Don't clear PHP buffer when an error occurs with debug=true

CHANGELOG

@@ -1,6 +1,6 @@
 * 1.42.2 (2019-XX-XX)
 
- * n/a
+ * Display partial output (PHP buffer) when an error occurs in debug mode
 
 * 1.42.1 (2019-06-04)
 

src/Extension/DebugExtension.php

@@ -54,7 +54,7 @@ function twig_var_dump(Environment $env, $context, array $vars = [])
         return;
     }
 
-    ob_start(function () { return ''; });
+    ob_start();
 
     if (!$vars) {
         $vars = [];

src/Node/MacroNode.php

@@ -104,7 +104,13 @@ class MacroNode extends Node
             ->outdent()
             ->write("]);\n\n")
             ->write("\$blocks = [];\n\n")
-            ->write("ob_start(function () { return ''; });\n")
+        ;
+        if ($compiler->getEnvironment()->isDebug()) {
+            $compiler->write("ob_start();\n");
+        } else {
+            $compiler->write("ob_start(function () { return ''; });\n");
+        }
+        $compiler
             ->write("try {\n")
             ->indent()
             ->subcompile($this->getNode('body'))

src/Node/SetNode.php

@@ -57,8 +57,12 @@ class SetNode extends Node implements NodeCaptureInterface
             $compiler->raw(')');
         } else {
             if ($this->getAttribute('capture')) {
+                if ($compiler->getEnvironment()->isDebug()) {
+                    $compiler->write("ob_start();\n");
+                } else {
+                    $compiler->write("ob_start(function () { return ''; });\n");
+                }
                 $compiler
-                    ->write("ob_start(function () { return ''; });\n")
                     ->subcompile($this->getNode('values'))
                 ;
             }

src/Node/SpacelessNode.php

@@ -31,7 +31,13 @@ class SpacelessNode extends Node
     {
         $compiler
             ->addDebugInfo($this)
-            ->write("ob_start(function () { return ''; });\n")
+        ;
+        if ($compiler->getEnvironment()->isDebug()) {
+            $compiler->write("ob_start();\n");
+        } else {
+            $compiler->write("ob_start(function () { return ''; });\n");
+        }
+        $compiler
             ->subcompile($this->getNode('body'))
             ->write("echo trim(preg_replace('/>\s+</', '><', ob_get_clean()));\n")
         ;

src/Template.php

@@ -253,7 +253,11 @@ abstract class Template implements \Twig_TemplateInterface
      */
     public function renderParentBlock($name, array $context, array $blocks = [])
     {
-        ob_start(function () { return ''; });
+        if ($this->env->isDebug()) {
+            ob_start();
+        } else {
+            ob_start(function () { return ''; });
+        }
         $this->displayParentBlock($name, $context, $blocks);
 
         return ob_get_clean();
@@ -274,7 +278,11 @@ abstract class Template implements \Twig_TemplateInterface
      */
     public function renderBlock($name, array $context, array $blocks = [], $useBlocks = true)
     {
-        ob_start(function () { return ''; });
+        if ($this->env->isDebug()) {
+            ob_start();
+        } else {
+            ob_start(function () { return ''; });
+        }
         $this->displayBlock($name, $context, $blocks, $useBlocks);
 
         return ob_get_clean();
@@ -417,7 +425,11 @@ abstract class Template implements \Twig_TemplateInterface
     public function render(array $context)
     {
         $level = ob_get_level();
-        ob_start(function () { return ''; });
+        if ($this->env->isDebug()) {
+            ob_start();
+        } else {
+            ob_start(function () { return ''; });
+        }
         try {
             $this->display($context);
         } catch (\Exception $e) {

src/TemplateWrapper.php

@@ -96,7 +96,11 @@ final class TemplateWrapper
     {
         $context = $this->env->mergeGlobals($context);
         $level = ob_get_level();
-        ob_start(function () { return ''; });
+        if ($this->env->isDebug()) {
+            ob_start();
+        } else {
+            ob_start(function () { return ''; });
+        }
         try {
             $this->template->displayBlock($name, $context);
         } catch (\Exception $e) {

test/Twig/Tests/ErrorTest.php

@@ -207,6 +207,20 @@ EOHTML
             ],
         ];
     }
+
+    public function testTwigLeakOutputInDebugMode()
+    {
+        $output = exec(sprintf('%s %s debug', \PHP_BINARY, __DIR__.'/Fixtures/errors/leak-output.php'));
+
+        $this->assertSame('Hello OOPS', $output);
+    }
+
+    public function testDoesNotTwigLeakOutput()
+    {
+        $output = exec(sprintf('%s %s', \PHP_BINARY, __DIR__.'/Fixtures/errors/leak-output.php'));
+
+        $this->assertSame('', $output);
+    }
 }
 
 class Twig_Tests_ErrorTest_Foo

test/Twig/Tests/Fixtures/errors/leak-output.php

@@ -0,0 +1,31 @@
+<?php
+
+require __DIR__.'/../../../../../vendor/autoload.php';
+
+use Twig\Environment;
+use Twig\Extension\AbstractExtension;
+use Twig\Loader\ArrayLoader;
+use Twig\TwigFilter;
+
+class BrokenExtension extends AbstractExtension
+{
+    public function getFilters()
+    {
+        return [
+            new TwigFilter('broken', [$this, 'broken']),
+        ];
+    }
+
+    public function broken()
+    {
+        die('OOPS');
+    }
+}
+
+$loader = new ArrayLoader([
+    'index.html.twig' => 'Hello {{ "world"|broken }}',
+]);
+$twig = new Environment($loader, ['debug' => isset($argv[1])]);
+$twig->addExtension(new BrokenExtension());
+
+echo $twig->render('index.html.twig');