Implement writeError throughout Composer

src/Composer/Autoload/ClassMapGenerator.php

@@ -92,7 +92,7 @@ class ClassMapGenerator
                 if (!isset($map[$class])) {
                     $map[$class] = $filePath;
                 } elseif ($io && $map[$class] !== $filePath && !preg_match('{/(test|fixture|example)s?/}i', strtr($map[$class].' '.$filePath, '\\', '/'))) {
-                    $io->write(
+                    $io->writeError(
                         '<warning>Warning: Ambiguous class resolution, "'.$class.'"'.
                         ' was found in both "'.$map[$class].'" and "'.$filePath.'", the first will be used.</warning>'
                     );

src/Composer/Cache.php

@@ -65,7 +65,7 @@ class Cache
         $file = preg_replace('{[^'.$this->whitelist.']}i', '-', $file);
         if ($this->enabled && file_exists($this->root . $file)) {
             if ($this->io->isDebug()) {
-                $this->io->write('Reading '.$this->root . $file.' from cache');
+                $this->io->writeError('Reading '.$this->root . $file.' from cache');
             }
 
             return file_get_contents($this->root . $file);
@@ -80,7 +80,7 @@ class Cache
             $file = preg_replace('{[^'.$this->whitelist.']}i', '-', $file);
 
             if ($this->io->isDebug()) {
-                $this->io->write('Writing '.$this->root . $file.' into cache');
+                $this->io->writeError('Writing '.$this->root . $file.' into cache');
             }
 
             try {
@@ -98,7 +98,7 @@ class Cache
                         @disk_free_space($this->root . dirname($file))
                     );
 
-                    $this->io->write($message);
+                    $this->io->writeError($message);
 
                     return false;
                 }
@@ -120,7 +120,7 @@ class Cache
             $this->filesystem->ensureDirectoryExists(dirname($this->root . $file));
 
             if ($this->io->isDebug()) {
-                $this->io->write('Writing '.$this->root . $file.' into cache');
+                $this->io->writeError('Writing '.$this->root . $file.' into cache');
             }
 
             return copy($source, $this->root . $file);
@@ -139,7 +139,7 @@ class Cache
             touch($this->root . $file);
 
             if ($this->io->isDebug()) {
-                $this->io->write('Reading '.$this->root . $file.' from cache');
+                $this->io->writeError('Reading '.$this->root . $file.' from cache');
             }
 
             return copy($this->root . $file, $target);

src/Composer/Command/AboutCommand.php

@@ -34,7 +34,7 @@ EOT
 
     protected function execute(InputInterface $input, OutputInterface $output)
     {
-        $output->writeln(<<<EOT
+        $this->getIO()->write(<<<EOT
 <info>Composer - Package Management for PHP</info>
 <comment>Composer is a dependency manager tracking local dependencies of your projects and libraries.
 See http://getcomposer.org/ for more information.</comment>

src/Composer/Command/ArchiveCommand.php

@@ -97,7 +97,7 @@ EOT
             $package = $this->getComposer()->getPackage();
         }
 
-        $io->write('<info>Creating the archive.</info>');
+        $io->writeError('<info>Creating the archive.</info>');
         $archiveManager->archive($package, $format, $dest);
 
         return 0;
@@ -105,14 +105,14 @@ EOT
 
     protected function selectPackage(IOInterface $io, $packageName, $version = null)
     {
-        $io->write('<info>Searching for the specified package.</info>');
+        $io->writeError('<info>Searching for the specified package.</info>');
 
         if ($composer = $this->getComposer(false)) {
             $localRepo = $composer->getRepositoryManager()->getLocalRepository();
             $repos = new CompositeRepository(array_merge(array($localRepo), $composer->getRepositoryManager()->getRepositories()));
         } else {
             $defaultRepos = Factory::createDefaultRepositories($this->getIO());
-            $io->write('No composer.json found in the current directory, searching packages from ' . implode(', ', array_keys($defaultRepos)));
+            $io->writeError('No composer.json found in the current directory, searching packages from ' . implode(', ', array_keys($defaultRepos)));
             $repos = new CompositeRepository($defaultRepos);
         }
 
@@ -125,14 +125,14 @@ EOT
 
         if (count($packages) > 1) {
             $package = reset($packages);
-            $io->write('<info>Found multiple matches, selected '.$package->getPrettyString().'.</info>');
-            $io->write('Alternatives were '.implode(', ', array_map(function ($p) { return $p->getPrettyString(); }, $packages)).'.');
-            $io->write('<comment>Please use a more specific constraint to pick a different package.</comment>');
+            $io->writeError('<info>Found multiple matches, selected '.$package->getPrettyString().'.</info>');
+            $io->writeError('Alternatives were '.implode(', ', array_map(function ($p) { return $p->getPrettyString(); }, $packages)).'.');
+            $io->writeError('<comment>Please use a more specific constraint to pick a different package.</comment>');
         } elseif ($packages) {
             $package = reset($packages);
-            $io->write('<info>Found an exact match '.$package->getPrettyString().'.</info>');
+            $io->writeError('<info>Found an exact match '.$package->getPrettyString().'.</info>');
         } else {
-            $io->write('<error>Could not find a package matching '.$packageName.'.</error>');
+            $io->writeError('<error>Could not find a package matching '.$packageName.'.</error>');
 
             return false;
         }

src/Composer/Command/ClearCacheCommand.php

@@ -51,21 +51,21 @@ EOT
         foreach ($cachePaths as $key => $cachePath) {
             $cachePath = realpath($cachePath);
             if (!$cachePath) {
-                $io->write("<info>Cache directory does not exist ($key): $cachePath</info>");
+                $io->writeError("<info>Cache directory does not exist ($key): $cachePath</info>");
 
                 return;
             }
             $cache = new Cache($io, $cachePath);
             if (!$cache->isEnabled()) {
-                $io->write("<info>Cache is not enabled ($key): $cachePath</info>");
+                $io->writeError("<info>Cache is not enabled ($key): $cachePath</info>");
 
                 return;
             }
 
-            $io->write("<info>Clearing cache ($key): $cachePath</info>");
+            $io->writeError("<info>Clearing cache ($key): $cachePath</info>");
             $cache->gc(0, 0);
         }
 
-        $io->write('<info>All caches cleared.</info>');
+        $io->writeError('<info>All caches cleared.</info>');
     }
 }

src/Composer/Command/ConfigCommand.php

@@ -33,15 +33,25 @@ class ConfigCommand extends Command
     protected $config;
 
     /**
-     * @var Composer\Json\JsonFile
+     * @var JsonFile
      */
     protected $configFile;
 
     /**
-     * @var Composer\Config\JsonConfigSource
+     * @var JsonConfigSource
      */
     protected $configSource;
 
+    /**
+     * @var JsonFile
+     */
+    protected $authConfigFile;
+
+    /**
+     * @var JsonConfigSource
+     */
+    protected $authConfigSource;
+
     /**
      * {@inheritDoc}
      */
@@ -247,7 +257,7 @@ EOT
                 $value = json_encode($value);
             }
 
-            $output->writeln($value);
+            $this->getIO()->write($value);
 
             return 0;
         }
@@ -474,9 +484,9 @@ EOT
             }
 
             if (is_string($rawVal) && $rawVal != $value) {
-                $output->writeln('[<comment>' . $k . $key . '</comment>] <info>' . $rawVal . ' (' . $value . ')</info>');
+                $this->getIO()->write('[<comment>' . $k . $key . '</comment>] <info>' . $rawVal . ' (' . $value . ')</info>');
             } else {
-                $output->writeln('[<comment>' . $k . $key . '</comment>] <info>' . $value . '</info>');
+                $this->getIO()->write('[<comment>' . $k . $key . '</comment>] <info>' . $value . '</info>');
             }
         }
     }

src/Composer/Command/CreateProjectCommand.php

@@ -106,7 +106,7 @@ EOT
         $this->updatePreferredOptions($config, $input, $preferSource, $preferDist);
 
         if ($input->getOption('no-custom-installers')) {
-            $output->writeln('<warning>You are using the deprecated option "no-custom-installers". Use "no-plugins" instead.</warning>');
+            $this->getIO()->writeError('<warning>You are using the deprecated option "no-custom-installers". Use "no-plugins" instead.</warning>');
             $input->setOption('no-plugins', true);
         }
 
@@ -196,7 +196,7 @@ EOT
                     }
                 }
             } catch (\Exception $e) {
-                $io->write('<error>An error occurred while removing the VCS metadata: '.$e->getMessage().'</error>');
+                $io->writeError('<error>An error occurred while removing the VCS metadata: '.$e->getMessage().'</error>');
             }
 
             $hasVcs = false;
@@ -288,10 +288,10 @@ EOT
             $directory = getcwd() . DIRECTORY_SEPARATOR . array_pop($parts);
         }
 
-        $io->write('<info>Installing ' . $package->getName() . ' (' . VersionParser::formatVersion($package, false) . ')</info>');
+        $io->writeError('<info>Installing ' . $package->getName() . ' (' . VersionParser::formatVersion($package, false) . ')</info>');
 
         if ($disablePlugins) {
-            $io->write('<info>Plugins have been disabled.</info>');
+            $io->writeError('<info>Plugins have been disabled.</info>');
         }
 
         if (0 === strpos($package->getPrettyVersion(), 'dev-') && in_array($package->getSourceType(), array('git', 'hg'))) {
@@ -311,7 +311,7 @@ EOT
 
         $installedFromVcs = 'source' === $package->getInstallationSource();
 
-        $io->write('<info>Created project in ' . $directory . '</info>');
+        $io->writeError('<info>Created project in ' . $directory . '</info>');
         chdir($directory);
 
         putenv('COMPOSER_ROOT_VERSION='.$package->getPrettyVersion());

src/Composer/Command/DependsCommand.php

@@ -96,9 +96,9 @@ EOT
 
         if ($messages) {
             sort($messages);
-            $output->writeln($messages);
+            $this->getIO()->write($messages);
         } else {
-            $output->writeln('<info>There is no installed package depending on "'.$needle.'".</info>');
+            $this->getIO()->writeError('<info>There is no installed package depending on "'.$needle.'".</info>');
         }
     }
 }

src/Composer/Command/DiagnoseCommand.php

@@ -59,8 +59,8 @@ EOT
             $commandEvent = new CommandEvent(PluginEvents::COMMAND, 'diagnose', $input, $output);
             $composer->getEventDispatcher()->dispatch($commandEvent->getName(), $commandEvent);
 
-            $output->write('Checking composer.json: ');
-            $this->outputResult($output, $this->checkComposerSchema());
+            $this->getIO()->write('Checking composer.json: ', false);
+            $this->outputResult($this->checkComposerSchema());
         }
 
         if ($composer) {
@@ -72,37 +72,37 @@ EOT
         $this->rfs = new RemoteFilesystem($this->getIO(), $config);
         $this->process = new ProcessExecutor($this->getIO());
 
-        $output->write('Checking platform settings: ');
-        $this->outputResult($output, $this->checkPlatform());
+        $this->getIO()->write('Checking platform settings: ', false);
+        $this->outputResult($this->checkPlatform());
 
-        $output->write('Checking git settings: ');
-        $this->outputResult($output, $this->checkGit());
+        $this->getIO()->write('Checking git settings: ', false);
+        $this->outputResult($this->checkGit());
 
-        $output->write('Checking http connectivity: ');
-        $this->outputResult($output, $this->checkHttp());
+        $this->getIO()->write('Checking http connectivity: ', false);
+        $this->outputResult($this->checkHttp());
 
         $opts = stream_context_get_options(StreamContextFactory::getContext('http://example.org'));
         if (!empty($opts['http']['proxy'])) {
-            $output->write('Checking HTTP proxy: ');
-            $this->outputResult($output, $this->checkHttpProxy());
-            $output->write('Checking HTTP proxy support for request_fulluri: ');
-            $this->outputResult($output, $this->checkHttpProxyFullUriRequestParam());
-            $output->write('Checking HTTPS proxy support for request_fulluri: ');
-            $this->outputResult($output, $this->checkHttpsProxyFullUriRequestParam());
+            $this->getIO()->write('Checking HTTP proxy: ', false);
+            $this->outputResult($this->checkHttpProxy());
+            $this->getIO()->write('Checking HTTP proxy support for request_fulluri: ', false);
+            $this->outputResult($this->checkHttpProxyFullUriRequestParam());
+            $this->getIO()->write('Checking HTTPS proxy support for request_fulluri: ', false);
+            $this->outputResult($this->checkHttpsProxyFullUriRequestParam());
         }
 
         if ($oauth = $config->get('github-oauth')) {
             foreach ($oauth as $domain => $token) {
-                $output->write('Checking '.$domain.' oauth access: ');
-                $this->outputResult($output, $this->checkGithubOauth($domain, $token));
+                $this->getIO()->write('Checking '.$domain.' oauth access: ', false);
+                $this->outputResult($this->checkGithubOauth($domain, $token));
             }
         } else {
-            $output->write('Checking github.com rate limit: ');
+            $this->getIO()->write('Checking github.com rate limit: ', false);
             $rate = $this->getGithubRateLimit('github.com');
 
             if (10 > $rate['remaining']) {
-                $output->writeln('<warning>WARNING</warning>');
-                $output->writeln(sprintf(
+                $this->getIO()->write('<warning>WARNING</warning>');
+                $this->getIO()->write(sprintf(
                     '<comment>Github has a rate limit on their API. '
                     . 'You currently have <options=bold>%u</options=bold> '
                     . 'out of <options=bold>%u</options=bold> requests left.' . PHP_EOL
@@ -112,15 +112,15 @@ EOT
                     $rate['limit']
                 ));
             } else {
-                $output->writeln('<info>OK</info>');
+                $this->getIO()->write('<info>OK</info>');
             }
         }
 
