Add the content moderation state widget to the layout builder entity form.

Here is a patch taken from #3004536.50 to kick it off, which will apply but fail based on the other blockers. The hook it is implementing currently doesn't exist.

We should review the test when it's combined with the form blocker. I was only able to get a fully working prototype by repacing LatestVersionSectionStorageOverride::deriveContextsFromRoute with a content_moderation-aware implementation.

I ran into #3032548: ContentModerationRouteSubscriber assumes all parameters in an entity form route contain a 'type' key when testing everything on an existing project locally.

If that other issue landed and the right revision was loaded, would $entity->toUrl('canonical') begin pointing to the correct place?

Hm, I'm afraid not. latest-version is a content_moderation provided route.

Adding to the test to prove why #2942907: Entity system does not provide an API for retrieving an entity variant that is safe for editing is a blocker.

In theory, content moderation could take the approach in the entity form sandbox and do something like the following, loading the latest revision and fiddling with the redirect URL:

/**
 * Implements hook_layout_builder_section_storage_alter().
 */
function content_moderation_layout_builder_section_storage_alter(&$definitions) {
  // @todo https://www.drupal.org/project/drupal/issues/3032287.
  $definitions['overrides']->setClass(LatestVersionOverridesSectionStorage::class);
}

Regardless of the blocker, not sure how to solve the redirect component.

I was able to make this patch green with either:

diff --git a/core/modules/layout_builder/src/Form/OverridesEntityForm.php b/core/modules/layout_builder/src/Form/OverridesEntityForm.php
index 6373e1062b..0493797061 100644
--- a/core/modules/layout_builder/src/Form/OverridesEntityForm.php
+++ b/core/modules/layout_builder/src/Form/OverridesEntityForm.php
@@ -8,6 +8,7 @@
 use Drupal\Core\Entity\EntityRepositoryInterface;
 use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\Context\EntityContext;
 use Drupal\layout_builder\LayoutTempstoreRepositoryInterface;
 use Drupal\layout_builder\Plugin\SectionStorage\OverridesSectionStorage;
 use Drupal\layout_builder\SectionStorageInterface;
@@ -118,6 +119,7 @@ public function save(array $form, FormStateInterface $form_state) {
 
     $this->layoutTempstoreRepository->delete($this->sectionStorage);
     $this->messenger()->addStatus($this->t('The layout override has been saved.'));
+    $this->sectionStorage->setContext('entity', EntityContext::fromEntity($this->entity));
     $form_state->setRedirectUrl($this->sectionStorage->getRedirectUrl());
     return $return;
   }

or

diff --git a/core/modules/layout_builder/src/Plugin/SectionStorage/OverridesSectionStorage.php b/core/modules/layout_builder/src/Plugin/SectionStorage/OverridesSectionStorage.php
index 4678c375d4..019e96ef4b 100644
--- a/core/modules/layout_builder/src/Plugin/SectionStorage/OverridesSectionStorage.php
+++ b/core/modules/layout_builder/src/Plugin/SectionStorage/OverridesSectionStorage.php
@@ -315,7 +315,7 @@ public function getDefaultSectionStorage() {
    * {@inheritdoc}
    */
   public function getRedirectUrl() {
-    $entity = $this->getEntity();
+    $entity = $this->entityRepository->getActive($this->getEntity()->getEntityTypeId(), $this->getEntity()->id());
     $rel = $entity instanceof RevisionableInterface && !$entity->isDefaultRevision() ? 'latest-version' : 'canonical';
     return $entity->toUrl($rel);
   }

However, the issue remains that the latest-revision route is provided by content_moderation.

How about a new hook instead? Adding a -1001 weight creates a form like:

If we feel like the hook is the right approach to integrate the latest-version route, we don't need either of those. What do you think of using that approach?

Latest approach based on slack discussion.

Thanks for the review.

1. This is a new hook that layout builder is firing, built with this use case in mind. I think it makes more sense for this hook to live in CM, then for another module to implement it and do a check for CM being installed. I'm thinking of this as content moderation is integrating with LB, not the other way around.
2. Good point, I think #2935939: Content Moderation hardcodes the 'edit' and 'default' form modes — other form modes are not supported is a good launching point for that.
3. Never seen this, but makes perfect sense to me.
4. Good catch.