bug#14606: 24.2; semantics of `backward-delete-char' changed in 24, breaking programs

bug#14606: 24.2; semantics of `backward-delete-char' changed in 24, breaking programs

[Taylor R Campbell]

This bug report will be sent to the Bug-GNU-Emacs mailing list
and the GNU bug tracker at debbugs.gnu.org.  Please check that
the From: line contains a valid email address.  After a delay of up
to one day, you should receive an acknowledgement at that address.

Please write in English if possible, as the Emacs maintainers
usually do not have translators for other languages.

Please describe exactly what actions triggered the bug, and
the precise symptoms of the bug.  If you can, give a recipe
starting from `emacs -Q':

In GNU Emacs 24, the semantics of `backward-delete-char' changed so
that it sometimes does far, far more than just deleting a character
backward.  This needlessly breaks programs that assumed it would do
just that, such as paredit.  In particular, if the region is active
and transient mark mode is enabled, it deletes the region, which, in
the case of paredit, wreaks havoc with the buffer.  If you want to
change the semantics, change the name, just like with
`backward-delete-char-untabify'.

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
For information about debugging Emacs, please read the file
/pkg/current/pkg/share/emacs/24.2/etc/DEBUG.


In GNU Emacs 24.2.1 (x86_64--netbsd, X toolkit, Xaw scroll bars)
 of 2013-01-20 on manticore
Configured using:
 `configure
 '--srcdir=/tmp/pkg/current/work/editors/emacs24/work/emacs-24.2'
 '--localstatedir=/pkg/current/pkg/var' '--without-dbus'
 '--x-includes=/usr/X11R7/include' '--x-libraries=/usr/X11R7/lib'
 '--with-x' '--with-xpm' '--with-jpeg' '--with-tiff' '--with-gif'
 '--with-png' '--with-x-toolkit=athena' '--prefix=/pkg/current/pkg'
 '--build=x86_64--netbsd' '--host=x86_64--netbsd'
 '--infodir=/pkg/current/pkg/info' '--mandir=/pkg/current/pkg/man'
 'build_alias=x86_64--netbsd' 'host_alias=x86_64--netbsd' 'CC=cc'
 'CFLAGS=-I/pkg/current/pkg/include -I/usr/include -I/usr/X11R7/include
 -I/usr/X11R7/include/freetype2' 'LDFLAGS=-L/pkg/current/pkg/lib
 -L/usr/lib -Wl,-R/usr/lib -Wl,-R/pkg/current/pkg/lib -L/usr/X11R7/lib
 -Wl,-R/usr/X11R7/lib' 'LIBS=' 'CPPFLAGS=-DTERMINFO
 -I/pkg/current/pkg/include -I/usr/include -I/usr/X11R7/include
 -I/usr/X11R7/include/freetype2''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Fundamental

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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
ESC x r e p o r t SPC e m a c s SPC b u g SPC DEL 
RET

Recent messages:
("emacs")
Loading term/xterm...done
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
easymenu mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail regexp-opt rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils time-date tooltip ediff-hook
vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image
fringe 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 files text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote make-network-process dynamic-setting
x-toolkit x multi-tty emacs)

bug#14606: 24.2; semantics of `backward-delete-char' changed in 24, breaking programs

[Glenn Morris]

Taylor R Campbell wrote:

> In GNU Emacs 24, the semantics of `backward-delete-char' changed so
> that it sometimes does far, far more than just deleting a character
> backward.  This needlessly breaks programs that assumed it would do
> just that, such as paredit.

In GNU Emacs 23.3 onwards:

C-h f delete-backward-char

  This is meant for interactive use only; from Lisp, better use
  `delete-char' with a negated argument.

And byte-compiling a file with contents:

  (defun foo ()
    (delete-backward-char 1))

results in:

  foo.el:1:8:Warning: `delete-backward-char' used from Lisp code
  That command is designed for interactive use only


So I think that ship has sailed and it's time to update your code.