diff --git a/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Compiler/CachePoolPass.php b/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Compiler/CachePoolPass.php
index 233b01fb43..e4a86dc6ef 100644
--- a/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Compiler/CachePoolPass.php
+++ b/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Compiler/CachePoolPass.php
@@ -36,7 +36,6 @@ class CachePoolPass implements CompilerPassInterface
         }
         $seed .= '.'.$container->getParameter('kernel.name').'.'.$container->getParameter('kernel.environment');
 
-        $aliases = $container->getAliases();
         $attributes = array(
             'provider',
             'namespace',
@@ -59,9 +58,9 @@ class CachePoolPass implements CompilerPassInterface
                 $tags[0]['namespace'] = $this->getNamespace($seed, $id);
             }
             if (isset($tags[0]['clearer'])) {
-                $clearer = strtolower($tags[0]['clearer']);
-                while (isset($aliases[$clearer])) {
-                    $clearer = (string) $aliases[$clearer];
+                $clearer = $tags[0]['clearer'];
+                while ($container->hasAlias($clearer)) {
+                    $clearer = (string) $container->getAlias($clearer);
                 }
             } else {
                 $clearer = null;
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php
index 7254ed34a7..8b9dd97f00 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php
@@ -320,26 +320,26 @@ abstract class FrameworkExtensionTest extends TestCase
         $packages = $container->getDefinition('assets.packages');
 
         // default package
-        $defaultPackage = $container->getDefinition($packages->getArgument(0));
+        $defaultPackage = $container->getDefinition((string) $packages->getArgument(0));
         $this->assertUrlPackage($container, $defaultPackage, array('http://cdn.example.com'), 'SomeVersionScheme', '%%s?version=%%s');
 
         // packages
         $packages = $packages->getArgument(1);
         $this->assertCount(5, $packages);
 
-        $package = $container->getDefinition($packages['images_path']);
+        $package = $container->getDefinition((string) $packages['images_path']);
         $this->assertPathPackage($container, $package, '/foo', 'SomeVersionScheme', '%%s?version=%%s');
 
-        $package = $container->getDefinition($packages['images']);
+        $package = $container->getDefinition((string) $packages['images']);
         $this->assertUrlPackage($container, $package, array('http://images1.example.com', 'http://images2.example.com'), '1.0.0', '%%s?version=%%s');
 
-        $package = $container->getDefinition($packages['foo']);
+        $package = $container->getDefinition((string) $packages['foo']);
         $this->assertPathPackage($container, $package, '', '1.0.0', '%%s-%%s');
 
-        $package = $container->getDefinition($packages['bar']);
+        $package = $container->getDefinition((string) $packages['bar']);
         $this->assertUrlPackage($container, $package, array('https://bar2.example.com'), 'SomeVersionScheme', '%%s?version=%%s');
 
-        $package = $container->getDefinition($packages['bar_version_strategy']);
+        $package = $container->getDefinition((string) $packages['bar_version_strategy']);
         $this->assertEquals('assets.custom_version_strategy', (string) $package->getArgument(1));
     }
 
@@ -349,7 +349,7 @@ abstract class FrameworkExtensionTest extends TestCase
         $packages = $container->getDefinition('assets.packages');
 
         // default package
-        $defaultPackage = $container->getDefinition($packages->getArgument(0));
+        $defaultPackage = $container->getDefinition((string) $packages->getArgument(0));
         $this->assertEquals('assets.custom_version_strategy', (string) $defaultPackage->getArgument(1));
     }
 
@@ -865,7 +865,7 @@ abstract class FrameworkExtensionTest extends TestCase
 
     private function assertVersionStrategy(ContainerBuilder $container, Reference $reference, $version, $format)
     {
-        $versionStrategy = $container->getDefinition($reference);
+        $versionStrategy = $container->getDefinition((string) $reference);
         if (null === $version) {
             $this->assertEquals('assets.empty_version_strategy', (string) $reference);
         } else {
diff --git a/src/Symfony/Bundle/SecurityBundle/DependencyInjection/SecurityExtension.php b/src/Symfony/Bundle/SecurityBundle/DependencyInjection/SecurityExtension.php
index 5595b08d30..51de15b215 100644
--- a/src/Symfony/Bundle/SecurityBundle/DependencyInjection/SecurityExtension.php
+++ b/src/Symfony/Bundle/SecurityBundle/DependencyInjection/SecurityExtension.php
@@ -407,7 +407,7 @@ class SecurityExtension extends Extension
         $config->replaceArgument(8, isset($firewall['access_denied_handler']) ? $firewall['access_denied_handler'] : null);
         $config->replaceArgument(9, isset($firewall['access_denied_url']) ? $firewall['access_denied_url'] : null);
 
