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[mediawiki.git] / includes / resourceloader / ResourceLoader.php

<?php
/**
 * Base class for resource loading system.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @author Roan Kattouw
 * @author Trevor Parscal
 */

use MediaWiki\MediaWikiServices;
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use WrappedString\WrappedString;

/**
 * Dynamic JavaScript and CSS resource loading system.
 *
 * Most of the documentation is on the MediaWiki documentation wiki starting at:
 *    https://www.mediawiki.org/wiki/ResourceLoader
 */
class ResourceLoader implements LoggerAwareInterface {
        /** @var int */
        protected static $filterCacheVersion = 7;

        /** @var bool */
        protected static $debugMode = null;

        /** @var array */
        private $lessVars = null;

        /**
         * Module name/ResourceLoaderModule object pairs
         * @var array
         */
        protected $modules = [];

        /**
         * Associative array mapping module name to info associative array
         * @var array
         */
        protected $moduleInfos = [];

        /** @var Config $config */
        protected $config;

        /**
         * Associative array mapping framework ids to a list of names of test suite modules
         * like [ 'qunit' => [ 'mediawiki.tests.qunit.suites', 'ext.foo.tests', ... ], ... ]
         * @var array
         */
        protected $testModuleNames = [];

        /**
         * E.g. [ 'source-id' => 'http://.../load.php' ]
         * @var array
         */
        protected $sources = [];

        /**
         * Errors accumulated during current respond() call.
         * @var array
         */
        protected $errors = [];

        /**
         * @var MessageBlobStore
         */
        protected $blobStore;

        /**
         * @var LoggerInterface
         */
        private $logger;

        /** @var string JavaScript / CSS pragma to disable minification. **/
        const FILTER_NOMIN = '/*@nomin*/';

        /**
         * Load information stored in the database about modules.
         *
         * This method grabs modules dependencies from the database and updates modules
         * objects.
         *
         * This is not inside the module code because it is much faster to
         * request all of the information at once than it is to have each module
         * requests its own information. This sacrifice of modularity yields a substantial
         * performance improvement.
         *
         * @param array $moduleNames List of module names to preload information for
         * @param ResourceLoaderContext $context Context to load the information within
         */
        public function preloadModuleInfo( array $moduleNames, ResourceLoaderContext $context ) {
                if ( !$moduleNames ) {
                        // Or else Database*::select() will explode, plus it's cheaper!
                        return;
                }
                $dbr = wfGetDB( DB_REPLICA );
                $skin = $context->getSkin();
                $lang = $context->getLanguage();

                // Batched version of ResourceLoaderModule::getFileDependencies
                $vary = "$skin|$lang";
                $res = $dbr->select( 'module_deps', [ 'md_module', 'md_deps' ], [
                                'md_module' => $moduleNames,
                                'md_skin' => $vary,
                        ], __METHOD__
                );

                // Prime in-object cache for file dependencies
                $modulesWithDeps = [];
                foreach ( $res as $row ) {
                        $module = $this->getModule( $row->md_module );
                        if ( $module ) {
                                $module->setFileDependencies( $context, ResourceLoaderModule::expandRelativePaths(
                                        FormatJson::decode( $row->md_deps, true )
                                ) );
                                $modulesWithDeps[] = $row->md_module;
                        }
                }
                // Register the absence of a dependency row too
                foreach ( array_diff( $moduleNames, $modulesWithDeps ) as $name ) {
                        $module = $this->getModule( $name );
                        if ( $module ) {
                                $this->getModule( $name )->setFileDependencies( $context, [] );
                        }
                }

                // Batched version of ResourceLoaderWikiModule::getTitleInfo
                ResourceLoaderWikiModule::preloadTitleInfo( $context, $dbr, $moduleNames );

                // Prime in-object cache for message blobs for modules with messages
                $modules = [];
                foreach ( $moduleNames as $name ) {
                        $module = $this->getModule( $name );
                        if ( $module && $module->getMessages() ) {
                                $modules[$name] = $module;
                        }
                }
                $store = $this->getMessageBlobStore();
                $blobs = $store->getBlobs( $modules, $lang );
                foreach ( $blobs as $name => $blob ) {
                        $modules[$name]->setMessageBlob( $blob, $lang );
                }
        }

        /**
         * Run JavaScript or CSS data through a filter, caching the filtered result for future calls.
         *
         * Available filters are:
         *
         *    - minify-js \see JavaScriptMinifier::minify
         *    - minify-css \see CSSMin::minify
         *
         * If $data is empty, only contains whitespace or the filter was unknown,
         * $data is returned unmodified.
         *
         * @param string $filter Name of filter to run
         * @param string $data Text to filter, such as JavaScript or CSS text
         * @param array $options Keys:
         *  - (bool) cache: Whether to allow caching this data. Default: true.
         * @return string Filtered data, or a comment containing an error message
         */
        public static function filter( $filter, $data, array $options = [] ) {
                if ( strpos( $data, ResourceLoader::FILTER_NOMIN ) !== false ) {
                        return $data;
                }

                if ( isset( $options['cache'] ) && $options['cache'] === false ) {
                        return self::applyFilter( $filter, $data );
                }

                $stats = RequestContext::getMain()->getStats();
                $cache = ObjectCache::getLocalServerInstance( CACHE_ANYTHING );

                $key = $cache->makeGlobalKey(
                        'resourceloader',
                        'filter',
                        $filter,
                        self::$filterCacheVersion, md5( $data )
                );

                $result = $cache->get( $key );
                if ( $result === false ) {
                        $stats->increment( "resourceloader_cache.$filter.miss" );
                        $result = self::applyFilter( $filter, $data );
                        $cache->set( $key, $result, 24 * 3600 );
                } else {
                        $stats->increment( "resourceloader_cache.$filter.hit" );
                }
                if ( $result === null ) {
                        // Cached failure
                        $result = $data;
                }

                return $result;
        }

        private static function applyFilter( $filter, $data ) {
                $data = trim( $data );
                if ( $data ) {
                        try {
                                $data = ( $filter === 'minify-css' )
                                        ? CSSMin::minify( $data )
                                        : JavaScriptMinifier::minify( $data );
                        } catch ( Exception $e ) {
                                MWExceptionHandler::logException( $e );
                                return null;
                        }
                }
                return $data;
        }

        /* Methods */

        /**
         * Register core modules and runs registration hooks.
         * @param Config $config [optional]
         * @param LoggerInterface $logger [optional]
         */
        public function __construct( Config $config = null, LoggerInterface $logger = null ) {
                global $IP;

                $this->logger = $logger ?: new NullLogger();

                if ( !$config ) {
                        $this->logger->debug( __METHOD__ . ' was called without providing a Config instance' );
                        $config = MediaWikiServices::getInstance()->getMainConfig();
                }
                $this->config = $config;

