Avoid inflooping in thing-at-point-looking-at

* lisp/thingatpt.el (thing-at-point-looking-at): Avoid inflooping
with regular expressions whose matching doesn't move point.
(Bug#22756)
Describe the argument DISTANCE in the doc string.

diff --git a/lisp/thingatpt.el b/lisp/thingatpt.el
index 1686c02ada393dacf07885db0cb098ce38be3ea2..9920fa06d0c86893b8cdcdeb16973e3216159079 100644 (file)
--- a/lisp/thingatpt.el
+++ b/lisp/thingatpt.el
@@ -489,19 +489,26 @@ looks like an email address, \"ftp://\" if it starts with
 (defun thing-at-point-looking-at (regexp &optional distance)
   "Return non-nil if point is in or just after a match for REGEXP.
 Set the match data from the earliest such match ending at or after
-point."
+point.
+
+Optional argument DISTANCE limits search for REGEXP forward and
+back from point."
   (save-excursion
     (let ((old-point (point))
          (forward-bound (and distance (+ (point) distance)))
          (backward-bound (and distance (- (point) distance)))
-         match)
+         match prev-pos new-pos)
       (and (looking-at regexp)
           (>= (match-end 0) old-point)
           (setq match (point)))
       ;; Search back repeatedly from end of next match.
       ;; This may fail if next match ends before this match does.
       (re-search-forward regexp forward-bound 'limit)
-      (while (and (re-search-backward regexp backward-bound t)
+      (setq prev-pos (point))
+      (while (and (setq new-pos (re-search-backward regexp backward-bound t))
+                  ;; Avoid inflooping with some regexps, such as "^",
+                  ;; matching which never moves point.
+                  (< new-pos prev-pos)
                  (or (> (match-beginning 0) old-point)
                      (and (looking-at regexp)  ; Extend match-end past search start
                           (>= (match-end 0) old-point)