[ruby-core:98802] [Ruby master Bug#16504] `foo(*args, &args.pop)` should pass all elements of args

Issue #16504 has been updated by Eregon (Benoit Daloze).


Do we have an idea of how much overhead would it be to disable this not-correct optimization?
Arrays are copy-on-write so it seems not so expensive to have an extra array, and also guarantees the callee cannot mutate the original array.
I'd rather we don't compromise semantics because optimizations are too limited.

For the `&:symbol` case, we could check if Symbol#to_proc is redefined.
For the `&local_var` case, we could check if it's already a Proc.

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Bug #16504: `foo(*args, &args.pop)` should pass all elements of args
https://bugs.ruby-lang.org/issues/16504#change-86164

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
https://bugs.ruby-lang.org/issues/16500?next_issue_id=16499&prev_issue_id=16501#note-7

```
# in 2.7
args = [1, 2, -> {}]; foo(   *args, &args.pop) #=> passes [1, 2] (bug; [1, 2, ->{}] is expected)
args = [1, 2, -> {}]; foo(0, *args, &args.pop) #=> passes [0, 1, 2, ->{}] (good)
```



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