From a5628bdbe2fdb8267242678991f30b37edfd4b69 Mon Sep 17 00:00:00 2001
From: Matthieu Auger <mail@matthieuauger.com>
Date: Mon, 13 Oct 2014 00:36:35 +0200
Subject: [PATCH] Displays friendly message if the event does not have any
 registered listeners

---
 .../Command/EventDispatcherDebugCommand.php    | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/Symfony/Bundle/FrameworkBundle/Command/EventDispatcherDebugCommand.php b/src/Symfony/Bundle/FrameworkBundle/Command/EventDispatcherDebugCommand.php
index dff1c3d28fc5..f5cbd96d9eb7 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Command/EventDispatcherDebugCommand.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Command/EventDispatcherDebugCommand.php
@@ -58,14 +58,28 @@ protected function configure()
      */
     protected function execute(InputInterface $input, OutputInterface $output)
     {
+        $dispatcher = $this->getEventDispatcher();
+
         if ($event = $input->getArgument('event')) {
+            if (!$dispatcher->hasListeners($event)) {
+                $formatter = $this->getHelperSet()->get('formatter');
+
+                $formattedBlock = $formatter->formatBlock(
+                    sprintf('[NOTE] The event "%s" does not have any registered listeners.', $event),
+                    'fg=yellow',
+                    true
+                );
+
+                $output->writeln($formattedBlock);
+
+                return;
+            }
+
             $options = array('event' => $event);
         } else {
             $options = array();
         }
 
-        $dispatcher = $this->getEventDispatcher();
-
         $helper = new DescriptorHelper();
         $options['format'] = $input->getOption('format');
         $options['raw_text'] = $input->getOption('raw');