drupal/core/modules/comment/comment.module

<?php

/**
 * @file
 * Enables users to comment on published content.
 *
 * When installed, the Comment module creates a field that facilitates a
 * discussion board for each Drupal entity to which a comment field is attached.
 * Users can post comments to discuss a forum topic, story, collaborative
 * book page, user etc.
 */

use Drupal\comment\CommentInterface;
use Drupal\comment\Entity\CommentType;
use Drupal\Core\Entity\FieldableEntityInterface;
use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
use Drupal\Core\Entity\Entity\EntityViewMode;
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
use Drupal\Core\Render\Element;
use Drupal\Core\Link;
use Drupal\Core\Url;
use Drupal\field\FieldConfigInterface;
use Drupal\field\FieldStorageConfigInterface;
use Drupal\node\NodeInterface;
use Drupal\user\RoleInterface;
use Drupal\user\UserInterface;

/**
 * Anonymous posters cannot enter their contact information.
 *
 * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.0.
 *   Use \Drupal\comment\CommentInterface::ANONYMOUS_MAYNOT_CONTACT instead.
 *
 * @see https://www.drupal.org/node/2831620
 */
const COMMENT_ANONYMOUS_MAYNOT_CONTACT = 0;

/**
 * Anonymous posters may leave their contact information.
 *
 * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.0.
 *   Use \Drupal\comment\CommentInterface::ANONYMOUS_MAY_CONTACT instead.
 *
 * @see https://www.drupal.org/node/2831620
 */
const COMMENT_ANONYMOUS_MAY_CONTACT = 1;

/**
 * Anonymous posters are required to leave their contact information.
 *
 * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.0.
 *   Use \Drupal\comment\CommentInterface::ANONYMOUS_MUST_CONTACT instead.
 *
 * @see https://www.drupal.org/node/2831620
 */
const COMMENT_ANONYMOUS_MUST_CONTACT = 2;

/**
 * The time cutoff for comments marked as read for entity types other node.
 *
 * Comments changed before this time are always marked as read.
 * Comments changed after this time may be marked new, updated, or read,
 * depending on their state for the current user. Defaults to 30 days ago.
 *
 * @todo Remove when https://www.drupal.org/node/1029708 lands.
 */
define('COMMENT_NEW_LIMIT', REQUEST_TIME - 30 * 24 * 60 * 60);

/**
 * Implements hook_help().
 */
function comment_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    case 'help.page.comment':
      $output = '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Comment module allows users to comment on site content, set commenting defaults and permissions, and moderate comments. For more information, see the <a href=":comment">online documentation for the Comment module</a>.', [':comment' => 'https://www.drupal.org/documentation/modules/comment']) . '</p>';
      $output .= '<h3>' . t('Uses') . '</h3>';
      $output .= '<dl>';
      $output .= '<dt>' . t('Enabling commenting') . '</dt>';
      $output .= '<dd>' . t('Comment functionality can be enabled for any entity sub-type (for example, a <a href=":content-type">content type</a>) by adding a <em>Comments</em> field on its <em>Manage fields page</em>. Adding or removing commenting for an entity through the user interface requires the <a href=":field_ui">Field UI</a> module to be enabled, even though the commenting functionality works without it. For more information on fields and entities, see the <a href=":field">Field module help page</a>.', [':content-type' => (\Drupal::moduleHandler()->moduleExists('node')) ? Url::fromRoute('entity.node_type.collection')->toString() : '#', ':field' => Url::fromRoute('help.page', ['name' => 'field'])->toString(), ':field_ui' => (\Drupal::moduleHandler()->moduleExists('field_ui')) ? Url::fromRoute('help.page', ['name' => 'field_ui'])->toString() : '#']) . '</dd>';
      $output .= '<dt>' . t('Configuring commenting settings') . '</dt>';
      $output .= '<dd>' . t('Commenting settings can be configured by editing the <em>Comments</em> field on the <em>Manage fields page</em> of an entity type if the <em>Field UI module</em> is enabled. Configuration includes the label of the comments field, the number of comments to be displayed, and whether they are shown in threaded list. Commenting can be configured as: <em>Open</em> to allow new comments, <em>Closed</em> to view existing comments, but prevent new comments, or <em>Hidden</em> to hide existing comments and prevent new comments. Changing this configuration for an entity type will not change existing entity items.') . '</dd>';
      $output .= '<dt>' . t('Overriding default settings') . '</dt>';
      $output .= '<dd>' . t('Users with the appropriate permissions can override the default commenting settings of an entity type when they create an item of that type.') . '</dd>';
      $output .= '<dt>' . t('Adding comment types') . '</dt>';
      $output .= '<dd>' . t('Additional <em>comment types</em> can be created per entity sub-type and added on the <a href=":field">Comment types page</a>. If there are multiple comment types available you can select the appropriate one after adding a <em>Comments field</em>.', [':field' => Url::fromRoute('entity.comment_type.collection')->toString()]) . '</dd>';
      $output .= '<dt>' . t('Approving and managing comments') . '</dt>';
      $output .= '<dd>' . t('Comments from users who have the <em>Skip comment approval</em> permission are published immediately. All other comments are placed in the <a href=":comment-approval">Unapproved comments</a> queue, until a user who has permission to <em>Administer comments and comment settings</em> publishes or deletes them. Published comments can be bulk managed on the <a href=":admin-comment">Published comments</a> administration page. When a comment has no replies, it remains editable by its author, as long as the author has <em>Edit own comments</em> permission.', [':comment-approval' => Url::fromRoute('comment.admin_approval')->toString(), ':admin-comment' => Url::fromRoute('comment.admin')->toString()]) . '</dd>';
      $output .= '</dl>';
      return $output;