-        $container->setAlias(new Alias('security.user_checker.'.$id, false), $firewall['user_checker']);
+        $container->setAlias('security.user_checker.'.$id, new Alias($firewall['user_checker'], false));
 
         foreach ($this->factories as $position) {
             foreach ($position as $factory) {
diff --git a/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/CompleteConfigurationTest.php b/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/CompleteConfigurationTest.php
index bbce61a758..cbdb6e8f0f 100644
--- a/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/CompleteConfigurationTest.php
+++ b/src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/CompleteConfigurationTest.php
@@ -73,7 +73,7 @@ abstract class CompleteConfigurationTest extends \PHPUnit_Framework_TestCase
             $arguments = $contextDef->getArguments();
             $listeners[] = array_map(function ($ref) { return (string) $ref; }, $arguments['index_0']);
 
-            $configDef = $container->getDefinition($arguments['index_2']);
+            $configDef = $container->getDefinition((string) $arguments['index_2']);
             $configs[] = array_values($configDef->getArguments());
         }
 
@@ -234,7 +234,7 @@ abstract class CompleteConfigurationTest extends \PHPUnit_Framework_TestCase
                 );
             } elseif (3 === $i) {
                 $this->assertEquals('IS_AUTHENTICATED_ANONYMOUSLY', $attributes[0]);
-                $expression = $container->getDefinition($attributes[1])->getArgument(0);
+                $expression = $container->getDefinition((string) $attributes[1])->getArgument(0);
                 $this->assertEquals("token.getUsername() matches '/^admin/'", $expression);
             }
         }
diff --git a/src/Symfony/Bundle/TwigBundle/TwigEngine.php b/src/Symfony/Bundle/TwigBundle/TwigEngine.php
index 76daad58a3..503c55f6af 100644
--- a/src/Symfony/Bundle/TwigBundle/TwigEngine.php
+++ b/src/Symfony/Bundle/TwigBundle/TwigEngine.php
@@ -49,16 +49,12 @@ class TwigEngine extends BaseEngine implements EngineInterface
         try {
             return parent::render($name, $parameters);
         } catch (\Twig_Error $e) {
-            if ($name instanceof TemplateReference) {
+            if ($name instanceof TemplateReference && !method_exists($e, 'setSourceContext')) {
                 try {
                     // try to get the real name of the template where the error occurred
                     $name = $e->getTemplateName();
                     $path = (string) $this->locator->locate($this->parser->parse($name));
-                    if (method_exists($e, 'setSourceContext')) {
-                        $e->setSourceContext(new \Twig_Source('', $name, $path));
-                    } else {
-                        $e->setTemplateName($path);
-                    }
+                    $e->setTemplateName($path);
                 } catch (\Exception $e2) {
                 }
             }
diff --git a/src/Symfony/Component/ClassLoader/ClassCollectionLoader.php b/src/Symfony/Component/ClassLoader/ClassCollectionLoader.php
index 15e3a5a822..0079e8a798 100644
--- a/src/Symfony/Component/ClassLoader/ClassCollectionLoader.php
+++ b/src/Symfony/Component/ClassLoader/ClassCollectionLoader.php
@@ -305,7 +305,13 @@ REGEX;
      */
     private static function writeCacheFile($file, $content)
     {
-        $tmpFile = tempnam(dirname($file), basename($file));
+        $dir = dirname($file);
+        if (!is_writable($dir)) {
+            throw new \RuntimeException(sprintf('Cache directory "%s" is not writable.', $dir));
+        }
+
+        $tmpFile = tempnam($dir, basename($file));
+
         if (false !== @file_put_contents($tmpFile, $content) && @rename($tmpFile, $file)) {
             @chmod($file, 0666 & ~umask());
 
