broken packages can be found at [4].
>
> Keep in mind that those figures only approximate reality. For instance, we
> patch packages sometimes to make their builds succeed even though the
> pristine version would not, and so far much more effort has gone into
> fixing 7.8.4 builds than we spent on fixing 7.10.1 builds. Also, some
> packages may compile fine when you run "cabal install <foo>" on your
> workstation, but those builds may fail in the context of NixOS for
> whatever reason. If anyone were to repeat this experiment on Darwin,
> Windows, Ubuntu, or Red Hat, the results would be different from our
> numbers!
>
> Still, based on the information we have, it's probably fair to say that
> the GHC 7.10.1 update breaks approximately 30% of all Haskell builds that
> worked with 7.8.4.
>
> Best regards,
> Peter
>
>
>
> [1] https://github.com/nixos/nixpkgs
> [2] http://hydra.cryp.to/jobset/nixpkgs/haskell-updates
> [3] http://hydra.cryp.to/jobset/nixpkgs/haskell-updates-ghc7101
> [4] http://hydra.cryp.to/eval/304489#tabs-still-fail
>
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