GNU bug report logs - #21615
24.5; font-lock-extend-region-wholelines' infinite loop

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: brubar.cs <at> gmail.com
Subject: bug#21615: closed (Re: bug#21615: 24.5; font-lock-extend-region-wholelines'
 infinite loop)
Date: Fri, 09 Oct 2015 08:15:03 +0000

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

Your bug report

#21615: 24.5; font-lock-extend-region-wholelines' infinite loop

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 21615 <at> debbugs.gnu.org.

-- 
21615: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=21615
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Eli Zaretskii <eliz <at> gnu.org>
To: brubar.cs <at> gmail.com
Cc: 21615-done <at> debbugs.gnu.org
Subject: Re: bug#21615: 24.5; font-lock-extend-region-wholelines' infinite loop
Date: Fri, 09 Oct 2015 11:14:15 +0300

> From: brubar.cs <at> gmail.com
> Date: Sun, 04 Oct 2015 19:34:07 +0200
> 
> 
> The function `font-lock-extend-region-wholelines' uses `bolp' to check
> if point is at the beginning of the line, and, if not, it calls
> `line-beginning-position' to move to the beginning of the line.
> 
> Here is the code from `font-lock-extend-region-wholelines':
> 
> ,----
> | (goto-char font-lock-beg)
> | (unless (bolp)
> |   (setq changed t font-lock-beg (line-beginning-position)))
> `----
> 
> 
> But, `line-beginning-position' moves to the beginning of the line *OR*
> to the beginning of a *field*. Thus, if point is at the beginning of a
> field that is not at the beginning of a line, `changed' is set to t but
> the region is not changed. As `font-lock-extend-region-wholelines' is
> called again until it doesn't signal a change, we end up in an infinite
> loop.
> 
> 
> 
> To reproduce, use the attached file and run it like that:
> 
> 
> ,----
> | emacs -Q --file test-font-lock-infloop.el --eval '(progn (eval-buffer) (DO-NOT-EVAL-ME))'
> `----

Thanks, I fixed that in the development sources.

[Message part 3 (message/rfc822, inline)]

From: brubar.cs <at> gmail.com
To: bug-gnu-emacs <at> gnu.org
Subject: 24.5; font-lock-extend-region-wholelines' infinite loop
Date: Sun, 04 Oct 2015 19:34:07 +0200

The function `font-lock-extend-region-wholelines' uses `bolp' to check
if point is at the beginning of the line, and, if not, it calls
`line-beginning-position' to move to the beginning of the line.

Here is the code from `font-lock-extend-region-wholelines':

,----
| (goto-char font-lock-beg)
| (unless (bolp)
|   (setq changed t font-lock-beg (line-beginning-position)))
`----


But, `line-beginning-position' moves to the beginning of the line *OR*
to the beginning of a *field*. Thus, if point is at the beginning of a
field that is not at the beginning of a line, `changed' is set to t but
the region is not changed. As `font-lock-extend-region-wholelines' is
called again until it doesn't signal a change, we end up in an infinite
loop.



To reproduce, use the attached file and run it like that:


,----
| emacs -Q --file test-font-lock-infloop.el --eval '(progn (eval-buffer) (DO-NOT-EVAL-ME))'
`----


Bruno.

In GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.14.9)
 of 2015-09-22 on tosh-laptop
Windowing system distributor `The X.Org Foundation', version 11.0.11502000
Configured using:
 `configure --prefix=/usr --build=x86_64-pc-linux-gnu
 --host=x86_64-pc-linux-gnu --mandir=/usr/share/man
 --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc
 --localstatedir=/var/lib --disable-dependency-tracking
 --disable-silent-rules --libdir=/usr/lib64 --program-suffix=-emacs-24
 --infodir=/usr/share/info/emacs-24 --localstatedir=/var
 --enable-locallisppath=/etc/emacs:/usr/share/emacs/site-lisp
 --with-gameuser=:gamestat --without-compress-install
 --with-file-notification=inotify --enable-acl --with-dbus
 --without-gnutls --without-gpm --without-hesiod --without-kerberos
 --without-kerberos5 --with-xml2 --without-selinux --without-wide-int
 --with-zlib --with-sound=alsa --with-x --without-ns --without-gconf
 --without-gsettings --without-toolkit-scroll-bars --without-gif
 --with-jpeg --with-png --with-rsvg --without-tiff --with-xpm
 --with-imagemagick --with-xft --without-libotf --without-m17n-flt
 --with-x-toolkit=gtk3 GENTOO_PACKAGE=app-editors/emacs-24.5 'CFLAGS=-O2
 -pipe -march=native' CPPFLAGS= 'LDFLAGS=-Wl,-O1 -Wl,--as-needed''

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit
current-kill: Kill ring is empty
delete-backward-char: Text is read-only

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None found.

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Memory information:
((conses 16 71404 9137)
 (symbols 48 17534 0)
 (miscs 40 37 138)
 (strings 32 9208 4463)
 (string-bytes 1 253754)
 (vectors 16 8909)
 (vector-slots 8 383166 18279)
 (floats 8 63 99)
 (intervals 56 222 10)
 (buffers 960 11)
 (heap 1024 24783 718))

===File
/home/bruno/WorkingDirectory/Community/Emacs/Gnu-Emacs/test-font-lock-infloop.el===
(defun DO-NOT-EVAL-ME ()
  "FREEZE YOUR EMACS.

DO NOT RUN IN YOUR MAIN EMACS.

Run this file as follows:

   emacs -Q --file test-font-lock-infloop.el --eval '(progn (eval-buffer) (DO-NOT-EVAL-ME))'

Then, type something between \"TYPE HERE==>>>\" and \"<<<==TYPE HERE\".

Your Emacs should now hangs.
    
GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.14.9)
But should work with any Emacs."

  ;; Publish our own custom function to extend the region to fontify.
  ;; 
  ;;    The first function can say whatever it wants (changed=t or
  ;;    nil), it's ignored. Thus, we need to push
  ;;    `font-lock-extend-region-wholelines' into the second position
  ;;    to show the bug.
  ;;    
  (add-hook 'font-lock-extend-region-functions
	    (lambda () :whatever))

  ;; Put a 'field property between the two "TYPE HERE" below.
  ;; Typing there will make Emacs hangs ... well, if not before.
  ;;     
  (let ((beg (re-search-forward "TYPE HERE==>>>"))
	(end (re-search-forward "<<<==TYPE HERE"))
	)
    (add-text-properties beg end '(field :hang front-sticky t))
    ))

(DO-NOT-EVAL-ME)




;; TYPE HERE==>>>          <<<==TYPE HERE
============================================================

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