Prior to v1.18.0 I used the following vode to reach the struct definition in a module from __before_compile__/2 callback.

    defp fields(module) do
      module
      |> Module.get_attribute(:__struct__, %{})
      |> Map.delete(:__struct__)
      |> Map.keys()
    end

I know that’s the undocumented, internal feature, but I did not manage to find a better way of doing this. In v1.18.0 this :__struct__ module attribute has gone. By digging down the rabbit hole, I managed to do the following:

    defp fields(module) do
      with {set, _bag} <- module |> :elixir_module.data_tables(),
           true <- :ets.member(set, {:elixir, :struct}),
           [{{:elixir, :struct}, [_ | _] = fields}] <- :ets.lookup(set, {:elixir, :struct}) do
        for %{field: field} <- fields, do: field
      end
    end

While it works, it looks extremely hacky and might break again tomorrow. Is there the correct way of doing that that I am missing?