Re: guix environment

[David Thompson <dthompson2@worcester.edu>]

Ludovic Courtès <ludo@gnu.org> writes:

> LGTM, please push!

Pushed.

> 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.

Yes, I had thought about this, but couldn't think of a way to preserve
that information throughout the program.

> 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.
>
>   2. by using (build-things (list "/the/output/path")) and resorting to
>      ‘build-derivations’ only if the ‘build-things’ call did nothing
>      (when passed a non-.drv store item, ‘build-things’ tries to
>      substitute and does nothing if that fails.)
>
> Thoughts?

I don't like option #1.  I haven't fully grokked option #2, but I guess
that will be the next thing to try.

Thanks for the nudge in the right direction.

-- 
David Thompson
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