Actually format search error Status objects nicely

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

<?php
/**
 * Resource loader module based on local JavaScript/CSS files.
 *
 * 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
 */

/**
 * ResourceLoader module based on local JavaScript/CSS files.
 */
class ResourceLoaderFileModule extends ResourceLoaderModule {
        /* Protected Members */

        /** @var string Local base path, see __construct() */
        protected $localBasePath = '';

        /** @var string Remote base path, see __construct() */
        protected $remoteBasePath = '';

        /**
         * @var array List of paths to JavaScript files to always include
         * @par Usage:
         * @code
         * array( [file-path], [file-path], ... )
         * @endcode
         */
        protected $scripts = array();

        /**
         * @var array List of JavaScript files to include when using a specific language
         * @par Usage:
         * @code
         * array( [language-code] => array( [file-path], [file-path], ... ), ... )
         * @endcode
         */
        protected $languageScripts = array();

        /**
         * @var array List of JavaScript files to include when using a specific skin
         * @par Usage:
         * @code
         * array( [skin-name] => array( [file-path], [file-path], ... ), ... )
         * @endcode
         */
        protected $skinScripts = array();

        /**
         * @var array List of paths to JavaScript files to include in debug mode
         * @par Usage:
         * @code
         * array( [skin-name] => array( [file-path], [file-path], ... ), ... )
         * @endcode
         */
        protected $debugScripts = array();

        /**
         * @var array List of paths to JavaScript files to include in the startup module
         * @par Usage:
         * @code
         * array( [file-path], [file-path], ... )
         * @endcode
         */
        protected $loaderScripts = array();

        /**
         * @var array List of paths to CSS files to always include
         * @par Usage:
         * @code
         * array( [file-path], [file-path], ... )
         * @endcode
         */
        protected $styles = array();

        /**
         * @var array List of paths to CSS files to include when using specific skins
         * @par Usage:
         * @code
         * array( [file-path], [file-path], ... )
         * @endcode
         */
        protected $skinStyles = array();

        /**
         * @var array List of modules this module depends on
         * @par Usage:
         * @code
         * array( [file-path], [file-path], ... )
         * @endcode
         */
        protected $dependencies = array();

        /**
         * @var string File name containing the body of the skip function
         */
        protected $skipFunction = null;

        /**
         * @var array List of message keys used by this module
         * @par Usage:
         * @code
         * array( [message-key], [message-key], ... )
         * @endcode
         */
        protected $messages = array();

        /** @var string Name of group to load this module in */
        protected $group;

        /** @var string Position on the page to load this module at */
        protected $position = 'bottom';

        /** @var bool Link to raw files in debug mode */
        protected $debugRaw = true;

        /** @var bool Whether mw.loader.state() call should be omitted */
        protected $raw = false;

        protected $targets = array( 'desktop' );

        /**
         * @var bool Whether getStyleURLsForDebug should return raw file paths,
         * or return load.php urls
         */
        protected $hasGeneratedStyles = false;

        /**
         * @var array Cache for mtime
         * @par Usage:
         * @code
         * array( [hash] => [mtime], [hash] => [mtime], ... )
         * @endcode
         */
        protected $modifiedTime = array();

        /**
         * @var array Place where readStyleFile() tracks file dependencies
         * @par Usage:
         * @code
         * array( [file-path], [file-path], ... )
         * @endcode
         */
        protected $localFileRefs = array();

