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

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

On Fri, Feb 12, 2016 at 4:07 PM, Ludovic Courtès <ludo@gnu.org> wrote:
> "Thompson, David" <dthompson2@worcester.edu> skribis:
>
>> 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!
>
> It took me a while but I’ve finally finished it and pushed as 779aa00.
>
> I took a different strategy for the tests, which is to rely (in part) on
> the output of ‘guix gc --references’ to determine whether the profile
> contains all we need.

Thank you!  I'm excited that this is finally in master.

- Dave