    case 'entity.comment_type.collection':
      $output = '<p>' . t('This page provides a list of all comment types on the site and allows you to manage the fields, form and display settings for each.') . '</p>';
      return $output;
  }
}

/**
 * Entity URI callback.
 */
function comment_uri(CommentInterface $comment) {
  return new Url(
    'entity.comment.canonical',
    [
      'comment' => $comment->id(),
    ],
    ['fragment' => 'comment-' . $comment->id()]
  );
}

/**
 * Implements hook_entity_extra_field_info().
 */
function comment_entity_extra_field_info() {
  $return = [];
  foreach (CommentType::loadMultiple() as $comment_type) {
    $return['comment'][$comment_type->id()] = [
      'form' => [
        'author' => [
          'label' => t('Author'),
          'description' => t('Author textfield'),
          'weight' => -2,
        ],
      ],
    ];
    $return['comment'][$comment_type->id()]['display']['links'] = [
      'label' => t('Links'),
      'description' => t('Comment operation links'),
      'weight' => 100,
      'visible' => TRUE,
    ];
  }

  return $return;
}

/**
 * Implements hook_theme().
 */
function comment_theme() {
  return [
    'comment' => [
      'render element' => 'elements',
    ],
    'field__comment' => [
      'base hook' => 'field',
    ],
  ];
}

/**
 * Implements hook_ENTITY_TYPE_create() for 'field_config'.
 */
function comment_field_config_create(FieldConfigInterface $field) {
  if ($field->getType() == 'comment' && !$field->isSyncing()) {
    // Assign default values for the field.
    $default_value = $field->getDefaultValueLiteral();
    $default_value += [[]];
    $default_value[0] += [
      'status' => CommentItemInterface::OPEN,
      'cid' => 0,
      'last_comment_timestamp' => 0,
      'last_comment_name' => '',
      'last_comment_uid' => 0,
      'comment_count' => 0,
    ];
    $field->setDefaultValue($default_value);
  }
}

/**
 * Implements hook_ENTITY_TYPE_update() for 'field_config'.
 */
function comment_field_config_update(FieldConfigInterface $field) {
  if ($field->getType() == 'comment') {
    // Comment field settings also affects the rendering of *comment* entities,
    // not only the *commented* entities.
    \Drupal::entityTypeManager()->getViewBuilder('comment')->resetCache();
  }
}

/**
 * Implements hook_ENTITY_TYPE_insert() for 'field_storage_config'.
 */
function comment_field_storage_config_insert(FieldStorageConfigInterface $field_storage) {
  if ($field_storage->getType() == 'comment') {
    // Check that the target entity type uses an integer ID.
    $entity_type_id = $field_storage->getTargetEntityTypeId();
    if (!_comment_entity_uses_integer_id($entity_type_id)) {
      throw new \UnexpectedValueException('You cannot attach a comment field to an entity with a non-integer ID field');
    }
  }
}