                // Add 'local' source first
                $this->addSource( 'local', $config->get( 'LoadScript' ) );

                // Add other sources
                $this->addSource( $config->get( 'ResourceLoaderSources' ) );

                // Register core modules
                $this->register( include "$IP/resources/Resources.php" );
                $this->register( include "$IP/resources/ResourcesOOUI.php" );
                // Register extension modules
                $this->register( $config->get( 'ResourceModules' ) );
                Hooks::run( 'ResourceLoaderRegisterModules', [ &$this ] );

                if ( $config->get( 'EnableJavaScriptTest' ) === true ) {
                        $this->registerTestModules();
                }

                $this->setMessageBlobStore( new MessageBlobStore( $this, $this->logger ) );
        }

        /**
         * @return Config
         */
        public function getConfig() {
                return $this->config;
        }

        /**
         * @since 1.26
         * @param LoggerInterface $logger
         */
        public function setLogger( LoggerInterface $logger ) {
                $this->logger = $logger;
        }

        /**
         * @since 1.27
         * @return LoggerInterface
         */
        public function getLogger() {
                return $this->logger;
        }

        /**
         * @since 1.26
         * @return MessageBlobStore
         */
        public function getMessageBlobStore() {
                return $this->blobStore;
        }

        /**
         * @since 1.25
         * @param MessageBlobStore $blobStore
         */
        public function setMessageBlobStore( MessageBlobStore $blobStore ) {
                $this->blobStore = $blobStore;
        }

        /**
         * Register a module with the ResourceLoader system.
         *
         * @param mixed $name Name of module as a string or List of name/object pairs as an array
         * @param array $info Module info array. For backwards compatibility with 1.17alpha,
         *   this may also be a ResourceLoaderModule object. Optional when using
         *   multiple-registration calling style.
         * @throws MWException If a duplicate module registration is attempted
         * @throws MWException If a module name contains illegal characters (pipes or commas)
         * @throws MWException If something other than a ResourceLoaderModule is being registered
         * @return bool False if there were any errors, in which case one or more modules were
         *   not registered
         */
        public function register( $name, $info = null ) {
                $moduleSkinStyles = $this->config->get( 'ResourceModuleSkinStyles' );

                // Allow multiple modules to be registered in one call
                $registrations = is_array( $name ) ? $name : [ $name => $info ];
                foreach ( $registrations as $name => $info ) {
                        // Warn on duplicate registrations
                        if ( isset( $this->moduleInfos[$name] ) ) {
                                // A module has already been registered by this name
                                $this->logger->warning(
                                        'ResourceLoader duplicate registration warning. ' .
                                        'Another module has already been registered as ' . $name
                                );
                        }

                        // Check $name for validity
                        if ( !self::isValidModuleName( $name ) ) {
                                throw new MWException( "ResourceLoader module name '$name' is invalid, "
                                        . "see ResourceLoader::isValidModuleName()" );
                        }

                        // Attach module
                        if ( $info instanceof ResourceLoaderModule ) {
                                $this->moduleInfos[$name] = [ 'object' => $info ];
                                $info->setName( $name );
                                $this->modules[$name] = $info;
                        } elseif ( is_array( $info ) ) {
                                // New calling convention
                                $this->moduleInfos[$name] = $info;
                        } else {
                                throw new MWException(
                                        'ResourceLoader module info type error for module \'' . $name .
                                        '\': expected ResourceLoaderModule or array (got: ' . gettype( $info ) . ')'
                                );
                        }

                        // Last-minute changes

                        // Apply custom skin-defined styles to existing modules.
                        if ( $this->isFileModule( $name ) ) {
                                foreach ( $moduleSkinStyles as $skinName => $skinStyles ) {
                                        // If this module already defines skinStyles for this skin, ignore $wgResourceModuleSkinStyles.
                                        if ( isset( $this->moduleInfos[$name]['skinStyles'][$skinName] ) ) {
                                                continue;
                                        }

                                        // If $name is preceded with a '+', the defined style files will be added to 'default'
                                        // skinStyles, otherwise 'default' will be ignored as it normally would be.
                                        if ( isset( $skinStyles[$name] ) ) {
                                                $paths = (array)$skinStyles[$name];
                                                $styleFiles = [];
                                        } elseif ( isset( $skinStyles['+' . $name] ) ) {
                                                $paths = (array)$skinStyles['+' . $name];
                                                $styleFiles = isset( $this->moduleInfos[$name]['skinStyles']['default'] ) ?
                                                        (array)$this->moduleInfos[$name]['skinStyles']['default'] :
                                                        [];
                                        } else {
                                                continue;
                                        }

                                        // Add new file paths, remapping them to refer to our directories and not use settings
                                        // from the module we're modifying, which come from the base definition.
                                        list( $localBasePath, $remoteBasePath ) =
                                                ResourceLoaderFileModule::extractBasePaths( $skinStyles );

                                        foreach ( $paths as $path ) {
                                                $styleFiles[] = new ResourceLoaderFilePath( $path, $localBasePath, $remoteBasePath );
                                        }

                                        $this->moduleInfos[$name]['skinStyles'][$skinName] = $styleFiles;
                                }
                        }
                }
        }

        public function registerTestModules() {
                global $IP;

                if ( $this->config->get( 'EnableJavaScriptTest' ) !== true ) {
                        throw new MWException( 'Attempt to register JavaScript test modules '
                                . 'but <code>$wgEnableJavaScriptTest</code> is false. '
                                . 'Edit your <code>LocalSettings.php</code> to enable it.' );
                }

                // Get core test suites
                $testModules = [];
                $testModules['qunit'] = [];
                // Get other test suites (e.g. from extensions)
                Hooks::run( 'ResourceLoaderTestModules', [ &$testModules, &$this ] );

                // Add the testrunner (which configures QUnit) to the dependencies.
                // Since it must be ready before any of the test suites are executed.
                foreach ( $testModules['qunit'] as &$module ) {
                        // Make sure all test modules are top-loading so that when QUnit starts
                        // on document-ready, it will run once and finish. If some tests arrive
                        // later (possibly after QUnit has already finished) they will be ignored.
                        $module['position'] = 'top';
                        $module['dependencies'][] = 'test.mediawiki.qunit.testrunner';
                }

                $testModules['qunit'] =
                        ( include "$IP/tests/qunit/QUnitTestResources.php" ) + $testModules['qunit'];

                foreach ( $testModules as $id => $names ) {
                        // Register test modules
                        $this->register( $testModules[$id] );

                        // Keep track of their names so that they can be loaded together
                        $this->testModuleNames[$id] = array_keys( $testModules[$id] );
                }
        }

