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+<?php
+/**
+ * Fetching and processing of interface messages.
+ *
+ * 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 Niklas Laxström
+ */
+
+/**
+ * The Message class provides methods which fulfil two basic services:
+ *  - fetching interface messages
+ *  - processing messages into a variety of formats
+ *
+ * First implemented with MediaWiki 1.17, the Message class is intended to
+ * replace the old wfMsg* functions that over time grew unusable.
+ * @see https://www.mediawiki.org/wiki/Manual:Messages_API for equivalences
+ * between old and new functions.
+ *
+ * You should use the wfMessage() global function which acts as a wrapper for
+ * the Message class. The wrapper let you pass parameters as arguments.
+ *
+ * The most basic usage cases would be:
+ *
+ * @code
+ *     // Initialize a Message object using the 'some_key' message key
+ *     $message = wfMessage( 'some_key' );
+ *
+ *     // Using two parameters those values are strings 'value1' and 'value2':
+ *     $message = wfMessage( 'some_key',
+ *          'value1', 'value2'
+ *     );
+ * @endcode
+ *
+ * @section message_global_fn Global function wrapper:
+ *
+ * Since wfMessage() returns a Message instance, you can chain its call with
+ * a method. Some of them return a Message instance too so you can chain them.
+ * You will find below several examples of wfMessage() usage.
+ *
+ * Fetching a message text for interface message:
+ *
+ * @code
+ *    $button = Xml::button(
+ *         wfMessage( 'submit' )->text()
+ *    );
+ * @endcode
+ *
+ * A Message instance can be passed parameters after it has been constructed,
+ * use the params() method to do so:
+ *
+ * @code
+ *     wfMessage( 'welcome-to' )
+ *         ->params( $wgSitename )
+ *         ->text();
+ * @endcode
+ *
+ * {{GRAMMAR}} and friends work correctly:
+ *
+ * @code
+ *    wfMessage( 'are-friends',
+ *        $user, $friend
+ *    );
+ *    wfMessage( 'bad-message' )
+ *         ->rawParams( '<script>...</script>' )
+ *         ->escaped();
+ * @endcode
+ *
+ * @section message_language Changing language:
+ *
+ * Messages can be requested in a different language or in whatever current
+ * content language is being used. The methods are:
+ *     - Message->inContentLanguage()
+ *     - Message->inLanguage()
+ *
+ * Sometimes the message text ends up in the database, so content language is
+ * needed:
+ *
+ * @code
+ *    wfMessage( 'file-log',
+ *        $user, $filename
+ *    )->inContentLanguage()->text();
+ * @endcode
+ *
+ * Checking whether a message exists:
+ *
+ * @code
+ *    wfMessage( 'mysterious-message' )->exists()
+ *    // returns a boolean whether the 'mysterious-message' key exist.
+ * @endcode
+ *
+ * If you want to use a different language:
+ *
+ * @code
+ *    $userLanguage = $user->getOption( 'language' );
+ *    wfMessage( 'email-header' )
+ *         ->inLanguage( $userLanguage )
+ *         ->plain();
+ * @endcode
+ *
+ * @note You can parse the text only in the content or interface languages
+ *
+ * @section message_compare_old Comparison with old wfMsg* functions:
+ *
+ * Use full parsing:
+ *
+ * @code
+ *     // old style:
+ *     wfMsgExt( 'key', [ 'parseinline' ], 'apple' );
+ *     // new style:
+ *     wfMessage( 'key', 'apple' )->parse();
+ * @endcode
+ *
+ * Parseinline is used because it is more useful when pre-building HTML.
+ * In normal use it is better to use OutputPage::(add|wrap)WikiMsg.
+ *
+ * Places where HTML cannot be used. {{-transformation is done.
+ * @code
+ *     // old style:
+ *     wfMsgExt( 'key', [ 'parsemag' ], 'apple', 'pear' );
+ *     // new style:
+ *     wfMessage( 'key', 'apple', 'pear' )->text();
+ * @endcode
+ *
+ * Shortcut for escaping the message too, similar to wfMsgHTML(), but
+ * parameters are not replaced after escaping by default.
+ * @code
+ *     $escaped = wfMessage( 'key' )
+ *          ->rawParams( 'apple' )
+ *          ->escaped();
+ * @endcode
+ *
+ * @section message_appendix Appendix:
+ *
+ * @todo
+ * - test, can we have tests?
+ * - this documentation needs to be extended
+ *
+ * @see https://www.mediawiki.org/wiki/WfMessage()
+ * @see https://www.mediawiki.org/wiki/New_messages_API
+ * @see https://www.mediawiki.org/wiki/Localisation
+ *
+ * @since 1.17
+ */
+class Message implements MessageSpecifier, Serializable {
+	/** Use message text as-is */
+	const FORMAT_PLAIN = 'plain';
+	/** Use normal wikitext -> HTML parsing (the result will be wrapped in a block-level HTML tag) */
+	const FORMAT_BLOCK_PARSE = 'block-parse';
+	/** Use normal wikitext -> HTML parsing but strip the block-level wrapper */
+	const FORMAT_PARSE = 'parse';
+	/** Transform {{..}} constructs but don't transform to HTML */
+	const FORMAT_TEXT = 'text';
+	/** Transform {{..}} constructs, HTML-escape the result */
+	const FORMAT_ESCAPED = 'escaped';
+
+	/**
+	 * Mapping from Message::listParam() types to Language methods.
