Issue #2878556 by plach, matsbla, vijaycs85, Gábor Hojtsy, catch, gabesullice, effulgentsia, hchonov, hass, amateescu, xjm: Ensure that changes to untranslatable fields affect only one translation in pending revisions

core/lib/Drupal/Core/Entity/ContentEntityBase.php

@@ -20,6 +20,10 @@ use Drupal\Core\TypedData\TypedDataInterface;
  */
 abstract class ContentEntityBase extends Entity implements \IteratorAggregate, ContentEntityInterface, TranslationStatusInterface {
 
+  use EntityChangesDetectionTrait {
+    getFieldsToSkipFromTranslationChangesCheck as traitGetFieldsToSkipFromTranslationChangesCheck;
+  }
+
   /**
    * The plain data values of the contained fields.
    *
@@ -1373,17 +1377,7 @@ abstract class ContentEntityBase extends Entity implements \IteratorAggregate, C
    *   An array of field names.
    */
   protected function getFieldsToSkipFromTranslationChangesCheck() {
-    /** @var \Drupal\Core\Entity\ContentEntityTypeInterface $entity_type */
-    $entity_type = $this->getEntityType();
-    // A list of known revision metadata fields which should be skipped from
-    // the comparision.
-    $fields = [
-      $entity_type->getKey('revision'),
-      'revision_translation_affected',
-    ];
-    $fields = array_merge($fields, array_values($entity_type->getRevisionMetadataKeys()));
-
-    return $fields;
+    return $this->traitGetFieldsToSkipFromTranslationChangesCheck($this);
   }
 
   /**
@@ -1423,10 +1417,15 @@ abstract class ContentEntityBase extends Entity implements \IteratorAggregate, C
     // The list of fields to skip from the comparision.
     $skip_fields = $this->getFieldsToSkipFromTranslationChangesCheck();
 
+    // We also check untranslatable fields, so that a change to those will mark
+    // all translations as affected, unless they are configured to only affect
+    // the default translation.
+    $skip_untranslatable_fields = !$this->isDefaultTranslation() && $this->isDefaultTranslationAffectedOnly();
+
     foreach ($this->getFieldDefinitions() as $field_name => $definition) {
       // @todo Avoid special-casing the following fields. See
       //    https://www.drupal.org/node/2329253.
-      if (in_array($field_name, $skip_fields, TRUE)) {
+      if (in_array($field_name, $skip_fields, TRUE) || ($skip_untranslatable_fields && !$definition->isTranslatable())) {
         continue;
       }
       $field = $this->get($field_name);
@@ -1447,4 +1446,14 @@ abstract class ContentEntityBase extends Entity implements \IteratorAggregate, C
     return FALSE;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function isDefaultTranslationAffectedOnly() {
+    $bundle_name = $this->bundle();
+    $bundle_info = \Drupal::service('entity_type.bundle.info')
+      ->getBundleInfo($this->getEntityTypeId());
+    return !empty($bundle_info[$bundle_name]['untranslatable_fields.default_translation_affected']);
+  }
+
 }

core/lib/Drupal/Core/Entity/ContentEntityStorageBase.php

@@ -227,13 +227,13 @@ abstract class ContentEntityStorageBase extends EntityStorageBase implements Con
       $active_langcode = $entity->language()->getId();
       $skipped_field_names = array_flip($this->getRevisionTranslationMergeSkippedFieldNames());
 
-      // Default to preserving the untranslatable field values in the default
-      // revision, otherwise we may expose data that was not meant to be
-      // accessible.
+      // By default we copy untranslatable field values from the default
+      // revision, unless they are configured to affect only the default
+      // translation. This way we can ensure we always have only one affected
+      // translation in pending revisions. This constraint is enforced by
+      // EntityUntranslatableFieldsConstraintValidator.
       if (!isset($keep_untranslatable_fields)) {
-        // @todo Implement a more complete default logic in
-        //    https://www.drupal.org/project/drupal/issues/2878556.
-        $keep_untranslatable_fields = FALSE;
+        $keep_untranslatable_fields = $entity->isDefaultTranslation() && $entity->isDefaultTranslationAffectedOnly();
       }
 
       /** @var \Drupal\Core\Entity\ContentEntityInterface $default_revision */
@@ -262,6 +262,13 @@ abstract class ContentEntityStorageBase extends EntityStorageBase implements Con
         // No need to copy untranslatable field values more than once.
         $keep_untranslatable_fields = TRUE;
       }
+
+      // The "original" property is used in various places to detect changes in
+      // field values with respect to the stored ones. If the property is not
+      // defined, the stored version is loaded explicitly. Since the merged
+      // revision generated here is not stored anywhere, we need to populate the
+      // "original" property manually, so that changes can be properly detected.
+      $new_revision->original = clone $new_revision;
     }
 
     // Eventually mark the new revision as such.

