Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

core/modules/forum/src/Breadcrumb/ForumBreadcrumbBuilderBase.php

@@ -67,7 +67,7 @@ abstract class ForumBreadcrumbBuilderBase  implements BreadcrumbBuilderInterface
    */
   public function build(RouteMatchInterface $route_match) {
     $breadcrumb = new Breadcrumb();
-    $breadcrumb->setCacheContexts(['route']);
+    $breadcrumb->addCacheContexts(['route']);
 
     $links[] = Link::createFromRoute($this->t('Home'), '<front>');
 

core/modules/forum/src/Controller/ForumController.php

@@ -224,7 +224,6 @@ class ForumController extends ControllerBase {
       '#sortby' => $config->get('topics.order'),
       '#forums_per_page' => $config->get('topics.page_limit'),
     );
-    $build['#attached']['library'][] = 'forum/forum.index';
     if (empty($term->forum_container->value)) {
       $build['#attached']['feed'][] = array('taxonomy/term/' . $term->id() . '/feed', 'RSS - ' . $term->getName());
     }

core/modules/forum/src/Form/Overview.php

@@ -87,9 +87,9 @@ class Overview extends OverviewTerms {
     unset($form['actions']['reset_alphabetical']);
 
     // Use the existing taxonomy overview submit handler.
-    $form['terms']['#empty'] = $this->t('No containers or forums available. <a href="@container">Add container</a> or <a href="@forum">Add forum</a>.', array(
-      '@container' => $this->url('forum.add_container'),
-      '@forum' => $this->url('forum.add_forum')
+    $form['terms']['#empty'] = $this->t('No containers or forums available. <a href=":container">Add container</a> or <a href=":forum">Add forum</a>.', array(
+      ':container' => $this->url('forum.add_container'),
+      ':forum' => $this->url('forum.add_forum')
     ));
     return $form;
   }

core/modules/forum/src/ForumUninstallValidator.php

@@ -76,9 +76,9 @@ class ForumUninstallValidator implements ModuleUninstallValidatorInterface {
       $vocabulary = $this->getForumVocabulary();
       if ($this->hasTermsForVocabulary($vocabulary)) {
         if ($vocabulary->access('view')) {
-          $reasons[] = $this->t('To uninstall Forum, first delete all <a href="@url">%vocabulary</a> terms', [
+          $reasons[] = $this->t('To uninstall Forum, first delete all <a href=":url">%vocabulary</a> terms', [
             '%vocabulary' => $vocabulary->label(),
-            '@url' => $vocabulary->url('overview-form'),
+            ':url' => $vocabulary->url('overview-form'),
           ]);
         }
         else {

core/modules/forum/src/Tests/ForumTest.php

@@ -83,6 +83,7 @@ class ForumTest extends WebTestBase {
   protected function setUp() {
     parent::setUp();
     $this->drupalPlaceBlock('system_breadcrumb_block');
+    $this->drupalPlaceBlock('page_title_block');
 
     // Create users.
     $this->adminUser = $this->drupalCreateUser(array(

core/modules/forum/src/Tests/Migrate/d6/MigrateForumConfigsTest.php

@@ -20,9 +20,7 @@ class MigrateForumConfigsTest extends MigrateDrupal6TestBase {
   use SchemaCheckTestTrait;
 
   /**
-   * Modules to enable.
-   *
-   * @var array
+   * {@inheritdoc}
    */
   public static $modules = array('comment', 'forum', 'taxonomy');
 
@@ -31,11 +29,7 @@ class MigrateForumConfigsTest extends MigrateDrupal6TestBase {
    */
   protected function setUp() {
     parent::setUp();
-    $this->prepareMigrations(array(
-      'd6_taxonomy_vocabulary' => array(
-        array(array(1), array('vocabulary_1_i_0_')),
-      )
-    ));
+    $this->executeMigration('d6_taxonomy_vocabulary');
     $this->executeMigration('d6_forum_settings');
   }
 

core/modules/forum/src/Tests/Migrate/d7/MigrateForumSettingsTest.php

@@ -0,0 +1,54 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\forum\Tests\d7\MigrateForumSettingsTest.
+ */
+
+namespace Drupal\forum\Tests\Migrate\d7;
+
+use Drupal\migrate\Entity\Migration;
+use Drupal\migrate\MigrateExecutable;
+use Drupal\migrate_drupal\Tests\d7\MigrateDrupal7TestBase;
+
+/**
+ * Tests migration of Forum's variables to configuration.
+ *
+ * @group forum
+ */
+class MigrateForumSettingsTest extends MigrateDrupal7TestBase {
+
+  // Don't alphabetize these. They're in dependency order.
+  public static $modules = [
+    'comment',
+    'field',
+    'filter',
+    'text',
+    'node',
+    'taxonomy',
+    'forum',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->executeMigration('d7_taxonomy_vocabulary');
+    $this->executeMigration('d7_forum_settings');
+  }
+
+  /**
+   * Tests the migration of Forum's settings to configuration.
+   */
+  public function testForumSettingsMigration() {
+    $config = $this->config('forum.settings');
+    $this->assertIdentical(9, $config->get('block.active.limit'));
+    $this->assertIdentical(4, $config->get('block.new.limit'));
+    $this->assertIdentical(10, $config->get('topics.hot_threshold'));
+    $this->assertIdentical(25, $config->get('topics.page_limit'));
+    $this->assertIdentical(1, $config->get('topics.order'));
+    $this->assertIdentical('forums', $config->get('vocabulary'));
+  }
+
+}