diff --git a/src/Symfony/Bundle/TwigBundle/Command/DebugCommand.php b/src/Symfony/Bundle/TwigBundle/Command/DebugCommand.php
new file mode 100644
index 0000000000000..a2bf79ee726fa
--- /dev/null
+++ b/src/Symfony/Bundle/TwigBundle/Command/DebugCommand.php
@@ -0,0 +1,187 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bundle\TwigBundle\Command;
+
+use Symfony\Bundle\FrameworkBundle\Command\ContainerAwareCommand;
+use Symfony\Component\Console\Input\InputArgument;
+use Symfony\Component\Console\Input\InputOption;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+/**
+ * Lists twig functions, filters, globals and tests present in the current project
+ *
+ * @author Jordi Boggiano <j.boggiano@seld.be>
+ */
+class DebugCommand extends ContainerAwareCommand
+{
+    protected function configure()
+    {
+        $this
+            ->setName('twig:debug')
+            ->setDefinition(array(
+                new InputArgument('filter', InputArgument::OPTIONAL, 'Show details for all entries matching this filter'),
+                new InputOption('format', null, InputOption::VALUE_REQUIRED, 'Output format: text or json', 'text'),
+            ))
+            ->setDescription('Shows a list of twig functions, filters, globals and tests')
+            ->setHelp(<<<EOF
+The <info>%command.name%</info> command outputs a list of twig functions,
+filters, globals and tests. Output can be filtered with an optional argument.
+
+<info>php %command.full_name%</info>
+
+The command lists all functions, filters, etc.
+
+<info>php %command.full_name% date</info>
+
+The command lists everything that contains the word date.
+
+<info>php %command.full_name% --format=json</info>
+
+The command lists everything in a machine readable json format.
+EOF
+            )
+        ;
+    }
+
+    protected function execute(InputInterface $input, OutputInterface $output)
+    {
+        $twig = $this->getContainer()->get('twig');
+        $types = array('functions', 'filters', 'tests', 'globals');
+
+        if ($input->getOption('format') === 'json') {
+            $data = array();
+            foreach ($types as $type) {
+                foreach ($twig->{'get'.ucfirst($type)}() as $name => $entity) {
+                    $data[$type][$name] = $this->getMetadata($type, $entity);
+                }
+            }
+            $data['tests'] = array_keys($data['tests']);
+            $output->writeln(json_encode($data));
+
+            return 0;
+        }
+
+        $filter = $input->getArgument('filter');
+
+        foreach ($types as $index => $type) {
+            $items = array();
+            foreach ($twig->{'get'.ucfirst($type)}() as $name => $entity) {
+                if (!$filter || false !== strpos($name, $filter)) {
+                    $items[$name] = $name . $this->getPrettyMetadata($type, $entity);
+                }
+            }
+
+            if (!$items) {
+                continue;
+            }
+            if ($index > 0) {
+                $output->writeln('');
+            }
+            $output->writeln('<info>' . ucfirst($type) . '</info>');
+            ksort($items);
+            foreach ($items as $item) {
+                $output->writeln('  '.$item);
+            }
+        }
+
+        return 0;
+    }
+
+    private function getMetadata($type, $entity)
+    {
+        if ($type === 'globals') {
+            return $entity;
+        }
+        if ($type === 'tests') {
+            return;
+        }
+        if ($type === 'functions' || $type === 'filters') {
+            $args = array();
+            $cb = $entity->getCallable();
+            if (is_null($cb)) {
+                return;
+            }
+            if (is_array($cb)) {
+                if (!method_exists($cb[0], $cb[1])) {
+                    return;
+                }
+                $refl = new \ReflectionMethod($cb[0], $cb[1]);
+            } elseif (is_object($cb) && is_callable($cb)) {
+                $refl = new \ReflectionMethod($cb, '__invoke');
+            } elseif (function_exists($cb)) {
+                $refl = new \ReflectionFunction($cb);
+            } elseif (is_string($cb) && preg_match('{^(.+)::(.+)$}', $cb, $m) && method_exists($m[1], $m[2])) {
+                $refl = new \ReflectionMethod($m[1], $m[2]);
+            } else {
+                throw new \UnexpectedValueException('Unsupported callback type');
+            }
+
+            // filter out context/environment args
+            $args = array_filter($refl->getParameters(), function ($param) use ($entity) {
+                if ($entity->needsContext() && $param->getName() === 'context') {
+                    return false;
+                }
+
+                return !$param->getClass() || $param->getClass()->getName() !== 'Twig_Environment';
+            });
+
+            // format args
+            $args = array_map(function ($param) {
+                if ($param->isDefaultValueAvailable()) {
+                    return $param->getName() . ' = ' . json_encode($param->getDefaultValue());
+                }
+
+                return $param->getName();
+            }, $args);
+
+            if ($type === 'filters') {
+                // remove the value the filter is applied on
+                array_shift($args);
+            }
+
+            return $args;
+        }
+    }
+
+    private function getPrettyMetadata($type, $entity)
+    {
+        if ($type === 'tests') {
+            return '';
+        }
+
+        try {
+            $meta = $this->getMetadata($type, $entity);
+            if ($meta === null) {
+                return '(unknown?)';
+            }
+        } catch (\UnexpectedValueException $e) {
+            return ' <error>' . $e->getMessage() . '</error>';
+        }
+
+        if ($type === 'globals') {
+            if (is_object($meta)) {
+                return ' = object('.get_class($meta).')';
+            }
+
+            return ' = '.substr(@json_encode($meta), 0, 50);
+        }
+
+        if ($type === 'functions') {
+            return '(' . implode(', ', $meta) . ')';
+        }
+
+        if ($type === 'filters') {
+            return $meta ? '(' . implode(', ', $meta) . ')' : '';
+        }
+    }
+}

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