        /* Methods */

        /**
         * Constructs a new module from an options array.
         *
         * @param array $options List of options; if not given or empty, an empty module will be
         *     constructed
         * @param string $localBasePath Base path to prepend to all local paths in $options. Defaults
         *     to $IP
         * @param string $remoteBasePath Base path to prepend to all remote paths in $options. Defaults
         *     to $wgScriptPath
         *
         * Below is a description for the $options array:
         * @throws MWException
         * @par Construction options:
         * @code
         *     array(
         *         // Base path to prepend to all local paths in $options. Defaults to $IP
         *         'localBasePath' => [base path],
         *         // Base path to prepend to all remote paths in $options. Defaults to $wgScriptPath
         *         'remoteBasePath' => [base path],
         *         // Equivalent of remoteBasePath, but relative to $wgExtensionAssetsPath
         *         'remoteExtPath' => [base path],
         *         // Scripts to always include
         *         'scripts' => [file path string or array of file path strings],
         *         // Scripts to include in specific language contexts
         *         'languageScripts' => array(
         *             [language code] => [file path string or array of file path strings],
         *         ),
         *         // Scripts to include in specific skin contexts
         *         'skinScripts' => array(
         *             [skin name] => [file path string or array of file path strings],
         *         ),
         *         // Scripts to include in debug contexts
         *         'debugScripts' => [file path string or array of file path strings],
         *         // Scripts to include in the startup module
         *         'loaderScripts' => [file path string or array of file path strings],
         *         // Modules which must be loaded before this module
         *         'dependencies' => [module name string or array of module name strings],
         *         // Styles to always load
         *         'styles' => [file path string or array of file path strings],
         *         // Styles to include in specific skin contexts
         *         'skinStyles' => array(
         *             [skin name] => [file path string or array of file path strings],
         *         ),
         *         // Messages to always load
         *         'messages' => [array of message key strings],
         *         // Group which this module should be loaded together with
         *         'group' => [group name string],
         *         // Position on the page to load this module at
         *         'position' => ['bottom' (default) or 'top']
         *         // Function that, if it returns true, makes the loader skip this module.
         *         // The file must contain valid JavaScript for execution in a private function.
         *         // The file must not contain the "function () {" and "}" wrapper though.
         *         'skipFunction' => [file path]
         *     )
         * @endcode
         */
        public function __construct( $options = array(), $localBasePath = null,
                $remoteBasePath = null
        ) {
                global $IP, $wgScriptPath, $wgResourceBasePath;
                $this->localBasePath = $localBasePath === null ? $IP : $localBasePath;
                if ( $remoteBasePath !== null ) {
                        $this->remoteBasePath = $remoteBasePath;
                } else {
                        $this->remoteBasePath = $wgResourceBasePath === null ? $wgScriptPath : $wgResourceBasePath;
                }

                if ( isset( $options['remoteExtPath'] ) ) {
                        global $wgExtensionAssetsPath;
                        $this->remoteBasePath = $wgExtensionAssetsPath . '/' . $options['remoteExtPath'];
                }

                foreach ( $options as $member => $option ) {
                        switch ( $member ) {
                                // Lists of file paths
                                case 'scripts':
                                case 'debugScripts':
                                case 'loaderScripts':
                                case 'styles':
                                        $this->{$member} = (array)$option;
                                        break;
                                // Collated lists of file paths
                                case 'languageScripts':
                                case 'skinScripts':
                                case 'skinStyles':
                                        if ( !is_array( $option ) ) {
                                                throw new MWException(
                                                        "Invalid collated file path list error. " .
                                                        "'$option' given, array expected."
                                                );
                                        }
                                        foreach ( $option as $key => $value ) {
                                                if ( !is_string( $key ) ) {
                                                        throw new MWException(
                                                                "Invalid collated file path list key error. " .
                                                                "'$key' given, string expected."
                                                        );
                                                }
                                                $this->{$member}[$key] = (array)$value;
                                        }
                                        break;
                                // Lists of strings
                                case 'dependencies':
                                case 'messages':
                                case 'targets':
                                        // Normalise
                                        $option = array_values( array_unique( (array)$option ) );
                                        sort( $option );

                                        $this->{$member} = $option;
                                        break;
                                // Single strings
                                case 'group':
                                case 'position':
                                case 'localBasePath':
                                case 'remoteBasePath':
                                case 'skipFunction':
                                        $this->{$member} = (string)$option;
                                        break;
                                // Single booleans
                                case 'debugRaw':
                                case 'raw':
                                        $this->{$member} = (bool)$option;
                                        break;
                        }
                }
                // Make sure the remote base path is a complete valid URL,
                // but possibly protocol-relative to avoid cache pollution
                $this->remoteBasePath = wfExpandUrl( $this->remoteBasePath, PROTO_RELATIVE );
        }

        /**
         * Gets all scripts for a given context concatenated together.
         *
         * @param ResourceLoaderContext $context Context in which to generate script
         * @return string JavaScript code for $context
         */
        public function getScript( ResourceLoaderContext $context ) {
                $files = $this->getScriptFiles( $context );
                return $this->readScriptFiles( $files );
        }

