Issue #2537732 by Xano, tim.plunkett, gnuget, claudiu.cristea, drunken monkey,...

Issue #2537732 by Xano, tim.plunkett, gnuget, claudiu.cristea, drunken monkey, bojanz: PluginFormInterface must have access to the complete $form_state (introduce SubFormState for embedded forms)

core/lib/Drupal/Core/Condition/ConditionPluginBase.php

@@ -5,6 +5,7 @@
 use Drupal\Core\Executable\ExecutableManagerInterface;
 use Drupal\Core\Executable\ExecutablePluginBase;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformStateInterface;
 use Drupal\Core\Plugin\ContextAwarePluginAssignmentTrait;
 
 /**
@@ -47,6 +48,9 @@ public function isNegated() {
    * {@inheritdoc}
    */
   public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    if ($form_state instanceof SubformStateInterface) {
+      $form_state = $form_state->getCompleteFormState();
+    }
     $contexts = $form_state->getTemporaryValue('gathered_contexts') ?: [];
     $form['context_mapping'] = $this->addContextAssignmentElement($this, $contexts);
     $form['negate'] = array(
@@ -68,6 +72,9 @@ public function validateConfigurationForm(array &$form, FormStateInterface $form
    */
   public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
     $this->configuration['negate'] = $form_state->getValue('negate');
+    if ($form_state->hasValue('context_mapping')) {
+      $this->setContextMapping($form_state->getValue('context_mapping'));
+    }
   }
 
   /**

core/lib/Drupal/Core/Form/FormState.php

@@ -11,6 +11,8 @@
  */
 class FormState implements FormStateInterface {
 
+  use FormStateValuesTrait;
+
   /**
    * Tracks if any errors have been set on any form.
    *
@@ -246,7 +248,8 @@ class FormState implements FormStateInterface {
    *
    * This property is uncacheable.
    *
-   * @var array
+   * @var array|null
+   *   The submitted user input array, or NULL if no input was submitted yet.
    */
   protected $input;
 
@@ -977,67 +980,6 @@ public function &getValues() {
     return $this->values;
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function &getValue($key, $default = NULL) {
-    $exists = NULL;
-    $value = &NestedArray::getValue($this->getValues(), (array) $key, $exists);
-    if (!$exists) {
-      $value = $default;
-    }
-    return $value;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setValues(array $values) {
-    $this->values = $values;
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setValue($key, $value) {
-    NestedArray::setValue($this->getValues(), (array) $key, $value, TRUE);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function unsetValue($key) {
-    NestedArray::unsetValue($this->getValues(), (array) $key);
-    return $this;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function hasValue($key) {
-    $exists = NULL;
-    $value = NestedArray::getValue($this->getValues(), (array) $key, $exists);
-    return $exists && isset($value);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function isValueEmpty($key) {
-    $exists = NULL;
-    $value = NestedArray::getValue($this->getValues(), (array) $key, $exists);
-    return !$exists || empty($value);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setValueForElement(array $element, $value) {
-    return $this->setValue($element['#parents'], $value);
-  }
-
   /**
    * {@inheritdoc}
    */

