Store private announcements in object.data["announcements"], filter them on display

lib/pleroma/web/activity_pub/utils.ex

@@ -494,7 +494,7 @@ defmodule Pleroma.Web.ActivityPub.Utils do
   @spec add_announce_to_object(Activity.t(), Object.t()) ::
           {:ok, Object.t()} | {:error, Ecto.Changeset.t()}
   def add_announce_to_object(
-        %Activity{data: %{"actor" => actor, "cc" => [Pleroma.Constants.as_public()]}},
+        %Activity{data: %{"actor" => actor}},
         object
       ) do
     announcements = take_announcements(object)

lib/pleroma/web/mastodon_api/controllers/status_controller.ex

@@ -242,7 +242,19 @@ defmodule Pleroma.Web.MastodonAPI.StatusController do
   def reblogged_by(%{assigns: %{user: user}} = conn, %{"id" => id}) do
     with %Activity{} = activity <- Activity.get_by_id_with_object(id),
          {:visible, true} <- {:visible, Visibility.visible_for_user?(activity, user)},
-         %Object{data: %{"announcements" => announces}} <- Object.normalize(activity) do
+         %Object{data: %{"announcements" => announces, "id" => ap_id}} <-
+           Object.normalize(activity) do
+      announces =
+        "Announce"
+        |> Activity.Queries.by_type()
+        |> Ecto.Query.where([a], a.actor in ^announces)
+        # this is to use the index
+        |> Activity.Queries.by_object_id(ap_id)
+        |> Repo.all()
+        |> Enum.filter(&Visibility.visible_for_user?(&1, user))
+        |> Enum.map(& &1.actor)
+        |> Enum.uniq()
+
       users =
         User
         |> Ecto.Query.where([u], u.ap_id in ^announces)