Do not turn on keyword_init for Struct subclass if keyword hash is empty

This was accidentally turned on because there was no checking for
Qundef.

Also, since only a single keyword is currently supported, simplify
the rb_get_kwargs call.

1 files changed, 4 insertions, 0 deletions

diff --git a/test/ruby/test_struct.rb b/test/ruby/test_struct.rb
index 502affef07..ec0a29026b 100644
--- a/test/ruby/test_struct.rb
+++ b/test/ruby/test_struct.rb
@@ -96,6 +96,10 @@ module TestStruct
     assert_equal([:utime, :stime, :cutime, :cstime], Process.times.members)
   end
 
+  def test_struct_new_with_empty_hash
+    assert_equal({:a=>1}, Struct.new(:a, {}).new({:a=>1}).a)
+  end
+
   def test_struct_new_with_keyword_init
     @Struct.new("KeywordInitTrue", :a, :b, keyword_init: true)
     @Struct.new("KeywordInitFalse", :a, :b, keyword_init: false)