GNU bug report logs - #22490
24.5; (newline 0) fails when point not after newline

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Dan Torop <dant <at> pnym.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.5; (newline 0) fails when point not after newline
Date: Fri, 29 Jan 2016 13:46:47 -0500

The function "newline" with an argument of 0 will fail unless called
when the character before the point is a newline. To test, start a new
Emacs session, type space, then evaluate "(newline 0)". It should
fail with a backtrace:

Debugger entered--Lisp error: (cl-assertion-failed (eq 10
(char-before)))
  signal(cl-assertion-failed ((eq 10 (char-before))))
  #[0
  "`Sf\304=\204^N^@\305\306\307C\"\210^K\203^[^@\310`\311\300!Z`\"\210\212\302b\210\312
  \210\313\314!\2034^@\315 \316V\2034^@`\317
  |\210)\301\206=^@\320\321\322\"\207" [0 nil 193 use-hard-newlines 10
  signal cl-assertion-failed (eq 10 (char-before))
  set-hard-newline-properties prefix-numeric-value beginning-of-line
  looking-at "[     ]$" current-left-margin 0 line-end-position
  move-to-left-margin nil t] 4 "\n\n(fn)"]()
  self-insert-command(0)
  newline(0)
  eval((newline 0) nil)
  eval-expression((newline 0) nil)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)

If one instead types a newline then (newline 0), the call will be a
NOP, as expected.

This appears to be the result of commit
62ee8b1a59d5343197cb59d9f0a52e07a23af1d8, intended to catch
bug # 18913, in particular the (cl-assert (eq ?\n (char-before)))
in post-self-insert-hook.

While it may seem absurd to execute (newline 0), this can have a
purpose, e.g. when programmatically inserting an arbitrary number of
newlines at the start of an empty buffer.




In GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.6)
 of 2016-01-22 on binet, modified by Debian
Windowing system distributor `The X.Org Foundation', version
11.0.11703000
System Description:     Debian GNU/Linux testing (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/emacs24:/etc/emacs:/usr/local/share/emacs/24.5/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.5/site-lisp:/usr/share/emacs/site-lisp
 --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/emacs24:/etc/emacs:/usr/local/share/emacs/24.5/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.5/site-lisp:/usr/share/emacs/site-lisp
 --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars
 'CFLAGS=-g -O2 -fstack-protector-strong -Wformat
 -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

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

Major mode: Lisp Interaction

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.
Entering debugger...
Back to top level.
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
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help-fns mail-prsvr mail-utils help-mode easymenu debug time-date
tooltip electric uniquify ediff-hook vc-hooks lisp-float-type mwheel
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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 gfilenotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 72870 4889)
 (symbols 48 17717 0)
 (miscs 40 39 113)
 (strings 32 9443 4228)
 (string-bytes 1 261156)
 (vectors 16 9072)
 (vector-slots 8 385056 15878)
 (floats 8 65 84)
 (intervals 56 229 4)
 (buffers 960 13)
 (heap 1024 16429 964))

Message #12 received at 22490-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Dan Torop <dant <at> pnym.net>
Cc: 22490-done <at> debbugs.gnu.org
Subject: Re: 24.5; (newline 0) fails when point not after newline
Date: Sat, 19 Mar 2016 21:35:07 +0200

> From: Dan Torop <dant <at> pnym.net>
> Date: Fri, 29 Jan 2016 13:46:47 -0500
> 
> The function "newline" with an argument of 0 will fail unless called
> when the character before the point is a newline. To test, start a new
> Emacs session, type space, then evaluate "(newline 0)". It should
> fail with a backtrace:
> 
> Debugger entered--Lisp error: (cl-assertion-failed (eq 10
> (char-before)))

Thanks, I fixed this for the upcoming Emacs 25.1.

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