[ruby/psych] Check that Data members match exactly

* Fixes ruby/psych#760

ruby/psych@952008c898

Author: eregon

test/psych/test_data.rb

@@ -64,6 +64,31 @@ def test_load
       assert_equal "hello", obj.bar
       assert_equal "bar",   obj.foo
     end
+
+    def test_members_must_be_identical
+      TestData.const_set :D, Data.define(:a, :b)
+      d = Psych.dump(TestData::D.new(1, 2))
+
+      # more members
+      TestData.send :remove_const, :D
+      TestData.const_set :D, Data.define(:a, :b, :c)
+      e = assert_raise(ArgumentError) { Psych.unsafe_load d }
+      assert_equal 'missing keyword: :c', e.message
+
+      # less members
+      TestData.send :remove_const, :D
+      TestData.const_set :D, Data.define(:a)
+      e = assert_raise(ArgumentError) { Psych.unsafe_load d }
+      assert_equal 'unknown keyword: :b', e.message
+
+      # completely different members
+      TestData.send :remove_const, :D
+      TestData.const_set :D, Data.define(:foo, :bar)
+      e = assert_raise(ArgumentError) { Psych.unsafe_load d }
+      assert_equal 'unknown keywords: :a, :b', e.message
+    ensure
+      TestData.send :remove_const, :D
+    end
   end
 end