bug#22629: [PATCH 0/4] 'guix pull' produces a self-contained Guix

[Fis Trivial]

Hi, first of all, thanks for the improvement. It's really exciting know
progress in guix.

But I have a few questions around this change. Just curiosity. :)

> Hello Guix!
>
> Here is the “new” ‘guix pull’ that we discussed notably in this thread:
>
>   https://bugs.gnu.org/22629
>
> The major difference is that instead of just building a bunch of modules
> and putting them under ~/.config/guix/latest, it now produces a
> standalone package (with bin/guix, share/info/guix.info, etc.) and puts
> it in a profile under ~/.config/guix/current.  Quoth the manual:
>
>      The result of running ‘guix pull’ is a “profile” available under
>   ‘~/.config/guix/current’ containing the latest Guix.  Thus, make sure to
>   add it to the beginning of your search path so that you use the latest
>   version, and similarly for the Info manual (*note Documentation::):
>
>        export PATH="$HOME/.config/guix/current/bin:$PATH"
>        export INFOPATH="$HOME/.config/guix/current/share/info:$INFOPATH"
>

This sounds like something could be done by guix itself, choosing the
right profile path by $HOME. Since guix has absolute control about this
piece of information?

>      This ‘~/.config/guix/current’ profile works like any other profile
>   created by ‘guix package’ (*note Invoking guix package::).  That is, you
>   can list generations, roll back to the previous generation—i.e., the
>   previous Guix—and so on:
>
>        $ guix package -p ~/.config/guix/current -l
>        Generation 1   May 25 2018 10:06:41
>          guix 221951a out     
> /gnu/store/i4dfk7vw5k112s49jrhl6hwsfnh6wr7l-guix-221951af4
>
>        Generation 2   May 27 2018 19:07:47
>         + guix        2fbae00 out     
> /gnu/store/44cv9hyvxg34xf5kblf5dz57hc52y4bm-guix-2fbae006f
>         - guix        221951a out     
> /gnu/store/i4dfk7vw5k112s49jrhl6hwsfnh6wr7l-guix-221951af4
>
>        Generation 3   May 30 2018 16:11:39    (current)
>         + guix        a076f19 out     
> /gnu/store/332czkicwwg6lc3x4aqbw5q2mq12s7fj-guix-a076f1990
>         - guix        2fbae00 out     
> /gnu/store/44cv9hyvxg34xf5kblf5dz57hc52y4bm-guix-2fbae006f
>        $ guix package -p ~/.config/guix/current --roll-back
>        switched from generation 3 to 2
>
>> There are two requirements it fulfills in terms of compatibility:
>
>   1. The modified ‘build-aux/build-self.scm’ still does the right thing
>      when evaluated by an “old” Guix—that is, it produces a bunch of
>      modules for use in ~/.config/guix/latest as before.
>
>   2. The modified ‘guix pull’ produces ~/.config/guix/current even when
>      invoked on a commit of a past Guix.  That is, it automatically
>      produces a ‘guix’ command using the modules returned by the old
>      ‘build-self.scm’.
>
>
> We could add ‘guix pull’ options for convenient: ‘--roll-back’,
> ‘--profile’, etc.
>

Nice~

> Going forward, additional “channels” could be presented as entries in
> the ~/.config/guix/current manifest.
>
> Caveats:
>
>   1. The ~/.config/guix/current profile really lives there.  That is,
>      unlike ~/.guix-profile, it’s not in /var/guix/profiles/per-user.
>      That could be an issue for cluster setups where home directories
>      are not scanned by the Guix GC.  Cluster folks, please tell me!

What does that mean? We have a guix directory under $HOME/.config,
inside there's a symlink to /gnu/store/...-guix-<commit>. Does "really
lives there" mean the new profile is not a symlink but a concrete
directory or hard link?
>
>   2. The translated Info manual is not built.  Julien: could you turn
>      the big ‘xref_command’ in a script or something that we can more
>      easily reuse in (guix self)?
>
>   3. C++ code is not built.  I wonder which will come first: getting rid
>      of the C++ code, or building it?  :-)
>
In the future world, how do we update guix daemon? Is't still running
guix pull && guix package -u under root user?