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diff --git a/www/wiki/includes/cache/CacheDependency.php b/www/wiki/includes/cache/CacheDependency.php
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+<?php
+/**
+ * Data caching with dependencies.
+ *
+ * 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
+ * @ingroup Cache
+ */
+use MediaWiki\MediaWikiServices;
+
+/**
+ * This class stores an arbitrary value along with its dependencies.
+ * Users should typically only use DependencyWrapper::getValueFromCache(),
+ * rather than instantiating one of these objects directly.
+ * @ingroup Cache
+ */
+class DependencyWrapper {
+	private $value;
+	/** @var CacheDependency[] */
+	private $deps;
+
+	/**
+	 * @param mixed $value The user-supplied value
+	 * @param CacheDependency|CacheDependency[] $deps A dependency or dependency
+	 *   array. All dependencies must be objects implementing CacheDependency.
+	 */
+	function __construct( $value = false, $deps = [] ) {
+		$this->value = $value;
+
+		if ( !is_array( $deps ) ) {
+			$deps = [ $deps ];
+		}
+
+		$this->deps = $deps;
+	}
+
+	/**
+	 * Returns true if any of the dependencies have expired
+	 *
+	 * @return bool
+	 */
+	function isExpired() {
+		foreach ( $this->deps as $dep ) {
+			if ( $dep->isExpired() ) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	/**
+	 * Initialise dependency values in preparation for storing. This must be
+	 * called before serialization.
+	 */
+	function initialiseDeps() {
+		foreach ( $this->deps as $dep ) {
+			$dep->loadDependencyValues();
+		}
+	}
+
+	/**
+	 * Get the user-defined value
+	 * @return bool|mixed
+	 */
+	function getValue() {
+		return $this->value;
+	}
+
+	/**
+	 * Store the wrapper to a cache
+	 *
+	 * @param BagOStuff $cache
+	 * @param string $key
+	 * @param int $expiry
+	 */
+	function storeToCache( $cache, $key, $expiry = 0 ) {
+		$this->initialiseDeps();
+		$cache->set( $key, $this, $expiry );
+	}
+
+	/**
+	 * Attempt to get a value from the cache. If the value is expired or missing,
+	 * it will be generated with the callback function (if present), and the newly
+	 * calculated value will be stored to the cache in a wrapper.
+	 *
+	 * @param BagOStuff $cache
+	 * @param string $key The cache key
+	 * @param int $expiry The expiry timestamp or interval in seconds
+	 * @param bool|callable $callback The callback for generating the value, or false
+	 * @param array $callbackParams The function parameters for the callback
+	 * @param array $deps The dependencies to store on a cache miss. Note: these
+	 *    are not the dependencies used on a cache hit! Cache hits use the stored
+	 *    dependency array.
+	 *
+	 * @return mixed The value, or null if it was not present in the cache and no
+	 *    callback was defined.
+	 */
+	static function getValueFromCache( $cache, $key, $expiry = 0, $callback = false,
+		$callbackParams = [], $deps = []
+	) {
+		$obj = $cache->get( $key );
+
+		if ( is_object( $obj ) && $obj instanceof DependencyWrapper && !$obj->isExpired() ) {
+			$value = $obj->value;
+		} elseif ( $callback ) {
+			$value = call_user_func_array( $callback, $callbackParams );
+			# Cache the newly-generated value
+			$wrapper = new DependencyWrapper( $value, $deps );
+			$wrapper->storeToCache( $cache, $key, $expiry );
+		} else {
+			$value = null;
+		}
+
+		return $value;
+	}
+}
+
+/**
+ * @ingroup Cache
+ */
+abstract class CacheDependency {
+	/**
+	 * Returns true if the dependency is expired, false otherwise
+	 */
+	abstract function isExpired();
+
+	/**
+	 * Hook to perform any expensive pre-serialize loading of dependency values.
+	 */
+	function loadDependencyValues() {
+	}
+}
+
+/**
+ * @ingroup Cache
+ */
+class FileDependency extends CacheDependency {
+	private $filename;
+	private $timestamp;
+
+	/**
+	 * Create a file dependency
+	 *
+	 * @param string $filename The name of the file, preferably fully qualified
+	 * @param null|bool|int $timestamp The unix last modified timestamp, or false if the
+	 *        file does not exist. If omitted, the timestamp will be loaded from
+	 *        the file.
+	 *
+	 * A dependency on a nonexistent file will be triggered when the file is
+	 * created. A dependency on an existing file will be triggered when the
+	 * file is changed.
+	 */
+	function __construct( $filename, $timestamp = null ) {
+		$this->filename = $filename;
+		$this->timestamp = $timestamp;
+	}
+
+	/**
+	 * @return array
+	 */
+	function __sleep() {
+		$this->loadDependencyValues();
+
+		return [ 'filename', 'timestamp' ];
+	}
+
+	function loadDependencyValues() {
+		if ( is_null( $this->timestamp ) ) {
+			Wikimedia\suppressWarnings();
+			# Dependency on a non-existent file stores "false"
+			# This is a valid concept!
+			$this->timestamp = filemtime( $this->filename );
+			Wikimedia\restoreWarnings();
+		}
+	}
+
+	/**
+	 * @return bool
+	 */
+	function isExpired() {
+		Wikimedia\suppressWarnings();
+		$lastmod = filemtime( $this->filename );
+		Wikimedia\restoreWarnings();
+		if ( $lastmod === false ) {
+			if ( $this->timestamp === false ) {
+				# Still nonexistent
+				return false;
+			} else {
+				# Deleted
+				wfDebug( "Dependency triggered: {$this->filename} deleted.\n" );
+
+				return true;
+			}
+		} else {
+			if ( $lastmod > $this->timestamp ) {
+				# Modified or created
+				wfDebug( "Dependency triggered: {$this->filename} changed.\n" );
+
+				return true;
+			} else {
+				# Not modified
+				return false;
+			}
+		}
+	}
+}
+
+/**
+ * @ingroup Cache
+ */
+class GlobalDependency extends CacheDependency {
+	private $name;
+	private $value;
+
+	function __construct( $name ) {
+		$this->name = $name;
+		$this->value = $GLOBALS[$name];
+	}
+
+	/**
+	 * @return bool
+	 */
+	function isExpired() {
+		if ( !isset( $GLOBALS[$this->name] ) ) {
+			return true;
+		}
+
+		return $GLOBALS[$this->name] != $this->value;
+	}
+}
+
+/**
+ * @ingroup Cache
+ */
+class MainConfigDependency extends CacheDependency {
+	private $name;
+	private $value;
+
+	function __construct( $name ) {
+		$this->name = $name;
+		$this->value = $this->getConfig()->get( $this->name );
+	}
+
+	private function getConfig() {
+		return MediaWikiServices::getInstance()->getMainConfig();
+	}
+
+	/**
+	 * @return bool
+	 */
+	function isExpired() {
+		if ( !$this->getConfig()->has( $this->name ) ) {
+			return true;
+		}
+
+		return $this->getConfig()->get( $this->name ) != $this->value;
+	}
+}
+
+/**
+ * @ingroup Cache
+ */
+class ConstantDependency extends CacheDependency {
+	private $name;
+	private $value;
+
+	function __construct( $name ) {
+		$this->name = $name;
+		$this->value = constant( $name );
+	}
+
+	/**
+	 * @return bool
+	 */
+	function isExpired() {
+		return constant( $this->name ) != $this->value;
+	}
+}