[Console] Skip commands from ConsoleCommandEvent

Use case: We have different variations of the same application, for which
only certain commands are allowed. Right now this is done in a custom
Application class, but it would be much easier to just be able to skip
commands from a listener, where you can disable commands via the Event
object.

This patch provides this feature and corresponding test cases.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes - for Console tests
| Fixed tickets | None
| License       | MIT
| Doc PR        | None

src/Symfony/Component/Console/Application.php

@@ -892,6 +892,7 @@ class Application
         $event = new ConsoleCommandEvent($command, $input, $output);
         $this->dispatcher->dispatch(ConsoleEvents::COMMAND, $event);
 
+        if ($event->commandShouldRun()) {
             try {
                 $exitCode = $command->run($input, $output);
             } catch (\Exception $e) {
@@ -903,6 +904,9 @@ class Application
 
                 throw $event->getException();
             }
+        } else {
+            $exitCode = ConsoleCommandEvent::RETURN_CODE_DISABLED;
+        }
 
         $event = new ConsoleTerminateEvent($command, $input, $output, $exitCode);
         $this->dispatcher->dispatch(ConsoleEvents::TERMINATE, $event);

src/Symfony/Component/Console/Event/ConsoleCommandEvent.php

@@ -12,10 +12,51 @@
 namespace Symfony\Component\Console\Event;
 
 /**
- * Allows to do things before the command is executed.
+ * Allows to do things before the command is executed, like skipping the command or changing the input.
  *
  * @author Fabien Potencier <fabien@symfony.com>
  */
 class ConsoleCommandEvent extends ConsoleEvent
 {
+    /**
+     * The return code for skipped commands, this will also be passed into the terminate event
+     */
+    const RETURN_CODE_DISABLED = 113;
+
+    /**
+     * Indicates if the command should be run or skipped
+     *
+     * @var bool
+     */
+    private $commandShouldRun = true;
+
+    /**
+     * Disables the command, so it won't be run
+     *
+     * @return bool
+     */
+    public function disableCommand()
+    {
+        return $this->commandShouldRun = false;
+    }
+
+    /**
+     * Enables the command
+     *
+     * @return bool
+     */
+    public function enableCommand()
+    {
+        return $this->commandShouldRun = true;
+    }
+
+    /**
+     * Returns true if the command is runnable, false otherwise
+     *
+     * @return bool
+     */
+    public function commandShouldRun()
+    {
+        return $this->commandShouldRun;
+    }
 }

src/Symfony/Component/Console/Tests/ApplicationTest.php

@@ -891,6 +891,22 @@ class ApplicationTest extends \PHPUnit_Framework_TestCase
         $this->assertContains('before.foo.after.caught.', $tester->getDisplay());
     }
 
+    public function testRunWithDispatcherSkippingCommand()
+    {
+        $application = new Application();
+        $application->setDispatcher($this->getDispatcher(true));
+        $application->setAutoExit(false);
+
+        $application->register('foo')->setCode(function (InputInterface $input, OutputInterface $output) {
+            $output->write('foo.');
+        });
+
+        $tester = new ApplicationTester($application);
+        $exitCode = $tester->run(array('command' => 'foo'));
+        $this->assertContains('before.after.', $tester->getDisplay());
+        $this->assertEquals(ConsoleCommandEvent::RETURN_CODE_DISABLED, $exitCode);
+    }
+
     public function testTerminalDimensions()
     {
         $application = new Application();
@@ -906,16 +922,22 @@ class ApplicationTest extends \PHPUnit_Framework_TestCase
         $this->assertSame(array($width, 80), $application->getTerminalDimensions());
     }
 
-    protected function getDispatcher()
+    protected function getDispatcher($skipCommand = false)
     {
         $dispatcher = new EventDispatcher();
-        $dispatcher->addListener('console.command', function (ConsoleCommandEvent $event) {
+        $dispatcher->addListener('console.command', function (ConsoleCommandEvent $event) use ($skipCommand) {
             $event->getOutput()->write('before.');
+
+            if ($skipCommand) {
+                $event->disableCommand();
+            }
         });
-        $dispatcher->addListener('console.terminate', function (ConsoleTerminateEvent $event) {
+        $dispatcher->addListener('console.terminate', function (ConsoleTerminateEvent $event) use ($skipCommand) {
             $event->getOutput()->write('after.');
 
-            $event->setExitCode(128);
+            if (!$skipCommand) {
+                $event->setExitCode(113);
+            }
         });
         $dispatcher->addListener('console.exception', function (ConsoleExceptionEvent $event) {
             $event->getOutput()->writeln('caught.');