-        $output->write('Checking disk free space: ');
-        $this->outputResult($output, $this->checkDiskSpace($config));
+        $this->getIO()->write('Checking disk free space: ', false);
+        $this->outputResult($this->checkDiskSpace($config));
 
-        $output->write('Checking composer version: ');
-        $this->outputResult($output, $this->checkVersion());
+        $this->getIO()->write('Checking composer version: ', false);
+        $this->outputResult($this->checkVersion());
 
         return $this->failures;
     }
@@ -308,17 +308,17 @@ EOT
         return true;
     }
 
-    private function outputResult(OutputInterface $output, $result)
+    private function outputResult($result)
     {
         if (true === $result) {
-            $output->writeln('<info>OK</info>');
+            $this->getIO()->write('<info>OK</info>');
         } else {
             $this->failures++;
-            $output->writeln('<error>FAIL</error>');
+            $this->getIO()->write('<error>FAIL</error>');
             if ($result instanceof \Exception) {
-                $output->writeln('['.get_class($result).'] '.$result->getMessage());
+                $this->getIO()->write('['.get_class($result).'] '.$result->getMessage());
             } elseif ($result) {
-                $output->writeln(trim($result));
+                $this->getIO()->write(trim($result));
             }
         }
     }

src/Composer/Command/DumpAutoloadCommand.php

@@ -55,9 +55,9 @@ EOT
         $optimize = $input->getOption('optimize') || $config->get('optimize-autoloader') || $config->get('classmap-authoritative');
 
         if ($optimize) {
-            $output->writeln('<info>Generating optimized autoload files</info>');
+            $this->getIO()->writeError('<info>Generating optimized autoload files</info>');
         } else {
-            $output->writeln('<info>Generating autoload files</info>');
+            $this->getIO()->writeError('<info>Generating autoload files</info>');
         }
 
         $generator = $composer->getAutoloadGenerator();

src/Composer/Command/GlobalCommand.php

@@ -72,7 +72,7 @@ EOT
         // change to global dir
         $config = Factory::createConfig();
         chdir($config->get('home'));
-        $output->writeln('<info>Changed current directory to '.$config->get('home').'</info>');
+        $this->getIO()->writeError('<info>Changed current directory to '.$config->get('home').'</info>');
 
         // create new input without "global" command prefix
         $input = new StringInput(preg_replace('{\bg(?:l(?:o(?:b(?:a(?:l)?)?)?)?)?\b}', '', $input->__toString(), 1));

src/Composer/Command/HomeCommand.php

@@ -71,7 +71,7 @@ EOT
 
             if (!$package instanceof CompletePackageInterface) {
                 $return = 1;
-                $output->writeln('<warning>Package '.$packageName.' not found</warning>');
+                $this->getIO()->writeError('<warning>Package '.$packageName.' not found</warning>');
 
                 continue;
             }
@@ -84,13 +84,13 @@ EOT
 
             if (!filter_var($url, FILTER_VALIDATE_URL)) {
                 $return = 1;
-                $output->writeln('<warning>'.($input->getOption('homepage') ? 'Invalid or missing homepage' : 'Invalid or missing repository URL').' for '.$packageName.'</warning>');
+                $this->getIO()->writeError('<warning>'.($input->getOption('homepage') ? 'Invalid or missing homepage' : 'Invalid or missing repository URL').' for '.$packageName.'</warning>');
 
                 continue;
             }
 
             if ($input->getOption('show')) {
-                $output->writeln(sprintf('<info>%s</info>', $url));
+                $this->getIO()->write(sprintf('<info>%s</info>', $url));
             } else {
                 $this->openBrowser($url);
             }
@@ -145,7 +145,7 @@ EOT
         } elseif (0 === $osx) {
             passthru('open ' . $url);
         } else {
-            $this->getIO()->write('no suitable browser opening command found, open yourself: ' . $url);
+            $this->getIO()->writeError('no suitable browser opening command found, open yourself: ' . $url);
         }
     }
 

src/Composer/Command/InitCommand.php

@@ -117,13 +117,13 @@ EOT
         $json = $file->encode($options);
 
         if ($input->isInteractive()) {
-            $output->writeln(array(
+            $this->getIO()->writeError(array(
                 '',
                 $json,
                 ''
             ));
             if (!$dialog->askConfirmation($output, $dialog->getQuestion('Do you confirm generation', 'yes', '?'), true)) {
-                $output->writeln('<error>Command aborted</error>');
+                $this->getIO()->writeError('<error>Command aborted</error>');
 
                 return 1;
             }
@@ -154,14 +154,14 @@ EOT
 
         $dialog = $this->getHelperSet()->get('dialog');
         $formatter = $this->getHelperSet()->get('formatter');
-        $output->writeln(array(
+        $this->getIO()->writeError(array(
             '',
             $formatter->formatBlock('Welcome to the Composer config generator', 'bg=blue;fg=white', true),
             ''
         ));
 
         // namespace
-        $output->writeln(array(
+        $this->getIO()->writeError(array(
             '',
             'This command will guide you through creating your composer.json config.',
             '',
@@ -266,7 +266,7 @@ EOT
         );
         $input->setOption('license', $license);
 
-        $output->writeln(array(
+        $this->getIO()->writeError(array(
             '',
             'Define your dependencies.',
             ''
@@ -316,7 +316,7 @@ EOT
                     $version = $this->findBestVersionForPackage($input, $requirement['name']);
                     $requirement['version'] = $version;
 
-                    $output->writeln(sprintf(
+                    $this->getIO()->writeError(sprintf(
                         'Using version <info>%s</info> for <info>%s</info>',
                         $requirement['version'],
                         $requirement['name']
@@ -345,14 +345,14 @@ EOT
 
                 // no match, prompt which to pick
                 if (!$exactMatch) {
-                    $output->writeln(array(
+                    $this->getIO()->writeError(array(
                         '',
                         sprintf('Found <info>%s</info> packages matching <info>%s</info>', count($matches), $package),
                         ''
                     ));
 
-                    $output->writeln($choices);
-                    $output->writeln('');
+                    $this->getIO()->writeError($choices);
+                    $this->getIO()->writeError('');
 
                     $validator = function ($selection) use ($matches) {
                         if ('' === $selection) {
@@ -392,7 +392,7 @@ EOT
                     if (false === $constraint) {
                         $constraint = $this->findBestVersionForPackage($input, $package);
 
-                        $output->writeln(sprintf(
+                        $this->getIO()->writeError(sprintf(
                             'Using version <info>%s</info> for <info>%s</info>',
                             $constraint,
                             $package

src/Composer/Command/InstallCommand.php

@@ -65,18 +65,18 @@ EOT
     protected function execute(InputInterface $input, OutputInterface $output)
     {
         if ($args = $input->getArgument('packages')) {
-            $output->writeln('<error>Invalid argument '.implode(' ', $args).'. Use "composer require '.implode(' ', $args).'" instead to add packages to your composer.json.</error>');
+            $this->getIO()->writeError('<error>Invalid argument '.implode(' ', $args).'. Use "composer require '.implode(' ', $args).'" instead to add packages to your composer.json.</error>');
 
             return 1;
         }
 
         if ($input->getOption('no-custom-installers')) {
-            $output->writeln('<warning>You are using the deprecated option "no-custom-installers". Use "no-plugins" instead.</warning>');
+            $this->getIO()->writeError('<warning>You are using the deprecated option "no-custom-installers". Use "no-plugins" instead.</warning>');
             $input->setOption('no-plugins', true);
         }
 
         if ($input->getOption('dev')) {
-            $output->writeln('<warning>You are using the deprecated option "dev". Dev packages are installed by default now.</warning>');
+            $this->getIO()->writeError('<warning>You are using the deprecated option "dev". Dev packages are installed by default now.</warning>');
         }
 
         $composer = $this->getComposer(true, $input->getOption('no-plugins'));

src/Composer/Command/LicensesCommand.php

@@ -68,10 +68,10 @@ EOT
 
         switch ($format = $input->getOption('format')) {
             case 'text':
-                $output->writeln('Name: <comment>'.$root->getPrettyName().'</comment>');
-                $output->writeln('Version: <comment>'.$versionParser->formatVersion($root).'</comment>');
-                $output->writeln('Licenses: <comment>'.(implode(', ', $root->getLicense()) ?: 'none').'</comment>');
-                $output->writeln('Dependencies:');
+                $this->getIO()->write('Name: <comment>'.$root->getPrettyName().'</comment>');
+                $this->getIO()->write('Version: <comment>'.$versionParser->formatVersion($root).'</comment>');
+                $this->getIO()->write('Licenses: <comment>'.(implode(', ', $root->getLicense()) ?: 'none').'</comment>');
+                $this->getIO()->write('Dependencies:');
 
                 $table = new Table($output);
                 $table->setStyle('borderless');
@@ -94,7 +94,7 @@ EOT
                     );
                 }
 
-                $output->writeln(JsonFile::encode(array(
+                $this->getIO()->write(JsonFile::encode(array(
                     'name'         => $root->getPrettyName(),
                     'version'      => $versionParser->formatVersion($root),
                     'license'      => $root->getLicense(),

src/Composer/Command/RemoveCommand.php

@@ -73,7 +73,7 @@ EOT
             if (isset($composer[$type][$package])) {
                 $json->removeLink($type, $package);
             } elseif (isset($composer[$altType][$package])) {
-                $output->writeln('<warning>'.$package.' could not be found in '.$type.' but it is present in '.$altType.'</warning>');
+                $this->getIO()->writeError('<warning>'.$package.' could not be found in '.$type.' but it is present in '.$altType.'</warning>');
                 $dialog = $this->getHelperSet()->get('dialog');
                 if ($this->getIO()->isInteractive()) {
                     if ($dialog->askConfirmation($output, $dialog->getQuestion('Do you want to remove it from '.$altType, 'yes', '?'), true)) {
@@ -81,7 +81,7 @@ EOT
                     }
                 }
             } else {
-                $output->writeln('<warning>'.$package.' is not required in your composer.json and has not been removed</warning>');
+                $this->getIO()->writeError('<warning>'.$package.' is not required in your composer.json and has not been removed</warning>');
             }
         }
 
@@ -111,7 +111,7 @@ EOT
 
         $status = $install->run();
         if ($status !== 0) {
-            $output->writeln("\n".'<error>Removal failed, reverting '.$file.' to its original content.</error>');
+            $this->getIO()->writeError("\n".'<error>Removal failed, reverting '.$file.' to its original content.</error>');
             file_put_contents($jsonFile->getPath(), $composerBackup);
         }
 

src/Composer/Command/RequireCommand.php

@@ -67,17 +67,17 @@ EOT
 
         $newlyCreated = !file_exists($file);
         if (!file_exists($file) && !file_put_contents($file, "{\n}\n")) {
-            $output->writeln('<error>'.$file.' could not be created.</error>');
+            $this->getIO()->writeError('<error>'.$file.' could not be created.</error>');
 
             return 1;
         }
         if (!is_readable($file)) {
-            $output->writeln('<error>'.$file.' is not readable.</error>');
+            $this->getIO()->writeError('<error>'.$file.' is not readable.</error>');
 
             return 1;
         }
         if (!is_writable($file)) {
-            $output->writeln('<error>'.$file.' is not writable.</error>');
+            $this->getIO()->writeError('<error>'.$file.' is not writable.</error>');
 
             return 1;
         }
@@ -122,7 +122,7 @@ EOT
             $json->write($composerDefinition);
         }
 
-        $output->writeln('<info>'.$file.' has been '.($newlyCreated ? 'created' : 'updated').'</info>');
+        $this->getIO()->writeError('<info>'.$file.' has been '.($newlyCreated ? 'created' : 'updated').'</info>');
 
         if ($input->getOption('no-update')) {
             return 0;
@@ -154,10 +154,10 @@ EOT
         $status = $install->run();
         if ($status !== 0) {
             if ($newlyCreated) {
-                $output->writeln("\n".'<error>Installation failed, deleting '.$file.'.</error>');
+                $this->getIO()->writeError("\n".'<error>Installation failed, deleting '.$file.'.</error>');
                 unlink($json->getPath());
             } else {
-                $output->writeln("\n".'<error>Installation failed, reverting '.$file.' to its original content.</error>');
+                $this->getIO()->writeError("\n".'<error>Installation failed, reverting '.$file.' to its original content.</error>');
                 file_put_contents($json->getPath(), $composerBackup);
             }
         }

src/Composer/Command/RunScriptCommand.php

@@ -66,7 +66,7 @@ EOT
     protected function execute(InputInterface $input, OutputInterface $output)
     {
         if ($input->getOption('list')) {
-            return $this->listScripts($input, $output);
+            return $this->listScripts();
         } elseif (!$input->getArgument('script')) {
             throw new \RunTimeException('Missing required argument "script"');
         }
@@ -95,7 +95,7 @@ EOT
         return $composer->getEventDispatcher()->dispatchScript($script, $input->getOption('dev') || !$input->getOption('no-dev'), $args);
     }
 
-    protected function listScripts(InputInterface $input, OutputInterface $output)
+    protected function listScripts()
     {
         $scripts = $this->getComposer()->getPackage()->getScripts();
 
