New in Symfony 6.4: Build Dir Improvements

APP_BUILD_DIR Support

Contributed by Roland Franssen in #50951

By default, the getBuildDir() method in the Symfony Kernel class returns $this->getCacheDir() for backward-compatibility reasons. In Symfony 6.4 we've improved this method to check first the value of the APP_BUILD_DIR environment variable:

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public function getBuildDir(): string
{
    if (isset($_SERVER['APP_BUILD_DIR'])) {
        return $_SERVER['APP_BUILD_DIR'].'/'.$this->environment;
    }

    return parent::getBuildDir();
}

These changes were added to the Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait, which is used in the App\Kernel class created by default in new Symfony applications. This will simplify the deployment of Symfony applications to read-only filesystems like Docker containers or AWS Lambda.

Using Build Dir to Generate More Contents

Contributed by Quentin D. in #50391

The build_dir feature is probably underused in Symfony. By default, only the compiled container is dumped in the build_dir. All the other read-only compiled artifacts are dumped into the cache_dir: the router cache, Doctrine proxy classes, Symfony Config classes, translations, etc.

In order to improve this, we're making a change in the cache warmer classes. The warmUp() method of the WarmableInterface now accepts a second argument with the $buildDir value:

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namespace Symfony\Component\HttpKernel\CacheWarmer;

 interface WarmableInterface
 {
-    public function warmUp(string $cacheDir): array;
+    public function warmUp(string $cacheDir/* , string $buildDir = null */): array;
 }

Thanks to this change, you can now store read-only artifacts more easily in the build_dir, which is the best location for them. In order to make the change backward-compatible, we added the argument as a comment in 6.4 (and it will be a true argument in Symfony 7.0).

This change will trigger deprecation messages when updating your applications to Symfony 6.4. Make sure to add this change to your warmers (and to contribute this change to third-party bundles used in your applications) so you can later upgrade to Symfony 7.