Fix installer issues introduces by MediaWikiServices

This fixes three issues with the installer:

1) Make sure LocalizationCache can find the installer's i18n files.
2) Make sure we don't try to use an SqlBagOStuff for caching before we have
   a functioning database.
3) Don't try to output HTML when redirecting (this is unrelated to
   MediaWikiServices, but came up during testing)

Bug: T135169
Change-Id: I7caa932024cd771d6fa226a3ac6001c3148ecc9c

2 files changed, 38 insertions, 4 deletions

diff --git a/includes/cache/CacheDependency.php b/includes/cache/CacheDependency.php
index 2d29d8651306..a59ba97d0a00 100644
--- a/includes/cache/CacheDependency.php
+++ b/includes/cache/CacheDependency.php
@@ -20,6 +20,7 @@
  * @file
  * @ingroup Cache
  */
+use MediaWiki\MediaWikiServices;
 
 /**
  * This class stores an arbitrary value along with its dependencies.
@@ -247,6 +248,34 @@ class GlobalDependency extends CacheDependency {
 /**
  * @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;
diff --git a/includes/cache/localisation/LocalisationCache.php b/includes/cache/localisation/LocalisationCache.php
index dd7d81a33c04..0fb9ed856100 100644
--- a/includes/cache/localisation/LocalisationCache.php
+++ b/includes/cache/localisation/LocalisationCache.php
@@ -23,6 +23,7 @@
 use Cdb\Reader as CdbReader;
 use Cdb\Writer as CdbWriter;
 use CLDRPluralRuleParser\Evaluator;
+use MediaWiki\MediaWikiServices;
 
 /**
  * Class for caching the contents of localisation files, Messages*.php
@@ -802,12 +803,15 @@ class LocalisationCache {
 	 * @return array
 	 */
 	public function getMessagesDirs() {
-		global $wgMessagesDirs, $IP;
+		global $IP;
+
+		$config = MediaWikiServices::getInstance()->getMainConfig();
+		$messagesDirs = $config->get( 'MessagesDirs' );
 		return [
 			'core' => "$IP/languages/i18n",
 			'api' => "$IP/includes/api/i18n",
 			'oojs-ui' => "$IP/resources/lib/oojs-ui/i18n",
-		] + $wgMessagesDirs;
+		] + $messagesDirs;
 	}
 
 	/**
@@ -958,8 +962,9 @@ class LocalisationCache {
 
 		# Add cache dependencies for any referenced globals
 		$deps['wgExtensionMessagesFiles'] = new GlobalDependency( 'wgExtensionMessagesFiles' );
-		// $wgMessagesDirs is used in LocalisationCache::getMessagesDirs()
-		$deps['wgMessagesDirs'] = new GlobalDependency( 'wgMessagesDirs' );
+		// The 'MessagesDirs' config setting is used in LocalisationCache::getMessagesDirs().
+		// We use the key 'wgMessagesDirs' for historical reasons.
+		$deps['wgMessagesDirs'] = new MainConfigDependency( 'MessagesDirs' );
 		$deps['version'] = new ConstantDependency( 'LocalisationCache::VERSION' );
 
 		# Add dependencies to the cache entry