core/lib/Drupal/Core/Form/FormStateValuesTrait.php

+<?php
+
+namespace Drupal\Core\Form;
+
+use Drupal\Component\Utility\NestedArray;
+
+/**
+ * Provides methods to manage form state values.
+ *
+ * @see \Drupal\Core\Form\FormStateInterface
+ *
+ * @ingroup form_api
+ */
+trait FormStateValuesTrait {
+
+  /**
+   * Implements \Drupal\Core\Form\FormStateInterface::getValues()
+   */
+  abstract public function &getValues();
+
+  /**
+   * Implements \Drupal\Core\Form\FormStateInterface::getValue()
+   */
+  public function &getValue($key, $default = NULL) {
+    $exists = NULL;
+    $value = &NestedArray::getValue($this->getValues(), (array) $key, $exists);
+    if (!$exists) {
+      $value = $default;
+    }
+    return $value;
+  }
+
+  /**
+   * Implements \Drupal\Core\Form\FormStateInterface::setValues()
+   */
+  public function setValues(array $values) {
+    $existing_values = &$this->getValues();
+    $existing_values = $values;
+    return $this;
+  }
+
+  /**
+   * Implements \Drupal\Core\Form\FormStateInterface::setValue()
+   */
+  public function setValue($key, $value) {
+    NestedArray::setValue($this->getValues(), (array) $key, $value, TRUE);
+    return $this;
+  }
+
+  /**
+   * Implements \Drupal\Core\Form\FormStateInterface::unsetValue()
+   */
+  public function unsetValue($key) {
+    NestedArray::unsetValue($this->getValues(), (array) $key);
+    return $this;
+  }
+
+  /**
+   * Implements \Drupal\Core\Form\FormStateInterface::hasValue()
+   */
+  public function hasValue($key) {
+    $exists = NULL;
+    $value = NestedArray::getValue($this->getValues(), (array) $key, $exists);
+    return $exists && isset($value);
+  }
+
+  /**
+   * Implements \Drupal\Core\Form\FormStateInterface::isValueEmpty()
+   */
+  public function isValueEmpty($key) {
+    $exists = NULL;
+    $value = NestedArray::getValue($this->getValues(), (array) $key, $exists);
+    return !$exists || empty($value);
+  }
+
+  /**
+   * Implements \Drupal\Core\Form\FormStateInterface::setValueForElement()
+   */
+  public function setValueForElement(array $element, $value) {
+    return $this->setValue($element['#parents'], $value);
+  }
+
+}

core/lib/Drupal/Core/Form/SubformState.php

+<?php
+
+namespace Drupal\Core\Form;
+
+use Drupal\Component\Utility\NestedArray;
+
+/**
+ * Stores information about the state of a subform.
+ */
+class SubformState extends FormStateDecoratorBase implements SubformStateInterface {
+
+  use FormStateValuesTrait;
+
+  /**
+   * The parent form.
+   *
+   * @var mixed[]
+   */
+  protected $parentForm;
+
+  /**
+   * The subform.
+   *
+   * @var mixed[]
+   */
+  protected $subform;
+
+  /**
+   * Constructs a new instance.
+   *
+   * @param mixed[] $subform
+   *   The subform for which to create a form state.
+   * @param mixed[] $parent_form
+   *   The subform's parent form.
+   * @param \Drupal\Core\Form\FormStateInterface $parent_form_state
+   *   The parent form state.
+   */
+  protected function __construct(array &$subform, array &$parent_form, FormStateInterface $parent_form_state) {
+    $this->decoratedFormState = $parent_form_state;
+    $this->parentForm = $parent_form;
+    $this->subform = $subform;
+  }
+
+  /**
+   * Creates a new instance for a subform.
+   *
+   * @param mixed[] $subform
+   *   The subform for which to create a form state.
+   * @param mixed[] $parent_form
+   *   The subform's parent form.
+   * @param \Drupal\Core\Form\FormStateInterface $parent_form_state
+   *   The parent form state.
+   *
+   * @return static
+   */
+  public static function createForSubform(array &$subform, array &$parent_form, FormStateInterface $parent_form_state) {
+    return new static($subform, $parent_form, $parent_form_state);
+  }
+
+  /**
+   * Gets the subform's parents relative to its parent form.
+   *
+   * @param string $property
+   *   The property name (#parents or #array_parents).
+   *
+   * @return mixed
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown when the requested property does not exist.
+   * @throws \UnexpectedValueException
+   *   Thrown when the subform is not contained by the given parent form.
+   */
+  protected function getParents($property) {
+    foreach ([$this->subform, $this->parentForm] as $form) {
+      if (!isset($form[$property]) || !is_array($form[$property])) {
+        throw new \RuntimeException(sprintf('The subform and parent form must contain the %s property, which must be an array. Try calling this method from a #process callback instead.', $property));
+      }
+    }
+
+    $relative_subform_parents = $this->subform[$property];
+    // Remove all of the subform's parents that are also the parent form's
+    // parents, so we are left with the parents relative to the parent form.
+    foreach ($this->parentForm[$property] as $parent_form_parent) {
+      if ($parent_form_parent !== $relative_subform_parents[0]) {
+        // The parent form's parents are the subform's parents as well. If we
+        // find no match, that means the given subform is not contained by the
+        // given parent form.
+        throw new \UnexpectedValueException('The subform is not contained by the given parent form.');
+      }
+      array_shift($relative_subform_parents);
+    }
+
+    return $relative_subform_parents;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function &getValues() {
+    $exists = NULL;
+    $values = &NestedArray::getValue(parent::getValues(), $this->getParents('#parents'), $exists);
+    if (!$exists) {
+      $values = [];
+    }
+    elseif (!is_array($values)) {
+      throw new \UnexpectedValueException('The form state values do not belong to the subform.');
+    }
+
+    return $values;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCompleteFormState() {
+    return $this->decoratedFormState instanceof SubformStateInterface ? $this->decoratedFormState->getCompleteFormState() : $this->decoratedFormState;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setLimitValidationErrors($limit_validation_errors) {
+    if (is_array($limit_validation_errors)) {
+      $limit_validation_errors = array_merge($this->getParents('#parents'), $limit_validation_errors);
+    }
+
+    return parent::setLimitValidationErrors($limit_validation_errors);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getLimitValidationErrors() {
+    $limit_validation_errors = parent::getLimitValidationErrors();
+    if (is_array($limit_validation_errors)) {
+      return array_slice($limit_validation_errors, count($this->getParents('#parents')));
+
+    }
+    return $limit_validation_errors;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setErrorByName($name, $message = '') {
+    $parents = $this->subform['#array_parents'];
+    $parents[] = $name;
+    $name = implode('][', $parents);
+    parent::setErrorByName($name, $message);
+
+    return $this;
+  }
+
+}