/**
 * Implements hook_ENTITY_TYPE_delete() for 'field_config'.
 */
function comment_field_config_delete(FieldConfigInterface $field) {
  if ($field->getType() == 'comment') {
    // Delete all comments that used by the entity bundle.
    $entity_query = \Drupal::entityQuery('comment');
    $entity_query->condition('entity_type', $field->getEntityTypeId());
    $entity_query->condition('field_name', $field->getName());
    $cids = $entity_query->execute();
    $comment_storage = \Drupal::entityTypeManager()->getStorage('comment');
    $comments = $comment_storage->loadMultiple($cids);
    $comment_storage->delete($comments);
  }
}

/**
 * Implements hook_node_links_alter().
 */
function comment_node_links_alter(array &$links, NodeInterface $node, array &$context) {
  // Comment links are only added to node entity type for backwards
  // compatibility. Should you require comment links for other entity types you
  // can do so by implementing a new field formatter.
  // @todo Make this configurable from the formatter. See
  //   https://www.drupal.org/node/1901110.

  $comment_links = \Drupal::service('comment.link_builder')->buildCommentedEntityLinks($node, $context);
  $links += $comment_links;
}

/**
 * Implements hook_entity_view().
 */
function comment_entity_view(array &$build, EntityInterface $entity, EntityViewDisplayInterface $display, $view_mode) {
  if ($entity instanceof FieldableEntityInterface && $view_mode == 'rss' && $display->getComponent('links')) {
    /** @var \Drupal\comment\CommentManagerInterface $comment_manager */
    $comment_manager = \Drupal::service('comment.manager');
    $fields = $comment_manager->getFields($entity->getEntityTypeId());
    foreach ($fields as $field_name => $detail) {
      if ($entity->hasField($field_name) && $entity->get($field_name)->status != CommentItemInterface::HIDDEN) {
        // Add a comments RSS element which is a URL to the comments of this
        // entity.
        $options = [
          'fragment' => 'comments',
          'absolute' => TRUE,
        ];
        $entity->rss_elements[] = [
          'key' => 'comments',
          'value' => $entity->toUrl('canonical', $options)->toString(),
        ];
      }
    }
  }
}

/**
 * Implements hook_ENTITY_TYPE_view_alter() for node entities.
 */
function comment_node_view_alter(array &$build, EntityInterface $node, EntityViewDisplayInterface $display) {
  if (\Drupal::moduleHandler()->moduleExists('history')) {
    $build['#attributes']['data-history-node-id'] = $node->id();
  }
}

/**
 * Generates an array for rendering a comment.
 *
 * @param \Drupal\comment\CommentInterface $comment
 *   The comment object.
 * @param string $view_mode
 *   (optional) View mode; for instance, 'full', 'teaser', etc. Defaults to
 *   'full'.
 * @param string $langcode
 *   (optional) A language code to use for rendering. Defaults to the global
 *   content language of the current request.
 *
 * @return array
 *   An array as expected by \Drupal\Core\Render\RendererInterface::render().
 *
 * @deprecated in Drupal 8.x and will be removed before Drupal 9.0.
 *   Use \Drupal::entityTypeManager()->getViewBuilder('comment')->view().
 *
 * @see https://www.drupal.org/node/3033656
 */
function comment_view(CommentInterface $comment, $view_mode = 'full', $langcode = NULL) {
  @trigger_error("comment_view() is deprecated in Drupal 8.0.0 and will be removed before Drupal 9.0.0. Use \Drupal::entityTypeManager()->getViewBuilder('comment')->view() instead. See https://www.drupal.org/node/3033656", E_USER_DEPRECATED);
  return \Drupal::entityTypeManager()
    ->getViewBuilder('comment')
    ->view($comment, $view_mode, $langcode);
}

