Highlight buffer modifications

Question

As of Emacs 22.1 (at least), 'save-buffers-kill-emacs (the default binding for C-x C-c) prompts you for each unsaved buffer that has a file. Type a d when prompted to save and see the diff.

From the help documentation:

Save some modified file-visiting buffers.  Asks user about each one.
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-with-file'.

If you look at the prompt, it should say something like:

Save file /path/to/file.txt? (y, n, !, ., q, C-r, d, or C-h) 

Typing C-h gives you a little more verbose description (but d is what you are asking for):

Type SPC or `y' to save the current buffer;
DEL or `n' to skip the current buffer;
RET or `q' to give up on the save (skip all remaining buffers);
C-g to quit (cancel the whole command);
! to save all remaining buffers;
C-r to view this buffer;
d to view changes in this buffer;
or . (period) to save the current buffer and exit.

I use diff-buffer-with-file, and select the file that the buffer came from (which is the default anyway for the command... just hit enter).

You can also use highlight-changes-mode, though this won't track changes until you turn it on, so not so useful if you want to see what changed when you're closing a file that has not been in this mode :-)

You can have highlight-changes-mode enabled. It will display all changes in red. However it won't show you whitespace changes and will mark removals only with an red _. See also http://www.emacswiki.org/emacs/TrackChanges.

I found this post about tracking changes by djcb most helpful regarding tracking changes in Emacs. The trick is to add the following to your .emacs:

;; higlight changes in documents
(global-highlight-changes-mode t)
(setq highlight-changes-visibility-initial-state nil); initially hide

and then toggle highlight-changes-visible-mode when you want to see what has changed.

In this case I type undo to see the last change (usually some stray character which got typed in the wrong window, since I save early and often).

It would be nice if there were some other indication of the current changes, e.g. in the border like quick diff in Eclipse text editors.