Type check the APC value in LoadBalancer::doWait()

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

<?php
/**
 * Abstraction for ResourceLoader modules.
 *
 * 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 Trevor Parscal
 * @author Roan Kattouw
 */

use MediaWiki\MediaWikiServices;
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use Wikimedia\ScopedCallback;

/**
 * Abstraction for ResourceLoader modules, with name registration and maxage functionality.
 */
abstract class ResourceLoaderModule implements LoggerAwareInterface {
        # Type of resource
        const TYPE_SCRIPTS = 'scripts';
        const TYPE_STYLES = 'styles';
        const TYPE_COMBINED = 'combined';

        # Desired load type
        // Module only has styles (loaded via <style> or <link rel=stylesheet>)
        const LOAD_STYLES = 'styles';
        // Module may have other resources (loaded via mw.loader from a script)
        const LOAD_GENERAL = 'general';

        # sitewide core module like a skin file or jQuery component
        const ORIGIN_CORE_SITEWIDE = 1;

        # per-user module generated by the software
        const ORIGIN_CORE_INDIVIDUAL = 2;

        # sitewide module generated from user-editable files, like MediaWiki:Common.js, or
        # modules accessible to multiple users, such as those generated by the Gadgets extension.
        const ORIGIN_USER_SITEWIDE = 3;

        # per-user module generated from user-editable files, like User:Me/vector.js
        const ORIGIN_USER_INDIVIDUAL = 4;

        # an access constant; make sure this is kept as the largest number in this group
        const ORIGIN_ALL = 10;

        # script and style modules form a hierarchy of trustworthiness, with core modules like
        # skins and jQuery as most trustworthy, and user scripts as least trustworthy.  We can
        # limit the types of scripts and styles we allow to load on, say, sensitive special
        # pages like Special:UserLogin and Special:Preferences
        protected $origin = self::ORIGIN_CORE_SITEWIDE;

        /* Protected Members */

        protected $name = null;
        protected $targets = [ 'desktop' ];

        // In-object cache for file dependencies
        protected $fileDeps = [];
        // In-object cache for message blob (keyed by language)
        protected $msgBlobs = [];
        // In-object cache for version hash
        protected $versionHash = [];
        // In-object cache for module content
        protected $contents = [];

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

        /**
         * @var array|bool
         */
        protected $deprecated = false;

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

        /* Methods */

        /**
         * Get this module's name. This is set when the module is registered
         * with ResourceLoader::register()
         *
         * @return string|null Name (string) or null if no name was set
         */
        public function getName() {
                return $this->name;
        }

        /**
         * Set this module's name. This is called by ResourceLoader::register()
         * when registering the module. Other code should not call this.
         *
         * @param string $name Name
         */
        public function setName( $name ) {
                $this->name = $name;
        }

        /**
         * Get this module's origin. This is set when the module is registered
         * with ResourceLoader::register()
         *
         * @return int ResourceLoaderModule class constant, the subclass default
         *     if not set manually
         */
        public function getOrigin() {
                return $this->origin;
        }

        /**
         * @param ResourceLoaderContext $context
         * @return bool
         */
        public function getFlip( $context ) {
                global $wgContLang;

                return $wgContLang->getDir() !== $context->getDirection();
        }

        /**
         * Get JS representing deprecation information for the current module if available
         *
         * @return string JavaScript code
         */
        protected function getDeprecationInformation() {
                $deprecationInfo = $this->deprecated;
                if ( $deprecationInfo ) {
                        $name = $this->getName();
                        $warning = 'This page is using the deprecated ResourceLoader module "' . $name . '".';
                        if ( !is_bool( $deprecationInfo ) && isset( $deprecationInfo['message'] ) ) {
                                $warning .= "\n" . $deprecationInfo['message'];
                        }
                        return Xml::encodeJsCall(
                                'mw.log.warn',
                                [ $warning ]
                        );
                } else {
                        return '';
                }
        }

        /**
         * Get all JS for this module for a given language and skin.
         * Includes all relevant JS except loader scripts.
         *
         * @param ResourceLoaderContext $context
         * @return string JavaScript code
         */
        public function getScript( ResourceLoaderContext $context ) {
                // Stub, override expected
                return '';
        }