/**
 * Constructs render array from an array of loaded comments.
 *
 * @param \Drupal\comment\CommentInterface[] $comments
 *   An array of comments as returned by entity_load_multiple().
 * @param string $view_mode
 *   (optional) View mode; for instance, 'full', 'teaser', etc. Defaults to
 *   'full'.
 * @param string $langcode
 *   (optional) A string indicating the language field values are to be shown
 *   in. If no language is provided the current content language is used.
 *   Defaults to NULL.
 *
 * @return array
 *   An array in the format expected by
 *   \Drupal\Core\Render\RendererInterface::render().
 *
 * @deprecated in Drupal 8.x and will be removed before Drupal 9.0.
 *   Use \Drupal::entityTypeManager()->getViewBuilder('comment')->viewMultiple().
 *
 * @see https://www.drupal.org/node/3033656
 * @see \Drupal\Core\Render\RendererInterface::render()
 */
function comment_view_multiple($comments, $view_mode = 'full', $langcode = NULL) {
  @trigger_error("comment_view_multiple() is deprecated in Drupal 8.0.0 and will be removed before Drupal 9.0.0. Use \Drupal::entityTypeManager()->getViewBuilder('comment')->viewMultiple() instead. See https://www.drupal.org/node/3033656", E_USER_DEPRECATED);
  return \Drupal::entityTypeManager()
    ->getViewBuilder('comment')
    ->viewMultiple($comments, $view_mode, $langcode);
}

/**
 * Implements hook_form_FORM_ID_alter() for field_ui_field_storage_add_form.
 */
function comment_form_field_ui_field_storage_add_form_alter(&$form, FormStateInterface $form_state) {
  $route_match = \Drupal::routeMatch();
  if ($form_state->get('entity_type_id') == 'comment' && $route_match->getParameter('commented_entity_type')) {
    $form['#title'] = \Drupal::service('comment.manager')->getFieldUIPageTitle($route_match->getParameter('commented_entity_type'), $route_match->getParameter('field_name'));
  }
  if (!_comment_entity_uses_integer_id($form_state->get('entity_type_id'))) {
    $optgroup = (string) t('General');
    // You cannot use comment fields on entity types with non-integer IDs.
    unset($form['add']['new_storage_type']['#options'][$optgroup]['comment']);
  }
}

/**
 * Implements hook_form_FORM_ID_alter().
 */
function comment_form_field_ui_form_display_overview_form_alter(&$form, FormStateInterface $form_state) {
  $route_match = \Drupal::routeMatch();
  if ($form['#entity_type'] == 'comment' && $route_match->getParameter('commented_entity_type')) {
    $form['#title'] = \Drupal::service('comment.manager')->getFieldUIPageTitle($route_match->getParameter('commented_entity_type'), $route_match->getParameter('field_name'));
  }
}

/**
 * Implements hook_form_FORM_ID_alter().
 */
function comment_form_field_ui_display_overview_form_alter(&$form, FormStateInterface $form_state) {
  $route_match = \Drupal::routeMatch();
  if ($form['#entity_type'] == 'comment' && $route_match->getParameter('commented_entity_type')) {
    $form['#title'] = \Drupal::service('comment.manager')->getFieldUIPageTitle($route_match->getParameter('commented_entity_type'), $route_match->getParameter('field_name'));
  }
}

/**
 * Implements hook_entity_storage_load().
 *
 * @see \Drupal\comment\Plugin\Field\FieldType\CommentItem::propertyDefinitions()
 */
function comment_entity_storage_load($entities, $entity_type) {
  // Comments can only be attached to content entities, so skip others.
  if (!\Drupal::entityTypeManager()->getDefinition($entity_type)->entityClassImplements(FieldableEntityInterface::class)) {
    return;
  }
  if (!\Drupal::service('comment.manager')->getFields($entity_type)) {
    // Do not query database when entity has no comment fields.
    return;
  }
  // Load comment information from the database and update the entity's
  // comment statistics properties, which are defined on each CommentItem field.
  $result = \Drupal::service('comment.statistics')->read($entities, $entity_type);
  foreach ($result as $record) {
    // Skip fields that entity does not have.
    if (!$entities[$record->entity_id]->hasField($record->field_name)) {
      continue;
    }
    $comment_statistics = $entities[$record->entity_id]->get($record->field_name);
    $comment_statistics->cid = $record->cid;
    $comment_statistics->last_comment_timestamp = $record->last_comment_timestamp;
    $comment_statistics->last_comment_name = $record->last_comment_name;
    $comment_statistics->last_comment_uid = $record->last_comment_uid;
    $comment_statistics->comment_count = $record->comment_count;
  }
}