@@ -103,9 +103,9 @@ EOT
             return 0;
         }
 
-        $output->writeln('<info>scripts:</info>');
+        $this->getIO()->writeError('<info>scripts:</info>');
         foreach ($scripts as $name => $script) {
-            $output->writeln('  ' . $name);
+            $this->getIO()->write('  ' . $name);
         }
 
         return 0;

src/Composer/Command/SearchCommand.php

@@ -62,7 +62,7 @@ EOT
             $repos = new CompositeRepository(array_merge(array($installedRepo), $composer->getRepositoryManager()->getRepositories()));
         } else {
             $defaultRepos = Factory::createDefaultRepositories($this->getIO());
-            $output->writeln('No composer.json found in the current directory, showing packages from ' . implode(', ', array_keys($defaultRepos)));
+            $this->getIO()->writeError('No composer.json found in the current directory, showing packages from ' . implode(', ', array_keys($defaultRepos)));
             $installedRepo = $platformRepo;
             $repos = new CompositeRepository(array_merge(array($installedRepo), $defaultRepos));
         }
@@ -78,7 +78,7 @@ EOT
         $results = $repos->search(implode(' ', $input->getArgument('tokens')), $flags);
 
         foreach ($results as $result) {
-            $output->writeln($result['name'] . (isset($result['description']) ? ' '. $result['description'] : ''));
+            $this->getIO()->write($result['name'] . (isset($result['description']) ? ' '. $result['description'] : ''));
         }
     }
 }

src/Composer/Command/SelfUpdateCommand.php

@@ -84,13 +84,13 @@ EOT
         $updateVersion = $input->getArgument('version') ?: $latestVersion;
 
         if (preg_match('{^[0-9a-f]{40}$}', $updateVersion) && $updateVersion !== $latestVersion) {
-            $output->writeln('<error>You can not update to a specific SHA-1 as those phars are not available for download</error>');
+            $this->getIO()->writeError('<error>You can not update to a specific SHA-1 as those phars are not available for download</error>');
 
             return 1;
         }
 
         if (Composer::VERSION === $updateVersion) {
-            $output->writeln('<info>You are already using composer version '.$updateVersion.'.</info>');
+            $this->getIO()->writeError('<info>You are already using composer version '.$updateVersion.'.</info>');
 
             return 0;
         }
@@ -104,11 +104,11 @@ EOT
             self::OLD_INSTALL_EXT
         );
 
-        $output->writeln(sprintf("Updating to version <info>%s</info>.", $updateVersion));
+        $this->getIO()->writeError(sprintf("Updating to version <info>%s</info>.", $updateVersion));
         $remoteFilename = $baseUrl . (preg_match('{^[0-9a-f]{40}$}', $updateVersion) ? '/composer.phar' : "/download/{$updateVersion}/composer.phar");
         $remoteFilesystem->copy(self::HOMEPAGE, $remoteFilename, $tempFilename, !$input->getOption('no-progress'));
         if (!file_exists($tempFilename)) {
-            $output->writeln('<error>The download of the new composer version failed for an unexpected reason</error>');
+            $this->getIO()->writeError('<error>The download of the new composer version failed for an unexpected reason</error>');
 
             return 1;
         }
@@ -120,22 +120,22 @@ EOT
             $fs = new Filesystem;
             foreach ($finder as $file) {
                 $file = (string) $file;
-                $output->writeln('<info>Removing: '.$file.'</info>');
+                $this->getIO()->writeError('<info>Removing: '.$file.'</info>');
                 $fs->remove($file);
             }
         }
 
         if ($err = $this->setLocalPhar($localFilename, $tempFilename, $backupFile)) {
-            $output->writeln('<error>The file is corrupted ('.$err->getMessage().').</error>');
-            $output->writeln('<error>Please re-run the self-update command to try again.</error>');
+            $this->getIO()->writeError('<error>The file is corrupted ('.$err->getMessage().').</error>');
+            $this->getIO()->writeError('<error>Please re-run the self-update command to try again.</error>');
 
             return 1;
         }
 
         if (file_exists($backupFile)) {
-            $output->writeln('Use <info>composer self-update --rollback</info> to return to version '.Composer::VERSION);
+            $this->getIO()->writeError('Use <info>composer self-update --rollback</info> to return to version '.Composer::VERSION);
         } else {
-            $output->writeln('<warning>A backup of the current version could not be written to '.$backupFile.', no rollback possible</warning>');
+            $this->getIO()->writeError('<warning>A backup of the current version could not be written to '.$backupFile.', no rollback possible</warning>');
         }
     }
 
@@ -160,9 +160,9 @@ EOT
         }
 
         $oldFile = $rollbackDir . "/{$rollbackVersion}" . self::OLD_INSTALL_EXT;
-        $output->writeln(sprintf("Rolling back to version <info>%s</info>.", $rollbackVersion));
+        $this->getIO()->writeError(sprintf("Rolling back to version <info>%s</info>.", $rollbackVersion));
         if ($err = $this->setLocalPhar($localFilename, $oldFile)) {
-            $output->writeln('<error>The backup file was corrupted ('.$err->getMessage().') and has been removed.</error>');
+            $this->getIO()->writeError('<error>The backup file was corrupted ('.$err->getMessage().') and has been removed.</error>');
 
             return 1;
         }

src/Composer/Command/ShowCommand.php

@@ -84,7 +84,7 @@ EOT
             } else {
                 $defaultRepos = Factory::createDefaultRepositories($this->getIO());
                 $repos = new CompositeRepository($defaultRepos);
-                $output->writeln('No composer.json found in the current directory, showing available packages from ' . implode(', ', array_keys($defaultRepos)));
+                $this->getIO()->writeError('No composer.json found in the current directory, showing available packages from ' . implode(', ', array_keys($defaultRepos)));
             }
         } elseif ($composer) {
             $localRepo = $composer->getRepositoryManager()->getLocalRepository();
@@ -92,7 +92,7 @@ EOT
             $repos = new CompositeRepository(array_merge(array($installedRepo), $composer->getRepositoryManager()->getRepositories()));
         } else {
             $defaultRepos = Factory::createDefaultRepositories($this->getIO());
-            $output->writeln('No composer.json found in the current directory, showing available packages from ' . implode(', ', array_keys($defaultRepos)));
+            $this->getIO()->writeError('No composer.json found in the current directory, showing available packages from ' . implode(', ', array_keys($defaultRepos)));
             $installedRepo = $platformRepo;
             $repos = new CompositeRepository(array_merge(array($installedRepo), $defaultRepos));
         }
@@ -119,9 +119,9 @@ EOT
             $this->printLinks($input, $output, $package, 'requires');
             $this->printLinks($input, $output, $package, 'devRequires', 'requires (dev)');
             if ($package->getSuggests()) {
-                $output->writeln("\n<info>suggests</info>");
+                $this->getIO()->write("\n<info>suggests</info>");
                 foreach ($package->getSuggests() as $suggested => $reason) {
-                    $output->writeln($suggested . ' <comment>' . $reason . '</comment>');
+                    $this->getIO()->write($suggested . ' <comment>' . $reason . '</comment>');
                 }
             }
             $this->printLinks($input, $output, $package, 'provides');
@@ -172,7 +172,7 @@ EOT
         foreach (array('<info>platform</info>:' => true, '<comment>available</comment>:' => false, '<info>installed</info>:' => true) as $type => $showVersion) {
             if (isset($packages[$type])) {
                 if ($tree) {
-                    $output->writeln($type);
+                    $this->getIO()->write($type);
                 }
                 ksort($packages[$type]);
 
@@ -222,10 +222,10 @@ EOT
                     } else {
                         $output->write($indent . $package);
                     }
-                    $output->writeln('');
+                    $this->getIO()->write('');
                 }
                 if ($tree) {
-                    $output->writeln('');
+                    $this->getIO()->write('');
                 }
             }
         }
@@ -285,53 +285,53 @@ EOT
      */
     protected function printMeta(InputInterface $input, OutputInterface $output, CompletePackageInterface $package, array $versions, RepositoryInterface $installedRepo, RepositoryInterface $repos)
     {
-        $output->writeln('<info>name</info>     : ' . $package->getPrettyName());
-        $output->writeln('<info>descrip.</info> : ' . $package->getDescription());
-        $output->writeln('<info>keywords</info> : ' . join(', ', $package->getKeywords() ?: array()));
+        $this->getIO()->write('<info>name</info>     : ' . $package->getPrettyName());
+        $this->getIO()->write('<info>descrip.</info> : ' . $package->getDescription());
+        $this->getIO()->write('<info>keywords</info> : ' . join(', ', $package->getKeywords() ?: array()));
         $this->printVersions($input, $output, $package, $versions, $installedRepo, $repos);
-        $output->writeln('<info>type</info>     : ' . $package->getType());
-        $output->writeln('<info>license</info>  : ' . implode(', ', $package->getLicense()));
-        $output->writeln('<info>source</info>   : ' . sprintf('[%s] <comment>%s</comment> %s', $package->getSourceType(), $package->getSourceUrl(), $package->getSourceReference()));
-        $output->writeln('<info>dist</info>     : ' . sprintf('[%s] <comment>%s</comment> %s', $package->getDistType(), $package->getDistUrl(), $package->getDistReference()));
-        $output->writeln('<info>names</info>    : ' . implode(', ', $package->getNames()));
+        $this->getIO()->write('<info>type</info>     : ' . $package->getType());
+        $this->getIO()->write('<info>license</info>  : ' . implode(', ', $package->getLicense()));
+        $this->getIO()->write('<info>source</info>   : ' . sprintf('[%s] <comment>%s</comment> %s', $package->getSourceType(), $package->getSourceUrl(), $package->getSourceReference()));
+        $this->getIO()->write('<info>dist</info>     : ' . sprintf('[%s] <comment>%s</comment> %s', $package->getDistType(), $package->getDistUrl(), $package->getDistReference()));
+        $this->getIO()->write('<info>names</info>    : ' . implode(', ', $package->getNames()));
 
         if ($package->isAbandoned()) {
             $replacement = ($package->getReplacementPackage() !== null)
                 ? ' The author suggests using the ' . $package->getReplacementPackage(). ' package instead.'
                 : null;
 
-            $output->writeln(
+            $this->getIO()->writeError(
                 sprintf('<error>Attention: This package is abandoned and no longer maintained.%s</error>', $replacement)
             );
         }
 
         if ($package->getSupport()) {
-            $output->writeln("\n<info>support</info>");
+            $this->getIO()->write("\n<info>support</info>");
             foreach ($package->getSupport() as $type => $value) {
-                $output->writeln('<comment>' . $type . '</comment> : '.$value);
+                $this->getIO()->write('<comment>' . $type . '</comment> : '.$value);
             }
         }
 
         if ($package->getAutoload()) {
-            $output->writeln("\n<info>autoload</info>");
+            $this->getIO()->write("\n<info>autoload</info>");
             foreach ($package->getAutoload() as $type => $autoloads) {
-                $output->writeln('<comment>' . $type . '</comment>');
+                $this->getIO()->write('<comment>' . $type . '</comment>');
 
                 if ($type === 'psr-0') {
                     foreach ($autoloads as $name => $path) {
-                        $output->writeln(($name ?: '*') . ' => ' . (is_array($path) ? implode(', ', $path) : ($path ?: '.')));
+                        $this->getIO()->write(($name ?: '*') . ' => ' . (is_array($path) ? implode(', ', $path) : ($path ?: '.')));
                     }
                 } elseif ($type === 'psr-4') {
                     foreach ($autoloads as $name => $path) {
-                        $output->writeln(($name ?: '*') . ' => ' . (is_array($path) ? implode(', ', $path) : ($path ?: '.')));
+                        $this->getIO()->write(($name ?: '*') . ' => ' . (is_array($path) ? implode(', ', $path) : ($path ?: '.')));
                     }
                 } elseif ($type === 'classmap') {
-                    $output->writeln(implode(', ', $autoloads));
+                    $this->getIO()->write(implode(', ', $autoloads));
                 }
             }
             if ($package->getIncludePaths()) {
-                $output->writeln('<comment>include-path</comment>');
-                $output->writeln(implode(', ', $package->getIncludePaths()));
+                $this->getIO()->write('<comment>include-path</comment>');
+                $this->getIO()->write(implode(', ', $package->getIncludePaths()));
             }
         }
     }
@@ -355,7 +355,7 @@ EOT
 
         $versions = implode(', ', $versions);
 
-        $output->writeln('<info>versions</info> : ' . $versions);
+        $this->getIO()->write('<info>versions</info> : ' . $versions);
     }
 
     /**
@@ -371,10 +371,10 @@ EOT
     {
         $title = $title ?: $linkType;
         if ($links = $package->{'get'.ucfirst($linkType)}()) {
-            $output->writeln("\n<info>" . $title . "</info>");
+            $this->getIO()->write("\n<info>" . $title . "</info>");
 
             foreach ($links as $link) {
-                $output->writeln($link->getTarget() . ' <comment>' . $link->getPrettyConstraint() . '</comment>');
+                $this->getIO()->write($link->getTarget() . ' <comment>' . $link->getPrettyConstraint() . '</comment>');
             }
         }
     }

src/Composer/Command/StatusCommand.php

@@ -76,9 +76,9 @@ EOT
 
         // output errors/warnings
         if (!$errors) {
-            $output->writeln('<info>No local changes</info>');
+            $this->getIO()->writeError('<info>No local changes</info>');
         } else {
-            $output->writeln('<error>You have changes in the following dependencies:</error>');
+            $this->getIO()->writeError('<error>You have changes in the following dependencies:</error>');
         }
 
         foreach ($errors as $path => $changes) {
@@ -86,15 +86,15 @@ EOT
                 $indentedChanges = implode("\n", array_map(function ($line) {
                     return '    ' . ltrim($line);
                 }, explode("\n", $changes)));
-                $output->writeln('<info>'.$path.'</info>:');
-                $output->writeln($indentedChanges);
+                $this->getIO()->write('<info>'.$path.'</info>:');
+                $this->getIO()->write($indentedChanges);
             } else {
-                $output->writeln($path);
+                $this->getIO()->write($path);
             }
         }
 
         if ($errors && !$input->getOption('verbose')) {
-            $output->writeln('Use --verbose (-v) to see modified files');
+            $this->getIO()->writeError('Use --verbose (-v) to see modified files');
         }
 
