fix(activitypub): accept emoji reactions with a single tag object

Ported from Akkoma 462225880.

Co-authored-by: Oneric <oneric@oneric.stub>

changelog.d/emoji-react-single-tag.fix

@@ -0,0 +1 @@
+Accept incoming emoji reactions whose tag is a single object instead of an array

lib/pleroma/web/activity_pub/object_validators/emoji_react_validator.ex

@@ -57,7 +57,7 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidators.EmojiReactValidator do
       |> CommonFixes.fix_actor()
       |> CommonFixes.fix_activity_addressing()
 
-    data = Map.put_new(data, "tag", [])
+    data = fix_tag(data)
 
     case Object.normalize(data["object"]) do
       %Object{} = object ->
@@ -70,6 +70,10 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidators.EmojiReactValidator do
     end
   end
 
+  # JSON-LD compaction turns a single-element array into a bare object
+  defp fix_tag(%{"tag" => %{} = tag} = data), do: Map.put(data, "tag", [tag])
+  defp fix_tag(data), do: Map.put_new(data, "tag", [])
+
   defp fix_emoji_qualification(%{"content" => emoji} = data) do
     new_emoji = Pleroma.Emoji.fully_qualify_emoji(emoji)
 

test/pleroma/web/activity_pub/transmogrifier/emoji_react_handling_test.exs

@@ -86,6 +86,31 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier.EmojiReactHandlingTest do
            )
   end
 
+  test "it works for incoming custom emoji reactions with a single tag object" do
+    user = insert(:user)
+    other_user = insert(:user, local: false)
+    {:ok, activity} = CommonAPI.post(user, %{status: "hello"})
+
+    data =
+      File.read!("test/fixtures/custom-emoji-reaction.json")
+      |> Jason.decode!()
+      |> Map.put("object", activity.data["object"])
+      |> Map.put("actor", other_user.ap_id)
+
+    [tag] = data["tag"]
+    data = Map.put(data, "tag", tag)
+
+    {:ok, %Activity{data: data, local: false}} = Transmogrifier.handle_incoming(data)
+
+    assert data["content"] == ":hanapog:"
+    assert [%{"name" => "hanapog"}] = data["tag"]
+
+    object = Object.get_by_ap_id(data["object"])
+    url = tag["icon"]["url"]
+
+    assert match?([["hanapog", _, ^url]], object.data["reactions"])
+  end
+
   test "it works for incoming unqualified emoji reactions" do
     user = insert(:user)
     other_user = insert(:user, local: false)