bug#67290: (current-profile) only works when invoked as a process named "guix"

[Ian Eure]

When you invoke `guix repl', the current-profile and current-channels 
procedures reflect my current profile and channel configuration:

    l0p!ieure~$ guix repl
    GNU Guile 3.0.9
    Copyright (C) 1995-2023 Free Software Foundation, Inc.

    Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
    This program is free software, and you are welcome to redistribute it
    under certain conditions; type `,show c' for details.

    Enter `,help' for help.
    scheme@(guix-user)> ,m (guix describe)
    scheme@(guix describe)> (current-profile)
    $1 = "/home/ieure/.config/guix/current"
    scheme@(guix describe)> (length (current-channels))
    $2 = 3
    scheme@(guix describe)> 

If you run `guile', they do not:

    l0p!ieure~$ guile
    GNU Guile 3.0.9
    Copyright (C) 1995-2023 Free Software Foundation, Inc.

    Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
    This program is free software, and you are welcome to redistribute it
    under certain conditions; type `,show c' for details.

    Enter `,help' for help.
    scheme@(guile-user)> ,m (guix describe)
    scheme@(guix describe)> (current-profile)
    $1 = #f
    scheme@(guix describe)> (length (current-channels))
    $2 = 1
    scheme@(guix describe)> 

The issue seems to be that current-profile checks the name of the program which 
was invoked, and always returns #f unless the name ends with "bin/guix".  Since 
"guile" doesn’t, they don’t work as expected.  See: 
https://git.savannah.gnu.org/cgit/guix.git/tree/guix/describe.scm#n64

I discovered this when I was using emacs-guix to debug one of my package 
definitions, which inherits from a package in a non-default channel.  While I 
can load the .scm file into Geiser no matter what channels are configured, it 
can’t use the module containing the package definition it inherits from.  This 
also appears to be the root cause behind this three-year-old bug report for 
emacs-guix: https://gitlab.com/emacs-guix/emacs-guix/-/issues/17

I’m not sure what the rationale is for this behavior, so I don’t have a 
suggestion for a fix, but it’s definitely a bug.

Thanks,

  — Ian