amp-validation-error-logger.php

<?php
/**
 * AMP Validation Error Logger plugin initialization file.
 *
 * @package   AMP_Validation_Error_Logger
 * @author    Weston Ruter, Google
 * @license   GPL-2.0-or-later
 * @copyright 2019 Google Inc.
 *
 * @wordpress-plugin
 * Plugin Name: AMP Validation Error Logger
 * Plugin URI: https://gist.github.com/westonruter/4ff8545e653efeeafe5b994c530a568e
 * Description: Append AMP Validation errors to the body as comments and if WP_DEBUG_LOG is enabled add AMP validation errors to the PHP error log.
 * Version: 0.2
 * Author: Weston Ruter, Google
 * Author URI: https://weston.ruter.net/
 * License: GNU General Public License v2 (or later)
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 * Gist Plugin URI: https://gist.github.com/westonruter/4ff8545e653efeeafe5b994c530a568e
 */

namespace AMP_Validation_Error_Logger;

use AMP_Validation_Error_Taxonomy;
use AMP_Validation_Manager;
use DOMDocument;
use DOMNode;
use WP_Term;

add_filter(
	'amp_validation_error',
	function( $validation_error, $args ) {
		$term_data = AMP_Validation_Error_Taxonomy::prepare_validation_error_taxonomy_term( $validation_error );
		$term      = AMP_Validation_Error_Taxonomy::get_term( $term_data['slug'] );
		$slug      = $term_data['slug'];

		if ( $term instanceof WP_Term && in_array( $term->term_group, [ 0, 1, 2, 3 ], true ) ) {
			$term_status = $term->term_group;
		} else {
			$term_status = AMP_Validation_Manager::is_sanitization_auto_accepted( $validation_error ) ? AMP_Validation_Error_Taxonomy::VALIDATION_ERROR_NEW_ACCEPTED_STATUS : AMP_Validation_Error_Taxonomy::VALIDATION_ERROR_NEW_REJECTED_STATUS;
		}

		$removed  = (bool) ( $term_status & 1 );
		$reviewed = (bool) ( $term_status & 2 );

		// Append validation errors as HTML comments at the end of the document.
		if ( isset( $args['node'] ) && $args['node'] instanceof DOMNode && $args['node']->ownerDocument instanceof DOMDocument ) {
			/**
			 * Document.
			 *
			 * @var DOMDocument $dom
			 */
			$dom = $args['node']->ownerDocument;
			$dom->appendChild( $dom->createTextNode( "\n" ) );
			$comment = $dom->createComment(
				sprintf(
					'amp_validation_error(%s):%s',
					wp_json_encode( compact( 'removed', 'reviewed', 'slug' ) ),
					wp_json_encode( $validation_error, JSON_UNESCAPED_SLASHES | JSON_PRETTY_PRINT )
				)
			);
			$dom->appendChild( $comment );
		}

		// Also add the errors to the error log if WP_DEBUG_LOG is enabled.
		if ( defined( 'WP_DEBUG_LOG' ) && WP_DEBUG_LOG ) {
			error_log( // phpcs:ignore
				sprintf(
					'amp_validation_error(%s)@%s: %s',
					wp_json_encode( compact( 'removed', 'reviewed', 'slug' ) ),
					remove_query_arg( [ 'amp_validate', 'amp_cache_bust' ], wp_unslash( $_SERVER['REQUEST_URI'] ) ),
					wp_json_encode( $validation_error, JSON_UNESCAPED_SLASHES )
				)
			);
		}

		return $validation_error;
	},
	PHP_INT_MAX,
	2
);

Installation instructions: https://gist.github.com/westonruter/6110fbc4bef0c4b8c021a112012f7e9c