/**
 * Implements hook_entity_insert().
 */
function comment_entity_insert(EntityInterface $entity) {
  // Allow bulk updates and inserts to temporarily disable the
  // maintenance of the {comment_entity_statistics} table.
  if (\Drupal::state()->get('comment.maintain_entity_statistics') &&
    $fields = \Drupal::service('comment.manager')->getFields($entity->getEntityTypeId())) {
    \Drupal::service('comment.statistics')->create($entity, $fields);
  }
}

/**
 * Implements hook_entity_predelete().
 */
function comment_entity_predelete(EntityInterface $entity) {
  // Entities can have non-numeric IDs, but {comment} and
  // {comment_entity_statistics} tables have integer columns for entity ID, and
  // PostgreSQL throws exceptions if you attempt query conditions with
  // mismatched types. So, we need to verify that the ID is numeric (even for an
  // entity type that has an integer ID, $entity->id() might be a string
  // containing a number), and then cast it to an integer when querying.
  if ($entity instanceof FieldableEntityInterface && is_numeric($entity->id())) {
    $entity_query = \Drupal::entityQuery('comment');
    $entity_query->condition('entity_id', (int) $entity->id());
    $entity_query->condition('entity_type', $entity->getEntityTypeId());
    $cids = $entity_query->execute();
    $comment_storage = \Drupal::entityTypeManager()->getStorage('comment');
    $comments = $comment_storage->loadMultiple($cids);
    $comment_storage->delete($comments);
    \Drupal::service('comment.statistics')->delete($entity);
  }
}

/**
 * Determines if an entity type is using an integer-based ID definition.
 *
 * @param string $entity_type_id
 *   The ID the represents the entity type.
 *
 * @return bool
 *   Returns TRUE if the entity type has an integer-based ID definition and
 *   FALSE otherwise.
 */
function _comment_entity_uses_integer_id($entity_type_id) {
  $entity_type = \Drupal::entityTypeManager()->getDefinition($entity_type_id);
  $entity_type_id_key = $entity_type->getKey('id');
  if ($entity_type_id_key === FALSE) {
    return FALSE;
  }
  $field_definitions = \Drupal::service('entity_field.manager')->getBaseFieldDefinitions($entity_type->id());
  $entity_type_id_definition = $field_definitions[$entity_type_id_key];
  return $entity_type_id_definition->getType() === 'integer';
}

/**
 * Implements hook_node_update_index().
 */
function comment_node_update_index(EntityInterface $node) {
  $index_comments = &drupal_static(__FUNCTION__);

  if ($index_comments === NULL) {
    // Do not index in the following three cases:
    // 1. 'Authenticated user' can search content but can't access comments.
    // 2. 'Anonymous user' can search content but can't access comments.
    // 3. Any role can search content but can't access comments and access
    // comments is not granted by the 'authenticated user' role. In this case
    // all users might have both permissions from various roles but it is also
    // possible to set up a user to have only search content and so a user
    // edit could change the security situation so it is not safe to index the
    // comments.
    $index_comments = TRUE;
    $roles = \Drupal::entityTypeManager()->getStorage('user_role')->loadMultiple();
    $authenticated_can_access = $roles[RoleInterface::AUTHENTICATED_ID]->hasPermission('access comments');
    foreach ($roles as $rid => $role) {
      if ($role->hasPermission('search content') && !$role->hasPermission('access comments')) {
        if ($rid == RoleInterface::AUTHENTICATED_ID || $rid == RoleInterface::ANONYMOUS_ID || !$authenticated_can_access) {
          $index_comments = FALSE;
          break;
        }
      }
    }
  }

  $build = [];

  if ($index_comments) {
    foreach (\Drupal::service('comment.manager')->getFields('node') as $field_name => $info) {
      // Skip fields that entity does not have.
      if (!$node->hasField($field_name)) {
        continue;
      }
      $field_definition = $node->getFieldDefinition($field_name);
      $mode = $field_definition->getSetting('default_mode');
      $comments_per_page = $field_definition->getSetting('per_page');
      if ($node->get($field_name)->status) {
        $comments = \Drupal::entityTypeManager()->getStorage('comment')
          ->loadThread($node, $field_name, $mode, $comments_per_page);
        if ($comments) {
          $build[] = \Drupal::entityTypeManager()->getViewBuilder('comment')->viewMultiple($comments);
        }
      }
    }
  }
  return \Drupal::service('renderer')->renderPlain($build);
}

