get_search_comments_feed_link( string $search_query = '', string $feed = '' )

function get_search_comments_feed_link($search_query = '', $feed = '') {
	global $wp_rewrite;

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

	$link = get_search_feed_link($search_query, $feed);

	$permastruct = $wp_rewrite->get_search_permastruct();

	if ( empty($permastruct) )
		$link = add_query_arg('feed', 'comments-' . $feed, $link);
	else
		$link = add_query_arg('withcomments', 1, $link);

	/** This filter is documented in wp-includes/link-template.php */
	return apply_filters( 'search_feed_link', $link, $feed, 'comments' );
}