Limits Wordpress search results to only the 'post' post type.

wp-limit-search-results.php

<?php
/**
 * @file wp-limit-search-results.php
 *
 * Limits the website search results to just searching posts.
 *
 * @package wplsr
 * @since 1.0.0
 */


add_filter( 'pre_get_posts', 'wplsr_adjust_search_query' );
/**
 * Function that limits search queries to only 'post' post types.
 *
 * @since 1.0.0
 *
 * @param $query WP_Query object
 * @return object
 */
function wplsr_adjust_search_query($query) {

    if ( $query->is_main_query() && $query->is_search && ! is_admin() ) {
        $query->set( 'post_type', array( 'post' ) );
    }

    return $query;

}