bug#17365: 24.3; Visiting tags table in combination with fill column indicator causes Emacs to hang

[Jon Dufresne <jon.dufresne@gmail.com>]

The following recipe causes Emacs to hang 100%.

0. Start in a mercurial repository directory.
1. Run "emacs -Q -l /path/to/test.el"
2. M-x project-compile-and-visit-tags-table
3. Wait for completion.
4. M-x project-compile-and-visit-tags-table
5. Receive prompt: "Tags file /path/to/TAGS has changed, read new
contents? (yes or no)"
6. Type "yes"
7. Emacs hangs, must send kill signal to close.

The goal of test.el is to re-compile and visit the TAGS file while
coexisting with fci-mode. If there is a better way to accomplish the
same thing, I'd be interested to know.

It is possible that this is a bug in fci-mode, however, it seems to me
that a buggy third party script should not be capable of freezing the
entire Emacs process, so I am filing it here. Removing fci-mode removes
the freezing.

The test.el:

---
(require 'package)
(add-to-list 'package-archives
             '("melpa" . "http://melpa.milkbox.net/packages/"))
(package-initialize)
(package-refresh-contents)
(package-install 'fill-column-indicator)

(require 'fill-column-indicator)
(setq-default fci-rule-column 80)
(defun fci-mode-on ()
  "Turn fci-mode on."
  (fci-mode 1))
(define-globalized-minor-mode global-fci-mode
  fci-mode
  fci-mode-on)
(global-fci-mode 1)

(defun project-compile-and-visit-tags-table ()
  "Compile TAGS file at the project ROOT directory."
  (interactive)
  (let ((root (project-root)))
    (when root
      (add-hook 'compilation-finish-functions #'project-visit-tags-table)
      (compile (format "ctags -e -R --exclude=updates --languages=PHP -o %s %s"
                       (concat root "TAGS") root)))))

(defun project-visit-tags-table (buffer string)
  "Tell tags commands to use tags table at the project root."
  (when (string= string "finished\n")
    (visit-tags-table (concat (project-root) "TAGS")))
  (remove-hook 'compilation-finish-functions #'project-visit-tags-table))

(defun project-root ()
  "Return the project's root directory."
  (locate-dominating-file default-directory ".hg"))
---




In GNU Emacs 24.3.1 (x86_64-redhat-linux-gnu, GTK+ Version 3.10.8)
 of 2014-04-18 on buildvm-19.phx2.fedoraproject.org
Windowing system distributor `Fedora Project', version 11.0.11404000
System Description:	Fedora release 20 (Heisenbug)

Configured using:
 `configure '--build=x86_64-redhat-linux-gnu'
 '--host=x86_64-redhat-linux-gnu' '--program-prefix='
 '--disable-dependency-tracking' '--prefix=/usr' '--exec-prefix=/usr'
 '--bindir=/usr/bin' '--sbindir=/usr/sbin' '--sysconfdir=/etc'
 '--datadir=/usr/share' '--includedir=/usr/include'
 '--libdir=/usr/lib64' '--libexecdir=/usr/libexec'
 '--localstatedir=/var' '--sharedstatedir=/var/lib'
 '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--with-dbus'
 '--with-gif' '--with-jpeg' '--with-png' '--with-rsvg' '--with-tiff'
 '--with-xft' '--with-xpm' '--with-x-toolkit=gtk3' '--with-gpm=no'
 'build_alias=x86_64-redhat-linux-gnu'
 'host_alias=x86_64-redhat-linux-gnu' 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g
 -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions
 -fstack-protector-strong --param=ssp-buffer-size=4
 -grecord-gcc-switches -m64 -mtune=generic' 'LDFLAGS=-Wl,-z,relro ''

Important settings:
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-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 input:
M-x r e p o <tab> r <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils help-mode easymenu time-date tooltip ediff-hook
vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment lisp-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote make-network-process dbusbind dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty emacs)