        /**
         * Add a foreign source of modules.
         *
         * Source IDs are typically the same as the Wiki ID or database name (e.g. lowercase a-z).
         *
         * @param array|string $id Source ID (string), or [ id1 => loadUrl, id2 => loadUrl, ... ]
         * @param string|array $loadUrl load.php url (string), or array with loadUrl key for
         *  backwards-compatibility.
         * @throws MWException
         */
        public function addSource( $id, $loadUrl = null ) {
                // Allow multiple sources to be registered in one call
                if ( is_array( $id ) ) {
                        foreach ( $id as $key => $value ) {
                                $this->addSource( $key, $value );
                        }
                        return;
                }

                // Disallow duplicates
                if ( isset( $this->sources[$id] ) ) {
                        throw new MWException(
                                'ResourceLoader duplicate source addition error. ' .
                                'Another source has already been registered as ' . $id
                        );
                }

                // Pre 1.24 backwards-compatibility
                if ( is_array( $loadUrl ) ) {
                        if ( !isset( $loadUrl['loadScript'] ) ) {
                                throw new MWException(
                                        __METHOD__ . ' was passed an array with no "loadScript" key.'
                                );
                        }

                        $loadUrl = $loadUrl['loadScript'];
                }

                $this->sources[$id] = $loadUrl;
        }

        /**
         * Get a list of module names.
         *
         * @return array List of module names
         */
        public function getModuleNames() {
                return array_keys( $this->moduleInfos );
        }

        /**
         * Get a list of test module names for one (or all) frameworks.
         *
         * If the given framework id is unknkown, or if the in-object variable is not an array,
         * then it will return an empty array.
         *
         * @param string $framework Get only the test module names for one
         *   particular framework (optional)
         * @return array
         */
        public function getTestModuleNames( $framework = 'all' ) {
                /** @todo api siteinfo prop testmodulenames modulenames */
                if ( $framework == 'all' ) {
                        return $this->testModuleNames;
                } elseif ( isset( $this->testModuleNames[$framework] )
                        && is_array( $this->testModuleNames[$framework] )
                ) {
                        return $this->testModuleNames[$framework];
                } else {
                        return [];
                }
        }

        /**
         * Check whether a ResourceLoader module is registered
         *
         * @since 1.25
         * @param string $name
         * @return bool
         */
        public function isModuleRegistered( $name ) {
                return isset( $this->moduleInfos[$name] );
        }

        /**
         * Get the ResourceLoaderModule object for a given module name.
         *
         * If an array of module parameters exists but a ResourceLoaderModule object has not
         * yet been instantiated, this method will instantiate and cache that object such that
         * subsequent calls simply return the same object.
         *
         * @param string $name Module name
         * @return ResourceLoaderModule|null If module has been registered, return a
         *  ResourceLoaderModule instance. Otherwise, return null.
         */
        public function getModule( $name ) {
                if ( !isset( $this->modules[$name] ) ) {
                        if ( !isset( $this->moduleInfos[$name] ) ) {
                                // No such module
                                return null;
                        }
                        // Construct the requested object
                        $info = $this->moduleInfos[$name];
                        /** @var ResourceLoaderModule $object */
                        if ( isset( $info['object'] ) ) {
                                // Object given in info array
                                $object = $info['object'];
                        } else {
                                if ( !isset( $info['class'] ) ) {
                                        $class = 'ResourceLoaderFileModule';
                                } else {
                                        $class = $info['class'];
                                }
                                /** @var ResourceLoaderModule $object */
                                $object = new $class( $info );
                                $object->setConfig( $this->getConfig() );
                                $object->setLogger( $this->logger );
                        }
                        $object->setName( $name );
                        $this->modules[$name] = $object;
                }

                return $this->modules[$name];
        }

        /**
         * Return whether the definition of a module corresponds to a simple ResourceLoaderFileModule.
         *
         * @param string $name Module name
         * @return bool
         */
        protected function isFileModule( $name ) {
                if ( !isset( $this->moduleInfos[$name] ) ) {
                        return false;
                }
                $info = $this->moduleInfos[$name];
                if ( isset( $info['object'] ) || isset( $info['class'] ) ) {
                        return false;
                }
                return true;
        }

        /**
         * Get the list of sources.
         *
         * @return array Like [ id => load.php url, ... ]
         */
        public function getSources() {
                return $this->sources;
        }

        /**
         * Get the URL to the load.php endpoint for the given
         * ResourceLoader source
         *
         * @since 1.24
         * @param string $source
         * @throws MWException On an invalid $source name
         * @return string
         */
        public function getLoadScript( $source ) {
                if ( !isset( $this->sources[$source] ) ) {
                        throw new MWException( "The $source source was never registered in ResourceLoader." );
                }
                return $this->sources[$source];
        }

        /**
         * @since 1.26
         * @param string $value
         * @return string Hash
         */
        public static function makeHash( $value ) {
                $hash = hash( 'fnv132', $value );
                return Wikimedia\base_convert( $hash, 16, 36, 7 );
        }

        /**
         * Add an error to the 'errors' array and log it.
         *
         * Should only be called from within respond().
         *
         * @since 1.29
         * @param Exception $e
         * @param string $msg
         * @param array $context
         */
        protected function outputErrorAndLog( Exception $e, $msg, array $context = [] ) {
                MWExceptionHandler::logException( $e );
                $this->logger->warning(
                        $msg,
                        $context + [ 'exception' => $e ]
                );
                $this->errors[] = self::formatExceptionNoComment( $e );
        }

        /**
         * Helper method to get and combine versions of multiple modules.
         *
         * @since 1.26
         * @param ResourceLoaderContext $context
         * @param string[] $modules List of known module names
         * @return string Hash
         */
        public function getCombinedVersion( ResourceLoaderContext $context, array $moduleNames ) {
                if ( !$moduleNames ) {
                        return '';
                }
                $hashes = array_map( function ( $module ) use ( $context ) {
                        try {
                                return $this->getModule( $module )->getVersionHash( $context );
                        } catch ( Exception $e ) {
                                // If modules fail to compute a version, do still consider the versions
                                // of other modules - don't set an empty string E-Tag for the whole request.
                                // See also T152266 and StartupModule::getModuleRegistrations().
                                $this->outputErrorAndLog( $e,
                                        'Calculating version for "{module}" failed: {exception}',
                                        [
                                                'module' => $module,
                                        ]
                                );
                                return '';
                        }
                }, $moduleNames );
                return self::makeHash( implode( '', $hashes ) );
        }

