Add _:inReplyToAtomUri to ActivityPub (#4702)

app/serializers/activitypub/activity_serializer.rb

@@ -10,7 +10,7 @@ class ActivityPub::ActivitySerializer < ActiveModel::Serializer
   end
 
   def type
-    object.reblog? ? 'Announce' : 'Create'
+    announce? ? 'Announce' : 'Create'
   end
 
   def actor
@@ -24,4 +24,8 @@ class ActivityPub::ActivitySerializer < ActiveModel::Serializer
   def cc
     ActivityPub::TagManager.instance.cc(object)
   end
+
+  def announce?
+    object.reblog?
+  end
 end

app/serializers/activitypub/note_serializer.rb

@@ -9,6 +9,7 @@ class ActivityPub::NoteSerializer < ActiveModel::Serializer
   has_many :virtual_tags, key: :tag
 
   attribute :atom_uri, key: '_:atomUri', if: :local?
+  attribute :in_reply_to_atom_uri, key: '_:inReplyToAtomUri'
 
   def id
     ActivityPub::TagManager.instance.uri_for(object)
@@ -64,6 +65,12 @@ class ActivityPub::NoteSerializer < ActiveModel::Serializer
     ::TagManager.instance.uri_for(object)
   end
 
+  def in_reply_to_atom_uri
+    return unless object.reply?
+
+    ::TagManager.instance.uri_for(object.thread)
+  end
+
   def local?
     object.account.local?
   end