/**
 * Implements hook_cron().
 */
function comment_cron() {
  // Store the maximum possible comments per thread (used for node search
  // ranking by reply count).
  \Drupal::state()->set('comment.node_comment_statistics_scale', 1.0 / max(1, \Drupal::service('comment.statistics')->getMaximumCount('node')));
}

/**
 * Implements hook_node_search_result().
 *
 * Formats a comment count string and returns it, for display with search
 * results.
 */
function comment_node_search_result(EntityInterface $node) {
  $comment_fields = \Drupal::service('comment.manager')->getFields('node');
  $comments = 0;
  $open = FALSE;
  foreach ($comment_fields as $field_name => $info) {
    // Skip fields that entity does not have.
    if (!$node->hasField($field_name)) {
      continue;
    }
    // Do not make a string if comments are hidden.
    $status = $node->get($field_name)->status;
    if (\Drupal::currentUser()->hasPermission('access comments') && $status != CommentItemInterface::HIDDEN) {
      if ($status == CommentItemInterface::OPEN) {
        // At least one comment field is open.
        $open = TRUE;
      }
      $comments += $node->get($field_name)->comment_count;
    }
  }
  // Do not make a string if there are no comment fields, or no comments exist
  // or all comment fields are hidden.
  if ($comments > 0 || $open) {
    return ['comment' => \Drupal::translation()->formatPlural($comments, '1 comment', '@count comments')];
  }
}

/**
 * Implements hook_user_cancel().
 */
function comment_user_cancel($edit, UserInterface $account, $method) {
  switch ($method) {
    case 'user_cancel_block_unpublish':
      $comments = \Drupal::entityTypeManager()->getStorage('comment')->loadByProperties(['uid' => $account->id()]);
      foreach ($comments as $comment) {
        $comment->setUnpublished();
        $comment->save();
      }
      break;

    case 'user_cancel_reassign':
      /** @var \Drupal\comment\CommentInterface[] $comments */
      $comments = \Drupal::entityTypeManager()->getStorage('comment')->loadByProperties(['uid' => $account->id()]);
      foreach ($comments as $comment) {
        $comment->setOwnerId(0);
        $comment->setAuthorName(\Drupal::config('user.settings')->get('anonymous'));
        $comment->save();
      }
      break;
  }
}

/**
 * Implements hook_ENTITY_TYPE_predelete() for user entities.
 */
function comment_user_predelete($account) {
  $entity_query = \Drupal::entityQuery('comment');
  $entity_query->condition('uid', $account->id());
  $cids = $entity_query->execute();
  $comment_storage = \Drupal::entityTypeManager()->getStorage('comment');
  $comments = $comment_storage->loadMultiple($cids);
  $comment_storage->delete($comments);
}

/**
 * Generates a comment preview.
 *
 * @param \Drupal\comment\CommentInterface $comment
 *   The comment entity to preview.
 * @param Drupal\Core\Form\FormStateInterface $form_state
 *   The current state of the form.
 *
 * @return array
 *   An array as expected by \Drupal\Core\Render\RendererInterface::render().
 */
function comment_preview(CommentInterface $comment, FormStateInterface $form_state) {
  $preview_build = [];
  $entity = $comment->getCommentedEntity();

  if (!$form_state->getErrors()) {
    $comment->in_preview = TRUE;
    $comment_build = \Drupal::entityTypeManager()->getViewBuilder('comment')->view($comment);
    $comment_build['#weight'] = -100;

    $preview_build['comment_preview'] = $comment_build;
  }

  if ($comment->hasParentComment()) {
    $build = [];
    $parent = $comment->getParentComment();
    if ($parent && $parent->isPublished()) {
      $build = \Drupal::entityTypeManager()->getViewBuilder('comment')->view($parent);
    }
  }
  else {
    // The comment field output includes rendering the parent entity of the
    // thread to which the comment is a reply. The rendered entity output
    // includes the comment reply form, which contains the comment preview and
    // therefore the rendered parent entity. This results in an infinite loop of
    // parent entity output rendering the comment form and the comment form
    // rendering the parent entity. To prevent this infinite loop we temporarily
    // set the value of the comment field on a clone of the entity to hidden
    // before calling entity_view(). That way when the output of the commented
    // entity is rendered, it excludes the comment field output.
    $field_name = $comment->getFieldName();
    $entity = clone $entity;
    $entity->$field_name->status = CommentItemInterface::HIDDEN;
    $build = \Drupal::entityTypeManager()
      ->getViewBuilder($entity->getEntityTypeId())
      ->view($entity, 'full');
  }