        /**
         * Get the expected value of the 'version' query parameter.
         *
         * This is used by respond() to set a short Cache-Control header for requests with
         * information newer than the current server has. This avoids pollution of edge caches.
         * Typically during deployment. (T117587)
         *
         * This MUST match return value of `mw.loader#getCombinedVersion()` client-side.
         *
         * @since 1.28
         * @param ResourceLoaderContext $context
         * @param string[] $modules List of module names
         * @return string Hash
         */
        public function makeVersionQuery( ResourceLoaderContext $context ) {
                // As of MediaWiki 1.28, the server and client use the same algorithm for combining
                // version hashes. There is no technical reason for this to be same, and for years the
                // implementations differed. If getCombinedVersion in PHP (used for StartupModule and
                // E-Tag headers) differs in the future from getCombinedVersion in JS (used for 'version'
                // query parameter), then this method must continue to match the JS one.
                $moduleNames = [];
                foreach ( $context->getModules() as $name ) {
                        if ( !$this->getModule( $name ) ) {
                                // If a versioned request contains a missing module, the version is a mismatch
                                // as the client considered a module (and version) we don't have.
                                return '';
                        }
                        $moduleNames[] = $name;
                }
                return $this->getCombinedVersion( $context, $moduleNames );
        }

        /**
         * Output a response to a load request, including the content-type header.
         *
         * @param ResourceLoaderContext $context Context in which a response should be formed
         */
        public function respond( ResourceLoaderContext $context ) {
                // Buffer output to catch warnings. Normally we'd use ob_clean() on the
                // top-level output buffer to clear warnings, but that breaks when ob_gzhandler
                // is used: ob_clean() will clear the GZIP header in that case and it won't come
                // back for subsequent output, resulting in invalid GZIP. So we have to wrap
                // the whole thing in our own output buffer to be sure the active buffer
                // doesn't use ob_gzhandler.
                // See https://bugs.php.net/bug.php?id=36514
                ob_start();

                // Find out which modules are missing and instantiate the others
                $modules = [];
                $missing = [];
                foreach ( $context->getModules() as $name ) {
                        $module = $this->getModule( $name );
                        if ( $module ) {
                                // Do not allow private modules to be loaded from the web.
                                // This is a security issue, see bug 34907.
                                if ( $module->getGroup() === 'private' ) {
                                        $this->logger->debug( "Request for private module '$name' denied" );
                                        $this->errors[] = "Cannot show private module \"$name\"";
                                        continue;
                                }
                                $modules[$name] = $module;
                        } else {
                                $missing[] = $name;
                        }
                }

                try {
                        // Preload for getCombinedVersion() and for batch makeModuleResponse()
                        $this->preloadModuleInfo( array_keys( $modules ), $context );
                } catch ( Exception $e ) {
                        $this->outputErrorAndLog( $e, 'Preloading module info failed: {exception}' );
                }

                // Combine versions to propagate cache invalidation
                $versionHash = '';
                try {
                        $versionHash = $this->getCombinedVersion( $context, array_keys( $modules ) );
                } catch ( Exception $e ) {
                        $this->outputErrorAndLog( $e, 'Calculating version hash failed: {exception}' );
                }

                // See RFC 2616 § 3.11 Entity Tags
                // https://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.11
                $etag = 'W/"' . $versionHash . '"';

                // Try the client-side cache first
                if ( $this->tryRespondNotModified( $context, $etag ) ) {
                        return; // output handled (buffers cleared)
                }

                // Use file cache if enabled and available...
                if ( $this->config->get( 'UseFileCache' ) ) {
                        $fileCache = ResourceFileCache::newFromContext( $context );
                        if ( $this->tryRespondFromFileCache( $fileCache, $context, $etag ) ) {
                                return; // output handled
                        }
                }

                // Generate a response
                $response = $this->makeModuleResponse( $context, $modules, $missing );

                // Capture any PHP warnings from the output buffer and append them to the
                // error list if we're in debug mode.
                if ( $context->getDebug() ) {
                        $warnings = ob_get_contents();
                        if ( strlen( $warnings ) ) {
                                $this->errors[] = $warnings;
                        }
                }

                // Save response to file cache unless there are errors
                if ( isset( $fileCache ) && !$this->errors && !count( $missing ) ) {
                        // Cache single modules and images...and other requests if there are enough hits
                        if ( ResourceFileCache::useFileCache( $context ) ) {
                                if ( $fileCache->isCacheWorthy() ) {
                                        $fileCache->saveText( $response );
                                } else {
                                        $fileCache->incrMissesRecent( $context->getRequest() );
                                }
                        }
                }

                $this->sendResponseHeaders( $context, $etag, (bool)$this->errors );

                // Remove the output buffer and output the response
                ob_end_clean();

                if ( $context->getImageObj() && $this->errors ) {
                        // We can't show both the error messages and the response when it's an image.
                        $response = implode( "\n\n", $this->errors );
                } elseif ( $this->errors ) {
                        $errorText = implode( "\n\n", $this->errors );
                        $errorResponse = self::makeComment( $errorText );
                        if ( $context->shouldIncludeScripts() ) {
                                $errorResponse .= 'if (window.console && console.error) {'
                                        . Xml::encodeJsCall( 'console.error', [ $errorText ] )
                                        . "}\n";
                        }

                        // Prepend error info to the response
                        $response = $errorResponse . $response;
                }

                $this->errors = [];
                echo $response;
        }

        /**
         * Send main response headers to the client.
         *
         * Deals with Content-Type, CORS (for stylesheets), and caching.
         *
         * @param ResourceLoaderContext $context
         * @param string $etag ETag header value
         * @param bool $errors Whether there are errors in the response
         * @return void
         */
        protected function sendResponseHeaders( ResourceLoaderContext $context, $etag, $errors ) {
                $rlMaxage = $this->config->get( 'ResourceLoaderMaxage' );
                // Use a short cache expiry so that updates propagate to clients quickly, if:
                // - No version specified (shared resources, e.g. stylesheets)
                // - There were errors (recover quickly)
                // - Version mismatch (T117587, T47877)
                if ( is_null( $context->getVersion() )
                        || $errors
                        || $context->getVersion() !== $this->makeVersionQuery( $context )
                ) {
                        $maxage = $rlMaxage['unversioned']['client'];
                        $smaxage = $rlMaxage['unversioned']['server'];
                // If a version was specified we can use a longer expiry time since changing
                // version numbers causes cache misses
                } else {
                        $maxage = $rlMaxage['versioned']['client'];
                        $smaxage = $rlMaxage['versioned']['server'];
                }
                if ( $context->getImageObj() ) {
                        // Output different headers if we're outputting textual errors.
                        if ( $errors ) {
                                header( 'Content-Type: text/plain; charset=utf-8' );
                        } else {
                                $context->getImageObj()->sendResponseHeaders( $context );
                        }
                } elseif ( $context->getOnly() === 'styles' ) {
                        header( 'Content-Type: text/css; charset=utf-8' );
                        header( 'Access-Control-Allow-Origin: *' );
                } else {
                        header( 'Content-Type: text/javascript; charset=utf-8' );
                }
                // See RFC 2616 § 14.19 ETag
                // https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.19
                header( 'ETag: ' . $etag );
                if ( $context->getDebug() ) {
                        // Do not cache debug responses
                        header( 'Cache-Control: private, no-cache, must-revalidate' );
                        header( 'Pragma: no-cache' );
                } else {
                        header( "Cache-Control: public, max-age=$maxage, s-maxage=$smaxage" );
                        $exp = min( $maxage, $smaxage );
                        header( 'Expires: ' . wfTimestamp( TS_RFC2822, $exp + time() ) );
                }
        }