core/lib/Drupal/Core/Entity/EntityChangesDetectionTrait.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace Drupal\Core\Entity;
+
+/**
+ * Provides helper methods to detect changes in an entity object.
+ *
+ * @internal This may be replaced by a proper entity comparison handler.
+ */
+trait EntityChangesDetectionTrait {
+
+  /**
+   * Returns an array of field names to skip when checking for changes.
+   *
+   * @param \Drupal\Core\Entity\ContentEntityInterface $entity
+   *   A content entity object.
+   *
+   * @return string[]
+   *   An array of field names.
+   */
+  protected function getFieldsToSkipFromTranslationChangesCheck(ContentEntityInterface $entity) {
+    /** @var \Drupal\Core\Entity\ContentEntityTypeInterface $entity_type */
+    $entity_type = $entity->getEntityType();
+
+    // A list of known revision metadata fields which should be skipped from
+    // the comparision.
+    $fields = [
+      $entity_type->getKey('revision'),
+      $entity_type->getKey('revision_translation_affected'),
+    ];
+    $fields = array_merge($fields, array_values($entity_type->getRevisionMetadataKeys()));
+
+    return $fields;
+  }
+
+}

core/lib/Drupal/Core/Entity/EntityType.php

@@ -311,11 +311,16 @@ class EntityType extends PluginDefinition implements EntityTypeInterface {
       $this->checkStorageClass($this->handlers['storage']);
     }
 
-    // Automatically add the EntityChanged constraint if the entity type tracks
-    // the changed time.
+    // Automatically add the "EntityChanged" constraint if the entity type
+    // tracks the changed time.
     if ($this->entityClassImplements(EntityChangedInterface::class)) {
       $this->addConstraint('EntityChanged');
     }
+    // Automatically add the "EntityUntranslatableFields" constraint if we have
+    // an entity type supporting translatable fields and pending revisions.
+    if ($this->entityClassImplements(ContentEntityInterface::class)) {
+      $this->addConstraint('EntityUntranslatableFields');
+    }
 
     // Ensure a default list cache tag is set.
     if (empty($this->list_cache_tags)) {

core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/EntityUntranslatableFieldsConstraint.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Drupal\Core\Entity\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Validation constraint for the entity changed timestamp.
+ *
+ * @Constraint(
+ *   id = "EntityUntranslatableFields",
+ *   label = @Translation("Entity untranslatable fields", context = "Validation"),
+ *   type = {"entity"}
+ * )
+ */
+class EntityUntranslatableFieldsConstraint extends Constraint {
+
+  public $message = 'Non translatable fields can only be changed when updating the current revision or the original language.';
+
+}

core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/EntityUntranslatableFieldsConstraintValidator.php

@@ -0,0 +1,128 @@
+<?php
+
+namespace Drupal\Core\Entity\Plugin\Validation\Constraint;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\ContentEntityInterface;
+use Drupal\Core\Entity\EntityChangesDetectionTrait;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Field\ChangedFieldItemList;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+/**
+ * Validates the EntityChanged constraint.
+ */
+class EntityUntranslatableFieldsConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
+
+  use EntityChangesDetectionTrait;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * Constructs an EntityUntranslatableFieldsConstraintValidator object.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager) {
+    $this->entityTypeManager = $entity_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity_type.manager')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($entity, Constraint $constraint) {
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
+
+    // Untranslatable field restrictions apply only to pending revisions of
+    // multilingual entities.
+    if ($entity->isNew() || $entity->isDefaultRevision() || !$entity->isTranslatable() || !$entity->getEntityType()->isRevisionable()) {
+      return;
+    }
+
+    // To avoid unintentional reverts and data losses, we forbid changes to
+    // untranslatable fields in pending revisions for multilingual entities. The
+    // only case where changes in pending revisions are acceptable is when
+    // untranslatable fields affect only the default translation, in which case
+    // a pending revision contains only one affected translation. Even in this
+    // case, multiple translations would be affected in a single revision, if we
+    // allowed changes to untranslatable fields while editing non-default
+    // translations, so that is forbidden too.
+    if ($this->hasUntranslatableFieldsChanges($entity)) {
+      if ($entity->isDefaultTranslationAffectedOnly()) {
+        foreach ($entity->getTranslationLanguages(FALSE) as $langcode => $language) {
+          if ($entity->getTranslation($langcode)->hasTranslationChanges()) {
+            $this->context->addViolation($constraint->message);
+            break;
+          }
+        }
+      }
+      else {
+        $this->context->addViolation($constraint->message);
+      }
+    }
+  }
+
+  /**
+   * Checks whether an entity has untranslatable field changes.
+   *
+   * @param \Drupal\Core\Entity\ContentEntityInterface $entity
+   *   A content entity object.
+   *
+   * @return bool
+   *   TRUE if untranslatable fields have changes, FALSE otherwise.
+   */
+  protected function hasUntranslatableFieldsChanges(ContentEntityInterface $entity) {
+    $skip_fields = $this->getFieldsToSkipFromTranslationChangesCheck($entity);
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $original */
+    if (isset($entity->original)) {
+      $original = $entity->original;
+    }
+    else {
+      $original = $this->entityTypeManager
+        ->getStorage($entity->getEntityTypeId())
+        ->loadRevision($entity->getLoadedRevisionId());
+    }
+
+    foreach ($entity->getFieldDefinitions() as $field_name => $definition) {
+      if (in_array($field_name, $skip_fields, TRUE) || $definition->isTranslatable() || $definition->isComputed()) {
+        continue;
+      }
+
+      // When saving entities in the user interface, the changed timestamp is
+      // automatically incremented by ContentEntityForm::submitForm() even if
+      // nothing was actually changed. Thus, the changed time needs to be
+      // ignored when determining whether there are any actual changes in the
+      // entity.
+      $field = $entity->get($field_name);
+      if ($field instanceof ChangedFieldItemList) {
+        continue;
+      }
+
+      $items = $field->filterEmptyItems();
+      $original_items = $original->get($field_name)->filterEmptyItems();
+      if (!$items->equals($original_items)) {
+        return TRUE;
+      }
+    }
+
+    return FALSE;
+  }
+
+}

core/lib/Drupal/Core/Entity/TranslatableRevisionableInterface.php

@@ -71,4 +71,13 @@ interface TranslatableRevisionableInterface extends TranslatableInterface, Revis
    */
   public function setRevisionTranslationAffectedEnforced($enforced);
 
