bug#29789: 25.1; Emacs blocks user input when using visual-fill-column in wide terminals

[Luis Gerhorst]

1. Run Emacs in a wide terminal (about 150 characters, 100 isn't
enough): emacs -nw -Q

2. Load a arbitrary theme: M-x load-theme adwaita

3. Load visual-fill-column. E.g. by copying
https://raw.githubusercontent.com/joostkremers/visual-fill-column/c0e5ec8f88a7598f7afdee565978410bee0de2a0/visual-fill-column.el
into the scratch buffer and typing M-x eval-buffer.

There is nothing suspicious about the code, regular lisp code should not
be able to block Emacs (I believe). It does not seem to contain any loops that 
block the main thread. The maintainer knows about the issue but say's it may be 
an issue with low-level code. In GUI Emacs it works.

4. Open a buffer and enable visual-fill-column-mode: M-x
visual-fill-column-mode

5. Your Emacs is now blocked. In ZSH when I type C-g C-g I'm back in my
shell which displays the message "zsh: suspended emacs -nw -Q".

This bug has been encountered by multiple users on different operating
systems (Debian, Ubuntu and macOS) running different versions of Emacs
(24.5 to 26.0), some reported it here:
https://github.com/joostkremers/visual-fill-column/issues/1



In GNU Emacs 25.1.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2017-09-15, modified by Debian built on trouble
System Description:     Debian GNU/Linux 9.3 (stretch)

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --with-x=yes --with-x-toolkit=gtk3
 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs25-wN2qS3/emacs25-25.1+1=. 
-fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

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

Major mode: GFM

Minor modes in effect:
  luis-text-wrap-mode: t
  visual-fill-column-mode: t
  adaptive-wrap-prefix-mode: t
  diff-auto-refine-mode: t
  shell-dirtrack-mode: t
  ws-butler-mode: t
  show-paren-mode: t
  frame-restore-mode: t
  winner-mode: t
  global-company-mode: t
  company-mode: t
  which-key-mode: t
  flx-ido-mode: t
  ido-vertical-mode: t
  crm-custom-mode: t
  ido-ubiquitous-mode: t
  ido-everywhere: t
  projectile-global-mode: t
  projectile-mode: t
  recentf-mode: t
  global-auto-revert-mode: t
  override-global-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  visual-line-mode: t
  transient-mark-mode: t

Recent messages:
Source file ‘/home/cip/2016/un65esoq/.emacs.d/elpa/bind-key-2.3/bind-key.el’ 
newer than byte-compiled file
Loading /home/cip/2016/un65esoq/.emacs.d/recentf...done
Cleaning up the recentf list...done (0 removed)
Source file ‘/home/cip/2016/un65esoq/.emacs.d/elpa/s-1.12.0/s.el’ newer than 
byte-compiled file
Source file 
‘/home/cip/2016/un65esoq/.emacs.d/elpa/company-0.9.4/company-dabbrev.el’ newer 
than byte-compiled file
Unable to load color "brightgreen" [12 times]
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark saved where search started
Visual-Fill-Column mode enabled in current buffer
GNU Emacs 25.1.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.11) of 2017-09-15, 
modified by Debian

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/usr/share/emacs25/site-lisp/auctex/tex-fold
/home/cip/2016/un65esoq/.emacs.d/elpa/auctex-12.1.0/toolbar-x hides 
/usr/share/emacs25/site-lisp/auctex/toolbar-x
/home/cip/2016/un65esoq/.emacs.d/elpa/auctex-12.1.0/texmathp hides 
/usr/share/emacs25/site-lisp/auctex/texmathp
/home/cip/2016/un65esoq/.emacs.d/elpa/auctex-12.1.0/prv-emacs hides 
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/home/cip/2016/un65esoq/.emacs.d/elpa/auctex-12.1.0/auctex hides 
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/usr/share/emacs/site-lisp/tex-site
/usr/share/emacs/25.1/site-lisp/debian-startup hides 
/usr/share/emacs/site-lisp/debian-startup
/usr/share/emacs/25.1/site-lisp/why3 hides /usr/share/emacs/site-lisp/why3
/usr/share/emacs25/site-lisp/cmake-data/cmake-mode hides 
/usr/share/emacs/site-lisp/cmake-mode
/home/cip/2016/un65esoq/.emacs.d/elpa/dsvn-20130120.1257/dsvn hides 
/usr/share/emacs/site-lisp/dsvn
/usr/share/emacs/site-lisp/rst hides /usr/share/emacs/25.1/lisp/textmodes/rst
/home/cip/2016/un65esoq/.emacs.d/elpa/scala-mode-1.0.0/ob-scala hides 
/usr/share/emacs/25.1/lisp/org/ob-scala
/usr/share/emacs25/site-lisp/latex-cjk-thai/thai-word hides 
/usr/share/emacs/25.1/lisp/language/thai-word
/usr/share/emacs/25.1/site-lisp/slime/lib/ert-x hides 
/usr/share/emacs/25.1/lisp/emacs-lisp/ert-x
/usr/share/emacs/25.1/site-lisp/slime/lib/ert hides 
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/usr/share/emacs/site-lisp/auctex/prv-emacs

Features:
(shadow sort mail-extr emacsbug message rfc822 mml mml-sec epg mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mail-utils smex luis-text-wrap
visual-fill-column adaptive-wrap markdown-mode derived url-parse
url-vars noutline outline misearch multi-isearch dired-aux
minibuffer-complete-cycle vc-git diff-mode bookmark pp xcscope dired
term/xterm xterm paredit aggressive-indent lisp-mnt
luis-comment-auto-fill fillcode python tramp-sh tramp tramp-compat
auth-source eieio eieio-core gnus-util mm-util help-fns mail-prsvr
password-cache tramp-loaddefs trampver ucs-normalize shell pcomplete
format-spec json map cc-mode cc-fonts cc-guess cc-menus cc-styles
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python-environment epc ctable concurrent deferred subr-x luis-iterm
luis-apps luis-mail luis-modes luis-terminal luis-xml luis-make
luis-scala luis-sbt luis-java luis-lua luis-asm luis-org luis-c luis-nxc
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luis-markdown luis-elisp luis-look paren solarized-dark-theme solarized
powerline cl-macs powerline-separators color powerline-themes
luis-user-interaction luis-misc desktop frameset frame-restore
luis-compile luis-movement saveplace winner luis-modification
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company-dabbrev company-elisp find-func company luis-interactive
time-date which-key flx-ido flx ido-vertical-mode crm-custom
ido-completing-read+ warnings memoize s cus-edit cus-start cus-load ido
luis-files projectile grep compile comint ansi-color ring ibuf-ext
ibuffer dash thingatpt recentf tree-widget wid-edit autorevert
filenotify luis-integration use-package diminish bind-key luis-packages
cl-seq cl finder-inf edmacro kmacro info package epg-config seq byte-opt
gv bytecomp byte-compile cl-extra help-mode easymenu cconv luis-private
luis-machine-local benchmark-init advice cl-loaddefs pcase cl-lib
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sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
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 (symbols 48 43035 0)
 (miscs 40 574 465)
 (strings 32 104884 16016)
 (string-bytes 1 3270643)
 (vectors 16 79586)
 (vector-slots 8 1717257 54052)
 (floats 8 8003 1977)
 (intervals 56 1023 0)
 (buffers 976 440))