        /**
         * Respond with HTTP 304 Not Modified if appropiate.
         *
         * If there's an If-None-Match header, respond with a 304 appropriately
         * and clear out the output buffer. If the client cache is too old then do nothing.
         *
         * @param ResourceLoaderContext $context
         * @param string $etag ETag header value
         * @return bool True if HTTP 304 was sent and output handled
         */
        protected function tryRespondNotModified( ResourceLoaderContext $context, $etag ) {
                // See RFC 2616 § 14.26 If-None-Match
                // https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26
                $clientKeys = $context->getRequest()->getHeader( 'If-None-Match', WebRequest::GETHEADER_LIST );
                // Never send 304s in debug mode
                if ( $clientKeys !== false && !$context->getDebug() && in_array( $etag, $clientKeys ) ) {
                        // There's another bug in ob_gzhandler (see also the comment at
                        // the top of this function) that causes it to gzip even empty
                        // responses, meaning it's impossible to produce a truly empty
                        // response (because the gzip header is always there). This is
                        // a problem because 304 responses have to be completely empty
                        // per the HTTP spec, and Firefox behaves buggily when they're not.
                        // See also https://bugs.php.net/bug.php?id=51579
                        // To work around this, we tear down all output buffering before
                        // sending the 304.
                        wfResetOutputBuffers( /* $resetGzipEncoding = */ true );

                        HttpStatus::header( 304 );

                        $this->sendResponseHeaders( $context, $etag, false );
                        return true;
                }
                return false;
        }

        /**
         * Send out code for a response from file cache if possible.
         *
         * @param ResourceFileCache $fileCache Cache object for this request URL
         * @param ResourceLoaderContext $context Context in which to generate a response
         * @param string $etag ETag header value
         * @return bool If this found a cache file and handled the response
         */
        protected function tryRespondFromFileCache(
                ResourceFileCache $fileCache,
                ResourceLoaderContext $context,
                $etag
        ) {
                $rlMaxage = $this->config->get( 'ResourceLoaderMaxage' );
                // Buffer output to catch warnings.
                ob_start();
                // Get the maximum age the cache can be
                $maxage = is_null( $context->getVersion() )
                        ? $rlMaxage['unversioned']['server']
                        : $rlMaxage['versioned']['server'];
                // Minimum timestamp the cache file must have
                $good = $fileCache->isCacheGood( wfTimestamp( TS_MW, time() - $maxage ) );
                if ( !$good ) {
                        try { // RL always hits the DB on file cache miss...
                                wfGetDB( DB_REPLICA );
                        } catch ( DBConnectionError $e ) { // ...check if we need to fallback to cache
                                $good = $fileCache->isCacheGood(); // cache existence check
                        }
                }
                if ( $good ) {
                        $ts = $fileCache->cacheTimestamp();
                        // Send content type and cache headers
                        $this->sendResponseHeaders( $context, $etag, false );
                        $response = $fileCache->fetchText();
                        // Capture any PHP warnings from the output buffer and append them to the
                        // response in a comment if we're in debug mode.
                        if ( $context->getDebug() ) {
                                $warnings = ob_get_contents();
                                if ( strlen( $warnings ) ) {
                                        $response = self::makeComment( $warnings ) . $response;
                                }
                        }
                        // Remove the output buffer and output the response
                        ob_end_clean();
                        echo $response . "\n/* Cached {$ts} */";
                        return true; // cache hit
                }
                // Clear buffer
                ob_end_clean();

                return false; // cache miss
        }

        /**
         * Generate a CSS or JS comment block.
         *
         * Only use this for public data, not error message details.
         *
         * @param string $text
         * @return string
         */
        public static function makeComment( $text ) {
                $encText = str_replace( '*/', '* /', $text );
                return "/*\n$encText\n*/\n";
        }

        /**
         * Handle exception display.
         *
         * @param Exception $e Exception to be shown to the user
         * @return string Sanitized text in a CSS/JS comment that can be returned to the user
         */
        public static function formatException( $e ) {
                return self::makeComment( self::formatExceptionNoComment( $e ) );
        }

        /**
         * Handle exception display.
         *
         * @since 1.25
         * @param Exception $e Exception to be shown to the user
         * @return string Sanitized text that can be returned to the user
         */
        protected static function formatExceptionNoComment( $e ) {
                global $wgShowExceptionDetails;

                if ( !$wgShowExceptionDetails ) {
                        return MWExceptionHandler::getPublicLogMessage( $e );
                }

                return MWExceptionHandler::getLogMessage( $e ) .
                        "\nBacktrace:\n" .
                        MWExceptionHandler::getRedactedTraceAsString( $e );
        }

        /**
         * Generate code for a response.
         *
         * @param ResourceLoaderContext $context Context in which to generate a response
         * @param ResourceLoaderModule[] $modules List of module objects keyed by module name
         * @param string[] $missing List of requested module names that are unregistered (optional)
         * @return string Response data
         */
        public function makeModuleResponse( ResourceLoaderContext $context,
                array $modules, array $missing = []
        ) {
                $out = '';
                $states = [];

                if ( !count( $modules ) && !count( $missing ) ) {
                        return <<<MESSAGE
/* This file is the Web entry point for MediaWiki's ResourceLoader:
   <https://www.mediawiki.org/wiki/ResourceLoader>. In this request,
   no modules were requested. Max made me put this here. */
MESSAGE;
                }

                $image = $context->getImageObj();
                if ( $image ) {
                        $data = $image->getImageData( $context );
                        if ( $data === false ) {
                                $data = '';
                                $this->errors[] = 'Image generation failed';
                        }
                        return $data;
                }

                foreach ( $missing as $name ) {
                        $states[$name] = 'missing';
                }

                // Generate output
                $isRaw = false;

                $filter = $context->getOnly() === 'styles' ? 'minify-css' : 'minify-js';

                foreach ( $modules as $name => $module ) {
                        try {
                                $content = $module->getModuleContent( $context );
                                $implementKey = $name . '@' . $module->getVersionHash( $context );
                                $strContent = '';