diff --git a/src/Symfony/Component/DependencyInjection/ContainerBuilder.php b/src/Symfony/Component/DependencyInjection/ContainerBuilder.php
index 63206f5cad..044d72cb54 100644
--- a/src/Symfony/Component/DependencyInjection/ContainerBuilder.php
+++ b/src/Symfony/Component/DependencyInjection/ContainerBuilder.php
@@ -436,7 +436,7 @@ class ContainerBuilder extends Container implements TaggedContainerInterface
         }
 
         if (!isset($this->definitions[$id]) && isset($this->aliasDefinitions[$id])) {
-            return $this->get($this->aliasDefinitions[$id], $invalidBehavior);
+            return $this->get((string) $this->aliasDefinitions[$id], $invalidBehavior);
         }
 
         try {
@@ -1240,14 +1240,14 @@ class ContainerBuilder extends Container implements TaggedContainerInterface
     /**
      * Shares a given service in the container.
      *
-     * @param Definition $definition
-     * @param mixed      $service
-     * @param string     $id
+     * @param Definition  $definition
+     * @param mixed       $service
+     * @param string|null $id
      */
     private function shareService(Definition $definition, $service, $id)
     {
-        if ($definition->isShared()) {
-            $this->services[$lowerId = strtolower($id)] = $service;
+        if (null !== $id && $definition->isShared()) {
+            $this->services[strtolower($id)] = $service;
         }
     }
 
diff --git a/src/Symfony/Component/DependencyInjection/Dumper/YamlDumper.php b/src/Symfony/Component/DependencyInjection/Dumper/YamlDumper.php
index b8d936658f..b6c4e6639c 100644
--- a/src/Symfony/Component/DependencyInjection/Dumper/YamlDumper.php
+++ b/src/Symfony/Component/DependencyInjection/Dumper/YamlDumper.php
@@ -170,7 +170,7 @@ class YamlDumper extends Dumper
             return sprintf("    %s: '@%s'\n", $alias, $id);
         }
 
-        return sprintf("    %s:\n        alias: %s\n        public: false", $alias, $id);
+        return sprintf("    %s:\n        alias: %s\n        public: false\n", $alias, $id);
     }
 
     /**
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Compiler/AutowirePassTest.php b/src/Symfony/Component/DependencyInjection/Tests/Compiler/AutowirePassTest.php
index 0b8ab9374a..640bbbae91 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Compiler/AutowirePassTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Compiler/AutowirePassTest.php
@@ -213,13 +213,13 @@ class AutowirePassTest extends \PHPUnit_Framework_TestCase
         $this->assertCount(1, $container->getDefinition('coop_tilleuls')->getArguments());
         $this->assertEquals('autowired.symfony\component\dependencyinjection\tests\compiler\dunglas', $container->getDefinition('coop_tilleuls')->getArgument(0));
 
-        $dunglasDefinition = $container->getDefinition('autowired.symfony\component\dependencyinjection\tests\compiler\dunglas');
+        $dunglasDefinition = $container->getDefinition('autowired.Symfony\Component\DependencyInjection\Tests\Compiler\Dunglas');
         $this->assertEquals(__NAMESPACE__.'\Dunglas', $dunglasDefinition->getClass());
         $this->assertFalse($dunglasDefinition->isPublic());
         $this->assertCount(1, $dunglasDefinition->getArguments());
         $this->assertEquals('autowired.symfony\component\dependencyinjection\tests\compiler\lille', $dunglasDefinition->getArgument(0));
 
-        $lilleDefinition = $container->getDefinition('autowired.symfony\component\dependencyinjection\tests\compiler\lille');
+        $lilleDefinition = $container->getDefinition('autowired.Symfony\Component\DependencyInjection\Tests\Compiler\Lille');
         $this->assertEquals(__NAMESPACE__.'\Lille', $lilleDefinition->getClass());
     }
 
diff --git a/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php b/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php
index 31e9e97c63..20c171c798 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php
@@ -144,7 +144,7 @@ class ContainerTest extends \PHPUnit_Framework_TestCase
     {
         $sc = new Container();
         $sc->set('foo', $foo = new \stdClass());
-        $this->assertEquals($foo, $sc->get('foo'), '->set() sets a service');
+        $this->assertSame($foo, $sc->get('foo'), '->set() sets a service');
     }
 