        /**
         * @param ResourceLoaderContext $context
         * @return array
         */
        public function getScriptURLsForDebug( ResourceLoaderContext $context ) {
                $urls = array();
                foreach ( $this->getScriptFiles( $context ) as $file ) {
                        $urls[] = $this->getRemotePath( $file );
                }
                return $urls;
        }

        /**
         * @return bool
         */
        public function supportsURLLoading() {
                return $this->debugRaw;
        }

        /**
         * Get loader script.
         *
         * @return string|false JavaScript code to be added to startup module
         */
        public function getLoaderScript() {
                if ( count( $this->loaderScripts ) === 0 ) {
                        return false;
                }
                return $this->readScriptFiles( $this->loaderScripts );
        }

        /**
         * Get all styles for a given context.
         *
         * @param ResourceLoaderContext $context
         * @return array CSS code for $context as an associative array mapping media type to CSS text.
         */
        public function getStyles( ResourceLoaderContext $context ) {
                $styles = $this->readStyleFiles(
                        $this->getStyleFiles( $context ),
                        $this->getFlip( $context )
                );
                // Collect referenced files
                $this->localFileRefs = array_unique( $this->localFileRefs );
                // If the list has been modified since last time we cached it, update the cache
                try {
                        if ( $this->localFileRefs !== $this->getFileDependencies( $context->getSkin() ) ) {
                                $dbw = wfGetDB( DB_MASTER );
                                $dbw->replace( 'module_deps',
                                        array( array( 'md_module', 'md_skin' ) ), array(
                                                'md_module' => $this->getName(),
                                                'md_skin' => $context->getSkin(),
                                                'md_deps' => FormatJson::encode( $this->localFileRefs ),
                                        )
                                );
                        }
                } catch ( Exception $e ) {
                        wfDebugLog( 'resourceloader', __METHOD__ . ": failed to update DB: $e" );
                }
                return $styles;
        }

        /**
         * @param ResourceLoaderContext $context
         * @return array
         */
        public function getStyleURLsForDebug( ResourceLoaderContext $context ) {
                if ( $this->hasGeneratedStyles ) {
                        // Do the default behaviour of returning a url back to load.php
                        // but with only=styles.
                        return parent::getStyleURLsForDebug( $context );
                }
                // Our module consists entirely of real css files,
                // in debug mode we can load those directly.
                $urls = array();
                foreach ( $this->getStyleFiles( $context ) as $mediaType => $list ) {
                        $urls[$mediaType] = array();
                        foreach ( $list as $file ) {
                                $urls[$mediaType][] = $this->getRemotePath( $file );
                        }
                }
                return $urls;
        }

        /**
         * Gets list of message keys used by this module.
         *
         * @return array List of message keys
         */
        public function getMessages() {
                return $this->messages;
        }

        /**
         * Gets the name of the group this module should be loaded in.
         *
         * @return string Group name
         */
        public function getGroup() {
                return $this->group;
        }

        /**
         * @return string
         */
        public function getPosition() {
                return $this->position;
        }

        /**
         * Gets list of names of modules this module depends on.
         *
         * @return array List of module names
         */
        public function getDependencies() {
                return $this->dependencies;
        }

        /**
         * Get the skip function.
         *
         * @return string|null
         */
        public function getSkipFunction() {
                if ( !$this->skipFunction ) {
                        return null;
                }

                global $wgResourceLoaderValidateStaticJS;
                $localPath = $this->getLocalPath( $this->skipFunction );
                if ( !file_exists( $localPath ) ) {
                        throw new MWException( __METHOD__ . ": skip function file not found: \"$localPath\"" );
                }
                $contents = file_get_contents( $localPath );
                if ( $wgResourceLoaderValidateStaticJS ) {
                        $contents = $this->validateScriptFile( $fileName, $contents );
                }
                return $contents;
        }

        /**
         * @return bool
         */
        public function isRaw() {
                return $this->raw;
        }

