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How to Work with Compiler Passes

How to Work with Compiler Passes

Compiler passes give you an opportunity to manipulate other service definitions that have been registered with the service container. You can read about how to create them in the components section "Execute Code During Compilation".

Compiler passes are registered in the build() method of the application kernel:

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// src/Kernel.php
namespace App;

use App\DependencyInjection\Compiler\CustomPass;
use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\HttpKernel\Kernel as BaseKernel;

class Kernel extends BaseKernel
{
    use MicroKernelTrait;

    // ...

    protected function build(ContainerBuilder $container): void
    {
        $container->addCompilerPass(new CustomPass());
    }
}

One of the most common use-cases of compiler passes is to work with tagged services. In those cases, instead of creating a compiler pass, you can make the kernel implement CompilerPassInterface and process the services inside the process() method:

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// src/Kernel.php
namespace App;

use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\HttpKernel\Kernel as BaseKernel;

class Kernel extends BaseKernel implements CompilerPassInterface
{
    use MicroKernelTrait;

    // ...

    public function process(ContainerBuilder $container)
    {
        // in this method you can manipulate the service container:
        // for example, changing some container service:
        $container->getDefinition('app.some_private_service')->setPublic(true);

        // or processing tagged services:
        foreach ($container->findTaggedServiceIds('some_tag') as $id => $tags) {
            // ...
        }
    }
}

Working with Compiler Passes in Bundles

Bundles can define compiler passes in the build() method of the main bundle class (this is not needed when implementing the process() method in the extension):

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// src/MyBundle/MyBundle.php
namespace App\MyBundle;

use Symfony\Component\HttpKernel\Bundle\Bundle;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use App\DependencyInjection\Compiler\CustomPass;

class MyBundle extends Bundle
{
    public function build(ContainerBuilder $container)
    {
        parent::build($container);

        $container->addCompilerPass(new CustomPass());
    }
}

If you are using custom service tags in a bundle then by convention, tag names consist of the name of the bundle (lowercase, underscores as separators), followed by a dot, and finally the "real" name. For example, if you want to introduce some sort of "transport" tag in your AcmeMailerBundle, you should call it acme_mailer.transport.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.