[HttpKernel] Deprecate returning a ContainerBuilder from KernelInterface::registerContainerConfiguration()

Author: nicolas-grekas

CHANGELOG.md

@@ -7,7 +7,8 @@ CHANGELOG
  * Deprecate `ArgumentInterface`
  * Add `ArgumentMetadata::getAttributes()`
  * Deprecate `ArgumentMetadata::getAttribute()`, use `getAttributes()` instead
- * marked the class `Symfony\Component\HttpKernel\EventListener\DebugHandlersListener` as internal
+ * Mark the class `Symfony\Component\HttpKernel\EventListener\DebugHandlersListener` as internal
+ * Deprecate returning a `ContainerBuilder` from `KernelInterface::registerContainerConfiguration()`
 
 5.2.0
 -----

Kernel.php

@@ -642,6 +642,7 @@ protected function buildContainer()
         $this->prepareContainer($container);
 
         if (null !== $cont = $this->registerContainerConfiguration($this->getContainerLoader($container))) {
+            trigger_deprecation('symfony/http-kernel', '5.3', 'Returning a ContainerBuilder from "%s::registerContainerConfiguration()" is deprecated.', get_debug_type($this));
             $container->merge($cont);
         }