Validate translated conditions in compile time

The macro `Trans.QueryBuilder.translated/3` now validates the translated
fields before the macro expansion step. We will receive an error in
compilation time when adding conditions on untranslatable fields.

lib/trans/query_builder.ex

@@ -1,8 +1,13 @@
 if Code.ensure_loaded?(Ecto.Query) do
   defmodule Trans.QueryBuilder do
 
-    defmacro translated(translatable, opts) do
-      generate_query(schema(translatable), field(translatable), locale(opts))
+    defmacro translated(module, translatable, opts) do
+      with field <- field(translatable) do
+        Module.eval_quoted __CALLER__, [
+          __validate_fields__(module, field)
+        ]
+        generate_query(schema(translatable), field, locale(opts))
+      end
     end
 
     defp generate_query(schema, nil, locale) do
@@ -21,7 +26,7 @@ if Code.ensure_loaded?(Ecto.Query) do
       case Keyword.fetch(opts, :locale) do
         {:ok, locale} when is_atom(locale)   -> to_string(locale)
         {:ok, locale} when is_binary(locale) -> locale
-        _ -> error_unspecified_locale()
+        _ -> raise ArgumentError, mesage: "You must specify a locale for the query. For example `translated(x.field, locale: :en)`."
       end
     end
 
@@ -31,8 +36,18 @@ if Code.ensure_loaded?(Ecto.Query) do
     defp field({{:., _, [_schema, field]}, _metadata, _args}), do: to_string(field)
     defp field(_), do: nil
 
-    defp error_unspecified_locale do
-      raise ArgumentError, mesage: "You must specify a locale for the query. For example `translated(x.field, locale: :en)`."
+    @doc false
+    def __validate_fields__(module, field) do
+      quote do
+        with field <- unquote(field) do
+          cond do
+            is_nil(field) -> nil
+            not Trans.translatable?(unquote(module), unquote(field)) ->
+              raise ArgumentError, message: "'#{inspect(unquote(module))}' module must declare '#{inspect(unquote(field))}' as translatable"
+            true -> nil
+          end
+        end
+      end
     end
 
   end

test/query_builder_test.exs

@@ -17,31 +17,31 @@ defmodule QueryBuilderTest do
 
   test "should find only one article translated to ES" do
     count = Repo.one(from a in Article,
-      where: not is_nil(translated(a, locale: :es)),
+      where: not is_nil(translated(Article, a, locale: :es)),
       select: count(a.id)
     )
     assert count == 1
   end
 
   test "should not find any article translated to DE" do
     count = Repo.one(from a in Article,
-      where: not is_nil(translated(a, locale: :de)),
+      where: not is_nil(translated(Article, a, locale: :de)),
       select: count(a.id))
     assert count == 0
   end
 
   test "should find an article by its FR title",
   %{translated_article: article} do
     matches = Repo.all(from a in Article,
-      where: translated(a.title, locale: :fr) == ^article.translations["fr"]["title"])
+      where: translated(Article, a.title, locale: :fr) == ^article.translations["fr"]["title"])
     assert Enum.count(matches) == 1
     assert hd(matches).id == article.id
   end
 
   test "should not find an article by a non existant translation" do
     count = Repo.one(from a in Article,
       select: count(a.id),
-      where: translated(a.title, locale: :es) == "FAKE TITLE")
+      where: translated(Article, a.title, locale: :es) == "FAKE TITLE")
     assert count == 0
   end
 
@@ -54,7 +54,7 @@ defmodule QueryBuilderTest do
       |> Enum.join(" ")
       |> Kernel.<>("%")
     matches = Repo.all(from a in Article,
-      where: ilike(translated(a.body, locale: :es), ^first_words))
+      where: ilike(translated(Article, a.body, locale: :es), ^first_words))
     assert Enum.count(matches) == 1
     assert hd(matches).id == article.id
   end
@@ -70,7 +70,7 @@ defmodule QueryBuilderTest do
       |> Kernel.<>("%")
     count = Repo.one(from a in Article,
       select: count(a.id),
-      where: like(translated(a.body, locale: :fr), ^first_words))
+      where: like(translated(Article, a.body, locale: :fr), ^first_words))
     assert count == 0
   end
 
@@ -84,8 +84,21 @@ defmodule QueryBuilderTest do
       |> String.upcase
       |> Kernel.<>("%")
     matches = Repo.all(from a in Article,
-      where: ilike(translated(a.body, locale: :fr), ^first_words))
+      where: ilike(translated(Article, a.body, locale: :fr), ^first_words))
     assert Enum.count(matches) == 1
     assert hd(matches).id == article.id
   end
+
+  test "should raise when adding conditions to an untranslatable field" do
+    # Since the QueryBuilder errors are emitted during compilation, we do a
+    # little trick to delay the compilation of the query until the test
+    # is running, so we can catch the raised error.
+    query = quote do
+      Repo.all(from a in Article,
+        where: not is_nil(translated(Article, a.translations, locale: :es)))
+    end
+    assert_raise ArgumentError, fn ->
+      Module.eval_quoted __ENV__, query
+    end
+  end
 end