bug#40589: ^L printed when resizing Emacs split window using ksh93

[Mike Kupfer]

Lars Ingebrigtsen wrote:

> I tried to reproduce this in Emacs 26.1 (and 28), but I was unable to.
> Do you have a recipe, starting from "emacs -Q", that displays the
> problem?
> 
> I tried:
> 
> emacs -Q
> (setq shell-file-name "/bin/ksh")
> M-x shell
> 
> and then resizing the window, and nothing untoward happened.

Try

  emacs -Q
  M-x shell
  $ ksh
  C-x 2

On my Debian desktop (running Buster), that's enough to provoke
misbehavior, without even resizing.  Resizing just makes the issue more
apparent. :-) This is with Emacs 27.2 and Emacs 28 (15c57fc4cc); the
build information for Emacs 28 is below.  (The git changeset doesn't
match what I just wrote because my build includes a couple MH-E fixes
that I need to get reviewed before pushing to savannah.)

I also see the problem on a Debian Bullseye test system, using the
bundled Emacs 27.1 (emacs-lucid build).

cheers,
mike

In GNU Emacs 28.0.50 (build 5, x86_64-pc-linux-gnu, X toolkit, cairo version 
1.16.0, Xaw scroll bars)
 of 2021-06-06 built on alto
Repository revision: d933668e2d15cbb8e1fa367d97d2bff2559ff838
Repository branch: master-mdk
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Configured using:
 'configure --prefix=/usr/new'

Configured features:
CAIRO FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG LIBSELINUX
LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND THREADS TIFF
TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM LUCID ZLIB

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

Major mode: Shell

Minor modes in effect:
  shell-dirtrack-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
rfc822 mml mml-sec epa derived epg epg-config gnus-util rmail
rmail-loaddefs auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache json map 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 sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils help-mode
cl-loaddefs cl-lib shell pcomplete comint ansi-color ring iso-transl
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
easymenu timer select scroll-bar mouse jit-lock font-lock syntax
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 button loaddefs faces cus-face macroexp files
window text-properties overlay sha1 md5 base64 format env code-pages
mule custom widget hashtable-print-readable backquote threads inotify
dynamic-setting system-font-setting font-render-setting cairo x-toolkit
x multi-tty make-network-process emacs)

Memory information:
((conses 16 56240 5854)
 (symbols 48 7118 1)
 (strings 32 21011 1185)
 (string-bytes 1 677693)
 (vectors 16 13412)
 (vector-slots 8 178144 7617)
 (floats 8 27 48)
 (intervals 56 416 0)
 (buffers 992 12))