+	 * @var array
+	 */
+	protected static $listTypeMap = [
+		'comma' => 'commaList',
+		'semicolon' => 'semicolonList',
+		'pipe' => 'pipeList',
+		'text' => 'listToText',
+	];
+
+	/**
+	 * In which language to get this message. True, which is the default,
+	 * means the current user language, false content language.
+	 *
+	 * @var bool
+	 */
+	protected $interface = true;
+
+	/**
+	 * In which language to get this message. Overrides the $interface setting.
+	 *
+	 * @var Language|bool Explicit language object, or false for user language
+	 */
+	protected $language = false;
+
+	/**
+	 * @var string The message key. If $keysToTry has more than one element,
+	 * this may change to one of the keys to try when fetching the message text.
+	 */
+	protected $key;
+
+	/**
+	 * @var string[] List of keys to try when fetching the message.
+	 */
+	protected $keysToTry;
+
+	/**
+	 * @var array List of parameters which will be substituted into the message.
+	 */
+	protected $parameters = [];
+
+	/**
+	 * @var string
+	 * @deprecated
+	 */
+	protected $format = 'parse';
+
+	/**
+	 * @var bool Whether database can be used.
+	 */
+	protected $useDatabase = true;
+
+	/**
+	 * @var Title Title object to use as context.
+	 */
+	protected $title = null;
+
+	/**
+	 * @var Content Content object representing the message.
+	 */
+	protected $content = null;
+
+	/**
+	 * @var string
+	 */
+	protected $message;
+
+	/**
+	 * @since 1.17
+	 * @param string|string[]|MessageSpecifier $key Message key, or array of
+	 * message keys to try and use the first non-empty message for, or a
+	 * MessageSpecifier to copy from.
+	 * @param array $params Message parameters.
+	 * @param Language $language [optional] Language to use (defaults to current user language).
+	 * @throws InvalidArgumentException
+	 */
+	public function __construct( $key, $params = [], Language $language = null ) {
+		if ( $key instanceof MessageSpecifier ) {
+			if ( $params ) {
+				throw new InvalidArgumentException(
+					'$params must be empty if $key is a MessageSpecifier'
+				);
+			}
+			$params = $key->getParams();
+			$key = $key->getKey();
+		}
+
+		if ( !is_string( $key ) && !is_array( $key ) ) {
+			throw new InvalidArgumentException( '$key must be a string or an array' );
+		}
+
+		$this->keysToTry = (array)$key;
+
+		if ( empty( $this->keysToTry ) ) {
+			throw new InvalidArgumentException( '$key must not be an empty list' );
+		}
+
+		$this->key = reset( $this->keysToTry );
+
+		$this->parameters = array_values( $params );
+		// User language is only resolved in getLanguage(). This helps preserve the
+		// semantic intent of "user language" across serialize() and unserialize().
+		$this->language = $language ?: false;
+	}
+
+	/**
+	 * @see Serializable::serialize()
+	 * @since 1.26
+	 * @return string
+	 */
+	public function serialize() {
+		return serialize( [
+			'interface' => $this->interface,
+			'language' => $this->language ? $this->language->getCode() : false,
+			'key' => $this->key,
+			'keysToTry' => $this->keysToTry,
+			'parameters' => $this->parameters,
+			'format' => $this->format,
+			'useDatabase' => $this->useDatabase,
+			'title' => $this->title,
+		] );
+	}
+
+	/**
+	 * @see Serializable::unserialize()
+	 * @since 1.26
+	 * @param string $serialized
+	 */
+	public function unserialize( $serialized ) {
+		$data = unserialize( $serialized );
+		$this->interface = $data['interface'];
+		$this->key = $data['key'];
+		$this->keysToTry = $data['keysToTry'];
+		$this->parameters = $data['parameters'];
+		$this->format = $data['format'];
+		$this->useDatabase = $data['useDatabase'];
+		$this->language = $data['language'] ? Language::factory( $data['language'] ) : false;
+		$this->title = $data['title'];
+	}
+
+	/**
+	 * @since 1.24
+	 *
+	 * @return bool True if this is a multi-key message, that is, if the key provided to the
+	 * constructor was a fallback list of keys to try.
+	 */
+	public function isMultiKey() {
+		return count( $this->keysToTry ) > 1;
+	}
+
+	/**
+	 * @since 1.24
+	 *
+	 * @return string[] The list of keys to try when fetching the message text,
+	 * in order of preference.
+	 */
+	public function getKeysToTry() {
+		return $this->keysToTry;
+	}
+
+	/**
+	 * Returns the message key.
+	 *
+	 * If a list of multiple possible keys was supplied to the constructor, this method may
+	 * return any of these keys. After the message has been fetched, this method will return
+	 * the key that was actually used to fetch the message.
+	 *
+	 * @since 1.21
+	 *
+	 * @return string
+	 */
+	public function getKey() {
+		return $this->key;
+	}
+
+	/**
+	 * Returns the message parameters.
+	 *
+	 * @since 1.21
+	 *
+	 * @return array
+	 */
+	public function getParams() {
+		return $this->parameters;
+	}
+
+	/**
+	 * Returns the message format.
+	 *
+	 * @since 1.21
+	 *
+	 * @return string
+	 * @deprecated since 1.29 formatting is not stateful
+	 */
+	public function getFormat() {
+		wfDeprecated( __METHOD__, '1.29' );
+		return $this->format;
+	}
+
+	/**
+	 * Returns the Language of the Message.
