bug#39075: 28.0.50; Emacs hangs on 100% CPU and grows beyond bounds in shell-mode

[Pieter van Oostrum <pieter@vanoostrum.org>]

1) Emacs -Q
2) M-x shell
3) type some command, and use some filename completions on the way
(using TAB).
4) Type a semicolon (;)

Now Emacs hangs, the ; does not appear, and it doesn't react to a C-g typed.
It uses 100% CPU and memory grows beyond bounds, eventually just making
my whole computer unresponsive.

Typing a whole series of C-g's might stop the loop (with the ; appearing
then) or it might crash Emacs:
Fatal error 11: Segmentation fault
Abort trap: 6

This report is typed in a session where the sequence of C-g's did stop
the loop.
The C-g caused this message:
Error in post-command-hook (completion-in-region--postch): (quit)
Although the option Enter debugger on Quit/C-g was set, no backtrace was
generated.

This emacs was compiled from master today, but it also happens in earlier versions.


In GNU Emacs 28.0.50 (build 1, i686-apple-darwin10.0.0, NS appkit-1561.61 Version 10.13.6 (Build 17G10021))
 of 2020-01-10 built on cochabamba.vanoostrum.org
Repository revision: 17cfd708575c351d030f8b05c5921d1867028d79
Repository branch: fix
Windowing system distributor 'Apple', version 10.3.1561
System Description:  Mac OS X 10.13.6

Recent messages:
Quit
No match [2 times]
~ 
Error in post-command-hook (completion-in-region--postch): (quit)
Quit [2 times]
Complete, but not unique
Making completion list...
Complete, but not unique
Error in post-command-hook (completion-in-region--postch): (quit)
Quit
Quit
Configured using:
 'configure --build i686-apple-darwin10.0.0 --without-dbus --with-ns
 build_alias=i686-apple-darwin10.0.0 'CFLAGS=-pipe -march=nocona'
 PKG_CONFIG_PATH=/opt/local/lib/pkgconfig/:/usr/X11R6/pkgconfig/:/usr/local/lib/pkgconfig/:/usr/lib/pkgconfig/'

Configured features:
RSVG GLIB NOTIFY KQUEUE ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS XIM
NS MODULES THREADS PDUMPER LCMS2

Important settings:
  value of $LC_CTYPE: UTF-8
  value of $LANG: en_GB.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
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
shell pcomplete comint ansi-color ring tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/ns-win ns-win
ucs-normalize mule-util 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 kqueue cocoa ns
lcms2 multi-tty make-network-process emacs)

Memory information:
((conses 16 55230 57689)
 (symbols 48 7130 11)
 (strings 32 18286 5181)
 (string-bytes 1 600859)
 (vectors 16 11939)
 (vector-slots 8 157593 69152)
 (floats 8 19 126)
 (intervals 56 1161 97)
 (buffers 1000 14))

-- 
Pieter van Oostrum <pieter@vanoostrum.org>
www: http://pieter.vanoostrum.org/
PGP key: [8DAE142BE17999C4]


-- 
Pieter van Oostrum <pieter@vanoostrum.org>
www: http://pieter.vanoostrum.org/
PGP key: [8DAE142BE17999C4]