core/modules/contact/contact.info.yml              |  2 +
 .../contact/src/Controller/ContactController.php   |  3 +
 .../contact/src/Tests/ContactFormCacheTagsTest.php | 98 ++++++++++++++++++++++
 core/modules/editor/src/Element.php                |  8 ++
 .../filter/src/Tests/FilterFormatCacheTagsTest.php | 96 +++++++++++++++++++++
 5 files changed, 207 insertions(+)

diff --git a/core/modules/contact/contact.info.yml b/core/modules/contact/contact.info.yml
index a50d17d..e02742d 100644
--- a/core/modules/contact/contact.info.yml
+++ b/core/modules/contact/contact.info.yml
@@ -5,3 +5,5 @@ package: Core
 version: VERSION
 core: 8.x
 configure: contact.form_list
+dependencies:
+  - field
diff --git a/core/modules/contact/src/Controller/ContactController.php b/core/modules/contact/src/Controller/ContactController.php
index cffbf5a..5759fc6 100644
--- a/core/modules/contact/src/Controller/ContactController.php
+++ b/core/modules/contact/src/Controller/ContactController.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\contact\Controller;
 
+use Drupal\contact\Entity\ContactForm;
 use Drupal\Core\Controller\ControllerBase;
 use Drupal\Core\Datetime\DateFormatter;
 use Drupal\Core\Flood\FloodInterface;
@@ -104,6 +105,7 @@ public function contactSitePage(ContactFormInterface $contact_form = NULL) {
 
     $form = $this->entityFormBuilder()->getForm($message);
     $form['#title'] = String::checkPlain($contact_form->label());
+    $form['#cache']['tags'] = drupal_merge_cache_tags($contact_form->getCacheTag(), entity_get_form_display('contact_message', 'feedback', 'default')->getCacheTag());
     return $form;
   }
 
@@ -129,6 +131,7 @@ public function contactPersonalPage(UserInterface $user) {
 
     $form = $this->entityFormBuilder()->getForm($message);
     $form['#title'] = $this->t('Contact @username', array('@username' => $user->getUsername()));
+    $form['#cache']['tags'] = drupal_merge_cache_tags(ContactForm::load('personal')->getCacheTag(), entity_get_form_display('contact_message', 'personal', 'default')->getCacheTag());
     return $form;
   }
 
diff --git a/core/modules/contact/src/Tests/ContactFormCacheTagsTest.php b/core/modules/contact/src/Tests/ContactFormCacheTagsTest.php
new file mode 100644
index 0000000..5b1f2b5
--- /dev/null
+++ b/core/modules/contact/src/Tests/ContactFormCacheTagsTest.php
@@ -0,0 +1,98 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\contact\Tests\ContactFormCacheTagsTest.
+ */
+
+namespace Drupal\contact\Tests;
+
+use Drupal\contact\Entity\ContactForm;
+use Drupal\system\Tests\Cache\PageCacheTagsTestBase;
+use Drupal\user\Entity\Role;
+
+/**
+ * Tests the Contact form entity's cache tags.
+ *
+ * @group contact
+ */
+class ContactFormCacheTagsTest extends PageCacheTagsTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = array('contact');
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    // Give anonymous users permission to access contact forms, so that we can
+    // verify the cache tags of cached versions of contact form pages.
+    Role::load(DRUPAL_ANONYMOUS_RID)
+      ->grantPermission('access site-wide contact form')
+      ->grantPermission('access user contact forms')
+      ->save();
+  }
+
+  /**
+   * Tests cache tags presence and invalidation of the Contact form entity.
+   *
+   * Tests the following cache tags:
+   * - ['contact_form' => '<contact form ID>']
+   */
+  public function testContactForm() {
+    // Test the site-wide contact form. Rendered by
+    // ContactController::contactSitePage().
+    $this->assertContactForm('feedback', 'contact');
+
+    // Test a personal contact form. Rendered by
+    // ContactController::contactPersonalPage().
+    $this->assertContactForm('personal', 'user/1/contact');
+  }
+
+  /**
+   * Asserts whether a contact form is correctly tagged with cache tags.
+   *
+   * @param string $id
+   *   A contact form entity ID.
+   * @param $path
+   *   The corresponding path, where this contact form is rendered.
+   */
+  protected function assertContactForm($id, $path) {
+    // Prime the page cache.
+    $this->verifyPageCache($path, 'MISS');
+
+    // Verify a cache hit, but also the presence of the correct cache tags.
+    $expected_tags = array(
+      'theme:stark',
+      'theme_global_settings:1',
+      'contact_form:' . $id,
+      'entity_form_display:contact_message.' . $id . '.default',
+      'rendered:1',
+    );
+    $this->verifyPageCache($path, 'HIT', $expected_tags);
+
+    // Verify that after modifying the contact form, there is a cache miss.
+    $this->pass('Test modification of contact form.', 'Debug');
+    ContactForm::load($id)->save();
+    $this->verifyPageCache($path, 'MISS');
+
+    // Verify a cache hit.
+    $this->verifyPageCache($path, 'HIT', $expected_tags);
+
+    // Verify that after modifying the contact form's form display, there is a
+    // cache miss.
+    $this->pass('Test modification of form display of contact form.', 'Debug');
+    $entity_form_display = entity_get_form_display('contact_message', $id, 'default');
+    $entity_form_display->enforceIsNew(FALSE)->save();
+
+    $this->verifyPageCache($path, 'MISS');
+
+    // Verify a cache hit.
+    $this->verifyPageCache($path, 'HIT', $expected_tags);
+  }
+
+}
diff --git a/core/modules/editor/src/Element.php b/core/modules/editor/src/Element.php
index f0b97bf..da1aef2 100644
--- a/core/modules/editor/src/Element.php
+++ b/core/modules/editor/src/Element.php
@@ -52,6 +52,7 @@ function preRenderTextFormat(array $element) {
     $format_ids = array_keys($element['format']['format']['#options']);
 
