bug#45042: 27.1; emacs -nw on Windows does not always update cursor position on screen

[Ed Avis]

I installed the GNU Emacs build for Microsoft Windows x86_64 from the

GNU FTP site.  Rather than the graphical interface I am running it in

text mode using 'emacs.exe -nw'.  If run from the ancient Windows

command prompt (cmd.exe) this works well.  But in other terminal

emulators there is a strange problem where the cursor position is not

always updated.

For example, run Emacs inside the Alacritty terminal emulator.  Moving

point up and down with the arrow keys (or C-p and C-n) works, but moving

left and right (with arrows, C-b, C-f) does not update the visible

cursor on screen.  Point did move, as you can see by typing some

characters, and the visible cursor will update when you move up or down,

but horizontal movement doesn't seem to display.

If this were just one terminal emulator I would not suggest it as a bug

in Emacs, but the same thing happens when running an ssh server on the

Windows machine and running emacs -nw over ssh from another Windows

machine.  The cursor movement problem happens whether the ssh client is

OpenSSH (ssh.exe) running in cmd.exe, or ssh.exe running in Alacritty,

or from PuTTY (which combines ssh client and terminal emulator).

Quick experiments with setting TERM to 'vt100' instead of 'xterm' did

not find a fix.  Is there something Emacs can do to make sure the cursor

position on screen is always updated?

In GNU Emacs 27.1 (build 1, x86_64-w64-mingw32)

 of 2020-08-21 built on CIRROCUMULUS

Repository revision: 86d8d76aa36037184db0b2897c434cdaab1a9ae8

Repository branch: HEAD

Windowing system distributor 'Microsoft Corp.', version 10.0.18363

System Description: Microsoft Windows 10 Pro (v10.0.1909.18363.1198)

Recent messages:

For information about GNU Emacs and the GNU system, type C-h C-a.

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: ENG

  locale-coding-system: cp1252

Major mode: Fundamental

Minor modes in effect:

  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

  auto-composition-mode: t

  auto-encryption-mode: t

  auto-compression-mode: t

  buffer-read-only: 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 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/w32console 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 43590 9530)

 (symbols 48 6020 1)

 (strings 32 15201 1632)

 (string-bytes 1 502900)

 (vectors 16 6718)

 (vector-slots 8 78458 6176)

 (floats 8 18 317)

 (intervals 56 187 0)

 (buffers 1000 12))

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