[ruby-core:107837] [Ruby master Feature#18621] Fiber.yield loses the fact it was kwargs from Fiber#resume

Issue #18621 has been updated by Eregon (Benoit Daloze).

Backport deleted (2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: REQUIRED, 3.1: REQUIRED)
ruby -v deleted (ruby 3.2.0dev (2022-03-03T08:56:31Z master c1790f8c11) [x86_64-linux])
Status changed from Open to Rejected
Tracker changed from Bug to Feature

>  So in order for it to work, the final line would need to be: foo(*[args])

Right, due to `make_passing_arg` indeed.

> Be aware that if you go this direction, even if we remove the ruby2_keywords methods, the support for automatically treating hashes as keywords can never be removed, it must remain part of Ruby forever.

This is a very good point, I think this is not worth fixing in light of that.

I noticed this while implementing Ruby 3 kwargs in TruffleRuby, that basically the knowledge of "were kewargs passed" is lost in this case for `Fiber#resume` + `Fiber.yield`.
But it's also kind of natural since `Fiber.yield` already "packs" the arguments as a single Object or an Array, and there is no built-in object to represent all arguments currently: `*args, **kwargs` (and maybe also `&block`).

I'll reject this as I think it's not really needed in practice (one could pass a lambda doing the call with kwargs), and relying on the `ruby2_keywords` flag for this seems hacky.

----------------------------------------
Feature #18621: Fiber.yield loses the fact it was kwargs from Fiber#resume
https://bugs.ruby-lang.org/issues/18621#change-96767

* Author: Eregon (Benoit Daloze)
* Status: Rejected
* Priority: Normal
----------------------------------------
```ruby
f = Fiber.new do
  args = Fiber.yield
  args
end
f.resume
args = f.resume(a: 1)
Hash.ruby2_keywords_hash?(args) # => false, but should be true, isn't it?
```

This also means if there is `foo(*args)` later and `foo` would require kwargs it would fail:

```ruby
def foo(a: 1) = a

f = Fiber.new do
  args = Fiber.yield
  args
end
f.resume
args = f.resume(a: 1)
foo(*args)
# =>
# -:1:in `foo': wrong number of arguments (given 1, expected 0) (ArgumentError)
# 	from -:9:in `<main>'
```

cc @jeremyevans0 @mame



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