     // Early-return if no text editor is associated with any of the text formats.
+    /** @var \Drupal\editor\EditorInterface[] $editors */
     $editors = Editor::loadMultiple($format_ids);
     if (count($editors) === 0) {
       return $element;
@@ -84,6 +85,13 @@ function preRenderTextFormat(array $element) {
       $element['format']['guidelines'][$format_id]['#access'] = FALSE;
     }
 
+    // Associate the Text Editor's cache tags.
+    $cache_tags = isset($element['#cache']['tags']) ? $element['#cache']['tags'] : [];
+    foreach ($editors as $editor) {
+      $cache_tags = drupal_merge_cache_tags($cache_tags, $editor->getCacheTag());
+    }
+    $element['#cache']['tags'] = $cache_tags;
+
     // Attach Text Editor module's (this module) library.
     $element['#attached']['library'][] = 'editor/drupal.editor';
 
diff --git a/core/modules/filter/src/Tests/FilterFormatCacheTagsTest.php b/core/modules/filter/src/Tests/FilterFormatCacheTagsTest.php
new file mode 100644
index 0000000..e8b7872
--- /dev/null
+++ b/core/modules/filter/src/Tests/FilterFormatCacheTagsTest.php
@@ -0,0 +1,96 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\filter\Tests\FilterFormatCacheTagsTest.
+ */
+
+namespace Drupal\filter\Tests;
+
+use Drupal\block_content\Entity\BlockContent;
+use Drupal\filter\Entity\FilterFormat;
+use Drupal\system\Tests\Cache\PageCacheTagsTestBase;
+
+/**
+ * Tests the Text format entity's cache tags.
+ *
+ * @group filter
+ */
+class FilterFormatCacheTagsTest extends PageCacheTagsTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = array('filter', 'block_content');
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    // Create a "Llama" custom block. This is not the subject under test, but we
+    // need *some* way of rendering filtered text onto the page. This is easier
+    // than creating an entire test module just for this purpose.
+    BlockContent::create([
+      'info' => 'Llama',
+      'type' => 'basic',
+      'body' => [
+        'value' => 'The name "llama" was adopted by European settlers from native Peruvians.',
+        'format' => 'plain_text',
+      ],
+    ])->save();
+
+    // Place it, so we can look at cache tags on the front page.
+    $this->drupalPlaceBlock('block_content:' . BlockContent::load(1)->uuid());
+  }
+
+  /**
+   * Tests cache tags presence and invalidation of the Text format entity.
+   *
+   * Tests the following cache tags:
+   * - ['filter_format' => '<text format ID>']
+   */
+  public function testRenderedFilterFormat() {
+    $id = 'plain_text';
+    $path = '<front>';
+
+    $block_content = BlockContent::load(1);
+    $matching_block_ids = array_keys(entity_load_multiple_by_properties('block', ['plugin' => 'block_content:' . $block_content->uuid()]));
+    $base_tags= array(
+      'theme:stark',
+      'theme_global_settings:1',
+      'block_view:1',
+      'block:' . $matching_block_ids[0],
+      'block_plugin:block_content__' . $block_content->uuid(),
+      'block_content_view:1',
+      'block_content:1',
+      'rendered:1',
+    );
+
+    // Prime the page cache.
+    $this->verifyPageCache($path, 'MISS');
+
+    // Verify a cache hit, but also the presence of the correct cache tags.
+    $expected_tags = $base_tags;
+    $expected_tags[] = 'filter_format:plain_text';
+    $this->verifyPageCache($path, 'HIT', $expected_tags);
+
+    // Verify that after modifying the text format, there is a cache miss.
+    $this->pass('Test modification of text format.', 'Debug');
+    FilterFormat::load($id)->save();
+    $this->verifyPageCache($path, 'MISS');
+
+    // Verify a cache hit.
+    $this->verifyPageCache($path, 'HIT', $expected_tags);
+
+    // Verify that after deleting the text format, there is a cache miss.
+    $this->pass('Test deletion of text format.', 'Debug');
+    FilterFormat::load($id)->delete();
+    $this->verifyPageCache($path, 'MISS');
+
+    // Verify a cache hit.
+    $this->verifyPageCache($path, 'HIT', $base_tags);
+  }
+
+}