GNU bug report logs - #7736
24.0.50; perl-mode infinite loop

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: jidanni <at> jidanni.org
To: bug-gnu-emacs <at> gnu.org
Subject: 24.0.50; perl-mode infinite loop
Date: Sat, 25 Dec 2010 21:41:26 +0800

[Message part 1 (text/plain, inline)]

Man, you gotta see this. On this attached file,

[r.pl (text/x-perl, attachment)]

[Message part 3 (text/plain, inline)]

save in /tmp, and run emacs -Q -nw /tmp/r.pl

Now move the cursor down and attempt to change shttp to s[http .
As you insert the [ an infinite loop begins.
You probably can break out with a C-g, but you might need a
$ killall -HUP emacs

In GNU Emacs 24.0.50.1 (i486-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2010-12-14 on elegiac, modified by Debian
 (emacs-snapshot package, version 1:20101212-2)

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  value of $LC_CTYPE: zh_TW.UTF-8
  value of $LC_MESSAGES: C
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: C
  value of $LANG: zh_TW.UTF-8
  value of $XMODIFIERS: @im=SCIM
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Message #8 received at 7736 <at> debbugs.gnu.org (full text, mbox):

From: Chong Yidong <cyd <at> stupidchicken.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 7736 <at> debbugs.gnu.org, rfrancoise <at> debian.org, jidanni <at> jidanni.org
Subject: Re: bug#7736: 24.0.50; perl-mode infinite loop
Date: Sat, 22 Jan 2011 20:18:34 -0500

jidanni <at> jidanni.org writes:

> Man, you gotta see this. On this attached file,
>
> save in /tmp, and run emacs -Q -nw /tmp/r.pl
>
> Now move the cursor down and attempt to change shttp to s[http .
> As you insert the [ an infinite loop begins.

This bug was apparently introduced by syntax-propertize on the trunk.
Stefan, could you take a look?

2010-09-10  Stefan Monnier  <monnier <at> iro.umontreal.ca>

   * progmodes/perl-mode.el (perl-syntax-propertize-function): New fun to
   replace perl-font-lock-syntactic-keywords.
   (perl-syntax-propertize-special-constructs): New fun to replace
   perl-font-lock-special-syntactic-constructs.
   (perl-font-lock-syntactic-face-function): New fun.
   (perl-mode): Use it.

Message #11 received at 7736 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Chong Yidong <cyd <at> stupidchicken.com>
Cc: 7736 <at> debbugs.gnu.org, rfrancoise <at> debian.org, jidanni <at> jidanni.org
Subject: Re: bug#7736: 24.0.50; perl-mode infinite loop
Date: Sun, 23 Jan 2011 19:53:04 -0500

>> Man, you gotta see this. On this attached file,
>> save in /tmp, and run emacs -Q -nw /tmp/r.pl
>> Now move the cursor down and attempt to change shttp to s[http .
>> As you insert the [ an infinite loop begins.
> This bug was apparently introduced by syntax-propertize on the trunk.
> Stefan, could you take a look?

Sure (as well as the ruby one),


        Stefan

Message #16 received at 7736-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: jidanni <at> jidanni.org
Cc: rfrancoise <at> debian.org, 7736-done <at> debbugs.gnu.org
Subject: Re: bug#7736: 24.0.50; perl-mode infinite loop
Date: Mon, 24 Jan 2011 15:13:07 -0500

> Man, you gotta see this. On this attached file,
> save in /tmp, and run emacs -Q -nw /tmp/r.pl

> Now move the cursor down and attempt to change shttp to s[http .
> As you insert the [ an infinite loop begins.

Indeed, thanks for that test case.  I've installed the patch below
which should fix the problem.


        Stefan


=== modified file 'lisp/progmodes/perl-mode.el'
--- lisp/progmodes/perl-mode.el	2011-01-14 17:18:41 +0000
+++ lisp/progmodes/perl-mode.el	2011-01-24 20:05:18 +0000
@@ -360,7 +360,8 @@
      (t
       ;; This is regexp like quote thingy.
       (setq char (char-after (nth 8 state)))
-      (let ((twoargs (save-excursion
+      (let ((startpos (point))
+            (twoargs (save-excursion
                        (goto-char (nth 8 state))
                        (skip-syntax-backward " ")
                        (skip-syntax-backward "w")
@@ -384,7 +385,8 @@
 			  (goto-char (1+ (nth 8 state)))
 			  (up-list 1)
 			  t)
-		      (scan-error nil))
+                      ;; In case of error, make sure we don't move backward.
+		      (scan-error (goto-char startpos) nil))
 		  (not (or (nth 8 (parse-partial-sexp
 				   (point) limit nil nil state 'syntax-table))
 			   ;; If we have a self-paired opener and a twoargs

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