bug#67830: 30.0.50; find-file completion sometimes unexpectedly omits directories

[Markus Triska <triska@metalevel.at>]

To reproduce this issue, please first create the directory ~/issue/.git,
and the file ~/issue/.gitignore, for example with:

    $ mkdir issue
    $ cd issue/
    $ mkdir .git
    $ touch .gitignore

Then, from your home directory, start Emacs with:

    $ emacs -Q

and do:

    C-x C-f ~/issue/.git TAB

As expected, the minibuffer displays:

    [Complete, but not unique]

and Emacs also shows the 2 possible completions:

    2 possible completions:
    .git/
    .gitignore

In contrast, when I do:

    C-x C-f ~/issue/. TAB

then the minibuffer prematurely completes it to the file:

    ~/issue/.gitignore

This is even though the directory ~/issue/.git exists, and also forms a
valid and expected completion of "~/issue/.".

The expected behaviour is the same as above, on the grounds that
"~/issue/." is a proper prefix of "~/issue/.git" and therefore should
never yield fewer possible completions.

Thank you and all the best,
Markus


In GNU Emacs 30.0.50 (build 1, x86_64-apple-darwin18.2.0, X toolkit,
 cairo version 1.17.6, Xaw scroll bars) of 2023-09-11 built on
 mac
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description:  Mac OS X 10.14.2

Configured using:
 'configure --prefix=/opt/local --disable-silent-rules --without-ns
 --without-dbus --without-gconf --without-libotf --without-m17n-flt
 --with-libgmp --with-gnutls --with-json --with-xml2 --with-modules
 --with-sqlite3 --with-webp --infodir /opt/local/share/info/emacs
 --with-x-toolkit=lucid --without-xaw3d --without-imagemagick --with-xpm
 --with-jpeg --with-tiff --with-gif --with-png --with-lcms2
 --without-rsvg --with-xft --with-native-compilation=aot
 --with-tree-sitter 'CFLAGS=-pipe -Os -Wno-attributes
 -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk -arch
 x86_64' 'CPPFLAGS=-I/opt/local/include
 -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk'
 'LDFLAGS=-L/opt/local/lib -Wl,-headerpad_max_install_names -lfreetype
 -lfontconfig -Wl,-rpath /opt/local/lib/gcc12 -Wl,-no_pie
 -Wl,-syslibroot,/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk
 -arch x86_64''

Configured features:
ACL CAIRO FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LCMS2 LIBXML2 MODULES NATIVE_COMP NOTIFY KQUEUE PDUMPER PNG SQLITE3
THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINPUT2
XPM LUCID ZLIB