  $preview_build['comment_output_below'] = $build;
  $preview_build['comment_output_below']['#weight'] = 100;

  return $preview_build;
}

/**
 * Implements hook_preprocess_HOOK() for block templates.
 */
function comment_preprocess_block(&$variables) {
  if ($variables['configuration']['provider'] == 'comment') {
    $variables['attributes']['role'] = 'navigation';
  }
}

/**
 * Prepares variables for comment templates.
 *
 * Default template: comment.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - elements: An associative array containing the comment and entity objects.
 *     Array keys: #comment, #commented_entity.
 */
function template_preprocess_comment(&$variables) {
  /** @var \Drupal\Core\Datetime\DateFormatterInterface $date_formatter */
  $date_formatter = \Drupal::service('date.formatter');
  /** @var \Drupal\comment\CommentInterface $comment */
  $comment = $variables['elements']['#comment'];
  $commented_entity = $comment->getCommentedEntity();
  $variables['comment'] = $comment;
  $variables['commented_entity'] = $commented_entity;
  $variables['threaded'] = $variables['elements']['#comment_threaded'];

  $account = $comment->getOwner();
  $username = [
    '#theme' => 'username',
    '#account' => $account,
  ];
  $variables['author'] = \Drupal::service('renderer')->render($username);
  $variables['author_id'] = $comment->getOwnerId();
  $variables['new_indicator_timestamp'] = $comment->getChangedTime();
  $variables['created'] = $date_formatter->format($comment->getCreatedTime());
  // Avoid calling DateFormatterInterface::format() twice on the same timestamp.
  if ($comment->getChangedTime() == $comment->getCreatedTime()) {
    $variables['changed'] = $variables['created'];
  }
  else {
    $variables['changed'] = $date_formatter->format($comment->getChangedTime());
  }

  if (theme_get_setting('features.comment_user_picture')) {
    // To change user picture settings (for instance, image style), edit the
    // 'compact' view mode on the User entity.
    $variables['user_picture'] = \Drupal::entityTypeManager()
      ->getViewBuilder('user')
      ->view($account, 'compact');
  }
  else {
    $variables['user_picture'] = [];
  }

  if (isset($comment->in_preview)) {
    $variables['title'] = Link::fromTextAndUrl($comment->getSubject(), Url::fromRoute('<front>'))->toString();
    $variables['permalink'] = Link::fromTextAndUrl(t('Permalink'), Url::fromRoute('<front>'))->toString();
  }
  else {
    $uri = $comment->permalink();
    $attributes = $uri->getOption('attributes') ?: [];
    $attributes += ['class' => ['permalink'], 'rel' => 'bookmark'];
    $uri->setOption('attributes', $attributes);
    $variables['title'] = Link::fromTextAndUrl($comment->getSubject(), $uri)->toString();

    $variables['permalink'] = Link::fromTextAndUrl(t('Permalink'), $comment->permalink())->toString();
  }

  $variables['submitted'] = t('Submitted by @username on @datetime', ['@username' => $variables['author'], '@datetime' => $variables['created']]);

