Issue #2521852 by znerol, dawehner: Make it possible to use your own exception handler

core/lib/Drupal/Core/DrupalKernel.php

@@ -594,6 +594,9 @@ public function handle(Request $request, $type = self::MASTER_REQUEST, $catch =
    *
    * @return Response
    *   A Response instance
+   *
+   * @throws \Exception
+   *   If the passed in exception cannot be turned into a response.
    */
   protected function handleException(\Exception $e, $request, $type) {
     if ($e instanceof HttpExceptionInterface) {
@@ -602,24 +605,7 @@ protected function handleException(\Exception $e, $request, $type) {
       return $response;
     }
     else {
-      // @todo: _drupal_log_error() and thus _drupal_exception_handler() prints
-      // the message directly. Extract a function which generates and returns it
-      // instead, then remove the output buffer hack here.
-      ob_start();
-      try {
-        // @todo: The exception handler prints the message directly. Extract a
-        // function which returns the message instead.
-        _drupal_exception_handler($e);
-      }
-      catch (\Exception $e) {
-        $message = Settings::get('rebuild_message', 'If you have just changed code (for example deployed a new module or moved an existing one) read <a href="https://www.drupal.org/documentation/rebuild">https://www.drupal.org/documentation/rebuild</a>');
-        if ($message && Settings::get('rebuild_access', FALSE)) {
-          $rebuild_path = $GLOBALS['base_url'] . '/rebuild.php';
-          $message .= " or run the <a href=\"$rebuild_path\">rebuild script</a>";
-        }
-        print $message;
-      }
-      return new Response(ob_get_clean(), 500);
+      throw $e;
     }
   }
 

core/modules/system/src/Tests/System/UncaughtExceptionTest.php

@@ -89,17 +89,77 @@ public function testUncaughtException() {
     $this->assertText($this->expectedExceptionMessage);
   }
 
+  /**
+   * Tests uncaught exception handling with custom exception handler.
+   */
+  public function testUncaughtExceptionCustomExceptionHandler() {
+    $settings_filename = $this->siteDirectory . '/settings.php';
+    chmod($settings_filename, 0777);
+    $settings_php = file_get_contents($settings_filename);
+    $settings_php .= "\n";
+    $settings_php .= "set_exception_handler(function() {\n";
+    $settings_php .= "  header('HTTP/1.1 418 I\'m a teapot');\n";
+    $settings_php .= "  print('Oh oh, flying teapots');\n";
+    $settings_php .= "});\n";
+    file_put_contents($settings_filename, $settings_php);
+
+    \Drupal::state()->set('error_service_test.break_bare_html_renderer', TRUE);
+
+    $this->drupalGet('');
+    $this->assertResponse(418);
+    $this->assertNoText('The website encountered an unexpected error. Please try again later.');
+    $this->assertNoText('Oh oh, bananas in the instruments');
+    $this->assertText('Oh oh, flying teapots');
+  }
+
   /**
    * Tests a missing dependency on a service.
    */
   public function testMissingDependency() {
     $this->expectedExceptionMessage = 'Argument 1 passed to Drupal\error_service_test\LonelyMonkeyClass::__construct() must be an instance of Drupal\Core\Database\Connection, non';
     $this->drupalGet('broken-service-class');
+    $this->assertResponse(500);
 
     $this->assertRaw('The website encountered an unexpected error.');
     $this->assertRaw($this->expectedExceptionMessage);
   }
 
+  /**
+   * Tests a missing dependency on a service with a custom error handler.
+   */
+  public function testMissingDependencyCustomErrorHandler() {
+    $settings_filename = $this->siteDirectory . '/settings.php';
+    chmod($settings_filename, 0777);
+    $settings_php = file_get_contents($settings_filename);
+    $settings_php .= "\n";
+    $settings_php .= "set_error_handler(function() {\n";
+    $settings_php .= "  header('HTTP/1.1 418 I\'m a teapot');\n";
+    $settings_php .= "  print('Oh oh, flying teapots');\n";
+    $settings_php .= "  exit();\n";
+    $settings_php .= "});\n";
+    file_put_contents($settings_filename, $settings_php);
+
+    $this->drupalGet('broken-service-class');
+    $this->assertResponse(418);
+    $this->assertRaw('Oh oh, flying teapots');
+
+    $message = 'Argument 1 passed to Drupal\error_service_test\LonelyMonkeyClass::__construct() must be an instance of Drupal\Core\Database\Connection, non';
+
+    $this->assertNoRaw('The website encountered an unexpected error.');
+    $this->assertNoRaw($message);
+
+    $found_exception = FALSE;
+    foreach ($this->assertions as &$assertion) {
+      if (strpos($assertion['message'], $message) !== FALSE) {
+        $found_exception = TRUE;
+        $this->deleteAssert($assertion['message_id']);
+        unset($assertion);
+      }
+    }
+
+    $this->assertTrue($found_exception, 'Ensure that the exception of a missing constructor argument was triggered.');
+  }
+
   /**
    * Tests a container which has an error.
    */
@@ -121,6 +181,7 @@ public function testErrorContainer() {
 
     $this->expectedExceptionMessage = 'Argument 1 passed to Drupal\system\Tests\Bootstrap\ErrorContainer::Drupal\system\Tests\Bootstrap\{closur';
     $this->drupalGet('');
+    $this->assertResponse(500);
 
     $this->assertRaw($this->expectedExceptionMessage);
   }
@@ -146,6 +207,7 @@ public function testExceptionContainer() {
 
     $this->expectedExceptionMessage = 'Thrown exception during Container::get';
     $this->drupalGet('');
+    $this->assertResponse(500);
 
 
     $this->assertRaw('The website encountered an unexpected error');
@@ -182,6 +244,7 @@ public function testLostDatabaseConnection() {
     $this->writeSettings($settings);
 
     $this->drupalGet('');
+    $this->assertResponse(500);
     $this->assertRaw('PDOException');
   }