bug #39944 [HttpKernel] Configure the ErrorHandler even when it is overriden (nicolas-grekas)

This PR was merged into the 4.4 branch.

Discussion
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[HttpKernel] Configure the ErrorHandler even when it is overriden

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Fixes the part of getsentry/sentry-symfony#421 that is about `DebugHandlersListener`.

Commits
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31817b4 [HttpKernel] Configure the ErrorHandler even when it is overriden

Author: nicolas-grekas

src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php

@@ -33,6 +33,7 @@
  */
 class DebugHandlersListener implements EventSubscriberInterface
 {
+    private $earlyHandler;
     private $exceptionHandler;
     private $logger;
     private $levels;
@@ -53,6 +54,10 @@ class DebugHandlersListener implements EventSubscriberInterface
      */
     public function __construct(callable $exceptionHandler = null, LoggerInterface $logger = null, $levels = \E_ALL, ?int $throwAt = \E_ALL, bool $scream = true, $fileLinkFormat = null, bool $scope = true)
     {
+        $handler = set_exception_handler('var_dump');
+        $this->earlyHandler = \is_array($handler) ? $handler[0] : null;
+        restore_exception_handler();
+
         $this->exceptionHandler = $exceptionHandler;
         $this->logger = $logger;
         $this->levels = null === $levels ? \E_ALL : $levels;
@@ -79,6 +84,10 @@ public function configure(Event $event = null)
         $handler = \is_array($handler) ? $handler[0] : null;
         restore_exception_handler();
 
+        if (!$handler instanceof ErrorHandler && !$handler instanceof LegacyErrorHandler) {
+            $handler = $this->earlyHandler;
+        }
+
         if ($this->logger || null !== $this->throwAt) {
             if ($handler instanceof ErrorHandler || $handler instanceof LegacyErrorHandler) {
                 if ($this->logger) {