bug#45896: Non-pull ‘guix’ should know its channels

["Ludovic Courtès" <ludo@gnu.org>]

Ludovic Courtès <ludo@gnu.org> skribis:

> Likewise, on foreign distros, /usr/local/bin/guix may point to a ‘guix
> pull’-guix, but because of the symlink, ‘guix describe’ won’t work:
>
> $ type -P guix
> /home/ludo/.config/guix/current/bin/guix
> $ guix describe
> Generacio 171	Jan 11 2021 11:38:39	(nuna)
>   guix 458cb25
>     repository URL: https://git.savannah.gnu.org/git/guix.git
>     branch: master
>     commit: 458cb25b9e7e7c954f468023abea2bebb5d8c75b
> $ ln -s $(type -P guix) /tmp
> $ /tmp/guix describe
> guix describe: error: failed to determine origin
> hint: Perhaps this `guix' command was not obtained with `guix pull'? Its
> version string is 458cb25b9e7e7c954f468023abea2bebb5d8c75b.

This problem extends beyond that: channel modules are not found if the
symlink is dereferenced:

--8<---------------cut here---------------start------------->8---
$ /tmp/guix-science/bin/guix describe 
Generacio 1     Jan 26 2021 14:13:46    (nuna)
  guix-past 829923f
    repository URL: https://gitlab.inria.fr/guix-hpc/guix-past
    branch: master
    commit: 829923f01f894f1e687735627025ada26230832f
  guix-science cf87b05
    repository URL: https://github.com/guix-science/guix-science.git
    branch: master
    commit: cf87b0501c4a38b96edf41025a27bf1cb91f521a
  guix 51418c3
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 51418c32d95d8188d8877616829f26479f1135c6
$ $(readlink -f /tmp/guix-science/bin/guix) describe 
guix describe: error: failed to determine origin
hint: Perhaps this `guix' command was not obtained with `guix pull'? Its version string is 51418c32d95d8188d8877616829f26479f1135c6.

$ /tmp/guix-science/bin/guix build python2@2.4 -n
La jenaj derivoj estus konstruataj:
   /gnu/store/xsk3vg48dfbwcc5w8pn08x5x15n5prpz-python2-2.4.6.drv
   /gnu/store/pnxh0lx28iydhw354xgcfbzk9r6zs6dx-Python-2.4.6.tar.xz.drv
   /gnu/store/fi2my0k9lfag52siz1h7xqwqbzwjkirc-Python-2.4.6.tar.bz2.drv
14.2 MB would be downloaded:
   /gnu/store/6wn346cbw1mh6264v426pwj2klgvxr0z-gcc-5.5.0
$ $(readlink -f /tmp/guix-science/bin/guix) build python2@2.4 -n
guix build: error: python2: pako ne trovita por versio 2.4
--8<---------------cut here---------------end--------------->8---

Ludo’.