bug#15224: 24.3; newline does not move point to next line

bug#15224: 24.3; newline does not move point to next line

[Nils Anders Danielsson]

Bug description
---------------

In some situations newline fails to move point to the next line, even
though the newly inserted line is blank.

To reproduce the bug, run the following command:

   emacs -Q --eval '(progn (fundamental-mode)

                           (modify-syntax-entry ?/  ". 124b")
                           (modify-syntax-entry ?*  ". 23")
                           (modify-syntax-entry ?\n "> b")

                           (setq comment-start "// ")

                           (auto-fill-mode 1)
                           (setq fill-column 9)
                           (setq comment-auto-fill-only-comments t)

                           (insert "/*  //x  x")
                           (newline))'

Expected result: A newline character should be inserted, and point
should move to the next line.

Actual result: A newline character is inserted, but point is not moved.
The *Messages* buffer contains the following message:

   comment-search-backward: Beginning of buffer

The definition of comment-search-backward contains the following
possibly relevant comment:

   ;; FIXME: If a comment-start appears inside a comment, we may erroneously
   ;; stop there.  This can be rather bad in general, but since
   ;; comment-search-backward is only used to find the comment-column (in
   ;; comment-set-column) and to find the comment-start string (via
   ;; comment-beginning) in indent-new-comment-line, it should be harmless.

Emacs configuration
-------------------

In GNU Emacs 24.3.1 (i686-pc-linux-gnu, GTK+ Version 3.6.4)
  of 2013-08-22 on meitnerium, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11303000
System Description:	Ubuntu 13.04

Configured using:
  `configure '--build' 'i686-linux-gnu' '--build' 'i686-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/24.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.3/site-lisp:/usr/share/emacs/site-lisp'
  '--with-crt-dir=/usr/lib/i386-linux-gnu' '--with-x=yes'
  '--with-x-toolkit=gtk3' '--with-toolkit-scroll-bars'
  'build_alias=i686-linux-gnu' 'CFLAGS=-g -O2 -fstack-protector
  --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall'
  'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro'
  'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
   value of $LC_COLLATE: en_GB.UTF-8
   value of $LC_CTYPE: en_GB.UTF-8
   value of $LC_MESSAGES: en_GB.UTF-8
   value of $LC_MONETARY: sv_SE.UTF-8
   value of $LC_NUMERIC: sv_SE.UTF-8
   value of $LC_TIME: en_DK.UTF-8
   value of $LANG: en_GB.UTF-8
   locale-coding-system: utf-8-unix
   default enable-multibyte-characters: t

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)

-- 
/NAD

bug#15224: 24.3; newline does not move point to next line

[Lars Ingebrigtsen]

Nils Anders Danielsson <nad@cse.gu.se> writes:

> Bug description
> ---------------
>
> In some situations newline fails to move point to the next line, even
> though the newly inserted line is blank.
>
> To reproduce the bug, run the following command:
>
>   emacs -Q --eval '(progn (fundamental-mode)
>
>                           (modify-syntax-entry ?/  ". 124b")
>                           (modify-syntax-entry ?*  ". 23")
>                           (modify-syntax-entry ?\n "> b")
>
>                           (setq comment-start "// ")
>
>                           (auto-fill-mode 1)
>                           (setq fill-column 9)
>                           (setq comment-auto-fill-only-comments t)
>
>                           (insert "/*  //x  x")
>                           (newline))'
>
> Expected result: A newline character should be inserted, and point
> should move to the next line.
>
> Actual result: A newline character is inserted, but point is not moved.
> The *Messages* buffer contains the following message:
>
>   comment-search-backward: Beginning of buffer

(I'm going through old bug reports that have unfortunately gotten no
responses yet.)

I'm unable to reproduce this bug in Emacs 27, so I'm guessing it's been
fixed in the intervening years.  If you can still see this bug in Emacs
27, please reopen the bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no