Deduplicate source references when merging extracted messages (#441)

* Deduplicate source references when merging extracted messages

Two extraction calls that resolve to the same msgid at the same file:line
each contribute a reference group, and merge_messages_after_checks/2
concatenates them without uniquing. Macro-generated code produces N calls
attributed to a single line, so the same  comment is written N times.

 on the very next line is already uniqued; this makes
 consistent with it.

* Update test/gettext/extractor_test.exs

Co-authored-by: Jonatan Männchen <jonatan@maennchen.ch>

---------

Co-authored-by: Jonatan Männchen <jonatan@maennchen.ch>

Author: rigzad

lib/gettext/extractor_agent.ex

@@ -102,7 +102,7 @@ defmodule Gettext.ExtractorAgent do
 
   defp merge_messages_after_checks(message_1, message_2) do
     message_1
-    |> Map.put(:references, message_1.references ++ message_2.references)
+    |> Map.put(:references, Enum.uniq(message_1.references ++ message_2.references))
     |> Map.put(
       :extracted_comments,
       Enum.uniq(message_1.extracted_comments ++ message_2.extracted_comments)

test/gettext/extractor_test.exs

@@ -476,6 +476,41 @@ defmodule Gettext.ExtractorTest do
     Extractor.disable()
   end
 
+  test "duplicate references for one message are recorded once" do
+    Extractor.enable()
+
+    code = """
+    defmodule Gettext.ExtractorTest.SameLineGettext do
+      use Gettext.Backend, otp_app: :test_application
+    end
+
+    defmodule SameLine do
+      require Gettext.Macros
+
+      def bar do
+        [Gettext.Macros.gettext_with_backend(Gettext.ExtractorTest.SameLineGettext, "foo"), Gettext.Macros.gettext_with_backend(Gettext.ExtractorTest.SameLineGettext, "foo")]
+      end
+    end
+    """
+
+    Code.compile_string(code, Path.join(File.cwd!(), "same_line.ex"))
+
+    [{_path, {:changed, contents}}] =
+      :test_application
+      |> Extractor.pot_files([])
+      |> Enum.reject(&match?({_path, :unchanged}, &1))
+
+    references =
+      contents
+      |> IO.iodata_to_binary()
+      |> String.split("\n")
+      |> Enum.filter(&String.starts_with?(&1, "#: same_line.ex"))
+
+    assert references == ["#: same_line.ex:9"]
+  after
+    Extractor.disable()
+  end
+
   defp write_file(path, contents) do
     path |> Path.dirname() |> File.mkdir_p!()
     File.write!(path, contents)