1-script.php

<?php

require 'vendor/autoload.php';

use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Dumper\PhpDumper;

$container = new ContainerBuilder();
$container->setParameter('env', '%env(TEST)%');

$container->compile();
$dumper = new PhpDumper($container);

echo $dumper->dump();

2-dump-output.php

<?php

use Symfony\Component\DependencyInjection\Argument\RewindableGenerator;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\DependencyInjection\Container;
use Symfony\Component\DependencyInjection\Exception\LogicException;
use Symfony\Component\DependencyInjection\Exception\ParameterNotFoundException;
use Symfony\Component\DependencyInjection\Exception\RuntimeException;
use Symfony\Component\DependencyInjection\ParameterBag\FrozenParameterBag;
use Symfony\Component\DependencyInjection\ParameterBag\ParameterBagInterface;

/**
 * @internal This class has been auto-generated by the Symfony Dependency Injection Component.
 */
class ProjectServiceContainer extends Container
{
    protected $parameters = [];

    public function __construct()
    {
        $this->parameters = $this->getDefaultParameters();

        $this->services = $this->privates = [];

        $this->aliases = [];
    }

    public function compile(): void
    {
        throw new LogicException('You cannot compile a dumped container that was already compiled.');
    }

    public function isCompiled(): bool
    {
        return true;
    }

    public function getParameter(string $name): array|bool|string|int|float|\UnitEnum|null
    {
        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || \array_key_exists($name, $this->parameters))) {
            throw new ParameterNotFoundException($name);
        }

        if (isset($this->loadedDynamicParameters[$name])) {
            $value = $this->loadedDynamicParameters[$name] ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
        } else {
            $value = $this->parameters[$name];
        }

        return $value;
    }

    public function hasParameter(string $name): bool
    {
        return isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || \array_key_exists($name, $this->parameters);
    }

    public function setParameter(string $name, $value): void
    {
        throw new LogicException('Impossible to call set() on a frozen ParameterBag.');
    }

    public function getParameterBag(): ParameterBagInterface
    {
        if (!isset($this->parameterBag)) {
            $parameters = $this->parameters;
            foreach ($this->loadedDynamicParameters as $name => $loaded) {
                $parameters[$name] = $loaded ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
            }
            $this->parameterBag = new FrozenParameterBag($parameters, []);
        }

        return $this->parameterBag;
    }

    private $loadedDynamicParameters = [
        'env' => false,
    ];
    private $dynamicParameters = [];

    private function getDynamicParameter(string $name)
    {
        $container = $this;
        $value = match ($name) {
            'env' => $container->getEnv('TEST'),
            default => throw new ParameterNotFoundException($name),
        };
        $this->loadedDynamicParameters[$name] = true;

        return $this->dynamicParameters[$name] = $value;
    }

    protected function getDefaultParameters(): array
    {
        return [

        ];
    }
}