(defun vc-pijul-diff (files &optional _rev1 _rev2 buffer async)

(defun vc-pijul-diff (files &optional _rev1 rev2 buffer async)

    (apply #'vc-pijul--async "diff" buffer files))))

    (cond
     ((null rev2) (apply #'vc-pijul--async "diff" buffer files))
     ((apply #'vc-pijul--async "change" buffer (list rev2))))
    1)))
(defun vc-pijul-previous-revision (file rev)
  "Return the previous revision of REV for FILE.
If there is no previous revision return nil."
  (with-temp-buffer
    (cond
     ((apply
       #'vc-pijul--out-ok
       (append (list "log" "--hash-only" "--")
               (cond (file (list file)))))
      (goto-char (point-min))
      (cond
       ((search-forward rev nil t)
        (forward-line 1)
        (cond
         ((< (point) (point-max))
          (buffer-substring (point) (point-at-eol))))))))))
(defun vc-pijul-next-revision (file rev)
  "Return the next revision of REV for FILE.
If there is no next revision return nil."
  (with-temp-buffer
    (cond
     ((vc-pijul--out-ok
       "log" "--hash-only" "--" file)
      (goto-char (point-min))
      (cond
       ((search-forward rev nil t)
        (forward-line 0)
        (cond
         ((> (point) (point-min))
          (forward-line -1)
          (buffer-substring (point) (point-at-eol))))))))))