Source

File: wp-includes/feed.php

function the_permalink_rss() {
	/**
	 * Filters the permalink to the post for use in feeds.
	 *
	 * @since 2.3.0
	 *
	 * @param string $post_permalink The current post permalink.
	 */
	echo esc_url( apply_filters( 'the_permalink_rss', get_permalink() ) );
}