LinkFormatter.php

1. 8.x drupal/core/modules/link/lib/Drupal/link/Plugin/field/formatter/LinkFormatter.php
2. 8.x drupal/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/field/formatter/LinkFormatter.php

<?php

/**
 * @file
 * Contains \Drupal\taxonomy\Plugin\field\formatter\LinkFormatter.
 */
namespace Drupal\taxonomy\Plugin\field\formatter;

use Drupal\field\Annotation\FieldFormatter;
use Drupal\Core\Annotation\Translation;
use Drupal\Core\Entity\EntityInterface;
use Drupal\field\Plugin\Type\Formatter\FormatterBase;
use Drupal\taxonomy\Plugin\field\formatter\TaxonomyFormatterBase;

/**
 * Plugin implementation of the 'taxonomy_term_reference_link' formatter.
 *
 * @FieldFormatter(
 *   id = "taxonomy_term_reference_link",
 *   module = "taxonomy",
 *   label = @Translation("Link"),
 *   field_types = {
 *     "taxonomy_term_reference"
 *   }
 * )
 */
class LinkFormatter extends TaxonomyFormatterBase {

  /**
   * {@inheritdoc}
   */
  public function viewElements(EntityInterface $entity, $langcode, array $items) {
    $elements = array();

    // Terms without tid do not exist yet, theme such terms as just their name.
    foreach ($items as $delta => $item) {
      if (!$item['tid']) {
        $elements[$delta] = array(
          '#markup' => check_plain($item['entity']
            ->label()),
        );
      }
      else {
        $term = $item['entity'];
        $uri = $term
          ->uri();
        $elements[$delta] = array(
          '#type' => 'link',
          '#title' => $term
            ->label(),
          '#href' => $uri['path'],
          '#options' => $uri['options'],
        );
      }
    }
    return $elements;
  }

}