rector/config/set/symfony31.php

<?php

declare(strict_types=1);

use Rector\Generic\Rector\ClassMethod\ArgumentDefaultValueReplacerRector;
use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;

return static function (ContainerConfigurator $containerConfigurator): void {
    $services = $containerConfigurator->services();

    $services->set(ArgumentDefaultValueReplacerRector::class)
        ->call('configure', [[
            ArgumentDefaultValueReplacerRector::REPLACES_BY_METHOD_AND_TYPES => [
                # replace args - covers https://github.com/symfony/symfony/blob/3.4/UPGRADE-3.1.md#yaml
                'Symfony\Component\Yaml\Yaml' => [
                    'parse' => [
                        1 => [
                            [
                                'before' => [false, false, true],
                                'after' => 'Symfony\Component\Yaml\Yaml::PARSE_OBJECT_FOR_MAP',
                            ], [
                                'before' => [false, true],
                                'after' => 'Symfony\Component\Yaml\Yaml::PARSE_OBJECT',
                            ], [
                                'before' => true,
                                'after' => 'Symfony\Component\Yaml\Yaml::PARSE_EXCEPTION_ON_INVALID_TYPE',
                            ], [
                                'before' => false,
                                'after' => 0,
                            ],
                        ],
                    ],
                    'dump' => [
                        3 => [
                            [
                                'before' => [false, true],
                                'after' => 'Symfony\Component\Yaml\Yaml::DUMP_OBJECT',
                            ], [
                                'before' => true,
                                'after' => 'Symfony\Component\Yaml\Yaml::DUMP_EXCEPTION_ON_INVALID_TYPE',
                            ],
                        ],
                    ],
                ],
            ],
        ]]);
};