bug#48331: Emacs' describe-package doesn't work for packages managed by guix

[Andrew Tropin]

> That looks like it'd mess with people's installed ELPA packages.  In
> general, hacks based on package-directory-list don't feel very stable.

If you talk about ~/.emacs.d/elpa, it won't, because there is a separate
package-user-dir variable for that.

The problem can arise if we have emacs installed in a few profiles, I'm
not sure if it is a good idea to do so, but it is possible, in such a case
we will have a few items in the package-directory-list.  A fix for that:

(setq package-directory-list
      (mapcar (apply-partially 'string-remove-suffix "/elpa")
              package-directory-list)))

> Also, this seems to rely on us not deleting the -pkg.el, but probably
> won't work for packages, that don't ship it, e.g. emacs-howm.

It's true, but it seems relatively easy to implement a build phase,
which will generate -pgk.el in case it is missing.