From: "mame (Yusuke Endoh)" <noreply@...>
Date: 2022-03-22T05:31:29+00:00
Subject: [ruby-core:108013] [Ruby master Bug#18625] ruby2_keywords does not unmark the hash if the receiving method has a *rest parameter

Issue #18625 has been updated by mame (Yusuke Endoh).


As far as I understand, this change will break the following code:

```
def target(a:)
  p a
end

# after the patch, ruby2_keywords is requried here
def bar(*args)
  target(*args)
end

ruby2_keywords def foo(*args)
  bar(*args)
end

p foo(a: 42) #=> 42 in Ruby 3.1
             #=> ArgumentError after the patch
```

After the patch, we need to add `ruby2_keywords` to the definition of `bar`.

According to our previous experience, rails is using this kind of multi-stage delegation pattern so much. Maybe we need to ask the core developers of rails to check and support the change. cc/ @kamipo

----------------------------------------
Bug #18625: ruby2_keywords does not unmark the hash if the receiving method has a *rest parameter
https://bugs.ruby-lang.org/issues/18625#change-96970

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
The code below shows the inconsistency.
In all cases the `marked` Hash is copied at call sites using `some_call(*args)`, however for the case of `splat` it keeps the ruby2_keywords flag to true, and not false as expected.
This can be observed in user code and will hurt migration from `ruby2_keywords` to other ways of delegation (`(...)` and `(*args, **kwargs)`).
I believe this is another manifestation of #16466.

```ruby
ruby2_keywords def foo(*args)
  args
end

def single(arg)
  arg
end

def splat(*args)
  args.last
end

def kwargs(**kw)
  kw
end

h = { a: 1 }
args = foo(**h)
marked = args.last
Hash.ruby2_keywords_hash?(marked) # => true

after_usage = single(*args)
after_usage == h # => true
after_usage.equal?(marked) # => false
p Hash.ruby2_keywords_hash?(after_usage) # => false

after_usage = splat(*args)
after_usage == h # => true
after_usage.equal?(marked) # => false
p Hash.ruby2_keywords_hash?(after_usage) # => true, BUG, should be false

after_usage = kwargs(*args)
after_usage == h # => true
after_usage.equal?(marked) # => false
p Hash.ruby2_keywords_hash?(after_usage) # => false

Hash.ruby2_keywords_hash?(marked) # => true
```

I'm implementing Ruby 3 kwargs in TruffleRuby and this came up as an inconsistency in specs.
In TruffleRuby it's also basically not possible to implement this behavior, because at a splat call site where we check for a last Hash argument marked as ruby2_keywords, we have no idea of which method will be called yet, and so cannot differentiate behavior based on that.

cc @jeremyevans0 @mame



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