foreign-toplevel: send enter if needed on output bind

Currently the output enter event is never sent if the client has not
yet bound the output, which happens every time the compositor creates a
new output.

To fix this, listen for the output bind event and inform clients as
if needed.

include/wlr/types/wlr_foreign_toplevel_management_v1.h

@@ -36,10 +36,13 @@ enum wlr_foreign_toplevel_handle_v1_state {
 
 struct wlr_foreign_toplevel_handle_v1_output {
 	struct wl_list link; // wlr_foreign_toplevel_handle_v1::outputs
-	struct wl_listener output_destroy;
 	struct wlr_output *output;
-
 	struct wlr_foreign_toplevel_handle_v1 *toplevel;
+
+	// private state
+
+	struct wl_listener output_bind;
+	struct wl_listener output_destroy;
 };
 
 struct wlr_foreign_toplevel_handle_v1 {

types/wlr_foreign_toplevel_management_v1.c

@@ -257,6 +257,23 @@ static void toplevel_send_output(struct wlr_foreign_toplevel_handle_v1 *toplevel
 	toplevel_update_idle_source(toplevel);
 }
 
+static void toplevel_handle_output_bind(struct wl_listener *listener,
+		void *data) {
+	struct wlr_foreign_toplevel_handle_v1_output *toplevel_output =
+		wl_container_of(listener, toplevel_output, output_bind);
+	struct wlr_output_event_bind *event = data;
+	struct wl_client *client = wl_resource_get_client(event->resource);
+
+	struct wl_resource *resource;
+	wl_resource_for_each(resource, &toplevel_output->toplevel->resources) {
+		if (wl_resource_get_client(resource) == client) {
+		    send_output_to_resource(resource, toplevel_output->output, true);
+		}
+	}
+
+	toplevel_update_idle_source(toplevel_output->toplevel);
+}
+
 static void toplevel_handle_output_destroy(struct wl_listener *listener,
 		void *data) {
 	struct wlr_foreign_toplevel_handle_v1_output *toplevel_output =
@@ -286,6 +303,9 @@ void wlr_foreign_toplevel_handle_v1_output_enter(
 	toplevel_output->toplevel = toplevel;
 	wl_list_insert(&toplevel->outputs, &toplevel_output->link);
 
+	toplevel_output->output_bind.notify = toplevel_handle_output_bind;
+	wl_signal_add(&output->events.bind, &toplevel_output->output_bind);
+
 	toplevel_output->output_destroy.notify = toplevel_handle_output_destroy;
 	wl_signal_add(&output->events.destroy, &toplevel_output->output_destroy);
 
@@ -295,6 +315,7 @@ void wlr_foreign_toplevel_handle_v1_output_enter(
 static void toplevel_output_destroy(
 		struct wlr_foreign_toplevel_handle_v1_output *toplevel_output) {
 	wl_list_remove(&toplevel_output->link);
+	wl_list_remove(&toplevel_output->output_bind.link);
 	wl_list_remove(&toplevel_output->output_destroy.link);
 	free(toplevel_output);
 }