Introduce mediawiki.RegExp module

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

<?php
/**
 * Abstraction for resource loader 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
 */

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

        # 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 = array( 'desktop' );

        // In-object cache for file dependencies
        protected $fileDeps = array();
        // In-object cache for message blob mtime
        protected $msgBlobMtime = array();
        // In-object cache for version hash
        protected $versionHash = array();
        // In-object cache for module content
        protected $contents = array();

        // Whether the position returned by getPosition() is defined in the module configuration
        // and not a default value
        protected $isPositionDefined = false;

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

        /* 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;
        }

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

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

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

        /**
         * 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 array();
        }

        /**
         * @return Config
         * @since 1.24
         */
        public function getConfig() {
                if ( $this->config === null ) {
                        // Ugh, fall back to default
                        $this->config = ConfigFactory::getDefaultInstance()->makeConfig( 'main' );
                }

                return $this->config;
        }

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

        /**
         * 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( array( $this->getName() ) );
                $derivative->setOnly( 'scripts' );
                $derivative->setDebug( true );

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

                return array( $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 array( 'screen' => '.foo { width: 0 }' );
         *  or array( 'screen' => array( '.foo { width: 0 }' ) );
         */
        public function getStyles( ResourceLoaderContext $context ) {
                // Stub, override expected
                return array();
        }

        /**
         * 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 Array( mediaType => array( URL1, URL2, ... ), ... )
         */
        public function getStyleURLsForDebug( ResourceLoaderContext $context ) {
                $resourceLoader = $context->getResourceLoader();
                $derivative = new DerivativeResourceLoaderContext( $context );
                $derivative->setModules( array( $this->getName() ) );
                $derivative->setOnly( 'styles' );
                $derivative->setDebug( true );

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

                return array( 'all' => array( $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 array();
        }

        /**
         * 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';
        }

        /**
         * Where on the HTML page should this module's JS be loaded?
         *  - 'top': in the "<head>"
         *  - 'bottom': at the bottom of the "<body>"
         *
         * @return string
         */
        public function getPosition() {
                return 'bottom';
        }

        /**
         * Whether the position returned by getPosition() is a default value or comes from the module
         * definition. This method is meant to be short-lived, and is only useful until classes added via
         * addModuleStyles with a default value define an explicit position. See getModuleStyles() in
         * OutputPage for the related migration warning.
         *
         * @return bool
         * @since  1.26
         */
        public function isPositionDefault() {
                return !$this->isPositionDefined;
        }

        /**
         * 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 the loader JS for this module, if set.
         *
         * @return mixed JavaScript loader code as a string or boolean false if no custom loader set
         */
        public function getLoaderScript() {
                // Stub, override expected
                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.
         *
         * To add dependencies dynamically on the client side, use a custom
         * loader script, see getLoaderScript()
         *
         * 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 array();
        }

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

        /**
         * 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.
         * Currently these are only image files referenced by the module's CSS.
         *
         * @param string $skin Skin name
         * @return array List of files
         */
        public function getFileDependencies( $skin ) {
                // Try in-object cache first
                if ( isset( $this->fileDeps[$skin] ) ) {
                        return $this->fileDeps[$skin];
                }

                $dbr = wfGetDB( DB_SLAVE );
                $deps = $dbr->selectField( 'module_deps', 'md_deps', array(
                                'md_module' => $this->getName(),
                                'md_skin' => $skin,
                        ), __METHOD__
                );
                if ( !is_null( $deps ) ) {
                        $this->fileDeps[$skin] = (array)FormatJson::decode( $deps, true );
                } else {
                        $this->fileDeps[$skin] = array();
                }
                return $this->fileDeps[$skin];
        }

        /**
         * Set preloaded file dependency information. Used so we can load this
         * information for all modules at once.
         * @param string $skin Skin name
         * @param array $deps Array of file names
         */
        public function setFileDependencies( $skin, $deps ) {
                $this->fileDeps[$skin] = $deps;
        }

        /**
         * Get the last modification timestamp of the messages in this module for a given language.
         * @param string $lang Language code
         * @return int UNIX timestamp
         */
        public function getMsgBlobMtime( $lang ) {
                if ( !isset( $this->msgBlobMtime[$lang] ) ) {
                        if ( !count( $this->getMessages() ) ) {
                                return 1;
                        }

                        $dbr = wfGetDB( DB_SLAVE );
                        $msgBlobMtime = $dbr->selectField( 'msg_resource', 'mr_timestamp', array(
                                        'mr_resource' => $this->getName(),
                                        'mr_lang' => $lang
                                ), __METHOD__
                        );
                        // If no blob was found, but the module does have messages, that means we need
                        // to regenerate it. Return NOW
                        if ( $msgBlobMtime === false ) {
                                $msgBlobMtime = wfTimestampNow();
                        }
                        $this->msgBlobMtime[$lang] = wfTimestamp( TS_UNIX, $msgBlobMtime );
                }
                return $this->msgBlobMtime[$lang];
        }

        /**
         * Set a preloaded message blob last modification timestamp. Used so we
         * can load this information for all modules at once.
         * @param string $lang Language code
         * @param int $mtime UNIX timestamp
         */
        public function setMsgBlobMtime( $lang, $mtime ) {
                $this->msgBlobMtime[$lang] = $mtime;
        }

        /**
         * 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();

                // 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 = array();

                // 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 = array();
                        // Don't create empty stylesheets like array( '' => '' ) 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 = array(
                                                '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] = array();
                                                                foreach ( $style as $cssText ) {
                                                                        if ( is_string( $cssText ) ) {
                                                                                $stylePairs[$media][] = $rl->filter( 'minify-css', $cssText );
                                                                        }
                                                                }
                                                        } elseif ( is_string( $style ) ) {
                                                                $stylePairs[$media] = $rl->filter( 'minify-css', $style );
                                                        }
                                                }
                                        }
                                        // Wrap styles into @media groups as needed and flatten into a numerical array
                                        $styles = array(
                                                'css' => $rl->makeCombinedStyles( $stylePairs )
                                        );
                                }
                        }
                        $content['styles'] = $styles;
                }

                // Messages
                $blobs = $rl->getMessageBlobStore()->get(
                        $rl,
                        array( $this->getName() => $this ),
                        $context->getLanguage()
                );
                if ( isset( $blobs[$this->getName()] ) ) {
                        $content['messagesBlob'] = $blobs[$this->getName()];
                }

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

                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( array() );
                // 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 Exception( '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[] = array(
         *         '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().
         *
         * - getMsgBlobMtime()
         *
         * @since 1.23
         * @param ResourceLoaderContext $context
         * @return array|null
         */
        public function getDefinitionSummary( ResourceLoaderContext $context ) {
                return array(
                        '_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
                        // Use CACHE_ANYTHING since filtering is very slow compared to DB queries
                        $key = wfMemcKey( 'resourceloader', 'jsparse', self::$parseCacheVersion, md5( $contents ) );
                        $cache = wfGetCache( CACHE_ANYTHING );
                        $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
         * but returns 1 instead.
         * @param string $filename File name
         * @return int UNIX timestamp
         */
        protected static function safeFilemtime( $filename ) {
                MediaWiki\suppressWarnings();
                $mtime = filemtime( $filename ) ?: 1;
                MediaWiki\restoreWarnings();

                return $mtime;
        }
}