bug#60021: 29.0.60; Eshell completion errors in the presence of buffer redirects

[Daniel Mendler]

1. Start emacs -Q
2. M-x eshell
3. ls > #<*scratch*> TAB

The following error is observed:

Debugger entered--Lisp error: (wrong-type-argument stringp #<buffer *scratch*>)
  pcomplete-match("\\`--[^=]+=\\(.*\\)" 0)
  pcomplete-here-using-help("ls --help")
  pcomplete/ls()
  pcomplete-completions()
  pcomplete-completions-at-point()

In GNU Emacs 29.0.60 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw scroll bars) of 2022-12-11 built on projects
Repository revision: f221105723dc8d3ee9f3c8d1c2717058afbc6666
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Configured using:
 'configure --prefix=/home/user/emacs/install --with-json
 --with-native-compilation --with-x-toolkit=athena --without-dbus
 --without-selinux --without-threads --without-gsettings --with-cairo'

Configured features:
CAIRO FREETYPE GIF GLIB GMP GNUTLS HARFBUZZ JPEG JSON LIBXML2 MODULES
NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 TIFF
TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM XINPUT2 XPM LUCID ZLIB

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

Major mode: Debugger

Minor modes in effect:
  shell-dirtrack-mode: t
  tooltip-mode: t
  global-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
  buffer-read-only: 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 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-fns
radix-tree cl-print byte-opt debug backtrace find-func pcmpl-unix
em-unix em-term term disp-table shell ehelp em-script em-prompt em-ls
em-hist em-pred em-glob em-extpipe em-cmpl em-dirs esh-var pcomplete
comint ansi-osc ansi-color ring em-basic em-banner em-alias esh-mode
eshell esh-cmd generator esh-ext esh-opt esh-proc esh-io esh-arg
esh-module esh-groups esh-util cus-edit pp cus-start cus-load wid-edit
cl-loaddefs comp comp-cstr warnings icons subr-x rx cl-seq cl-macs gv
cl-extra help-mode bytecomp byte-compile cl-lib files-x rmc iso-transl
tooltip cconv eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode 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 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 inotify
dynamic-setting font-render-setting cairo x-toolkit xinput2 x multi-tty
make-network-process native-compile emacs)

Memory information:
((conses 16 134689 10796)
 (symbols 48 11140 0)
 (strings 32 32175 1832)
 (string-bytes 1 996479)
 (vectors 16 21968)
 (vector-slots 8 436129 17427)
 (floats 8 49 31)
 (intervals 56 529 0)
 (buffers 976 14))