Force the installation of the newly required packages in require command

src/Composer/Command/RequireCommand.php

@@ -17,6 +17,7 @@ use Symfony\Component\Console\Input\InputArgument;
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\OutputInterface;
 use Composer\Factory;
+use Composer\Installer;
 use Composer\Json\JsonFile;
 use Composer\Json\JsonManipulator;
 use Composer\Json\JsonValidationException;
@@ -32,13 +33,14 @@ class RequireCommand extends InitCommand
     {
         $this
             ->setName('require')
-            ->setDescription('Adds a required package to a composer.json')
+            ->setDescription('Adds required packages to your composer.json and installs them')
             ->setDefinition(array(
                 new InputArgument('packages', InputArgument::IS_ARRAY | InputArgument::OPTIONAL, 'Required package with a version constraint, e.g. foo/bar:1.0.0 or foo/bar=1.0.0 or "foo/bar 1.0.0"'),
                 new InputOption('dev', null, InputOption::VALUE_NONE, 'Add requirement to require-dev.'),
+                new InputOption('prefer-source', null, InputOption::VALUE_NONE, 'Forces installation from package sources when possible, including VCS information.'),
             ))
             ->setHelp(<<<EOT
-The require command adds requirements to your composer.json
+The require command adds required packages to your composer.json and installs them
 
 EOT
             )
@@ -80,6 +82,21 @@ EOT
         }
 
         $output->writeln('<info>'.$file.' has been updated</info>');
+
+        // Update packages
+        $composer = $this->getComposer();
+        $io = $this->getIO();
+        $install = Installer::create($io, $composer);
+
+        $install
+            ->setVerbose($input->getOption('verbose'))
+            ->setPreferSource($input->getOption('prefer-source'))
+            ->setDevMode($input->getOption('dev'))
+            ->setUpdate(true)
+            ->setUpdateWhitelist($requirements);
+        ;
+
+        return $install->run() ? 0 : 1;
     }
 
     private function updateFileCleanly($json, array $base, array $new, $requireKey)