bug#42983: "sudo -E guix pull" breaks ~/.config/guix/current for regular user

[Danny Milosavljevic]

Hello,

Paul <paul@denknerd.org> reported on IRC that his guix behaved strangely.  Upon
investigation we found that the following happens (on a Guix system), when 
logged
in as regular user (not root):

$ readlink ~/.config/guix/current
/var/guix/profiles/per-user/dannym/current-guix
$ sudo -E guix pull
$ readlink ~/.config/guix/current
/var/guix/profiles/per-user/root/current-guix

You can also rm -f ~/.config/guix/current after that and do everything above
again and it will happen again.  It even happens when guix pull has nothing to
do.

That doesn't seem right.  We should at least try to prevent this from happening,
or warn or something.

The guix package manager that did that is:

$ sudo -E guix describe
Generation 64   Aug 22 2020 11:41:04    (current)
  guix dad963a
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: dad963a4393ea51409baa63817b26b449ed58338
  heads 50b97d4
    repository URL: https://github.com/daym/heads-guix.git
    branch: wip-musl
    commit: 50b97d446ebafd0be7a0e19d87cd236882093244

$ sudo -i
# guix describe
Generation 64   22. August 2020 11:41:04        (aktuell)
  guix dad963a
    Repository-URL: https://git.savannah.gnu.org/git/guix.git
    Branch: master
    Commit: dad963a4393ea51409baa63817b26b449ed58338
  heads 50b97d4
    Repository-URL: https://github.com/daym/heads-guix.git
    Branch: wip-musl
    Commit: 50b97d446ebafd0be7a0e19d87cd236882093244

pgppbfwkxhxea.pgp
Description: OpenPGP digital signature