Ediff's overlay priorities cause more trouble than they solve.

* lisp/vc/ediff-init.el (ediff-shadow-overlay-priority): Remove variable.
(ediff-highest-priority): Remove function.
* lisp/vc/ediff-util.el (ediff-highlight-diff-in-one-buffer):
* lisp/vc/ediff-diff.el (ediff-set-diff-overlays-in-one-buffer)
(ediff-set-fine-diff-properties-in-one-buffer): Don't mess with
overlay priorities.

Fixes: debbugs:17234

lisp/ChangeLog

+2014-04-10  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+	Ediff's overlay priorities cause more trouble than they solve.
+	* vc/ediff-init.el (ediff-shadow-overlay-priority): Remove variable.
+	(ediff-highest-priority): Remove function (bug#17234).
+	* vc/ediff-util.el (ediff-highlight-diff-in-one-buffer):
+	* vc/ediff-diff.el (ediff-set-diff-overlays-in-one-buffer)
+	(ediff-set-fine-diff-properties-in-one-buffer): Don't mess with
+	overlay priorities.
+
 2014-04-10  Feng Li  <fengli@gmail.com>  (tiny change)
 	* progmodes/pascal.el (pascal-font-lock-keywords): Fix incorrect format

lisp/vc/ediff-diff.el

@@ -587,7 +587,6 @@ one optional arguments, diff-number to refine.")
 	    (setq pt-saved (ediff-with-current-buffer buff (point)))))
       (setq overlay (ediff-make-bullet-proof-overlay begin end buff))
 
-      (ediff-overlay-put overlay 'priority ediff-shadow-overlay-priority)
       (ediff-overlay-put overlay 'ediff-diff-num current-diff)
       (if (and (ediff-has-face-support-p)
 	       ediff-use-faces ediff-highlight-all-diffs)
@@ -822,20 +821,9 @@ one optional arguments, diff-number to refine.")
 		  'default
 		(ediff-get-symbol-from-alist
 		 buf-type ediff-fine-diff-face-alist)
-		))
-	(priority (if default
-		      0
-		    (1+ (or (ediff-overlay-get
-			     (symbol-value
-			      (ediff-get-symbol-from-alist
-			       buf-type
-			       ediff-current-diff-overlay-alist))
-			     'priority)
-			    0)))))
-    (mapcar (lambda (overl)
-	      (ediff-set-overlay-face overl face)
-	      (ediff-overlay-put overl 'priority priority))
-	    fine-diff-vector)))
+		)))
+    (dolist (overl fine-diff-vector)
+      (ediff-set-overlay-face overl face))))
 
 ;; Set overlays over the regions that denote delimiters
 (defun ediff-set-fine-overlays-for-combined-merge (diff-list reg-num)

lisp/vc/ediff-init.el

@@ -707,9 +707,6 @@ shown in brighter colors."
 ;; List of difference overlays disturbed by working with the current diff.
 (defvar ediff-disturbed-overlays nil "")
 
-;; Priority of non-selected overlays.
-(defvar ediff-shadow-overlay-priority  100 "")
-
 (defcustom ediff-version-control-package 'vc
   "Version control package used.
 Currently, Ediff supports vc.el, rcs.el, pcl-cvs.el, and generic-sc.el.  The
@@ -1329,34 +1326,6 @@ this variable represents.")
 (ediff-defvar-local ediff-current-diff-overlay-Ancestor nil
   "Overlay for the current difference region in the ancestor buffer.")
 
-;; Compute priority of a current ediff overlay.
-(defun ediff-highest-priority (start end buffer)
-  (let ((pos (max 1 (1- start)))
-	ovr-list)
-    (if (featurep 'xemacs)
-	(1+ ediff-shadow-overlay-priority)
-      (ediff-with-current-buffer buffer
-	(while (< pos (min (point-max) (1+ end)))
-	  (setq ovr-list (append (overlays-at pos) ovr-list))
-	  (setq pos (next-overlay-change pos)))
-	(+ 1 ediff-shadow-overlay-priority
-	   (apply 'max
-		  (cons
-		   1
-		   (mapcar
-		    (lambda (ovr)
-		      (if (and ovr
-			       ;; exclude ediff overlays from priority
-			       ;; calculation, or else priority will keep
-			       ;; increasing
-			       (null (ediff-overlay-get ovr 'ediff))
-			       (null (ediff-overlay-get ovr 'ediff-diff-num)))
-			  ;; use the overlay priority or 0
-			  (or (ediff-overlay-get ovr 'priority) 0)
-			0))
-		    ovr-list))))))))
-
-
 (defvar ediff-toggle-read-only-function 'toggle-read-only
   "Function to be used to toggle read-only status of the buffer.
 If nil, Ediff tries using the command bound to C-x C-q.")

lisp/vc/ediff-util.el

@@ -3023,8 +3023,6 @@ Hit \\[ediff-recenter] to reset the windows afterward."
 	(if (featurep 'xemacs)
 	    (ediff-move-overlay current-diff-overlay begin end-hilit)
 	  (ediff-move-overlay current-diff-overlay begin end-hilit buff))
-	(ediff-overlay-put current-diff-overlay 'priority
-			   (ediff-highest-priority begin end-hilit buff))
 	(ediff-overlay-put current-diff-overlay 'ediff-diff-num n)
 
 	;; unhighlight the background overlay for diff n so it won't