[ruby-core:78944] [Ruby trunk Bug#13096] error using undef_method + refinements

Issue #13096 has been reported by Ryan Davis.

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Bug #13096: error using undef_method + refinements
https://bugs.ruby-lang.org/issues/13096

* Author: Ryan Davis
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.3 or 2.4
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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I've got a bug report on minitest/mock that I've reduced to the following:

~~~ ruby
class Object
  def to_query            # remove this, works fine
  end
end

Object.prepend Module.new # remove this, works fine

module ObjectExtensions
  refine ::Object do
    def to_query          # remove this, works fine
    end
  end
end

class Mock
  instance_methods.each do |m|
    next if m =~ /object_id|__send__/
    undef_method m
  end
end
~~~

giving me the error:

~~~
bug671.rb:18:in `undef_method': undefined method `to_query' for class `Mock' (NameError)
	from bug671.rb:18:in `block in <class:Mock>'
	from bug671.rb:16:in `each'
	from bug671.rb:16:in `<class:Mock>'
	from bug671.rb:15:in `<main>'
~~~

This code comes from activesupport via regular requires, so this is a real problem for me.

Looks like the culprit might be here:

https://github.com/ruby/ruby/blob/v2_4_0/vm_method.c#L1187

I'd expect to be able to undef anything that comes back from `instance_methods` regardless of whether there is a refinement in place or not.

Additionally, the error message is just plain wrong. The method is most certainly defined (twice!) and should be improved.



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