Resurrecting top-notch continuous integration for Guile

["Ludovic Courtès" <ludo@gnu.org>]

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Hello Guilers!

(And hello Guix—that’s about an interesting use case. :-))

Back in 2009, together with Rob Vermaas of NixOS, we set up continuous
integration for Guile (among other GNU packages), using Nix coupled with
Hydra, its continuous integration (CI) system:

  https://lists.gnu.org/archive/html/guile-devel/2009-11/msg00084.html

The CI jobs still exist although they’ve been bitrotting for ~10 years:

  https://hydra.nixos.org/jobset/gnu/guile-2-0
  https://git.savannah.gnu.org/cgit/hydra-recipes.git/tree/guile/release.nix

Ten years ago is when I embarked on this side project *cough* called
Guix (Guix = Guile + Nix, see?).  To close the loop, it’s natural to
reinstate CI, but this time with Guix and Cuirass, its companion CI
tool—Guile code all the way down!  You can see these new CI jobs on the
build farm of the Guix project:

  https://ci.guix.gnu.org/jobset/guile

(Speaking of which, I hereby ask fellow Guix hackers to voice any
concerns they may have regarding this use of project resources.)

Code for these jobs is currently in a Guile branch:

  https://git.savannah.gnu.org/cgit/guile.git/log/?h=wip-cuirass-ci

This branch brings several things:

  1. The ‘guix.scm’ file at the top can be used to spawn a shell with a
     development environment for Guix:

       guix shell

     It can also be used to (cross-)build Guile, as in:

       guix build -f guix.scm --target=x86_64-w64-mingw32

  2. ‘build-aux/manifest.scm’ defines a Guix “manifest” for several
     Guile builds we may want to test: building with Clang,
     cross-compiling to MinGW and RISCV and whatnot, building with
     ‘--disable-threads’, etc.

  3. There’s a ‘.guix-channel’ file at the top, meaning that Guile can
     be used as a Guix “channel” providing additional packages.  You’d
     do that by having something as following in
     ~/.config/guix/channels.scm and then running ‘guix pull’:

       (cons (channel
              (name 'guile)
              (url "https://git.savannah.gnu.org/git/guile.git")
              (branch "wip-cuirass-ci"))
             %default-channels)

     This is arguably the weirdest part, but that’s how we get Cuirass
     to consume Guile.

There’s still much tweaking we can do, but the basics are in place, and
I find it pretty cool.  :-)  If there are no objections, I’ll merge this
branch into “main”.  It’s going to be nice to have a dashboard to look
at before the next release!

Feedback welcome!

Ludo’.

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