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

[Andrew Tropin]

> > In other words, no particular thought was given to -pkg.el. It was
> > simply dropped along with many other files. So, if consensus is
> > reachedthat keeping -pkg.el is a good idea, there is no reason to not
> > do that.
> Thanks for clearing that up.  In that case, I don't have any qualms
> about including them either.

Cool, seems we can get -pkg.el files back.

> Multi-profile Emacs should be supported, but this also breaks on
> foreign distros with foreign distro ELPA.  Again, hacking variables is
> not the solution (and even if it was, it'd be better to patch the emacs
> default value, not that this is a good idea either).

Yep, the last snippet supports multi-profile Emacs.  Installing packages
for Emacs via a few different package manager sounds like a very bad
practice) I agree that current implementation with updating variables
isn't perfect and it doesn't cover the use case, which I expect to be
rare (packages from Guix will be listed in list-packages, files from
foreign distro PM won't).  I can dive into package.el implementation and
spend some time next week providing a different workaround.

BTW, can you remind me why we do not place packages under
site-lisp/elpa/NAME-VERSION? It seems almost the same as
site-lisp/NAME-VERSION, but everything related to describe-package and
other functions will work out of the box.  This way it will work even
with a foreign distro use case.