…finition (yceruto)This PR was merged into the 4.2-dev branch.Discussion----------[OptionsResolver] Added support for nesting options definition| Q             | A| ------------- | ---| Branch?       | master| Bug fix?      | no| New feature?  | yes| BC breaks?    | no| Deprecations? | no| Tests pass?   | yes| Fixed tickets |#4833| License       | MIT| Doc PR        |symfony/symfony-docs#9995I'd like to propose an alternative to#27251 and#18134 with a different approach.It would allow you to create a nested options system with required options, validation (type, value),normalization and more.<details> <summary><strong>Short documentation</strong></summary>**To define a nested option, you can pass a closure as the default value of the option with an `OptionsResolver` argument:**```php$resolver    ->defaults([        'connection' => 'default',        'database' => function (OptionsResolver $resolver) {            $resolver                ->setRequired(['dbname', 'host', ...])                ->setDefaults([                    'driver' => 'pdo_sqlite',                    'port' => function (Options $options) {                        return 'pdo_mysql' === $options['driver'] ? 3306 : null,                    },                    'logging' => true,                ])                ->setAllowedValues('driver', ['pdo_sqlite', 'pdo_mysql'])                ->setAllowedTypes('port', 'int')                ->setAllowedTypes('logging', 'bool')                // ...        },    ]);$resolver->resolve(array(    'database' => array(        'dbname' => 'demo',        'host' => 'localhost',        'driver' => 'pdo_mysql',    ),));// returns: array(//    'connection' => 'default',//    'database' => array(//        'dbname' => 'demo',//        'host' => 'localhost',//        'driver' => 'pdo_mysql',//        'port' => 3306,//        'logging' => true,//    ),//)```Based on this instance, you can define the options under ``database`` and its desired defaultvalue.**If the default value of a child option depend on another option defined in parent level,adds a second ``Options`` argument to the closure:**```php$resolver    ->defaults([        'profiling' => false,        'database' => function (OptionsResolver $resolver, Options $parent) {            $resolver                ->setDefault('logging', $parent['profiling'])                ->setAllowedTypes('logging', 'bool');        },    ]);```**Access to nested options from lazy or normalize functions in parent level:**```php$resolver    ->defaults([        'version' => function (Options $options) {            return $options['database']['server_version'];        },        'database' => function (OptionsResolver $resolver) {            $resolver                ->setDefault('server_version', 3.15)                ->setAllowedTypes('server_version', 'numeric')                // ...        },    ]);```As condition, for nested options you must to pass an array of values to resolve it on runtime, otherwise an exception will be thrown:```php$resolver->resolve(); // OK$resolver->resolve(['database' => []]); // OK$resolver->resolve(['database' => null); // KO (Exception!)```</details>---Demo apphttps://github.com/yceruto/nested-optionsresolver-demoCommits-------d04e40b Added support for nested options definition