        /**
         * Get the last modified timestamp of this module.
         *
         * Last modified timestamps are calculated from the highest last modified
         * timestamp of this module's constituent files as well as the files it
         * depends on. This function is context-sensitive, only performing
         * calculations on files relevant to the given language, skin and debug
         * mode.
         *
         * @param ResourceLoaderContext $context Context in which to calculate
         *     the modified time
         * @return int UNIX timestamp
         * @see ResourceLoaderModule::getFileDependencies
         */
        public function getModifiedTime( ResourceLoaderContext $context ) {
                if ( isset( $this->modifiedTime[$context->getHash()] ) ) {
                        return $this->modifiedTime[$context->getHash()];
                }
                wfProfileIn( __METHOD__ );

                $files = array();

                // Flatten style files into $files
                $styles = self::collateFilePathListByOption( $this->styles, 'media', 'all' );
                foreach ( $styles as $styleFiles ) {
                        $files = array_merge( $files, $styleFiles );
                }

                $skinFiles = self::collateFilePathListByOption(
                        self::tryForKey( $this->skinStyles, $context->getSkin(), 'default' ),
                        'media',
                        'all'
                );
                foreach ( $skinFiles as $styleFiles ) {
                        $files = array_merge( $files, $styleFiles );
                }

                // Final merge, this should result in a master list of dependent files
                $files = array_merge(
                        $files,
                        $this->scripts,
                        $context->getDebug() ? $this->debugScripts : array(),
                        self::tryForKey( $this->languageScripts, $context->getLanguage() ),
                        self::tryForKey( $this->skinScripts, $context->getSkin(), 'default' ),
                        $this->loaderScripts
                );
                if ( $this->skipFunction ) {
                        $files[] = $this->skipFunction;
                }
                $files = array_map( array( $this, 'getLocalPath' ), $files );
                // File deps need to be treated separately because they're already prefixed
                $files = array_merge( $files, $this->getFileDependencies( $context->getSkin() ) );

                // If a module is nothing but a list of dependencies, we need to avoid
                // giving max() an empty array
                if ( count( $files ) === 0 ) {
                        $this->modifiedTime[$context->getHash()] = 1;
                        wfProfileOut( __METHOD__ );
                        return $this->modifiedTime[$context->getHash()];
                }

                wfProfileIn( __METHOD__ . '-filemtime' );
                $filesMtime = max( array_map( array( __CLASS__, 'safeFilemtime' ), $files ) );
                wfProfileOut( __METHOD__ . '-filemtime' );

                $this->modifiedTime[$context->getHash()] = max(
                        $filesMtime,
                        $this->getMsgBlobMtime( $context->getLanguage() ),
                        $this->getDefinitionMtime( $context )
                );

                wfProfileOut( __METHOD__ );
                return $this->modifiedTime[$context->getHash()];
        }

        /**
         * Get the definition summary for this module.
         *
         * @return array
         */
        public function getDefinitionSummary( ResourceLoaderContext $context ) {
                $summary = array(
                        'class' => get_class( $this ),
                );
                foreach ( array(
                        'scripts',
                        'debugScripts',
                        'loaderScripts',
                        'styles',
                        'languageScripts',
                        'skinScripts',
                        'skinStyles',
                        'dependencies',
                        'messages',
                        'targets',
                        'group',
                        'position',
                        'skipFunction',
                        'localBasePath',
                        'remoteBasePath',
                        'debugRaw',
                        'raw',
                ) as $member ) {
                        $summary[$member] = $this->{$member};
                };
                return $summary;
        }

        /* Protected Methods */

        /**
         * @param string $path
         * @return string
         */
        protected function getLocalPath( $path ) {
                return "{$this->localBasePath}/$path";
        }

        /**
         * @param string $path
         * @return string
         */
        protected function getRemotePath( $path ) {
                return "{$this->remoteBasePath}/$path";
        }

        /**
         * Infer the stylesheet language from a stylesheet file path.
         *
         * @since 1.22
         * @param string $path
         * @return string The stylesheet language name
         */
        public function getStyleSheetLang( $path ) {
                return preg_match( '/\.less$/i', $path ) ? 'less' : 'css';
        }

