Get rid of useless fourth argument in defexception

Author: José Valim

lib/elixir/lib/kernel.ex

@@ -1515,9 +1515,14 @@ defmodule Kernel do
      string;
 
   """
-  defmacro defexception(name, fields, opts // [], do_block // []) do
-    opts = Keyword.merge(opts, do_block)
-    opts = Keyword.put(opts, :do, quote do
+  defmacro defexception(name, fields, do_block // []) do
+    { fields, do_block } =
+      case is_list(fields) and Keyword.get(fields, :do, false) do
+        false -> { fields, do_block }
+        other -> { Keyword.delete(fields, :do), [do: other] }
+      end
+
+    do_block = Keyword.put(do_block, :do, quote do
       @moduledoc nil
       record_type message: binary
 
@@ -1527,11 +1532,11 @@ defmodule Kernel do
       @doc false
       def exception(args, self), do: update(args, self)
 
-      unquote(Keyword.get opts, :do)
+      unquote(Keyword.get do_block, :do)
     end)
 
     fields = quote do: [__exception__: :__exception__] ++ unquote(fields)
-    record = Record.defrecord(name, fields, opts)
+    record = Record.defrecord(name, fields, do_block)
 
     quote do
       { :module, name, _, _ } = unquote(record)

lib/elixir/test/elixir/exception_test.exs

@@ -102,6 +102,13 @@ defmodule Kernel.ExceptionTest do
            [file: ^file, line: 95]} = stacktrace # line is sensitive
   end
 
+  test :defexception do
+    defexception SampleError, field: :ok do
+      # Check do block is properly inline
+      def message(_), do: "hello"
+    end
+  end
+
   defp empty_tuple, do: {}
   defp a_tuple, do: { :foo, :bar, :baz }
   defp a_list,  do: [ :foo, :bar, :baz ]