marshal.c: Support dump and load of a Hash with the ruby2_keywords flag

It is useful for a program that dumps and load arguments (like drb).
In future, they should deal with both positional arguments and keyword
ones explicitly, but until ruby2_keywords is deprecated, it is good to
support the flag in marshal.

The implementation is similar to String's encoding; it is dumped as a
hidden instance variable.

[Feature #16501]

1 files changed, 14 insertions, 0 deletions

diff --git a/test/ruby/test_marshal.rb b/test/ruby/test_marshal.rb
index 74ea75ee42..dbeee825da 100644
--- a/test/ruby/test_marshal.rb
+++ b/test/ruby/test_marshal.rb
@@ -754,4 +754,18 @@ class TestMarshal < Test::Unit::TestCase
       Marshal.dump(obj)
     end
   end
+
+  ruby2_keywords def ruby2_keywords_hash(*a)
+    a.last
+  end
+
+  def ruby2_keywords_test(key: 1)
+    key
+  end
+
+  def test_marshal_with_ruby2_keywords_hash
+    flagged_hash = ruby2_keywords_hash(key: 42)
+    hash = Marshal.load(Marshal.dump(flagged_hash))
+    assert_equal(42, ruby2_keywords_test(*[hash]))
+  end
 end