bug#40872: First installed package on guix system is not instantly usable

[Stefan]

Hi Marius!

> This is odd, as /etc/profile contains a workaround for this exact
> problem (notice the else clause):
> 
> # Arrange so that ~/.config/guix/current comes first.
> for profile in "$HOME/.guix-profile" "$HOME/.config/guix/current"
> do
>  if [ -f "$profile/etc/profile" ]
>  then
>    # Load the user profile's settings.
>    GUIX_PROFILE="$profile" ; \
>    . "$profile/etc/profile"
>  else
>    # At least define this one so that basic things just work
>    # when the user installs their first package.
>    export PATH="$profile/bin:$PATH"
>  fi
> done
> 
> Can you investigate why this is ineffective on your system?

Previously I had some packages installed, but I rolled-back to generation 0. I 
found this in my scroll-back buffer:

stefan@guix ~/development/guix$ guix package --roll-back
Folgende Ableitung wird erstellt:
   /gnu/store/l0n6l104ldj7nz6kdyi7l8v5yjnc9p9g-profile.drv
building profile with 0 packages...
Von Generation „1“ zu „0“ gewechselt

By rolling back it created a new generation 0 profile which is now lying around 
with this kind of empty file: 

stefan@guix ~$ cat .guix-profile/etc/profile 
# Source this file to define all the relevant environment variables in Bash
# for this profile.  You may want to define the 'GUIX_PROFILE' environment
# variable to point to the "visible" name of the profile, like this:
#
#  GUIX_PROFILE=/path/to/profile ; \
#  source /path/to/profile/etc/profile
#
# When GUIX_PROFILE is undefined, the various environment variables refer
# to this specific profile generation.

So the test for the existence of this file does not fail, but it doesn't change 
PATH either. This is the profile content, it has no bin/ folder to add to PATH:

stefan@guix ~$ ls -lA /gnu/store/yyxqc1rhz2i062xq8lbfrhhmiyf6pzvp-profile
insgesamt 12
dr-xr-xr-x 2 root root 4096  1. Jan 1970  etc/
-r--r--r-- 4 root root   37  1. Jan 1970  manifest


Bye

Stefan