+	 *
+	 * @since 1.23
+	 *
+	 * @return Language
+	 */
+	public function getLanguage() {
+		// Defaults to false which means current user language
+		return $this->language ?: RequestContext::getMain()->getLanguage();
+	}
+
+	/**
+	 * Factory function that is just wrapper for the real constructor. It is
+	 * intended to be used instead of the real constructor, because it allows
+	 * chaining method calls, while new objects don't.
+	 *
+	 * @since 1.17
+	 *
+	 * @param string|string[]|MessageSpecifier $key
+	 * @param mixed $param,... Parameters as strings.
+	 *
+	 * @return Message
+	 */
+	public static function newFromKey( $key /*...*/ ) {
+		$params = func_get_args();
+		array_shift( $params );
+		return new self( $key, $params );
+	}
+
+	/**
+	 * Transform a MessageSpecifier or a primitive value used interchangeably with
+	 * specifiers (a message key string, or a key + params array) into a proper Message.
+	 *
+	 * Also accepts a MessageSpecifier inside an array: that's not considered a valid format
+	 * but is an easy error to make due to how StatusValue stores messages internally.
+	 * Further array elements are ignored in that case.
+	 *
+	 * @param string|array|MessageSpecifier $value
+	 * @return Message
+	 * @throws InvalidArgumentException
+	 * @since 1.27
+	 */
+	public static function newFromSpecifier( $value ) {
+		$params = [];
+		if ( is_array( $value ) ) {
+			$params = $value;
+			$value = array_shift( $params );
+		}
+
+		if ( $value instanceof Message ) { // Message, RawMessage, ApiMessage, etc
+			$message = clone $value;
+		} elseif ( $value instanceof MessageSpecifier ) {
+			$message = new Message( $value );
+		} elseif ( is_string( $value ) ) {
+			$message = new Message( $value, $params );
+		} else {
+			throw new InvalidArgumentException( __METHOD__ . ': invalid argument type '
+				. gettype( $value ) );
+		}
+
+		return $message;
+	}
+
+	/**
+	 * Factory function accepting multiple message keys and returning a message instance
+	 * for the first message which is non-empty. If all messages are empty then an
+	 * instance of the first message key is returned.
+	 *
+	 * @since 1.18
+	 *
+	 * @param string|string[] $keys,... Message keys, or first argument as an array of all the
+	 * message keys.
+	 *
+	 * @return Message
+	 */
+	public static function newFallbackSequence( /*...*/ ) {
+		$keys = func_get_args();
+		if ( func_num_args() == 1 ) {
+			if ( is_array( $keys[0] ) ) {
+				// Allow an array to be passed as the first argument instead
+				$keys = array_values( $keys[0] );
+			} else {
+				// Optimize a single string to not need special fallback handling
+				$keys = $keys[0];
+			}
+		}
+		return new self( $keys );
+	}
+
+	/**
+	 * Get a title object for a mediawiki message, where it can be found in the mediawiki namespace.
+	 * The title will be for the current language, if the message key is in
+	 * $wgForceUIMsgAsContentMsg it will be append with the language code (except content
+	 * language), because Message::inContentLanguage will also return in user language.
+	 *
+	 * @see $wgForceUIMsgAsContentMsg
+	 * @return Title
+	 * @since 1.26
+	 */
+	public function getTitle() {
+		global $wgContLang, $wgForceUIMsgAsContentMsg;
+
+		$title = $this->key;
+		if (
+			!$this->language->equals( $wgContLang )
+			&& in_array( $this->key, (array)$wgForceUIMsgAsContentMsg )
+		) {
+			$code = $this->language->getCode();
+			$title .= '/' . $code;
+		}
+
+		return Title::makeTitle( NS_MEDIAWIKI, $wgContLang->ucfirst( strtr( $title, ' ', '_' ) ) );
+	}
+
+	/**
+	 * Adds parameters to the parameter list of this message.
+	 *
+	 * @since 1.17
+	 *
+	 * @param mixed $args,... Parameters as strings or arrays from
+	 *  Message::numParam() and the like, or a single array of parameters.
+	 *
+	 * @return Message $this
+	 */
+	public function params( /*...*/ ) {
+		$args = func_get_args();
+
+		// If $args has only one entry and it's an array, then it's either a
+		// non-varargs call or it happens to be a call with just a single
+		// "special" parameter. Since the "special" parameters don't have any
+		// numeric keys, we'll test that to differentiate the cases.
+		if ( count( $args ) === 1 && isset( $args[0] ) && is_array( $args[0] ) ) {
+			if ( $args[0] === [] ) {
+				$args = [];
+			} else {
+				foreach ( $args[0] as $key => $value ) {
+					if ( is_int( $key ) ) {
+						$args = $args[0];
+						break;
+					}
+				}
+			}
+		}
+
+		$this->parameters = array_merge( $this->parameters, array_values( $args ) );
+		return $this;
+	}
+
+	/**
+	 * Add parameters that are substituted after parsing or escaping.
+	 * In other words the parsing process cannot access the contents
+	 * of this type of parameter, and you need to make sure it is
+	 * sanitized beforehand.  The parser will see "$n", instead.
+	 *
+	 * @since 1.17
+	 *
+	 * @param mixed $params,... Raw parameters as strings, or a single argument that is
+	 * an array of raw parameters.
