bug#7277: 24.0.50; Can't revert diff-buffer-with-file

[rogers-emacs]

   The problem, of course, is that the temp file is deleted shortly
after "diff" exits, so the default revert-buffer function installed by
"diff" fails.  The simplest solution seems to be to install a new
revert-buffer function that redoes the whole process of checking for a
file buffer and writing the temp file.  The attached patch does a
minimal refactoring of "diff" and "diff-buffer-with-file" to do just
that, while trying to DTRT if the user renames the diff buffer or kills
the original buffer.

                                        -- Bob Rogers
                                           http://www.rgrjr.com/

diff --git a/lisp/files.el b/lisp/files.el
index d5f60b7..603c014 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -4512,24 +4512,42 @@ Before and after saving the buffer, this function runs
   "View the differences between BUFFER and its associated file.
 This requires the external program `diff' to be in your `exec-path'."
   (interactive "bBuffer: ")
-  (with-current-buffer (get-buffer (or buffer (current-buffer)))
+  (diff-buffer-internal (get-buffer (or buffer (current-buffer)))
+                       (get-buffer-create "*Diff*"))
+  ;; return always nil, so that save-buffers-kill-emacs will not move
+  ;; over to the next unsaved buffer when calling `d'.
+  nil)
+
+(defvar diff-buffer-buffer)    ;; suppress compiler warnings.
+
+(defun diff-buffer-internal (buffer result-buffer)
+  (if (not (and buffer (buffer-name buffer)))
+      (error "Original buffer deleted."))
+  (with-current-buffer buffer
     (if (and buffer-file-name
             (file-exists-p buffer-file-name))
        (let ((tempfile (make-temp-file "buffer-content-")))
          (unwind-protect
              (progn
                (write-region nil nil tempfile nil 'nomessage)
-               (diff buffer-file-name tempfile nil t)
-               (sit-for 0))
+               ;; No asynch so we don't delete the temp file prematurely.
+               (diff-into-buffer result-buffer buffer-file-name tempfile
+                                 nil t)
+               (sit-for 0)
+               ;; Now revise the revert-buffer-function, since the
+               ;; default will not be able to find the temp file.
+               (with-current-buffer result-buffer
+                 (set (make-local-variable 'diff-buffer-buffer) buffer)
+                 (setq revert-buffer-function
+                       (lambda (ignore-auto noconfirm)
+                         (diff-buffer-internal diff-buffer-buffer
+                                               (current-buffer))))))
            (when (file-exists-p tempfile)
              (delete-file tempfile))))
       (message "Buffer %s has no associated file on disc" (buffer-name))
       ;; Display that message for 1 second so that user can read it
       ;; in the minibuffer.
-      (sit-for 1)))
-  ;; return always nil, so that save-buffers-kill-emacs will not move
-  ;; over to the next unsaved buffer when calling `d'.
-  nil)
+      (sit-for 1))))
 
 (defvar save-some-buffers-action-alist
   `((?\C-r
diff --git a/lisp/vc/diff.el b/lisp/vc/diff.el
index e79e72c..1a835b5 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