bug#71778: 30.0.60; Eshell hangs when switching buffers during output redirection

[Sean Devlin <spd@toadstyle.org>]

Hi folks,

I've found it is possible to Eshell in the middle of a command. Here's a
recipe:

1. Emacs -Q
2. M-x eshell
3. In Eshell:

$ for x in 1 2 3 4 5 { echo hello ; sleep 2 } > #<buffer test>

4. While the above command is running, C-x b test
5. C-x b *eshell*

Observe that the loop will never finish and the Eshell buffer becomes
unresponsive. For example, pressing RET does nothing. Pressing C-c C-c
will terminate the command, but Eshell no longer accepts new commands.

Please let me know if I can provide additional information.

Thanks!

In GNU Emacs 30.0.60
Repository revision: fb11294d4156a4be45080ff286a8ee0d5a3ede9b
Repository branch: HEAD
Windowing system distributor 'Apple'
System Description:  macOS

Configured using:
'configure --with-ns'

Configured features:
ACL DBUS GLIB GNUTLS LCMS2 LIBXML2 MODULES NOTIFY KQUEUE NS PDUMPER PNG
RSVG SQLITE3 THREADS TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XIM ZLIB

Important settings:
  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
  show-paren-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
  minibuffer-regexp-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x 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 rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode 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 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 nadvice seq simple cl-generic
indonesian philippine 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 emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind kqueue cocoa ns
lcms2 multi-tty make-network-process emacs)

Memory information:
((conses 16 38769 9073) (symbols 48 5298 0) (strings 32 12476 2590)
(string-bytes 1 307951) (vectors 16 9391)
(vector-slots 8 114340 8902) (floats 8 21 3) (intervals 56 224 6)
(buffers 992 10))