Better exception message when class cannot be loaded

framework/CHANGELOG.md

@@ -62,6 +62,7 @@ Yii Framework 2 Change Log
 - Enh: Sort and Pagination can now create absolute URLs (cebe)
 - Enh: Added support for using array-typed arguments for console commands (qiangxue)
 - Enh: Added support for installing packages conforming to PSR-4 standard (qiangxue)
+- Enh: Better exception message when class cannot be loaded (samdark)
 - Chg #1519: `yii\web\User::loginRequired()` now returns the `Response` object instead of exiting the application (qiangxue)
 - Chg #1586: `QueryBuilder::buildLikeCondition()` will now escape special characters and use percentage characters by default (qiangxue)
 - Chg #1610: `Html::activeCheckboxList()` and `Html::activeRadioList()` will submit an empty string if no checkbox/radio is selected (qiangxue)

framework/yii/BaseYii.php

@@ -296,7 +296,7 @@ class BaseYii
 		include($classFile);
 
 		if (YII_DEBUG && !class_exists($className, false) && !interface_exists($className, false) && !trait_exists($className, false)) {
-			throw new UnknownClassException("Unable to find '$className' in file: $classFile");
+			throw new UnknownClassException("Unable to find '$className' in file: $classFile. Namespace missing?");
 		}
 	}