[debbugs-tracker] bug#33784: closed (27.0.50; some case c-backward-token-2 takes cpu more and emacs hang)

[GNU bug Tracking System]

Your message dated Thu, 20 Dec 2018 12:53:26 +0000
with message-id <address@hidden>
and subject line Re: bug#33784:
has caused the debbugs.gnu.org bug report #33784,
regarding 27.0.50; some case c-backward-token-2 takes cpu more and emacs hang
to be marked as done.

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-- 
33784: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=33784
GNU Bug Tracking System
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--- Begin Message --- Subject: 27.0.50; some case c-backward-token-2 takes cpu more and emacs hang Date: Tue, 18 Dec 2018 12:09:01 +0800

follow case:

(let ((str "#define SLOGE(...)\n ((void)__android_log_buf_print(LOG_ID_SYSTEM, ANDROID_LOG_ERROR, LOG_TAG,\n __VA_ARGS__))"))
(with-temp-buffer
(delay-mode-hooks (funcall 'c++-mode))
(insert str)
(font-lock-ensure)
(buffer-string)
)
)

execute up code, emacs will hang


In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
of 2018-12-18 built on xhyang-ThinkPad-T470p
Repository revision: 1691a51094d35ac4b2c311fa407c6b77eea7a105
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 16.04.3 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark set
#("#define SLOGE(...)
((void)__android_log_buf_print(LOG_ID_SYSTEM, ANDROID_LOG_ERROR, LOG_TAG,
__VA_ARGS__))" 0 1 (c-is-sws t c-in-sws t) 1 7 (c-in-sws t) 7 8 (c-in-sws t) 8 13 (c-in-sws t) 13 19 (c-in-sws t) 19 21 (c-in-sws t c-is-sws t) 21 22 (c-is-sws t))
next-line: End of buffer

Configured using:
'configure --enable-link-time-optimization --without-pop
--without-kerberos --without-kerberos5 --without-hesiod
--with-sound=alsa --with-x-toolkit=gtk3 --with-xpm --with-jpeg
--with-tiff --with-gif --with-png --with-rsvg --with-xml2
--with-imagemagick --with-xft --without-libotf --without-xim
--with-xaw3d --with-dbus --without-gconf --without-gsettings
--without-selinux --with-gnutls --with-zlib --with-modules
--with-file-notification=inotify --without-makeinfo --with-x
--exec-prefix=/usr/'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GLIB NOTIFY
INOTIFY GNUTLS LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11
XDBE XIM MODULES THREADS LCMS2 GMP

Important settings:
value of $LC_MONETARY: zh_CN.UTF-8
value of $LC_NUMERIC: zh_CN.UTF-8
value of $LC_TIME: zh_CN.UTF-8
value of $LANG: en_US.UTF-8
value of $XMODIFIERS: @im=fcitx
locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
tooltip-mode: t
global-eldoc-mode: t
eldoc-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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
mml-sec password-cache epa derived epg epg-config gnus-util rmail
rmail-loaddefs time-date mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils cc-mode cc-fonts easymenu
cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs
cl-loaddefs cl-lib elec-pair mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads dbusbind inotify lcms2 dynamic-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 114827 9593)
(symbols 48 22507 1)
(strings 32 34433 2178)
(string-bytes 1 1049070)
(vectors 16 16742)
(vector-slots 8 532827 13806)
(floats 8 49 68)
(intervals 56 261 1)
(buffers 992 11)
(heap 1024 38686 1099))

--- End Message ---

> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: bug#33784:
>
>
>
>
> Date: 
>
> Thu, 20 Dec 2018 12:53:26 +0000
>
>
>
>
> User-agent: 
>
> Mutt/1.10.1 (2018-07-13)
>
>
>
>
> Hello, xh.
>
> On Thu, Dec 20, 2018 at 15:18:49 +0800, xh yang wrote:
> > I found if remove first '\n' from the *str,then run emacs will not hang.*
> > *May be it has nothing to do with font-lock, just str parsing ?*
>
> Sorry for all the distraction in the last couple of days.  As you
> suggested in your opening post, the problem was a simple infinite loop
> involving c-backward-token-2.  This was in CC Mode's font-locking code.
>
> I've committed a fix to the emacs-26 branch, and it should find its way
> to the master branch within a few days.  I'm closing the bug.
>
> Here is the patch:
>
>
> # HG changeset patch
> # User Alan Mackenzie <address@hidden>
> # Date 1545307557 0
> #      Thu Dec 20 12:05:57 2018 +0000
> # Node ID 5319aa054ccb77924e19b836093c9e1b3ff91d4b
> # Parent  a3f28b92890acc5289cde497ea1335f4b39239d7
> Check result from c-backward-token-2 to avoid infinite loop
>
> This fixes bug #33784.
>
> * cc-fonts.el (c-get-fontification-context): While moving back over enclosing
> parentheses, check that c-backward-token-2 actually moves.
>
> diff -r a3f28b92890a -r 5319aa054ccb cc-fonts.el
> --- a/cc-fonts.el       Thu Dec 20 12:04:53 2018 +0000
> +++ b/cc-fonts.el       Thu Dec 20 12:05:57 2018 +0000
> @@ -1255,8 +1255,8 @@
>                 (save-excursion
>                   (goto-char match-pos)
>                   (while
> -                     (progn (c-backward-token-2)
> -                            (eq (char-after) ?\()))
> +                     (and (zerop (c-backward-token-2))
> +                          (eq (char-after) ?\()))
>                   (looking-at c-arithmetic-op-regexp)))
>            (cons nil nil))
>           ;; In a C++ member initialization list.
>
>
> Thanks, once more, for the bug report.
>
> -- 
> Alan Mackenzie (Nuremberg, Germany).
>
>
> --- End Message ---