Method and UnboundMethod can be sharable

with `RUBY_TYPED_FROZEN_SHAREABLE_NO_REC`,
if the receiver object is shareable on Method objects.

bootstraptest/test_ractor.rb

@@ -1203,6 +1203,28 @@ assert_equal '[:ok, "Proc\'s self is not shareable:"]', %q{
   end
 }
 
+# Ractor.make_sharable(Method/UnboundMethod)
+assert_equal 'true', %q{
+  # raise because receiver is unsharable
+  begin
+    _m0 = Ractor.make_shareable(self.method(:__id__))
+  rescue => e
+    raise e unless e.message =~ /can not make shareable object/
+  else
+    raise "no error"
+  end
+
+  # Method with sharable receiver
+  M1 = Ractor.make_shareable(Object.method(:__id__))
+
+  # UnboundMethod
+  M2 = Ractor.make_shareable(Object.instance_method(:__id__))
+
+  Ractor.new do
+    Object.__id__ == M1.call && M1.call == M2.bind_call(Object)
+  end.value
+}
+
 # Ractor.shareable?(recursive_objects)
 assert_equal '[false, false]', %q{
   y = []

proc.c

@@ -1668,7 +1668,7 @@ static const rb_data_type_t method_data_type = {
         NULL, // No external memory to report,
         bm_mark_and_move,
     },
-    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED | RUBY_TYPED_EMBEDDABLE
+    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED | RUBY_TYPED_EMBEDDABLE | RUBY_TYPED_FROZEN_SHAREABLE_NO_REC
 };
 
 VALUE

test/ruby/test_ractor.rb

@@ -47,7 +47,7 @@ class TestRactor < Test::Unit::TestCase
     def x.to_s
       raise "this should not be called"
     end
-    assert_unshareable(x, "can not make shareable object for #<Method: String#to_s()>", exception: Ractor::Error)
+    assert_unshareable(x, "can not make shareable object for #<Method: String#to_s()> because it refers unshareable objects", exception: Ractor::Error)
   end
 
   def test_default_thread_group