bug #61940 [DependencyInjection] Register a custom autoloader to generate *Config classes when they don't exist yet (alexandre-daubois)

This PR was merged into the 7.4 branch.

Discussion
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[DependencyInjection] Register a custom autoloader to generate `*Config` classes when they don't exist yet

| Q             | A
| ------------- | ---
| Branch?       | 7.4
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Issues        | -
| License       | MIT

When using classes like `FrameworkConfig` or `WebProfilerConfig` in the config, cache cannot be built as classes don't exist yet.

This PRs adds a custom class autoloader that checks if the requested `*Config` class exists under the `Symfony\Config` namespace, and triggers the class generation if necessary.

Commits
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28b25afc663 [DependencyInjection] Register a custom autoloader to generate `*Config` classes when they don't exist yet

Author: nicolas-grekas

Loader/PhpFileLoader.php

@@ -36,6 +36,7 @@
 class PhpFileLoader extends FileLoader
 {
     protected bool $autoRegisterAliasesForSinglyImplementedInterfaces = false;
+    private ?\Closure $configBuilderAutoloader = null;
 
     public function __construct(
         ContainerBuilder $container,
@@ -60,6 +61,14 @@ public function load(mixed $resource, ?string $type = null): mixed
         // Force load ContainerConfigurator to make env(), param() etc available.
         class_exists(ContainerConfigurator::class);
 
+        if ($autoloaderRegistered = !$this->configBuilderAutoloader && $this->generator) {
+            spl_autoload_register($this->configBuilderAutoloader = function (string $class) {
+                if (str_starts_with($class, 'Symfony\\Config\\') && str_ends_with($class, 'Config')) {
+                    $this->configBuilder($class);
+                }
+            });
+        }
+
         // the closure forbids access to the private scope in the included file
         $load = \Closure::bind(static function ($path, $env) use ($container, $loader, $resource, $type) {
             return include $path;
@@ -108,6 +117,11 @@ class_exists(ContainerConfigurator::class);
         } finally {
             $this->instanceof = [];
             $this->registerAliasesForSinglyImplementedInterfaces();
+
+            if ($autoloaderRegistered) {
+                spl_autoload_unregister($this->configBuilderAutoloader);
+                $this->configBuilderAutoloader = null;
+            }
         }
 
         return null;