ActivityDraft: mention the OP of a quoted post

lib/pleroma/web/common_api/activity_draft.ex

@@ -137,11 +137,11 @@ defmodule Pleroma.Web.CommonAPI.ActivityDraft do
   defp quote_post(%{params: %{quote_id: ""}} = draft), do: draft
 
   defp quote_post(%{params: %{quote_id: id}} = draft) when is_binary(id) do
-    %__MODULE__{draft | quote_post: Activity.get_by_id(id)}
-  end
-
-  defp quote_post(%{params: %{quote_id: %Activity{} = quote_post}} = draft) do
-    %__MODULE__{draft | quote_post: quote_post}
+    with %Activity{actor: actor_ap_id} = activity <- Activity.get_by_id(id) do
+      %__MODULE__{draft | quote_post: activity, mentions: [actor_ap_id]}
+    else
+      _ -> draft
+    end
   end
 
   defp quote_post(draft), do: draft
@@ -178,12 +178,15 @@ defmodule Pleroma.Web.CommonAPI.ActivityDraft do
     end
   end
 
-  defp content(draft) do
+  defp content(%{mentions: mentions} = draft) do
     {content_html, mentioned_users, tags} = Utils.make_content_html(draft)
 
+    mentioned_ap_ids =
+      Enum.map(mentioned_users, fn {_, mentioned_user} -> mentioned_user.ap_id end)
+
     mentions =
-      mentioned_users
-      |> Enum.map(fn {_, mentioned_user} -> mentioned_user.ap_id end)
+      mentions
+      |> Kernel.++(mentioned_ap_ids)
       |> Utils.get_addressed_users(draft.params[:to])
 
     %__MODULE__{draft | content_html: content_html, mentions: mentions, tags: tags}

test/pleroma/web/common_api_test.exs

@@ -807,6 +807,18 @@ defmodule Pleroma.Web.CommonAPITest do
       quote_post = Object.normalize(quote_post)
 
       assert quote_post.data["quoteUrl"] == quoted.data["id"]
+
+      # The OP is mentioned
+      assert quoted.data["actor"] in quote_post.data["to"]
+    end
+
+    test "quote posting with explicit addressing doesn't mention the OP" do
+      user = insert(:user)
+
+      {:ok, quoted} = CommonAPI.post(user, %{status: "Hello world"})
+      {:ok, quote_post} = CommonAPI.post(user, %{status: "nice post", quote_id: quoted.id, to: []})
+
+      assert Object.normalize(quote_post).data["to"] == [Pleroma.Constants.as_public()]
     end
   end