bug#13046: 23.4; Minimal Example to freeze emacs C++ mode (nasty interaction between templates & windows endline characters )

[Alan Mackenzie <acm@muc.de>]

Hello Yidong, Vadim, John.

On Sun, Dec 02, 2012 at 10:13:47AM +0800, Chong Yidong wrote:
> John Smith <drefleladi@gmail.com> writes:

> > Using emacs -Q,just open the attached minimal example and try typing
> > "std::string" in the body of the function. 
> > That should hang emacs forever (or at least it does on my up-to-date
> > ubuntu).

> I think this is a duplicate of Bug#11841.

> The patch posted in Bug#11841 does not completely fix this test case.
> Giving ^M whitespace syntax in CC mode, as Stefan suggested, seems like
> the easiest solution.  Alan, could you take another look?  It would be
> good to have this fixed in Emacs 24.3.

On Wed, Jul 25, 2012 at 11:58:22PM +0300, Vadim K wrote:
> Hello Alan,


> I've tried your patch and it worked fine for the original posted
> bad.cpp file. However I have found a variation of that file that still
> causes emacs to hang (see attached bad2.cpp).
[ Bug #11841 ]


I think the enclosed patch fixes these bugs.  Please try out the patch
and let us know if there are still any problems here.

The basic problem is that (forward-comment -1) doesn't recognise a CR
character as whitespace.  My first attempt to patch this, in July, was
only partly successful.

The specific problem was that (forward-comment -1) _sometimes_ goes back
over the LF in CRLF, sometimes not.  I've not discovered by what
criterion.



diff -r 1adcc48506f9 cc-engine.el
--- a/cc-engine.el	Sun Apr 22 09:42:29 2012 +0000
+++ b/cc-engine.el	Sun Dec 02 17:46:53 2012 +0000
@@ -1454,8 +1454,21 @@
 	    ;; return t when moving backwards at bob.
 	    (not (bobp))
 
-	    (if (let (open-paren-in-column-0-is-defun-start)
-		  (forward-comment -1))
+	    (if (let (open-paren-in-column-0-is-defun-start moved-comment)
+		  (while
+		      (and (not (setq moved-comment (forward-comment -1)))
+		      ;; Cope specifically with ^M^J here -
+		      ;; forward-comment sometimes gets stuck after ^Ms,
+		      ;; sometimes after ^M^J.
+			   (or
+			    (when (eq (char-before) ?\r)
+			      (backward-char)
+			      t)
+			    (when (and (eq (char-before) ?\n)
+				       (eq (char-before (1- (point))) ?\r))
+			      (backward-char 2)
+			      t))))
+		  moved-comment)
 		(if (looking-at "\\*/")
 		    ;; Emacs <= 20 and XEmacs move back over the
 		    ;; closer of a block comment that lacks an opener.



-- 
Alan Mackenzie (Nuremberg, Germany).