Show external command line if appropriate

Since I'm already dealing with the fish shell.

All of our supported shells seem to handle cursor position
in Unicode (wide character) codepoints.

It was easiest and most straight-forward to pass the data
through yet-unused program arguments.

The cursor position is marked by a Unicode glyph equivalent
to ACS_DIAMOND, although ncurses doesn't get a chance
to make any ACS translation.

README.adoc

@@ -55,7 +55,7 @@ To start using this navigator, put the following in your '.zshrc':
 ----
 sdn-navigate () {
   # ... possibly zle-line-init
-  while eval "`sdn`"; do
+  while eval "`sdn "$BUFFER" "$CURSOR"`"; do
     [ -z "$cd" ] || cd "$cd"
     [ -z "$insert" ] || LBUFFER="$LBUFFER$insert "
     [ -z "$helper" ] && break
@@ -74,7 +74,9 @@ To start using this navigator, put the following in your 'config.fish':
 ----
 function sdn-navigate
   set --local IFS
-  while eval (sdn | string replace -ar '^(.*?)=' 'set --$1 ')
+  set --local buffer (commandline)
+  set --local cursor (commandline --cursor)
+  while eval (sdn $buffer $cursor | string replace -ar '^(.*?)=' 'set --$1 ')
     test -z "$cd" || cd "$cd"
     test -z "$insert" || commandline --insert "$insert "
     test -z "$helper" && break
@@ -96,7 +98,7 @@ sdn-navigate () {
   SDN_L=$READLINE_LINE SDN_P=$READLINE_POINT
   READLINE_LINE=
 
-  while eval "`sdn`"; do
+  while eval "`sdn "$SDN_L" "$SDN_P"`"; do
     [[ -z "$cd" ]] || cd "$cd"
     [[ -z "$insert" ]] || {
       SDN_L="${SDN_L:0:$SDN_P}$insert ${SDN_L:$SDN_P}"
@@ -129,6 +131,7 @@ cursor 231 202
 bar 16 255 ul
 cwd bold
 input
+cmdline 102
 ....
 
 Filename colours are taken from the `LS_COLORS` environment variable.

sdn.cpp

@@ -495,6 +495,7 @@ struct level {
 };
 
 static struct {
+	wstring cmdline;                    ///< Outer command line
 	string cwd;                         ///< Current working directory
 	string start_dir;                   ///< Starting directory
 	vector<entry> entries;              ///< Current directory entries
@@ -525,9 +526,10 @@ static struct {
 	void (*editor_on_change) ();        ///< Callback on editor change
 	void (*editor_on_confirm) ();       ///< Callback on editor confirmation
 
-	enum { AT_CURSOR, AT_BAR, AT_CWD, AT_INPUT, AT_COUNT };
+	enum { AT_CURSOR, AT_BAR, AT_CWD, AT_INPUT, AT_CMDLINE, AT_COUNT };
-	chtype attrs[AT_COUNT] = {A_REVERSE, 0, A_BOLD, 0};
+	chtype attrs[AT_COUNT] = {A_REVERSE, 0, A_BOLD, 0, 0};
-	const char *attr_names[AT_COUNT] = {"cursor", "bar", "cwd", "input"};
+	const char *attr_names[AT_COUNT] =
+		{"cursor", "bar", "cwd", "input", "cmdline"};
 
 	map<int, chtype> ls_colors;         ///< LS_COLORS decoded
 	map<string, chtype> ls_exts;        ///< LS_COLORS file extensions
@@ -746,6 +748,9 @@ fun update () {
 	} else if (!g.message.empty ()) {
 		move (LINES - 1, 0);
 		print (apply_attrs (g.message, 0), COLS);
+	} else if (!g.cmdline.empty ()) {
+		move (LINES - 1, 0);
+		print (apply_attrs (g.cmdline, g.attrs[g.AT_CMDLINE]), COLS);
 	}
 
 	refresh ();
@@ -1352,6 +1357,18 @@ fun inotify_check () {
 		update ();
 }
 
+fun load_cmdline (int argc, char *argv[]) {
+	if (argc < 3)
+		return;
+
+	wstring line = to_wide (argv[1]); int point = atoi (argv[2]);
+	if (line.empty () || point < 0 || point > (int) line.length ())
+		return;
+
+	std::replace_if (line.begin (), line.end (), iswspace, L' ');
+	g.cmdline = line.substr (0, point) + L"◆" + line.substr (point);
+}
+
 fun decode_ansi_sgr (const vector<string> &v) -> chtype {
 	vector<int> args;
 	for (const auto &arg : v) {
@@ -1627,9 +1644,6 @@ fun save_config () {
 }
 
 int main (int argc, char *argv[]) {
-	(void) argc;
-	(void) argv;
-
 	// That bitch zle closes stdin before exec without redirection
 	(void) close (STDIN_FILENO);
 	if (open ("/dev/tty", O_RDWR)) {
@@ -1658,6 +1672,7 @@ int main (int argc, char *argv[]) {
 		return 1;
 	}
 
+	load_cmdline (argc, argv);
 	load_colors ();
 	g.start_dir = g.cwd = initial_cwd ();
 	reload (false);