Source

File: wp-includes/link-template.php

function the_permalink( $post = 0 ) {
	/**
	 * Filters the display of the permalink for the current post.
	 *
	 * @since 1.5.0
	 * @since 4.4.0 Added the `$post` parameter.
	 *
	 * @param string      $permalink The permalink for the current post.
	 * @param int|WP_Post $post      Post ID, WP_Post object, or 0. Default 0.
	 */
	echo esc_url( apply_filters( 'the_permalink', get_permalink( $post ), $post ) );
}