[Debug][ErrorHandler] Preserve next error handler

src/Symfony/Component/Debug/ErrorHandler.php

@@ -517,6 +517,11 @@ public function handleError($type, $message, $file, $line)
                 $errorAsException ? ['exception' => $errorAsException] : [],
             ];
         } else {
+            if (!\defined('HHVM_VERSION')) {
+                $currentErrorHandler = set_error_handler('var_dump');
+                restore_error_handler();
+            }
+
             try {
                 $this->isRecursive = true;
                 $level = ($type & $level) ? $this->loggers[$type][1] : LogLevel::DEBUG;
@@ -525,7 +530,7 @@ public function handleError($type, $message, $file, $line)
                 $this->isRecursive = false;
 
                 if (!\defined('HHVM_VERSION')) {
-                    set_error_handler([$this, __FUNCTION__]);
+                    set_error_handler($currentErrorHandler);
                 }
             }
         }

src/Symfony/Component/Debug/Tests/ErrorHandlerTest.php

@@ -12,12 +12,12 @@
 namespace Symfony\Component\Debug\Tests;
 
 use PHPUnit\Framework\TestCase;
-use Psr\Log\LoggerInterface;
 use Psr\Log\LogLevel;
 use Psr\Log\NullLogger;
 use Symfony\Component\Debug\BufferingLogger;
 use Symfony\Component\Debug\ErrorHandler;
 use Symfony\Component\Debug\Exception\SilencedErrorContext;
+use Symfony\Component\Debug\Tests\Fixtures\ErrorHandlerThatUsesThePreviousOne;
 use Symfony\Component\Debug\Tests\Fixtures\LoggerThatSetAnErrorHandler;
 
 /**
@@ -590,26 +590,40 @@ public function testCustomExceptionHandler()
     }
 
     /**
-     * @dataProvider errorHandlerIsNotLostWhenLoggingProvider
+     * @dataProvider errorHandlerWhenLoggingProvider
      */
-    public function testErrorHandlerIsNotLostWhenLogging($customErrorHandlerHasBeenPreviouslyDefined, LoggerInterface $logger)
+    public function testErrorHandlerWhenLogging($previousHandlerWasDefined, $loggerSetsAnotherHandler, $nextHandlerIsDefined)
     {
         try {
-            if ($customErrorHandlerHasBeenPreviouslyDefined) {
+            if ($previousHandlerWasDefined) {
                 set_error_handler('count');
             }
 
+            $logger = $loggerSetsAnotherHandler ? new LoggerThatSetAnErrorHandler() : new NullLogger();
+
             $handler = ErrorHandler::register();
             $handler->setDefaultLogger($logger);
 
+            if ($nextHandlerIsDefined) {
+                $handler = ErrorHandlerThatUsesThePreviousOne::register();
+            }
+
             @trigger_error('foo', E_USER_DEPRECATED);
             @trigger_error('bar', E_USER_DEPRECATED);
 
             $this->assertSame([$handler, 'handleError'], set_error_handler('var_dump'));
 
+            if ($logger instanceof LoggerThatSetAnErrorHandler) {
+                $this->assertCount(2, $logger->cleanLogs());
+            }
+
             restore_error_handler();
 
-            if ($customErrorHandlerHasBeenPreviouslyDefined) {
+            if ($previousHandlerWasDefined) {
+                restore_error_handler();
+            }
+
+            if ($nextHandlerIsDefined) {
                 restore_error_handler();
             }
         } finally {
@@ -618,13 +632,14 @@ public function testErrorHandlerIsNotLostWhenLogging($customErrorHandlerHasBeenP
         }
     }
 
-    public function errorHandlerIsNotLostWhenLoggingProvider()
+    public function errorHandlerWhenLoggingProvider()
     {
-        return [
-            [false, new NullLogger()],
-            [true, new NullLogger()],
-            [false, new LoggerThatSetAnErrorHandler()],
-            [true, new LoggerThatSetAnErrorHandler()],
-        ];
+        foreach ([false, true] as $previousHandlerWasDefined) {
+            foreach ([false, true] as $loggerSetsAnotherHandler) {
+                foreach ([false, true] as $nextHandlerIsDefined) {
+                    yield [$previousHandlerWasDefined, $loggerSetsAnotherHandler, $nextHandlerIsDefined];
+                }
+            }
+        }
     }
 }

src/Symfony/Component/Debug/Tests/Fixtures/ErrorHandlerThatUsesThePreviousOne.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Symfony\Component\Debug\Tests\Fixtures;
+
+class ErrorHandlerThatUsesThePreviousOne
+{
+    private static $previous;
+
+    public static function register()
+    {
+        $handler = new static();
+
+        self::$previous = set_error_handler([$handler, 'handleError']);
+
+        return $handler;
+    }
+
+    public function handleError($type, $message, $file, $line, $context)
+    {
+        return \call_user_func(self::$previous, $type, $message, $file, $line, $context);
+    }
+}

src/Symfony/Component/Debug/Tests/Fixtures/LoggerThatSetAnErrorHandler.php

@@ -2,13 +2,14 @@
 
 namespace Symfony\Component\Debug\Tests\Fixtures;
 
-use Psr\Log\AbstractLogger;
+use Symfony\Component\Debug\BufferingLogger;
 
-class LoggerThatSetAnErrorHandler extends AbstractLogger
+class LoggerThatSetAnErrorHandler extends BufferingLogger
 {
     public function log($level, $message, array $context = [])
     {
         set_error_handler('is_string');
+        parent::log($level, $message, $context);
         restore_error_handler();
     }
 }