bug#14303: 24.3; Bug in comment-search-backward

[Leo Liu]

On 2013-05-17 01:38 +0800, Stefan Monnier wrote:
> Right, that makes sense.
>
>
>         Stefan

In that case I plan to install the patch as attached.

I have found that it is very easy for people who provide customised
comment-start-skip to introduce bugs. For example octave mode used to
have "\\s<+\\s-*" as comment start skip and was lucky to work in the
buggy comment-search-backward.

I wonder what to do here. Better documentation on comment-start-skip to
inform people that it is used both in re-search-forward/backward and
better be anchored properly?


diff --git a/lisp/newcomment.el b/lisp/newcomment.el
index d55feaa3..db07e6a9 100644
--- a/lisp/newcomment.el
+++ b/lisp/newcomment.el
@@ -485,27 +485,26 @@ (defun comment-search-backward (&optional limit noerror)
 Moves point to inside the comment and returns the position of the
 comment-starter.  If no comment is found, moves point to LIMIT
 and raises an error or returns nil if NOERROR is non-nil."
-  ;; FIXME: If a comment-start appears inside a comment, we may erroneously
-  ;; stop there.  This can be rather bad in general, but since
-  ;; comment-search-backward is only used to find the comment-column (in
-  ;; comment-set-column) and to find the comment-start string (via
-  ;; comment-beginning) in indent-new-comment-line, it should be harmless.
-  (if (not (re-search-backward comment-start-skip limit t))
-      (unless noerror (error "No comment"))
-    (beginning-of-line)
-    (let* ((end (match-end 0))
-          (cs (comment-search-forward end t))
-          (pt (point)))
-      (if (not cs)
-         (progn (beginning-of-line)
-                (comment-search-backward limit noerror))
-       (while (progn (goto-char cs)
-                     (comment-forward)
-                     (and (< (point) end)
-                          (setq cs (comment-search-forward end t))))
-         (setq pt (point)))
-       (goto-char pt)
-       cs))))
+  (let (found end)
+    (while (and (not found) (re-search-backward comment-start-skip limit t))
+      (setq end (match-end 0))
+      (unless (and comment-use-syntax (nth 8 (syntax-ppss)))
+       (setq found t)))
+    (if (not found)
+       (unless noerror (error "No comment"))
+      (beginning-of-line)
+      (let ((cs (comment-search-forward end t))
+           (pt (point)))
+       (if (not cs)
+           (progn (beginning-of-line)
+                  (comment-search-backward limit noerror))
+         (while (progn (goto-char cs)
+                       (comment-forward)
+                       (and (< (point) end)
+                            (setq cs (comment-search-forward end t))))
+           (setq pt (point)))
+         (goto-char pt)
+         cs)))))
 
 (defun comment-beginning ()
   "Find the beginning of the enclosing comment.
-- 
1.8.2