bug#26276: 25.1; diff with DIRED error

[Glenn Morris]

Live System User wrote:

>    I then get the following *Diff* buffer with errors:
>
> diff -u /home/liveuser/file.txt\~ /home/liveuser/file.txt
> --- /home/liveuser/file.txt~  2017-03-15 08:23:58.796074954 -0400
> +++ /home/liveuser/file.txt   2017-03-15 08:29:17.400387624 -0400
> @@ -1,3 +1,5 @@
> +When describe-symbol C-h o
> +
>  Debugger entered--Lisp error: (wrong-number-of-arguments nil 1)
>    signal(wrong-number-of-arguments (nil 1))
>    (if (= (length --cl-rest--) 2) (car-safe (prog1 --cl-rest-- (setq 
> --cl-rest-- (cdr --cl-rest--)))) (signal (quote wrong-number-of-arguments) 
> (list nil (length --cl-rest--))))
>
> Diff finished.  Mon Mar 27 17:14:10 2017

I can't reproduce this.
If it still happens with current Emacs, please send backtrace after
M-x toggle-debug-on-error.