(save-some-buffers-action-alist): New variable.

(save-some-buffers): Use that.
(diff-buffer-with-file): New function.

1 files changed, 43 insertions, 12 deletions

diff --git a/lisp/files.el b/lisp/files.el
index 0983762356c..ac25232bafe 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2993,17 +2993,56 @@ After saving the buffer, this function runs `after-save-hook'."
                  (rename-file (cdr setmodes) buffer-file-name))))))
     setmodes))
 
+(defun diff-buffer-with-file (&optional buffer)
+  "View the differences between BUFFER and its associated file.
+This requires the external program \"diff\" to be in your `exec-path'."
+  (interactive "bBuffer: ")
+  (setq buffer (get-buffer (or buffer (current-buffer))))
+  (let ((buf-filename (buffer-file-name buffer)))
+    (unless buf-filename
+      (error "Buffer %s has no associated file" buffer))
+    (let ((tempfile (make-temp-file "buffer-content-")))
+      (unwind-protect
+          (progn
+            (with-current-buffer buffer
+              (save-restriction
+                (widen)
+                (write-region (point-min) (point-max) tempfile nil 'nomessage)))
+            (diff buf-filename tempfile))
+        (when (file-exists-p tempfile)
+          (delete-file tempfile)))
+      nil)))
+
+(defvar save-some-buffers-action-alist
+  '((?\C-r
+     (lambda (buf)
+       (view-buffer buf
+                    (lambda (ignore)
+                      (exit-recursive-edit)))
+       (recursive-edit)
+       ;; Return nil to ask about BUF again.
+       nil)
+     "display the current buffer")
+    (?d diff-buffer-with-file
+        "Show difference to last saved version"))
+  "ACTION-ALIST argument used in call to `map-y-or-n-p'.")
+(put 'save-some-buffers-action-alist 'risky-local-variable t)
+
 (defun save-some-buffers (&optional arg pred)
   "Save some modified file-visiting buffers.  Asks user about each one.
-You can answer `y' to save, `n' not to save, or `C-r' to look at the
-buffer in question with `view-buffer' before deciding.
+You can answer `y' to save, `n' not to save, `C-r' to look at the
+buffer in question with `view-buffer' before deciding or `d' to
+view the differences using `diff-buffer-to-file'.
 
 Optional argument (the prefix) non-nil means save all with no questions.
 Optional second argument PRED determines which buffers are considered:
 If PRED is nil, all the file-visiting buffers are considered.
 If PRED is t, then certain non-file buffers will also be considered.
 If PRED is a zero-argument function, it indicates for each buffer whether
-to consider it or not when called with that buffer current."
+to consider it or not when called with that buffer current.
+
+See `save-some-buffers-action-alist' if you want to
+change the additional actions you can take on files."
   (interactive "P")
   (save-window-excursion
     (let* ((queried nil)
@@ -3035,15 +3074,7 @@ to consider it or not when called with that buffer current."
                 (save-buffer)))
              (buffer-list)
              '("buffer" "buffers" "save")
-             (list (list ?\C-r (lambda (buf)
-                                 (view-buffer buf
-                                              (function
-                                               (lambda (ignore)
-                                                 (exit-recursive-edit))))
-                                 (recursive-edit)
-                                 ;; Return nil to ask about BUF again.
-                                 nil)
-                         "display the current buffer"))))
+             save-some-buffers-action-alist))
            (abbrevs-done
             (and save-abbrevs abbrevs-changed
                  (progn