fixed a bug in MessageSource and missingtranslation event

framework/CHANGELOG.md

@@ -47,6 +47,7 @@ Yii Framework 2 Change Log
 - Bug #2324: Fixed QueryBuilder bug when building a query with "query" option (mintao)
 - Bug #2399: Fixed the bug that AssetBundle did not handle relative URLs correctly (qiangxue)
 - Bug #2502: Unclear error message when `$_SERVER['DOCUMENT_ROOT']` is empty (samdark)
+- Bug #2519: MessageSource removed translation messages when event handler was bound to `missingTranslation`-event (cebe)
 - Bug: Fixed `Call to a member function registerAssetFiles() on a non-object` in case of wrong `sourcePath` for an asset bundle (samdark)
 - Bug: Fixed incorrect event name for `yii\jui\Spinner` (samdark)
 - Bug: Json::encode() did not handle objects that implement JsonSerializable interface correctly (cebe)

framework/i18n/MessageSource.php

@@ -91,12 +91,13 @@ class MessageSource extends Component
 
 	/**
 	 * Translates the specified message.
-	 * If the message is not found, a [[EVENT_MISSING_TRANSLATION|missingTranslation]] event will be triggered
-	 * and the original message will be returned.
-	 * @param string $category the category that the message belongs to
-	 * @param string $message the message to be translated
-	 * @param string $language the target language
-	 * @return string|boolean the translated message or false if translation wasn't found
+	 * If the message is not found, a [[EVENT_MISSING_TRANSLATION|missingTranslation]] event will be triggered.
+	 * If there is an event handler, it may provide a [[MissingTranslationEvent::$translatedMessage|fallback translation]].
+	 * If no fallback translation is provided this method will return `false`.
+	 * @param string $category the category that the message belongs to.
+	 * @param string $message the message to be translated.
+	 * @param string $language the target language.
+	 * @return string|boolean the translated message or false if translation wasn't found.
 	 */
 	protected function translateMessage($category, $message, $language)
 	{
@@ -113,7 +114,9 @@ class MessageSource extends Component
 				'language' => $language,
 			]);
 			$this->trigger(self::EVENT_MISSING_TRANSLATION, $event);
-			$this->_messages[$key] = $event->message;
+			if ($event->translatedMessage !== false) {
+				return $this->_messages[$key][$message] = $event->translatedMessage;
+			}
 		}
 		return false;
 	}

framework/i18n/MissingTranslationEvent.php

@@ -18,11 +18,17 @@ use yii\base\Event;
 class MissingTranslationEvent extends Event
 {
 	/**
-	 * @var string the message to be translated. An event handler may overwrite this property
-	 * with a translated version if possible.
+	 * @var string the message to be translated. An event handler may use this to provide a fallback translation
+	 * and set [[translatedMessage]] if possible.
 	 */
 	public $message;
 	/**
+	 * @var string|boolean the translated message. An event handler may overwrite this property
+	 * with a translated version of [[message]] if possible. Defaults to false meaning no translation
+	 * is available.
+	 */
+	public $translatedMessage = false;
+	/**
 	 * @var string the category that the message belongs to
 	 */
 	public $category;

tests/unit/framework/i18n/I18NTest.php

@@ -7,6 +7,7 @@
 
 namespace yiiunit\framework\i18n;
 
+use yii\base\Event;
 use yii\base\Model;
 use yii\i18n\I18N;
 use yii\i18n\PhpMessageSource;
@@ -98,6 +99,33 @@ class I18NTest extends TestCase
 	{
 		$this->assertEquals('1 item', $this->i18n->translate('test', '{0, number} {0, plural, one{item} other{items}}', 1, 'hu'));
 	}
+
+	/**
+	 * https://github.com/yiisoft/yii2/issues/2519
+	 */
+	public function testMissingTranslationEvent()
+	{
+		$this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
+		$this->assertEquals('Missing translation message.', $this->i18n->translate('test', 'Missing translation message.', [], 'de-DE'));
+		$this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
+
+		Event::on(PhpMessageSource::className(), PhpMessageSource::EVENT_MISSING_TRANSLATION, function($event) {});
+		$this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
+		$this->assertEquals('Missing translation message.', $this->i18n->translate('test', 'Missing translation message.', [], 'de-DE'));
+		$this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
+		Event::off(PhpMessageSource::className(), PhpMessageSource::EVENT_MISSING_TRANSLATION);
+
+		Event::on(PhpMessageSource::className(), PhpMessageSource::EVENT_MISSING_TRANSLATION, function($event) {
+			if ($event->message == 'Missing translation message.') {
+				$event->translatedMessage = 'TRANSLATION MISSING HERE!';
+			}
+		});
+		$this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
+		$this->assertEquals('Another missing translation message.', $this->i18n->translate('test', 'Another missing translation message.', [], 'de-DE'));
+		$this->assertEquals('TRANSLATION MISSING HERE!', $this->i18n->translate('test', 'Missing translation message.', [], 'de-DE'));
+		$this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
+		Event::off(PhpMessageSource::className(), PhpMessageSource::EVENT_MISSING_TRANSLATION);
+	}
 }
 
 class ParamModel extends Model