Hello!

Here’s a patch that fixes the issue, partly based on what the Nix folks
did.

For the client-connecting-over-TCP case, I added special handling:
‘set-build-options’ now passes a “user-name” property, potentially
allowing to create ‘per-user/$USER’ at that point (like you suggested,
Tobias.)

In a cluster setup, it means that the machine that runs ‘guix-daemon’
must see the same users as the machines where its clients run, but
that’s basically already what we expect:
<https://hpc.guix.info/blog/2017/11/installing-guix-on-a-cluster/>.

There’s one case that won’t be correctly handled: in a cluster setup, an
old client talking to a new daemon won’t provide info to create
‘per-user/$USER’, and thus ‘guix package’ & co. won’t be able to create
the user’s profile it it doesn’t already exist.  I think that’s hard to
avoid though.

Thoughts?

Thanks,
Ludo’.