        /**
         * Takes named templates by the module and returns an array mapping.
         *
         * @return array of templates mapping template alias to content
         */
        public function getTemplates() {
                // Stub, override expected.
                return [];
        }

        /**
         * @return Config
         * @since 1.24
         */
        public function getConfig() {
                if ( $this->config === null ) {
                        // Ugh, fall back to default
                        $this->config = MediaWikiServices::getInstance()->getMainConfig();
                }

                return $this->config;
        }

        /**
         * @param Config $config
         * @since 1.24
         */
        public function setConfig( Config $config ) {
                $this->config = $config;
        }

        /**
         * @since 1.27
         * @param LoggerInterface $logger
         * @return null
         */
        public function setLogger( LoggerInterface $logger ) {
                $this->logger = $logger;
        }

        /**
         * @since 1.27
         * @return LoggerInterface
         */
        protected function getLogger() {
                if ( !$this->logger ) {
                        $this->logger = new NullLogger();
                }
                return $this->logger;
        }

        /**
         * Get the URL or URLs to load for this module's JS in debug mode.
         * The default behavior is to return a load.php?only=scripts URL for
         * the module, but file-based modules will want to override this to
         * load the files directly.
         *
         * This function is called only when 1) we're in debug mode, 2) there
         * is no only= parameter and 3) supportsURLLoading() returns true.
         * #2 is important to prevent an infinite loop, therefore this function
         * MUST return either an only= URL or a non-load.php URL.
         *
         * @param ResourceLoaderContext $context
         * @return array Array of URLs
         */
        public function getScriptURLsForDebug( ResourceLoaderContext $context ) {
                $resourceLoader = $context->getResourceLoader();
                $derivative = new DerivativeResourceLoaderContext( $context );
                $derivative->setModules( [ $this->getName() ] );
                $derivative->setOnly( 'scripts' );
                $derivative->setDebug( true );

                $url = $resourceLoader->createLoaderURL(
                        $this->getSource(),
                        $derivative
                );

                return [ $url ];
        }

        /**
         * Whether this module supports URL loading. If this function returns false,
         * getScript() will be used even in cases (debug mode, no only param) where
         * getScriptURLsForDebug() would normally be used instead.
         * @return bool
         */
        public function supportsURLLoading() {
                return true;
        }

        /**
         * Get all CSS for this module for a given skin.
         *
         * @param ResourceLoaderContext $context
         * @return array List of CSS strings or array of CSS strings keyed by media type.
         *  like [ 'screen' => '.foo { width: 0 }' ];
         *  or [ 'screen' => [ '.foo { width: 0 }' ] ];
         */
        public function getStyles( ResourceLoaderContext $context ) {
                // Stub, override expected
                return [];
        }

        /**
         * Get the URL or URLs to load for this module's CSS in debug mode.
         * The default behavior is to return a load.php?only=styles URL for
         * the module, but file-based modules will want to override this to
         * load the files directly. See also getScriptURLsForDebug()
         *
         * @param ResourceLoaderContext $context
         * @return array [ mediaType => [ URL1, URL2, ... ], ... ]
         */
        public function getStyleURLsForDebug( ResourceLoaderContext $context ) {
                $resourceLoader = $context->getResourceLoader();
                $derivative = new DerivativeResourceLoaderContext( $context );
                $derivative->setModules( [ $this->getName() ] );
                $derivative->setOnly( 'styles' );
                $derivative->setDebug( true );

                $url = $resourceLoader->createLoaderURL(
                        $this->getSource(),
                        $derivative
                );

                return [ 'all' => [ $url ] ];
        }

        /**
         * Get the messages needed for this module.
         *
         * To get a JSON blob with messages, use MessageBlobStore::get()
         *
         * @return array List of message keys. Keys may occur more than once
         */
        public function getMessages() {
                // Stub, override expected
                return [];
        }

        /**
         * Get the group this module is in.
         *
         * @return string Group name
         */
        public function getGroup() {
                // Stub, override expected
                return null;
        }

        /**
         * Get the origin of this module. Should only be overridden for foreign modules.
         *
         * @return string Origin name, 'local' for local modules
         */
        public function getSource() {
                // Stub, override expected
                return 'local';
        }

        /**
         * From where in the page HTML should this module be loaded?
         *
         * @deprecated since 1.29 Obsolete. All modules load async from `<head>`.
         * @return string
         */
        public function getPosition() {
                return 'top';
        }

