[ruby-core:99362] [Ruby master Bug#17007] SystemStackError when using super inside Module included and lexically inside refinement

Issue #17007 has been updated by jeremyevans0 (Jeremy Evans).


Eregon (Benoit Daloze) wrote in #note-4:
> Thanks for the fix!
> BTW this changes the behavior on a new spec, is that intended? (result is [:A, :C] instead of [:A, :LOCAL, :C] on < 2.8)
> https://github.com/ruby/spec/commit/b0da11b52560860e844470d145acee0ff4d4acea?w=1

It's a consequence of the fix (skips the currently activated refinement during super), but I wouldn't say it is intended.  Ideally, the fix would only affect looping cases.  Unfortunately, I'm not sure if there is a better way to detect whether looping during super would occur.  I'm also not sure whether the approach I committed can detect all cases of looping (there may be other ways to introduce looping during super).

Maybe the refinements spec needs to be changed if we want to forbid looping, spelling out how to handle super in modules included in refinements where the refinements are activated at the point of super call.

----------------------------------------
Bug #17007: SystemStackError when using super inside Module included and lexically inside refinement
https://bugs.ruby-lang.org/issues/17007#change-86762

* Author: Eregon (Benoit Daloze)
* Status: Closed
* Priority: Normal
* Assignee: shugo (Shugo Maeda)
* ruby -v: ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
```ruby
class C
  def foo
    ["C"]
  end
end

refinement = Module.new do
  R = refine C do
    def foo
      ["R"] + super
    end

    include Module.new {
      def foo
        ["M"] + super
      end
    }
  end
end

using refinement
p C.new.foo
```

gives

```
$ ruby bug_refine_super.rb
Traceback (most recent call last):
	10920: from bug_refine_super.rb:22:in `<main>'
	10919: from bug_refine_super.rb:10:in `foo'
	10918: from bug_refine_super.rb:15:in `foo'
	10917: from bug_refine_super.rb:10:in `foo'
	10916: from bug_refine_super.rb:15:in `foo'
	10915: from bug_refine_super.rb:10:in `foo'
	10914: from bug_refine_super.rb:15:in `foo'
	10913: from bug_refine_super.rb:10:in `foo'
	 ... 10908 levels...
	    4: from bug_refine_super.rb:15:in `foo'
	    3: from bug_refine_super.rb:10:in `foo'
	    2: from bug_refine_super.rb:15:in `foo'
	    1: from bug_refine_super.rb:10:in `foo'
bug_refine_super.rb:15:in `foo': stack level too deep (SystemStackError)
```

OTOH defining the module lexically outside of `refine` works:
```ruby
m = Module.new {
  def foo
    ["M"] + super
  end
}
refinement = Module.new do
  R = refine C do
    def foo
      ["R"] + super
    end

    include m
  end
end

# result: ["R", "M", "C"]
```



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