CommentPermalinkFormatter.php

<?php

namespace Drupal\comment\Plugin\Field\FieldFormatter;

use Drupal\Component\Utility\Unicode;
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Field\Attribute\FieldFormatter;
use Drupal\Core\Field\FieldDefinitionInterface;
use Drupal\Core\Field\Plugin\Field\FieldFormatter\StringFormatter;
use Drupal\Core\StringTranslation\TranslatableMarkup;

/**
 * Plugin implementation of the 'comment_permalink' formatter.
 *
 * All the other entities use 'canonical' or 'revision' links to link the entity
 * to itself but comments use permalink URL.
 */
class CommentPermalinkFormatter extends StringFormatter {
    
    /**
     * {@inheritdoc}
     */
    protected function getEntityUrl(EntityInterface $comment) {
        
        /** @var \Drupal\comment\CommentInterface $comment */
        $comment_permalink = $comment->permalink();
        if ($comment->hasField('comment_body') && ($body = $comment->get('comment_body')->value)) {
            $attributes = $comment_permalink->getOption('attributes') ?: [];
            $attributes += [
                'title' => Unicode::truncate($body, 128),
            ];
            $comment_permalink->setOption('attributes', $attributes);
        }
        return $comment_permalink;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function isApplicable(FieldDefinitionInterface $field_definition) {
        return parent::isApplicable($field_definition) && $field_definition->getTargetEntityTypeId() === 'comment' && $field_definition->getName() === 'subject';
    }

}