core/lib/Drupal/Core/Form/SubformStateInterface.php

+<?php
+
+namespace Drupal\Core\Form;
+
+/**
+ * Stores information about the state of a subform.
+ *
+ * In the context of Drupal's Form API, a subform is a form definition array
+ * that will be nested into a "parent" form. For instance:
+ *
+ * @code
+ * $subform = [
+ *   'method' => [
+ *     '#type' => 'select',
+ *     // …
+ *   ],
+ * ];
+ * $form = [
+ *   // …
+ *   'settings' => $subform,
+ * ];
+ * @endcode
+ *
+ * All input fields nested under "settings" are then considered part of that
+ * "subform". The concept is used mostly when the subform is defined by a
+ * different class (potentially even in a different module) than the parent
+ * form. This is often the case for plugins: a plugin's buildConfigurationForm()
+ * would then be handed an instance of this interface as the second parameter.
+ *
+ * The benefit of doing this is that the plugin can then just define the form –
+ * and use the form state – as if it would define a "proper" form, not nested in
+ * some other form structure. This means that it won't have to know the key(s)
+ * under which its form structure will be nested – for instance, when retrieving
+ * the form values during form validation or submission.
+ *
+ * Contrary to "proper" forms, subforms don't translate to a <form> tag in the
+ * HTML response. Instead, they can only be discerned in the HTML code by the
+ * nesting of the input tags' names.
+ *
+ * @see \Drupal\Core\Plugin\PluginFormInterface::buildConfigurationForm()
+ */
+interface SubformStateInterface extends FormStateInterface {
+
+  /**
+   * Gets the complete form state.
+   *
+   * @return \Drupal\Core\Form\FormStateInterface
+   */
+  public function getCompleteFormState();
+
+}

