TableFormatter.php

<?php

namespace Drupal\file\Plugin\Field\FieldFormatter;

use Drupal\Core\Field\Attribute\FieldFormatter;
use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\StringTranslation\ByteSizeMarkup;
use Drupal\Core\StringTranslation\TranslatableMarkup;

/**
 * Plugin implementation of the 'file_table' formatter.
 */
class TableFormatter extends DescriptionAwareFileFormatterBase {
  
  /**
   * {@inheritdoc}
   */
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $elements = [];
    if ($files = $this->getEntitiesToView($items, $langcode)) {
      $header = [
        $this->t('Attachment'),
        $this->t('Size'),
      ];
      $rows = [];
      foreach ($files as $file) {
        $item = $file->_referringItem;
        $rows[] = [
          [
            'data' => [
              '#theme' => 'file_link',
              '#file' => $file,
              '#description' => $this->getSetting('use_description_as_link_text') ? $item->description : NULL,
              '#cache' => [
                'tags' => $file->getCacheTags(),
              ],
            ],
          ],
          [
            'data' => $file->getSize() !== NULL ? ByteSizeMarkup::create($file->getSize()) : $this->t('Unknown'),
          ],
        ];
      }
      $elements[0] = [];
      if (!empty($rows)) {
        $elements[0] = [
          '#theme' => 'table__file_formatter_table',
          '#header' => $header,
          '#rows' => $rows,
        ];
      }
    }
    return $elements;
  }

}