bug#9461: 24.0.50; Weird behaviour in "show-parent-mode"

[Juri Linkov <juri@jurta.org>]

>> Perhaps nothing should be highlighted when syntax of the previous
>> character is `escape' `\'.
>
> I think show-paren-mode should at least follow the same heuristic as the
> default blink-paren behavior, which indeed refrains from blinking the
> "open paren" when the close-paren is escaped.

I verified that the following patch provides this result:

=== modified file 'lisp/paren.el'
--- lisp/paren.el	2011-01-25 04:08:28 +0000
+++ lisp/paren.el	2011-09-09 09:46:03 +0000
@@ -135,13 +135,23 @@ (define-minor-mode show-paren-mode
 ;; and show it until input arrives.
 (defun show-paren-function ()
   (if show-paren-mode
-      (let ((oldpos (point))
+      (let* ((oldpos (point))
 	    (dir (cond ((eq (syntax-class (syntax-after (1- (point)))) 5) -1)
                        ((eq (syntax-class (syntax-after (point)))      4) 1)))
+	     (unescaped
+	      (when dir
+		;; Verify an even number of quoting characters precede the paren.
+		;; Follow the same logic as in `blink-matching-open'.
+		(= (if (= dir -1) 1 0)
+		   (logand 1 (- (point)
+				(save-excursion
+				  (if (= dir -1) (forward-char -1))
+				  (skip-syntax-backward "/\\")
+				  (point)))))))
 	    pos mismatch face)
 	;;
 	;; Find the other end of the sexp.
-	(when dir
+	(when unescaped
 	  (save-excursion
 	    (save-restriction
 	      ;; Determine the range within which to look for a match.

BTW, I don't understand one comment about escaped parens in `show-paren-function':

	      ;; Move back the other way and verify we get back to the
	      ;; starting point.  If not, these two parens don't really match.
	      ;; Maybe the one at point is escaped and doesn't really count.

It seems irrelevant to the current problem.