From: "shugo (Shugo Maeda) via ruby-core" <ruby-core@...>
Date: 2026-09-14T05:19:47+00:00
Subject: [ruby-core:126686] [Ruby Feature#22309] Allow super in a module method to work if method was called by refinement method super

Issue #22309 has been updated by shugo (Shugo Maeda).


I think a frame flag would fix the example I gave, but I do not see how it could handle the case where the block containing `super` outlives the refinement method's frame, because then there is no frame to walk or to flag. On the PR branch:

```ruby
module M
  def m = [:M, *super]
end
module R
  refine M do
    def m = Thread.new { [:R, *super] }.value
  end
end
using R

class Base
  prepend M
  def m = [:Base]
end
class C < Base
  prepend M
  def m = [:C, *super]
end

C.new.m
# expected: [:R, :M, :C, :R, :M, :Base]
# actual:   never returns
```

On the thread's stack there are only the block frame and the frame of `M#m`, so the walk finds nothing, falls back to the outer M, re-enters `C#m`, which reaches the inner refinement again and starts another thread, and so on. A lambda returned from the refinement method and called later has the same problem (it returns a wrong value instead of looping). Fiber and external enumerators would behave like the thread.

----------------------------------------
Feature #22309: Allow super in a module method to work if method was called by refinement method super
https://bugs.ruby-lang.org/issues/22309#change-118983

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
----------------------------------------
Ruby started allowing refinements of modules in 2.4. However, there was one limitation, which is that while the refinement method could call `super` to call the module method, the module method could not call `super`, because it did not have enough information to determine the appropriate ancestor. This limitation was known at the time and was accepted when module refinements were accepted in #12534.

As discussed in #22071, `super` wasn't actually prohibited in the module method, it just used the incorrect method lookup, looking for a super method in `BasicObject`. After discussion in #22071, I fixed this to use an explicit exception for this case, so an error was was raised for it.

While that addressed the incorrect super method lookup issue, it was an unsatisfying conclusion. I kept thinking about ways to actually fix the issue. My initial idea was to use a separate `T_ICLASS` for the module being refined in every class ancestry chain where it could be called via refinement `super`. However, that approach would result in a large amount of complexity, as well as potentially significant additional memory.

I am instead proposing an alternative approach which relies on the fact that when we call `super` in the module method, we know that the current method is a module method, and that the previous method in the call stack is a refinement method. We can walk up the call stack to find the refinement method, look at the previous method calling that to determine the class to use for the super lookup. Note that the previous method may use a different receiver/method, in which case we start with the receiver's class. There are cases where we need to do this multiple times, if there are multiple refinements or multiple modules being refined that have already called super to reach this point.  I'm not sure this alternative approach works in all cases, but I have gotten it to work every case I've tried:

* Module and refinement appears multiple times in the ancestor chain
* `super` calls both directly in method as well as in nested blocks in method
* Both refinement method and module method are bmethods
* Refinement refines multiple modules and both modules are involved in the same super call chain
* Multiple refinements of the same module method
* Use of ZSUPER aliases in the super call chain
* The `super` call in the module method is not found, and `NoMethodError` is raised correctly

We want the behavior of module refinement `super` to be consistent, so in addition to fixing `super` itself, we also need to fix `defined?(super)` as well as `Method#super_method` and `UnboundMethod#super_method`. `defined?(super)` is fixed by sharing the lookup that `super` now uses. However, `Method#super_method` and `UnboundMethod#super_method` require a different approach. Thankfully, `struct METHOD` already has a member named `iclass` that is used to implement `#super_method`. So we just need to make adjustments to the setting of the `iclass` member for `#super_method` to work.

Simple example:

```ruby
module M
  def m = [:M, *super]
end

class C
  prepend M
  def m = :C
end

module R
  refine M do
    def m = [:R, *super]
  end
end
using R

C.new.m
# => [:R, :M, :C]
```

I've submitted a pull request to implement this: https://github.com/ruby/ruby/pull/18797



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