bug#64242: [PATCH] Fix VC package build when there is no docs dir

[Eli Zaretskii]

> Date: Fri, 23 Jun 2023 08:45:03 +0300
> From:  Daniel Semyonov via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> This fixes a small mistake introduced recently in
> 'package-vc--build-documentation' which causes it to error out when its
> 'file' argument isn't a directory.

What do you mean by "isn't a directory"?  FILE is supposed to be a
documentation file, not a directory, see the doc string of this
function.  Do you mean that FILE is a relative file name so that
file-name-directory returns nil for it?  If so, I think the correct
fix would be to reverse the order:

  (docs-directory (file-name-directory (expand-file-name file)))

Can you show a recipe to reproduce this problem, preferably starting
from "emacs -Q"?

And finally, this issue exists on the emacs-29 release branch as well,
doesn't it?

Thanks.