        /**
         * Whether this module's JS expects to work without the client-side ResourceLoader module.
         * Returning true from this function will prevent mw.loader.state() call from being
         * appended to the bottom of the script.
         *
         * @return bool
         */
        public function isRaw() {
                return false;
        }

        /**
         * Get a list of modules this module depends on.
         *
         * Dependency information is taken into account when loading a module
         * on the client side.
         *
         * Note: It is expected that $context will be made non-optional in the near
         * future.
         *
         * @param ResourceLoaderContext $context
         * @return array List of module names as strings
         */
        public function getDependencies( ResourceLoaderContext $context = null ) {
                // Stub, override expected
                return [];
        }

        /**
         * Get target(s) for the module, eg ['desktop'] or ['desktop', 'mobile']
         *
         * @return array Array of strings
         */
        public function getTargets() {
                return $this->targets;
        }

        /**
         * Get the module's load type.
         *
         * @since 1.28
         * @return string ResourceLoaderModule LOAD_* constant
         */
        public function getType() {
                return self::LOAD_GENERAL;
        }

        /**
         * Get the skip function.
         *
         * Modules that provide fallback functionality can provide a "skip function". This
         * function, if provided, will be passed along to the module registry on the client.
         * When this module is loaded (either directly or as a dependency of another module),
         * then this function is executed first. If the function returns true, the module will
         * instantly be considered "ready" without requesting the associated module resources.
         *
         * The value returned here must be valid javascript for execution in a private function.
         * It must not contain the "function () {" and "}" wrapper though.
         *
         * @return string|null A JavaScript function body returning a boolean value, or null
         */
        public function getSkipFunction() {
                return null;
        }

        /**
         * Get the files this module depends on indirectly for a given skin.
         *
         * These are only image files referenced by the module's stylesheet.
         *
         * @param ResourceLoaderContext $context
         * @return array List of files
         */
        protected function getFileDependencies( ResourceLoaderContext $context ) {
                $vary = $context->getSkin() . '|' . $context->getLanguage();

                // Try in-object cache first
                if ( !isset( $this->fileDeps[$vary] ) ) {
                        $dbr = wfGetDB( DB_REPLICA );
                        $deps = $dbr->selectField( 'module_deps',
                                'md_deps',
                                [
                                        'md_module' => $this->getName(),
                                        'md_skin' => $vary,
                                ],
                                __METHOD__
                        );

                        if ( !is_null( $deps ) ) {
                                $this->fileDeps[$vary] = self::expandRelativePaths(
                                        (array)FormatJson::decode( $deps, true )
                                );
                        } else {
                                $this->fileDeps[$vary] = [];
                        }
                }
                return $this->fileDeps[$vary];
        }

        /**
         * Set in-object cache for file dependencies.
         *
         * This is used to retrieve data in batches. See ResourceLoader::preloadModuleInfo().
         * To save the data, use saveFileDependencies().
         *
         * @param ResourceLoaderContext $context
         * @param string[] $files Array of file names
         */
        public function setFileDependencies( ResourceLoaderContext $context, $files ) {
                $vary = $context->getSkin() . '|' . $context->getLanguage();
                $this->fileDeps[$vary] = $files;
        }

        /**
         * Set the files this module depends on indirectly for a given skin.
         *
         * @since 1.27
         * @param ResourceLoaderContext $context
         * @param array $localFileRefs List of files
         */
        protected function saveFileDependencies( ResourceLoaderContext $context, $localFileRefs ) {
                // Normalise array
                $localFileRefs = array_values( array_unique( $localFileRefs ) );
                sort( $localFileRefs );

                try {
                        // If the list has been modified since last time we cached it, update the cache
                        if ( $localFileRefs !== $this->getFileDependencies( $context ) ) {
                                $cache = ObjectCache::getLocalClusterInstance();
                                $key = $cache->makeKey( __METHOD__, $this->getName() );
                                $scopeLock = $cache->getScopedLock( $key, 0 );
                                if ( !$scopeLock ) {
                                        return; // T124649; avoid write slams
                                }

