Enabling ES6 for ResourceLoader validation

composer.json

@@ -1,4 +1,7 @@
 {
+	"require": {
+		"mck89/peast": "^1.16"
+	},
 	"require-dev": {
 		"liquipedia/sqllint": "*",
 		"mediawiki/mediawiki-codesniffer": "*",

src/ResourceLoader/ResourceLoaderArticlesModule.php

@@ -8,13 +8,19 @@
 
 use CSSJanus;
 use Less_Parser;
+use MediaWiki\MainConfigNames;
+use MediaWiki\MediaWikiServices;
 use MemoizedCallable;
+use Peast\Peast;
+use Peast\Syntax\Exception as PeastSyntaxException;
 use ResourceLoader;
 use ResourceLoaderContext;
 use ResourceLoaderWikiModule;
 
 class ResourceLoaderArticlesModule extends ResourceLoaderWikiModule {
 
+	private const USERJSPARSE_CACHE_VERSION = 3;
+
 	/**
 	 * Get list of pages used by this module
 	 *
@@ -39,6 +45,55 @@ protected function getPages( ResourceLoaderContext $context ) {
 		return $pages;
 	}
 
+	/**
+	 * Override of the same function in order to support ES6 files
+	 * Duplicate of https://gerrit.wikimedia.org/g/mediawiki/core/+/6fd9245f4ce47a77dc76f70994952cd6da2d1db7/includes/ResourceLoader/Module.php#1083
+	 * Can be removed when moving to a MW version >= 1.41
+	 * @param string $fileName
+	 * @param string $contents
+	 * @return string
+	 */
+	protected function validateScriptFile( $fileName, $contents ) {
+		if ( !$this->getConfig()->get( MainConfigNames::ResourceLoaderValidateJS ) ) {
+			return $contents;
+		}
+		$cache = MediaWikiServices::getInstance()->getMainWANObjectCache();
+		// Cache potentially slow parsing of JavaScript code during the
+		// critical path. This happens lazily when responding to requests
+		// for modules=site, modules=user, and Gadgets.
+		$error = $cache->getWithSetCallback(
+			$cache->makeKey(
+				'resourceloader-userjsparse',
+				self::USERJSPARSE_CACHE_VERSION,
+				md5( $contents ),
+				$fileName
+			),
+			$cache::TTL_WEEK,
+			static function () use ( $contents, $fileName ) {
+				try {
+					Peast::ES2020( $contents )->parse();
+				} catch ( PeastSyntaxException $e ) {
+					return $e->getMessage() . " on line " . $e->getPosition()->getLine();
+				}
+				// Cache success as null
+				return null;
+			}
+		);
+		if ( $error ) {
+			// Send the error to the browser console client-side.
+			// By returning this as replacement for the actual script,
+			// we ensure user-provided scripts are safe to include in a batch
+			// request, without risk of a syntax error in this blob breaking
+			// the response itself.
+			return 'mw.log.error(' .
+				json_encode(
+					'Parse error: ' . $error . ' for file ' . $fileName
+				) .
+				');';
+		}
+		return $contents;
+	}
+
 	/**
 	 * @param ResourceLoaderContext $context
 	 * @return array