bug#22272: 24.5; nonfunctional Emacs with a bad global mode (post-command-hook).

[brubar.cs@gmail.com]

Hi,

This report is about a possible improvement. The "bug" arises only after
a programming mistake.

Please find attached a recipe to reproduce a stupid thing I've done.

I was trying to define a new global minor mode. I ended up placing a
function that raises an unhandled error in `post-command-hook'.

Then, I had to kill my Emacs; I found no other way to recover control.

As the `post-command-hook' documentation says, Emacs could probably
do better here by discarding my non-working code.

To reproduce and *KILL YOUR EMACS*, launch a *NEW* Emacs like that:

   emacs -Q --load test-kill-your-emacs-with-global-mode.el A-NEW-FILE.txt --eval '(insert "modified")' --funcall BAD-global-mode 

I'm reporting this only to improve Emacs. I obviously fixed my code and
Emacs is awesome again!

Thanks,

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 11.0.11704000
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: Emacs-Lisp

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.
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
help-fns mail-prsvr mail-utils help-mode easymenu time-date tooltip
electric uniquify 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 prog-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 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 make-network-process
dbusbind inotify dynamic-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty emacs)

Memory information:
((conses 16 73069 6963)
 (symbols 48 17625 0)
 (miscs 40 44 138)
 (strings 32 9420 4003)
 (string-bytes 1 259885)
 (vectors 16 8991)
 (vector-slots 8 384143 17302)
 (floats 8 64 195)
 (intervals 56 372 4)
 (buffers 960 13)
 (heap 1024 36263 750))

===File
~/WorkingDirectory/Community/Emacs/Gnu-Emacs/test-kill-your-emacs-with-global-mode.el===
;; WARNING WARNING WARNING WARNING 
;; 
;;   Make your Emacs *UNUSABLE*
;; 
;; WARNING WARNING WARNING WARNING 
;; 
;; BUG report: nonfunctional Emacs with a bad global mode (post-command-hook).
;; 
;; What follows is a recipe to reproduce a stupid thing I've done.
;; The problem is that I had to kill my emacs; I found no other way to
;; recover control.
;; 
;; The following code reproduces the problem: it ends up placing a
;; function that raises an unhandled error in `post-command-hook'.
;; 
;; As the `post-command-hook' documentation says, Emacs could probably
;; do better here by discarding my stupid code.
;; 
;; Do not use like this:
;; 
;;    emacs -Q --load test-kill-your-emacs-with-global-mode.el A-NEW-FILE.txt --eval '(insert "modified")' --funcall BAD-global-mode 
;; 
;; 
;; 
(define-minor-mode BAD-minor-mode
  "BAD minor mode."
  )


(define-globalized-minor-mode BAD-global-mode
  BAD-minor-mode
  identity
  "BAD global mode."
  )
============================================================