* lisp/files.el: Make revert work with diff-buffer-with-file.

(diff-buffer-internal): New function extracted from diff-buffer-with-file
(diff-buffer-with-file): Use it.
* lisp/vc/diff.el (diff-into-buffer): New fun, extracted from diff.
(diff): Use it.

Fixes: debbugs:7277

1 files changed, 6 insertions, 2 deletions

diff --git a/lisp/vc/diff.el b/lisp/vc/diff.el
index e79e72c8b0d..1a835b59994 100644
--- a/lisp/vc/diff.el
+++ b/lisp/vc/diff.el
@@ -108,11 +108,16 @@ specified in `diff-switches' are passed to the diff command."
                   (read-file-name "Diff original file: "
                                   (file-name-directory newf) nil t)))
      (list oldf newf (diff-switches))))
+  (diff-into-buffer nil old new switches no-async))
+
+(defun diff-into-buffer (buf old new &optional switches no-async)
+  ;; Noninteractive helper for creating and reverting diff buffers.
   (setq new (expand-file-name new)
         old (expand-file-name old))
   (or switches (setq switches diff-switches)) ; If not specified, use default.
+  (or buf (setq buf (get-buffer-create "*Diff*")))
   (let* ((old-alt (file-local-copy old))
-        (new-alt (file-local-copy new))
+         (new-alt (file-local-copy new))
          (command
           (mapconcat 'identity
                      `(,diff-command
@@ -123,7 +128,6 @@ specified in `diff-switches' are passed to the diff command."
                        ,(shell-quote-argument (or old-alt old))
                        ,(shell-quote-argument (or new-alt new)))
                      " "))
-         (buf (get-buffer-create "*Diff*"))
          (thisdir default-directory)
          proc)
     (save-excursion