\Drupal\comment\CommentForm::save does not return a value

According to EntityFormInterface this method should return integer value indicating the result of the operation.

Unlike 🐛 function Drupal\Node\NodeForm::save() does not return a value Needs work this issue is a bit more complicated because in some conditions \Drupal\comment\CommentForm::save may not perform any operations. So that it's not clear what it should return.
Basically we have two options here.
1. Introduce new "SAVED" constant. Something like SAVED_SKIPPED
2. Refactor CommentForm to not check permissions in submit handler.