+	 *
+	 * @return Message $this
+	 */
+	public function rawParams( /*...*/ ) {
+		$params = func_get_args();
+		if ( isset( $params[0] ) && is_array( $params[0] ) ) {
+			$params = $params[0];
+		}
+		foreach ( $params as $param ) {
+			$this->parameters[] = self::rawParam( $param );
+		}
+		return $this;
+	}
+
+	/**
+	 * Add parameters that are numeric and will be passed through
+	 * Language::formatNum before substitution
+	 *
+	 * @since 1.18
+	 *
+	 * @param mixed $param,... Numeric parameters, or a single argument that is
+	 * an array of numeric parameters.
+	 *
+	 * @return Message $this
+	 */
+	public function numParams( /*...*/ ) {
+		$params = func_get_args();
+		if ( isset( $params[0] ) && is_array( $params[0] ) ) {
+			$params = $params[0];
+		}
+		foreach ( $params as $param ) {
+			$this->parameters[] = self::numParam( $param );
+		}
+		return $this;
+	}
+
+	/**
+	 * Add parameters that are durations of time and will be passed through
+	 * Language::formatDuration before substitution
+	 *
+	 * @since 1.22
+	 *
+	 * @param int|int[] $param,... Duration parameters, or a single argument that is
+	 * an array of duration parameters.
+	 *
+	 * @return Message $this
+	 */
+	public function durationParams( /*...*/ ) {
+		$params = func_get_args();
+		if ( isset( $params[0] ) && is_array( $params[0] ) ) {
+			$params = $params[0];
+		}
+		foreach ( $params as $param ) {
+			$this->parameters[] = self::durationParam( $param );
+		}
+		return $this;
+	}
+
+	/**
+	 * Add parameters that are expiration times and will be passed through
+	 * Language::formatExpiry before substitution
+	 *
+	 * @since 1.22
+	 *
+	 * @param string|string[] $param,... Expiry parameters, or a single argument that is
+	 * an array of expiry parameters.
+	 *
+	 * @return Message $this
+	 */
+	public function expiryParams( /*...*/ ) {
+		$params = func_get_args();
+		if ( isset( $params[0] ) && is_array( $params[0] ) ) {
+			$params = $params[0];
+		}
+		foreach ( $params as $param ) {
+			$this->parameters[] = self::expiryParam( $param );
+		}
+		return $this;
+	}
+
+	/**
+	 * Add parameters that are time periods and will be passed through
+	 * Language::formatTimePeriod before substitution
+	 *
+	 * @since 1.22
+	 *
+	 * @param int|int[] $param,... Time period parameters, or a single argument that is
+	 * an array of time period parameters.
+	 *
+	 * @return Message $this
+	 */
+	public function timeperiodParams( /*...*/ ) {
+		$params = func_get_args();
+		if ( isset( $params[0] ) && is_array( $params[0] ) ) {
+			$params = $params[0];
+		}
+		foreach ( $params as $param ) {
+			$this->parameters[] = self::timeperiodParam( $param );
+		}
+		return $this;
+	}
+
+	/**
+	 * Add parameters that are file sizes and will be passed through
+	 * Language::formatSize before substitution
+	 *
+	 * @since 1.22
+	 *
+	 * @param int|int[] $param,... Size parameters, or a single argument that is
+	 * an array of size parameters.
+	 *
+	 * @return Message $this
+	 */
+	public function sizeParams( /*...*/ ) {
+		$params = func_get_args();
+		if ( isset( $params[0] ) && is_array( $params[0] ) ) {
+			$params = $params[0];
+		}
+		foreach ( $params as $param ) {
+			$this->parameters[] = self::sizeParam( $param );
+		}
+		return $this;
+	}
+
+	/**
+	 * Add parameters that are bitrates and will be passed through
+	 * Language::formatBitrate before substitution
+	 *
+	 * @since 1.22
+	 *
+	 * @param int|int[] $param,... Bit rate parameters, or a single argument that is
+	 * an array of bit rate parameters.
+	 *
+	 * @return Message $this
+	 */
+	public function bitrateParams( /*...*/ ) {
+		$params = func_get_args();
+		if ( isset( $params[0] ) && is_array( $params[0] ) ) {
+			$params = $params[0];
+		}
+		foreach ( $params as $param ) {
+			$this->parameters[] = self::bitrateParam( $param );
+		}
+		return $this;
+	}
+
+	/**
+	 * Add parameters that are plaintext and will be passed through without
+	 * the content being evaluated.  Plaintext parameters are not valid as
+	 * arguments to parser functions. This differs from self::rawParams in
+	 * that the Message class handles escaping to match the output format.
+	 *
+	 * @since 1.25
+	 *
+	 * @param string|string[] $param,... plaintext parameters, or a single argument that is
+	 * an array of plaintext parameters.
+	 *
+	 * @return Message $this
+	 */
+	public function plaintextParams( /*...*/ ) {
+		$params = func_get_args();
+		if ( isset( $params[0] ) && is_array( $params[0] ) ) {
+			$params = $params[0];
+		}
+		foreach ( $params as $param ) {
+			$this->parameters[] = self::plaintextParam( $param );
+		}
+		return $this;
+	}
+
+	/**
+	 * Set the language and the title from a context object
+	 *
+	 * @since 1.19
+	 *
+	 * @param IContextSource $context
+	 *
+	 * @return Message $this
+	 */
+	public function setContext( IContextSource $context ) {
+		$this->inLanguage( $context->getLanguage() );
+		$this->title( $context->getTitle() );
+		$this->interface = true;
+
+		return $this;
+	}
+
+	/**
+	 * Request the message in any language that is supported.
