bug#73387: 30.0.90; C-x v v in diff-mode doesn't work after C-c C-n

[Juri Linkov <juri@linkov.net>]

>   (defun diff-vc-deduce-fileset ()
>     (let ((backend (vc-responsible-backend default-directory))
> +        (start (point-min))
> +        (end (point-max))
>           files)
>       (save-excursion
> -      (goto-char (point-min))
> -      (while (progn (diff-file-next) (not (eobp)))
> -        (push (diff-find-file-name nil t) files)))
> +      (save-restriction
> +        (widen)
> +        (goto-char start)
> +        (diff-beginning-of-file-and-junk)
> +        (while (progn (diff-file-next) (<= (point) end))
> +          (push (diff-find-file-name nil t) files))))
>       (list backend (delete nil (nreverse files)) nil nil 'patch)))

LGTM.

> But to really commit the narrowed diff I think you'll need to do
> something about this line in vc-next-action
>
>       ((eq model 'patch)
>        (vc-checkin files backend nil nil nil (buffer-string)))
>
> ...to specify altered buffer contents as the diff to use.

What is altered buffer contents?  Maybe widening is needed here as well?