GNU bug report logs - #65531
29.1; Inconsistent behaviour when restoring from ansi-term's alternate screen

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Hao Chi Kiang <hao.chi.kiang <at> liu.se>
To: "bug-gnu-emacs <at> gnu.org" <bug-gnu-emacs <at> gnu.org>
Subject: 29.1; Inconsistent behaviour when restoring from ansi-term's
 alternate screen
Date: Fri, 25 Aug 2023 10:00:30 +0000

Hi,

Emacs's ansi-term supports alternate screens and these can be used by
issuing `tput smcup' and `tput rmcup'. In ansi-term, there seems to be
a bug that results in the entire terminal being scrolled one line when
the cursor is at the end of the terminal. This means that the cursor
will be at a wrong position after restoring from alternate screen, as
shown is the following example.

Steps to reproduce
------------------

1. Open Emacs by `emacs -Q' in GUI mode
2. Maximize the GUI window so that it's wide enough to show a long shell
   command in one line.
2. C-x ansi-term
3. Issue the command in one line:
echo -n 'Hello'; tput sc; tput smcup; echo -n 'World'; tput rmcup; tput rc
4. Now the current line in the terminal should be `Hello~$ '. This is
   the correct behaviour.
5. Now press Enter key repeatedly until the cursor ends up at last line
   of the screen.
6. Issue the same command as in Step 3.
7. The terminal is now shows:
Hello
     ~$
   Notice this is a different output from that of Step 3.

The output given by Step 7 is wrong, or at least none of common
terminals such as xterm, tmux and konsole do this. 

I believe the problem is that in Step 7, the entire screen is scrolled
up by a line before the new $PS1 is printed. This is because I've been
developing a tab-completion functionality for a programming language,
and in my case even without $PS1 the entire screen is still scrolled.
You can also see this scrolling by appending '; sleep 999' to the
shell command at Step 3 in order to suppress $PS1.

Best regards,
Hao Chi Kiang

System Information
------------------

In GNU Emacs 29.1 (build 2, x86_64-unknown-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.16.0) of 2023-08-03 built on a-fsn-de
Windowing system distributor 'The X.Org Foundation', version 11.0.12101008
System Description: Void Linux

Configured using:
 'configure --with-x-toolkit=gtk3 --with-xwidgets --prefix=/usr
 --sysconfdir=/etc --sbindir=/usr/bin --bindir=/usr/bin
 --mandir=/usr/share/man --infodir=/usr/share/info --localstatedir=/var
 --host=x86_64-unknown-linux-gnu --build=x86_64-unknown-linux-gnu
 '--libdir=${exec_prefix}/lib64' --with-file-notification=inotify
 --with-modules --with-jpeg --with-tiff --with-gif --with-png
 --with-webp --with-xpm --with-rsvg --without-imagemagick --with-xml2
 --with-gnutls --with-sound --with-m17n-flt --with-json --with-harfbuzz
 --with-cairo --with-libgmp --with-sqlite --with-tree-sitter
 --with-native-compilation=aot 'CFLAGS=-fno-PIE -mtune=generic -O2 -pipe
 -g -ffile-prefix-map=/builddir/emacs-29.1=.' 'CPPFLAGS= '
 'LDFLAGS=-no-pie -Wl,--as-needed ''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LCMS2 LIBOTF LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER
PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS
TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM XWIDGETS GTK3 ZLIB

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: sv_SE.UTF-8
  value of $XMODIFIERS: @im=fcitx
  locale-coding-system: utf-8-unix

Major mode: Shell-script

Minor modes in effect:
  sh-electric-here-document-mode: t
  windmove-mode: t
  global-git-commit-mode: t
  magit-auto-revert-mode: t
  auto-revert-mode: t
  TeX-PDF-mode: t
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  visible-mark-mode: t
  minions-mode: t
  shackle-mode: t
  minibuffer-depth-indicate-mode: t
  icicle-mode: t
  global-corfu-mode: t
  corfu-mode: t
  pretty-control-l-mode: t
  global-whitespace-mode: t
  shell-dirtrack-mode: t
  override-global-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
/home/hckiang/.emacs.d/elpa/transient-20220717.1713/transient hides /usr/share/emacs/29.1/lisp/transient
/home/hckiang/.emacs.d/elpa/use-package-20210207.1926/use-package-delight hides /usr/share/emacs/29.1/lisp/use-package/use-package-delight
/home/hckiang/.emacs.d/elpa/use-package-20210207.1926/use-package-jump hides /usr/share/emacs/29.1/lisp/use-package/use-package-jump
/home/hckiang/.emacs.d/elpa/use-package-20210207.1926/use-package hides /usr/share/emacs/29.1/lisp/use-package/use-package
/home/hckiang/.emacs.d/elpa/use-package-20210207.1926/use-package-core hides /usr/share/emacs/29.1/lisp/use-package/use-package-core
/home/hckiang/.emacs.d/elpa/use-package-20210207.1926/use-package-bind-key hides /usr/share/emacs/29.1/lisp/use-package/use-package-bind-key
/home/hckiang/.emacs.d/elpa/use-package-20210207.1926/use-package-ensure hides /usr/share/emacs/29.1/lisp/use-package/use-package-ensure
/home/hckiang/.emacs.d/elpa/use-package-20210207.1926/use-package-diminish hides /usr/share/emacs/29.1/lisp/use-package/use-package-diminish
/home/hckiang/.emacs.d/elpa/use-package-20210207.1926/use-package-lint hides /usr/share/emacs/29.1/lisp/use-package/use-package-lint
/home/hckiang/.emacs.d/elpa/bind-key-20210210.1609/bind-key hides /usr/share/emacs/29.1/lisp/use-package/bind-key

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Memory information:
((conses 16 2024913 273749)
 (symbols 48 87084 3)
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 (string-bytes 1 13274489)
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