Avoid setting the visibility of refinement method entries

Since refinement search is always performed, these entries should always
be public. The method entry that the refinement search returns decides
the visibility.

Fixes [Bug #17822]

test/ruby/test_refinement.rb

@@ -2537,6 +2537,28 @@ class TestRefinement < Test::Unit::TestCase
     assert_equal(:second, klass.new.foo)
   end
 
+  class Bug17822
+    module Ext
+      refine(Bug17822) do
+        def foo = :refined
+      end
+    end
+
+    private(def foo = :not_refined)
+
+    module Client
+      using Ext
+      def self.call_foo
+        Bug17822.new.foo
+      end
+    end
+  end
+
+  # [Bug #17822]
+  def test_privatizing_refined_method
+    assert_equal(:refined, Bug17822::Client.call_foo)
+  end
+
   private
 
   def eval_using(mod, s)

vm_method.c

@@ -1409,11 +1409,16 @@ rb_export_method(VALUE klass, ID name, rb_method_visibility_t visi)
 	rb_vm_check_redefinition_opt_method(me, klass);
 
 	if (klass == defined_class || origin_class == defined_class) {
-	    METHOD_ENTRY_VISI_SET(me, visi);
-
-	    if (me->def->type == VM_METHOD_TYPE_REFINED && me->def->body.refined.orig_me) {
-		METHOD_ENTRY_VISI_SET((rb_method_entry_t *)me->def->body.refined.orig_me, visi);
-	    }
+            if (me->def->type == VM_METHOD_TYPE_REFINED) {
+                // Refinement method entries should always be public because the refinement
+                // search is always performed.
+                if (me->def->body.refined.orig_me) {
+                    METHOD_ENTRY_VISI_SET((rb_method_entry_t *)me->def->body.refined.orig_me, visi);
+                }
+            }
+            else {
+                METHOD_ENTRY_VISI_SET(me, visi);
+            }
             rb_clear_method_cache(klass, name);
 	}
 	else {