                                $vary = $context->getSkin() . '|' . $context->getLanguage();
                                $dbw = wfGetDB( DB_MASTER );
                                $dbw->replace( 'module_deps',
                                        [ [ 'md_module', 'md_skin' ] ],
                                        [
                                                'md_module' => $this->getName(),
                                                'md_skin' => $vary,
                                                // Use relative paths to avoid ghost entries when $IP changes (T111481)
                                                'md_deps' => FormatJson::encode( self::getRelativePaths( $localFileRefs ) ),
                                        ]
                                );

                                if ( $dbw->trxLevel() ) {
                                        $dbw->onTransactionResolution(
                                                function () use ( &$scopeLock ) {
                                                        ScopedCallback::consume( $scopeLock ); // release after commit
                                                },
                                                __METHOD__
                                        );
                                }
                        }
                } catch ( Exception $e ) {
                        wfDebugLog( 'resourceloader', __METHOD__ . ": failed to update DB: $e" );
                }
        }

        /**
         * Make file paths relative to MediaWiki directory.
         *
         * This is used to make file paths safe for storing in a database without the paths
         * becoming stale or incorrect when MediaWiki is moved or upgraded (T111481).
         *
         * @since 1.27
         * @param array $filePaths
         * @return array
         */
        public static function getRelativePaths( array $filePaths ) {
                global $IP;
                return array_map( function ( $path ) use ( $IP ) {
                        return RelPath\getRelativePath( $path, $IP );
                }, $filePaths );
        }

        /**
         * Expand directories relative to $IP.
         *
         * @since 1.27
         * @param array $filePaths
         * @return array
         */
        public static function expandRelativePaths( array $filePaths ) {
                global $IP;
                return array_map( function ( $path ) use ( $IP ) {
                        return RelPath\joinPath( $IP, $path );
                }, $filePaths );
        }

        /**
         * Get the hash of the message blob.
         *
         * @since 1.27
         * @param ResourceLoaderContext $context
         * @return string|null JSON blob or null if module has no messages
         */
        protected function getMessageBlob( ResourceLoaderContext $context ) {
                if ( !$this->getMessages() ) {
                        // Don't bother consulting MessageBlobStore
                        return null;
                }
                // Message blobs may only vary language, not by context keys
                $lang = $context->getLanguage();
                if ( !isset( $this->msgBlobs[$lang] ) ) {
                        $this->getLogger()->warning( 'Message blob for {module} should have been preloaded', [
                                'module' => $this->getName(),
                        ] );
                        $store = $context->getResourceLoader()->getMessageBlobStore();
                        $this->msgBlobs[$lang] = $store->getBlob( $this, $lang );
                }
                return $this->msgBlobs[$lang];
        }

        /**
         * Set in-object cache for message blobs.
         *
         * Used to allow fetching of message blobs in batches. See ResourceLoader::preloadModuleInfo().
         *
         * @since 1.27
         * @param string|null $blob JSON blob or null
         * @param string $lang Language code
         */
        public function setMessageBlob( $blob, $lang ) {
                $this->msgBlobs[$lang] = $blob;
        }

        /**
         * Get module-specific LESS variables, if any.
         *
         * @since 1.27
         * @param ResourceLoaderContext $context
         * @return array Module-specific LESS variables.
         */
        protected function getLessVars( ResourceLoaderContext $context ) {
                return [];
        }

        /**
         * Get an array of this module's resources. Ready for serving to the web.
         *
         * @since 1.26
         * @param ResourceLoaderContext $context
         * @return array
         */
        public function getModuleContent( ResourceLoaderContext $context ) {
                $contextHash = $context->getHash();
                // Cache this expensive operation. This calls builds the scripts, styles, and messages
                // content which typically involves filesystem and/or database access.
                if ( !array_key_exists( $contextHash, $this->contents ) ) {
                        $this->contents[$contextHash] = $this->buildContent( $context );
                }
                return $this->contents[$contextHash];
        }

        /**
         * Bundle all resources attached to this module into an array.
         *
         * @since 1.26
         * @param ResourceLoaderContext $context
         * @return array
         */
        final protected function buildContent( ResourceLoaderContext $context ) {
                $rl = $context->getResourceLoader();
                $stats = RequestContext::getMain()->getStats();
                $statStart = microtime( true );

                // Only include properties that are relevant to this context (e.g. only=scripts)
                // and that are non-empty (e.g. don't include "templates" for modules without
                // templates). This helps prevent invalidating cache for all modules when new
                // optional properties are introduced.
                $content = [];

