Create tombstone instead of object deletion

lib/pleroma/activity.ex

@@ -1,7 +1,7 @@
 defmodule Pleroma.Activity do
   use Ecto.Schema
   alias Pleroma.{Repo, Activity, Notification}
-  import Ecto.Query
+  import Ecto.{Query, Changeset}
 
   # https://github.com/tootsuite/mastodon/blob/master/app/models/notification.rb#L19
   @mastodon_notification_types %{
@@ -103,4 +103,22 @@ defmodule Pleroma.Activity do
   end
 
   def mastodon_notification_type(%Activity{}), do: nil
+
+  def get_tombstone(%Activity{data: data}, deleted \\ DateTime.utc_now()) do
+    %{
+      id: data["id"],
+      context: data["context"],
+      type: "tombstone",
+      published: data["published"],
+      deleted: deleted
+    }
+  end
+
+  def swap_data_with_tombstone(activity) do
+    tombstone = get_tombstone(activity)
+
+    activity
+    |> change(%{data: tombstone})
+    |> Repo.update()
+  end
 end

lib/pleroma/object.ex

@@ -62,9 +62,27 @@ defmodule Pleroma.Object do
     Object.change(%Object{}, %{data: %{"id" => context}})
   end
 
+  def get_tombstone(%Object{data: data}, deleted \\ DateTime.utc_now()) do
+    %{
+      id: data["id"],
+      type: "tombstone",
+      deleted: deleted
+    }
+  end
+
+  def swap_data_with_tombstone(object) do
+    tombstone = get_tombstone(object)
+
+    object
+    |> Object.change(%{data: tombstone})
+    |> Repo.update()
+  end
+
   def delete(%Object{data: %{"id" => id}} = object) do
-    with Repo.delete(object),
-         Repo.delete_all(Activity.all_non_create_by_object_ap_id_q(id)),
+    with swap_data_with_tombstone(object),
+         Activity.all_non_create_by_object_ap_id_q(id)
+         |> Repo.all()
+         |> Enum.each(&Activity.swap_data_with_tombstone/1),
          {:ok, true} <- Cachex.del(:object_cache, "object:#{id}") do
       {:ok, object}
     end

lib/pleroma/web/common_api/utils.ex

@@ -69,7 +69,12 @@ defmodule Pleroma.Web.CommonAPI.Utils do
     mentioned_users = Enum.map(mentions, fn {_, %{ap_id: ap_id}} -> ap_id end)
 
     if inReplyTo do
-      {Enum.uniq([inReplyTo.data["actor"] | mentioned_users]), []}
+      to =
+        [inReplyTo.data["actor"] | mentioned_users]
+        |> Enum.uniq()
+        |> Enum.reject(&is_nil/1)
+
+      {to, []}
     else
       {mentioned_users, []}
     end