+  /**
+   * Checks if untranslatable fields should affect only the default translation.
+   *
+   * @return bool
+   *   TRUE if untranslatable fields should affect only the default translation,
+   *   FALSE otherwise.
+   */
+  public function isDefaultTranslationAffectedOnly();
+
 }

core/modules/content_translation/config/schema/content_translation.schema.yml

@@ -18,3 +18,9 @@ language.content_settings.*.*.third_party.content_translation:
     enabled:
       type: boolean
       label: 'Content translation enabled'
+    bundle_settings:
+      type: sequence
+      label: 'Content translation bundle settings'
+      sequence:
+        type: string
+        label: 'Bundle settings values'

core/modules/content_translation/content_translation.admin.inc

@@ -5,6 +5,7 @@
  * The content translation administration forms.
  */
 
+use Drupal\content_translation\BundleTranslationSettingsInterface;
 use Drupal\Core\Config\Entity\ThirdPartySettingsInterface;
 use Drupal\Core\Entity\ContentEntityTypeInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
@@ -83,6 +84,7 @@ function _content_translation_form_language_content_settings_form_alter(array &$
     return;
   }
 
+  /** @var \Drupal\content_translation\ContentTranslationManagerInterface $content_translation_manager */
   $content_translation_manager = \Drupal::service('content_translation.manager');
   $default = $form['entity_types']['#default_value'];
   foreach ($default as $entity_type_id => $enabled) {
@@ -110,6 +112,23 @@ function _content_translation_form_language_content_settings_form_alter(array &$
         continue;
       }
 
+      // Displayed the "shared fields widgets" toggle.
+      if ($content_translation_manager instanceof BundleTranslationSettingsInterface) {
+        $settings = $content_translation_manager->getBundleTranslationSettings($entity_type_id, $bundle);
+        $form['settings'][$entity_type_id][$bundle]['settings']['content_translation']['untranslatable_fields_hide'] = [
+          '#type' => 'checkbox',
+          '#title' => t('Hide non translatable fields on translation forms'),
+          '#default_value' => !empty($settings['untranslatable_fields_hide']),
+          '#states' => [
+            'visible' => [
+              ':input[name="settings[' . $entity_type_id . '][' . $bundle . '][translatable]"]' => [
+                'checked' => TRUE,
+              ],
+            ],
+          ],
+        ];
+      }
+
       $fields = $entity_manager->getFieldDefinitions($entity_type_id, $bundle);
       if ($fields) {
         foreach ($fields as $field_name => $definition) {
@@ -317,6 +336,8 @@ function content_translation_form_language_content_settings_validate(array $form
  * @see content_translation_admin_settings_form_validate()
  */
 function content_translation_form_language_content_settings_submit(array $form, FormStateInterface $form_state) {
+  /** @var \Drupal\content_translation\ContentTranslationManagerInterface $content_translation_manager */
+  $content_translation_manager = \Drupal::service('content_translation.manager');
   $entity_types = $form_state->getValue('entity_types');
   $settings = &$form_state->getValue('settings');
 
@@ -347,7 +368,12 @@ function content_translation_form_language_content_settings_submit(array $form,
       }
       if (isset($bundle_settings['translatable'])) {
         // Store whether a bundle has translation enabled or not.
-        \Drupal::service('content_translation.manager')->setEnabled($entity_type_id, $bundle, $bundle_settings['translatable']);
+        $content_translation_manager->setEnabled($entity_type_id, $bundle, $bundle_settings['translatable']);
+
+        // Store any other bundle settings.
+        if ($content_translation_manager instanceof BundleTranslationSettingsInterface) {
+          $content_translation_manager->setBundleTranslationSettings($entity_type_id, $bundle, $bundle_settings['settings']['content_translation']);
+        }
 
         // Save translation_sync settings.
         if (!empty($bundle_settings['columns'])) {
@@ -367,8 +393,8 @@ function content_translation_form_language_content_settings_submit(array $form,
       }
     }
   }
+
   // Ensure entity and menu router information are correctly rebuilt.
   \Drupal::entityManager()->clearCachedDefinitions();
   \Drupal::service('router.builder')->setRebuildNeeded();
-
 }

core/modules/content_translation/content_translation.module

@@ -5,6 +5,7 @@
  * Allows entities to be translated into different languages.
  */
 
