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+<?php
+/**
+ * Delayed loading of global objects.
+ *
+ * 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
+ */
+use Wikimedia\ObjectFactory;
+
+/**
+ * Class to implement stub globals, which are globals that delay loading the
+ * their associated module code by deferring initialisation until the first
+ * method call.
+ *
+ * Note on reference parameters:
+ *
+ * If the called method takes any parameters by reference, the __call magic
+ * here won't work correctly. The solution is to unstub the object before
+ * calling the method.
+ *
+ * Note on unstub loops:
+ *
+ * Unstub loops (infinite recursion) sometimes occur when a constructor calls
+ * another function, and the other function calls some method of the stub. The
+ * best way to avoid this is to make constructors as lightweight as possible,
+ * deferring any initialisation which depends on other modules. As a last
+ * resort, you can use StubObject::isRealObject() to break the loop, but as a
+ * general rule, the stub object mechanism should be transparent, and code
+ * which refers to it should be kept to a minimum.
+ */
+class StubObject {
+	/** @var null|string */
+	protected $global;
+
+	/** @var null|string */
+	protected $class;
+
+	/** @var null|callable */
+	protected $factory;
+
+	/** @var array */
+	protected $params;
+
+	/**
+	 * @param string $global Name of the global variable.
+	 * @param string|callable $class Name of the class of the real object
+	 *                               or a factory function to call
+	 * @param array $params Parameters to pass to constructor of the real object.
+	 */
+	public function __construct( $global = null, $class = null, $params = [] ) {
+		$this->global = $global;
+		if ( is_callable( $class ) ) {
+			$this->factory = $class;
+		} else {
+			$this->class = $class;
+		}
+		$this->params = $params;
+	}
+
+	/**
+	 * Returns a bool value whenever $obj is a stub object. Can be used to break
+	 * a infinite loop when unstubbing an object.
+	 *
+	 * @param object $obj Object to check.
+	 * @return bool True if $obj is not an instance of StubObject class.
+	 */
+	public static function isRealObject( $obj ) {
+		return is_object( $obj ) && !$obj instanceof StubObject;
+	}
+
+	/**
+	 * Unstubs an object, if it is a stub object. Can be used to break a
+	 * infinite loop when unstubbing an object or to avoid reference parameter
+	 * breakage.
+	 *
+	 * @param object &$obj Object to check.
+	 * @return void
+	 */
+	public static function unstub( &$obj ) {
+		if ( $obj instanceof StubObject ) {
+			$obj = $obj->_unstub( 'unstub', 3 );
+		}
+	}
+
+	/**
+	 * Function called if any function exists with that name in this object.
+	 * It is used to unstub the object. Only used internally, PHP will call
+	 * self::__call() function and that function will call this function.
+	 * This function will also call the function with the same name in the real
+	 * object.
+	 *
+	 * @param string $name Name of the function called
+	 * @param array $args Arguments
+	 * @return mixed
+	 */
+	public function _call( $name, $args ) {
+		$this->_unstub( $name, 5 );
+		return call_user_func_array( [ $GLOBALS[$this->global], $name ], $args );
+	}
+
+	/**
+	 * Create a new object to replace this stub object.
+	 * @return object
+	 */
+	public function _newObject() {
+		$params = $this->factory
+			? [ 'factory' => $this->factory ]
+			: [ 'class' => $this->class ];
+		return ObjectFactory::getObjectFromSpec( $params + [
+			'args' => $this->params,
+			'closure_expansion' => false,
+		] );
+	}
+
+	/**
+	 * Function called by PHP if no function with that name exists in this
+	 * object.
+	 *
+	 * @param string $name Name of the function called
+	 * @param array $args Arguments
+	 * @return mixed
+	 */
+	public function __call( $name, $args ) {
+		return $this->_call( $name, $args );
+	}
+
+	/**
+	 * This function creates a new object of the real class and replace it in
+	 * the global variable.
+	 * This is public, for the convenience of external callers wishing to access
+	 * properties, e.g. eval.php
+	 *
+	 * @param string $name Name of the method called in this object.
+	 * @param int $level Level to go in the stack trace to get the function
+	 *   who called this function.
+	 * @return object The unstubbed version of itself
+	 * @throws MWException
+	 */
+	public function _unstub( $name = '_unstub', $level = 2 ) {
+		static $recursionLevel = 0;
+
+		if ( !$GLOBALS[$this->global] instanceof StubObject ) {
+			return $GLOBALS[$this->global]; // already unstubbed.
+		}
+
+		if ( get_class( $GLOBALS[$this->global] ) != $this->class ) {
+			$caller = wfGetCaller( $level );
+			if ( ++$recursionLevel > 2 ) {
+				throw new MWException( "Unstub loop detected on call of "
+					. "\${$this->global}->$name from $caller\n" );
+			}
+			wfDebug( "Unstubbing \${$this->global} on call of "
+				. "\${$this->global}::$name from $caller\n" );
+			$GLOBALS[$this->global] = $this->_newObject();
+			--$recursionLevel;
+			return $GLOBALS[$this->global];
+		}
+	}
+}
+
+/**
+ * Stub object for the user language. Assigned to the $wgLang global.
+ */
+class StubUserLang extends StubObject {
+
+	public function __construct() {
+		parent::__construct( 'wgLang' );
+	}
+
+	/**
+	 * Call Language::findVariantLink after unstubbing $wgLang.
+	 *
+	 * This method is implemented with a full signature rather than relying on
+	 * __call so that the pass-by-reference signature of the proxied method is
+	 * honored.
+	 *
+	 * @param string &$link The name of the link
+	 * @param Title &$nt The title object of the link
+	 * @param bool $ignoreOtherCond To disable other conditions when
+	 *   we need to transclude a template or update a category's link
+	 */
+	public function findVariantLink( &$link, &$nt, $ignoreOtherCond = false ) {
+		global $wgLang;
+		$this->_unstub( 'findVariantLink', 3 );
+		$wgLang->findVariantLink( $link, $nt, $ignoreOtherCond );
+	}
+
+	/**
+	 * @return Language
+	 */
+	public function _newObject() {
+		return RequestContext::getMain()->getLanguage();
+	}
+}