bug#53220: 27.2; scroll-up moves point +1 if text has display property

bug#53220: 27.2; scroll-up moves point +1 if text has display property

[awrhygty]

Evaluate the form below and type 'C-v', the current point moves next to
the beginning of line.
Similarly, if the current point is at the window-start and type 'M-v',
the buffer scrolls down and the point moves next to the original position.

(let ((buf (generate-new-buffer "tmp"))
      (line (propertize "A" 'display "B")))
  (switch-to-buffer buf)
  (dotimes (i 100)
    (insert line ?\n))
  (goto-char (point-min)))


In GNU Emacs 27.2 (build 1, x86_64-w64-mingw32)
 of 2021-03-26 built on CIRROCUMULUS
Repository revision: deef5efafb70f4b171265b896505b92b6eef24e6
Repository branch: HEAD
Windowing system distributor 'Microsoft Corp.', version 10.0.19043
System Description: Microsoft Windows 10 Pro (v10.0.2009.19043.1415)

Recent messages:

Configured using:
 'configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY W32NOTIFY ACL GNUTLS LIBXML2
HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS MODULES THREADS JSON PDUMPER LCMS2 GMP

Important settings:
  value of $LANG: JPN
  locale-coding-system: cp932

Major mode: Lisp Interaction

Minor modes in effect:
  shell-dirtrack-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  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:
(thingatpt compile cl-extra python tramp-sh tramp tramp-loaddefs
trampver tramp-integration files-x tramp-compat parse-time iso8601 shell
pcomplete comint ansi-color ring misearch multi-isearch gnutls
network-stream nsm mailalias smtpmail auth-source cl-seq eieio
eieio-core cl-macs eieio-loaddefs json map tabify help-mode pp 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 time-date
subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
term/bobcat japan-util tooltip eldoc electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel dos-w32 ls-lisp disp-table term/w32-win
w32-win w32-vars term/common-win 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 w32notify w32 lcms2 multi-tty make-network-process
emacs)

Memory information:
((conses 16 95675 19110)
 (symbols 48 9331 6)
 (strings 32 29767 1791)
 (string-bytes 1 1076264)
 (vectors 16 19788)
 (vector-slots 8 633500 100238)
 (floats 8 51 199)
 (intervals 56 1994 0)
 (buffers 1000 21))

bug#53220: 27.2; scroll-up moves point +1 if text has display property

[Lars Ingebrigtsen]

awrhygty@outlook.com writes:

> Evaluate the form below and type 'C-v', the current point moves next to
> the beginning of line.
> Similarly, if the current point is at the window-start and type 'M-v',
> the buffer scrolls down and the point moves next to the original position.
>
> (let ((buf (generate-new-buffer "tmp"))
>       (line (propertize "A" 'display "B")))
>   (switch-to-buffer buf)
>   (dotimes (i 100)
>     (insert line ?\n))
>   (goto-char (point-min)))

I can reproduce this behaviour in Emacs 29, too.

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

bug#53220: 27.2; scroll-up moves point +1 if text has display property

[Eli Zaretskii]

tags 53220 wontfix
close 53220
thanks

> From: awrhygty@outlook.com
> Date: Thu, 13 Jan 2022 03:07:51 +0900
> 
> 
> Evaluate the form below and type 'C-v', the current point moves next to
> the beginning of line.
> Similarly, if the current point is at the window-start and type 'M-v',
> the buffer scrolls down and the point moves next to the original position.
> 
> (let ((buf (generate-new-buffer "tmp"))
>       (line (propertize "A" 'display "B")))
>   (switch-to-buffer buf)
>   (dotimes (i 100)
>     (insert line ?\n))
>   (goto-char (point-min)))

Preserving the column by scrolling commands is tricky in the presence
of display properties.  I fixed the C-v case (at least partially),
because it was a low-hanging fruit.  But the general solution, if it's
at all possible, is too complicated, and I see no reason to jump
through hoops for such obscure use cases.  We try very hard to
preserve the column during C-n/C-p, and that should be enough.

So I'm closing this bug report.