source: tags/5.9/src/wp-includes/widgets/class-wp-widget-search.php

<?php
/**
 * Widget API: WP_Widget_Search class
 *
 * @package WordPress
 * @subpackage Widgets
 * @since 4.4.0
 */

/**
 * Core class used to implement a Search widget.
 *
 * @since 2.8.0
 *
 * @see WP_Widget
 */
class WP_Widget_Search extends WP_Widget {

        /**
         * Sets up a new Search widget instance.
         *
         * @since 2.8.0
         */
        public function __construct() {
                $widget_ops = array(
                        'classname'                   => 'widget_search',
                        'description'                 => __( 'A search form for your site.' ),
                        'customize_selective_refresh' => true,
                        'show_instance_in_rest'       => true,
                );
                parent::__construct( 'search', _x( 'Search', 'Search widget' ), $widget_ops );
        }

        /**
         * Outputs the content for the current Search widget instance.
         *
         * @since 2.8.0
         *
         * @param array $args     Display arguments including 'before_title', 'after_title',
         *                        'before_widget', and 'after_widget'.
         * @param array $instance Settings for the current Search widget instance.
         */
        public function widget( $args, $instance ) {
                $title = ! empty( $instance['title'] ) ? $instance['title'] : '';

                /** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
                $title = apply_filters( 'widget_title', $title, $instance, $this->id_base );

                echo $args['before_widget'];
                if ( $title ) {
                        echo $args['before_title'] . $title . $args['after_title'];
                }

                // Use current theme search form if it exists.
                get_search_form();

                echo $args['after_widget'];
        }

        /**
         * Outputs the settings form for the Search widget.
         *
         * @since 2.8.0
         *
         * @param array $instance Current settings.
         */
        public function form( $instance ) {
                $instance = wp_parse_args( (array) $instance, array( 'title' => '' ) );
                $title    = $instance['title'];
                ?>
                <p>
                        <label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
                        <input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>" />
                </p>
                <?php
        }

        /**
         * Handles updating settings for the current Search widget instance.
         *
         * @since 2.8.0
         *
         * @param array $new_instance New settings for this instance as input by the user via
         *                            WP_Widget::form().
         * @param array $old_instance Old settings for this instance.
         * @return array Updated settings.
         */
        public function update( $new_instance, $old_instance ) {
                $instance          = $old_instance;
                $new_instance      = wp_parse_args( (array) $new_instance, array( 'title' => '' ) );
                $instance['title'] = sanitize_text_field( $new_instance['title'] );
                return $instance;
        }

}