(diff-show-trailing-whitespaces): Remove function.

Move setting up whitepace-mode ...
(diff-mode): ... here.
(diff-mode-menu): Add a menu entry for showing trailing whitespace.

etc/NEWS

@@ -781,8 +781,8 @@ diff-auto-refine-mode.  It is bound to `C-c C-b'.
 buffer and tries to create ChangeLog entries for each change.
 It is bound to `C-x 4 A'.
 +++
-*** The new function `diff-show-trailing-whitespaces' shows
-trailing whitespace problems in the modified lines of a diff buffer.
+*** Turning on `whitespace-mode' in a diff buffer will show trailing
+whitespace problems in the modified lines.
 
 ** Dired
 +++

lisp/ChangeLog

+2009-01-10  Dan Nicolaescu  <dann@ics.uci.edu>
+
+	* diff-mode.el (diff-show-trailing-whitespaces): Remove function.
+	Move setting up whitepace-mode ...
+	(diff-mode): ... here.
+	(diff-mode-menu): Add a menu entry for showing trailing whitespace.
+
 2009-01-10  Chong Yidong  <cyd@stupidchicken.com>
 
 	* faces.el (x-font-family-list): Remove entirely.

lisp/diff-mode.el

@@ -183,6 +183,9 @@ when editing big diffs)."
     ["Unified -> Context"	diff-unified->context
      :help "Convert unified diffs to context diffs"]
     ;;["Fixup Headers"		diff-fixup-modifs	(not buffer-read-only)]
+    ["Show trailing whitespace" whitespace-mode
+     :style toggle :selected whitespace-mode
+     :help "Show trailing whitespace in modified lines"]
     "-----"
     ["Split hunk"		diff-split-hunk
      :active (diff-splittable-p)
@@ -1264,6 +1267,12 @@ a diff with \\[diff-reverse-direction].
   (set (make-local-variable 'end-of-defun-function)
        'diff-end-of-file)
 
+  ;; Set up `whitespace-mode' so that turning it on will show trailing
+  ;; whitespace problems on the modified lines of the diff.
+  (set (make-local-variable 'whitespace-style) '(trailing))
+  (set (make-local-variable 'whitespace-trailing-regexp)
+       "^[-\+!<>].*?\\([\t ]+\\)$")
+
   (setq buffer-read-only diff-default-read-only)
   ;; setup change hooks
   (if (not diff-update-on-the-fly)
@@ -1885,13 +1894,6 @@ I.e. like `add-change-log-entry-other-window' but applied to all hunks."
         ;; When there's no more hunks, diff-hunk-next signals an error.
 	(error nil)))))
 
-(defun diff-show-trailing-whitespaces ()
-  "Show trailing whitespaces in modified lines for diff-mode."
-  (interactive)
-  (let ((whitespace-style '(trailing))
-        (whitespace-trailing-regexp "^[-+!<>].*?\\([\t ]+\\)$"))
-    (whitespace-mode 1)))     ; display trailing whitespace in diff buffer
-
 ;; provide the package
 (provide 'diff-mode)