core/lib/Drupal/Core/Plugin/PluginFormInterface.php

@@ -31,7 +31,9 @@ interface PluginFormInterface {
    * @param array $form
    *   An associative array containing the initial structure of the plugin form.
    * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   The current state of the complete form.
+   *   The current state of the form. Calling code should pass on a subform
+   *   state created through
+   *   \Drupal\Core\Form\SubformState::createForSubform().
    *
    * @return array
    *   The form structure.
@@ -45,7 +47,9 @@ public function buildConfigurationForm(array $form, FormStateInterface $form_sta
    *   An associative array containing the structure of the plugin form as built
    *   by static::buildConfigurationForm().
    * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   The current state of the complete form.
+   *   The current state of the form. Calling code should pass on a subform
+   *   state created through
+   *   \Drupal\Core\Form\SubformState::createForSubform().
    */
   public function validateConfigurationForm(array &$form, FormStateInterface $form_state);
 
@@ -56,7 +60,9 @@ public function validateConfigurationForm(array &$form, FormStateInterface $form
    *   An associative array containing the structure of the plugin form as built
    *   by static::buildConfigurationForm().
    * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   The current state of the complete form.
+   *   The current state of the form. Calling code should pass on a subform
+   *   state created through
+   *   \Drupal\Core\Form\SubformState::createForSubform().
    */
   public function submitConfigurationForm(array &$form, FormStateInterface $form_state);
 

core/modules/block/src/BlockForm.php

@@ -9,8 +9,8 @@
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Executable\ExecutableManagerInterface;
 use Drupal\Core\Extension\ThemeHandlerInterface;
-use Drupal\Core\Form\FormState;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
 use Drupal\Core\Language\LanguageManagerInterface;
 use Drupal\Core\Plugin\ContextAwarePluginInterface;
 use Drupal\Core\Plugin\Context\ContextRepositoryInterface;
@@ -134,7 +134,9 @@ public function form(array $form, FormStateInterface $form_state) {
     $form_state->setTemporaryValue('gathered_contexts', $this->contextRepository->getAvailableContexts());
 
     $form['#tree'] = TRUE;
-    $form['settings'] = $this->getPluginForm($entity->getPlugin())->buildConfigurationForm(array(), $form_state);
+    $form['settings'] = [];
+    $subform_state = SubformState::createForSubform($form['settings'], $form, $form_state);
+    $form['settings'] = $this->getPluginForm($entity->getPlugin())->buildConfigurationForm($form['settings'], $subform_state);
     $form['visibility'] = $this->buildVisibilityInterface([], $form_state);
 
     // If creating a new block, calculate a safe default machine name.
@@ -294,11 +296,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
 
     // The Block Entity form puts all block plugin form elements in the
     // settings form element, so just pass that to the block for validation.
-    $settings = (new FormState())->setValues($form_state->getValue('settings'));
-    // Call the plugin validate handler.
-    $this->getPluginForm($this->entity->getPlugin())->validateConfigurationForm($form, $settings);
-    // Update the original form values.
-    $form_state->setValue('settings', $settings->getValues());
+    $this->getPluginForm($this->entity->getPlugin())->validateConfigurationForm($form['settings'], SubformState::createForSubform($form['settings'], $form, $form_state));
     $this->validateVisibility($form, $form_state);
   }
 
@@ -322,11 +320,7 @@ protected function validateVisibility(array $form, FormStateInterface $form_stat
 
       // Allow the condition to validate the form.
       $condition = $form_state->get(['conditions', $condition_id]);
-      $condition_values = (new FormState())
-        ->setValues($values);
-      $condition->validateConfigurationForm($form, $condition_values);
-      // Update the original form values.
-      $form_state->setValue(['visibility', $condition_id], $condition_values->getValues());
+      $condition->validateConfigurationForm($form['visibility'][$condition_id], SubformState::createForSubform($form['visibility'][$condition_id], $form, $form_state));
     }
   }
 
