Issue #3364109 by Wim Leers, effulgentsia, lauriii, phenaproxima, borisson_,...

use Drupal\Core\Config\Schema\Undefined;

use Drupal\Core\Extension\ModuleHandlerInterface;

use Drupal\Core\TypedData\TypedDataManager;

use Drupal\Core\Validation\Plugin\Validation\Constraint\FullyValidatableConstraint;

/**

 * Manages config schema type plugins.

        $data_definition[$key] = $value;

      }

    }

    // All values are optional by default (meaning they can be NULL), except for

    // mappings and sequences. A sequence can only be NULL when `nullable: true`

    // is set on the config schema type definition. This is unintuitive and

    // contradicts Drupal core's documentation.

    // @see https://www.drupal.org/node/2264179

    // @see https://www.drupal.org/node/1978714

    // To gradually evolve configuration schemas in the Drupal ecosystem to be

    // validatable, this needs to be clarified in a non-disruptive way. Any

    // config schema type definition — that is, a top-level entry in a

    // *.schema.yml file — can opt into stricter behavior, whereby a property

    // cannot be NULL unless it specifies `nullable: true`, by adding

    // `FullyValidatable` as a top-level validation constraint.

    // @see https://www.drupal.org/node/3364108

    // @see https://www.drupal.org/node/3364109

    // @see \Drupal\Core\TypedData\TypedDataManager::getDefaultConstraints()

    if ($parent) {

      $root_type_has_opted_in = FALSE;

      foreach ($parent->getRoot()->getConstraints() as $constraint) {

        if ($constraint instanceof FullyValidatableConstraint) {

          $root_type_has_opted_in = TRUE;

          break;

        }

      }

      if ($root_type_has_opted_in) {

        $data_definition->setRequired(!isset($data_definition['nullable']) || $data_definition['nullable'] === FALSE);

      }

    }

    return $data_definition;

  }

<?php

declare(strict_types = 1);

namespace Drupal\Core\Validation\Plugin\Validation\Constraint;

use Symfony\Component\Validator\Constraint;

/**

 * @Constraint(

 *   id = "FullyValidatable",

 *   label = @Translation("Whether this config schema type is fully validatable", context = "Validation"),

 * )

 */

final class FullyValidatableConstraint extends Constraint {}

<?php

declare(strict_types = 1);

namespace Drupal\Core\Validation\Plugin\Validation\Constraint;

use Symfony\Component\Validator\Constraint;

use Symfony\Component\Validator\ConstraintValidator;

/**

 * FullyValidatable constraint.

 *

 * @internal

 */

final class FullyValidatableConstraintValidator extends ConstraintValidator {

  /**

   * {@inheritdoc}

   */

  public function validate(mixed $value, Constraint $constraint) {

    // No-op.

  }

}

namespace Drupal\Core\Validation\Plugin\Validation\Constraint;

use Drupal\Core\Config\Schema\ArrayElement;

use Drupal\Core\TypedData\ComplexDataInterface;

use Drupal\Core\TypedData\ListInterface;

use Drupal\Core\TypedData\Validation\TypedDataAwareValidatorTrait;

   */

  public function validate($value, Constraint $constraint) {

    $typed_data = $this->getTypedData();

    if (($typed_data instanceof ListInterface || $typed_data instanceof ComplexDataInterface) && $typed_data->isEmpty()) {

    // TRICKY: the Mapping and Sequence data types both extend ArrayElement

    // (which implements ComplexDataInterface), but configuration schema sees a

    // substantial difference between an empty sequence/mapping and NULL. So we

    // want to make sure we don't treat an empty array as NULL.

    if (($typed_data instanceof ListInterface || $typed_data instanceof ComplexDataInterface) && !$typed_data instanceof ArrayElement && $typed_data->isEmpty()) {

      $value = NULL;

    }

    parent::validate($value, $constraint);

    assert($constraint instanceof ValidKeysConstraint);

    if (!is_array($value)) {

      // If the value is NULL, then the `NotNull` constraint validator will

      // set the appropriate validation error message.

      // @see \Drupal\Core\Validation\Plugin\Validation\Constraint\NotNullConstraintValidator

      if ($value === NULL) {

        return;

      }

      throw new UnexpectedTypeException($value, 'array');

    }