+use Drupal\content_translation\BundleTranslationSettingsInterface;
 use Drupal\Core\Access\AccessResult;
 use Drupal\Core\Entity\ContentEntityFormInterface;
 use Drupal\Core\Entity\ContentEntityInterface;
@@ -161,9 +162,15 @@ function content_translation_entity_type_alter(array &$entity_types) {
  * Implements hook_entity_bundle_info_alter().
  */
 function content_translation_entity_bundle_info_alter(&$bundles) {
-  foreach ($bundles as $entity_type => &$info) {
+  /** @var \Drupal\content_translation\ContentTranslationManagerInterface $content_translation_manager */
+  $content_translation_manager = \Drupal::service('content_translation.manager');
+  foreach ($bundles as $entity_type_id => &$info) {
     foreach ($info as $bundle => &$bundle_info) {
-      $bundle_info['translatable'] = \Drupal::service('content_translation.manager')->isEnabled($entity_type, $bundle);
+      $bundle_info['translatable'] = $content_translation_manager->isEnabled($entity_type_id, $bundle);
+      if ($content_translation_manager instanceof BundleTranslationSettingsInterface) {
+        $settings = $content_translation_manager->getBundleTranslationSettings($entity_type_id, $bundle);
+        $bundle_info['untranslatable_fields.default_translation_affected'] = !empty($settings['untranslatable_fields_hide']);
+      }
     }
   }
 }
@@ -319,6 +326,11 @@ function content_translation_form_alter(array &$form, FormStateInterface $form_s
       }
     }
 
+    // The footer region, if defined, may contain multilingual widgets so we
+    // need to always display it.
+    if (isset($form['footer'])) {
+      $form['footer']['#multilingual'] = TRUE;
+    }
   }
 }
 

core/modules/content_translation/src/BundleTranslationSettingsInterface.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace Drupal\content_translation;
+
+/**
+ * Interface providing support for content translation bundle settings.
+ */
+interface BundleTranslationSettingsInterface {
+
+  /**
+   * Returns translation settings for the specified bundle.
+   *
+   * @param string $entity_type_id
+   *   The entity type identifier.
+   * @param string $bundle
+   *   The bundle name.
+   *
+   * @return array
+   *   An associative array of values keyed by setting name.
+   */
+  public function getBundleTranslationSettings($entity_type_id, $bundle);
+
+  /**
+   * Sets translation settings for the specified bundle.
+   *
+   * @param string $entity_type_id
+   *   The entity type identifier.
+   * @param string $bundle
+   *   The bundle name.
+   * @param array $settings
+   *   An associative array of values keyed by setting name.
+   */
+  public function setBundleTranslationSettings($entity_type_id, $bundle, array $settings);
+
+}

core/modules/content_translation/src/ContentTranslationHandler.php

@@ -5,6 +5,7 @@ namespace Drupal\content_translation;
 use Drupal\Core\Access\AccessResult;
 use Drupal\Core\DependencyInjection\DependencySerializationTrait;
 use Drupal\Core\Entity\EntityChangedInterface;
+use Drupal\Core\Entity\EntityChangesDetectionTrait;
 use Drupal\Core\Entity\EntityHandlerInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityManagerInterface;
@@ -13,8 +14,10 @@ use Drupal\Core\Field\BaseFieldDefinition;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
+use Drupal\Core\Messenger\MessengerInterface;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
 use Drupal\user\Entity\User;
 use Drupal\user\EntityOwnerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -25,7 +28,10 @@ use Symfony\Component\DependencyInjection\ContainerInterface;
  * @ingroup entity_api
  */
 class ContentTranslationHandler implements ContentTranslationHandlerInterface, EntityHandlerInterface {
+
+  use EntityChangesDetectionTrait;
   use DependencySerializationTrait;
+  use StringTranslationTrait;
 
   /**
    * The type of the entity being translated.
@@ -70,6 +76,13 @@ class ContentTranslationHandler implements ContentTranslationHandlerInterface, E
    */
   protected $fieldStorageDefinitions;
 
+  /**
+   * The messenger service.
+   *
+   * @var \Drupal\Core\Messenger\MessengerInterface
+   */
+  protected $messenger;
+
   /**
    * Initializes an instance of the content translation controller.
    *
@@ -83,14 +96,17 @@ class ContentTranslationHandler implements ContentTranslationHandlerInterface, E
    *   The entity manager.
    * @param \Drupal\Core\Session\AccountInterface $current_user
    *   The current user.
+   * @param \Drupal\Core\Messenger\MessengerInterface $messenger
+   *   The messenger service.
    */
-  public function __construct(EntityTypeInterface $entity_type, LanguageManagerInterface $language_manager, ContentTranslationManagerInterface $manager, EntityManagerInterface $entity_manager, AccountInterface $current_user) {
+  public function __construct(EntityTypeInterface $entity_type, LanguageManagerInterface $language_manager, ContentTranslationManagerInterface $manager, EntityManagerInterface $entity_manager, AccountInterface $current_user, MessengerInterface $messenger) {
     $this->entityTypeId = $entity_type->id();
     $this->entityType = $entity_type;
     $this->languageManager = $language_manager;
     $this->manager = $manager;
     $this->currentUser = $current_user;
     $this->fieldStorageDefinitions = $entity_manager->getLastInstalledFieldStorageDefinitions($this->entityTypeId);
+    $this->messenger = $messenger;
   }
 