         // Dispatch post-status-command

src/Composer/Command/UpdateCommand.php

@@ -75,12 +75,12 @@ EOT
     protected function execute(InputInterface $input, OutputInterface $output)
     {
         if ($input->getOption('no-custom-installers')) {
-            $output->writeln('<warning>You are using the deprecated option "no-custom-installers". Use "no-plugins" instead.</warning>');
+            $this->getIO()->writeError('<warning>You are using the deprecated option "no-custom-installers". Use "no-plugins" instead.</warning>');
             $input->setOption('no-plugins', true);
         }
 
         if ($input->getOption('dev')) {
-            $output->writeln('<warning>You are using the deprecated option "dev". Dev packages are installed by default now.</warning>');
+            $this->getIO()->writeError('<warning>You are using the deprecated option "dev". Dev packages are installed by default now.</warning>');
         }
 
         $composer = $this->getComposer(true, $input->getOption('no-plugins'));

src/Composer/Command/ValidateCommand.php

@@ -57,12 +57,12 @@ EOT
         $file = $input->getArgument('file');
 
         if (!file_exists($file)) {
-            $output->writeln('<error>' . $file . ' not found.</error>');
+            $this->getIO()->writeError('<error>' . $file . ' not found.</error>');
 
             return 1;
         }
         if (!is_readable($file)) {
-            $output->writeln('<error>' . $file . ' is not readable.</error>');
+            $this->getIO()->writeError('<error>' . $file . ' is not readable.</error>');
 
             return 1;
         }
@@ -73,16 +73,16 @@ EOT
 
         // output errors/warnings
         if (!$errors && !$publishErrors && !$warnings) {
-            $output->writeln('<info>' . $file . ' is valid</info>');
+            $this->getIO()->write('<info>' . $file . ' is valid</info>');
         } elseif (!$errors && !$publishErrors) {
-            $output->writeln('<info>' . $file . ' is valid, but with a few warnings</info>');
-            $output->writeln('<warning>See http://getcomposer.org/doc/04-schema.md for details on the schema</warning>');
+            $this->getIO()->writeError('<info>' . $file . ' is valid, but with a few warnings</info>');
+            $this->getIO()->writeError('<warning>See http://getcomposer.org/doc/04-schema.md for details on the schema</warning>');
         } elseif (!$errors) {
-            $output->writeln('<info>' . $file . ' is valid for simple usage with composer but has</info>');
-            $output->writeln('<info>strict errors that make it unable to be published as a package:</info>');
-            $output->writeln('<warning>See http://getcomposer.org/doc/04-schema.md for details on the schema</warning>');
+            $this->getIO()->writeError('<info>' . $file . ' is valid for simple usage with composer but has</info>');
+            $this->getIO()->writeError('<info>strict errors that make it unable to be published as a package:</info>');
+            $this->getIO()->writeError('<warning>See http://getcomposer.org/doc/04-schema.md for details on the schema</warning>');
         } else {
-            $output->writeln('<error>' . $file . ' is invalid, the following errors/warnings were found:</error>');
+            $this->getIO()->writeError('<error>' . $file . ' is invalid, the following errors/warnings were found:</error>');
         }
 
         $messages = array(
@@ -92,7 +92,7 @@ EOT
 
         foreach ($messages as $style => $msgs) {
             foreach ($msgs as $msg) {
-                $output->writeln('<' . $style . '>' . $msg . '</' . $style . '>');
+                $this->getIO()->writeError('<' . $style . '>' . $msg . '</' . $style . '>');
             }
         }
 

src/Composer/Console/Application.php

@@ -15,6 +15,7 @@ namespace Composer\Console;
 use Symfony\Component\Console\Application as BaseApplication;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
+use Symfony\Component\Console\Output\ConsoleOutputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Output\ConsoleOutput;
 use Symfony\Component\Console\Formatter\OutputFormatter;
@@ -91,7 +92,7 @@ class Application extends BaseApplication
         $this->io = new ConsoleIO($input, $output, $this->getHelperSet());
 
         if (version_compare(PHP_VERSION, '5.3.2', '<')) {
-            $output->writeln('<warning>Composer only officially supports PHP 5.3.2 and above, you will most likely encounter problems with your PHP '.PHP_VERSION.', upgrading is strongly recommended.</warning>');
+            $this->getIO()->writeError('<warning>Composer only officially supports PHP 5.3.2 and above, you will most likely encounter problems with your PHP '.PHP_VERSION.', upgrading is strongly recommended.</warning>');
         }
 
         if (defined('COMPOSER_DEV_WARNING_TIME')) {
@@ -104,7 +105,7 @@ class Application extends BaseApplication
             }
             if ($commandName !== 'self-update' && $commandName !== 'selfupdate') {
                 if (time() > COMPOSER_DEV_WARNING_TIME) {
-                    $output->writeln(sprintf('<warning>Warning: This development build of composer is over 30 days old. It is recommended to update it by running "%s self-update" to get the latest version.</warning>', $_SERVER['PHP_SELF']));
+                    $this->getIO()->writeError(sprintf('<warning>Warning: This development build of composer is over 30 days old. It is recommended to update it by running "%s self-update" to get the latest version.</warning>', $_SERVER['PHP_SELF']));
                 }
             }
         }
@@ -117,8 +118,8 @@ class Application extends BaseApplication
         if ($newWorkDir = $this->getNewWorkingDir($input)) {
             $oldWorkingDir = getcwd();
             chdir($newWorkDir);
-            if ($output->getVerbosity() >= 4) {
-                $output->writeln('Changed CWD to ' . getcwd());
+            if ($this->getIO()->isDebug() >= 4) {
+                $this->getIO()->writeError('Changed CWD to ' . getcwd());
             }
         }
 
@@ -129,7 +130,7 @@ class Application extends BaseApplication
                 foreach ($composer['scripts'] as $script => $dummy) {
                     if (!defined('Composer\Script\ScriptEvents::'.str_replace('-', '_', strtoupper($script)))) {
                         if ($this->has($script)) {
-                            $output->writeln('<warning>A script named '.$script.' would override a native Composer function and has been skipped</warning>');
+                            $this->getIO()->writeError('<warning>A script named '.$script.' would override a native Composer function and has been skipped</warning>');
                         } else {
                             $this->add(new Command\ScriptAliasCommand($script));
                         }
@@ -150,7 +151,7 @@ class Application extends BaseApplication
         }
 
         if (isset($startTime)) {
-            $output->writeln('<info>Memory usage: '.round(memory_get_usage() / 1024 / 1024, 2).'MB (peak: '.round(memory_get_peak_usage() / 1024 / 1024, 2).'MB), time: '.round(microtime(true) - $startTime, 2).'s');
+            $this->getIO->writeError('<info>Memory usage: '.round(memory_get_usage() / 1024 / 1024, 2).'MB (peak: '.round(memory_get_peak_usage() / 1024 / 1024, 2).'MB), time: '.round(microtime(true) - $startTime, 2).'s');
         }
 
         return $result;
@@ -186,23 +187,27 @@ class Application extends BaseApplication
                     || (($df = @disk_free_space($dir = $config->get('vendor-dir'))) !== false && $df < $minSpaceFree)
                     || (($df = @disk_free_space($dir = sys_get_temp_dir())) !== false && $df < $minSpaceFree)
                 ) {
-                    $output->writeln('<error>The disk hosting '.$dir.' is full, this may be the cause of the following exception</error>');
+                    $this->getIO()->writeError('<error>The disk hosting '.$dir.' is full, this may be the cause of the following exception</error>');
                 }
             }
         } catch (\Exception $e) {
         }
 
         if (defined('PHP_WINDOWS_VERSION_BUILD') && false !== strpos($exception->getMessage(), 'The system cannot find the path specified')) {
-            $output->writeln('<error>The following exception may be caused by a stale entry in your cmd.exe AutoRun</error>');
-            $output->writeln('<error>Check https://getcomposer.org/doc/articles/troubleshooting.md#-the-system-cannot-find-the-path-specified-windows- for details</error>');
+            $this->getIO()->writeError('<error>The following exception may be caused by a stale entry in your cmd.exe AutoRun</error>');
+            $this->getIO()->writeError('<error>Check https://getcomposer.org/doc/articles/troubleshooting.md#-the-system-cannot-find-the-path-specified-windows- for details</error>');
         }
 
         if (false !== strpos($exception->getMessage(), 'fork failed - Cannot allocate memory')) {
-            $output->writeln('<error>The following exception is caused by a lack of memory and not having swap configured</error>');
-            $output->writeln('<error>Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open-fork-failed-errors for details</error>');
+            $this->getIO()->writeError('<error>The following exception is caused by a lack of memory and not having swap configured</error>');
+            $this->getIO()->writeError('<error>Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open-fork-failed-errors for details</error>');
         }
 
-        return parent::renderException($exception, $output);
+        if ($output instanceof ConsoleOutputInterface) {
+            parent::renderException($exception, $output->getErrorOutput());
+        } else {
+            parent::renderException($exception, $output);
+        }
     }
 
     /**
@@ -218,7 +223,7 @@ class Application extends BaseApplication
                 $this->composer = Factory::create($this->io, null, $disablePlugins);
             } catch (\InvalidArgumentException $e) {
                 if ($required) {
-                    $this->io->write($e->getMessage());
+                    $this->io->writeError($e->getMessage());
                     exit(1);
                 }
             } catch (JsonValidationException $e) {
@@ -323,7 +328,6 @@ class Application extends BaseApplication
     protected function getDefaultHelperSet()
     {
         $helperSet = parent::getDefaultHelperSet();
-
         $helperSet->set(new DialogHelper());
 
         return $helperSet;

src/Composer/Downloader/ArchiveDownloader.php

@@ -35,7 +35,7 @@ abstract class ArchiveDownloader extends FileDownloader
             $fileName = parent::download($package, $path);
 
             if ($this->io->isVerbose()) {
-                $this->io->write('    Extracting archive');
+                $this->io->writeError('    Extracting archive');
             }
 
             try {
@@ -77,7 +77,7 @@ abstract class ArchiveDownloader extends FileDownloader
 
                 // retry downloading if we have an invalid zip file
                 if ($retries && $e instanceof \UnexpectedValueException && class_exists('ZipArchive') && $e->getCode() === \ZipArchive::ER_NOZIP) {
-                    $this->io->write('    Invalid zip file, retrying...');
+                    $this->io->writeError('    Invalid zip file, retrying...');
                     usleep(500000);
                     continue;
                 }
@@ -88,7 +88,7 @@ abstract class ArchiveDownloader extends FileDownloader
             break;
         }
 
-        $this->io->write('');
+        $this->io->writeError('');
     }
 
     /**

src/Composer/Downloader/DownloadManager.php

@@ -192,7 +192,7 @@ class DownloadManager
 
         foreach ($sources as $i => $source) {
             if (isset($e)) {
-                $this->io->write('    <warning>Now trying to download from ' . $source . '</warning>');
+                $this->io->writeError('    <warning>Now trying to download from ' . $source . '</warning>');
             }
             $package->setInstallationSource($source);
             try {
@@ -206,7 +206,7 @@ class DownloadManager
                     throw $e;
                 }
 
-                $this->io->write(
+                $this->io->writeError(
                     '    <warning>Failed to download '.
                     $package->getPrettyName().
                     ' from ' . $source . ': '.

src/Composer/Downloader/FileDownloader.php

@@ -81,7 +81,7 @@ class FileDownloader implements DownloaderInterface
             throw new \InvalidArgumentException('The given package is missing url information');
         }
 
-        $this->io->write("  - Installing <info>" . $package->getName() . "</info> (<comment>" . VersionParser::formatVersion($package) . "</comment>)");
+        $this->io->writeError("  - Installing <info>" . $package->getName() . "</info> (<comment>" . VersionParser::formatVersion($package) . "</comment>)");
 
         $urls = $package->getDistUrls();
         while ($url = array_shift($urls)) {
@@ -89,11 +89,11 @@ class FileDownloader implements DownloaderInterface
                 return $this->doDownload($package, $path, $url);
             } catch (\Exception $e) {
                 if ($this->io->isDebug()) {
-                    $this->io->write('');
-                    $this->io->write('Failed: ['.get_class($e).'] '.$e->getCode().': '.$e->getMessage());
+                    $this->io->writeError('');
+                    $this->io->writeError('Failed: ['.get_class($e).'] '.$e->getCode().': '.$e->getMessage());
                 } elseif (count($urls)) {
-                    $this->io->write('');
-                    $this->io->write('    Failed, trying the next URL ('.$e->getCode().': '.$e->getMessage().')');
+                    $this->io->writeError('');
+                    $this->io->writeError('    Failed, trying the next URL ('.$e->getCode().': '.$e->getMessage().')');
                 }
 
                 if (!count($urls)) {
@@ -102,7 +102,7 @@ class FileDownloader implements DownloaderInterface
             }
         }
 
-        $this->io->write('');
+        $this->io->writeError('');
     }
 
     protected function doDownload(PackageInterface $package, $path, $url)
@@ -127,7 +127,7 @@ class FileDownloader implements DownloaderInterface
             // download if we don't have it in cache or the cache is invalidated
             if (!$this->cache || ($checksum && $checksum !== $this->cache->sha1($cacheKey)) || !$this->cache->copyTo($cacheKey, $fileName)) {
                 if (!$this->outputProgress) {
-                    $this->io->write('    Downloading');
+                    $this->io->writeError('    Downloading');
                 }
 
