CommentForm::form

public CommentForm::form(array $form, FormStateInterface $form_state)

public function form(array $form, FormStateInterface $form_state) {
  /** @var \Drupal\comment\CommentInterface $comment */
  $comment = $this->entity;
  $entity = $this->entityManager->getStorage($comment->getCommentedEntityTypeId())->load($comment->getCommentedEntityId());
  $field_name = $comment->getFieldName();
  $field_definition = $this->entityManager->getFieldDefinitions($entity->getEntityTypeId(), $entity->bundle())[$comment->getFieldName()];
  $config = $this->config('user.settings');

  // In several places within this function, we vary $form on:
  // - The current user's permissions.
  // - Whether the current user is authenticated or anonymous.
  // - The 'user.settings' configuration.
  // - The comment field's definition.
  $form['#cache']['contexts'][] = 'user.permissions';
  $form['#cache']['contexts'][] = 'user.roles:authenticated';
  $this->renderer->addCacheableDependency($form, $config);
  $this->renderer->addCacheableDependency($form, $field_definition->getConfig($entity->bundle()));

  // Use #comment-form as unique jump target, regardless of entity type.
  $form['#id'] = Html::getUniqueId('comment_form');
  $form['#theme'] = array('comment_form__' . $entity->getEntityTypeId() . '__' . $entity->bundle() . '__' . $field_name, 'comment_form');

  $anonymous_contact = $field_definition->getSetting('anonymous');
  $is_admin = $comment->id() && $this->currentUser->hasPermission('administer comments');

  if (!$this->currentUser->isAuthenticated() && $anonymous_contact != COMMENT_ANONYMOUS_MAYNOT_CONTACT) {
    $form['#attached']['library'][] = 'core/drupal.form';
    $form['#attributes']['data-user-info-from-browser'] = TRUE;
  }

  // If not replying to a comment, use our dedicated page callback for new
  // Comments on entities.
  if (!$comment->id() && !$comment->hasParentComment()) {
    $form['#action'] = $this->url('comment.reply', array('entity_type' => $entity->getEntityTypeId(), 'entity' => $entity->id(), 'field_name' => $field_name));
  }

  $comment_preview = $form_state->get('comment_preview');
  if (isset($comment_preview)) {
    $form += $comment_preview;
  }

  $form['author'] = array();
  // Display author information in a details element for comment moderators.
  if ($is_admin) {
    $form['author'] += array(
      '#type' => 'details',
      '#title' => $this->t('Administration'),
    );
  }

  // Prepare default values for form elements.
  $author = '';
  if ($is_admin) {
    if (!$comment->getOwnerId()) {
      $author = $comment->getAuthorName();
    }
    $status = $comment->getStatus();
    if (empty($comment_preview)) {
      $form['#title'] = $this->t('Edit comment %title', array(
        '%title' => $comment->getSubject(),
      ));
    }
  }
  else {
    $status = ($this->currentUser->hasPermission('skip comment approval') ? CommentInterface::PUBLISHED : CommentInterface::NOT_PUBLISHED);
  }

  $date = '';
  if ($comment->id()) {
    $date = !empty($comment->date) ? $comment->date : DrupalDateTime::createFromTimestamp($comment->getCreatedTime());
  }

  // The uid field is only displayed when a user with the permission
  // 'administer comments' is editing an existing comment from an
  // authenticated user.
  $owner = $comment->getOwner();
  $form['author']['uid'] = [
    '#type' => 'entity_autocomplete',
    '#target_type' => 'user',
    '#default_value' => $owner->isAnonymous() ? NULL : $owner,
    // A comment can be made anonymous by leaving this field empty therefore
    // there is no need to list them in the autocomplete.
    '#selection_settings' => ['include_anonymous' => FALSE],
    '#title' => $this->t('Authored by'),
    '#description' => $this->t('Leave blank for %anonymous.', ['%anonymous' => $config->get('anonymous')]),
    '#access' => $is_admin,
  ];

  // The name field is displayed when an anonymous user is adding a comment or
  // when a user with the permission 'administer comments' is editing an
  // existing comment from an anonymous user.
  $form['author']['name'] = array(
    '#type' => 'textfield',
    '#title' => $is_admin ? $this->t('Name for @anonymous', ['@anonymous' => $config->get('anonymous')]) : $this->t('Your name'),
    '#default_value' => $author,
    '#required' => ($this->currentUser->isAnonymous() && $anonymous_contact == COMMENT_ANONYMOUS_MUST_CONTACT),
    '#maxlength' => 60,
    '#access' => $this->currentUser->isAnonymous() || $is_admin,
    '#size' => 30,
    '#attributes' => [
      'data-drupal-default-value' => $config->get('anonymous'),
    ],
  );

  if ($is_admin) {
    // When editing a comment only display the name textfield if the uid field
    // is empty.
    $form['author']['name']['#states'] = [
      'visible' => [
        ':input[name="uid"]' => array('empty' => TRUE),
      ],
    ];
  }

  // Add author email and homepage fields depending on the current user.
  $form['author']['mail'] = array(
    '#type' => 'email',
    '#title' => $this->t('Email'),
    '#default_value' => $comment->getAuthorEmail(),
    '#required' => ($this->currentUser->isAnonymous() && $anonymous_contact == COMMENT_ANONYMOUS_MUST_CONTACT),
    '#maxlength' => 64,
    '#size' => 30,
    '#description' => $this->t('The content of this field is kept private and will not be shown publicly.'),
    '#access' => ($comment->getOwner()->isAnonymous() && $is_admin) || ($this->currentUser->isAnonymous() && $anonymous_contact != COMMENT_ANONYMOUS_MAYNOT_CONTACT),
  );

  $form['author']['homepage'] = array(
    '#type' => 'url',
    '#title' => $this->t('Homepage'),
    '#default_value' => $comment->getHomepage(),
    '#maxlength' => 255,
    '#size' => 30,
    '#access' => $is_admin || ($this->currentUser->isAnonymous() && $anonymous_contact != COMMENT_ANONYMOUS_MAYNOT_CONTACT),
  );

  // Add administrative comment publishing options.
  $form['author']['date'] = array(
    '#type' => 'datetime',
    '#title' => $this->t('Authored on'),
    '#default_value' => $date,
    '#size' => 20,
    '#access' => $is_admin,
  );

  $form['author']['status'] = array(
    '#type' => 'radios',
    '#title' => $this->t('Status'),
    '#default_value' => $status,
    '#options' => array(
      CommentInterface::PUBLISHED => $this->t('Published'),
      CommentInterface::NOT_PUBLISHED => $this->t('Not published'),
    ),
    '#access' => $is_admin,
  );

  return parent::form($form, $form_state, $comment);
}