+	 *
+	 * As a side effect interface message status is unconditionally
+	 * turned off.
+	 *
+	 * @since 1.17
+	 * @param Language|string $lang Language code or Language object.
+	 * @return Message $this
+	 * @throws MWException
+	 */
+	public function inLanguage( $lang ) {
+		if ( $lang instanceof Language ) {
+			$this->language = $lang;
+		} elseif ( is_string( $lang ) ) {
+			if ( !$this->language instanceof Language || $this->language->getCode() != $lang ) {
+				$this->language = Language::factory( $lang );
+			}
+		} elseif ( $lang instanceof StubUserLang ) {
+			$this->language = false;
+		} else {
+			$type = gettype( $lang );
+			throw new MWException( __METHOD__ . " must be "
+				. "passed a String or Language object; $type given"
+			);
+		}
+		$this->message = null;
+		$this->interface = false;
+		return $this;
+	}
+
+	/**
+	 * Request the message in the wiki's content language,
+	 * unless it is disabled for this message.
+	 *
+	 * @since 1.17
+	 * @see $wgForceUIMsgAsContentMsg
+	 *
+	 * @return Message $this
+	 */
+	public function inContentLanguage() {
+		global $wgForceUIMsgAsContentMsg;
+		if ( in_array( $this->key, (array)$wgForceUIMsgAsContentMsg ) ) {
+			return $this;
+		}
+
+		global $wgContLang;
+		$this->inLanguage( $wgContLang );
+		return $this;
+	}
+
+	/**
+	 * Allows manipulating the interface message flag directly.
+	 * Can be used to restore the flag after setting a language.
+	 *
+	 * @since 1.20
+	 *
+	 * @param bool $interface
+	 *
+	 * @return Message $this
+	 */
+	public function setInterfaceMessageFlag( $interface ) {
+		$this->interface = (bool)$interface;
+		return $this;
+	}
+
+	/**
+	 * Enable or disable database use.
+	 *
+	 * @since 1.17
+	 *
+	 * @param bool $useDatabase
+	 *
+	 * @return Message $this
+	 */
+	public function useDatabase( $useDatabase ) {
+		$this->useDatabase = (bool)$useDatabase;
+		$this->message = null;
+		return $this;
+	}
+
+	/**
+	 * Set the Title object to use as context when transforming the message
+	 *
+	 * @since 1.18
+	 *
+	 * @param Title $title
+	 *
+	 * @return Message $this
+	 */
+	public function title( $title ) {
+		$this->title = $title;
+		return $this;
+	}
+
+	/**
+	 * Returns the message as a Content object.
+	 *
+	 * @return Content
+	 */
+	public function content() {
+		if ( !$this->content ) {
+			$this->content = new MessageContent( $this );
+		}
+
+		return $this->content;
+	}
+
+	/**
+	 * Returns the message parsed from wikitext to HTML.
+	 *
+	 * @since 1.17
+	 *
+	 * @param string|null $format One of the FORMAT_* constants. Null means use whatever was used
+	 *   the last time (this is for B/C and should be avoided).
+	 *
+	 * @return string HTML
+	 */
+	public function toString( $format = null ) {
+		if ( $format === null ) {
+			$ex = new LogicException( __METHOD__ . ' using implicit format: ' . $this->format );
+			\MediaWiki\Logger\LoggerFactory::getInstance( 'message-format' )->warning(
+				$ex->getMessage(), [ 'exception' => $ex, 'format' => $this->format, 'key' => $this->key ] );
+			$format = $this->format;
+		}
+		$string = $this->fetchMessage();
+
+		if ( $string === false ) {
+			// Err on the side of safety, ensure that the output
+			// is always html safe in the event the message key is
+			// missing, since in that case its highly likely the
+			// message key is user-controlled.
+			// '⧼' is used instead of '<' to side-step any
+			// double-escaping issues.
+			// (Keep synchronised with mw.Message#toString in JS.)
+			return '⧼' . htmlspecialchars( $this->key ) . '⧽';
+		}
+
+		# Replace $* with a list of parameters for &uselang=qqx.
+		if ( strpos( $string, '$*' ) !== false ) {
+			$paramlist = '';
+			if ( $this->parameters !== [] ) {
+				$paramlist = ': $' . implode( ', $', range( 1, count( $this->parameters ) ) );
+			}
+			$string = str_replace( '$*', $paramlist, $string );
+		}
+
+		# Replace parameters before text parsing
+		$string = $this->replaceParameters( $string, 'before', $format );
+
+		# Maybe transform using the full parser
+		if ( $format === self::FORMAT_PARSE ) {
+			$string = $this->parseText( $string );
+			$string = Parser::stripOuterParagraph( $string );
+		} elseif ( $format === self::FORMAT_BLOCK_PARSE ) {
+			$string = $this->parseText( $string );
+		} elseif ( $format === self::FORMAT_TEXT ) {
+			$string = $this->transformText( $string );
+		} elseif ( $format === self::FORMAT_ESCAPED ) {
+			$string = $this->transformText( $string );
+			$string = htmlspecialchars( $string, ENT_QUOTES, 'UTF-8', false );
+		}
+
+		# Raw parameter replacement
+		$string = $this->replaceParameters( $string, 'after', $format );
+
+		return $string;
+	}
+
+	/**
+	 * Magic method implementation of the above (for PHP >= 5.2.0), so we can do, eg:
+	 *     $foo = new Message( $key );
+	 *     $string = "<abbr>$foo</abbr>";
+	 *
+	 * @since 1.18
+	 *
+	 * @return string
+	 */
+	public function __toString() {
+		// PHP doesn't allow __toString to throw exceptions and will
+		// trigger a fatal error if it does. So, catch any exceptions.
