Update to Drupal 8.0.0-beta15. For more information, see: https://www.drupal.org/node/2563023

core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php

@@ -7,7 +7,6 @@
 
 namespace Drupal\link\Plugin\Field\FieldFormatter;
 
-use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Field\FieldDefinitionInterface;
@@ -201,7 +200,7 @@ class LinkFormatter extends FormatterBase implements ContainerFactoryPluginInter
 
       if (!empty($settings['url_only']) && !empty($settings['url_plain'])) {
         $element[$delta] = array(
-          '#markup' => SafeMarkup::checkPlain($link_title),
+          '#plain_text' => $link_title,
         );
 
         if (!empty($item->_attributes)) {

core/modules/link/src/Plugin/migrate/cckfield/LinkField.php

@@ -0,0 +1,47 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\link\Plugin\migrate\cckfield\LinkField.
+ */
+
+namespace Drupal\link\Plugin\migrate\cckfield;
+
+use Drupal\migrate\Entity\MigrationInterface;
+use Drupal\migrate_drupal\Plugin\migrate\cckfield\CckFieldPluginBase;
+
+/**
+ * @PluginID("link")
+ */
+class LinkField extends CckFieldPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFieldFormatterMap() {
+    // See d6_field_formatter_settings.yml and CckFieldPluginBase
+    // processFieldFormatter().
+    return [
+      'default' => 'link',
+      'plain' => 'link',
+      'absolute' => 'link',
+      'title_plain' => 'link',
+      'url' => 'link',
+      'short' => 'link',
+      'label' => 'link',
+      'separate' => 'link_separate',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function processCckFieldValues(MigrationInterface $migration, $field_name, $data) {
+      $process = [
+        'plugin' => 'd6_cck_link',
+        'source' => $field_name,
+      ];
+      $migration->mergeProcessOfProperty($field_name, $process);
+  }
+
+}

core/modules/link/src/Plugin/migrate/process/d6/CckLink.php

@@ -0,0 +1,58 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\link\Plugin\migrate\process\d6\CckLink.
+ */
+
+namespace Drupal\link\Plugin\migrate\process\d6;
+
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\migrate\Entity\MigrationInterface;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * @MigrateProcessPlugin(
+ *   id = "d6_cck_link"
+ * )
+ */
+class CckLink extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->migration = $migration;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $migration
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    // Drupal 6 link attributes are double serialized.
+    $attributes = unserialize(unserialize($value['attributes']));
+
+    // Massage the values into the correct form for the link.
+    $route['uri'] = $value['url'];
+    $route['options']['attributes'] = $attributes;
+    $route['title'] = $value['title'];
+    return $route;
+  }
+
+}