     public function testSetWithNullResetTheService()
@@ -166,14 +166,14 @@ class ContainerTest extends \PHPUnit_Framework_TestCase
     {
         $sc = new ProjectServiceContainer();
         $sc->set('foo', $foo = new \stdClass());
-        $this->assertEquals($foo, $sc->get('foo'), '->get() returns the service for the given id');
-        $this->assertEquals($foo, $sc->get('Foo'), '->get() returns the service for the given id, and converts id to lowercase');
-        $this->assertEquals($sc->__bar, $sc->get('bar'), '->get() returns the service for the given id');
-        $this->assertEquals($sc->__foo_bar, $sc->get('foo_bar'), '->get() returns the service if a get*Method() is defined');
-        $this->assertEquals($sc->__foo_baz, $sc->get('foo.baz'), '->get() returns the service if a get*Method() is defined');
+        $this->assertSame($foo, $sc->get('foo'), '->get() returns the service for the given id');
+        $this->assertSame($foo, $sc->get('Foo'), '->get() returns the service for the given id, and converts id to lowercase');
+        $this->assertSame($sc->__bar, $sc->get('bar'), '->get() returns the service for the given id');
+        $this->assertSame($sc->__foo_bar, $sc->get('foo_bar'), '->get() returns the service if a get*Method() is defined');
+        $this->assertSame($sc->__foo_baz, $sc->get('foo.baz'), '->get() returns the service if a get*Method() is defined');
 
         $sc->set('bar', $bar = new \stdClass());
-        $this->assertEquals($bar, $sc->get('bar'), '->get() prefers to return a service defined with set() than one defined with a getXXXMethod()');
+        $this->assertSame($bar, $sc->get('bar'), '->get() prefers to return a service defined with set() than one defined with a getXXXMethod()');
 
         try {
             $sc->get('');
@@ -196,15 +196,15 @@ class ContainerTest extends \PHPUnit_Framework_TestCase
         $sc = new LegacyProjectServiceContainer();
         $sc->set('foo', $foo = new \stdClass());
 
-        $this->assertEquals($foo, $sc->get('foo'), '->get() returns the service for the given id');
-        $this->assertEquals($foo, $sc->get('Foo'), '->get() returns the service for the given id, and converts id to lowercase');
-        $this->assertEquals($sc->__bar, $sc->get('bar'), '->get() returns the service for the given id');
-        $this->assertEquals($sc->__foo_bar, $sc->get('foo_bar'), '->get() returns the service if a get*Method() is defined');
-        $this->assertEquals($sc->__foo_baz, $sc->get('foo.baz'), '->get() returns the service if a get*Method() is defined');
-        $this->assertEquals($sc->__foo_baz, $sc->get('foo\\baz'), '->get() returns the service if a get*Method() is defined');
+        $this->assertSame($foo, $sc->get('foo'), '->get() returns the service for the given id');
+        $this->assertSame($foo, $sc->get('Foo'), '->get() returns the service for the given id, and converts id to lowercase');
+        $this->assertSame($sc->__bar, $sc->get('bar'), '->get() returns the service for the given id');
+        $this->assertSame($sc->__foo_bar, $sc->get('foo_bar'), '->get() returns the service if a get*Method() is defined');
+        $this->assertSame($sc->__foo_baz, $sc->get('foo.baz'), '->get() returns the service if a get*Method() is defined');
+        $this->assertSame($sc->__foo_baz, $sc->get('foo\\baz'), '->get() returns the service if a get*Method() is defined');
 
         $sc->set('bar', $bar = new \stdClass());
-        $this->assertEquals($bar, $sc->get('bar'), '->get() prefers to return a service defined with set() than one defined with a getXXXMethod()');
+        $this->assertSame($bar, $sc->get('bar'), '->get() prefers to return a service defined with set() than one defined with a getXXXMethod()');
 
         try {
             $sc->get('');
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Dumper/PhpDumperTest.php b/src/Symfony/Component/DependencyInjection/Tests/Dumper/PhpDumperTest.php
index 9375129a4f..7e58f6e4c5 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Dumper/PhpDumperTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Dumper/PhpDumperTest.php
@@ -272,7 +272,7 @@ class PhpDumperTest extends \PHPUnit_Framework_TestCase
         $container->set('bar', $bar = new \stdClass());
         $container->setParameter('foo_bar', 'foo_bar');
 