        /**
         * Collates file paths by option (where provided).
         *
         * @param array $list List of file paths in any combination of index/path
         *     or path/options pairs
         * @param string $option Option name
         * @param mixed $default Default value if the option isn't set
         * @return array List of file paths, collated by $option
         */
        protected static function collateFilePathListByOption( array $list, $option, $default ) {
                $collatedFiles = array();
                foreach ( (array)$list as $key => $value ) {
                        if ( is_int( $key ) ) {
                                // File name as the value
                                if ( !isset( $collatedFiles[$default] ) ) {
                                        $collatedFiles[$default] = array();
                                }
                                $collatedFiles[$default][] = $value;
                        } elseif ( is_array( $value ) ) {
                                // File name as the key, options array as the value
                                $optionValue = isset( $value[$option] ) ? $value[$option] : $default;
                                if ( !isset( $collatedFiles[$optionValue] ) ) {
                                        $collatedFiles[$optionValue] = array();
                                }
                                $collatedFiles[$optionValue][] = $key;
                        }
                }
                return $collatedFiles;
        }

        /**
         * Get a list of element that match a key, optionally using a fallback key.
         *
         * @param array $list List of lists to select from
         * @param string $key Key to look for in $map
         * @param string $fallback Key to look for in $list if $key doesn't exist
         * @return array List of elements from $map which matched $key or $fallback,
         *  or an empty list in case of no match
         */
        protected static function tryForKey( array $list, $key, $fallback = null ) {
                if ( isset( $list[$key] ) && is_array( $list[$key] ) ) {
                        return $list[$key];
                } elseif ( is_string( $fallback )
                        && isset( $list[$fallback] )
                        && is_array( $list[$fallback] )
                ) {
                        return $list[$fallback];
                }
                return array();
        }

        /**
         * Get a list of file paths for all scripts in this module, in order of proper execution.
         *
         * @param ResourceLoaderContext $context
         * @return array List of file paths
         */
        protected function getScriptFiles( ResourceLoaderContext $context ) {
                $files = array_merge(
                        $this->scripts,
                        self::tryForKey( $this->languageScripts, $context->getLanguage() ),
                        self::tryForKey( $this->skinScripts, $context->getSkin(), 'default' )
                );
                if ( $context->getDebug() ) {
                        $files = array_merge( $files, $this->debugScripts );
                }

                return array_unique( $files );
        }

        /**
         * Get a list of file paths for all styles in this module, in order of proper inclusion.
         *
         * @param ResourceLoaderContext $context
         * @return array List of file paths
         */
        public function getStyleFiles( ResourceLoaderContext $context ) {
                return array_merge_recursive(
                        self::collateFilePathListByOption( $this->styles, 'media', 'all' ),
                        self::collateFilePathListByOption(
                                self::tryForKey( $this->skinStyles, $context->getSkin(), 'default' ),
                                'media',
                                'all'
                        )
                );
        }

        /**
         * Returns all style files used by this module
         * @return array
         */
        public function getAllStyleFiles() {
                $files = array();
                foreach ( (array)$this->styles as $key => $value ) {
                        if ( is_array( $value ) ) {
                                $path = $key;
                        } else {
                                $path = $value;
                        }
                        $files[] = $this->getLocalPath( $path );
                }
                return $files;
        }

        /**
         * Gets the contents of a list of JavaScript files.
         *
         * @param array $scripts List of file paths to scripts to read, remap and concetenate
         * @throws MWException
         * @return string Concatenated and remapped JavaScript data from $scripts
         */
        protected function readScriptFiles( array $scripts ) {
                global $wgResourceLoaderValidateStaticJS;
                if ( empty( $scripts ) ) {
                        return '';
                }
                $js = '';
                foreach ( array_unique( $scripts ) as $fileName ) {
                        $localPath = $this->getLocalPath( $fileName );
                        if ( !file_exists( $localPath ) ) {
                                throw new MWException( __METHOD__ . ": script file not found: \"$localPath\"" );
                        }
                        $contents = file_get_contents( $localPath );
                        if ( $wgResourceLoaderValidateStaticJS ) {
                                // Static files don't really need to be checked as often; unlike
                                // on-wiki module they shouldn't change unexpectedly without
                                // admin interference.
                                $contents = $this->validateScriptFile( $fileName, $contents );
                        }
                        $js .= $contents . "\n";
                }
                return $js;
        }

