Ensure self-announces do not widen the audience of the original post

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -346,7 +346,7 @@ def announce(
         local \\ true,
         public \\ true
       ) do
-    with true <- is_announceable?(object, user),
+    with true <- is_announceable?(object, user, public),
          announce_data <- make_announce_data(user, object, activity_id, public),
          {:ok, activity} <- insert(announce_data, local),
          {:ok, object} <- add_announce_to_object(activity, object),

lib/pleroma/web/activity_pub/visibility.ex

@@ -27,8 +27,9 @@ def is_private?(activity) do
     end
   end
 
-  def is_announceable?(activity, user) do
-    is_public?(activity) || activity.data["actor"] == user.ap_id
+  def is_announceable?(activity, user, public \\ true) do
+    is_public?(activity) ||
+      (!public && is_private?(activity) && activity.data["actor"] == user.ap_id)
   end
 
   def is_direct?(%Activity{data: %{"directMessage" => true}}), do: true