Merge branch '3.4' into 4.4

* 3.4:
  Fix undefined index for inconsistent command name definition

Author: fabpot

src/Symfony/Component/Console/Application.php

@@ -513,6 +513,11 @@ public function get($name)
             throw new CommandNotFoundException(sprintf('The command "%s" does not exist.', $name));
         }
 
+        // When the command has a different name than the one used at the command loader level
+        if (!isset($this->commands[$name])) {
+            throw new CommandNotFoundException(sprintf('The "%s" command cannot be found because it is registered under multiple names. Make sure you don\'t set a different name via constructor or "setName()".', $name));
+        }
+
         $command = $this->commands[$name];
 
         if ($this->wantHelps) {

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

@@ -1802,6 +1802,20 @@ public function testThrowingErrorListener()
         $tester = new ApplicationTester($application);
         $tester->run(['command' => 'foo']);
     }
+
+    public function testCommandNameMismatchWithCommandLoaderKeyThrows()
+    {
+        $this->expectException(CommandNotFoundException::class);
+        $this->expectExceptionMessage('The "test" command cannot be found because it is registered under multiple names. Make sure you don\'t set a different name via constructor or "setName()".');
+
+        $app = new Application();
+        $loader = new FactoryCommandLoader([
+            'test' => static function () { return new Command('test-command'); },
+        ]);
+
+        $app->setCommandLoader($loader);
+        $app->get('test');
+    }
 }
 
 class CustomApplication extends Application