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

[Andrew Tropin <andrew@trop.in>]

> > Most other package managers seem to respect "infrastructure" provided
> > by package.el.
> I don't think that statement is well-supported by the data we have.

Agree, that was an incorrect statement. I should have said something like:
there are some popular tools like use-package configuration helper, Nix
package manager, Spacemacs configuration framework, some elisp archives
and probably something else, which utilize and follow package.el.  Not
all of them use package.el itself, but they follow conventions and
describe-package help command and some other work correctly.

> Why should we let ELPA dictate our layout?  I have not even once tried
> customizing package.el for actual use since I got Guix, because the
> elpa importer is trivial.

We don't have to.  Actually, I'm very happy with the new (current) layout we
have right now.

I would say I find the following use case very confusing for newcomers:
- Install emacs package via Guix.
- Use built-in help C-h C-h, find C-h P.
- Get it to work for built-in packages, but not for packages installed by Guix.
- Get frustrated.

I think we could avoid this at least in two ways:
1. Use elpa/ subdirectory.
2. Keep current structure, set package-directory-list to .../site-lisp
instead of .../site-lisp/elpa by default.

> Thus we're not trying to keep in line with any specific package
> manager, we just need to make things work "with Emacs" in the sense
> that packages installed via Guix should have working autoloads and one
> should be able to (require ...) them.

Yes, but at the same time I don't see reasons why not to implement one
of two options above.  We can get both: working autoloads and working
built-in help function (+newcommers won't be so frustrated).

Personally, I'm quite happy that packages got their own subdirectories
and I'm fully satisfied with current state of it, but it would be cool
if inexperienced users will be able to use at least built-in help
commands for packages out of the box without additional configuration.

Hope my original point is a little better worded now.

-- 
Best regards,
Andrew Tropin