                 // try to download 3 times then fail hard
@@ -142,7 +142,7 @@ class FileDownloader implements DownloaderInterface
                             throw $e;
                         }
                         if ($this->io->isVerbose()) {
-                            $this->io->write('    Download failed, retrying...');
+                            $this->io->writeError('    Download failed, retrying...');
                         }
                         usleep(500000);
                     }
@@ -152,7 +152,7 @@ class FileDownloader implements DownloaderInterface
                     $this->cache->copyFrom($cacheKey, $fileName);
                 }
             } else {
-                $this->io->write('    Loading from cache');
+                $this->io->writeError('    Loading from cache');
             }
 
             if (!file_exists($fileName)) {
@@ -205,7 +205,7 @@ class FileDownloader implements DownloaderInterface
      */
     public function remove(PackageInterface $package, $path)
     {
-        $this->io->write("  - Removing <info>" . $package->getName() . "</info> (<comment>" . VersionParser::formatVersion($package) . "</comment>)");
+        $this->io->writeError("  - Removing <info>" . $package->getName() . "</info> (<comment>" . VersionParser::formatVersion($package) . "</comment>)");
         if (!$this->filesystem->removeDirectory($path)) {
             throw new \RuntimeException('Could not completely delete '.$path.', aborting.');
         }

src/Composer/Downloader/GitDownloader.php

@@ -45,7 +45,7 @@ class GitDownloader extends VcsDownloader
         $ref = $package->getSourceReference();
         $flag = defined('PHP_WINDOWS_VERSION_MAJOR') ? '/D ' : '';
         $command = 'git clone --no-checkout %s %s && cd '.$flag.'%2$s && git remote add composer %1$s && git fetch composer';
-        $this->io->write("    Cloning ".$ref);
+        $this->io->writeError("    Cloning ".$ref);
 
         $commandCallable = function ($url) use ($ref, $path, $command) {
             return sprintf($command, ProcessExecutor::escape($url), ProcessExecutor::escape($path), ProcessExecutor::escape($ref));
@@ -78,7 +78,7 @@ class GitDownloader extends VcsDownloader
         }
 
         $ref = $target->getSourceReference();
-        $this->io->write("    Checking out ".$ref);
+        $this->io->writeError("    Checking out ".$ref);
         $command = 'git remote set-url composer %s && git fetch composer && git fetch --tags composer';
 
         $commandCallable = function ($url) use ($command) {
@@ -143,10 +143,10 @@ class GitDownloader extends VcsDownloader
         $changes = array_map(function ($elem) {
             return '    '.$elem;
         }, preg_split('{\s*\r?\n\s*}', $changes));
-        $this->io->write('    <error>The package has modified files:</error>');
-        $this->io->write(array_slice($changes, 0, 10));
+        $this->io->writeError('    <error>The package has modified files:</error>');
+        $this->io->writeError(array_slice($changes, 0, 10));
         if (count($changes) > 10) {
-            $this->io->write('    <info>'.count($changes) - 10 . ' more files modified, choose "v" to view the full list</info>');
+            $this->io->writeError('    <info>'.count($changes) - 10 . ' more files modified, choose "v" to view the full list</info>');
         }
 
         while (true) {
@@ -167,21 +167,21 @@ class GitDownloader extends VcsDownloader
                     throw new \RuntimeException('Update aborted');
 
                 case 'v':
-                    $this->io->write($changes);
+                    $this->io->writeError($changes);
                     break;
 
                 case '?':
                 default:
                     help:
-                    $this->io->write(array(
+                    $this->io->writeError(array(
                         '    y - discard changes and apply the '.($update ? 'update' : 'uninstall'),
                         '    n - abort the '.($update ? 'update' : 'uninstall').' and let you manually clean things up',
                         '    v - view modified files',
                     ));
                     if ($update) {
-                        $this->io->write('    s - stash changes and try to reapply them after the update');
+                        $this->io->writeError('    s - stash changes and try to reapply them after the update');
                     }
-                    $this->io->write('    ? - print help');
+                    $this->io->writeError('    ? - print help');
                     break;
             }
         }
@@ -195,7 +195,7 @@ class GitDownloader extends VcsDownloader
         $path = $this->normalizePath($path);
         if ($this->hasStashedChanges) {
             $this->hasStashedChanges = false;
-            $this->io->write('    <info>Re-applying stashed changes</info>');
+            $this->io->writeError('    <info>Re-applying stashed changes</info>');
             if (0 !== $this->process->execute('git stash pop', $output, $path)) {
                 throw new \RuntimeException("Failed to apply stashed changes:\n\n".$this->process->getErrorOutput());
             }
@@ -261,7 +261,7 @@ class GitDownloader extends VcsDownloader
 
         // reference was not found (prints "fatal: reference is not a tree: $ref")
         if (false !== strpos($this->process->getErrorOutput(), $reference)) {
-            $this->io->write('    <warning>'.$reference.' is gone (history was rewritten?)</warning>');
+            $this->io->writeError('    <warning>'.$reference.' is gone (history was rewritten?)</warning>');
         }
 
         throw new \RuntimeException('Failed to execute ' . GitUtil::sanitizeUrl($command) . "\n\n" . $this->process->getErrorOutput());

src/Composer/Downloader/HgDownloader.php

@@ -27,7 +27,7 @@ class HgDownloader extends VcsDownloader
     {
         $url = ProcessExecutor::escape($url);
         $ref = ProcessExecutor::escape($package->getSourceReference());
-        $this->io->write("    Cloning ".$package->getSourceReference());
+        $this->io->writeError("    Cloning ".$package->getSourceReference());
         $command = sprintf('hg clone %s %s', $url, ProcessExecutor::escape($path));
         if (0 !== $this->process->execute($command, $ignoredOutput)) {
             throw new \RuntimeException('Failed to execute ' . $command . "\n\n" . $this->process->getErrorOutput());
@@ -45,7 +45,7 @@ class HgDownloader extends VcsDownloader
     {
         $url = ProcessExecutor::escape($url);
         $ref = ProcessExecutor::escape($target->getSourceReference());
-        $this->io->write("    Updating to ".$target->getSourceReference());
+        $this->io->writeError("    Updating to ".$target->getSourceReference());
 
         if (!is_dir($path.'/.hg')) {
             throw new \RuntimeException('The .hg directory is missing from '.$path.', see http://getcomposer.org/commit-deps for more information');

src/Composer/Downloader/PerforceDownloader.php

@@ -31,7 +31,7 @@ class PerforceDownloader extends VcsDownloader
         $ref = $package->getSourceReference();
         $label = $this->getLabelFromSourceReference($ref);
 
-        $this->io->write('    Cloning ' . $ref);
+        $this->io->writeError('    Cloning ' . $ref);
         $this->initPerforce($package, $path, $url);
         $this->perforce->setStream($ref);
         $this->perforce->p4Login($this->io);
@@ -85,7 +85,7 @@ class PerforceDownloader extends VcsDownloader
      */
     public function getLocalChanges(PackageInterface $package, $path)
     {
-        $this->io->write('Perforce driver does not check for local changes before overriding', true);
+        $this->io->writeError('Perforce driver does not check for local changes before overriding', true);
 
         return;
     }

src/Composer/Downloader/SvnDownloader.php

@@ -29,7 +29,7 @@ class SvnDownloader extends VcsDownloader
         SvnUtil::cleanEnv();
         $ref = $package->getSourceReference();
 
-        $this->io->write("    Checking out ".$package->getSourceReference());
+        $this->io->writeError("    Checking out ".$package->getSourceReference());
         $this->execute($url, "svn co", sprintf("%s/%s", $url, $ref), null, $path);
     }
 
@@ -52,7 +52,7 @@ class SvnDownloader extends VcsDownloader
             }
         }
 
-        $this->io->write("    Checking out " . $ref);
+        $this->io->writeError("    Checking out " . $ref);
         $this->execute($url, "svn switch" . $flags, sprintf("%s/%s", $url, $ref), $path);
     }
 
@@ -114,10 +114,10 @@ class SvnDownloader extends VcsDownloader
         $changes = array_map(function ($elem) {
             return '    '.$elem;
         }, preg_split('{\s*\r?\n\s*}', $changes));
-        $this->io->write('    <error>The package has modified files:</error>');
-        $this->io->write(array_slice($changes, 0, 10));
+        $this->io->writeError('    <error>The package has modified files:</error>');
+        $this->io->writeError(array_slice($changes, 0, 10));
         if (count($changes) > 10) {
-            $this->io->write('    <info>'.count($changes) - 10 . ' more files modified, choose "v" to view the full list</info>');
+            $this->io->writeError('    <info>'.count($changes) - 10 . ' more files modified, choose "v" to view the full list</info>');
         }
 
         while (true) {
@@ -130,12 +130,12 @@ class SvnDownloader extends VcsDownloader
                     throw new \RuntimeException('Update aborted');
 
                 case 'v':
-                    $this->io->write($changes);
+                    $this->io->writeError($changes);
                     break;
 
                 case '?':
                 default:
-                    $this->io->write(array(
+                    $this->io->writeError(array(
                         '    y - discard changes and apply the '.($update ? 'update' : 'uninstall'),
                         '    n - abort the '.($update ? 'update' : 'uninstall').' and let you manually clean things up',
                         '    v - view modified files',

src/Composer/Downloader/VcsDownloader.php

@@ -54,7 +54,7 @@ abstract class VcsDownloader implements DownloaderInterface, ChangeReportInterfa
             throw new \InvalidArgumentException('Package '.$package->getPrettyName().' is missing reference information');
         }
 
-        $this->io->write("  - Installing <info>" . $package->getName() . "</info> (<comment>" . VersionParser::formatVersion($package) . "</comment>)");
+        $this->io->writeError("  - Installing <info>" . $package->getName() . "</info> (<comment>" . VersionParser::formatVersion($package) . "</comment>)");
         $this->filesystem->emptyDirectory($path);
 
         $urls = $package->getSourceUrls();
@@ -67,9 +67,9 @@ abstract class VcsDownloader implements DownloaderInterface, ChangeReportInterfa
                 break;
             } catch (\Exception $e) {
                 if ($this->io->isDebug()) {
-                    $this->io->write('Failed: ['.get_class($e).'] '.$e->getMessage());
+                    $this->io->writeError('Failed: ['.get_class($e).'] '.$e->getMessage());
                 } elseif (count($urls)) {
-                    $this->io->write('    Failed, trying the next URL');
+                    $this->io->writeError('    Failed, trying the next URL');
                 }
                 if (!count($urls)) {
                     throw $e;
@@ -77,7 +77,7 @@ abstract class VcsDownloader implements DownloaderInterface, ChangeReportInterfa
             }
         }
 
-        $this->io->write('');
+        $this->io->writeError('');
     }
 
     /**
@@ -104,7 +104,7 @@ abstract class VcsDownloader implements DownloaderInterface, ChangeReportInterfa
             $to = VersionParser::formatVersion($target);
         }
 
-        $this->io->write("  - Updating <info>" . $name . "</info> (<comment>" . $from . "</comment> => <comment>" . $to . "</comment>)");
+        $this->io->writeError("  - Updating <info>" . $name . "</info> (<comment>" . $from . "</comment> => <comment>" . $to . "</comment>)");
 
         $this->cleanChanges($initial, $path, true);
         $urls = $target->getSourceUrls();
@@ -117,9 +117,9 @@ abstract class VcsDownloader implements DownloaderInterface, ChangeReportInterfa
                 break;
             } catch (\Exception $e) {
                 if ($this->io->isDebug()) {
-                    $this->io->write('Failed: ['.get_class($e).'] '.$e->getMessage());
+                    $this->io->writeError('Failed: ['.get_class($e).'] '.$e->getMessage());
                 } elseif (count($urls)) {
-                    $this->io->write('    Failed, trying the next URL');
+                    $this->io->writeError('    Failed, trying the next URL');
                 } else {
                     // in case of failed update, try to reapply the changes before aborting
                     $this->reapplyChanges($path);
@@ -146,12 +146,12 @@ abstract class VcsDownloader implements DownloaderInterface, ChangeReportInterfa
                     return '      ' . $line;
                 }, explode("\n", $logs)));
 
-                $this->io->write('    '.$message);
-                $this->io->write($logs);
+                $this->io->writeError('    '.$message);
+                $this->io->writeError($logs);
             }
         }
 
-        $this->io->write('');
+        $this->io->writeError('');
     }
 
     /**
@@ -159,7 +159,7 @@ abstract class VcsDownloader implements DownloaderInterface, ChangeReportInterfa
      */
     public function remove(PackageInterface $package, $path)
     {
-        $this->io->write("  - Removing <info>" . $package->getName() . "</info> (<comment>" . $package->getPrettyVersion() . "</comment>)");
+        $this->io->writeError("  - Removing <info>" . $package->getName() . "</info> (<comment>" . $package->getPrettyVersion() . "</comment>)");
         $this->cleanChanges($package, $path, false);
         if (!$this->filesystem->removeDirectory($path)) {
             throw new \RuntimeException('Could not completely delete '.$path.', aborting.');

src/Composer/EventDispatcher/EventDispatcher.php

@@ -154,11 +154,11 @@ class EventDispatcher
                 $methodName = substr($callable, strpos($callable, '::') + 2);
 
                 if (!class_exists($className)) {
-                    $this->io->write('<warning>Class '.$className.' is not autoloadable, can not call '.$event->getName().' script</warning>');
+                    $this->io->writeError('<warning>Class '.$className.' is not autoloadable, can not call '.$event->getName().' script</warning>');
                     continue;
                 }
                 if (!is_callable($callable)) {
-                    $this->io->write('<warning>Method '.$callable.' is not callable, can not call '.$event->getName().' script</warning>');
+                    $this->io->writeError('<warning>Method '.$callable.' is not callable, can not call '.$event->getName().' script</warning>');
                     continue;
                 }
 