   /**
@@ -102,7 +118,8 @@ class ContentTranslationHandler implements ContentTranslationHandlerInterface, E
       $container->get('language_manager'),
       $container->get('content_translation.manager'),
       $container->get('entity.manager'),
-      $container->get('current_user')
+      $container->get('current_user'),
+      $container->get('messenger')
     );
   }
 
@@ -269,6 +286,8 @@ class ContentTranslationHandler implements ContentTranslationHandlerInterface, E
    * {@inheritdoc}
    */
   public function entityFormAlter(array &$form, FormStateInterface $form_state, EntityInterface $entity) {
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
+
     $form_object = $form_state->getFormObject();
     $form_langcode = $form_object->getFormLangcode($form_state);
     $entity_langcode = $entity->getUntranslated()->language()->getId();
@@ -512,6 +531,20 @@ class ContentTranslationHandler implements ContentTranslationHandlerInterface, E
       $ignored_types = array_flip(['actions', 'value', 'hidden', 'vertical_tabs', 'token', 'details']);
     }
 
+    /** @var \Drupal\Core\Entity\ContentEntityForm $form_object */
+    $form_object = $form_state->getFormObject();
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
+    $entity = $form_object->getEntity();
+    $display_translatability_clue = !$entity->isDefaultTranslationAffectedOnly();
+    $hide_untranslatable_fields = $entity->isDefaultTranslationAffectedOnly() && !$entity->isDefaultTranslation();
+    $translation_form = $form_state->get(['content_translation', 'translation_form']);
+    $display_warning = FALSE;
+
+    // We use field definitions to identify untranslatable field widgets to be
+    // hidden. Fields that are not involved in translation changes checks should
+    // not be affected by this logic (the "revision_log" field, for instance).
+    $field_definitions = array_diff_key($entity->getFieldDefinitions(), array_flip($this->getFieldsToSkipFromTranslationChangesCheck($entity)));
+
     foreach (Element::children($element) as $key) {
       if (!isset($element[$key]['#type'])) {
         $this->entityFormSharedElements($element[$key], $form_state, $form);
@@ -524,11 +557,18 @@ class ContentTranslationHandler implements ContentTranslationHandlerInterface, E
         // Elements are considered to be non multilingual by default.
         if (empty($element[$key]['#multilingual'])) {
           // If we are displaying a multilingual entity form we need to provide
-          // translatability clues, otherwise the shared form elements should be
-          // hidden.
-          if (!$form_state->get(['content_translation', 'translation_form'])) {
+          // translatability clues, otherwise the non-multilingual form elements
+          // should be hidden.
+          if (!$translation_form) {
+            if ($display_translatability_clue) {
               $this->addTranslatabilityClue($element[$key]);
             }
+            // Hide widgets for untranslatable fields.
+            if ($hide_untranslatable_fields && isset($field_definitions[$key])) {
+              $element[$key]['#access'] = FALSE;
+              $display_warning = TRUE;
+            }
+          }
           else {
             $element[$key]['#access'] = FALSE;
           }
@@ -536,6 +576,11 @@ class ContentTranslationHandler implements ContentTranslationHandlerInterface, E
       }
     }
 
+    if ($display_warning && !$form_state->isSubmitted() && !$form_state->isRebuilding()) {
+      $url = $entity->getUntranslated()->toUrl('edit-form')->toString();
+      $this->messenger->addWarning($this->t('Fields that apply to all languages are hidden to avoid conflicting changes. <a href=":url">Edit them on the original language form</a>.', [':url' => $url]));
+    }
+
     return $element;
   }
 

core/modules/content_translation/src/ContentTranslationManager.php

@@ -8,7 +8,7 @@ use Drupal\Core\Entity\EntityManagerInterface;
 /**
  * Provides common functionality for content translation.
  */
-class ContentTranslationManager implements ContentTranslationManagerInterface {
+class ContentTranslationManager implements ContentTranslationManagerInterface, BundleTranslationSettingsInterface {
 
   /**
    * The entity type manager.
@@ -105,6 +105,23 @@ class ContentTranslationManager implements ContentTranslationManagerInterface {
     return $enabled;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function setBundleTranslationSettings($entity_type_id, $bundle, array $settings) {
+    $config = $this->loadContentLanguageSettings($entity_type_id, $bundle);
+    $config->setThirdPartySetting('content_translation', 'bundle_settings', $settings)
+      ->save();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getBundleTranslationSettings($entity_type_id, $bundle) {
+    $config = $this->loadContentLanguageSettings($entity_type_id, $bundle);
+    return $config->getThirdPartySetting('content_translation', 'bundle_settings', []);
+  }
+
   /**
    * Loads a content language config entity based on the entity type and bundle.
    *

core/modules/content_translation/tests/src/Functional/ContentTranslationTestBase.php

@@ -138,7 +138,7 @@ abstract class ContentTranslationTestBase extends BrowserTestBase {
    * Returns an array of permissions needed for the administrator.
    */
   protected function getAdministratorPermissions() {
-    return array_merge($this->getEditorPermissions(), $this->getTranslatorPermissions(), ['administer content translation']);
+    return array_merge($this->getEditorPermissions(), $this->getTranslatorPermissions(), ['administer languages', 'administer content translation']);
   }
 
   /**

core/modules/content_translation/tests/src/Functional/ContentTranslationUntranslatableFieldsTest.php