                // Scripts
                if ( $context->shouldIncludeScripts() ) {
                        // If we are in debug mode, we'll want to return an array of URLs if possible
                        // However, we can't do this if the module doesn't support it
                        // We also can't do this if there is an only= parameter, because we have to give
                        // the module a way to return a load.php URL without causing an infinite loop
                        if ( $context->getDebug() && !$context->getOnly() && $this->supportsURLLoading() ) {
                                $scripts = $this->getScriptURLsForDebug( $context );
                        } else {
                                $scripts = $this->getScript( $context );
                                // rtrim() because there are usually a few line breaks
                                // after the last ';'. A new line at EOF, a new line
                                // added by ResourceLoaderFileModule::readScriptFiles, etc.
                                if ( is_string( $scripts )
                                        && strlen( $scripts )
                                        && substr( rtrim( $scripts ), -1 ) !== ';'
                                ) {
                                        // Append semicolon to prevent weird bugs caused by files not
                                        // terminating their statements right (bug 27054)
                                        $scripts .= ";\n";
                                }
                        }
                        $content['scripts'] = $scripts;
                }

                // Styles
                if ( $context->shouldIncludeStyles() ) {
                        $styles = [];
                        // Don't create empty stylesheets like [ '' => '' ] for modules
                        // that don't *have* any stylesheets (bug 38024).
                        $stylePairs = $this->getStyles( $context );
                        if ( count( $stylePairs ) ) {
                                // If we are in debug mode without &only= set, we'll want to return an array of URLs
                                // See comment near shouldIncludeScripts() for more details
                                if ( $context->getDebug() && !$context->getOnly() && $this->supportsURLLoading() ) {
                                        $styles = [
                                                'url' => $this->getStyleURLsForDebug( $context )
                                        ];
                                } else {
                                        // Minify CSS before embedding in mw.loader.implement call
                                        // (unless in debug mode)
                                        if ( !$context->getDebug() ) {
                                                foreach ( $stylePairs as $media => $style ) {
                                                        // Can be either a string or an array of strings.
                                                        if ( is_array( $style ) ) {
                                                                $stylePairs[$media] = [];
                                                                foreach ( $style as $cssText ) {
                                                                        if ( is_string( $cssText ) ) {
                                                                                $stylePairs[$media][] =
                                                                                        ResourceLoader::filter( 'minify-css', $cssText );
                                                                        }
                                                                }
                                                        } elseif ( is_string( $style ) ) {
                                                                $stylePairs[$media] = ResourceLoader::filter( 'minify-css', $style );
                                                        }
                                                }
                                        }
                                        // Wrap styles into @media groups as needed and flatten into a numerical array
                                        $styles = [
                                                'css' => $rl->makeCombinedStyles( $stylePairs )
                                        ];
                                }
                        }
                        $content['styles'] = $styles;
                }

                // Messages
                $blob = $this->getMessageBlob( $context );
                if ( $blob ) {
                        $content['messagesBlob'] = $blob;
                }

                $templates = $this->getTemplates();
                if ( $templates ) {
                        $content['templates'] = $templates;
                }

                $statTiming = microtime( true ) - $statStart;
                $statName = strtr( $this->getName(), '.', '_' );
                $stats->timing( "resourceloader_build.all", 1000 * $statTiming );
                $stats->timing( "resourceloader_build.$statName", 1000 * $statTiming );

                return $content;
        }

        /**
         * Get a string identifying the current version of this module in a given context.
         *
         * Whenever anything happens that changes the module's response (e.g. scripts, styles, and
         * messages) this value must change. This value is used to store module responses in cache.
         * (Both client-side and server-side.)
         *
         * It is not recommended to override this directly. Use getDefinitionSummary() instead.
         * If overridden, one must call the parent getVersionHash(), append data and re-hash.
         *
         * This method should be quick because it is frequently run by ResourceLoaderStartUpModule to
         * propagate changes to the client and effectively invalidate cache.
         *
         * For backward-compatibility, the following optional data providers are automatically included:
         *
         * - getModifiedTime()
         * - getModifiedHash()
         *
         * @since 1.26
         * @param ResourceLoaderContext $context
         * @return string Hash (should use ResourceLoader::makeHash)
         */
        public function getVersionHash( ResourceLoaderContext $context ) {
                // The startup module produces a manifest with versions representing the entire module.
                // Typically, the request for the startup module itself has only=scripts. That must apply
                // only to the startup module content, and not to the module version computed here.
                $context = new DerivativeResourceLoaderContext( $context );
                $context->setModules( [] );
                // Version hash must cover all resources, regardless of startup request itself.
                $context->setOnly( null );
                // Compute version hash based on content, not debug urls.
                $context->setDebug( false );

