Declarative /etc/guix/acl?

[Ludovic Courtès]

Hi!

For some reason, /etc/guix/acl is not declarative on Guix System: we let
users modify it and assume it’s stateful, which can surprise users as in
<https://issues.guix.gnu.org/39819>.

Should we make it declarative, just like most of /etc?  I think so.  For
a build farm like berlin, it would force admins to explicitly list all
the authorized keys in their config—annoying change, but not a bad
thing.

WDYT?

The problem is the transition.  We would need to at least create a
backup of /etc/guix/acl on the next activation, or better yet, warn
users or error out at reconfigure time.

Thoughts?

Ludo’.