Subject: 27.1.91; abnormal whitespace-mode behavior

From: Frédéric Baldit <[email-masked]>
Date: Wed, 17 Feb 2021 15:06:14 +0100

--text follows this line--

Recipe to reproduce the bug:

1) I'm using emacs version 27.1.91 built from git sources in my /home
   directory (same bug is experimented with emacs version 26.1 installed
   from debian stable package). Command used to run emacs:

emacs -Q test.txt &

2) M-x whitespace-mode RET

3) type the following text («.» for spacebar key):

«....First line of text in emacs», then type RET

4) DEL DEL to suppress backward two spaces on line 2, then type text
«Second one»

5) M-2 M-b

6) TAB TAB TAB TAB: point should be at line 2, column 18, vertically
aligned with fourth word of line 1 («text»), but it is at column 26:
that's the bug.

Rq1: what is curious (to me) is that deactivating whitespace-mode
removes abnormally inserted tab character (8 spaces) and everything is
OK.

Rq2: I noted that with a different text, this behavior of
whitespace-mode disappears. For example, if one uses the following first
line of text:

«....This.is.a.first.line.of.text.with.a.few.words»,

then the result of typing TAB multiple times is as expected, with or
without whitespace-mode activated!

Rq3: as I'm not an emacs expert, I first posted on help-gnu-emacs list
in order to see if someone could explain me what I was missing:

https://lists.gnu.org/archive/html/help-gnu-emacs/2021-02/msg00321.html

Nobody explained me why I see this behavior (of whitespace-mode), thus I
came to the conclusion it might be a bug (both answers are from persons
using emacs 28.0.50). I must say that I followed as precisely as I could
the advices found to submit a bug, in particular I read and followed
«52-Reporting bugs» of emacs manual.

--end of bug description--

In GNU Emacs 27.1.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2021-02-04 built on Cornafion
Repository revision: 89f1634afcca318def07151424a21b81c70acd76
Repository branch: emacs-27
Windowing system distributor 'The X.Org Foundation', version
11.0.12004000 System Description: Debian GNU/Linux 10 (buster)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Whitespace mode enabled in current buffer
You can run the command ‘whitespace-mode’ with M-x whit-m RET
Whitespace mode enabled in current buffer
Auto-saving...done
Auto-saving...done
Making completion list...

Configured using:
 'configure --prefix=/home/fred/emacs-03022021/'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GSETTINGS GLIB NOTIFY INOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD PDUMPER
LCMS2 GMP

Important settings:
  value of $LC_MONETARY: fr_FR.UTF-8
  value of $LC_NUMERIC: fr_FR.UTF-8
  value of $LC_TIME: fr_FR.UTF-8
  value of $LANG: fr_FR.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Text

Minor modes in effect:
  whitespace-mode: t
  tooltip-mode: t
  global-eldoc-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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search seq
byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils time-date subr-x
cl-loaddefs cl-lib disp-table whitespace tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite charscript charprop case-table epa-hook
jka-cmpr-hook help simple abbrev obarray cl-preloaded 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 threads dbusbind inotify lcms2 dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 49999 5008)
 (symbols 48 6166 1)
 (strings 32 16282 1605)
 (string-bytes 1 538103)
 (vectors 16 10378)
 (vector-slots 8 138289 8918)
 (floats 8 20 41)
 (intervals 56 535 0)
 (buffers 1000 14))

--
  Frédéric Baldit