@@ -166,13 +166,13 @@ class EventDispatcher
                     $return = false === $this->executeEventPhpScript($className, $methodName, $event) ? 1 : 0;
                 } catch (\Exception $e) {
                     $message = "Script %s handling the %s event terminated with an exception";
-                    $this->io->write('<error>'.sprintf($message, $callable, $event->getName()).'</error>');
+                    $this->io->writeError('<error>'.sprintf($message, $callable, $event->getName()).'</error>');
                     throw $e;
                 }
             } else {
                 $args = implode(' ', array_map(array('Composer\Util\ProcessExecutor','escape'), $event->getArguments()));
                 if (0 !== ($exitCode = $this->process->execute($callable . ($args === '' ? '' : ' '.$args)))) {
-                    $this->io->write(sprintf('<error>Script %s handling the %s event returned with an error</error>', $callable, $event->getName()));
+                    $this->io->writeError(sprintf('<error>Script %s handling the %s event returned with an error</error>', $callable, $event->getName()));
 
                     throw new \RuntimeException('Error Output: '.$this->process->getErrorOutput(), $exitCode);
                 }

src/Composer/Factory.php

@@ -116,7 +116,7 @@ class Factory
         $file = new JsonFile($home.'/config.json');
         if ($file->exists()) {
             if ($io && $io->isDebug()) {
-                $io->write('Loading config file ' . $file->getPath());
+                $io->writeError('Loading config file ' . $file->getPath());
             }
             $config->merge($file->read());
         }
@@ -126,7 +126,7 @@ class Factory
         $file = new JsonFile($config->get('home').'/auth.json');
         if ($file->exists()) {
             if ($io && $io->isDebug()) {
-                $io->write('Loading config file ' . $file->getPath());
+                $io->writeError('Loading config file ' . $file->getPath());
             }
             $config->merge(array('config' => $file->read()));
         }
@@ -227,12 +227,12 @@ class Factory
         $config->merge($localConfig);
         if (isset($composerFile)) {
             if ($io && $io->isDebug()) {
-                $io->write('Loading config file ' . $composerFile);
+                $io->writeError('Loading config file ' . $composerFile);
             }
             $localAuthFile = new JsonFile(dirname(realpath($composerFile)) . '/auth.json');
             if ($localAuthFile->exists()) {
                 if ($io && $io->isDebug()) {
-                    $io->write('Loading config file ' . $localAuthFile->getPath());
+                    $io->writeError('Loading config file ' . $localAuthFile->getPath());
                 }
                 $config->merge(array('config' => $localAuthFile->read()));
                 $config->setAuthConfigSource(new JsonConfigSource($localAuthFile, true));
@@ -362,7 +362,7 @@ class Factory
             $composer = self::createComposer($io, $config->get('home') . '/composer.json', $disablePlugins, $config->get('home'), false);
         } catch (\Exception $e) {
             if ($io->isDebug()) {
-                $io->write('Failed to initialize global composer: '.$e->getMessage());
+                $io->writeError('Failed to initialize global composer: '.$e->getMessage());
             }
         }
 

src/Composer/IO/ConsoleIO.php

@@ -13,6 +13,7 @@
 namespace Composer\IO;
 
 use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\ConsoleOutputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Helper\HelperSet;
 use Symfony\Component\Process\ExecutableFinder;
@@ -29,6 +30,7 @@ class ConsoleIO extends BaseIO
     protected $output;
     protected $helperSet;
     protected $lastMessage;
+    protected $lastMessageErr;
     private $startTime;
 
     /**
@@ -94,6 +96,19 @@ class ConsoleIO extends BaseIO
      * {@inheritDoc}
      */
     public function write($messages, $newline = true)
+    {
+        $this->doWrite($messages, $newline, false);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function writeError($messages, $newline = true)
+    {
+        $this->doWrite($messages, $newline, true);
+    }
+
+    private function doWrite($messages, $newline, $stderr)
     {
         if (null !== $this->startTime) {
             $memoryUsage = memory_get_usage() / 1024 / 1024;
@@ -102,6 +117,13 @@ class ConsoleIO extends BaseIO
                 return sprintf('[%.1fMB/%.2fs] %s', $memoryUsage, $timeSpent, $message);
             }, (array) $messages);
         }
+
+        if (true === $stderr && $this->output instanceof ConsoleOutputInterface) {
+            $this->output->getErrorOutput()->write($messages, $newline);
+            $this->lastMessageErr = join($newline ? "\n" : '', (array) $messages);
+            return;
+        }
+
         $this->output->write($messages, $newline);
         $this->lastMessage = join($newline ? "\n" : '', (array) $messages);
     }

src/Composer/IO/IOInterface.php

@@ -64,6 +64,14 @@ interface IOInterface
      */
     public function write($messages, $newline = true);
 
+    /**
+     * Writes a message to the error output.
+     *
+     * @param string|array $messages The message as an array of lines or a single string
+     * @param bool         $newline  Whether to add a newline or not
+     */
+    public function writeError($messages, $newline = true);
+
     /**
      * Overwrites a previous message to the output.
      *

src/Composer/IO/NullIO.php

@@ -66,6 +66,13 @@ class NullIO extends BaseIO
     {
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    public function writeError($messages, $newline = true)
+    {
+    }
+
     /**
      * {@inheritDoc}
      */

src/Composer/Installer.php

@@ -177,7 +177,7 @@ class Installer
         // purge old require-dev packages to avoid conflicts with the new way of handling dev requirements
         $devRepo = new InstalledFilesystemRepository(new JsonFile($this->config->get('vendor-dir').'/composer/installed_dev.json'));
         if ($devRepo->getPackages()) {
-            $this->io->write('<warning>BC Notice: Removing old dev packages to migrate to the new require-dev handling.</warning>');
+            $this->io->writeError('<warning>BC Notice: Removing old dev packages to migrate to the new require-dev handling.</warning>');
             foreach ($devRepo->getPackages() as $package) {
                 if ($this->installationManager->isPackageInstalled($devRepo, $package)) {
                     $this->installationManager->uninstall($devRepo, new UninstallOperation($package));
@@ -243,7 +243,7 @@ class Installer
                     }
                 }
 
-                $this->io->write($suggestion['source'].' suggests installing '.$suggestion['target'].' ('.$suggestion['reason'].')');
+                $this->io->writeError($suggestion['source'].' suggests installing '.$suggestion['target'].' ('.$suggestion['reason'].')');
             }
         }
 
@@ -257,7 +257,7 @@ class Installer
                 ? 'Use ' . $package->getReplacementPackage() . ' instead'
                 : 'No replacement was suggested';
 
-            $this->io->write(
+            $this->io->writeError(
                 sprintf(
                     "<error>Package %s is abandoned, you should avoid using it. %s.</error>",
                     $package->getPrettyName(),
@@ -314,16 +314,16 @@ class Installer
                     $this->preferLowest
                 );
                 if ($updatedLock) {
-                    $this->io->write('<info>Writing lock file</info>');
+                    $this->io->writeError('<info>Writing lock file</info>');
                 }
             }
 
             if ($this->dumpAutoloader) {
                 // write autoloader
                 if ($this->optimizeAutoloader) {
-                    $this->io->write('<info>Generating optimized autoload files</info>');
+                    $this->io->writeError('<info>Generating optimized autoload files</info>');
                 } else {
-                    $this->io->write('<info>Generating autoload files</info>');
+                    $this->io->writeError('<info>Generating autoload files</info>');
                 }
 
                 $this->autoloadGenerator->setDevMode($this->devMode);
@@ -374,7 +374,7 @@ class Installer
             $this->package->getDevRequires()
         );
 
-        $this->io->write('<info>Loading composer repositories with package information</info>');
+        $this->io->writeError('<info>Loading composer repositories with package information</info>');
 
         // creating repository pool
         $policy = $this->createPolicy();
@@ -409,7 +409,7 @@ class Installer
         }
 
         if ($this->update) {
-            $this->io->write('<info>Updating dependencies'.($withDevReqs ? ' (including require-dev)' : '').'</info>');
+            $this->io->writeError('<info>Updating dependencies'.($withDevReqs ? ' (including require-dev)' : '').'</info>');
 
             $request->updateAll();
 
@@ -460,10 +460,10 @@ class Installer
                 }
             }
         } elseif ($installFromLock) {
-            $this->io->write('<info>Installing dependencies'.($withDevReqs ? ' (including require-dev)' : '').' from lock file</info>');
+            $this->io->writeError('<info>Installing dependencies'.($withDevReqs ? ' (including require-dev)' : '').' from lock file</info>');
 
             if (!$this->locker->isFresh()) {
-                $this->io->write('<warning>Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. Run update to update them.</warning>');
+                $this->io->writeError('<warning>Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. Run update to update them.</warning>');
             }
 
             foreach ($lockedRepository->getPackages() as $package) {
@@ -480,7 +480,7 @@ class Installer
                 $request->install($link->getTarget(), $link->getConstraint());
             }
         } else {
-            $this->io->write('<info>Installing dependencies'.($withDevReqs ? ' (including require-dev)' : '').'</info>');
+            $this->io->writeError('<info>Installing dependencies'.($withDevReqs ? ' (including require-dev)' : '').'</info>');
 
             if ($withDevReqs) {
                 $links = array_merge($this->package->getRequires(), $this->package->getDevRequires());
@@ -503,8 +503,8 @@ class Installer
             $operations = $solver->solve($request, $this->ignorePlatformReqs);
             $this->eventDispatcher->dispatchInstallerEvent(InstallerEvents::POST_DEPENDENCIES_SOLVING, $this->devMode, $policy, $pool, $installedRepo, $request, $operations);
         } catch (SolverProblemsException $e) {
-            $this->io->write('<error>Your requirements could not be resolved to an installable set of packages.</error>');
-            $this->io->write($e->getMessage());
+            $this->io->writeError('<error>Your requirements could not be resolved to an installable set of packages.</error>');
+            $this->io->writeError($e->getMessage());
 
             return max(1, $e->getCode());
         }
@@ -514,7 +514,7 @@ class Installer
 
         // execute operations
         if (!$operations) {
-            $this->io->write('Nothing to install or update');
+            $this->io->writeError('Nothing to install or update');
         }
 
         $operations = $this->movePluginsToFront($operations);
@@ -553,8 +553,8 @@ class Installer
                     && $operation->getTargetPackage()->getSourceReference() === $operation->getInitialPackage()->getSourceReference()
                 ) {
                     if ($this->io->isDebug()) {
-                        $this->io->write('  - Skipping update of '. $operation->getTargetPackage()->getPrettyName().' to the same reference-locked version');
-                        $this->io->write('');
+                        $this->io->writeError('  - Skipping update of '. $operation->getTargetPackage()->getPrettyName().' to the same reference-locked version');
+                        $this->io->writeError('');
                     }
 
                     continue;
@@ -568,11 +568,11 @@ class Installer
 
             // output non-alias ops in dry run, output alias ops in debug verbosity
             if ($this->dryRun && false === strpos($operation->getJobType(), 'Alias')) {
-                $this->io->write('  - ' . $operation);
-                $this->io->write('');
+                $this->io->writeError('  - ' . $operation);
+                $this->io->writeError('');
             } elseif ($this->io->isDebug() && false !== strpos($operation->getJobType(), 'Alias')) {
-                $this->io->write('  - ' . $operation);
-                $this->io->write('');
+                $this->io->writeError('  - ' . $operation);
+                $this->io->writeError('');
             }
 
             $this->installationManager->execute($localRepo, $operation);
@@ -583,12 +583,12 @@ class Installer
                 if ($reason instanceof Rule) {
                     switch ($reason->getReason()) {
                         case Rule::RULE_JOB_INSTALL:
-                            $this->io->write('    REASON: Required by root: '.$reason->getPrettyString($pool));
-                            $this->io->write('');
+                            $this->io->writeError('    REASON: Required by root: '.$reason->getPrettyString($pool));
+                            $this->io->writeError('');
                             break;
                         case Rule::RULE_PACKAGE_REQUIRES:
-                            $this->io->write('    REASON: '.$reason->getPrettyString($pool));
-                            $this->io->write('');
+                            $this->io->writeError('    REASON: '.$reason->getPrettyString($pool));
+                            $this->io->writeError('');
                             break;
                     }
                 }
@@ -1001,7 +1001,7 @@ class Installer
             }
 
             if (count($depPackages) == 0 && !$nameMatchesRequiredPackage && !in_array($packageName, array('nothing', 'lock'))) {
-                $this->io->write('<warning>Package "' . $packageName . '" listed for update is not installed. Ignoring.</warning>');
+                $this->io->writeError('<warning>Package "' . $packageName . '" listed for update is not installed. Ignoring.</warning>');
             }
 
             foreach ($depPackages as $depPackage) {

src/Composer/Installer/LibraryInstaller.php

@@ -197,7 +197,7 @@ class LibraryInstaller implements InstallerInterface
         foreach ($binaries as $bin) {
             $binPath = $this->getInstallPath($package).'/'.$bin;
             if (!file_exists($binPath)) {
-                $this->io->write('    <warning>Skipped installation of bin '.$bin.' for package '.$package->getName().': file not found in package</warning>');
+                $this->io->writeError('    <warning>Skipped installation of bin '.$bin.' for package '.$package->getName().': file not found in package</warning>');
                 continue;
             }
 
