EntityFormDisplay should update $form with cache tags of FieldConfig, FieldStorageConfig, EntityFormDisplay config entities

To clarify: There's nothing special about the user registration form, user registration form isn't the only entity form that is visible to anon users (not even the only one by default), we just don't have test coverage for others. The contact form is also accessible to anon by default, for example.

+++ b/core/modules/user/src/Tests/UserRegistrationTest.php
@@ -220,14 +220,23 @@ function testRegistrationWithUserFields() {
+    $check_cache_tags = function() {
+      $this->assertCacheTag('config:core.entity_form_display.user.user.register');
+      $this->assertCacheTag('config:field.field.user.user.test_user_field');
+      $this->assertCacheTag('config:field.storage.user.test_user_field');
+      $this->assertCacheTag('config:user.settings');
+    };

You like this pattern, but I personally prefer having a real method for those helper methods, I'm not wondering how those are reported, for example. You can name a real method asssertSomething() and then call to it will be shown, which is more helpful.

1. +++ b/core/lib/Drupal/Core/Entity/Entity/EntityFormDisplay.php
   @@ -150,6 +152,9 @@ public function getRenderer($field_name) {
   +    /** @var \Drupal\Core\Render\RendererInterface $renderer */
   +    $renderer = \Drupal::service('renderer');
   +
   

   Uh? Should this not be injected into the class?

2. +++ b/core/lib/Drupal/Core/Entity/Entity/EntityFormDisplay.php
   @@ -165,9 +170,23 @@ public function buildForm(FieldableEntityInterface $entity, array &$form, FormSt
   +        if ($field_definition instanceof ConfigEntityInterface) {
   +          $renderer->addDependency($form['name'], $field_definition);
   +          $field_storage_definition = $field_definition->getFieldStorageDefinition();
   +          if ($field_storage_definition instanceof ConfigEntityInterface) {
   

   Should these not check for CacheableDependencyInterface?

3. +++ b/core/lib/Drupal/Core/Entity/Entity/EntityFormDisplay.php
   @@ -165,9 +170,23 @@ public function buildForm(FieldableEntityInterface $entity, array &$form, FormSt
   +    // Associate the cache tags for the form display.
   +    $renderer->addDependency($form, $this);
   +
   

   Is it ensured that $this always implements CacheableDependencyInterface?

EntityFormDisplay is an entity so yes, it always implements that interface, and we can't inject dependencies in entities.

+++ b/core/lib/Drupal/Core/Entity/Entity/EntityFormDisplay.php
@@ -165,9 +174,23 @@ public function buildForm(FieldableEntityInterface $entity, array &$form, FormSt
+        $field_definition = $this->getFieldDefinition($name);
+        if ($field_definition instanceof CacheableDependencyInterface) {
+          $this->renderer->addDependency($form[$name], $field_definition);
+          $field_storage_definition = $field_definition->getFieldStorageDefinition();

I think the logic is not correct here:

Unless I miss something the field storage definition should be added regardless of the interface of the $field_definition.

E.g.:

if ($field_def instanceof ...) {
  $renderer->addDep();
}

if ($field_def) {
  $field_storage_def = ...;
  if ($field_stor_def instanceof ...) {
    $renderer->addDep();
  }
}

The rest looks good!

RTBC, looks great now!

This issue addresses a major bug and is allowed per https://www.drupal.org/core/beta-changes. Committed 4553018 and pushed to 8.0.x. Thanks!