get_feed_link( string $feed = '' )

function get_feed_link( $feed = '' ) {
	global $wp_rewrite;

	$permalink = $wp_rewrite->get_feed_permastruct();
	if ( '' != $permalink ) {
		if ( false !== strpos($feed, 'comments_') ) {
			$feed = str_replace('comments_', '', $feed);
			$permalink = $wp_rewrite->get_comment_feed_permastruct();
		}

		if ( get_default_feed() == $feed )
			$feed = '';

		$permalink = str_replace('%feed%', $feed, $permalink);
		$permalink = preg_replace('#/+#', '/', "/$permalink");
		$output =  home_url( user_trailingslashit($permalink, 'feed') );
	} else {
		if ( empty($feed) )
			$feed = get_default_feed();

		if ( false !== strpos($feed, 'comments_') )
			$feed = str_replace('comments_', 'comments-', $feed);

		$output = home_url("?feed={$feed}");
	}

	/**
	 * Filters the feed type permalink.
	 *
	 * @since WP-1.5.0
	 *
	 * @param string $output The feed permalink.
	 * @param string $feed   Feed type.
	 */
	return apply_filters( 'feed_link', $output, $feed );
}