Make NoPlaceholderTextPolicy history-aware

lib/pleroma/web/activity_pub/mrf/no_placeholder_text_policy.ex

@@ -6,14 +6,17 @@ defmodule Pleroma.Web.ActivityPub.MRF.NoPlaceholderTextPolicy do
   @moduledoc "Ensure no content placeholder is present (such as the dot from mastodon)"
   @behaviour Pleroma.Web.ActivityPub.MRF.Policy
 
+  @impl true
+  def history_awareness, do: :auto
+
   @impl true
   def filter(
         %{
-          "type" => "Create",
+          "type" => type,
           "object" => %{"content" => content, "attachment" => _} = _child_object
         } = object
       )
-      when content in [".", "<p>.</p>"] do
+      when type in ["Create", "Update"] and content in [".", "<p>.</p>"] do
     {:ok, put_in(object, ["object", "content"], "")}
   end
 

test/pleroma/web/activity_pub/mrf/no_placeholder_text_policy_test.exs

@@ -4,6 +4,7 @@
 
 defmodule Pleroma.Web.ActivityPub.MRF.NoPlaceholderTextPolicyTest do
   use Pleroma.DataCase, async: true
+  alias Pleroma.Web.ActivityPub.MRF
   alias Pleroma.Web.ActivityPub.MRF.NoPlaceholderTextPolicy
 
   test "it clears content object" do
@@ -20,6 +21,46 @@ defmodule Pleroma.Web.ActivityPub.MRF.NoPlaceholderTextPolicyTest do
     assert res["object"]["content"] == ""
   end
 
+  test "history-aware" do
+    message = %{
+      "type" => "Create",
+      "object" => %{
+        "content" => ".",
+        "attachment" => "image",
+        "formerRepresentations" => %{
+          "orderedItems" => [%{"content" => ".", "attachment" => "image"}]
+        }
+      }
+    }
+
+    assert {:ok, res} = MRF.filter_one(NoPlaceholderTextPolicy, message)
+
+    assert %{
+             "content" => "",
+             "formerRepresentations" => %{"orderedItems" => [%{"content" => ""}]}
+           } = res["object"]
+  end
+
+  test "works with Updates" do
+    message = %{
+      "type" => "Update",
+      "object" => %{
+        "content" => ".",
+        "attachment" => "image",
+        "formerRepresentations" => %{
+          "orderedItems" => [%{"content" => ".", "attachment" => "image"}]
+        }
+      }
+    }
+
+    assert {:ok, res} = MRF.filter_one(NoPlaceholderTextPolicy, message)
+
+    assert %{
+             "content" => "",
+             "formerRepresentations" => %{"orderedItems" => [%{"content" => ""}]}
+           } = res["object"]
+  end
+
   @messages [
     %{
       "type" => "Create",