The resize event was never deciding to actually resize the pane if there

was output in the pane faster than the timer would fire, so change how
it works to only defer the timer again if the pane was actually resized
within the last timer period. Reported by James Tai in GitHub issue
1880.

server-client.c

@@ -44,6 +44,7 @@ static void	server_client_set_title(struct client *);
 static void	server_client_reset_state(struct client *);
 static int	server_client_assume_paste(struct session *);
 static void	server_client_clear_overlay(struct client *);
+static void	server_client_resize_event(int, short, void *);
 
 static void	server_client_dispatch(struct imsg *, void *);
 static void	server_client_dispatch_command(struct client *, struct imsg *);
@@ -1319,19 +1320,11 @@ server_client_resize_force(struct window_pane *wp)
 	return (1);
 }
 
-/* Resize timer event. */
+/* Resize a pane. */
 static void
-server_client_resize_event(__unused int fd, __unused short events, void *data)
+server_client_resize_pane(struct window_pane *wp)
 {
-	struct window_pane	*wp = data;
-	struct winsize		 ws;
-
-	evtimer_del(&wp->resize_timer);
-
-	if (!(wp->flags & PANE_RESIZE))
-		return;
-	if (server_client_resize_force(wp))
-		return;
+	struct winsize	ws;
 
 	memset(&ws, 0, sizeof ws);
 	ws.ws_col = wp->sx;
@@ -1346,35 +1339,55 @@ server_client_resize_event(__unused int fd, __unused short events, void *data)
 	wp->osy = wp->sy;
 }
 
+/* Start the resize timer. */
+static void
+server_client_start_resize_timer(struct window_pane *wp)
+{
+	struct timeval	tv = { .tv_usec = 250000 };
+
+	if (!evtimer_pending(&wp->resize_timer, NULL))
+		evtimer_add(&wp->resize_timer, &tv);
+}
+
+/* Resize timer event. */
+static void
+server_client_resize_event(__unused int fd, __unused short events, void *data)
+{
+	struct window_pane	*wp = data;
+
+	evtimer_del(&wp->resize_timer);
+
+	if (~wp->flags & PANE_RESIZE)
+		return;
+	log_debug("%s: %%%u timer fired (was%s resized)", __func__, wp->id,
+	    (wp->flags & PANE_RESIZED) ? "" : " not");
+
+	if (wp->saved_grid == NULL && (wp->flags & PANE_RESIZED)) {
+		log_debug("%s: %%%u deferring timer", __func__, wp->id);
+		server_client_start_resize_timer(wp);
+	} else if (!server_client_resize_force(wp)) {
+		log_debug("%s: %%%u resizing pane", __func__, wp->id);
+		server_client_resize_pane(wp);
+	}
+	wp->flags &= ~PANE_RESIZED;
+}
+
 /* Check if pane should be resized. */
 static void
 server_client_check_resize(struct window_pane *wp)
 {
-	struct timeval	 tv = { .tv_usec = 250000 };
-
-	if (!(wp->flags & PANE_RESIZE))
+	if (~wp->flags & PANE_RESIZE)
 		return;
-	log_debug("%s: %%%u resize to %u,%u", __func__, wp->id, wp->sx, wp->sy);
 
 	if (!event_initialized(&wp->resize_timer))
 		evtimer_set(&wp->resize_timer, server_client_resize_event, wp);
 
-	/*
-	 * The first resize should happen immediately, so if the timer is not
-	 * running, do it now.
-	 */
-	if (!evtimer_pending(&wp->resize_timer, NULL))
-		server_client_resize_event(-1, 0, wp);
-
-	/*
-	 * If the pane is in the alternate screen, let the timer expire and
-	 * resize to give the application a chance to redraw. If not, keep
-	 * pushing the timer back.
-	 */
-	if (wp->saved_grid != NULL && evtimer_pending(&wp->resize_timer, NULL))
-		return;
-	evtimer_del(&wp->resize_timer);
-	evtimer_add(&wp->resize_timer, &tv);
+	if (!evtimer_pending(&wp->resize_timer, NULL)) {
+		log_debug("%s: %%%u starting timer", __func__, wp->id);
+		server_client_resize_pane(wp);
+		server_client_start_resize_timer(wp);
+	} else
+		log_debug("%s: %%%u timer running", __func__, wp->id);
 }
 
 /* Check whether pane should be focused. */

tmux.h

@@ -843,6 +843,7 @@ struct window_pane {
 #define PANE_STATUSDRAWN 0x400
 #define PANE_EMPTY 0x800
 #define PANE_STYLECHANGED 0x1000
+#define PANE_RESIZED 0x2000
 
 	int		 argc;
 	char	       **argv;

window.c

@@ -953,7 +953,7 @@ window_pane_resize(struct window_pane *wp, u_int sx, u_int sy)
 	if (wme != NULL && wme->mode->resize != NULL)
 		wme->mode->resize(wme, sx, sy);
 
-	wp->flags |= PANE_RESIZE;
+	wp->flags |= (PANE_RESIZE|PANE_RESIZED);
 }
 
 /*