@@ -0,0 +1,119 @@
+<?php
+
+namespace Drupal\Tests\content_translation\Functional;
+
+use Drupal\Core\Url;
+use Drupal\language\Entity\ConfigurableLanguage;
+
+/**
+ * Tests the untranslatable fields behaviors.
+ *
+ * @group content_translation
+ */
+class ContentTranslationUntranslatableFieldsTest extends ContentTranslationTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = ['language', 'content_translation', 'entity_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    // Configure one field as untranslatable.
+    $this->drupalLogin($this->administrator);
+    $edit = [
+      'settings[' . $this->entityTypeId . '][' . $this->bundle . '][fields][' . $this->fieldName . ']' => 0,
+    ];
+    $this->drupalPostForm('admin/config/regional/content-language', $edit, 'Save configuration');
+
+    /** @var \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager */
+    $entity_field_manager = $this->container->get('entity_field.manager');
+    $entity_field_manager->clearCachedFieldDefinitions();
+    $definitions = $entity_field_manager->getFieldDefinitions($this->entityTypeId, $this->bundle);
+    $this->assertFalse($definitions[$this->fieldName]->isTranslatable());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEditorPermissions() {
+    return array_merge(parent::getTranslatorPermissions(), ['administer entity_test content', 'view test entity']);
+  }
+
+  /**
+   * Tests that hiding untranslatable field widgets works correctly.
+   */
+  public function testHiddenWidgets() {
+    /** @var \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager */
+    $entity_type_manager = $this->container->get('entity_type.manager');
+    $id = $this->createEntity([], 'en');
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
+    $entity = $entity_type_manager
+      ->getStorage($this->entityTypeId)
+      ->load($id);
+
+    // Check that the untranslatable field widget is displayed on the edit form
+    // and no translatability clue is displayed yet.
+    $this->drupalGet($entity->toUrl('edit-form'));
+    $field_xpath = '//input[@name="' . $this->fieldName . '[0][value]"]';
+    $this->assertNotEmpty($this->xpath($field_xpath));
+    $clue_xpath = '//label[@for="edit-' . strtr($this->fieldName, '_', '-') . '-0-value"]/span[text()="(all languages)"]';
+    $this->assertEmpty($this->xpath($clue_xpath));
+
+    // Add a translation and check that the untranslatable field widget is
+    // displayed on the translation and edit forms along with translatability
+    // clues.
+    $add_url = Url::fromRoute("entity.{$this->entityTypeId}.content_translation_add", [
+      $entity->getEntityTypeId() => $entity->id(),
+      'source' => 'en',
+      'target' => 'it'
+    ]);
+    $this->drupalGet($add_url);
+    $this->assertNotEmpty($this->xpath($field_xpath));
+    $this->assertNotEmpty($this->xpath($clue_xpath));
+    $this->drupalPostForm(NULL, [], 'Save');
+
+    // Check that the widget is displayed along with its clue in the edit form
+    // for both languages.
+    $this->drupalGet($entity->toUrl('edit-form'));
+    $this->assertNotEmpty($this->xpath($field_xpath));
+    $this->assertNotEmpty($this->xpath($clue_xpath));
+    $it_language = ConfigurableLanguage::load('it');
+    $this->drupalGet($entity->toUrl('edit-form', ['language' => $it_language]));
+    $this->assertNotEmpty($this->xpath($field_xpath));
+    $this->assertNotEmpty($this->xpath($clue_xpath));
+
+    // Configure untranslatable field widgets to be hidden on non-default
+    // language edit forms.
+    $edit = [
+      'settings[' . $this->entityTypeId . '][' . $this->bundle . '][settings][content_translation][untranslatable_fields_hide]' => 1,
+    ];
+    $this->drupalPostForm('admin/config/regional/content-language', $edit, 'Save configuration');
+
+    // Verify that the widget is displayed in the default language edit form,
+    // but no clue is displayed.
+    $this->drupalGet($entity->toUrl('edit-form'));
+    $field_xpath = '//input[@name="' . $this->fieldName . '[0][value]"]';
+    $this->assertNotEmpty($this->xpath($field_xpath));
+    $this->assertEmpty($this->xpath($clue_xpath));
+
+    // Verify no widget is displayed on the non-default language edit form.
+    $this->drupalGet($entity->toUrl('edit-form', ['language' => $it_language]));
+    $this->assertEmpty($this->xpath($field_xpath));
+    $this->assertEmpty($this->xpath($clue_xpath));
+
+    // Verify a warning is displayed.
+    $this->assertSession()->pageTextContains('Fields that apply to all languages are hidden to avoid conflicting changes.');
+    $edit_path = $entity->toUrl('edit-form')->toString();
+    $link_xpath = '//a[@href=:edit_path and text()="Edit them on the original language form"]';
+    $elements = $this->xpath($link_xpath, [':edit_path' => $edit_path]);
+    $this->assertNotEmpty($elements);
+  }
+
+}

core/modules/node/src/Form/NodeRevisionRevertTranslationForm.php

@@ -88,10 +88,15 @@ class NodeRevisionRevertTranslationForm extends NodeRevisionRevertForm {
     $this->langcode = $langcode;
     $form = parent::buildForm($form, $form_state, $node_revision);
 
