(show-paren-function): Handle unbalanced parens as

mismatched.  When the unbalanced paren is an opening paren,
highlight it as mismatched.

diff --git a/lisp/paren.el b/lisp/paren.el
index 810fa691980cb2bf14e7f59250d07d43086bbde2..66d27fbb6aff55d0230eb8ba6bdb6a2013b7a09e 100644 (file)
--- a/lisp/paren.el
+++ b/lisp/paren.el
@@ -93,12 +93,14 @@ after `show-paren-delay' seconds of Emacs idle time."
                                      (min (point-max)
                                           (+ (point) blink-matching-paren-distance))))
                ;; Scan across one sexp within that range.
+               ;; Errors or nil mean there is a mismatch.
                (condition-case ()
                    (setq pos (scan-sexps (point) dir))
-                 (error nil))
-               ;; See if the "matching" paren is the right kind of paren
-               ;; to match the one we started at.
-               (if pos
+                 (error (setq pos t
+                              mismatch t)))
+               ;; If found a "matching" paren, see if it is the right
+               ;; kind of paren to match the one we started at.
+               (if (integerp pos)
                    (let ((beg (min pos oldpos)) (end (max pos oldpos)))
                      (and (/= (char-syntax (char-after beg)) ?\$)
                           (setq mismatch
@@ -127,28 +129,39 @@ after `show-paren-delay' seconds of Emacs idle time."
                        (message "Paren mismatch"))))
                )))
        (cond (pos
-              (if (= dir -1)
+              (if (or (= dir -1)
+                      (not (integerp pos)))
                   ;; If matching backwards, highlight the closeparen
                   ;; before point as well as its matching open.
-                  (progn
+                  ;; If matching forward, and the openparen is unbalanced,
+                  ;; highlight the paren at point to indicate misbalance.
+                  (let ((from (if (= dir 1)
+                                  (point)
+                                (1- (point))))
+                        (to (if (= dir 1)
+                                (1+ (point))
+                              (point))))
                     (if show-paren-overlay-1
                         (move-overlay show-paren-overlay-1
-                                      (+ (point) dir) (point)
+                                      from to
                                       (current-buffer))
                       (setq show-paren-overlay-1
-                            (make-overlay (+ (point) dir) (point))))
+                            (make-overlay from to)))
                     ;; Always set the overlay face, since it varies.
                     (overlay-put show-paren-overlay-1 'face face))
                 ;; Otherwise, turn off any such highlighting.
                 (and show-paren-overlay-1
                      (overlay-buffer show-paren-overlay-1)
                      (delete-overlay show-paren-overlay-1)))
-              ;; Turn on highlighting for the matching paren.
-              (if show-paren-overlay
-                  (move-overlay show-paren-overlay (- pos dir) pos
-                                (current-buffer))
-                (setq show-paren-overlay
-                      (make-overlay (- pos dir) pos)))
+              ;; Turn on highlighting for the matching paren, if found.
+              ;; If it's an unmatched paren, turn off any such highlighting.
+              (or (and (not (integerp pos))
+                       (delete-overlay show-paren-overlay))
+                  (if show-paren-overlay
+                      (move-overlay show-paren-overlay (- pos dir) pos
+                                    (current-buffer))
+                    (setq show-paren-overlay
+                          (make-overlay (- pos dir) pos))))
               ;; Always set the overlay face, since it varies.
               (overlay-put show-paren-overlay 'face face))
              (t