Update to Drupal 8.2.2. For more information, see https://www.drupal.org/project/drupal/releases/8.2.2

core/modules/ckeditor/src/Plugin/CKEditorPlugin/Internal.php

@@ -5,6 +5,7 @@ namespace Drupal\ckeditor\Plugin\CKEditorPlugin;
 use Drupal\ckeditor\CKEditorPluginBase;
 use Drupal\ckeditor\CKEditorPluginContextualInterface;
 use Drupal\ckeditor\CKEditorPluginManager;
+use Drupal\Component\Utility\Html;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
@@ -369,7 +370,7 @@ class Internal extends CKEditorPluginBase implements ContainerFactoryPluginInter
       foreach ($possible_format_tags as $tag) {
         $input = '<' . $tag . '>TEST</' . $tag . '>';
         $output = trim(check_markup($input, $editor->id()));
-        if ($input == $output) {
+        if (Html::load($output)->getElementsByTagName($tag)->length !== 0) {
           $format_tags[] = $tag;
         }
       }

core/modules/ckeditor/tests/modules/config/schema/ckeditor_test.schema.yml

@@ -5,3 +5,12 @@ ckeditor.plugin.llama_contextual_and_button:
     ultra_llama_mode:
       type: boolean
       label: 'Ultra llama mode'
+
+filter_settings.test_attribute_filter:
+  type: filter
+  label: 'Test Attribute Filter'
+  mapping:
+    tags:
+      type: sequence
+      sequence:
+        type: string

core/modules/ckeditor/tests/modules/src/Plugin/Filter/TestAttributeFilter.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Drupal\ckeditor_test\Plugin\Filter;
+
+use Drupal\Component\Utility\Html;
+use Drupal\filter\FilterProcessResult;
+use Drupal\filter\Plugin\FilterBase;
+
+/**
+ * A filter that adds a test attribute to any configured HTML tags.
+ *
+ * @Filter(
+ *   id = "test_attribute_filter",
+ *   title = @Translation("Test Attribute Filter"),
+ *   type = Drupal\filter\Plugin\FilterInterface::TYPE_TRANSFORM_REVERSIBLE,
+ *   settings = {
+ *     "tags" = {},
+ *   },
+ *   weight = -10
+ * )
+ */
+class TestAttributeFilter extends FilterBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function process($text, $langcode) {
+    $document = Html::load($text);
+    foreach ($this->settings['tags'] as $tag) {
+      $tag_elements = $document->getElementsByTagName($tag);
+      foreach ($tag_elements as $tag_element) {
+        $tag_element->setAttribute('test_attribute', 'test attribute value');
+      }
+    }
+    return new FilterProcessResult(Html::serialize($document));
+  }
+
+}

core/modules/ckeditor/tests/src/Kernel/Plugin/CKEditorPlugin/InternalTest.php

@@ -0,0 +1,140 @@
+<?php
+
+namespace Drupal\Tests\ckeditor\Kernel\Plugin\CKEditorPlugin;
+
+use Drupal\editor\Entity\Editor;
+use Drupal\filter\Entity\FilterFormat;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * @coversDefaultClass \Drupal\ckeditor\Plugin\CKEditorPlugin\Internal
+ *
+ * @group ckeditor
+ */
+class InternalTest extends KernelTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = [
+    'ckeditor',
+    'ckeditor_test',
+    'filter',
+    'editor',
+  ];
+
+  /**
+   * A testing text format.
+   *
+   * @var \Drupal\filter\Entity\FilterFormat
+   */
+  protected $format;
+
+  /**
+   * A testing text editor.
+   *
+   * @var \Drupal\editor\Entity\Editor
+   */
+  protected $editor;
+
+  /**
+   * The CKEditor plugin manager.
+   *
+   * @var \Drupal\Component\Plugin\PluginManagerInterface
+   */
+  protected $ckeditorPluginManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->installEntitySchema('editor');
+    $this->installEntitySchema('filter_format');
+
+    $this->format = FilterFormat::create([
+      'format' => 'test_format',
+      'name' => $this->randomMachineName(),
+    ]);
+    $this->format->save();
+
+    $this->editor = Editor::create([
+      'editor' => 'ckeditor',
+      'format' => 'test_format',
+      'settings' => [
+        'toolbar' => [
+          'rows' => [
+            [
+              [
+                'name' => 'Enabled Buttons',
+                'items' => [
+                  'Format',
+                ],
+              ],
+            ],
+          ],
+        ],
+      ],
+    ]);
+    $this->editor->save();
+
+    $this->ckeditorPluginManager = $this->container->get('plugin.manager.ckeditor.plugin');
+  }
+
+  /**
+   * Test the format tags settings.
+   *
+   * @dataProvider formatTagsSettingsTestCases
+   */
+  public function testFormatTagsSettings($filter_plugins, $expected_format_tags) {
+    foreach ($filter_plugins as $filter_plugin_id => $filter_plugin_settings) {
+      $this->format->setFilterConfig($filter_plugin_id, $filter_plugin_settings);
+    }
+    $this->format->save();
+
+    $internal_plugin = $this->ckeditorPluginManager->createInstance('internal', []);
+    $plugin_config = $internal_plugin->getConfig($this->editor);
+    $this->assertEquals($expected_format_tags, explode(';', $plugin_config['format_tags']));
+  }
+
+  /**
+   * A data provider for testFormatTagsSettings.
+   */
+  public function formatTagsSettingsTestCases() {
+    $all_tags = ['p', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'pre'];
+
+    return [
+      'No filter plugins enabled (all tags allowed)' => [
+        [],
+        $all_tags,
+      ],
+      'HTML filter plugin enabled (some tags filtered out)' => [
+        [
+          'filter_html' => [
+            'status' => 1,
+            'settings' => [
+              'allowed_html' => '<h1> <h2>',
+              'filter_html_help' => 1,
+              'filter_html_nofollow' => 0,
+            ],
+          ],
+        ],
+        ['p', 'h1', 'h2'],
+      ],
+      'Test attribute filter enabled (all tags allowed)' => [
+        [
+          'test_attribute_filter' => [
+            'status' => 1,
+            'settings' => [
+              'tags' => ['h1', 'h2'],
+            ],
+          ],
+        ],
+        $all_tags,
+      ],
+    ];
+  }
+
+}