convert exceptions to string before saving log messages

fixes #7305

framework/CHANGELOG.md

@@ -4,6 +4,7 @@ Yii Framework 2 Change Log
 2.0.5 under development
 -----------------------
 
+- Bug #7305: Logging of Exception objects resulted in failure of the logger i.e. no logs being written (cebe)
 - Bug #7707: client-side `trim` validator now passes the trimmed value to subsequent validators (nkovacs)
 - Bug #8322: `yii\behaviors\TimestampBehavior::touch()` now throws an exception if owner is new record (klimov-paul)
 - Enh #8070: `yii\console\controllers\MessageController` now sorts created messages, even if there is no new one, while saving to PHP file (klimov-paul)

framework/log/SyslogTarget.php

@@ -60,7 +60,12 @@ class SyslogTarget extends Target
         list($text, $level, $category, $timestamp) = $message;
         $level = Logger::getLevelName($level);
         if (!is_string($text)) {
-            $text = VarDumper::export($text);
+            // exceptions may not be serializable if in the call stack somewhere is a Closure
+            if ($text instanceof \Exception) {
+                $text = (string) $text;
+            } else {
+                $text = VarDumper::export($text);
+            }
         }
 
         $prefix = $this->getMessagePrefix($message);

framework/log/Target.php

@@ -9,6 +9,7 @@ namespace yii\log;
 
 use Yii;
 use yii\base\Component;
+use yii\base\ErrorHandler;
 use yii\base\InvalidConfigException;
 use yii\helpers\VarDumper;
 use yii\web\Request;
@@ -238,7 +239,12 @@ abstract class Target extends Component
         list($text, $level, $category, $timestamp) = $message;
         $level = Logger::getLevelName($level);
         if (!is_string($text)) {
-            $text = VarDumper::export($text);
+            // exceptions may not be serializable if in the call stack somewhere is a Closure
+            if ($text instanceof \Exception) {
+                $text = (string) $text;
+            } else {
+                $text = VarDumper::export($text);
+            }
         }
         $traces = [];
         if (isset($message[4])) {