bug#19816: 'guix environment' always downloads all the outputs of dependencies

["Thompson, David" <dthompson2@worcester.edu>]

On Sun, Dec 20, 2015 at 5:34 PM, Ludovic Courtès <ludo@gnu.org> wrote:
> ludo@gnu.org (Ludovic Courtès) skribis:
>
>>From <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=19641#16>:
>>
>> There’s another problem, though.  When a dependency is a multiple-output
>> package, all its outputs are added to the environment, because
>> ‘package->transitive-inputs’ discards the information of which output is
>> needed.
>>
>> So for instance, both the ‘out’ and the ‘debug’ output of Coreutils end
>> up being downloaded and added to the environment, even though only ‘out’
>> is an input.
>>
>> Now, the problem is that ‘build-derivations’ can only build *all* the
>> outputs of the given derivation.  This could be worked around either:
>>
>>   1. by creating a “sink” derivation, for instance with
>>      ‘profile-derivation’, that could refer precisely to the output(s)
>>      needed; not ideal.
>
> David, I think you had started looking at doing exactly this.  Do you
> have a preliminary patch you’d like to post?
>
> I understand you may be busy preparing the Lisp Game Jam now and I
> wouldn’t want to distract you from that.  ;-)  If you have something to
> share, I’m happy to help start from there though (says the guy who sees
> its ‘guix environment’ pointlessly downloading “debug” and “doc” outputs
> again.)

The wip-environment-profiles branch has the code I've written thus
far.  I rebased it on master and resolved some conflicts in hopefully
the right way. :)

When I last hacked on it I got into a fully working state AFAICT, but
the tests needed updating and that proved to be the most challenging
part.  If you're willing to finish it up, that would be awesome!

Thanks,

- Dave