Custom post type feed rewrite

gistfile1.php

<?php
function artigo_feed_rewrite( $wp_rewrite ) {
 
    $feed_rules = array(
        'feed/artigos'    =>  'index.php?post_type=listing&feed=rss2'
    );
 
    $wp_rewrite->rules = $feed_rules + $wp_rewrite->rules;
}
// regerar regras de permalinks depois de ativar / implementar esse código
add_filter( 'generate_rewrite_rules', 'artigo_feed_rewrite' );