[DependencyInjection] Fix #16461 Let Container::set() replace existing aliases

`Container::set()` now overrides any previously alias defined with the same name.

src/Symfony/Component/DependencyInjection/Container.php

@@ -200,6 +200,10 @@ class Container implements IntrospectableContainerInterface
             $this->scopedServices[$scope][$id] = $service;
         }
 
+        if (isset($this->aliases[$id])) {
+            unset($this->aliases[$id]);
+        }
+
         $this->services[$id] = $service;
 
         if (method_exists($this, $method = 'synchronize'.strtr($id, $this->underscoreMap).'Service')) {

src/Symfony/Component/DependencyInjection/Tests/ContainerBuilderTest.php

@@ -217,6 +217,16 @@ class ContainerBuilderTest extends \PHPUnit_Framework_TestCase
         $this->assertTrue(isset($aliases['foobar']));
     }
 
+    public function testSetReplacesAlias()
+    {
+        $builder = new ContainerBuilder();
+        $builder->setAlias('alias', 'aliased');
+        $builder->set('aliased', new \stdClass());
+
+        $builder->set('alias', $foo = new \stdClass());
+        $this->assertSame($foo, $builder->get('alias'), '->set() replaces an existing alias');
+    }
+
     public function testAddGetCompilerPass()
     {
         $builder = new ContainerBuilder();

src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php

@@ -152,6 +152,14 @@ class ContainerTest extends \PHPUnit_Framework_TestCase
         $this->assertSame($foo, $services['foo']['foo']);
     }
 
+    public function testSetReplacesAlias()
+    {
+        $c = new ProjectServiceContainer();
+
+        $c->set('alias', $foo = new \stdClass());
+        $this->assertSame($foo, $c->get('alias'), '->set() replaces an existing alias');
+    }
+
     public function testGet()
     {
         $sc = new ProjectServiceContainer();