Re: hydra.gnu.org now provides substitutes for ‘guix pull’

[swedebugia@riseup.net]

On June 22, 2018 9:32:58 AM GMT+02:00, ludo@gnu.org wrote: 

> Hello Guix,
> 
> Yesterday Clément and I discussed on IRC what it would take for Hydra to
> build build-aux/hydra/guix-modular.scm (i.e., the derivations that
> correspond to 'guix pull'.)  Clément rightly suggested that it was a
> matter of removing '--fresh-auto-compiled' from hydra-eval-guile-jobs¹,
> which I did, and it works:
> 
> https://hydra.gnu.org/jobset/guix/modular/

Fantastic!
This really drastically cut the time to pull for me. Now the only thing
that takes a toll is to compute the guix-derivation. Can we
skip/workaround that too? Maybe we can deduce this from the build hydra
already did?

I'm guessing that the computation is needed to map a commit to a
derivation that then maps to a build hydra has a substitute for. Hydra
according to my understanding already did all this. Maybe we can
communicate this to guix pull somehow?

Example 1 
I choose a commit that I know hydra has build e.g. 8edebd3
-> guix pull sees that this commit is already build and computed by
hydra.
-> guix pull fetches the resulting derivation and substitute and build
only the locale profile stuff.

Example 2
I simply run guix pull without knowing what hydra has done
-> guix pull checks the latest commit to master
-> checks if hydra has built it: no
-> informs the user and gives them an option to choose a commit a few
days back that hydra has built instead (saves time, power and is
environmentally friendly :) )
-> based on the users choice moves forward.

What do you think?