modifies the main WordPress query to include an array of post types

wp_custom_search_query.php

<?php 
/**
 * This function modifies the main WordPress query to include an array of 
 * post types instead of the default 'post' post type.
 *
 * @param object $query  The original query.
 * @return object $query The amended query.
 */
function trunkline_custom_search_query( $query ) {

if ($query->is_search) {
$query->set( 'post_type', array( 'post', 'job_listing', 'products', 'page' ) );
}
return $query;
}
add_filter( 'pre_get_posts', 'trunkline_custom_search_query');