Subject: 28.0.50; Spurious output from term-emulate-terminal when in line-mode

From: Massimiliano Mirra <[email-masked]>
Date: Fri, 28 May 2021 16:00:52 +0100

Spurious output is occasionally produced when running a command
with `make-term', and the command performs cursor movements and
partial screen clears.

- Reproduction #1 shows what happens when using `yarn' to install
  packages in a NodeJS project. (For ease and reliability of
  reproduction, a recording made with script(1) is run instead
  of the actual command.)

  Run with: emacs -Q -l repro-1.el
  Preview: https://asciinema.org/a/4mMv1aIrMmizwxr01AaEXMQqe

- Reproduction #2 shows a minimal (provided) Python program that
  creates a progress bar.

  Run with: emacs -Q -l repro-2.el
  Preview: https://asciinema.org/a/K6XCPbgkuqk6op4KQyiX9L5n7

The problem only happens in `term-line-mode' (the default).
`term-char-mode' works fine.  It is affected by the rate of output:
changing "scriptreplay" in repro-1.el to "scriptreplay -d 5" (5x
speed) still produces different, though still wrong, output.

The culprit appears to be following lines from `term-emulate-terminal'
in term.el; commenting them out fixes this problem:

   (when (and (> (point-max) (process-mark proc))
      (term-in-line-mode))
     (narrow-to-region (point-min) (process-mark proc)))

In GNU Emacs 28.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.29,
cairo version 1.17.4)
 of 2021-05-16 built on 956e3d7386ff
Repository revision: 78575c53fc8c78de1494822f9f6680e2a21308d6
Repository branch: pgtk-nativecomp
Windowing system distributor 'System Description: Arch Linux

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --mandir=/usr/share/man --with-gameuser=:games
 --with-sound=alsa --with-modules --with-x-toolkit=gtk3 --with-cairo
 --with-xwidgets --with-native-compilation --with-pgtk
 --without-compress-install --without-gconf --without-gsettings
 --without-m17n-flt --enable-autodepend --enable-link-time-optimization
 CC=/usr/bin/clang 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe
 -fno-plt -fexceptions -Wp,-D_FORTIFY_SOURCE=2,-D_GLIBCXX_ASSERTIONS
 -Wformat -Werror=format-security -fstack-clash-protection
 -fcf-protection -g -flto'
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now
 'CPP=/usr/bin/clang -E''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM HARFBUZZ JPEG JSON LCMS2
LIBOTF LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER
PGTK PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS XIM
XWIDGETS GTK3 ZLIB

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

Major mode: Lisp Interaction

Minor modes in effect:
  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:
(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 cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
iso-transl tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/pgtk-win pgtk-win 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 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
xwidget-internal dbusbind inotify dynamic-setting font-render-setting
cairo move-toolbar gtk x-toolkit pgtk lcms2 multi-tty
make-network-process native-compile emacs)

Memory information:
((conses 16 69245 8432)
 (symbols 48 6922 0)
 (strings 32 20554 2262)
 (string-bytes 1 684028)
 (vectors 16 13527)
 (vector-slots 8 293613 14217)
 (floats 8 22 39)
 (intervals 56 240 0)
 (buffers 992 10))

-- 
Massimiliano Mirra
massimilianomirra.com