bug#48331: [PATCH] guix: build: emacs-build-system: Make package.el aware of guix packages

[Ivan Sokolov]

> After updating the package-directory-list variable, functions like
> list-packages, describe-package become aware of packages installed by
> guix.

> ---
> This code is getting work done, but I'm not a very experienced elisp
> developer, so please review it thoroughly.

> +
> +(require 'package)
> +
> +;; Set `package-directory-list' to the value without elpa/ suffix
> +;; to match the structure of site-lisp directory of guix's emacs
> +;; build system.
> +;;;###autoload
> +(setq package-directory-list
> +      (list (string-remove-suffix "/elpa" (car package-directory-list))))
> +
>  (provide 'guix-emacs)

For future reference, this approach is absolutely unacceptable, no
package should modify customizable variables unless explicitly requested
by the user.