  if ($comment->hasParentComment()) {
    // Fetch and store the parent comment information for use in templates.
    $comment_parent = $comment->getParentComment();
    $account_parent = $comment_parent->getOwner();
    $variables['parent_comment'] = $comment_parent;
    $username = [
      '#theme' => 'username',
      '#account' => $account_parent,
    ];
    $variables['parent_author'] = \Drupal::service('renderer')->render($username);
    $variables['parent_created'] = $date_formatter->format($comment_parent->getCreatedTime());
    // Avoid calling DateFormatterInterface::format() twice on same timestamp.
    if ($comment_parent->getChangedTime() == $comment_parent->getCreatedTime()) {
      $variables['parent_changed'] = $variables['parent_created'];
    }
    else {
      $variables['parent_changed'] = $date_formatter->format($comment_parent->getChangedTime());
    }
    $permalink_uri_parent = $comment_parent->permalink();
    $attributes = $permalink_uri_parent->getOption('attributes') ?: [];
    $attributes += ['class' => ['permalink'], 'rel' => 'bookmark'];
    $permalink_uri_parent->setOption('attributes', $attributes);
    $variables['parent_title'] = Link::fromTextAndUrl($comment_parent->getSubject(), $permalink_uri_parent)->toString();
    $variables['parent_permalink'] = Link::fromTextAndUrl(t('Parent permalink'), $permalink_uri_parent)->toString();
    $variables['parent'] = t('In reply to @parent_title by @parent_username',
        ['@parent_username' => $variables['parent_author'], '@parent_title' => $variables['parent_title']]);
  }
  else {
    $variables['parent_comment'] = '';
    $variables['parent_author'] = '';
    $variables['parent_created'] = '';
    $variables['parent_changed'] = '';
    $variables['parent_title'] = '';
    $variables['parent_permalink'] = '';
    $variables['parent'] = '';
  }

  // Helpful $content variable for templates.
  foreach (Element::children($variables['elements']) as $key) {
    $variables['content'][$key] = $variables['elements'][$key];
  }

  // Set status to a string representation of comment->status.
  if (isset($comment->in_preview)) {
    $variables['status'] = 'preview';
  }
  else {
    $variables['status'] = $comment->isPublished() ? 'published' : 'unpublished';
  }

  // Add comment author user ID. Necessary for the comment-by-viewer library.
  $variables['attributes']['data-comment-user-id'] = $comment->getOwnerId();
  // Add anchor for each comment.
  $variables['attributes']['id'] = 'comment-' . $comment->id();
}

/**
 * Prepares variables for comment field templates.
 *
 * Default template: field--comment.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - element: An associative array containing render arrays for the list of
 *     comments, and the comment form. Array keys: comments, comment_form.
 *
 * @todo Rename to template_preprocess_field__comment() once
 *   https://www.drupal.org/node/939462 is resolved.
 */
function comment_preprocess_field(&$variables) {
  $element = $variables['element'];
  if ($element['#field_type'] == 'comment') {
    // Provide contextual information.
    $variables['comment_display_mode'] = $element[0]['#comment_display_mode'];
    $variables['comment_type'] = $element[0]['#comment_type'];

    // Append additional attributes (eg. RDFa) from the first field item.
    $variables['attributes'] += $variables['items'][0]['attributes']->storage();

    // Create separate variables for the comments and comment form.
    $variables['comments'] = $element[0]['comments'];
    $variables['comment_form'] = $element[0]['comment_form'];
  }
}

/**
 * Implements hook_ranking().
 */
function comment_ranking() {
  return \Drupal::service('comment.statistics')->getRankingInfo();
}

/**
 * Implements hook_ENTITY_TYPE_presave() for entity_view_display entities.
 */
function comment_entity_view_display_presave(EntityViewDisplayInterface $display) {
  // Act only on comment view displays being disabled.
  if ($display->isNew() || $display->getTargetEntityTypeId() !== 'comment' || $display->status()) {
    return;
  }
  $storage = \Drupal::entityTypeManager()->getStorage('entity_view_display');
  if (!$storage->loadUnchanged($display->getOriginalId())->status()) {
    return;
  }

  // Disable the comment field formatter when the used view display is disabled.
  foreach ($storage->loadMultiple() as $id => $view_display) {
    $changed = FALSE;
    /** @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface $view_display */
    foreach ($view_display->getComponents() as $field => $component) {
      if (isset($component['type']) && ($component['type'] === 'comment_default')) {
        if ($component['settings']['view_mode'] === $display->getMode()) {
          $view_display->removeComponent($field);
          /** @var \Drupal\Core\Entity\EntityViewModeInterface $mode */
          $mode = EntityViewMode::load($display->getTargetEntityTypeId() . '.' . $display->getMode());
          $arguments = [
            '@id' => $view_display->id(),
            '@name' => $field,
            '@display' => $mode->label(),
            '@mode' => $display->getMode(),
          ];
          \Drupal::logger('system')->warning("View display '@id': Comment field formatter '@name' was disabled because it is using the comment view display '@display' (@mode) that was just disabled.", $arguments);
          $changed = TRUE;
        }
      }
    }
    if ($changed) {
      $view_display->save();
    }
  }
}