Source

File: wp-includes/link-template.php

function get_search_feed_link( $search_query = '', $feed = '' ) {
	global $wp_rewrite;
	$link = get_search_link( $search_query );

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

	$permastruct = $wp_rewrite->get_search_permastruct();

	if ( empty( $permastruct ) ) {
		$link = add_query_arg( 'feed', $feed, $link );
	} else {
		$link  = trailingslashit( $link );
		$link .= "feed/$feed/";
	}

	/**
	 * Filters the search feed link.
	 *
	 * @since 2.5.0
	 *
	 * @param string $link Search feed link.
	 * @param string $feed Feed type. Possible values include 'rss2', 'atom'.
	 * @param string $type The search type. One of 'posts' or 'comments'.
	 */
	return apply_filters( 'search_feed_link', $link, $feed, 'posts' );
}