Focus events can cause trouble if left on and they can't be turned off

during idle periods (like the other states are) because we'd miss
events. So add a server option to control them. Defaults to off.

options-table.c

@@ -76,6 +76,11 @@ const struct options_table_entry server_options_table[] = {
 	  .default_num = 0
 	},
 
+	{ .name = "focus-events",
+	  .type = OPTIONS_TABLE_FLAG,
+	  .default_num = 0
+	},
+
 	{ .name = "quiet",
 	  .type = OPTIONS_TABLE_FLAG,
 	  .default_num = 0 /* overridden in main() */

server-client.c

@@ -548,6 +548,15 @@ server_client_check_focus(struct window_pane *wp)
 {
 	u_int		 i;
 	struct client	*c;
+	int		 push;
+
+	/* Are focus events off? */
+	if (!options_get_number(&global_options, "focus-events"))
+		return;
+
+	/* Do we need to push the focus state? */
+	push = wp->flags & PANE_FOCUSPUSH;
+	wp->flags &= ~PANE_FOCUSPUSH;
 
 	/* If we don't care about focus, forget it. */
 	if (!(wp->base.mode & MODE_FOCUSON))
@@ -580,13 +589,13 @@ server_client_check_focus(struct window_pane *wp)
 	}
 
 not_focused:
-	if (wp->flags & PANE_FOCUSED)
+	if (push || (wp->flags & PANE_FOCUSED))
 		bufferevent_write(wp->event, "\033[O", 3);
 	wp->flags &= ~PANE_FOCUSED;
 	return;
 
 focused:
-	if (!(wp->flags & PANE_FOCUSED))
+	if (push || !(wp->flags & PANE_FOCUSED))
 		bufferevent_write(wp->event, "\033[I", 3);
 	wp->flags |= PANE_FOCUSED;
 }

tmux.1

@@ -2092,6 +2092,14 @@ The default is 500 milliseconds.
 .Op Ic on | off
 .Xc
 If enabled, the server will exit when there are no attached clients.
+.It Xo Ic focus-events
+.Op Ic on | off
+.Xc
+When enabled, focus events are requested from the terminal if supported and
+passed through to applications running in
+.Nm .
+Attached clients should be detached and attached again after changing this
+option.
 .It Xo Ic quiet
 .Op Ic on | off
 .Xc

tmux.h

@@ -941,6 +941,7 @@ struct window_pane {
 #define PANE_DROP 0x2
 #define PANE_FOCUSED 0x4
 #define PANE_RESIZE 0x8
+#define PANE_FOCUSPUSH 0x10
 
 	char		*cmd;
 	char		*shell;
@@ -1232,6 +1233,7 @@ struct tty {
 #define TTY_UTF8 0x8
 #define TTY_STARTED 0x10
 #define TTY_OPENED 0x20
+#define TTY_FOCUS 0x40
 	int		 flags;
 
 	int		 term_flags;
@@ -1383,6 +1385,9 @@ struct cmd {
 	char			*file;
 	u_int			 line;
 
+#define CMD_CONTROL 0x1
+	int			 flags;
+
 	TAILQ_ENTRY(cmd)	 qentry;
 };
 struct cmd_list {

tty.c

@@ -219,8 +219,13 @@ tty_start_tty(struct tty *tty)
 	if (tty_term_has(tty->term, TTYC_KMOUS))
 		tty_puts(tty, "\033[?1000l\033[?1006l\033[?1005l");
 
-	if (tty_term_has(tty->term, TTYC_XT))
+	if (tty_term_has(tty->term, TTYC_XT)) {
+		if (options_get_number(&global_options, "focus-events")) {
+			tty->flags |= TTY_FOCUS;
+			tty_puts(tty, "\033[?1004h");
+		}
 		tty_puts(tty, "\033[c\033[>4;1m\033[m");
+	}
 
 	tty->cx = UINT_MAX;
 	tty->cy = UINT_MAX;
@@ -282,8 +287,13 @@ tty_stop_tty(struct tty *tty)
 	if (tty_term_has(tty->term, TTYC_KMOUS))
 		tty_raw(tty, "\033[?1000l\033[?1006l\033[?1005l");
 
-	if (tty_term_has(tty->term, TTYC_XT))
+	if (tty_term_has(tty->term, TTYC_XT)) {
+		if (tty->flags & TTY_FOCUS) {
+			tty->flags &= ~TTY_FOCUS;
+			tty_puts(tty, "\033[?1004l");
+		}
 		tty_raw(tty, "\033[>4m\033[m");
+	}
 
 	tty_raw(tty, tty_term_string(tty->term, TTYC_RMCUP));