[ruby-core:107003] [Ruby master Bug#18435] Calling `protected` on ancestor method changes result of `instance_methods(false)`

Issue #18435 has been updated by Eregon (Benoit Daloze).


I'm not fully clear on the expected semantics of private/protected/public in a subclass, that would probably be good to improve in the docs of these methods or in general docs.

However since the current semantics seems to clearly create new method entries on the subclass (when the visibility isn't already what's requested) then I think it would make a lot of sense to update the owner of the new method entry to be the subclass, since it's effectively defined on that class.

----------------------------------------
Bug #18435: Calling `protected` on ancestor method changes result of `instance_methods(false)`
https://bugs.ruby-lang.org/issues/18435#change-95835

* Author: ufuk (Ufuk Kayserilioglu)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.7.5p203 (2021-11-24 revision f69aeb8314) [x86_64-darwin20]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
As documented `instance_methods(false)` works as follows:

```ruby
module A
  def method1()  end
end

class B
  include A

  def method2()  end
end

p B.instance_methods(false) #=> [:method2]
```

However, calling `protected` on the method defined by `A`, unexpectedly changes the result of `instance_methods(false)` on `B`, even though the owner of the method is still `A`:
```ruby
module A
  def method1()  end
end

class B
  include A

  protected :method1

  def method2()  end
end

p B.instance_methods(false) #=> [:method1, :method2]
p B.instance_method(:method1).owner #=> A
```

In contrast, calling `private` or `public` on the same method does not cause any changes on the result of `B.instance_methods(false)`.

This feels like a bug in the implementation of `instance_methods(false)`, but, if it is by design, it should at least be documented on `Module#instance_methods`.

This reproduction script gives the same output all the way from Ruby 2.0 up to Ruby-HEAD:
https://wandbox.org/permlink/LqbXMBTYxURRZmDz



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