State of core-updates

[Andreas Enge <andreas@enge.fr>]

Hello all,

let me start with a call for help! I realise that it takes me about one
week and something close to 100GB on my poor 2-core laptop to rebuild
the bulk of core-updates up to the packages in my profile, and that is not
sustainable. It also forces me to do a "guix gc" between two runs, with
the danger of either doing it too late and having to restart the builds
(lived experience, one week lost), or losing and having to recompile
store items that effectively have not changed.

So it would be nice if someone could set up a more complete job for
core-updates on cuirass or QA, and maybe write up a how-to to see which
packages work and which ones need more love, preferably by architecture.
(Without offense, I honestly do not see what
   https://ci.guix.gnu.org/jobset/core-updates
tells me. There is one evaluation with 290 succeeding and 300 failing
builds, and another one with 7 succeeding and 4 failing builds. Or are
these only the newly succeeding or failing builds? There is the dashboard
which gives visual clues, but can it be used to extract a list of
"originally failing" packages, in the sense that the compilation fails
itself instead of just a dependency - otherwise said, the failures highest
up in the package graph, which need to be worked on? On QA I think so far
there is nothing for core-updates, and the bordeaux build farm probably
could not keep up while also working on issues from the tracker. Generally
speaking, I think we need more tooling and documentation of the tooling if
feature branches are to become a thing.)

Since the bootstrapping seems to have stabilised, that would allow more
people to work on packages closer to the leaves, since most of what
currently builds would be available as substitutes from the build farm
without everybody needing to go through a one-week compilation project.

Here is my eclectic selection of packages I would add to the job:
- guix (builds)
- icecat (builds)
- ungoogled-chromium (probably also builds)
- openjdk (pulls in rust!, and builds)
- unison (pulls in ocaml, and builds)
- calibre (pulls in qt@5 and python; the former builds, the latter still
  has some problems, among which the python bindings to qt, and packages
  failing their tests even when updating to the latest release)
- pandoc (pulls in ghc, which currently fails its tests @9.2.5)
Please suggest more leaf packages that exercise your favourite missing
language or application domain!

Andreas