bug#24089: 25.1; Dired: diff error on = <RET> if the file has a backup inside .~/

[Eli Zaretskii <eliz@gnu.org>]

> From: Jorge Peixoto de Morais Neto <jorge13515@gmail.com>
> Cc: 24089@debbugs.gnu.org
> Date: Fri, 29 Jul 2016 08:43:30 -0300
> 
> On Thu, 2016-07-28 at 18:05 +0300, Eli Zaretskii wrote:
> > It seems dired-diff was not prepared to deal with the situation where
> > the backup file is in another directory.  Does the patch below produce
> > good results?
> In my brief testing, the patch solves the problem only when = <RET> is invoked
> with point at the original file.  If it is invoked with point at the backup
> file (inside .~), a diff error still occurs.

I'm not sure why you expect that case to work.  How can Emacs
reverse-engineer backup-directory-alist, to figure out which of its
elements was in effect when the original file was backed up?  In your
example, there's only one element in the alist, but in general there
could be several.

It sounds like in this case the users cannot just press RET, they
should actually type a file name.  Am I missing something?