Broadcast deleted activity id on deletion to conform to MastoAPI streamig spec

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -311,14 +311,14 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
     user = User.get_cached_by_ap_id(actor)
     to = object.data["to"] || [] ++ object.data["cc"] || []
 
-    data = %{
-      "type" => "Delete",
-      "actor" => actor,
-      "object" => id,
-      "to" => to
-    }
-
-    with {:ok, _} <- Object.delete(object),
+    with {:ok, object, activity} <- Object.delete(object),
+         data <- %{
+           "type" => "Delete",
+           "actor" => actor,
+           "object" => id,
+           "to" => to,
+           "deleted_activity_id" => activity && activity.id
+         },
          {:ok, activity} <- insert(data, local),
          # Changing note count prior to enqueuing federation task in order to avoid race conditions on updating user.info
          {:ok, _actor} <- decrease_note_count_if_public(user, object),

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -736,6 +736,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
   def prepare_outgoing(%{"type" => _type} = data) do
     data =
       data
+      |> strip_internal_fields
       |> maybe_fix_object_url
       |> Map.merge(Utils.make_json_ld_header())
 
@@ -870,7 +871,8 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
       "announcements",
       "announcement_count",
       "emoji",
-      "context_id"
+      "context_id",
+      "deleted_activity_id"
     ])
   end