output: evacuate sticky containers only if new output has a workspace

Sticky floating containers on an otherwise empty workspace can only be
evacuated if the new output has an active workspace. The noop output may
not have one and in that case we have to move the whole workspace to the
new output.

include/sway/tree/workspace.h

@@ -132,4 +132,6 @@ void workspace_get_box(struct sway_workspace *workspace, struct wlr_box *box);
 
 size_t workspace_num_tiling_views(struct sway_workspace *ws);
 
+size_t workspace_num_sticky_containers(struct sway_workspace *ws);
+
 #endif

sway/tree/output.c

@@ -152,21 +152,18 @@ void output_enable(struct sway_output *output) {
 	arrange_root();
 }
 
-static void evacuate_sticky(struct sway_workspace *old_ws,
-		struct sway_output *new_output) {
-	struct sway_workspace *new_ws = output_get_active_workspace(new_output);
-	if (!sway_assert(new_ws, "New output does not have a workspace")) {
+static void evacuate_sticky(struct sway_container *con, void *data) {
+	if (container_is_floating(con) && con->is_sticky) {
+		struct sway_workspace *new_ws = data;
+		if (!sway_assert(new_ws, "Expected workspace to not be null")) {
 			return;
 		}
-	while (old_ws->floating->length) {
-		struct sway_container *sticky = old_ws->floating->items[0];
-		container_detach(sticky);
-		workspace_add_floating(new_ws, sticky);
-		container_handle_fullscreen_reparent(sticky);
-		container_floating_move_to_center(sticky);
-		ipc_event_window(sticky, "move");
+		container_detach(con);
+		workspace_add_floating(new_ws, con);
+		container_handle_fullscreen_reparent(con);
+		container_floating_move_to_center(con);
+		ipc_event_window(con, "move");
 	}
-	workspace_detect_urgent(new_ws);
 }
 
 static void output_evacuate(struct sway_output *output) {
@@ -195,17 +192,23 @@ static void output_evacuate(struct sway_output *output) {
 			new_output = root->noop_output;
 		}
 
+		struct sway_workspace *new_output_ws =
+			output_get_active_workspace(new_output);
+
 		if (workspace_is_empty(workspace)) {
-			// If floating is not empty, there are sticky containers to move
-			if (workspace->floating->length) {
-				evacuate_sticky(workspace, new_output);
+			// If the new output has an active workspace (the noop output may
+			// not have one), move all sticky containers to it
+			if (new_output_ws) {
+				workspace_for_each_container(workspace, evacuate_sticky,
+					new_output_ws);
+				workspace_detect_urgent(new_output_ws);
 			}
+
+			if (workspace_num_sticky_containers(workspace) == 0) {
 				workspace_begin_destroy(workspace);
 				continue;
 			}
-
-		struct sway_workspace *new_output_ws =
-			output_get_active_workspace(new_output);
+		}
 
 		workspace_output_add_priority(workspace, new_output);
 		output_add_workspace(new_output, workspace);

sway/tree/workspace.c

@@ -817,3 +817,16 @@ size_t workspace_num_tiling_views(struct sway_workspace *ws) {
 	workspace_for_each_container(ws, count_tiling_views, &count);
 	return count;
 }
+
+static void count_sticky_containers(struct sway_container *con, void *data) {
+	if (container_is_floating(con) && con->is_sticky) {
+		size_t *count = data;
+		*count += 1;
+	}
+}
+
+size_t workspace_num_sticky_containers(struct sway_workspace *ws) {
+	size_t count = 0;
+	workspace_for_each_container(ws, count_sticky_containers, &count);
+	return count;
+}