@@ -339,19 +333,15 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
     $entity = $this->entity;
     // The Block Entity form puts all block plugin form elements in the
     // settings form element, so just pass that to the block for submission.
-    // @todo Find a way to avoid this manipulation.
-    $settings = (new FormState())->setValues($form_state->getValue('settings'));
-
+    $sub_form_state = SubformState::createForSubform($form['settings'], $form, $form_state);
     // Call the plugin submit handler.
     $block = $entity->getPlugin();
-    $this->getPluginForm($block)->submitConfigurationForm($form, $settings);
+    $this->getPluginForm($block)->submitConfigurationForm($form, $sub_form_state);
     // If this block is context-aware, set the context mapping.
     if ($block instanceof ContextAwarePluginInterface && $block->getContextDefinitions()) {
-      $context_mapping = $settings->getValue('context_mapping', []);
+      $context_mapping = $sub_form_state->getValue('context_mapping', []);
       $block->setContextMapping($context_mapping);
     }
-    // Update the original form values.
-    $form_state->setValue('settings', $settings->getValues());
 
     $this->submitVisibility($form, $form_state);
 
@@ -380,16 +370,19 @@ protected function submitVisibility(array $form, FormStateInterface $form_state)
     foreach ($form_state->getValue('visibility') as $condition_id => $values) {
       // Allow the condition to submit the form.
       $condition = $form_state->get(['conditions', $condition_id]);
-      $condition_values = (new FormState())
-        ->setValues($values);
-      $condition->submitConfigurationForm($form, $condition_values);
+      $condition->submitConfigurationForm($form['visibility'][$condition_id], SubformState::createForSubform($form['visibility'][$condition_id], $form, $form_state));
+
+      // Setting conditions' context mappings is the plugins' responsibility.
+      // This code exists for backwards compatibility, because
+      // \Drupal\Core\Condition\ConditionPluginBase::submitConfigurationForm()
+      // did not set its own mappings until Drupal 8.2
+      // @todo Remove the code that sets context mappings in Drupal 9.0.0.
       if ($condition instanceof ContextAwarePluginInterface) {
         $context_mapping = isset($values['context_mapping']) ? $values['context_mapping'] : [];
         $condition->setContextMapping($context_mapping);
       }
-      // Update the original form values.
+
       $condition_configuration = $condition->getConfiguration();
-      $form_state->setValue(['visibility', $condition_id], $condition_configuration);
       // Update the visibility conditions on the block.
       $this->entity->getVisibilityConditions()->addInstanceId($condition_id, $condition_configuration);
     }

core/modules/block/src/Tests/BlockUiTest.php

@@ -288,4 +288,20 @@ public function testBlockPlacementIndicator() {
     $this->assertUrl('admin/structure/block/list/classy');
   }
 
+  /**
+   * Tests if validation errors are passed plugin form to the parent form.
+   */
+  public function testBlockValidateErrors() {
+    $this->drupalPostForm('admin/structure/block/add/test_settings_validation/classy', ['settings[digits]' => 'abc'], t('Save block'));
+
+    $arguments = [':message' => 'Only digits are allowed'];
+    $pattern = '//div[contains(@class,"messages messages--error")]/div[contains(text()[2],:message)]';
+    $elements = $this->xpath($pattern, $arguments);
+    $this->assertTrue($elements, 'Plugin error message found in parent form.');
+
+    $error_class_pattern = '//div[contains(@class,"form-item-settings-digits")]/input[contains(@class,"error")]';
+    $error_class = $this->xpath($error_class_pattern);
+    $this->assertTrue($error_class, 'Plugin error class found in parent form.');
+  }
+
 }

core/modules/block/tests/modules/block_test/src/Plugin/Block/TestSettingsValidationBlock.php

