[daniel@brockman.se: Emacs hangs when "foo\\|\\|bar" is in `font-lock-keywords']

[daniel@brockman.se: Emacs hangs when "foo\\|\\|bar" is in `font-lock-keywords']

[Richard M. Stallman]

You could describe this as user-error, but I think it might be easy
to make Font Lock bulletproof against null-matches in the regexps,
at least enough to avoid infinite loops.

Could someone please look at this and ack to me?

------- Start of forwarded message -------
To: emacs-pretest-bug@gnu.org
From: Daniel Brockman <daniel@brockman.se>
Date: Sun, 26 Jun 2005 22:54:51 +0200
Subject: Emacs hangs when "foo\\|\\|bar" is in `font-lock-keywords'
Sender: emacs-pretest-bug-bounces+rms=gnu.org@gnu.org
X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on monty-python
X-Spam-Level: 
X-Spam-Status: No, hits=0.1 required=5.0 tests=RCVD_IN_SORBS autolearn=no 
	version=2.63

Steps to reproduce:

C-u 1 M-x font-lock-mode RET
M-: (add-to-list 'font-lock-keywords "foo\\|\\|bar") RET
M-x font-lock-fontify-buffer RET

This causes Emacs to hang in a busy loop.


In GNU Emacs 22.0.50.1 (i386-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2005-05-21 on wigwam, modified by Debian
Distributor `The XFree86 Project, Inc', version 11.0.40300001
configured using `configure '--build' 'i386-linux' '--host' 'i386-linux' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--with-gif' '--enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/22.0.50/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/22.0.50/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/22.0.50/leim' '--with-x=yes' '--with-x-toolkit=athena' '--with-toolkit-scroll-bars' 'CFLAGS=-DDEBIAN -g -O2' 'build_alias=i386-linux' 'host_alias=i386-linux''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8
  default-enable-multibyte-characters: t

Major mode: Summary

Minor modes in effect:
  display-time-mode: t
  erc-track-mode: t
  erc-truncate-mode: t
  erc-services-mode: t
  erc-ring-mode: t
  erc-pcomplete-mode: t
  erc-notify-mode: t
  erc-netsplit-mode: t
  erc-log-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-button-mode: t
  erc-autojoin-mode: t
  erc-smiley-mode: t
  erc-irccontrols-mode: t
  erc-noncommands-mode: t
  erc-readonly-mode: t
  minibuffer-electric-default-mode: t
  server-mode: t
  show-paren-mode: t
  mouse-wheel-mode: t
  tooltip-mode: t
  auto-compression-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  temp-buffer-resize-mode: t
  column-number-mode: t
  line-number-mode: t
  next-error-follow-minor-mode:  Fol

Recent input:
t o SPC C-h C-h C-h C-h C-h C-h C-h C-h C-h C-h C-h 
C-h w h e r e <backspace> <backspace> <backspace> <backspace> 
<backspace> t o SPC d r o p SPC r a n d o m SPC e l 
i s C-h C-h C-h C-h f i l e s SPC i n t C-h <return> 
C-c g <f1> v <up> <return> C-x 1 <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <up> <up> <return> <return> M-x r e p 
o r <tab> RET

Recent messages:
Checking new news...done
Type C-x 1 to remove help window.  C-M-v to scroll the help.
Retrieving newsgroup: gmane.emacs.devel...
Loading gnus-ml...done
Opening nntp server on news.gmane.org...done
Fetching headers for gmane.emacs.devel...done
Scoring...done
Scoring...done
Generating summary...done
Loading emacsbug...done

- -- 
Daniel Brockman <daniel@brockman.se>

    So really, we all have to ask ourselves:
    Am I waiting for RMS to do this?   --TTN.


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------- End of forwarded message -------

Re: Fwd: Emacs hangs when "foo\\|\\|bar" is in `font-lock-keywords'

[Stefan Monnier]

> You could describe this as user-error, but I think it might be easy
> to make Font Lock bulletproof against null-matches in the regexps,
> at least enough to avoid infinite loops.

> Could someone please look at this and ack to me?

Would that do the trick,


        Stefan


Index: lisp/font-lock.el
===================================================================
RCS file: /cvsroot/emacs/emacs/lisp/font-lock.el,v
retrieving revision 1.268
diff -u -r1.268 font-lock.el
--- lisp/font-lock.el	4 Jul 2005 23:08:54 -0000	1.268
+++ lisp/font-lock.el	11 Jul 2005 21:43:36 -0000
@@ -1473,8 +1473,12 @@
       (while (and (< (point) end)
 		  (if (stringp matcher)
 		      (re-search-forward matcher end t)
-		    (funcall matcher end)))
-	(when (and font-lock-multiline
+		    (funcall matcher end))
+                  ;; Beware empty string matches since they will
+                  ;; loop indefinitely.
+                  (or (> (point) (match-beginning 0))
+                      (progn (forward-char 1) t)))
+        (when (and font-lock-multiline
 		   (>= (point)
 		       (save-excursion (goto-char (match-beginning 0))
 				       (forward-line 1) (point))))