                                // Append output
                                switch ( $context->getOnly() ) {
                                        case 'scripts':
                                                $scripts = $content['scripts'];
                                                if ( is_string( $scripts ) ) {
                                                        // Load scripts raw...
                                                        $strContent = $scripts;
                                                } elseif ( is_array( $scripts ) ) {
                                                        // ...except when $scripts is an array of URLs
                                                        $strContent = self::makeLoaderImplementScript( $implementKey, $scripts, [], [], [] );
                                                }
                                                break;
                                        case 'styles':
                                                $styles = $content['styles'];
                                                // We no longer seperate into media, they are all combined now with
                                                // custom media type groups into @media .. {} sections as part of the css string.
                                                // Module returns either an empty array or a numerical array with css strings.
                                                $strContent = isset( $styles['css'] ) ? implode( '', $styles['css'] ) : '';
                                                break;
                                        default:
                                                $scripts = isset( $content['scripts'] ) ? $content['scripts'] : '';
                                                if ( is_string( $scripts ) ) {
                                                        if ( $name === 'site' || $name === 'user' ) {
                                                                // Legacy scripts that run in the global scope without a closure.
                                                                // mw.loader.implement will use globalEval if scripts is a string.
                                                                // Minify manually here, because general response minification is
                                                                // not effective due it being a string literal, not a function.
                                                                if ( !ResourceLoader::inDebugMode() ) {
                                                                        $scripts = self::filter( 'minify-js', $scripts ); // T107377
                                                                }
                                                        } else {
                                                                $scripts = new XmlJsCode( $scripts );
                                                        }
                                                }
                                                $strContent = self::makeLoaderImplementScript(
                                                        $implementKey,
                                                        $scripts,
                                                        isset( $content['styles'] ) ? $content['styles'] : [],
                                                        isset( $content['messagesBlob'] ) ? new XmlJsCode( $content['messagesBlob'] ) : [],
                                                        isset( $content['templates'] ) ? $content['templates'] : []
                                                );
                                                break;
                                }

                                if ( !$context->getDebug() ) {
                                        $strContent = self::filter( $filter, $strContent );
                                }

                                $out .= $strContent;

                        } catch ( Exception $e ) {
                                $this->outputErrorAndLog( $e, 'Generating module package failed: {exception}' );

                                // Respond to client with error-state instead of module implementation
                                $states[$name] = 'error';
                                unset( $modules[$name] );
                        }
                        $isRaw |= $module->isRaw();
                }

                // Update module states
                if ( $context->shouldIncludeScripts() && !$context->getRaw() && !$isRaw ) {
                        if ( count( $modules ) && $context->getOnly() === 'scripts' ) {
                                // Set the state of modules loaded as only scripts to ready as
                                // they don't have an mw.loader.implement wrapper that sets the state
                                foreach ( $modules as $name => $module ) {
                                        $states[$name] = 'ready';
                                }
                        }

                        // Set the state of modules we didn't respond to with mw.loader.implement
                        if ( count( $states ) ) {
                                $stateScript = self::makeLoaderStateScript( $states );
                                if ( !$context->getDebug() ) {
                                        $stateScript = self::filter( 'minify-js', $stateScript );
                                }
                                $out .= $stateScript;
                        }
                } else {
                        if ( count( $states ) ) {
                                $this->errors[] = 'Problematic modules: ' .
                                        FormatJson::encode( $states, ResourceLoader::inDebugMode() );
                        }
                }

                return $out;
        }

        /**
         * Get names of modules that use a certain message.
         *
         * @param string $messageKey
         * @return array List of module names
         */
        public function getModulesByMessage( $messageKey ) {
                $moduleNames = [];
                foreach ( $this->getModuleNames() as $moduleName ) {
                        $module = $this->getModule( $moduleName );
                        if ( in_array( $messageKey, $module->getMessages() ) ) {
                                $moduleNames[] = $moduleName;
                        }
                }
                return $moduleNames;
        }

        /* Static Methods */

        /**
         * Return JS code that calls mw.loader.implement with given module properties.
         *
         * @param string $name Module name or implement key (format "`[name]@[version]`")
         * @param XmlJsCode|array|string $scripts Code as XmlJsCode (to be wrapped in a closure),
         *  list of URLs to JavaScript files, or a string of JavaScript for `$.globalEval`.
         * @param mixed $styles Array of CSS strings keyed by media type, or an array of lists of URLs
         *   to CSS files keyed by media type
         * @param mixed $messages List of messages associated with this module. May either be an
         *   associative array mapping message key to value, or a JSON-encoded message blob containing
         *   the same data, wrapped in an XmlJsCode object.
         * @param array $templates Keys are name of templates and values are the source of
         *   the template.
         * @throws MWException
         * @return string
         */
        protected static function makeLoaderImplementScript(
                $name, $scripts, $styles, $messages, $templates
        ) {
                if ( $scripts instanceof XmlJsCode ) {
                        $scripts = new XmlJsCode( "function ( $, jQuery, require, module ) {\n{$scripts->value}\n}" );
                } elseif ( !is_string( $scripts ) && !is_array( $scripts ) ) {
                        throw new MWException( 'Invalid scripts error. Array of URLs or string of code expected.' );
                }
                // mw.loader.implement requires 'styles', 'messages' and 'templates' to be objects (not
                // arrays). json_encode considers empty arrays to be numerical and outputs "[]" instead
                // of "{}". Force them to objects.
                $module = [
                        $name,
                        $scripts,
                        (object)$styles,
                        (object)$messages,
                        (object)$templates,
                ];
                self::trimArray( $module );

                return Xml::encodeJsCall( 'mw.loader.implement', $module, ResourceLoader::inDebugMode() );
        }

        /**
         * Returns JS code which, when called, will register a given list of messages.
         *
         * @param mixed $messages Either an associative array mapping message key to value, or a
         *   JSON-encoded message blob containing the same data, wrapped in an XmlJsCode object.
         * @return string
         */
        public static function makeMessageSetScript( $messages ) {
                return Xml::encodeJsCall(
                        'mw.messages.set',
                        [ (object)$messages ],
                        ResourceLoader::inDebugMode()
                );
        }

        /**
         * Combines an associative array mapping media type to CSS into a
         * single stylesheet with "@media" blocks.
         *
         * @param array $stylePairs Array keyed by media type containing (arrays of) CSS strings
         * @return array
         */
        public static function makeCombinedStyles( array $stylePairs ) {
                $out = [];
                foreach ( $stylePairs as $media => $styles ) {
                        // ResourceLoaderFileModule::getStyle can return the styles
                        // as a string or an array of strings. This is to allow separation in
                        // the front-end.
                        $styles = (array)$styles;
                        foreach ( $styles as $style ) {
                                $style = trim( $style );
                                // Don't output an empty "@media print { }" block (bug 40498)
                                if ( $style !== '' ) {
                                        // Transform the media type based on request params and config
                                        // The way that this relies on $wgRequest to propagate request params is slightly evil
                                        $media = OutputPage::transformCssMedia( $media );

