Delete a discussion when its last post is deleted. fixes #823

framework/core/src/Core/Listener/DiscussionMetadataUpdater.php

@@ -51,6 +51,12 @@ class DiscussionMetadataUpdater
     public function whenPostWasDeleted(PostWasDeleted $event)
     {
         $this->removePost($event->post);
+
+        $discussion = $event->post->discussion;
+
+        if ($discussion->comments_count === 0) {
+            $discussion->delete();
+        }
     }
 
     /**

framework/core/src/Core/Post.php

@@ -88,14 +88,6 @@ class Post extends AbstractModel
             $post->discussion->save();
         });
 
-        // Don't allow the first post in a discussion to be deleted, because
-        // it doesn't make sense. The discussion must be deleted instead.
-        static::deleting(function (Post $post) {
-            if ($post->number == 1) {
-                throw new DomainException('Cannot delete the first post of a discussion');
-            }
-        });
-
         static::deleted(function (Post $post) {
             $post->raise(new PostWasDeleted($post));
         });