bug symfony#25755 [Debug] prevent infinite loop with faulty exception handlers (nicolas-grekas)

This PR was merged into the 2.7 branch.

Discussion
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[Debug] prevent infinite loop with faulty exception handlers

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#25743
| License       | MIT
| Doc PR        | -

Commits
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5f397f8 [Debug] prevent infinite loop with faulty exception handlers

Author: fabpot

src/Symfony/Component/Debug/ErrorHandler.php

@@ -561,6 +561,8 @@ public static function handleFatalError(array $error = null)
 
         $handler = self::$reservedMemory = null;
         $handlers = array();
+        $previousHandler = null;
+        $sameHandlerLimit = 10;
 
         while (!is_array($handler) || !$handler[0] instanceof self) {
             $handler = set_exception_handler('var_dump');
@@ -570,7 +572,14 @@ public static function handleFatalError(array $error = null)
                 break;
             }
             restore_exception_handler();
-            array_unshift($handlers, $handler);
+
+            if ($handler !== $previousHandler) {
+                array_unshift($handlers, $handler);
+                $previousHandler = $handler;
+            } elseif (0 === --$sameHandlerLimit) {
+                $handler = null;
+                break;
+            }
         }
         foreach ($handlers as $h) {
             set_exception_handler($h);