Make move_account endpoint process non-existent users properly

Ref: emit-move

lib/pleroma/web/api_spec/operations/twitter_util_operation.ex

@@ -228,7 +228,8 @@ def move_account_operation do
             properties: %{status: %Schema{type: :string, example: "success"}}
           }),
         400 => Operation.response("Error", "application/json", ApiError),
-        403 => Operation.response("Error", "application/json", ApiError)
+        403 => Operation.response("Error", "application/json", ApiError),
+        404 => Operation.response("Error", "application/json", ApiError)
       }
     }
   end

lib/pleroma/web/twitter_api/controllers/util_controller.ex

@@ -173,12 +173,14 @@ def disable_account(%{assigns: %{user: user}} = conn, params) do
   def move_account(%{assigns: %{user: user}, body_params: body_params} = conn, %{}) do
     case CommonAPI.Utils.confirm_current_password(user, body_params.password) do
       {:ok, user} ->
-        with {:ok, target_user} <- find_user_by_nickname(body_params.target_account),
+        with {:ok, target_user} <- find_or_fetch_user_by_nickname(body_params.target_account),
              {:ok, _user} <- ActivityPub.move(user, target_user) do
           json(conn, %{status: "success"})
         else
-          {:not_found} ->
-            json(conn, %{error: "Target account not found."})
+          {:not_found, _} ->
+            conn
+            |> put_status(404)
+            |> json(%{error: "Target account not found."})
 
           {:error, error} ->
             json(conn, %{error: error})
@@ -233,6 +235,21 @@ defp find_user_by_nickname(nickname) do
     end
   end
 
+  defp find_or_fetch_user_by_nickname(nickname) do
+    user = User.get_by_nickname(nickname)
+
+    if user != nil and user.local do
+      {:ok, user}
+    else
+      with {:ok, user} <- User.fetch_by_nickname(nickname) do
+        {:ok, user}
+      else
+        _ ->
+          {:not_found, nil}
+      end
+    end
+  end
+
   def captcha(conn, _params) do
     json(conn, Pleroma.Captcha.new())
   end

test/pleroma/web/twitter_api/util_controller_test.exs

@@ -573,6 +573,25 @@ test "with proper permissions, valid password and target account does not alias
              }
     end
 
+    test "with proper permissions, valid password and target account does not exist",
+         %{
+           conn: conn
+         } do
+      target_nick = "not_found@mastodon.social"
+
+      conn =
+        conn
+        |> put_req_header("content-type", "multipart/form-data")
+        |> post("/api/pleroma/move_account", %{
+          "password" => "test",
+          "target_account" => target_nick
+        })
+
+      assert json_response_and_validate_schema(conn, 404) == %{
+               "error" => "Target account not found."
+             }
+    end
+
     test "with proper permissions, valid password and target account aliases this", %{
       conn: conn,
       user: user

test/support/http_request_mock.ex

@@ -725,6 +725,15 @@ def get(
      }}
   end
 
+  def get(
+        "https://mastodon.social/.well-known/webfinger?resource=acct:not_found@mastodon.social",
+        _,
+        _,
+        [{"accept", "application/xrd+xml,application/jrd+json"}]
+      ) do
+    {:ok, %Tesla.Env{status: 404}}
+  end
+
   def get("http://gs.example.org/.well-known/host-meta", _, _, _) do
     {:ok,
      %Tesla.Env{