wp_dashboard_cached_rss_widget( string $widget_id, callable $callback, array $check_urls = array() )

function wp_dashboard_cached_rss_widget( $widget_id, $callback, $check_urls = array() ) {
	$loading = '<p class="widget-loading hide-if-no-js">' . __( 'Loading&#8230;' ) . '</p><div class="hide-if-js notice notice-error inline"><p>' . __( 'This widget requires JavaScript.' ) . '</p></div>';
	$doing_ajax = wp_doing_ajax();

	if ( empty($check_urls) ) {
		$widgets = get_option( 'dashboard_widget_options' );
		if ( empty($widgets[$widget_id]['url']) && ! $doing_ajax ) {
			echo $loading;
			return false;
		}
		$check_urls = array( $widgets[$widget_id]['url'] );
	}

	$locale = get_user_locale();
	$cache_key = 'dash_v2_' . md5( $widget_id . '_' . $locale );
	if ( false !== ( $output = get_transient( $cache_key ) ) ) {
		echo $output;
		return true;
	}

	if ( ! $doing_ajax ) {
		echo $loading;
		return false;
	}

	if ( $callback && is_callable( $callback ) ) {
		$args = array_slice( func_get_args(), 3 );
		array_unshift( $args, $widget_id, $check_urls );
		ob_start();
		call_user_func_array( $callback, $args );
		set_transient( $cache_key, ob_get_flush(), 12 * HOUR_IN_SECONDS ); // Default lifetime in cache of 12 hours (same as the feeds)
	}

	return true;
}