@@ -216,7 +216,7 @@ class LibraryInstaller implements InstallerInterface
                     // is a fresh install of the vendor.
                     @chmod($link, 0777 & ~umask());
                 }
-                $this->io->write('    Skipped installation of bin '.$bin.' for package '.$package->getName().': name conflicts with an existing file');
+                $this->io->writeError('    Skipped installation of bin '.$bin.' for package '.$package->getName().': name conflicts with an existing file');
                 continue;
             }
             if (defined('PHP_WINDOWS_VERSION_BUILD')) {
@@ -226,7 +226,7 @@ class LibraryInstaller implements InstallerInterface
                     @chmod($link, 0777 & ~umask());
                     $link .= '.bat';
                     if (file_exists($link)) {
-                        $this->io->write('    Skipped installation of bin '.$bin.'.bat proxy for package '.$package->getName().': a .bat proxy was already installed');
+                        $this->io->writeError('    Skipped installation of bin '.$bin.'.bat proxy for package '.$package->getName().': a .bat proxy was already installed');
                     }
                 }
                 if (!file_exists($link)) {

src/Composer/Installer/PearInstaller.php

@@ -76,7 +76,7 @@ class PearInstaller extends LibraryInstaller
         $pearExtractor->extractTo($this->getInstallPath($package), array('php' => '/', 'script' => '/bin', 'data' => '/data'), $vars);
 
         if ($this->io->isVerbose()) {
-            $this->io->write('    Cleaning up');
+            $this->io->writeError('    Cleaning up');
         }
         $this->filesystem->unlink($packageArchive);
     }

src/Composer/Plugin/PluginManager.php

@@ -127,7 +127,7 @@ class PluginManager
                 }
 
                 if (!$requiresComposer->matches(new VersionConstraint('==', $this->versionParser->normalize(PluginInterface::PLUGIN_API_VERSION)))) {
-                    $this->io->write("<warning>The plugin ".$package->getName()." requires a version of composer-plugin-api that does not match your composer installation. You may need to run composer update with the '--no-plugins' option.</warning>");
+                    $this->io->writeError("<warning>The plugin ".$package->getName()." requires a version of composer-plugin-api that does not match your composer installation. You may need to run composer update with the '--no-plugins' option.</warning>");
                 }
 
                 $this->registerPackage($package);

src/Composer/Repository/ArtifactRepository.php

@@ -60,14 +60,14 @@ class ArtifactRepository extends ArrayRepository
             $package = $this->getComposerInformation($file);
             if (!$package) {
                 if ($io->isVerbose()) {
-                    $io->write("File <comment>{$file->getBasename()}</comment> doesn't seem to hold a package");
+                    $io->writeError("File <comment>{$file->getBasename()}</comment> doesn't seem to hold a package");
                 }
                 continue;
             }
 
             if ($io->isVerbose()) {
                 $template = 'Found package <info>%s</info> (<comment>%s</comment>) in file <info>%s</info>';
-                $io->write(sprintf($template, $package->getName(), $package->getPrettyVersion(), $file->getBasename()));
+                $io->writeError(sprintf($template, $package->getName(), $package->getPrettyVersion(), $file->getBasename()));
             }
 
             $this->addPackage($package);

src/Composer/Repository/ComposerRepository.php

@@ -434,7 +434,7 @@ class ComposerRepository extends ArrayRepository
         }
 
         if (!empty($data['warning'])) {
-            $this->io->write('<warning>Warning from '.$this->url.': '.$data['warning'].'</warning>');
+            $this->io->writeError('<warning>Warning from '.$this->url.': '.$data['warning'].'</warning>');
         }
 
         if (!empty($data['providers-lazy-url'])) {
@@ -613,8 +613,8 @@ class ComposerRepository extends ArrayRepository
 
                 if ($cacheKey && ($contents = $this->cache->read($cacheKey))) {
                     if (!$this->degradedMode) {
-                        $this->io->write('<warning>'.$e->getMessage().'</warning>');
-                        $this->io->write('<warning>'.$this->url.' could not be fully loaded, package information was loaded from the local cache and may be out of date</warning>');
+                        $this->io->writeError('<warning>'.$e->getMessage().'</warning>');
+                        $this->io->writeError('<warning>'.$this->url.' could not be fully loaded, package information was loaded from the local cache and may be out of date</warning>');
                     }
                     $this->degradedMode = true;
                     $data = JsonFile::parseJson($contents, $this->cache->getRoot().$cacheKey);

src/Composer/Repository/PearRepository.php

@@ -66,13 +66,13 @@ class PearRepository extends ArrayRepository
     {
         parent::initialize();
 
-        $this->io->write('Initializing PEAR repository '.$this->url);
+        $this->io->writeError('Initializing PEAR repository '.$this->url);
 
         $reader = new ChannelReader($this->rfs);
         try {
             $channelInfo = $reader->read($this->url);
         } catch (\Exception $e) {
-            $this->io->write('<warning>PEAR repository from '.$this->url.' could not be loaded. '.$e->getMessage().'</warning>');
+            $this->io->writeError('<warning>PEAR repository from '.$this->url.' could not be loaded. '.$e->getMessage().'</warning>');
 
             return;
         }
@@ -98,7 +98,7 @@ class PearRepository extends ArrayRepository
                     $normalizedVersion = $versionParser->normalize($version);
                 } catch (\UnexpectedValueException $e) {
                     if ($this->io->isVerbose()) {
-                        $this->io->write('Could not load '.$packageDefinition->getPackageName().' '.$version.': '.$e->getMessage());
+                        $this->io->writeError('Could not load '.$packageDefinition->getPackageName().' '.$version.': '.$e->getMessage());
                     }
                     continue;
                 }

src/Composer/Repository/Vcs/GitBitbucketDriver.php

@@ -149,7 +149,7 @@ class GitBitbucketDriver extends VcsDriver implements VcsDriverInterface
 
         if (!extension_loaded('openssl')) {
             if ($io->isVerbose()) {
-                $io->write('Skipping Bitbucket git driver for '.$url.' because the OpenSSL PHP extension is missing.');
+                $io->writeError('Skipping Bitbucket git driver for '.$url.' because the OpenSSL PHP extension is missing.');
             }
 
             return false;

src/Composer/Repository/Vcs/GitDriver.php

@@ -66,7 +66,7 @@ class GitDriver extends VcsDriver
                     };
                     $gitUtil->runCommand($commandCallable, $this->url, $this->repoDir);
                 } catch (\Exception $e) {
-                    $this->io->write('<error>Failed to update '.$this->url.', package information from this repository may be outdated ('.$e->getMessage().')</error>');
+                    $this->io->writeError('<error>Failed to update '.$this->url.', package information from this repository may be outdated ('.$e->getMessage().')</error>');
                 }
             } else {
                 // clean up directory and do a fresh clone into it

src/Composer/Repository/Vcs/GitHubDriver.php

@@ -266,7 +266,7 @@ class GitHubDriver extends VcsDriver
 
         if (!extension_loaded('openssl')) {
             if ($io->isVerbose()) {
-                $io->write('Skipping GitHub driver for '.$url.' because the OpenSSL PHP extension is missing.');
+                $io->writeError('Skipping GitHub driver for '.$url.' because the OpenSSL PHP extension is missing.');
             }
 
             return false;
@@ -333,7 +333,7 @@ class GitHubDriver extends VcsDriver
 
                     if (!$this->io->hasAuthentication($this->originUrl)) {
                         if (!$this->io->isInteractive()) {
-                            $this->io->write('<error>GitHub API limit exhausted. Failed to get metadata for the '.$this->url.' repository, try running in interactive mode so that you can enter your GitHub credentials to increase the API limit</error>');
+                            $this->io->writeError('<error>GitHub API limit exhausted. Failed to get metadata for the '.$this->url.' repository, try running in interactive mode so that you can enter your GitHub credentials to increase the API limit</error>');
                             throw $e;
                         }
 
@@ -344,7 +344,7 @@ class GitHubDriver extends VcsDriver
 
                     if ($rateLimited) {
                         $rateLimit = $this->getRateLimit($e->getHeaders());
-                        $this->io->write(sprintf(
+                        $this->io->writeError(sprintf(
                             '<error>GitHub API limit (%d calls/hr) is exhausted. You are already authorized so you have to wait until %s before doing more requests</error>',
                             $rateLimit['limit'],
                             $rateLimit['reset']
@@ -435,7 +435,7 @@ class GitHubDriver extends VcsDriver
         } catch (\RuntimeException $e) {
             $this->gitDriver = null;
 
-            $this->io->write('<error>Failed to clone the '.$this->generateSshUrl().' repository, try running in interactive mode so that you can enter your GitHub credentials</error>');
+            $this->io->writeError('<error>Failed to clone the '.$this->generateSshUrl().' repository, try running in interactive mode so that you can enter your GitHub credentials</error>');
             throw $e;
         }
     }

src/Composer/Repository/Vcs/HgBitbucketDriver.php

@@ -159,7 +159,7 @@ class HgBitbucketDriver extends VcsDriver
 
         if (!extension_loaded('openssl')) {
             if ($io->isVerbose()) {
-                $io->write('Skipping Bitbucket hg driver for '.$url.' because the OpenSSL PHP extension is missing.');
+                $io->writeError('Skipping Bitbucket hg driver for '.$url.' because the OpenSSL PHP extension is missing.');
             }
 
             return false;

src/Composer/Repository/Vcs/HgDriver.php

@@ -50,7 +50,7 @@ class HgDriver extends VcsDriver
             // update the repo if it is a valid hg repository
             if (is_dir($this->repoDir) && 0 === $this->process->execute('hg summary', $output, $this->repoDir)) {
                 if (0 !== $this->process->execute('hg pull', $output, $this->repoDir)) {
-                    $this->io->write('<error>Failed to update '.$this->url.', package information from this repository may be outdated ('.$this->process->getErrorOutput().')</error>');
+                    $this->io->writeError('<error>Failed to update '.$this->url.', package information from this repository may be outdated ('.$this->process->getErrorOutput().')</error>');
                 }
             } else {
                 // clean up directory and do a fresh clone into it

src/Composer/Repository/VcsRepository.php

@@ -127,14 +127,14 @@ class VcsRepository extends ArrayRepository
             }
         } catch (\Exception $e) {
             if ($verbose) {
-                $this->io->write('<error>Skipped parsing '.$driver->getRootIdentifier().', '.$e->getMessage().'</error>');
+                $this->io->writeError('<error>Skipped parsing '.$driver->getRootIdentifier().', '.$e->getMessage().'</error>');
             }
         }
 
         foreach ($driver->getTags() as $tag => $identifier) {
             $msg = 'Reading composer.json of <info>' . ($this->packageName ?: $this->url) . '</info> (<comment>' . $tag . '</comment>)';
             if ($verbose) {
-                $this->io->write($msg);
+                $this->io->writeError($msg);
             } else {
                 $this->io->overwrite($msg, false);
             }
@@ -144,7 +144,7 @@ class VcsRepository extends ArrayRepository
 
             if (!$parsedTag = $this->validateTag($tag)) {
                 if ($verbose) {
-                    $this->io->write('<warning>Skipped tag '.$tag.', invalid tag name</warning>');
+                    $this->io->writeError('<warning>Skipped tag '.$tag.', invalid tag name</warning>');
                 }
                 continue;
             }
@@ -152,7 +152,7 @@ class VcsRepository extends ArrayRepository
             try {
                 if (!$data = $driver->getComposerInformation($identifier)) {
                     if ($verbose) {
-                        $this->io->write('<warning>Skipped tag '.$tag.', no composer file</warning>');
+                        $this->io->writeError('<warning>Skipped tag '.$tag.', no composer file</warning>');
                     }
                     continue;
                 }
@@ -173,19 +173,19 @@ class VcsRepository extends ArrayRepository
                 // broken package, version doesn't match tag
                 if ($data['version_normalized'] !== $parsedTag) {
                     if ($verbose) {
-                        $this->io->write('<warning>Skipped tag '.$tag.', tag ('.$parsedTag.') does not match version ('.$data['version_normalized'].') in composer.json</warning>');
+                        $this->io->writeError('<warning>Skipped tag '.$tag.', tag ('.$parsedTag.') does not match version ('.$data['version_normalized'].') in composer.json</warning>');
                     }
                     continue;
                 }
 
                 if ($verbose) {
-                    $this->io->write('Importing tag '.$tag.' ('.$data['version_normalized'].')');
+                    $this->io->writeError('Importing tag '.$tag.' ('.$data['version_normalized'].')');
                 }
 
                 $this->addPackage($this->loader->load($this->preProcess($driver, $data, $identifier)));
             } catch (\Exception $e) {
                 if ($verbose) {
-                    $this->io->write('<warning>Skipped tag '.$tag.', '.($e instanceof TransportException ? 'no composer file was found' : $e->getMessage()).'</warning>');
+                    $this->io->writeError('<warning>Skipped tag '.$tag.', '.($e instanceof TransportException ? 'no composer file was found' : $e->getMessage()).'</warning>');
                 }
                 continue;
             }
@@ -198,14 +198,14 @@ class VcsRepository extends ArrayRepository
         foreach ($driver->getBranches() as $branch => $identifier) {
             $msg = 'Reading composer.json of <info>' . ($this->packageName ?: $this->url) . '</info> (<comment>' . $branch . '</comment>)';
             if ($verbose) {
-                $this->io->write($msg);
+                $this->io->writeError($msg);
             } else {
                 $this->io->overwrite($msg, false);
             }
 
             if (!$parsedBranch = $this->validateBranch($branch)) {
                 if ($verbose) {
-                    $this->io->write('<warning>Skipped branch '.$branch.', invalid name</warning>');
+                    $this->io->writeError('<warning>Skipped branch '.$branch.', invalid name</warning>');
                 }
                 continue;
             }
@@ -213,7 +213,7 @@ class VcsRepository extends ArrayRepository
             try {
                 if (!$data = $driver->getComposerInformation($identifier)) {
                     if ($verbose) {
-                        $this->io->write('<warning>Skipped branch '.$branch.', no composer file</warning>');
+                        $this->io->writeError('<warning>Skipped branch '.$branch.', no composer file</warning>');
                     }
                     continue;
                 }
@@ -230,7 +230,7 @@ class VcsRepository extends ArrayRepository
                 }
 
                 if ($verbose) {
-                    $this->io->write('Importing branch '.$branch.' ('.$data['version'].')');
+                    $this->io->writeError('Importing branch '.$branch.' ('.$data['version'].')');
                 }
 