                                        if ( $media === '' || $media == 'all' ) {
                                                $out[] = $style;
                                        } elseif ( is_string( $media ) ) {
                                                $out[] = "@media $media {\n" . str_replace( "\n", "\n\t", "\t" . $style ) . "}";
                                        }
                                        // else: skip
                                }
                        }
                }
                return $out;
        }

        /**
         * Returns a JS call to mw.loader.state, which sets the state of a
         * module or modules to a given value. Has two calling conventions:
         *
         *    - ResourceLoader::makeLoaderStateScript( $name, $state ):
         *         Set the state of a single module called $name to $state
         *
         *    - ResourceLoader::makeLoaderStateScript( [ $name => $state, ... ] ):
         *         Set the state of modules with the given names to the given states
         *
         * @param string $name
         * @param string $state
         * @return string
         */
        public static function makeLoaderStateScript( $name, $state = null ) {
                if ( is_array( $name ) ) {
                        return Xml::encodeJsCall(
                                'mw.loader.state',
                                [ $name ],
                                ResourceLoader::inDebugMode()
                        );
                } else {
                        return Xml::encodeJsCall(
                                'mw.loader.state',
                                [ $name, $state ],
                                ResourceLoader::inDebugMode()
                        );
                }
        }

        /**
         * Returns JS code which calls the script given by $script. The script will
         * be called with local variables name, version, dependencies and group,
         * which will have values corresponding to $name, $version, $dependencies
         * and $group as supplied.
         *
         * @param string $name Module name
         * @param string $version Module version hash
         * @param array $dependencies List of module names on which this module depends
         * @param string $group Group which the module is in.
         * @param string $source Source of the module, or 'local' if not foreign.
         * @param string $script JavaScript code
         * @return string
         */
        public static function makeCustomLoaderScript( $name, $version, $dependencies,
                $group, $source, $script
        ) {
                $script = str_replace( "\n", "\n\t", trim( $script ) );
                return Xml::encodeJsCall(
                        "( function ( name, version, dependencies, group, source ) {\n\t$script\n} )",
                        [ $name, $version, $dependencies, $group, $source ],
                        ResourceLoader::inDebugMode()
                );
        }

        private static function isEmptyObject( stdClass $obj ) {
                foreach ( $obj as $key => $value ) {
                        return false;
                }
                return true;
        }

        /**
         * Remove empty values from the end of an array.
         *
         * Values considered empty:
         *
         * - null
         * - []
         * - new XmlJsCode( '{}' )
         * - new stdClass() // (object) []
         *
         * @param Array $array
         */
        private static function trimArray( array &$array ) {
                $i = count( $array );
                while ( $i-- ) {
                        if ( $array[$i] === null
                                || $array[$i] === []
                                || ( $array[$i] instanceof XmlJsCode && $array[$i]->value === '{}' )
                                || ( $array[$i] instanceof stdClass && self::isEmptyObject( $array[$i] ) )
                        ) {
                                unset( $array[$i] );
                        } else {
                                break;
                        }
                }
        }

        /**
         * Returns JS code which calls mw.loader.register with the given
         * parameters. Has three calling conventions:
         *
         *   - ResourceLoader::makeLoaderRegisterScript( $name, $version,
         *        $dependencies, $group, $source, $skip
         *     ):
         *        Register a single module.
         *
         *   - ResourceLoader::makeLoaderRegisterScript( [ $name1, $name2 ] ):
         *        Register modules with the given names.
         *
         *   - ResourceLoader::makeLoaderRegisterScript( [
         *        [ $name1, $version1, $dependencies1, $group1, $source1, $skip1 ],
         *        [ $name2, $version2, $dependencies1, $group2, $source2, $skip2 ],
         *        ...
         *     ] ):
         *        Registers modules with the given names and parameters.
         *
         * @param string $name Module name
         * @param string $version Module version hash
         * @param array $dependencies List of module names on which this module depends
         * @param string $group Group which the module is in
         * @param string $source Source of the module, or 'local' if not foreign
         * @param string $skip Script body of the skip function
         * @return string
         */
        public static function makeLoaderRegisterScript( $name, $version = null,
                $dependencies = null, $group = null, $source = null, $skip = null
        ) {
                if ( is_array( $name ) ) {
                        // Build module name index
                        $index = [];
                        foreach ( $name as $i => &$module ) {
                                $index[$module[0]] = $i;
                        }

                        // Transform dependency names into indexes when possible, they will be resolved by
                        // mw.loader.register on the other end
                        foreach ( $name as &$module ) {
                                if ( isset( $module[2] ) ) {
                                        foreach ( $module[2] as &$dependency ) {
                                                if ( isset( $index[$dependency] ) ) {
                                                        $dependency = $index[$dependency];
                                                }
                                        }
                                }
                        }

                        array_walk( $name, [ 'self', 'trimArray' ] );

                        return Xml::encodeJsCall(
                                'mw.loader.register',
                                [ $name ],
                                ResourceLoader::inDebugMode()
                        );
                } else {
                        $registration = [ $name, $version, $dependencies, $group, $source, $skip ];
                        self::trimArray( $registration );
                        return Xml::encodeJsCall(
                                'mw.loader.register',
                                $registration,
                                ResourceLoader::inDebugMode()
                        );
                }
        }

        /**
         * Returns JS code which calls mw.loader.addSource() with the given
         * parameters. Has two calling conventions:
         *
         *   - ResourceLoader::makeLoaderSourcesScript( $id, $properties ):
         *       Register a single source
         *
         *   - ResourceLoader::makeLoaderSourcesScript( [ $id1 => $loadUrl, $id2 => $loadUrl, ... ] );
         *       Register sources with the given IDs and properties.
         *
         * @param string $id Source ID
         * @param string $loadUrl load.php url
         * @return string
         */
        public static function makeLoaderSourcesScript( $id, $loadUrl = null ) {
                if ( is_array( $id ) ) {
                        return Xml::encodeJsCall(
                                'mw.loader.addSource',
                                [ $id ],
                                ResourceLoader::inDebugMode()
                        );
                } else {
                        return Xml::encodeJsCall(
                                'mw.loader.addSource',
                                [ $id, $loadUrl ],
                                ResourceLoader::inDebugMode()
                        );
                }
        }

        /**
         * Returns JS code which runs given JS code if the client-side framework is
         * present.
         *
         * @deprecated since 1.25; use makeInlineScript instead
         * @param string $script JavaScript code
         * @return string
         */
        public static function makeLoaderConditionalScript( $script ) {
                return '(window.RLQ=window.RLQ||[]).push(function(){' .
                        trim( $script ) . '});';
        }

        /**
         * Construct an inline script tag with given JS code.
         *
         * The code will be wrapped in a closure, and it will be executed by ResourceLoader
         * only if the client has adequate support for MediaWiki JavaScript code.
         *
         * @param string $script JavaScript code
         * @return WrappedString HTML
         */
        public static function makeInlineScript( $script ) {
                $js = self::makeLoaderConditionalScript( $script );
                return new WrappedString(
                        Html::inlineScript( $js ),
                        '<script>(window.RLQ=window.RLQ||[]).push(function(){',
                        '});</script>'
                );
        }