+    // Unless untranslatable fields are configured to affect only the default
+    // translation, we need to ask the user whether they should be included in
+    // the revert process.
+    $default_translation_affected = $this->revision->isDefaultTranslationAffectedOnly();
     $form['revert_untranslated_fields'] = [
       '#type' => 'checkbox',
       '#title' => $this->t('Revert content shared among translations'),
-      '#default_value' => FALSE,
+      '#default_value' => $default_translation_affected && $this->revision->getTranslation($this->langcode)->isDefaultTranslation(),
+      '#access' => !$default_translation_affected,
     ];
 
     return $form;

core/modules/system/tests/modules/entity_test/entity_test.module

@@ -217,6 +217,9 @@ function entity_test_entity_bundle_info_alter(&$bundles) {
       if ($state->get('entity_test.translation')) {
         foreach ($all_bundle_info as $bundle_name => &$bundle_info) {
           $bundle_info['translatable'] = TRUE;
+          if ($state->get('entity_test.untranslatable_fields.default_translation_affected')) {
+            $bundle_info['untranslatable_fields.default_translation_affected'] = TRUE;
+          }
         }
       }
     }

core/modules/system/tests/modules/entity_test/src/Entity/EntityTestMulRev.php

@@ -58,7 +58,8 @@ class EntityTestMulRev extends EntityTestRev {
 
     $fields['non_mul_field'] = BaseFieldDefinition::create('string')
       ->setLabel(t('Non translatable'))
-      ->setDescription(t('A non-translatable string field'));
+      ->setDescription(t('A non-translatable string field'))
+      ->setRevisionable(TRUE);
 
     return $fields;
   }

core/modules/system/tests/modules/entity_test/src/Entity/EntityTestMulRevChanged.php

@@ -71,6 +71,7 @@ class EntityTestMulRevChanged extends EntityTestMulChanged {
     $fields['name']->setRevisionable(TRUE);
     $fields['user_id']->setRevisionable(TRUE);
     $fields['changed']->setRevisionable(TRUE);
+    $fields['not_translatable']->setRevisionable(TRUE);
 
     return $fields;
   }

core/tests/Drupal/KernelTests/Core/Entity/EntityDecoupledTranslationRevisionsTest.php

@@ -3,6 +3,7 @@
 namespace Drupal\KernelTests\Core\Entity;
 
 use Drupal\Core\Entity\ContentEntityInterface;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\entity_test\Entity\EntityTestMulRev;
 use Drupal\language\Entity\ConfigurableLanguage;
 use Drupal\user\Entity\User;
@@ -215,6 +216,9 @@ class EntityDecoupledTranslationRevisionsTest extends EntityKernelTestBase {
 
     $sets['Default behavior - Untranslatable fields affect all revisions'] = [
       [
+        ['en', TRUE, TRUE],
+        ['it', FALSE, TRUE, FALSE],
+        ['en', FALSE, TRUE, FALSE],
         ['en', TRUE, TRUE],
         ['it', TRUE, TRUE],
         ['en', FALSE],
@@ -222,6 +226,23 @@ class EntityDecoupledTranslationRevisionsTest extends EntityKernelTestBase {
         ['en', TRUE],
         ['it', TRUE],
       ],
+      FALSE,
+    ];
+
+    $sets['Alternative behavior - Untranslatable fields affect only default translation'] = [
+      [
+        ['en', TRUE, TRUE],
+        ['it', FALSE, TRUE, FALSE],
+        ['en', FALSE, TRUE],
+        ['it', FALSE],
+        ['it', TRUE],
+        ['en', TRUE, TRUE],
+        ['it', FALSE],
+        ['en', FALSE],
+        ['it', TRUE],
+        ['en', TRUE, TRUE],
+      ],
+      TRUE,
     ];
 
     return $sets;
@@ -234,11 +255,20 @@ class EntityDecoupledTranslationRevisionsTest extends EntityKernelTestBase {
    *   An array with arrays of arguments for the ::doSaveNewRevision() method as
    *   values. Every child array corresponds to a method invocation.
    *
+   * @param bool $default_translation_affected
+   *   Whether untranslatable field changes affect all revisions or only the
+   *   default revision.
+   *
    * @covers ::createRevision
+   * @covers \Drupal\Core\Entity\Plugin\Validation\Constraint\EntityUntranslatableFieldsConstraintValidator::validate
    *
    * @dataProvider dataTestUntranslatableFields
    */
-  public function testUntranslatableFields($sequence) {
+  public function testUntranslatableFields($sequence, $default_translation_affected) {
+    // Configure the untranslatable fields edit mode.
+    $this->state->set('entity_test.untranslatable_fields.default_translation_affected', $default_translation_affected);
+    $this->bundleInfo->clearCachedBundles();
+
     // Test that a new entity is always valid.
     $entity = EntityTestMulRev::create();
     $entity->set('non_mul_field', 0);
@@ -289,14 +319,23 @@ class EntityDecoupledTranslationRevisionsTest extends EntityKernelTestBase {
   protected function doEditStep($active_langcode, $default_revision, $untranslatable_update = FALSE, $valid = TRUE) {
     $this->stepInfo = [$active_langcode, $default_revision, $untranslatable_update, $valid];
 
