bug#47457: 28.0.50; Infinite loop in cc-mode/isearch

[David Welch]

Reproduction:

        Run: emacs -Q ccmode-1.cpp

        Enter: C-S (isearch)

        Enter: yyyyI

        emacs hangs at this point.

It seems to be very dependent on the number of lines displayed in the

frame. It reproduces for me at fullscreen (54 lines) but not in a

smaller window.

The backtrace at the hang is:-

  c-looking-at-inexpr-block(538 nil t)

  c-beginning-of-statement-1(538 nil t)

  c-beginning-of-decl-1(538)

  font-lock-fontify-keywords-region(2003 2126 nil)

  font-lock-default-fontify-region(2003 2126 nil)

  funcall(font-lock-default-fontify-region 2003 2126 nil)

  c-font-lock-fontify-region(2024 2126 nil)

  font-lock-fontify-region(2024 2126)

  #f(compiled-function (fun) #<bytecode -0x1557681c5c448d3b>)(font-lock-fontify-region)

  run-hook-wrapped(#f(compiled-function (fun) #<bytecode -0x1557681c5c448d3b>) font-lock-fontify-region)

  jit-lock--run-functions(2024 2126)

  jit-lock-fontify-now(2024 2524)

  jit-lock-function(2024)

  redisplay_internal\ \(C\ function\)()

  redisplay()

  sit-for(0)

  isearch-lazy-highlight-new-loop()

  isearch-update()

  isearch-search-and-update()

  isearch-process-search-string("I" "I")

  isearch-process-search-char(73 1)

  isearch-printing-char(73 1)

  funcall-interactively(isearch-printing-char 73 1)

  call-interactively(isearch-printing-char nil nil)

  command-execute(isearch-printing-char)

The loop is in this part of c-looking-at-inexpr-block

    ;; Search for a C++11 "->" which suggests a lambda declaration.

      (when (and (c-major-mode-is 'c++-mode)

(setq haskell-op-pos

      (save-excursion

(while

    (progn

      (c-syntactic-skip-backward "^;=}>" closest-lim t)

      (and (eq (char-before) ?>)

   (c-backward-token-2)

   (not (looking-at c-haskell-op-re)))))

(and (looking-at c-haskell-op-re)

     (point)))))

(goto-char haskell-op-pos))

    (point) is 9 on entry to the function then c-syntactic-skip-backward

    sets it to 538(=limit) and then the while loop repeats infinitely.

I bisected it to the git commit 92c56300c317c9e5573dca787a2cf20f777b317,

in particular this change.

@@ -5481,7 +5492,7 @@ c-syntactic-skip-backward

             (progn

               ;; Skip syntactic ws afterwards so that we don't stop at the

               ;; end of a comment if `skip-chars' is something like "^/".

-              (c-backward-syntactic-ws)

+              (c-backward-syntactic-ws limit)

               (point)))))

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30, cairo version 1.15.10)

 of 2021-03-29 built on david-welch

Repository revision: ee3a4e3d1be656cd0df71ed197dc5f102556f0e0

Repository branch: master

Windowing system distributor 'The X.Org Foundation', version 11.0.11906000

System Description: Ubuntu 18.04.5 LTS

Configured using:

 'configure --with-x=yes --with-x-toolkit=gtk3 --with-xwidgets=yes

 --prefix=/home/dw/devel/emacs/install_latest

 --sharedstatedir=/home/dw/devel/emacs/install_latest/var/lib

 --with-modules=yes'

Configured features:

ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG

JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY

INOTIFY PDUMPER PNG RSVG SOUND THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE

XIM XPM XWIDGETS GTK3 ZLIB

Important settings:

  value of $LANG: en_GB.UTF-8

  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 dired dired-loaddefs

rfc822 mml mml-sec epa derived epg epg-config gnus-util rmail

rmail-loaddefs auth-source cl-seq eieio eieio-core cl-macs

eieio-loaddefs password-cache json map text-property-search time-date

subr-x seq byte-opt gv bytecomp byte-compile cconv 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-langs

cc-bytecomp misearch multi-isearch cc-mode cc-fonts cc-guess cc-menus

cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs vc-git diff-mode

easy-mmode vc-dispatcher cl-loaddefs cl-lib jka-compr iso-transl 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 tab-bar menu-bar rfn-eshadow isearch

easymenu timer select scroll-bar mouse jit-lock font-lock syntax

font-core term/tty-colors frame minibuffer 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

cl-preloaded nadvice button loaddefs faces cus-face macroexp files

window text-properties overlay sha1 md5 base64 format env code-pages

mule custom widget hashtable-print-readable backquote threads

xwidget-internal dbusbind inotify lcms2 dynamic-setting

system-font-setting font-render-setting cairo move-toolbar gtk x-toolkit

x multi-tty make-network-process emacs)

Memory information:

((conses 16 121289 6866)

 (symbols 48 10033 1)

 (strings 32 28030 1947)

 (string-bytes 1 980939)

 (vectors 16 16597)

 (vector-slots 8 207848 8652)

 (floats 8 24 45)

 (intervals 56 226 0)

 (buffers 992 11))

ccmode-1.cpp
Description: ccmode-1.cpp