Issue #22309 has been updated by shugo (Shugo Maeda). Thank you for working on this. I checked out the PR branch and tested it. The stack walk can be fooled. It assumes that the frame below the refinement frame, if it has the same `self` and the same method id, is the frame that called `super`. That frame may instead have reached the refinement by an ordinary call, in which case an ancestor is skipped: ```ruby module M def m(x) = [:M, *super] end module R refine M do def m(x) = [:R, *super] end end using R class Base prepend M def m(x) = [:Base] end class C < Base prepend M def m(x) = x ? [:C1, *m(false)] : [:C2, *super] end C.new.m(true) # expected: [:R, :M, :C1, :R, :M, :C2, :R, :M, :Base] # actual: [:R, :M, :C1, :R, :M, :Base] ``` This requires M to appear twice in the receiver's ancestry (with `prepend` as above, or by including M into a superclass after a subclass already included it); with a single iclass of M the search has only one place to land, so it cannot go wrong. The fallback (the first iclass of M in the receiver's ancestry) is not always right either: on `C` above, `C.new.method(:m).super_method.super_method.super_method` correctly denotes the refinement method for the inner M, but calling it restarts from the outer M, because the walk stops at the `Method#call` frame and the iclass the `Method` object knows about never reaches the frame. YJIT and ZJIT also need attention. With `--yjit` or `--zjit` (call threshold 1 or 2), the scenario of `test_super_in_refined_module_method` returns `"RFB"` instead of `"RFGAB"`: both JITs compute the superclass of the refinement's M iclass as BasicObject and, since `BasicObject#a` exists, dispatch there directly. I think these problems are inherent in inferring the ancestor from the call stack: the information that is actually needed is which iclass of M in the receiver's ancestry the dispatch went through, and it is discarded when `vm_call_refined` switches to the refinement's method entry. About the alternative you described:
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 afraid that, despite the additional complexity and memory, this is the only way to get correct behavior. The refinement method's `super` has to come back to the iclass of M in the receiver's ancestry, hit the REFINED entry there and fall through to `orig_me` with that iclass as `defined_class`, the same way class refinements work today; nothing short of a per-iclass refinement chain gives the module method's frame that information. The memory cost could be limited by creating the chain lazily in `search_refined_method`, keyed by the iclass of M it was dispatched through, so that only the (`using` scope, M iclass) pairs actually reached through refinement dispatch get one, but the complexity you mentioned remains. ---------------------------------------- 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-118979 * 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 -- https://bugs.ruby-lang.org/