Create Wordpress widget that outputs shortcode

functions.php

<?
function sidebarbrief_func($atts) {
	extract(shortcode_atts(array('foo' => 'something'), $atts));
  global $more; // Declare global $more (before the loop).
  $posts_query = new WP_Query( array( 'post_type' => array('brief'),  'tag_id' => 16, posts_per_page => 1 ) );
 
  $output = '<h1>News in Brief</h1>'; 
  while ( $posts_query->have_posts() ) : $posts_query->the_post();
    $more = 0; // Set (inside the loop) to display content above the more tag.
    $output .= '<div class="brief">';
    $output .=  apply_filters('the_content', get_the_content(''));
    $output .= ' <a href="' . get_permalink() . '" class="read_more">Read more briefs &rarr;</a>';
    $output .= '</div>';
  endwhile;

  wp_reset_postdata(); // Reset Post Data
  
  return $output;
}
add_shortcode('sidebarbrief', 'sidebarbrief_func');


add_action( 'widgets_init', 'load_theme_widgets' );

function load_theme_widgets() {
	register_widget( 'news_brief_widget' );
}

		class news_brief_widget extends WP_Widget {

			function news_brief_widget() {
				$widget_ops = array( 'classname' => 'news_in_brief', 'description' => __('Display news briefs') );
				$control_ops = array( 'width' => 300, 'height' => 350 );
				$this->WP_Widget( 'product_selector', __('News in Brief'), $widget_ops, $control_ops );
			}

			/* output */
			function widget( $args, $instance ) {
				extract( $args );
        echo do_shortcode("[sidebarbrief]");
      }

}