compositor: add wlr_surface_role.client_commit

include/wlr/types/wlr_compositor.h

@@ -81,6 +81,15 @@ struct wlr_surface_role {
 	 * For example, this applies to cursor surfaces.
 	 */
 	bool no_object;
+	/**
+	 * Called when the client sends the wl_surface.commit request. May be NULL.
+	 * Typically used to check that the pending state is valid, and send
+	 * protocol errors if not.
+	 *
+	 * If the role is represented by an object, this is only called if
+	 * such object exists.
+	 */
+	void (*client_commit)(struct wlr_surface *surface);
 	/**
 	 * Called when a new surface state is committed. May be NULL.
 	 *

types/wlr_compositor.c

@@ -565,6 +565,11 @@ static void surface_handle_commit(struct wl_client *client,
 	struct wlr_surface *surface = wlr_surface_from_resource(resource);
 	surface_finalize_pending(surface);
 
+	if (surface->role != NULL && surface->role->client_commit != NULL &&
+			(surface->role_resource != NULL || surface->role->no_object)) {
+		surface->role->client_commit(surface);
+	}
+
 	wl_signal_emit_mutable(&surface->events.client_commit, NULL);
 
 	if (surface->pending.cached_state_locks > 0 || !wl_list_empty(&surface->cached)) {