        /**
         * Returns JS code which will set the MediaWiki configuration array to
         * the given value.
         *
         * @param array $configuration List of configuration values keyed by variable name
         * @return string
         */
        public static function makeConfigSetScript( array $configuration ) {
                return Xml::encodeJsCall(
                        'mw.config.set',
                        [ $configuration ],
                        ResourceLoader::inDebugMode()
                );
        }

        /**
         * Convert an array of module names to a packed query string.
         *
         * For example, [ 'foo.bar', 'foo.baz', 'bar.baz', 'bar.quux' ]
         * becomes 'foo.bar,baz|bar.baz,quux'
         * @param array $modules List of module names (strings)
         * @return string Packed query string
         */
        public static function makePackedModulesString( $modules ) {
                $groups = []; // [ prefix => [ suffixes ] ]
                foreach ( $modules as $module ) {
                        $pos = strrpos( $module, '.' );
                        $prefix = $pos === false ? '' : substr( $module, 0, $pos );
                        $suffix = $pos === false ? $module : substr( $module, $pos + 1 );
                        $groups[$prefix][] = $suffix;
                }

                $arr = [];
                foreach ( $groups as $prefix => $suffixes ) {
                        $p = $prefix === '' ? '' : $prefix . '.';
                        $arr[] = $p . implode( ',', $suffixes );
                }
                $str = implode( '|', $arr );
                return $str;
        }

        /**
         * Determine whether debug mode was requested
         * Order of priority is 1) request param, 2) cookie, 3) $wg setting
         * @return bool
         */
        public static function inDebugMode() {
                if ( self::$debugMode === null ) {
                        global $wgRequest, $wgResourceLoaderDebug;
                        self::$debugMode = $wgRequest->getFuzzyBool( 'debug',
                                $wgRequest->getCookie( 'resourceLoaderDebug', '', $wgResourceLoaderDebug )
                        );
                }
                return self::$debugMode;
        }

        /**
         * Reset static members used for caching.
         *
         * Global state and $wgRequest are evil, but we're using it right
         * now and sometimes we need to be able to force ResourceLoader to
         * re-evaluate the context because it has changed (e.g. in the test suite).
         */
        public static function clearCache() {
                self::$debugMode = null;
        }

        /**
         * Build a load.php URL
         *
         * @since 1.24
         * @param string $source Name of the ResourceLoader source
         * @param ResourceLoaderContext $context
         * @param array $extraQuery
         * @return string URL to load.php. May be protocol-relative if $wgLoadScript is, too.
         */
        public function createLoaderURL( $source, ResourceLoaderContext $context,
                $extraQuery = []
        ) {
                $query = self::createLoaderQuery( $context, $extraQuery );
                $script = $this->getLoadScript( $source );

                return wfAppendQuery( $script, $query );
        }

        /**
         * Helper for createLoaderURL()
         *
         * @since 1.24
         * @see makeLoaderQuery
         * @param ResourceLoaderContext $context
         * @param array $extraQuery
         * @return array
         */
        protected static function createLoaderQuery( ResourceLoaderContext $context, $extraQuery = [] ) {
                return self::makeLoaderQuery(
                        $context->getModules(),
                        $context->getLanguage(),
                        $context->getSkin(),
                        $context->getUser(),
                        $context->getVersion(),
                        $context->getDebug(),
                        $context->getOnly(),
                        $context->getRequest()->getBool( 'printable' ),
                        $context->getRequest()->getBool( 'handheld' ),
                        $extraQuery
                );
        }

        /**
         * Build a query array (array representation of query string) for load.php. Helper
         * function for createLoaderURL().
         *
         * @param array $modules
         * @param string $lang
         * @param string $skin
         * @param string $user
         * @param string $version
         * @param bool $debug
         * @param string $only
         * @param bool $printable
         * @param bool $handheld
         * @param array $extraQuery
         *
         * @return array
         */
        public static function makeLoaderQuery( $modules, $lang, $skin, $user = null,
                $version = null, $debug = false, $only = null, $printable = false,
                $handheld = false, $extraQuery = []
        ) {
                $query = [
                        'modules' => self::makePackedModulesString( $modules ),
                        'lang' => $lang,
                        'skin' => $skin,
                        'debug' => $debug ? 'true' : 'false',
                ];
                if ( $user !== null ) {
                        $query['user'] = $user;
                }
                if ( $version !== null ) {
                        $query['version'] = $version;
                }
                if ( $only !== null ) {
                        $query['only'] = $only;
                }
                if ( $printable ) {
                        $query['printable'] = 1;
                }
                if ( $handheld ) {
                        $query['handheld'] = 1;
                }
                $query += $extraQuery;

                // Make queries uniform in order
                ksort( $query );
                return $query;
        }

        /**
         * Check a module name for validity.
         *
         * Module names may not contain pipes (|), commas (,) or exclamation marks (!) and can be
         * at most 255 bytes.
         *
         * @param string $moduleName Module name to check
         * @return bool Whether $moduleName is a valid module name
         */
        public static function isValidModuleName( $moduleName ) {
                return strcspn( $moduleName, '!,|', 0, 255 ) === strlen( $moduleName );
        }

        /**
         * Returns LESS compiler set up for use with MediaWiki
         *
         * @since 1.27
         * @param array $extraVars Associative array of extra (i.e., other than the
         *   globally-configured ones) that should be used for compilation.
         * @throws MWException
         * @return Less_Parser
         */
        public function getLessCompiler( $extraVars = [] ) {
                // When called from the installer, it is possible that a required PHP extension
                // is missing (at least for now; see bug 47564). If this is the case, throw an
                // exception (caught by the installer) to prevent a fatal error later on.
                if ( !class_exists( 'Less_Parser' ) ) {
                        throw new MWException( 'MediaWiki requires the less.php parser' );
                }

                $parser = new Less_Parser;
                $parser->ModifyVars( array_merge( $this->getLessVars(), $extraVars ) );
                $parser->SetImportDirs(
                        array_fill_keys( $this->config->get( 'ResourceLoaderLESSImportPaths' ), '' )
                );
                $parser->SetOption( 'relativeUrls', false );

                return $parser;
        }

        /**
         * Get global LESS variables.
         *
         * @since 1.27
         * @return array Map of variable names to string CSS values.
         */
        public function getLessVars() {
                if ( !$this->lessVars ) {
                        $lessVars = $this->config->get( 'ResourceLoaderLESSVars' );
                        Hooks::run( 'ResourceLoaderGetLessVars', [ &$lessVars ] );
                        $this->lessVars = $lessVars;
                }
                return $this->lessVars;
        }
}