[Config] ensure moving away from Serializable wont break cache:clear

Author: nicolas-grekas

ResourceCheckerConfigCache.php

@@ -156,18 +156,19 @@ private function safelyUnserialize($file)
     {
         $e = null;
         $meta = false;
+        $content = file_get_contents($file);
         $signalingException = new \UnexpectedValueException();
         $prevUnserializeHandler = ini_set('unserialize_callback_func', '');
         $prevErrorHandler = set_error_handler(function ($type, $msg, $file, $line, $context = []) use (&$prevErrorHandler, $signalingException) {
-            if (E_WARNING === $type && 'Class __PHP_Incomplete_Class has no unserializer' === $msg) {
+            if (__FILE__ === $file) {
                 throw $signalingException;
             }
 
             return $prevErrorHandler ? $prevErrorHandler($type, $msg, $file, $line, $context) : false;
         });
 
         try {
-            $meta = unserialize(file_get_contents($file));
+            $meta = unserialize($content);
         } catch (\Error $e) {
         } catch (\Exception $e) {
         }