[root@localhost ~]# umount obash_completion: _comp_compgen: -C: invalid directory name `'
verlay

$ mkdir overlay
$ mount -t tmpfs tmpfs overlay/
$ umount o[TAB]bash_completion: _comp_compgen: -C: invalid directory name `'
verlay

$ mkdir overlay
$ mount -t tmpfs tmpfs overlay/
$ umount o[TAB]verlay

$ echo "$BASH_VERSION"
5.2.15(1)-release
$ IFS=.; echo "${BASH_COMPLETION_VERSINFO[*]}"
2.12.0

# Add relative paths to COMPREPLY
if [[ $cur && $cur != /* ]]; then
    local realcur
    [[ $cur == */ ]] && # don't let readlink drop last / from path
        realcur="$(readlink -f "$cur." 2>/dev/null)/" ||
        realcur=$(readlink -f "$cur" 2>/dev/null)
    if [[ $realcur ]]; then
        local dirrealcur="" dircur="" basecur
        if [[ $cur == */* ]]; then
            dirrealcur="${realcur%/*}/"
            dircur="${cur%/*}/"
        fi
        basecur=${cur#"$dircur"}
        local i
        for i in ${!COMPREPLY[*]}; do
            [[ ${COMPREPLY[i]} == "$realcur"* ]] &&
                _comp_compgen -aC "$dircur" -c "$basecur" -- \
                    -f -d -P "$dircur" -X "!${COMPREPLY[i]##"$dirrealcur"}"
        done
    fi
fi

C)
    if [[ ! $OPTARG ]]; then
        printf 'bash_completion: %s: -C: invalid directory name `%s'\''\n' "$FUNCNAME" "$OPTARG" >&2
        return 2
    fi
    _dir=$OPTARG
    ;;