Copy emoji in the subject from parent post

Sometimes people put emoji in the subject, which results in the subject
looking broken if someone replies to it from a server that does not
have the said emoji under the same shortcode. This patch solves the problem
by extending the emoji set available in the summary to that of the parent
post.

lib/pleroma/web/common_api/activity_draft.ex

@@ -5,6 +5,7 @@
 defmodule Pleroma.Web.CommonAPI.ActivityDraft do
   alias Pleroma.Activity
   alias Pleroma.Conversation.Participation
+  alias Pleroma.Object
   alias Pleroma.Web.CommonAPI
   alias Pleroma.Web.CommonAPI.Utils
 
@@ -186,6 +187,32 @@ defp sensitive(draft) do
   defp object(draft) do
     emoji = Map.merge(Pleroma.Emoji.Formatter.get_emoji_map(draft.full_payload), draft.emoji)
 
+    # Sometimes people create posts with subject containing emoji,
+    # since subjects are usually copied this will result in a broken
+    # subject when someone replies from an instance that does not have
+    # the emoji or has it under different shortcode. This is an attempt
+    # to mitigate this by copying emoji from inReplyTo if they are present
+    # in the subject.
+    summary_emoji =
+      with %Activity{} <- draft.in_reply_to,
+           %Object{data: %{"tag" => [_ | _] = tag}} <- Object.normalize(draft.in_reply_to) do
+        Enum.reduce(tag, %{}, fn
+          %{"type" => "Emoji", "name" => name, "icon" => %{"url" => url}}, acc ->
+            if String.contains?(draft.summary, name) do
+              Map.put(acc, name, url)
+            else
+              acc
+            end
+
+          _, acc ->
+            acc
+        end)
+      else
+        _ -> %{}
+      end
+
+    emoji = Map.merge(emoji, summary_emoji)
+
     object =
       Utils.make_note_data(draft)
       |> Map.put("emoji", emoji)

test/fixtures/tesla_mock/emoji-in-summary.json

@@ -0,0 +1,49 @@
+{
+  "@context": [
+    "https://www.w3.org/ns/activitystreams",
+    "https://patch.cx/schemas/litepub-0.1.jsonld",
+    {
+      "@language": "und"
+    }
+  ],
+  "actor": "https://patch.cx/users/rin",
+  "attachment": [],
+  "attributedTo": "https://patch.cx/users/rin",
+  "cc": [
+    "https://patch.cx/users/rin/followers"
+  ],
+  "content": ":joker_disapprove: <br><br>just grabbing a test fixture, nevermind me",
+  "context": "https://patch.cx/contexts/2c3ce4b4-18b1-4b1a-8965-3932027b5326",
+  "conversation": "https://patch.cx/contexts/2c3ce4b4-18b1-4b1a-8965-3932027b5326",
+  "id": "https://patch.cx/objects/a399c28e-c821-4820-bc3e-4afeb044c16f",
+  "published": "2021-03-22T16:54:46.461939Z",
+  "sensitive": null,
+  "source": ":joker_disapprove: \r\n\r\njust grabbing a test fixture, nevermind me",
+  "summary": ":joker_smile: ",
+  "tag": [
+    {
+      "icon": {
+        "type": "Image",
+        "url": "https://patch.cx/emoji/custom/joker_disapprove.png"
+      },
+      "id": "https://patch.cx/emoji/custom/joker_disapprove.png",
+      "name": ":joker_disapprove:",
+      "type": "Emoji",
+      "updated": "1970-01-01T00:00:00Z"
+    },
+    {
+      "icon": {
+        "type": "Image",
+        "url": "https://patch.cx/emoji/custom/joker_smile.png"
+      },
+      "id": "https://patch.cx/emoji/custom/joker_smile.png",
+      "name": ":joker_smile:",
+      "type": "Emoji",
+      "updated": "1970-01-01T00:00:00Z"
+    }
+  ],
+  "to": [
+    "https://www.w3.org/ns/activitystreams#Public"
+  ],
+  "type": "Note"
+}

test/pleroma/web/common_api_test.exs

@@ -25,6 +25,11 @@ defmodule Pleroma.Web.CommonAPITest do
 
   require Pleroma.Constants
 
+  setup_all do
+    Tesla.Mock.mock_global(fn env -> apply(HttpRequestMock, :request, [env]) end)
+    :ok
+  end
+
   setup do: clear_config([:instance, :safe_dm_mentions])
   setup do: clear_config([:instance, :limit])
   setup do: clear_config([:instance, :max_pinned_statuses])
@@ -517,6 +522,27 @@ test "it adds an emoji on an external site" do
       assert url == "#{Pleroma.Web.base_url()}/emoji/blank.png"
     end
 
+    test "it copies emoji from the subject of the parent post" do
+      %Object{} =
+        object =
+        Object.normalize("https://patch.cx/objects/a399c28e-c821-4820-bc3e-4afeb044c16f",
+          fetch: true
+        )
+
+      activity = Activity.get_create_by_object_ap_id(object.data["id"])
+      user = insert(:user)
+
+      {:ok, reply_activity} =
+        CommonAPI.post(user, %{
+          in_reply_to_id: activity.id,
+          status: ":joker_disapprove:",
+          spoiler_text: ":joker_smile:"
+        })
+
+      assert Object.normalize(reply_activity).data["emoji"][":joker_smile:"]
+      refute Object.normalize(reply_activity).data["emoji"][":joker_disapprove:"]
+    end
+
     test "deactivated users can't post" do
       user = insert(:user, is_active: false)
       assert {:error, _} = CommonAPI.post(user, %{status: "ye"})

test/support/http_request_mock.ex

@@ -1278,6 +1278,15 @@ def get("https://osada.macgirvin.com/", _, "", [{"accept", "text/html"}]) do
      }}
   end
 
+  def get("https://patch.cx/objects/a399c28e-c821-4820-bc3e-4afeb044c16f", _, _, _) do
+    {:ok,
+     %Tesla.Env{
+       status: 200,
+       body: File.read!("test/fixtures/tesla_mock/emoji-in-summary.json"),
+       headers: activitypub_object_headers()
+     }}
+  end
+
   def get(url, query, body, headers) do
     {:error,
      "Mock response not implemented for GET #{inspect(url)}, #{query}, #{inspect(body)}, #{