bug#62734: Always fully rebuild autoloads in package-generate-autoloads

[Eli Zaretskii <eliz@gnu.org>]

> From: Philip Kaludercic <philipk@posteo.net>
> Cc: 62734@debbugs.gnu.org, "'Eli Zaretskii'" <eliz@gnu.org>
> Date: Fri, 28 Apr 2023 15:00:02 +0000
> 
> Leo Georg Gaskin <leo.gaskin@le0.gs> writes:
> 
> > Tags: patch
> >
> > Hello!
> >
> > I've been using the new package-vc.el functionality to great effect,
> > but I have also come across a somewhat annoying bug.  If I use any of
> > the provided commands to rebuild my local package while a autoloads
> > file is already present, the newly generated autoloads file is
> > consistently either incomplete or empty.
> >
> > The easiest way I've found to fix this is simply changing the
> > `package-generate-autoloads' function to always rebuild the autoloads
> > file by passing the relevant option to `loaddefs-generate'.  I think
> > this change also makes sense on a larger scale, as package generation
> > taking into account older build artifacts seems unintuitive.
> >
> > The attached patch implements this change.
> >
> > I've read that for small changes like this no copyright assignment
> > is needed.  If I have misunderstood, please point me to the relevant
> > documents so I can sign them.  Please also let me know if I have
> > messed something up or you need any additional information.
> 
> It seems to me that your fix is the easiest way to tackle the issue,
> without having to do a deep-dive into loaddefs.  Eli, can this be
> applied to emacs-29?  An alternative fix would be to restrict the
> changes to package-vc, but that seems like an unnecessary duplication,
> since the change doesn't affect package.

I don't understand the original problem (what does package-vc.el have
to do with rebuilding local packages? and why is a newly generated
loaddefs file incomplete or empty?), and I certainly don't think I
understand the effects of this change on the other usage scenarios.
Why would we want to unconditionally rebuild all the loaddefs files
every time package-generate-autoloads is invoked?  OTOH, that function
is not really documented, so maybe I don't understand what is it
supposed to do and in which conditions.

IOW, I think we need more details about the problem and the proposed
solution.