EntityRevision should calls parent::getIds();

+++ b/core/modules/migrate/src/Plugin/migrate/destination/EntityRevision.php
@@ -72,6 +72,8 @@ protected function save(ContentEntityInterface $entity, array $old_destination_i
+    $ids = parent::getIds();

I think core revision support here intentionally intends to only track revisions, not a composite of revision and entity id. However, while reviewing this, I did note that we are not supporting revisions that are multi-lingual. Is that an issue that should be addressed?

We don't cover multi-lingual, because we aren't calling parent (rightfully so). But we do probably want to track the langcode on revisions, if the revision is multi-lingual. I've addressed that in #2809793-12: EntityReference migrate destination, but ideally CEB would have the multi-lingual code broken out into a protected function so I can just call it from ERR, rather than copy/pasting it.

revisions in D8 don't store a composite. Only the vid. This destination plugin was built for migrating in those values into core. If it returns a composite, it will break migrations of revisions from D6/D7. However, revisions do support mult-lingual. So we should suck in that data (me thinks).

Patch doesn't apply.

The old patch wasn't what we wanted so I didn't bother re-rolling it.

On reviewing this it looks like it is a won't fix based on the comments in #5

Changing to NR to allow for replies.

This needs an IS update at the very least. We might need to track the langcode for revisions. Which is my last point in #5. Of course, that has BC implications.

Since I'm doing a lot of multilingual.....

The proposed resolution points out that the langcode was added in #2921661: Add support to migrate multilingual revisions.

EntityRevision::getIds()

    if ($this->isTranslationDestination()) {
      $langcode_key = $this->getKey('langcode');
      if (!$langcode_key) {
        throw new MigrateException(sprintf('The "%s" entity type does not support translations.', $this->storage->getEntityTypeId()));
      }
      $ids[$langcode_key] = $this->getDefinitionFromEntity($langcode_key);

Sounds good.