        /**
         * Gets the contents of a list of CSS files.
         *
         * @param array $styles List of media type/list of file paths pairs, to read, remap and
         * concetenate
         *
         * @param bool $flip
         *
         * @throws MWException
         * @return array List of concatenated and remapped CSS data from $styles,
         *     keyed by media type
         */
        public function readStyleFiles( array $styles, $flip ) {
                if ( empty( $styles ) ) {
                        return array();
                }
                foreach ( $styles as $media => $files ) {
                        $uniqueFiles = array_unique( $files );
                        $styleFiles = array();
                        foreach ( $uniqueFiles as $file ) {
                                $styleFiles[] = $this->readStyleFile( $file, $flip );
                        }
                        $styles[$media] = implode( "\n", $styleFiles );
                }
                return $styles;
        }

        /**
         * Reads a style file.
         *
         * This method can be used as a callback for array_map()
         *
         * @param string $path File path of style file to read
         * @param bool $flip
         *
         * @return string CSS data in script file
         * @throws MWException if the file doesn't exist
         */
        protected function readStyleFile( $path, $flip ) {
                $localPath = $this->getLocalPath( $path );
                if ( !file_exists( $localPath ) ) {
                        $msg = __METHOD__ . ": style file not found: \"$localPath\"";
                        wfDebugLog( 'resourceloader', $msg );
                        throw new MWException( $msg );
                }

                if ( $this->getStyleSheetLang( $path ) === 'less' ) {
                        $style = $this->compileLESSFile( $localPath );
                        $this->hasGeneratedStyles = true;
                } else {
                        $style = file_get_contents( $localPath );
                }

                if ( $flip ) {
                        $style = CSSJanus::transform( $style, true, false );
                }
                $dirname = dirname( $path );
                if ( $dirname == '.' ) {
                        // If $path doesn't have a directory component, don't prepend a dot
                        $dirname = '';
                }
                $dir = $this->getLocalPath( $dirname );
                $remoteDir = $this->getRemotePath( $dirname );
                // Get and register local file references
                $this->localFileRefs = array_merge(
                        $this->localFileRefs,
                        CSSMin::getLocalFileReferences( $style, $dir )
                );
                return CSSMin::remap(
                        $style, $dir, $remoteDir, true
                );
        }

        /**
         * Get whether CSS for this module should be flipped
         * @param ResourceLoaderContext $context
         * @return bool
         */
        public function getFlip( $context ) {
                return $context->getDirection() === 'rtl';
        }

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

        /**
         * Generate a cache key for a LESS file.
         *
         * The cache key varies on the file name and the names and values of global
         * LESS variables.
         *
         * @since 1.22
         * @param string $fileName File name of root LESS file.
         * @return string Cache key
         */
        protected static function getLESSCacheKey( $fileName ) {
                $vars = json_encode( ResourceLoader::getLESSVars() );
                $hash = md5( $fileName . $vars );
                return wfMemcKey( 'resourceloader', 'less', $hash );
        }

        /**
         * Compile a LESS file into CSS.
         *
         * If invalid, returns replacement CSS source consisting of the compilation
         * error message encoded as a comment. To save work, we cache a result object
         * which comprises the compiled CSS and the names & mtimes of the files
         * that were processed. lessphp compares the cached & current mtimes and
         * recompiles as necessary.
         *
         * @since 1.22
         * @throws Exception If Less encounters a parse error
         * @throws MWException If Less compilation returns unexpection result
         * @param string $fileName File path of LESS source
         * @return string CSS source
         */
        protected function compileLESSFile( $fileName ) {
                $key = self::getLESSCacheKey( $fileName );
                $cache = wfGetCache( CACHE_ANYTHING );

                // The input to lessc. Either an associative array representing the
                // cached results of a previous compilation, or the string file name if
                // no cache result exists.
                $source = $cache->get( $key );
                if ( !is_array( $source ) || !isset( $source['root'] ) ) {
                        $source = $fileName;
                }

                $compiler = ResourceLoader::getLessCompiler();
                $result = null;

                $result = $compiler->cachedCompile( $source );

                if ( !is_array( $result ) ) {
                        throw new MWException( 'LESS compiler result has type '
                                . gettype( $result ) . '; array expected.' );
                }

                $this->localFileRefs += array_keys( $result['files'] );
                $cache->set( $key, $result );
                return $result['compiled'];
        }
}