Multiple profiles with Guix Home

[Liliana Marie Prikler]

Hi Guix,

it's been a while since the discussion of whether or not to collect
multiple profiles into a single directory [1].  This suggestion takes
inspiration from that, but goes a vastly different route.  Instead of
using environment variables to control Guix, it takes advantage of the
recently added Guix Home, even if it is still a technical preview.

So, what's the proposition?  I suggest we modify home-profile-service-
type (or add a new service) such that it takes a list of <home-profile> 
records instead of a list of packages.  This record would be defined as

  (define-record-type* <home-profile> home-profile
    make-home-profile home-profile? this-home-profile
    (location home-profile-location) ; string, e.g. $HOME/.guix-profile
    (short-name home-profile-short-name) ; string or #f, if given
                                         ; construct a symlink in
                                         ; /var/guix/.../per-user/
    (manifest %home-profile-manifest) ; <manifest> or #f
    (packages home-profile-packages) ; list of <package> or #f
                                     ; fallback for manifest
    (enabled? home-profile-enabled?) ; boolean, default #t
    [...])

  (define (home-profile-manifest home-profile)
    (or (%home-profile-manifest home-profile)
        (and=> (home-profile-packages home-profile) 
               packages->manifest))))

On init/reconfigure, `guix home' creates/updates all home-profiles
which have a home-profile-manifest that is not #f and links them to the
appropriate locations.  It also creates a shell startup script that
loads those profiles that are enabled?, even if they have no manifest
(this can be used to e.g. declare a pull profile, which `guix home'
can't manage).  

Some existing home services would need to be adapted towards this
multiple profile usage.  For instance, home-fontconfig-service-type
would need to accept a list of directories, rather than hardcode its
value.

What do y'all think?

<https://lists.gnu.org/archive/html/guix-devel/2019-12/msg00358.html>