+<?php
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Provides a test settings validation block.
+ *
+ * @Block(
+ *  id = "test_settings_validation",
+ *  admin_label = @Translation("Test settings validation block"),
+ * )
+ */
+class TestSettingsValidationBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockForm($form, FormStateInterface $form_state) {
+    return ['digits' => ['#type' => 'textfield']] + $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockValidate($form, FormStateInterface $form_state) {
+    if (!ctype_digit($form_state->getValue('digits'))) {
+      $form_state->setErrorByName('digits', $this->t('Only digits are allowed'));
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return ['#markup' => 'foo'];
+  }
+
+}

core/modules/image/src/Form/ImageEffectFormBase.php

@@ -3,8 +3,8 @@
 namespace Drupal\image\Form;
 
 use Drupal\Core\Form\FormBase;
-use Drupal\Core\Form\FormState;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
 use Drupal\image\ConfigurableImageEffectInterface;
 use Drupal\image\ImageStyleInterface;
 use Drupal\Component\Plugin\Exception\PluginNotFoundException;
@@ -25,7 +25,7 @@ abstract class ImageEffectFormBase extends FormBase {
   /**
    * The image effect.
    *
-   * @var \Drupal\image\ImageEffectInterface
+   * @var \Drupal\image\ImageEffectInterface|\Drupal\image\ConfigurableImageEffectInterface
    */
   protected $imageEffect;
 
@@ -73,7 +73,9 @@ public function buildForm(array $form, FormStateInterface $form_state, ImageStyl
       '#value' => $this->imageEffect->getPluginId(),
     );
 
-    $form['data'] = $this->imageEffect->buildConfigurationForm(array(), $form_state);
+    $form['data'] = [];
+    $subform_state = SubformState::createForSubform($form['data'], $form, $form_state);
+    $form['data'] = $this->imageEffect->buildConfigurationForm($form['data'], $subform_state);
     $form['data']['#tree'] = TRUE;
 
     // Check the URL for a weight, then the image effect, otherwise use default.
@@ -102,10 +104,7 @@ public function buildForm(array $form, FormStateInterface $form_state, ImageStyl
   public function validateForm(array &$form, FormStateInterface $form_state) {
     // The image effect configuration is stored in the 'data' key in the form,
     // pass that through for validation.
-    $effect_data = (new FormState())->setValues($form_state->getValue('data'));
-    $this->imageEffect->validateConfigurationForm($form, $effect_data);
-    // Update the original form values.
-    $form_state->setValue('data', $effect_data->getValues());
+    $this->imageEffect->validateConfigurationForm($form['data'], SubformState::createForSubform($form['data'], $form, $form_state));
   }
 
   /**
@@ -116,10 +115,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
 
     // The image effect configuration is stored in the 'data' key in the form,
     // pass that through for submission.
-    $effect_data = (new FormState())->setValues($form_state->getValue('data'));
-    $this->imageEffect->submitConfigurationForm($form, $effect_data);
-    // Update the original form values.
-    $form_state->setValue('data', $effect_data->getValues());
+    $this->imageEffect->submitConfigurationForm($form['data'], SubformState::createForSubform($form['data'], $form, $form_state));
 
     $this->imageEffect->setWeight($form_state->getValue('weight'));
     if (!$this->imageEffect->getUuid()) {

core/modules/image/src/Tests/ImageEffectsTest.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\image\Tests;
 
+use Drupal\image\Entity\ImageStyle;
 use Drupal\system\Tests\Image\ToolkitTestBase;
 
 /**
@@ -162,6 +163,26 @@ function testImageEffectsCaching() {
     $this->assertTrue($effects == $cached_effects, 'Cached effects are the same as generated effects.');
   }
 
+  /**
+   * Tests if validation errors are passed plugin form to the parent form.
+   */
+  public function testEffectFormValidationErrors() {
+    $account = $this->drupalCreateUser(['administer image styles']);
+    $this->drupalLogin($account);
+    /** @var \Drupal\image\ImageStyleInterface $style */
+    $style = ImageStyle::load('thumbnail');
+    // Image Scale is the only effect shipped with 'thumbnail', by default.
+    $uuids = $style->getEffects()->getInstanceIds();
+    $uuid = key($uuids);