New command diff-revert-and-kill-hunk

* lisp/vc/diff-mode.el (diff-revert-and-kill-hunk): New
command (bug#73407).
(diff-ask-before-revert-and-kill-hunk): New user option.
(diff-apply-buffer): New optional BEG, END and REVERSE
arguments.  Return nil if buffers were saved, or the number of
failed applications.
(diff-mode-map): Bind the new command to C-c M-r.
(diff-mode-menu): New entry for the new command.
* doc/emacs/files.texi (Diff Mode):
* etc/NEWS: Document the change.

1 files changed, 15 insertions, 0 deletions

diff --git a/doc/emacs/files.texi b/doc/emacs/files.texi
index 709cb0910e6..b7d6b6f9f7b 100644
--- a/doc/emacs/files.texi
+++ b/doc/emacs/files.texi
@@ -1682,6 +1682,21 @@ reverse of the hunk, which changes the ``new'' version into the ``old''
 version.  If @code{diff-jump-to-old-file} is non-@code{nil}, apply the
 hunk to the ``old'' version of the file instead.
 
+@findex diff-revert-and-kill-hunk
+@item C-c M-r
+Reverse-apply this hunk to the target file, and then kill it
+(@code{diff-revert-and-kill-hunk}).  Save the buffer visiting the target
+file.
+
+This command is useful in buffers generated by @w{@kbd{C-x v =}} and
+@w{@kbd{C-x v D}} (@pxref{Old Revisions}).  These buffers present you
+with a view of the changes you've made, and then you can use this
+command to drop changes you didn't intend, or no longer want.
+
+This is a destructive operation, so by default, this command asks you to
+confirm you really want to reverse-apply and kill the hunk.  You can
+customize @code{diff-ask-before-revert-and-kill-hunk} to change that.
+
 @findex diff-apply-buffer
 @item C-c @key{RET} a
 Apply all the hunks in the buffer (@code{diff-apply-buffer}).  If the