Issue #2855068 by jian he, larowlan, andypost, mrinalini9, Jody Lynn,...

   */

  public static function preCreate(EntityStorageInterface $storage, array &$values) {

    if (empty($values['comment_type']) && !empty($values['field_name']) && !empty($values['entity_type'])) {

      $field_storage = FieldStorageConfig::loadByName($values['entity_type'], $values['field_name']);

      $values['comment_type'] = $field_storage->getSetting('comment_type');

      $fields = \Drupal::service('entity_field.manager')->getFieldStorageDefinitions($values['entity_type']);

      $values['comment_type'] = $fields[$values['field_name']]->getSetting('comment_type');

    }

  }

name: 'Comment base field test'

type: module

description: 'Test comment as a base field'

package: Testing

version: VERSION

dependencies:

  - drupal:comment

  - drupal:entity_test

langcode: en

status: true

id: test_comment_type

label: Test comment type

target_entity_type_id: comment_test_base_field

description: 'Test comment type.'

<?php

namespace Drupal\comment_base_field_test\Entity;

use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;

use Drupal\Core\Entity\EntityTypeInterface;

use Drupal\Core\Field\BaseFieldDefinition;

use Drupal\entity_test\Entity\EntityTest;

/**

 * Defines a test entity class for comment as a base field.

 *

 * @ContentEntityType(

 *   id = "comment_test_base_field",

 *   label = @Translation("Test comment - base field"),

 *   base_table = "comment_test_base_field",

 *   entity_keys = {

 *     "id" = "id",

 *     "uuid" = "uuid",

 *     "bundle" = "type"

 *   },

 * )

 */

class CommentTestBaseField extends EntityTest {

  public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {

    $fields = parent::baseFieldDefinitions($entity_type);

    $fields['test_comment'] = BaseFieldDefinition::create('comment')

      ->setLabel(t('A comment field'))

      ->setSetting('comment_type', 'test_comment_type')

      ->setDefaultValue([

        'status' => CommentItemInterface::OPEN,

      ]);

    return $fields;

  }

}

<?php

namespace Drupal\Tests\comment\Kernel;

use Drupal\comment\CommentInterface;

use Drupal\comment\Entity\Comment;

use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;

use Drupal\comment_base_field_test\Entity\CommentTestBaseField;

use Drupal\Core\Language\LanguageInterface;

use Drupal\KernelTests\KernelTestBase;

/**

 * Tests that comment as a base field.

 *

 * @group comment

 */

class CommentBaseFieldTest extends KernelTestBase {

  /**

   * {@inheritdoc}

   */

  public static $modules = [

    'system',

    'user',

    'comment',

    'comment_base_field_test',

  ];

  protected function setUp(): void {

    parent::setUp();

    $this->installEntitySchema('comment_test_base_field');

    $this->installEntitySchema('comment');

    $this->installSchema('system', ['sequences']);

    $this->installEntitySchema('user');

  }

  /**

   * Tests comment as a base field.

   */

  public function testCommentBaseField() {

    // Verify entity creation.

    $entity = CommentTestBaseField::create([

      'name' => $this->randomMachineName(),

      'test_comment' => CommentItemInterface::OPEN,

    ]);

    $entity->save();

    $comment = Comment::create([

      'entity_id' => $entity->id(),

      'entity_type' => 'comment_test_base_field',

      'field_name' => 'test_comment',

      'pid' => 0,

      'uid' => 0,

      'status' => CommentInterface::PUBLISHED,

      'subject' => $this->randomMachineName(),

      'hostname' => '127.0.0.1',

      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,

      'comment_body' => [['value' => $this->randomMachineName()]],

    ]);

    $comment->save();

    $this->assertEquals('test_comment_type', $comment->bundle());

  }

}