+
+		try {
+			return $this->toString( self::FORMAT_PARSE );
+		} catch ( Exception $ex ) {
+			try {
+				trigger_error( "Exception caught in " . __METHOD__ . " (message " . $this->key . "): "
+					. $ex, E_USER_WARNING );
+			} catch ( Exception $ex ) {
+				// Doh! Cause a fatal error after all?
+			}
+
+			return '⧼' . htmlspecialchars( $this->key ) . '⧽';
+		}
+	}
+
+	/**
+	 * Fully parse the text from wikitext to HTML.
+	 *
+	 * @since 1.17
+	 *
+	 * @return string Parsed HTML.
+	 */
+	public function parse() {
+		$this->format = self::FORMAT_PARSE;
+		return $this->toString( self::FORMAT_PARSE );
+	}
+
+	/**
+	 * Returns the message text. {{-transformation is done.
+	 *
+	 * @since 1.17
+	 *
+	 * @return string Unescaped message text.
+	 */
+	public function text() {
+		$this->format = self::FORMAT_TEXT;
+		return $this->toString( self::FORMAT_TEXT );
+	}
+
+	/**
+	 * Returns the message text as-is, only parameters are substituted.
+	 *
+	 * @since 1.17
+	 *
+	 * @return string Unescaped untransformed message text.
+	 */
+	public function plain() {
+		$this->format = self::FORMAT_PLAIN;
+		return $this->toString( self::FORMAT_PLAIN );
+	}
+
+	/**
+	 * Returns the parsed message text which is always surrounded by a block element.
+	 *
+	 * @since 1.17
+	 *
+	 * @return string HTML
+	 */
+	public function parseAsBlock() {
+		$this->format = self::FORMAT_BLOCK_PARSE;
+		return $this->toString( self::FORMAT_BLOCK_PARSE );
+	}
+
+	/**
+	 * Returns the message text. {{-transformation is done and the result
+	 * is escaped excluding any raw parameters.
+	 *
+	 * @since 1.17
+	 *
+	 * @return string Escaped message text.
+	 */
+	public function escaped() {
+		$this->format = self::FORMAT_ESCAPED;
+		return $this->toString( self::FORMAT_ESCAPED );
+	}
+
+	/**
+	 * Check whether a message key has been defined currently.
+	 *
+	 * @since 1.17
+	 *
+	 * @return bool
+	 */
+	public function exists() {
+		return $this->fetchMessage() !== false;
+	}
+
+	/**
+	 * Check whether a message does not exist, or is an empty string
+	 *
+	 * @since 1.18
+	 * @todo FIXME: Merge with isDisabled()?
+	 *
+	 * @return bool
+	 */
+	public function isBlank() {
+		$message = $this->fetchMessage();
+		return $message === false || $message === '';
+	}
+
+	/**
+	 * Check whether a message does not exist, is an empty string, or is "-".
+	 *
+	 * @since 1.18
+	 *
+	 * @return bool
+	 */
+	public function isDisabled() {
+		$message = $this->fetchMessage();
+		return $message === false || $message === '' || $message === '-';
+	}
+
+	/**
+	 * @since 1.17
+	 *
+	 * @param mixed $raw
+	 *
+	 * @return array Array with a single "raw" key.
+	 */
+	public static function rawParam( $raw ) {
+		return [ 'raw' => $raw ];
+	}
+
+	/**
+	 * @since 1.18
+	 *
+	 * @param mixed $num
+	 *
+	 * @return array Array with a single "num" key.
+	 */
+	public static function numParam( $num ) {
+		return [ 'num' => $num ];
+	}
+
+	/**
+	 * @since 1.22
+	 *
+	 * @param int $duration
+	 *
+	 * @return int[] Array with a single "duration" key.
+	 */
+	public static function durationParam( $duration ) {
+		return [ 'duration' => $duration ];
+	}
+
+	/**
+	 * @since 1.22
+	 *
+	 * @param string $expiry
+	 *
+	 * @return string[] Array with a single "expiry" key.
+	 */
+	public static function expiryParam( $expiry ) {
+		return [ 'expiry' => $expiry ];
+	}
+
+	/**
+	 * @since 1.22
+	 *
+	 * @param int $period
+	 *
+	 * @return int[] Array with a single "period" key.
+	 */
+	public static function timeperiodParam( $period ) {
+		return [ 'period' => $period ];
+	}
+
+	/**
+	 * @since 1.22
+	 *
+	 * @param int $size
+	 *
+	 * @return int[] Array with a single "size" key.
+	 */
+	public static function sizeParam( $size ) {
+		return [ 'size' => $size ];
+	}
+
+	/**
+	 * @since 1.22
+	 *
+	 * @param int $bitrate
+	 *
+	 * @return int[] Array with a single "bitrate" key.
