src/AppKernel.php
public function registerContainerConfiguration(LoaderInterface $loader)
    {
        $loader->load(function (ContainerBuilder $container) use ($loader) {
            $container->loadFromExtension('framework', [
                'router' => [
                    'resource' => 'kernel:loadRoutes',
                    'type' => 'service',
                ],
            ]);

            $this->configFiles = array_unique($this->configFiles);
            foreach ($this->configFiles as $path) {
                $loader->load($path);
            }

            $container->addObjectResource($this);
        });
    }
public function registerContainerConfiguration(LoaderInterface $loader)
    {
        $loader->load(function (ContainerBuilder $container) use ($loader) {
            $container->loadFromExtension('framework', [
                'router' => [
                    'resource' => 'kernel:loadRoutes',
                    'type' => 'service',
                ],
            ]);

            $this->configFiles = array_unique($this->configFiles);
            foreach ($this->configFiles as $path) {
                $loader->load($path);
            }

            $container->addObjectResource($this);
        });
    }
(From MicroKernelTrait)
{@inheritdoc}