                // Cache this somewhat expensive operation. Especially because some classes
                // (e.g. startup module) iterate more than once over all modules to get versions.
                $contextHash = $context->getHash();
                if ( !array_key_exists( $contextHash, $this->versionHash ) ) {

                        if ( $this->enableModuleContentVersion() ) {
                                // Detect changes directly
                                $str = json_encode( $this->getModuleContent( $context ) );
                        } else {
                                // Infer changes based on definition and other metrics
                                $summary = $this->getDefinitionSummary( $context );
                                if ( !isset( $summary['_cacheEpoch'] ) ) {
                                        throw new LogicException( 'getDefinitionSummary must call parent method' );
                                }
                                $str = json_encode( $summary );

                                $mtime = $this->getModifiedTime( $context );
                                if ( $mtime !== null ) {
                                        // Support: MediaWiki 1.25 and earlier
                                        $str .= strval( $mtime );
                                }

                                $mhash = $this->getModifiedHash( $context );
                                if ( $mhash !== null ) {
                                        // Support: MediaWiki 1.25 and earlier
                                        $str .= strval( $mhash );
                                }
                        }

                        $this->versionHash[$contextHash] = ResourceLoader::makeHash( $str );
                }
                return $this->versionHash[$contextHash];
        }

        /**
         * Whether to generate version hash based on module content.
         *
         * If a module requires database or file system access to build the module
         * content, consider disabling this in favour of manually tracking relevant
         * aspects in getDefinitionSummary(). See getVersionHash() for how this is used.
         *
         * @return bool
         */
        public function enableModuleContentVersion() {
                return false;
        }

        /**
         * Get the definition summary for this module.
         *
         * This is the method subclasses are recommended to use to track values in their
         * version hash. Call this in getVersionHash() and pass it to e.g. json_encode.
         *
         * Subclasses must call the parent getDefinitionSummary() and build on that.
         * It is recommended that each subclass appends its own new array. This prevents
         * clashes or accidental overwrites of existing keys and gives each subclass
         * its own scope for simple array keys.
         *
         * @code
         *     $summary = parent::getDefinitionSummary( $context );
         *     $summary[] = [
         *         'foo' => 123,
         *         'bar' => 'quux',
         *     ];
         *     return $summary;
         * @endcode
         *
         * Return an array containing values from all significant properties of this
         * module's definition.
         *
         * Be careful not to normalise too much. Especially preserve the order of things
         * that carry significance in getScript and getStyles (T39812).
         *
         * Avoid including things that are insiginificant (e.g. order of message keys is
         * insignificant and should be sorted to avoid unnecessary cache invalidation).
         *
         * This data structure must exclusively contain arrays and scalars as values (avoid
         * object instances) to allow simple serialisation using json_encode.
         *
         * If modules have a hash or timestamp from another source, that may be incuded as-is.
         *
         * A number of utility methods are available to help you gather data. These are not
         * called by default and must be included by the subclass' getDefinitionSummary().
         *
         * - getMessageBlob()
         *
         * @since 1.23
         * @param ResourceLoaderContext $context
         * @return array|null
         */
        public function getDefinitionSummary( ResourceLoaderContext $context ) {
                return [
                        '_class' => get_class( $this ),
                        '_cacheEpoch' => $this->getConfig()->get( 'CacheEpoch' ),
                ];
        }

        /**
         * Get this module's last modification timestamp for a given context.
         *
         * @deprecated since 1.26 Use getDefinitionSummary() instead
         * @param ResourceLoaderContext $context Context object
         * @return int|null UNIX timestamp
         */
        public function getModifiedTime( ResourceLoaderContext $context ) {
                return null;
        }