                 $packageData = $this->preProcess($driver, $data, $identifier);
@@ -241,16 +241,16 @@ class VcsRepository extends ArrayRepository
                 $this->addPackage($package);
             } catch (TransportException $e) {
                 if ($verbose) {
-                    $this->io->write('<warning>Skipped branch '.$branch.', no composer file was found</warning>');
+                    $this->io->writeError('<warning>Skipped branch '.$branch.', no composer file was found</warning>');
                 }
                 continue;
             } catch (\Exception $e) {
                 if (!$verbose) {
-                    $this->io->write('');
+                    $this->io->writeError('');
                 }
                 $this->branchErrorOccurred = true;
-                $this->io->write('<error>Skipped branch '.$branch.', '.$e->getMessage().'</error>');
-                $this->io->write('');
+                $this->io->writeError('<error>Skipped branch '.$branch.', '.$e->getMessage().'</error>');
+                $this->io->writeError('');
                 continue;
             }
         }

src/Composer/Util/Git.php

@@ -122,7 +122,7 @@ class Git
                         }
                     }
 
-                    $this->io->write('    Authentication required (<info>'.parse_url($url, PHP_URL_HOST).'</info>):');
+                    $this->io->writeError('    Authentication required (<info>'.parse_url($url, PHP_URL_HOST).'</info>):');
                     $auth = array(
                         'username'  => $this->io->ask('      Username: ', $defaultUsername),
                         'password'  => $this->io->askAndHideAnswer('      Password: '),

src/Composer/Util/GitHub.php

@@ -77,11 +77,11 @@ class GitHub
     public function authorizeOAuthInteractively($originUrl, $message = null)
     {
         if ($message) {
-            $this->io->write($message);
+            $this->io->writeError($message);
         }
 
-        $this->io->write(sprintf('A token will be created and stored in "%s", your password will never be stored', $this->config->getAuthConfigSource()->getName()));
-        $this->io->write('To revoke access to this token you can visit https://github.com/settings/applications');
+        $this->io->writeError(sprintf('A token will be created and stored in "%s", your password will never be stored', $this->config->getAuthConfigSource()->getName()));
+        $this->io->writeError('To revoke access to this token you can visit https://github.com/settings/applications');
 
         $otp = null;
         $attemptCounter = 0;
@@ -105,13 +105,13 @@ class GitHub
                     }
 
                     if (401 === $e->getCode()) {
-                        $this->io->write('Bad credentials.');
+                        $this->io->writeError('Bad credentials.');
                     } else {
-                        $this->io->write('Maximum number of login attempts exceeded. Please try again later.');
+                        $this->io->writeError('Maximum number of login attempts exceeded. Please try again later.');
                     }
 
-                    $this->io->write('You can also manually create a personal token at https://github.com/settings/applications');
-                    $this->io->write('Add it using "composer config github-oauth.github.com <token>"');
+                    $this->io->writeError('You can also manually create a personal token at https://github.com/settings/applications');
+                    $this->io->writeError('Add it using "composer config github-oauth.github.com <token>"');
 
                     continue;
                 }
@@ -166,7 +166,7 @@ class GitHub
             )
         ));
 
-        $this->io->write('Token successfully created');
+        $this->io->writeError('Token successfully created');
 
         return JsonFile::parseJson($json);
     }
@@ -184,14 +184,14 @@ class GitHub
             list($required, $method) = array_map('trim', explode(';', substr(strstr($headers[$key], ':'), 1)));
 
             if ('required' === $required) {
-                $this->io->write('Two-factor Authentication');
+                $this->io->writeError('Two-factor Authentication');
 
                 if ('app' === $method) {
-                    $this->io->write('Open the two-factor authentication app on your device to view your authentication code and verify your identity.');
+                    $this->io->writeError('Open the two-factor authentication app on your device to view your authentication code and verify your identity.');
                 }
 
                 if ('sms' === $method) {
-                    $this->io->write('You have been sent an SMS message with an authentication code to verify your identity.');
+                    $this->io->writeError('You have been sent an SMS message with an authentication code to verify your identity.');
                 }
 
                 return $this->io->ask('Authentication Code: ');

src/Composer/Util/ProcessExecutor.php

@@ -45,7 +45,7 @@ class ProcessExecutor
     {
         if ($this->io && $this->io->isDebug()) {
             $safeCommand = preg_replace('{(://[^:/\s]+:)[^@\s/]+}i', '$1****', $command);
-            $this->io->write('Executing command ('.($cwd ?: 'CWD').'): '.$safeCommand);
+            $this->io->writeError('Executing command ('.($cwd ?: 'CWD').'): '.$safeCommand);
         }
 
         // make sure that null translate to the proper directory in case the dir is a symlink

src/Composer/Util/RemoteFilesystem.php

@@ -146,7 +146,7 @@ class RemoteFilesystem
         $options = $this->getOptionsForUrl($originUrl, $additionalOptions);
 
         if ($this->io->isDebug()) {
-            $this->io->write((substr($fileUrl, 0, 4) === 'http' ? 'Downloading ' : 'Reading ') . $fileUrl);
+            $this->io->writeError((substr($fileUrl, 0, 4) === 'http' ? 'Downloading ' : 'Reading ') . $fileUrl);
         }
         if (isset($options['github-token'])) {
             $fileUrl .= (false === strpos($fileUrl, '?') ? '?' : '&') . 'access_token='.$options['github-token'];
@@ -158,7 +158,7 @@ class RemoteFilesystem
         $ctx = StreamContextFactory::getContext($fileUrl, $options, array('notification' => array($this, 'callbackGet')));
 
         if ($this->progress) {
-            $this->io->write("    Downloading: <comment>connection...</comment>", false);
+            $this->io->writeError("    Downloading: <comment>connection...</comment>", false);
         }
 
         $errorMessage = '';

src/Composer/Util/Svn.php

@@ -111,7 +111,7 @@ class Svn
             }
             $output .= $buffer;
             if ($verbose) {
-                $io->write($buffer, false);
+                $io->writeError($buffer, false);
             }
         };
         $status = $this->process->execute($svnCommand, $handler, $cwd);
@@ -169,7 +169,7 @@ class Svn
             );
         }
 
-        $this->io->write("The Subversion server ({$this->url}) requested credentials:");
+        $this->io->writeError("The Subversion server ({$this->url}) requested credentials:");
 
         $this->hasAuth = true;
         $this->credentials['username'] = $this->io->ask("Username: ");

tests/Composer/Test/ApplicationTest.php

@@ -29,7 +29,7 @@ class ApplicationTest extends TestCase
             ->will($this->returnValue('list'));
 
         $outputMock->expects($this->once())
-            ->method("writeln")
+            ->method("write")
             ->with($this->equalTo(sprintf('<warning>Warning: This development build of composer is over 30 days old. It is recommended to update it by running "%s self-update" to get the latest version.</warning>', $_SERVER['PHP_SELF'])));
 
         if (!defined('COMPOSER_DEV_WARNING_TIME')) {

tests/Composer/Test/Autoload/ClassMapGeneratorTest.php

@@ -128,7 +128,7 @@ class ClassMapGeneratorTest extends \PHPUnit_Framework_TestCase
         $msg = '';
 
         $io->expects($this->once())
-            ->method('write')
+            ->method('writeError')
             ->will($this->returnCallback(function ($text) use (&$msg) {
                 $msg = $text;
             }));

tests/Composer/Test/Downloader/PerforceDownloaderTest.php

@@ -120,7 +120,7 @@ class PerforceDownloaderTest extends \PHPUnit_Framework_TestCase
         $ref = 'SOURCE_REF@123';
         $label = 123;
         $this->package->expects($this->once())->method('getSourceReference')->will($this->returnValue($ref));
-        $this->io->expects($this->once())->method('write')->with($this->stringContains('Cloning '.$ref));
+        $this->io->expects($this->once())->method('writeError')->with($this->stringContains('Cloning '.$ref));
         $perforceMethods = array('setStream', 'p4Login', 'writeP4ClientSpec', 'connectClient', 'syncCodeBase', 'cleanupClientSpec');
         $perforce = $this->getMockBuilder('Composer\Util\Perforce', $perforceMethods)->disableOriginalConstructor()->getMock();
         $perforce->expects($this->at(0))->method('initializePath')->with($this->equalTo($this->testPath));
@@ -143,7 +143,7 @@ class PerforceDownloaderTest extends \PHPUnit_Framework_TestCase
         $ref = 'SOURCE_REF';
         $label = null;
         $this->package->expects($this->once())->method('getSourceReference')->will($this->returnValue($ref));
-        $this->io->expects($this->once())->method('write')->with($this->stringContains('Cloning '.$ref));
+        $this->io->expects($this->once())->method('writeError')->with($this->stringContains('Cloning '.$ref));
         $perforceMethods = array('setStream', 'p4Login', 'writeP4ClientSpec', 'connectClient', 'syncCodeBase', 'cleanupClientSpec');
         $perforce = $this->getMockBuilder('Composer\Util\Perforce', $perforceMethods)->disableOriginalConstructor()->getMock();
         $perforce->expects($this->at(0))->method('initializePath')->with($this->equalTo($this->testPath));

tests/Composer/Test/EventDispatcher/EventDispatcherTest.php

@@ -33,7 +33,7 @@ class EventDispatcherTest extends TestCase
         ), $io);
 
         $io->expects($this->once())
-            ->method('write')
+            ->method('writeError')
             ->with('<error>Script Composer\Test\EventDispatcher\EventDispatcherTest::call handling the post-install-cmd event terminated with an exception</error>');
 
         $dispatcher->dispatchScript(ScriptEvents::POST_INSTALL_CMD, false);
@@ -189,7 +189,7 @@ class EventDispatcherTest extends TestCase
             ->will($this->returnValue($listener));
 
         $io->expects($this->once())
-            ->method('write')
+            ->method('writeError')
             ->with($this->equalTo('<error>Script '.$code.' handling the post-install-cmd event returned with an error</error>'));
 
         $this->setExpectedException('RuntimeException');

tests/Composer/Test/Fixtures/functional/create-project-command.test

@@ -1,6 +1,6 @@
 --RUN--
 create-project seld/jsonlint %testDir% 1.0.0 --prefer-source -n
---EXPECT--
+--EXPECT-ERROR--
 Installing seld/jsonlint (1.0.0)
   - Installing seld/jsonlint (1.0.0)
     Cloning 3b4bc2a96ff5d3fe6866bfe9dd0c845246705791

tests/Composer/Test/Fixtures/functional/create-project-shows-full-hash-for-dev-packages.test

@@ -1,4 +1,4 @@
 --RUN--
 create-project --repository-url=packages.json -v seld/jsonlint %testDir% dev-master
---EXPECT-REGEX--
+--EXPECT-ERROR-REGEX--
 {^Installing seld/jsonlint \(dev-master [a-f0-9]{40}\)}

tests/Composer/Test/IO/ConsoleIOTest.php

@@ -49,6 +49,22 @@ class ConsoleIOTest extends TestCase
         $consoleIO->write('some information about something', false);
     }
 
+    public function testWriteError()
+    {
+        $inputMock = $this->getMock('Symfony\Component\Console\Input\InputInterface');
+        $outputMock = $this->getMock('Symfony\Component\Console\Output\ConsoleOutputInterface');
+        $outputMock->expects($this->once())
+            ->method('getErrorOutput')
+            ->willReturn($outputMock);
+        $outputMock->expects($this->once())
+            ->method('write')
+            ->with($this->equalTo('some information about something'), $this->equalTo(false));
+        $helperMock = $this->getMock('Symfony\Component\Console\Helper\HelperSet');
+
+        $consoleIO = new ConsoleIO($inputMock, $outputMock, $helperMock);
+        $consoleIO->writeError('some information about something', false);
+    }
+
     public function testWriteWithMultipleLineStringWhenDebugging()
     {
         $inputMock = $this->getMock('Symfony\Component\Console\Input\InputInterface');

tests/Composer/Test/InstallerTest.php

@@ -149,11 +149,15 @@ class InstallerTest extends TestCase
 
         $output = null;
         $io = $this->getMock('Composer\IO\IOInterface');
+        $callback = function ($text, $newline) use (&$output) {
+            $output .= $text . ($newline ? "\n" : "");
+        };
         $io->expects($this->any())
             ->method('write')
-            ->will($this->returnCallback(function ($text, $newline) use (&$output) {
-                $output .= $text . ($newline ? "\n" : "");
-            }));
+            ->will($this->returnCallback($callback));
+        $io->expects($this->any())
+            ->method('writeError')
+            ->will($this->returnCallback($callback));
 
         $composer = FactoryMock::create($io, $composerConfig);
 
@@ -195,10 +199,7 @@ class InstallerTest extends TestCase
         $composer->setAutoloadGenerator($autoloadGenerator);
         $composer->setEventDispatcher($eventDispatcher);
 
-        $installer = Installer::create(
-            $io,
-            $composer
-        );
+        $installer = Installer::create($io, $composer);
 
         $application = new Application;
         $application->get('install')->setCode(function ($input, $output) use ($installer) {

tests/Composer/Test/Util/GitHubTest.php

@@ -34,7 +34,7 @@ class GitHubTest extends \PHPUnit_Framework_TestCase
         $io = $this->getIOMock();
         $io
             ->expects($this->at(0))
-            ->method('write')
+            ->method('writeError')
             ->with($this->message)
         ;
         $io