+	 */
+	public static function bitrateParam( $bitrate ) {
+		return [ 'bitrate' => $bitrate ];
+	}
+
+	/**
+	 * @since 1.25
+	 *
+	 * @param string $plaintext
+	 *
+	 * @return string[] Array with a single "plaintext" key.
+	 */
+	public static function plaintextParam( $plaintext ) {
+		return [ 'plaintext' => $plaintext ];
+	}
+
+	/**
+	 * @since 1.29
+	 *
+	 * @param array $list
+	 * @param string $type 'comma', 'semicolon', 'pipe', 'text'
+	 * @return array Array with "list" and "type" keys.
+	 */
+	public static function listParam( array $list, $type = 'text' ) {
+		if ( !isset( self::$listTypeMap[$type] ) ) {
+			throw new InvalidArgumentException(
+				"Invalid type '$type'. Known types are: " . implode( ', ', array_keys( self::$listTypeMap ) )
+			);
+		}
+		return [ 'list' => $list, 'type' => $type ];
+	}
+
+	/**
+	 * Substitutes any parameters into the message text.
+	 *
+	 * @since 1.17
+	 *
+	 * @param string $message The message text.
+	 * @param string $type Either "before" or "after".
+	 * @param string $format One of the FORMAT_* constants.
+	 *
+	 * @return string
+	 */
+	protected function replaceParameters( $message, $type = 'before', $format ) {
+		// A temporary marker for $1 parameters that is only valid
+		// in non-attribute contexts. However if the entire message is escaped
+		// then we don't want to use it because it will be mangled in all contexts
+		// and its unnessary as ->escaped() messages aren't html.
+		$marker = $format === self::FORMAT_ESCAPED ? '$' : '$\'"';
+		$replacementKeys = [];
+		foreach ( $this->parameters as $n => $param ) {
+			list( $paramType, $value ) = $this->extractParam( $param, $format );
+			if ( $type === 'before' ) {
+				if ( $paramType === 'before' ) {
+					$replacementKeys['$' . ( $n + 1 )] = $value;
+				} else /* $paramType === 'after' */ {
+					// To protect against XSS from replacing parameters
+					// inside html attributes, we convert $1 to $'"1.
+					// In the event that one of the parameters ends up
+					// in an attribute, either the ' or the " will be
+					// escaped, breaking the replacement and avoiding XSS.
+					$replacementKeys['$' . ( $n + 1 )] = $marker . ( $n + 1 );
+				}
+			} else {
+				if ( $paramType === 'after' ) {
+					$replacementKeys[$marker . ( $n + 1 )] = $value;
+				}
+			}
+		}
+		$message = strtr( $message, $replacementKeys );
+		return $message;
+	}
+
+	/**
+	 * Extracts the parameter type and preprocessed the value if needed.
+	 *
+	 * @since 1.18
+	 *
+	 * @param mixed $param Parameter as defined in this class.
+	 * @param string $format One of the FORMAT_* constants.
+	 *
+	 * @return array Array with the parameter type (either "before" or "after") and the value.
+	 */
+	protected function extractParam( $param, $format ) {
+		if ( is_array( $param ) ) {
+			if ( isset( $param['raw'] ) ) {
+				return [ 'after', $param['raw'] ];
+			} elseif ( isset( $param['num'] ) ) {
+				// Replace number params always in before step for now.
+				// No support for combined raw and num params
+				return [ 'before', $this->getLanguage()->formatNum( $param['num'] ) ];
+			} elseif ( isset( $param['duration'] ) ) {
+				return [ 'before', $this->getLanguage()->formatDuration( $param['duration'] ) ];
+			} elseif ( isset( $param['expiry'] ) ) {
+				return [ 'before', $this->getLanguage()->formatExpiry( $param['expiry'] ) ];
+			} elseif ( isset( $param['period'] ) ) {
+				return [ 'before', $this->getLanguage()->formatTimePeriod( $param['period'] ) ];
+			} elseif ( isset( $param['size'] ) ) {
+				return [ 'before', $this->getLanguage()->formatSize( $param['size'] ) ];
+			} elseif ( isset( $param['bitrate'] ) ) {
+				return [ 'before', $this->getLanguage()->formatBitrate( $param['bitrate'] ) ];
+			} elseif ( isset( $param['plaintext'] ) ) {
+				return [ 'after', $this->formatPlaintext( $param['plaintext'], $format ) ];
+			} elseif ( isset( $param['list'] ) ) {
+				return $this->formatListParam( $param['list'], $param['type'], $format );
+			} else {
+				if ( !is_scalar( $param ) ) {
+					$param = serialize( $param );
+				}
+				\MediaWiki\Logger\LoggerFactory::getInstance( 'Bug58676' )->warning(
+					'Invalid parameter for message "{msgkey}": {param}',
+					[
+						'exception' => new Exception,
+						'msgkey' => $this->getKey(),
+						'param' => htmlspecialchars( $param ),
+					]
+				);
+
+				return [ 'before', '[INVALID]' ];
+			}
+		} elseif ( $param instanceof Message ) {
+			// Match language, flags, etc. to the current message.
+			$msg = clone $param;
+			if ( $msg->language !== $this->language || $msg->useDatabase !== $this->useDatabase ) {
+				// Cache depends on these parameters
+				$msg->message = null;
+			}
+			$msg->interface = $this->interface;
+			$msg->language = $this->language;
+			$msg->useDatabase = $this->useDatabase;
+			$msg->title = $this->title;
+
+			// DWIM
+			if ( $format === 'block-parse' ) {
+				$format = 'parse';
+			}
+			$msg->format = $format;
+
+			// Message objects should not be before parameters because
+			// then they'll get double escaped. If the message needs to be
+			// escaped, it'll happen right here when we call toString().
