compositor: handle renderer destroy

Don't leave a stale renderer pointer behind.

include/wlr/types/wlr_compositor.h

@@ -247,6 +247,7 @@ struct wlr_compositor {
 	struct wlr_renderer *renderer; // may be NULL
 
 	struct wl_listener display_destroy;
+	struct wl_listener renderer_destroy;
 
 	struct {
 		struct wl_signal new_surface;

types/wlr_compositor.c

@@ -1348,10 +1348,20 @@ static void compositor_handle_display_destroy(
 		wl_container_of(listener, compositor, display_destroy);
 	wl_signal_emit_mutable(&compositor->events.destroy, NULL);
 	wl_list_remove(&compositor->display_destroy.link);
+	wl_list_remove(&compositor->renderer_destroy.link);
 	wl_global_destroy(compositor->global);
 	free(compositor);
 }
 
+static void compositor_handle_renderer_destroy(
+		struct wl_listener *listener, void *data) {
+	struct wlr_compositor *compositor =
+		wl_container_of(listener, compositor, renderer_destroy);
+	compositor->renderer = NULL;
+	wl_list_remove(&compositor->renderer_destroy.link);
+	wl_list_init(&compositor->renderer_destroy.link);
+}
+
 struct wlr_compositor *wlr_compositor_create(struct wl_display *display,
 		uint32_t version, struct wlr_renderer *renderer) {
 	assert(version <= COMPOSITOR_VERSION);
@@ -1375,6 +1385,13 @@ struct wlr_compositor *wlr_compositor_create(struct wl_display *display,
 	compositor->display_destroy.notify = compositor_handle_display_destroy;
 	wl_display_add_destroy_listener(display, &compositor->display_destroy);
 
+	if (renderer != NULL) {
+		compositor->renderer_destroy.notify = compositor_handle_renderer_destroy;
+		wl_signal_add(&renderer->events.destroy, &compositor->renderer_destroy);
+	} else {
+		wl_list_init(&compositor->renderer_destroy.link);
+	}
+
 	return compositor;
 }