        /**
         * Helper method for providing a version hash to getVersionHash().
         *
         * @deprecated since 1.26 Use getDefinitionSummary() instead
         * @param ResourceLoaderContext $context
         * @return string|null Hash
         */
        public function getModifiedHash( ResourceLoaderContext $context ) {
                return null;
        }

        /**
         * Back-compat dummy for old subclass implementations of getModifiedTime().
         *
         * This method used to use ObjectCache to track when a hash was first seen. That principle
         * stems from a time that ResourceLoader could only identify module versions by timestamp.
         * That is no longer the case. Use getDefinitionSummary() directly.
         *
         * @deprecated since 1.26 Superseded by getVersionHash()
         * @param ResourceLoaderContext $context
         * @return int UNIX timestamp
         */
        public function getHashMtime( ResourceLoaderContext $context ) {
                if ( !is_string( $this->getModifiedHash( $context ) ) ) {
                        return 1;
                }
                // Dummy that is > 1
                return 2;
        }

        /**
         * Back-compat dummy for old subclass implementations of getModifiedTime().
         *
         * @since 1.23
         * @deprecated since 1.26 Superseded by getVersionHash()
         * @param ResourceLoaderContext $context
         * @return int UNIX timestamp
         */
        public function getDefinitionMtime( ResourceLoaderContext $context ) {
                if ( $this->getDefinitionSummary( $context ) === null ) {
                        return 1;
                }
                // Dummy that is > 1
                return 2;
        }

        /**
         * Check whether this module is known to be empty. If a child class
         * has an easy and cheap way to determine that this module is
         * definitely going to be empty, it should override this method to
         * return true in that case. Callers may optimize the request for this
         * module away if this function returns true.
         * @param ResourceLoaderContext $context
         * @return bool
         */
        public function isKnownEmpty( ResourceLoaderContext $context ) {
                return false;
        }

        /** @var JSParser Lazy-initialized; use self::javaScriptParser() */
        private static $jsParser;
        private static $parseCacheVersion = 1;

        /**
         * Validate a given script file; if valid returns the original source.
         * If invalid, returns replacement JS source that throws an exception.
         *
         * @param string $fileName
         * @param string $contents
         * @return string JS with the original, or a replacement error
         */
        protected function validateScriptFile( $fileName, $contents ) {
                if ( $this->getConfig()->get( 'ResourceLoaderValidateJS' ) ) {
                        // Try for cache hit
                        $cache = ObjectCache::getMainWANInstance();
                        $key = $cache->makeKey(
                                'resourceloader',
                                'jsparse',
                                self::$parseCacheVersion,
                                md5( $contents )
                        );
                        $cacheEntry = $cache->get( $key );
                        if ( is_string( $cacheEntry ) ) {
                                return $cacheEntry;
                        }

                        $parser = self::javaScriptParser();
                        try {
                                $parser->parse( $contents, $fileName, 1 );
                                $result = $contents;
                        } catch ( Exception $e ) {
                                // We'll save this to cache to avoid having to validate broken JS over and over...
                                $err = $e->getMessage();
                                $result = "mw.log.error(" .
                                        Xml::encodeJsVar( "JavaScript parse error: $err" ) . ");";
                        }

                        $cache->set( $key, $result );
                        return $result;
                } else {
                        return $contents;
                }
        }

        /**
         * @return JSParser
         */
        protected static function javaScriptParser() {
                if ( !self::$jsParser ) {
                        self::$jsParser = new JSParser();
                }
                return self::$jsParser;
        }

        /**
         * Safe version of filemtime(), which doesn't throw a PHP warning if the file doesn't exist.
         * Defaults to 1.
         *
         * @param string $filePath File path
         * @return int UNIX timestamp
         */
        protected static function safeFilemtime( $filePath ) {
                MediaWiki\suppressWarnings();
                $mtime = filemtime( $filePath ) ?: 1;
                MediaWiki\restoreWarnings();
                return $mtime;
        }

        /**
         * Compute a non-cryptographic string hash of a file's contents.
         * If the file does not exist or cannot be read, returns an empty string.
         *
         * @since 1.26 Uses MD4 instead of SHA1.
         * @param string $filePath File path
         * @return string Hash
         */
        protected static function safeFileHash( $filePath ) {
                return FileContentsHasher::getFileContentsHash( $filePath );
        }
}