bug#65089: 30.0.50; shell-command filename completion unexpected behavior change

[Mauro Aranda <maurooaranda@gmail.com>]

Before running emacs, setup a directory tree like this:
mkdir bug bug/foo-1 bug/foo-2 bug/foo-1/bar bug/foo-2/bar
under HOME, for simplicity.

Now, with emacs -Q:
M-!
ls ~/bug/bar
Put point between "/" and "b" of "bar" and type TAB
emacs says "No match", but I expected it to offer completions, foo-1 and
foo-2.

That was the behavior, at least in Emacs 28.  Reverting the following
commit, returns this behavior for me:

commit a9941269683fe50673d0aa81feefb7a9d3d8a6b9
Author: Augusto Stoffel <arstoffel@gmail.com>
Date:   Thu Sep 8 11:09:42 2022 +0200

     pcomplete: Generate completions from --help messages

     * lisp/pcomplete.el (pcomplete-from-help): New function (and hash
     table) to get pcomplete candidates from help messages.
     (pcomplete-here-using-help): Helper function to define pcomplete for
     simple commands
     (pcomplete-completions-at-point): Provide annotation-function and
     company-docsig properties.
     * lisp/pcmpl-git.el: New file, provides pcomplete for Git.
     * lisp/pcmpl-gnu.el: Add pcomplete for awk, gpg and gdb, emacs and
     emacsclient.
     * lisp/pcmpl-linux.el: Add pcomplete for systemctl and journalctl.
     * lisp/pcmpl-rpm.el: Add pcomplete for dnf.
     * lisp/pcmpl-unix.el: Add pcomplete for sudo and most commands found
     in GNU Coreutils.
     * lisp/pcmpl-x.el: Add pcomplete for tex, pdftex, latex, pdflatex,
     rigrep and rclone.
     * test/lisp/pcomplete-tests.el (pcomplete-test-parse-gpg-help,
     pcomplete-test-parse-git-help): Tests for the new functions.


And my current workaround is to move pcomplete-completions-at-point to
the end in shell-dynamic-complete-functions, following what was done in
Bug#34330.


In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
  3.24.33, cairo version 1.16.0) of 2023-08-03 built on tbb-desktop
Repository revision: 0c2152222ad16ba9e68cdb27fc281755ec187620
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12201001
System Description: Ubuntu 22.04.2 LTS

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

Important settings:
   value of $LC_MONETARY: es_AR.UTF-8
   value of $LC_NUMERIC: es_AR.UTF-8
   value of $LC_TIME: es_AR.UTF-8
   value of $LANG: en_US.UTF-8
   value of $XMODIFIERS: @im=ibus
   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
   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/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 threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo gtk
x-toolkit xinput2 x multi-tty move-toolbar make-network-process emacs)

Memory information:
((conses 16 46943 13845) (symbols 48 5701 0) (strings 32 16383 1535)
  (string-bytes 1 545790) (vectors 16 11987)
  (vector-slots 8 210580 14004) (floats 8 21 23) (intervals 56 209 0)
  (buffers 984 10))