[ruby-core:101981] [Ruby master Bug#17519] set_visibility fails when a prepended module and a refinement both exist

Issue #17519 has been reported by fledman (David Feldman).

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Bug #17519: set_visibility fails when a prepended module and a refinement both exist
https://bugs.ruby-lang.org/issues/17519

* Author: fledman (David Feldman)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin19]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
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the set_visibility functions (aka public/private/protected) fail with NameError when:
* called on a specific object's singleton class
* for a specific method
* and both of the following are true
 * any module has been prepended to the object's class
 * a refinement exists for the specific method

note that the refinement does not need to ever be used

I have reproduced this on 3.0.0, 2.7.2, and 2.6.6 (those were the only 3 version I tested)

``` ruby
def test_visibility(function)
  h1 = {x:1, y:1}
  h2 = {x:2, y:2}

  h1.singleton_class.send(:private, function)
  h2.singleton_class.send(:public, function)

  begin
    puts h1.public_send(function, :x)
  rescue NoMethodError => err
    puts "hit NoMethodError as expected: #{err.inspect}"
  end

  puts h2.public_send(function, :x)
end
```

succeeds without any prepended modules or refinements:
```ruby
irb> test_visibility :except
hit NoMethodError as expected: #<NoMethodError: private method `except' called for {:x=>1, :y=>1}:Hash>
{:y=>2}
=> nil
```

succeeds with only a prepended module:
```ruby
irb> module Nothing; end; Hash.prepend(Nothing); Hash.ancestors
=> [Nothing, Hash, Enumerable, Object, PP::ObjectMixin, Kernel, BasicObject]

irb> test_visibility :except
hit NoMethodError as expected: #<NoMethodError: private method `except' called for {:x=>1, :y=>1}:Hash>
{:y=>2}
=> nil
```

succeeds with only a refinement:
```ruby
irb> module NeverUsed
  refine Hash do
    def except(*keys)
      {never: 'used'}
    end
  end
end
=> #<refinement:Hash@NeverUsed>

irb> test_visibility :except
hit NoMethodError as expected: #<NoMethodError: private method `except' called for {:x=>1, :y=>1}:Hash>
{:y=>2}
=> nil
```

fails with both a refinement and a prepended module:
```ruby
irb> module Nothing; end; Hash.prepend(Nothing); Hash.ancestors
=> [Nothing, Hash, Enumerable, Object, PP::ObjectMixin, Kernel, BasicObject]

irb> module NeverUsed
  refine Hash do
    def except(*keys)
      {never: 'used'}
    end
  end
end
=> #<refinement:Hash@NeverUsed>

irb> test_visibility :except
Traceback (most recent call last):
        6: from .rubies/ruby-3.0.0/bin/irb:23:in `<main>'
        5: from .rubies/ruby-3.0.0/bin/irb:23:in `load'
        4: from .rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/irb-1.3.0/exe/irb:11:in `<top (required)>'
        3: from (irb):25:in `<main>'
        2: from (irb):5:in `test_visibility'
        1: from (irb):5:in `private'
NameError (undefined method `except' for class `#<Class:#<Hash:0x00007ffd6b176f18>>')
Did you mean?  exec

# non-refined method still works
irb> test_visibility :fetch
hit NoMethodError as expected: #<NoMethodError: private method `fetch' called for {:x=>1, :y=>1}:Hash>
2
=> nil
```



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