zsh:ls-show-hidden: Fix non_existing arg parsing

`ls` prints a warning if a non-flag argument is specified that does not
exist.

Previously ls-show-hidden assumed that all arguments that are neither a
directory nor an otherwise existing file are flags. As all flags are
passed to the ls call the warning still got printed, but this also lead
to the current working directory (i.e. `.`) being added to the
directories to process.

If `ls` expects an argument to a flag, it is always passed in the format
`--flag=arg` where the equal sign is mandatory. This makes it possible
to simply filter out all flags (and their arguments) from the other
arguments without needing to know which flags take an argument and which
don't.

Fix this behaviour by printing the same warning as `ls` does when an
argument is neither a flag, nor a directory nor an existing file. Also
only add `.` to the directories if *really* only flags were passed.

.config/zsh/autoload/ls-show-hidden

@@ -14,28 +14,38 @@ builtin emulate -L zsh -o no_glob_dots -o null_glob
 # files should always be listed.
 builtin local LS_SHOW_ALL_DIRS=${LS_SHOW_ALL_DIRS:-"dotfiles|\.config"}
 
+# ANSI escape codes to print in color
+builtin local ansi_bold_red=$'\e[31;1m'
+builtin local ansi_reset=$'\e[m'
+
 builtin local LS_COMMAND=ls
 # Use GNU version if available under MacOS
 if [[ $OSTYPE =~ darwin ]] && (( $+commands[gls] )); then
 	LS_COMMAND=gls
 fi
 
+builtin local non_existing=0
 builtin local -a dirs files
-# Pop files and folders from arguments and put them in the corresponding array.
-# All other arguments are kept.
+# Pop files and folders from arguments and put them in the corresponding array,
+# keep flags (ls takes flag-arguments behind a '=') and warn when non-existing
+# arguments were passed.
 for arg in "$@"; do
 	shift
-	if [[ -d "$arg" ]]; then
+	if [[ ${arg#-} != $arg ]]; then
+		set -- "$@" "$arg"
+	elif [[ -d "$arg" ]]; then
 		dirs+="$arg"
 	elif [[ -e "$arg" ]]; then
 		files+="$arg"
 	else
-		set -- "$@" "$arg"
+		printf >&2 "%s%s: cannot access '%s': No such file or directory%s\n" \
+			"$ansi_bold_red" "$0" "$arg" "$ansi_reset"
+		non_existing=1
 	fi
 done
 
 # Print working directory when only flags were given as arguments.
-if ! (( ${#dirs} + ${#files} )); then
+if ! (( ${#dirs} + ${#files} + $non_existing )); then
 	dirs+=.
 fi