Use Trans.translatable?/2 from Translator module

lib/trans/translator.ex

@@ -63,31 +63,21 @@ defmodule Trans.Translator do
   @spec translate(struct, atom, atom) :: any
   def translate(%{__struct__: module} = struct, locale, field)
   when is_atom(locale) and is_atom(field) do
-    translatable_fields = get_translatable_fields(module)
-    raise_if_untranslatable(translatable_fields, field)
-
-    translated_field = with {:ok, all_translations} <- Map.fetch(struct, :translations),
-                            {:ok, translations_for_locale} <- Map.fetch(all_translations, to_string(locale)),
-                            {:ok, translated_field} <- Map.fetch(translations_for_locale, to_string(field)),
-      do: translated_field
-    case translated_field do
-      :error -> Map.fetch!(struct, field) # Fallback to the default value
-      _ -> translated_field # Return the translated value
+    unless Trans.translatable?(struct, field) do
+      raise "'#{inspect(module)}' module must declare '#{inspect(field)}' as translatable"
     end
-  end
-
-  defp get_translatable_fields(module) do
-    if module.__info__(:functions)[:__trans__] do
-      module.__trans__(:fields)
-    else
-      raise "#{module} must use `Trans` in order to be translated"
+    # Return the translation or fall back to the default value
+    case translated_field(struct, locale, field) do
+      :error -> Map.fetch!(struct, field)
+      translation -> translation
     end
   end
 
-  defp raise_if_untranslatable(fields, field) do
-    unless Enum.member?(fields, field) do
-      raise "'#{field}' is not translatable. Translatable fields are #{inspect(fields)}"
-    end
+  defp translated_field(struct, locale, field) do
+    with {:ok, all_translations}        <- Map.fetch(struct, :translations),
+         {:ok, translations_for_locale} <- Map.fetch(all_translations, to_string(locale)),
+         {:ok, translated_field}        <- Map.fetch(translations_for_locale, to_string(field)),
+      do: translated_field
   end
 
 end

test/translator_test.exs

@@ -19,8 +19,7 @@ defmodule TranslatorTest do
   end
 
   test "raise error wen translating an untraslatable attribute" do
-    expected_message = "'fake_attr' is not translatable. Translatable fields are [:title, :body]"
-    assert_raise RuntimeError, expected_message, fn ->
+    assert_raise RuntimeError, "'Trans.Article' module must declare ':fake_attr' as translatable", fn ->
       Translator.translate(build(:article), :es, :fake_attr)
     end
   end