+    // If changes to untranslatable fields affect only the default translation,
+    // we can different values for untranslatable fields in the various
+    // revision translations, so we need to track their previous value per
+    // language.
+    $all_translations_affected = !$this->state->get('entity_test.untranslatable_fields.default_translation_affected');
+    $previous_untranslatable_field_langcode = $all_translations_affected ? LanguageInterface::LANGCODE_DEFAULT : $active_langcode;
+
     // Initialize previous data tracking.
     if (!isset($this->translations)) {
       $this->translations[$active_langcode] = EntityTestMulRev::create();
       $this->previousRevisionId[$active_langcode] = 0;
+      $this->previousUntranslatableFieldValue[$previous_untranslatable_field_langcode] = NULL;
     }
     if (!isset($this->translations[$active_langcode])) {
       $this->translations[$active_langcode] = reset($this->translations)->addTranslation($active_langcode);
       $this->previousRevisionId[$active_langcode] = 0;
+      $this->previousUntranslatableFieldValue[$active_langcode] = NULL;
     }
 
     // We want to update previous data only if we expect a valid result,
@@ -304,10 +343,12 @@ class EntityDecoupledTranslationRevisionsTest extends EntityKernelTestBase {
     if ($valid) {
       $entity = &$this->translations[$active_langcode];
       $previous_revision_id = &$this->previousRevisionId[$active_langcode];
+      $previous_untranslatable_field_value = &$this->previousUntranslatableFieldValue[$previous_untranslatable_field_langcode];
     }
     else {
       $entity = clone $this->translations[$active_langcode];
       $previous_revision_id = $this->previousRevisionId[$active_langcode];
+      $previous_untranslatable_field_value = $this->previousUntranslatableFieldValue[$previous_untranslatable_field_langcode];
     }
 
     // Check that after instantiating a new revision for the specified
@@ -332,10 +373,21 @@ class EntityDecoupledTranslationRevisionsTest extends EntityKernelTestBase {
       $this->assertEquals($previous_label, $entity->label(), $this->formatMessage('Loaded translatable field value does not match the previous one.'));
     }
 
+    // Check that the previous untranslatable field value is loaded in the new
+    // revision as expected. When we are dealing with a non default translation
+    // the expected value is always the one stored in the default revision, as
+    // untranslatable fields can only be changed in the default translation or
+    // in the default revision, depending on the configured mode.
     $value = $entity->get('non_mul_field')->value;
     if (isset($previous_untranslatable_field_value)) {
       $this->assertEquals($previous_untranslatable_field_value, $value, $this->formatMessage('Loaded untranslatable field value does not match the previous one.'));
     }
+    elseif (!$entity->isDefaultTranslation()) {
+      /** @var \Drupal\Core\Entity\ContentEntityInterface $default_revision */
+      $default_revision = $this->storage->loadUnchanged($entity->id());
+      $expected_value = $default_revision->get('non_mul_field')->value;
+      $this->assertEquals($expected_value, $value, $this->formatMessage('Loaded untranslatable field value does not match the previous one.'));
+    }
 
     // Perform a change and store it.
     $label = $this->generateNewEntityLabel($entity, $previous_revision_id, TRUE);
@@ -345,12 +397,13 @@ class EntityDecoupledTranslationRevisionsTest extends EntityKernelTestBase {
       // the new value, besides the upcoming revision ID. Useful to analyze test
       // failures.
       $prev = 0;
-      if (isset($value)) {
-        preg_match('/^\d+ -> (\d+)$/', $value, $matches);
+      if (isset($previous_untranslatable_field_value)) {
+        preg_match('/^\d+ -> (\d+)$/', $previous_untranslatable_field_value, $matches);
         $prev = $matches[1];
       }
       $value = $prev . ' -> ' . ($entity->getLoadedRevisionId() + 1);
       $entity->set('non_mul_field', $value);
+      $previous_untranslatable_field_value = $value;
     }
 
     $violations = $entity->validate();
@@ -378,7 +431,7 @@ class EntityDecoupledTranslationRevisionsTest extends EntityKernelTestBase {
       // translation was marked as affected.
       foreach ($entity->getTranslationLanguages() as $langcode => $language) {
         $translation = $entity->getTranslation($langcode);
-        $rta_expected = $langcode == $active_langcode || $untranslatable_update;
+        $rta_expected = $langcode == $active_langcode || ($untranslatable_update && $all_translations_affected);
         $this->assertEquals($rta_expected, $translation->isRevisionTranslationAffected(), $this->formatMessage("'$langcode' translation incorrectly affected"));
         $label_expected = $label;
         if ($langcode !== $active_langcode) {

core/tests/Drupal/KernelTests/Core/Entity/EntityTypeConstraintsTest.php

@@ -24,7 +24,11 @@ class EntityTypeConstraintsTest extends EntityKernelTestBase {
     // Test reading the annotation. There should be two constraints, the defined
     // constraint and the automatically added EntityChanged constraint.
     $entity_type = $this->entityManager->getDefinition('entity_test_constraints');
-    $default_constraints = ['NotNull' => [], 'EntityChanged' => NULL];
+    $default_constraints = [
+      'NotNull' => [],
+      'EntityChanged' => NULL,
+      'EntityUntranslatableFields' => NULL,
+    ];
     $this->assertEqual($default_constraints, $entity_type->getConstraints());
 
     // Enable our test module and test extending constraints.