Fix whitespace highlighting of context diffs.

* lisp/vc/diff-mode.el (diff-setup-whitespace): New function.
(diff-mode): Use it.

* lisp/vc/diff.el (diff-sentinel):
* lisp/vc/vc.el (vc-diff-finish): Call diff-setup-whitespace to assign
Whitespace mode variables based on diff style.

Fixes: debbugs:8612

4 files changed, 41 insertions, 14 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index cad73c2e2e7..4ec3b1934a4 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,12 @@
+2012-04-25  Chong Yidong  <cyd@gnu.org>
+
+        * vc/diff-mode.el (diff-setup-whitespace): New function.
+        (diff-mode): Use it.
+
+        * vc/diff.el (diff-sentinel):
+        * vc/vc.el (vc-diff-finish): Call diff-setup-whitespace to assign
+        Whitespace mode variables based on diff style (Bug#8612).
+
 2012-04-25  Leo Liu  <sdl.web@gmail.com>
 
         * files.el (auto-mode-alist): Use javascript-mode instead.
diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index 8b6b85dd22e..c92371fc90b 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -1283,11 +1283,7 @@ 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) '(face trailing))
-  (set (make-local-variable 'whitespace-trailing-regexp)
-       "^[-\+!<>].*?\\([\t ]+\\)$")
+  (diff-setup-whitespace)
 
   (setq buffer-read-only diff-default-read-only)
   ;; setup change hooks
@@ -1332,6 +1328,22 @@ the mode if ARG is omitted or nil.
 
 ;;; Handy hook functions ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
+(defun diff-setup-whitespace ()
+  "Set up Whitespace mode variables for the current Diff mode buffer.
+This sets `whitespace-style' and `whitespace-trailing-regexp' so
+that Whitespace mode shows trailing whitespace problems on the
+modified lines of the diff."
+  (set (make-local-variable 'whitespace-style) '(face trailing))
+  (let ((style (save-excursion
+                 (goto-char (point-min))
+                 (when (re-search-forward diff-hunk-header-re nil t)
+                   (goto-char (match-beginning 0))
+                   (diff-hunk-style)))))
+    (set (make-local-variable 'whitespace-trailing-regexp)
+         (if (eq style 'context)
+             "^[-\+!] .*?\\([\t ]+\\)$"
+           "^[-\+!<>].*?\\([\t ]+\\)$"))))
+
 (defun diff-delete-if-empty ()
   ;; An empty diff file means there's no more diffs to integrate, so we
   ;; can just remove the file altogether.  Very handy for .rej files if we
diff --git a/lisp/vc/diff.el b/lisp/vc/diff.el
index 05208894356..dd4b4757e88 100644
--- a/lisp/vc/diff.el
+++ b/lisp/vc/diff.el
@@ -30,6 +30,8 @@
 
 ;;; Code:
 
+(declare-function diff-setup-whitespace "diff-mode" ())
+
 (eval-when-compile (require 'cl))
 
 (defgroup diff nil
@@ -64,6 +66,7 @@ If optional args OLD-TEMP-FILE and/or NEW-TEMP-FILE are non-nil,
 delete the temporary files so named."
   (if old-temp-file (delete-file old-temp-file))
   (if new-temp-file (delete-file new-temp-file))
+  (diff-setup-whitespace)
   (save-excursion
     (goto-char (point-max))
     (let ((inhibit-read-only t))
diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 9ca9e00b8af..433383502da 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -655,6 +655,8 @@
 (require 'vc-dispatcher)
 (require 'ediff)
 
+(declare-function diff-setup-whitespace "diff-mode" ())
+
 (eval-when-compile
   (require 'cl)
   (require 'dired))
@@ -1524,17 +1526,18 @@ to override the value of `vc-diff-switches' and `diff-switches'."
   ;; possibility of an empty output is for an async process.
   (when (buffer-live-p buffer)
     (let ((window (get-buffer-window buffer t))
-          (emptyp (zerop (buffer-size buffer))))
+          (emptyp (zerop (buffer-size buffer))))
       (with-current-buffer buffer
-        (and messages emptyp
-             (let ((inhibit-read-only t))
-               (insert (cdr messages) ".\n")
-               (message "%s" (cdr messages))))
-        (goto-char (point-min))
-        (when window
-          (shrink-window-if-larger-than-buffer window)))
+        (and messages emptyp
+             (let ((inhibit-read-only t))
+               (insert (cdr messages) ".\n")
+               (message "%s" (cdr messages))))
+        (diff-setup-whitespace)
+        (goto-char (point-min))
+        (when window
+          (shrink-window-if-larger-than-buffer window)))
       (when (and messages (not emptyp))
-        (message "%sdone" (car messages))))))
+        (message "%sdone" (car messages))))))
 
 (defvar vc-diff-added-files nil
   "If non-nil, diff added files by comparing them to /dev/null.")