Retrieves the current post’s trackback URL.

There is a check to see if permalink’s have been enabled and if so, will
retrieve the pretty path. If permalinks weren’t enabled, the ID of the
current post is used and appended to the correct page to go to.

function get_trackback_url() {
	if ( get_option( 'permalink_structure' ) ) {
		$trackback_url = trailingslashit( get_permalink() ) . user_trailingslashit( 'trackback', 'single_trackback' );
	} else {
		$trackback_url = get_option( 'siteurl' ) . '/wp-trackback.php?p=' . get_the_ID();
	}

	/**
	 * Filters the returned trackback URL.
	 *
	 * @since 2.2.0
	 *
	 * @param string $trackback_url The trackback URL.
	 */
	return apply_filters( 'trackback_url', $trackback_url );
}