-        $this->assertEquals($bar, $container->get('bar'), '->set() overrides an already defined service');
+        $this->assertSame($bar, $container->get('bar'), '->set() overrides an already defined service');
     }
 
     public function testOverrideServiceWhenUsingADumpedContainerAndServiceIsUsedFromAnotherOne()
@@ -308,7 +308,7 @@ class PhpDumperTest extends \PHPUnit_Framework_TestCase
         $container->compile();
         $dumper = new PhpDumper($container);
 
-        $this->assertEquals(file_get_contents(self::$fixturesPath.'/php/services24.php'), $dumper->dump());
+        $this->assertStringEqualsFile(self::$fixturesPath.'/php/services24.php', $dumper->dump());
     }
 
     public function testEnvParameter()
@@ -466,8 +466,7 @@ class PhpDumperTest extends \PHPUnit_Framework_TestCase
         $container->compile();
         $dumper = new PhpDumper($container);
 
-        $dump = $dumper->dump(array('class' => 'Symfony_DI_PhpDumper_Test_Closure_Proxy'));
-        $this->assertEquals(file_get_contents(self::$fixturesPath.'/php/services31.php'), $dumper->dump());
+        $this->assertStringEqualsFile(self::$fixturesPath.'/php/services31.php', $dumper->dump());
         $res = $container->getResources();
         $this->assertSame(realpath(self::$fixturesPath.'/containers/container31.php'), array_pop($res)->getResource());
     }
@@ -481,8 +480,7 @@ class PhpDumperTest extends \PHPUnit_Framework_TestCase
         $container->compile();
         $dumper = new PhpDumper($container);
 
-        $dump = $dumper->dump(array('class' => 'Symfony_DI_PhpDumper_Test_Closure_Proxy_Php71'));
-        $this->assertEquals(file_get_contents(self::$fixturesPath.'/php/services32.php'), $dumper->dump());
+        $this->assertStringEqualsFile(self::$fixturesPath.'/php/services32.php', $dumper->dump());
         $res = $container->getResources();
         $this->assertSame(realpath(self::$fixturesPath.'/containers/container32.php'), array_pop($res)->getResource());
     }
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services6.yml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services6.yml
index 5f22bc1cae..20ed7e315a 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services6.yml
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services6.yml
@@ -18,8 +18,6 @@ services:
         calls:
             - [ setBar, [ foo, '@foo', [true, false] ] ]
     alias_for_foo: '@foo'
-    another_third_alias_for_foo:
-        alias: foo
     another_alias_for_foo:
         alias: foo
         public: false
@@ -27,6 +25,8 @@ services:
         class: Request
         synthetic: true
         lazy: true
+    another_third_alias_for_foo:
+        alias: foo
     decorator_service:
         decorates: decorated
     decorator_service_with_name:
diff --git a/src/Symfony/Component/HttpKernel/Tests/Bundle/BundleTest.php b/src/Symfony/Component/HttpKernel/Tests/Bundle/BundleTest.php
index fe05fe8d44..a8b91453c6 100644
--- a/src/Symfony/Component/HttpKernel/Tests/Bundle/BundleTest.php
+++ b/src/Symfony/Component/HttpKernel/Tests/Bundle/BundleTest.php
@@ -57,7 +57,7 @@ class BundleTest extends \PHPUnit_Framework_TestCase
     public function testHttpKernelRegisterCommandsIgnoresCommandsThatAreRegisteredAsServices()
     {
         $container = new ContainerBuilder();
-        $container->register('console.command.Symfony_Component_HttpKernel_Tests_Fixtures_ExtensionPresentBundle_Command_FooCommand', 'Symfony\Component\HttpKernel\Tests\Fixtures\ExtensionPresentBundle\Command\FooCommand');
+        $container->register('console.command.symfony_component_httpkernel_tests_fixtures_extensionpresentbundle_command_foocommand', 'Symfony\Component\HttpKernel\Tests\Fixtures\ExtensionPresentBundle\Command\FooCommand');
 
         $application = $this->getMockBuilder('Symfony\Component\Console\Application')->getMock();
         // add() is never called when the found command classes are already registered as services