bug#66705: ‘guix shell -CW’ provides a Guix command without extra channels

["Ludovic Courtès" <ludovic.courtes@inria.fr>]

Hello!

I’m glad to report that this bug is fixed by
c90a4e8dcd6ac650392ffcc039273baf145aa3cc.

In these examples, you can see that all my channels are present, both in
a bare-bones ‘shell -CW’ (where bin/ is a direct symlink to the ‘guix
pull’ profile) and in ‘shell -CW coreutils’ (where bin/ fuses that of
coreutils and that of guix):

--8<---------------cut here---------------start------------->8---
$ guix time-machine -- shell -CW -- guix describe
  shepherd 33bcc05
    repository URL: https://git.savannah.gnu.org/git/shepherd.git
    branch: devel
    commit: 33bcc0517c0036589aeb55633d3b8e40a7157973
  guile 54c4753
    repository URL: https://git.savannah.gnu.org/git/guile.git
    branch: main
    commit: 54c4753dd3f7506bee2778b36d7263b613ffd579
  guix b7eb1a8
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: b7eb1a8116b2caee7acf26fb963ae998fbdb4253
$ guix time-machine -- shell -CW coreutils -- guix describe
  shepherd 33bcc05
    repository URL: https://git.savannah.gnu.org/git/shepherd.git
    branch: devel
    commit: 33bcc0517c0036589aeb55633d3b8e40a7157973
  guile 54c4753
    repository URL: https://git.savannah.gnu.org/git/guile.git
    branch: main
    commit: 54c4753dd3f7506bee2778b36d7263b613ffd579
  guix b7eb1a8
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: b7eb1a8116b2caee7acf26fb963ae998fbdb4253
--8<---------------cut here---------------end--------------->8---

And of course, packages from these channels are now found:

--8<---------------cut here---------------start------------->8---
$ guix time-machine -- shell -CW -- guix build shepherd guile -n
substitute: updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
substitute: updating substitutes from 'https://bordeaux.guix.gnu.org'... 100.0%
substitute: updating substitutes from 'https://guix.bordeaux.inria.fr'... 100.0%
The following files would be downloaded:
  /gnu/store/d3kc0pww2ff9p06w0g30l0yag68ygns1-shepherd-0.10.99-tarball
  /gnu/store/k0jnqjxs43ra248rb0hqbb31yjbvb9jy-guile-3.0.99-git-debug
  /gnu/store/21q3cm08gda1yd9pi0vwrksvhgjk3qx8-guile-3.0.99-git
$ guix time-machine -- shell -CW coreutils -- guix build shepherd guile -n
The following files would be downloaded:
  /gnu/store/d3kc0pww2ff9p06w0g30l0yag68ygns1-shepherd-0.10.99-tarball
  /gnu/store/k0jnqjxs43ra248rb0hqbb31yjbvb9jy-guile-3.0.99-git-debug
  /gnu/store/21q3cm08gda1yd9pi0vwrksvhgjk3qx8-guile-3.0.99-git
--8<---------------cut here---------------end--------------->8---

Ludo’.