[TwigBundle] Restore the preview mechanism

src/Symfony/Bridge/Twig/ErrorRenderer/TwigErrorRenderer.php

@@ -14,6 +14,7 @@ namespace Symfony\Bridge\Twig\ErrorRenderer;
 use Symfony\Component\ErrorHandler\ErrorRenderer\ErrorRendererInterface;
 use Symfony\Component\ErrorHandler\ErrorRenderer\HtmlErrorRenderer;
 use Symfony\Component\ErrorHandler\Exception\FlattenException;
+use Symfony\Component\HttpFoundation\RequestStack;
 use Twig\Environment;
 use Twig\Error\LoaderError;
 use Twig\Loader\ExistsLoaderInterface;
@@ -30,8 +31,15 @@ class TwigErrorRenderer implements ErrorRendererInterface
     private $fallbackErrorRenderer;
     private $debug;
 
-    public function __construct(Environment $twig, HtmlErrorRenderer $fallbackErrorRenderer = null, bool $debug = false)
+    /**
+     * @param bool|callable $debug The debugging mode as a boolean or a callable that should return it
+     */
+    public function __construct(Environment $twig, HtmlErrorRenderer $fallbackErrorRenderer = null, $debug = false)
     {
+        if (!\is_bool($debug) && !\is_callable($debug)) {
+            throw new \TypeError(sprintf('Argument 2 passed to %s() must be a boolean or a callable, %s given.', __METHOD__, \is_object($debug) ? \get_class($debug) : \gettype($debug)));
+        }
+
         $this->twig = $twig;
         $this->fallbackErrorRenderer = $fallbackErrorRenderer ?? new HtmlErrorRenderer();
         $this->debug = $debug;
@@ -43,8 +51,9 @@ class TwigErrorRenderer implements ErrorRendererInterface
     public function render(\Throwable $exception): FlattenException
     {
         $exception = $this->fallbackErrorRenderer->render($exception);
+        $debug = \is_bool($this->debug) ? $this->debug : ($this->debug)($exception);
 
-        if ($this->debug || !$template = $this->findTemplate($exception->getStatusCode())) {
+        if ($debug || !$template = $this->findTemplate($exception->getStatusCode())) {
             return $exception;
         }
 
@@ -56,6 +65,17 @@ class TwigErrorRenderer implements ErrorRendererInterface
         ]));
     }
 
+    public static function isDebug(RequestStack $requestStack, bool $debug): \Closure
+    {
+        return static function () use ($requestStack, $debug): bool {
+            if (!$request = $requestStack->getCurrentRequest()) {
+                return $debug;
+            }
+
+            return $debug && $request->attributes->getBoolean('showException', true);
+        };
+    }
+
     private function findTemplate(int $statusCode): ?string
     {
         $template = sprintf('@Twig/Exception/error%s.html.twig', $statusCode);

src/Symfony/Bundle/TwigBundle/Resources/config/twig.xml

@@ -165,7 +165,13 @@
         <service id="twig.error_renderer.html" class="Symfony\Bridge\Twig\ErrorRenderer\TwigErrorRenderer" decorates="error_renderer.html">
             <argument type="service" id="twig" />
             <argument type="service" id="twig.error_renderer.html.inner" />
-            <argument>%kernel.debug%</argument>
+            <argument type="service">
+                <service>
+                    <factory class="Symfony\Bridge\Twig\ErrorRenderer\TwigErrorRenderer" method="isDebug" />
+                    <argument type="service" id="request_stack" />
+                    <argument>%kernel.debug%</argument>
+                </service>
+            </argument>
         </service>
     </services>
 </container>

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

@@ -550,7 +550,7 @@ class ErrorHandlerTest extends TestCase
         $handler->handleException(new \Exception());
     }
 
-    public function testSendPhpResponse()
+    public function testRenderException()
     {
         $handler = new ErrorHandler();
         $handler->setExceptionHandler([$handler, 'renderException']);