Always return nil for undefined options (#2308)

Author: José Valim

lib/elixir/lib/option_parser.ex

@@ -152,9 +152,9 @@ defmodule OptionParser do
         # the option exist but it has wrong value
         do_parse(rest, config, opts, args, [{option, value}|invalid])
 
-      {:undefined, option, value, rest} ->
+      {:undefined, option, _value, rest} ->
         # the option does not exist (for strict cases)
-        do_parse(rest, config, opts, args, [{option, value}|invalid])
+        do_parse(rest, config, opts, args, [{option, nil}|invalid])
 
       {:error, ["--"|rest]} ->
         {Enum.reverse(opts), Enum.reverse(args, rest), Enum.reverse(invalid)}

lib/elixir/test/elixir/option_parser_test.exs

@@ -198,7 +198,7 @@ defmodule OptionParserTest do
 
     assert OptionParser.parse(["--source", "from_docs/", "--doc=show"],
                               strict: [source: :string, docs: :string])
-           == {[source: "from_docs/"], [], [doc: "show"]}
+           == {[source: "from_docs/"], [], [doc: nil]}
   end
 
   test "parses - as argument" do