bug#65345: guix-pull --list-generations is slow

[Olivier Dion]

Hi,

Calling `guix-pull --list-generations' is very slow on my system with 37
generations.

$ time guix pull --list-generations > /dev/null
real    0m58.702s
user    1m8.418s
sys     0m1.527s

Also, it takes a lot of CPU (100% of a core).

$ guix describe:
  guix 7b2b0a5
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 7b2b0a5e1d635fb0e3d2d3e9141ac27c2db644b5

>From a search in pull.scm, I think that the culprit is in the
`channel-news-for-commit' procedure.

Thanks,

old
-- 
Olivier Dion
EfficiOS Inc.
https://www.efficios.com