[ruby/ostruct] Add test that frozen OpenStructs are Ractor-shareable

Merged: https://github.com/ruby/ruby/pull/3593

lib/ostruct.rb

@@ -62,6 +62,8 @@
 #   first_pet                 # => #<OpenStruct name="Rowdy">
 #   first_pet == second_pet   # => true
 #
+# Ractor compatibility: A frozen OpenStruct with shareable values is itself shareable.
+#
 # == Caveats
 #
 # An OpenStruct utilizes Ruby's method lookup structure to find and define the

test/ostruct/test_ostruct.rb

@@ -298,4 +298,15 @@ class TC_OpenStruct < Test::Unit::TestCase
     o.foo = 42
     assert_equal 42, o.foo
   end
+
+  def test_ractor
+    obj1 = OpenStruct.new(a: 42, b: 42)
+    obj1.c = 42
+    obj1.freeze
+
+    obj2 = Ractor.new obj1 do |obj|
+      obj
+    end.take
+    assert obj1.object_id == obj2.object_id
+  end if defined?(Ractor)
 end