+			return [ 'after', $msg->toString( $format ) ];
+		} else {
+			return [ 'before', $param ];
+		}
+	}
+
+	/**
+	 * Wrapper for what ever method we use to parse wikitext.
+	 *
+	 * @since 1.17
+	 *
+	 * @param string $string Wikitext message contents.
+	 *
+	 * @return string Wikitext parsed into HTML.
+	 */
+	protected function parseText( $string ) {
+		$out = MessageCache::singleton()->parse(
+			$string,
+			$this->title,
+			/*linestart*/true,
+			$this->interface,
+			$this->getLanguage()
+		);
+
+		return $out instanceof ParserOutput
+			? $out->getText( [
+				'enableSectionEditLinks' => false,
+				// Wrapping messages in an extra <div> is probably not expected. If
+				// they're outside the content area they probably shouldn't be
+				// targeted by CSS that's targeting the parser output, and if
+				// they're inside they already are from the outer div.
+				'unwrap' => true,
+			] )
+			: $out;
+	}
+
+	/**
+	 * Wrapper for what ever method we use to {{-transform wikitext.
+	 *
+	 * @since 1.17
+	 *
+	 * @param string $string Wikitext message contents.
+	 *
+	 * @return string Wikitext with {{-constructs replaced with their values.
+	 */
+	protected function transformText( $string ) {
+		return MessageCache::singleton()->transform(
+			$string,
+			$this->interface,
+			$this->getLanguage(),
+			$this->title
+		);
+	}
+
+	/**
+	 * Wrapper for what ever method we use to get message contents.
+	 *
+	 * @since 1.17
+	 *
+	 * @return string
+	 * @throws MWException If message key array is empty.
+	 */
+	protected function fetchMessage() {
+		if ( $this->message === null ) {
+			$cache = MessageCache::singleton();
+
+			foreach ( $this->keysToTry as $key ) {
+				$message = $cache->get( $key, $this->useDatabase, $this->getLanguage() );
+				if ( $message !== false && $message !== '' ) {
+					break;
+				}
+			}
+
+			// NOTE: The constructor makes sure keysToTry isn't empty,
+			//       so we know that $key and $message are initialized.
+			$this->key = $key;
+			$this->message = $message;
+		}
+		return $this->message;
+	}
+
+	/**
+	 * Formats a message parameter wrapped with 'plaintext'. Ensures that
+	 * the entire string is displayed unchanged when displayed in the output
+	 * format.
+	 *
+	 * @since 1.25
+	 *
+	 * @param string $plaintext String to ensure plaintext output of
+	 * @param string $format One of the FORMAT_* constants.
+	 *
+	 * @return string Input plaintext encoded for output to $format
+	 */
+	protected function formatPlaintext( $plaintext, $format ) {
+		switch ( $format ) {
+			case self::FORMAT_TEXT:
+			case self::FORMAT_PLAIN:
+				return $plaintext;
+
+			case self::FORMAT_PARSE:
+			case self::FORMAT_BLOCK_PARSE:
+			case self::FORMAT_ESCAPED:
+			default:
+				return htmlspecialchars( $plaintext, ENT_QUOTES );
+		}
+	}
+
+	/**
+	 * Formats a list of parameters as a concatenated string.
+	 * @since 1.29
+	 * @param array $params
+	 * @param string $listType
+	 * @param string $format One of the FORMAT_* constants.
+	 * @return array Array with the parameter type (either "before" or "after") and the value.
+	 */
+	protected function formatListParam( array $params, $listType, $format ) {
+		if ( !isset( self::$listTypeMap[$listType] ) ) {
+			$warning = 'Invalid list type for message "' . $this->getKey() . '": '
+				. htmlspecialchars( $listType )
+				. ' (params are ' . htmlspecialchars( serialize( $params ) ) . ')';
+			trigger_error( $warning, E_USER_WARNING );
+			$e = new Exception;
+			wfDebugLog( 'Bug58676', $warning . "\n" . $e->getTraceAsString() );
+			return [ 'before', '[INVALID]' ];
+		}
+		$func = self::$listTypeMap[$listType];
+
+		// Handle an empty list sensibly
+		if ( !$params ) {
+			return [ 'before', $this->getLanguage()->$func( [] ) ];
+		}
+
+		// First, determine what kinds of list items we have
+		$types = [];
+		$vars = [];
+		$list = [];
+		foreach ( $params as $n => $p ) {
+			list( $type, $value ) = $this->extractParam( $p, $format );
+			$types[$type] = true;
+			$list[] = $value;
+			$vars[] = '$' . ( $n + 1 );
+		}
+
+		// Easy case: all are 'before' or 'after', so just join the
+		// values and use the same type.
+		if ( count( $types ) === 1 ) {
+			return [ key( $types ), $this->getLanguage()->$func( $list ) ];
+		}
+
+		// Hard case: We need to process each value per its type, then
+		// return the concatenated values as 'after'. We handle this by turning
+		// the list into a RawMessage and processing that as a parameter.
+		$vars = $this->getLanguage()->$func( $vars );
+		return $this->extractParam( new RawMessage( $vars, $params ), $format );
+	}
+}