描述：

为侧边栏注册一个小工具

用法：

<?php 
wp_register_sidebar_widget(
    $id, 
    $name, 
    $output_callback, 
    $options, 
    $params,
    ... 
); 
?> 

参数：

$id

(int/string) (必填) 要注册的小工具的ID.

默认值: None

$name

(string) (必填) 要注册的小工具的的标题.

默认值: None

$output_callback

(callback) (必填) 在小工具被调用时运行.

默认值: None

$options

(array/string) (可选) 小工具设置选项.

默认值: None

$params,...

(mixed) (可选) 要添加到小小工具的参数.

默认值: None

源文件：

/**
 * Register an instance of a widget.
 *
 * The default widget option is 'classname' that can be overridden.
 *
 * The function can also be used to un-register widgets when `$output_callback`
 * parameter is an empty string.
 *
 * @since 2.2.0
 *
 * @global array $wp_registered_widgets       Uses stored registered widgets.
 * @global array $wp_register_widget_defaults Retrieves widget defaults.
 * @global array $wp_registered_widget_updates
 * @global array $_wp_deprecated_widgets_callbacks
 *
 * @param int|string $id              Widget ID.
 * @param string     $name            Widget display title.
 * @param callback   $output_callback Run when widget is called.
 * @param array      $options {
 *     Optional. An array of supplementary widget options for the instance.
 *
 *     @type string $classname   Class name for the widget's HTML container. Default is a shortened
 *                               version of the output callback name.
 *     @type string $description Widget description for display in the widget administration
 *                               panel and/or theme.
 * }
 */
function wp_register_sidebar_widget( $id, $name, $output_callback, $options = array() ) {
	global $wp_registered_widgets, $wp_registered_widget_controls, $wp_registered_widget_updates, $_wp_deprecated_widgets_callbacks;

	$id = strtolower($id);

	if ( empty($output_callback) ) {
		unset($wp_registered_widgets[$id]);
		return;
	}

	$id_base = _get_widget_id_base($id);
	if ( in_array($output_callback, $_wp_deprecated_widgets_callbacks, true) && !is_callable($output_callback) ) {
		unset( $wp_registered_widget_controls[ $id ] );
		unset( $wp_registered_widget_updates[ $id_base ] );
		return;
	}

	$defaults = array('classname' => $output_callback);
	$options = wp_parse_args($options, $defaults);
	$widget = array(
		'name' => $name,
		'id' => $id,
		'callback' => $output_callback,
		'params' => array_slice(func_get_args(), 4)
	);
	$widget = array_merge($widget, $options);

	if ( is_callable($output_callback) && ( !isset($wp_registered_widgets[$id]) || did_action( 'widgets_init' ) ) ) {

		/**
		 * Fires once for each registered widget.
		 *
		 * @since 3.0.0
		 *
		 * @param array $widget An array of default widget arguments.
		 */
		do_action( 'wp_register_sidebar_widget', $widget );
		$wp_registered_widgets[$id] = $widget;
	}
}