Update to Drupal 8.1.5. For more information, see https://www.drupal.org/project/drupal/releases/8.1.5

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

@@ -7,7 +7,11 @@ use Drupal\migrate_drupal\Plugin\migrate\cckfield\CckFieldPluginBase;
 
 /**
  * @MigrateCckField(
- *   id = "link"
+ *   id = "link",
+ *   core = {6},
+ *   type_map = {
+ *     "link_field" = "link"
+ *   }
  * )
  */
 class LinkField extends CckFieldPluginBase {

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

@@ -36,6 +36,32 @@ class CckLink extends ProcessPluginBase implements ContainerFactoryPluginInterfa
     );
   }
 
+  /**
+   * Turn a Drupal 6 URI into a Drupal 8-compatible format.
+   *
+   * @param string $uri
+   *   The 'url' value from Drupal 6.
+   *
+   * @return string
+   *   The Drupal 8-compatible URI.
+   *
+   * @see \Drupal\link\Plugin\Field\FieldWidget\LinkWidget::getUserEnteredStringAsUri()
+   */
+  protected function canonicalizeUri($uri) {
+    // If we already have a scheme, we're fine.
+    if (empty($uri) || !is_null(parse_url($uri, PHP_URL_SCHEME))) {
+      return $uri;
+    }
+
+    // Remove the <front> component of the URL.
+    if (strpos($uri, '<front>') === 0) {
+      $uri = substr($uri, strlen('<front>'));
+    }
+
+    // Add the internal: scheme and ensure a leading slash.
+    return 'internal:/' . ltrim($uri, '/');
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -51,7 +77,7 @@ class CckLink extends ProcessPluginBase implements ContainerFactoryPluginInterfa
     }
 
     // Massage the values into the correct form for the link.
-    $route['uri'] = $value['url'];
+    $route['uri'] = $this->canonicalizeUri($value['url']);
     $route['options']['attributes'] = $attributes;
     $route['title'] = $value['title'];
     return $route;

core/modules/link/tests/src/Unit/Plugin/migrate/process/d6/CckLinkTest.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace Drupal\Tests\link\Unit\Plugin\migrate\process\d6;
+
+use Drupal\link\Plugin\migrate\process\d6\CckLink;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @group Link
+ */
+class CckLinkTest extends UnitTestCase {
+
+  /**
+   * Test the url transformations in the CckLink process plugin.
+   *
+   * @dataProvider canonicalizeUriDataProvider
+   */
+  public function testCanonicalizeUri($url, $expected) {
+    $link_plugin = new CckLink([], '', [], $this->getMock('\Drupal\migrate\Plugin\MigrationInterface'));
+    $transformed = $link_plugin->transform([
+      'url' => $url,
+      'title' => '',
+      'attributes' => serialize([]),
+    ], $this->getMock('\Drupal\migrate\MigrateExecutableInterface'), $this->getMockBuilder('\Drupal\migrate\Row')->disableOriginalConstructor()->getMock(), NULL);
+    $this->assertEquals($expected, $transformed['uri']);
+  }
+
+  /**
+   * Data provider for testCanonicalizeUri.
+   */
+  public function canonicalizeUriDataProvider() {
+    return [
+      'Simple front-page' => [
+        '<front>',
+        'internal:/',
+      ],
+      'Front page with query' => [
+        '<front>?query=1',
+        'internal:/?query=1',
+      ],
+      'No leading forward slash' => [
+        'node/10',
+        'internal:/node/10',
+      ],
+      'Leading forward slash' => [
+        '/node/10',
+        'internal:/node/10',
+      ],
+      'Existing scheme' => [
+        'scheme:test',
+        'scheme:test',
+      ],
+    ];
+  }
+
+}