[ruby-core:118770] [Ruby master Bug#20640] Evaluation Order Issue in f(**h, &h.delete(key))

Issue #20640 has been updated by mame (Yusuke Endoh).


Briefly discussed at the dev meeting, and we found more pedantic case. We would like to see how much of a performance penalty it would bring to see if it should be fixed.

```ruby
def f(*a, **kw) kw[:a].class end

h = {a: 1}
foo = Object.new
foo.define_singleton_method(:to_proc) do
  h.clear
  proc {}
end
p f(**h, &foo) #=> expected: Integer, actual: NilClass
```



----------------------------------------
Bug #20640: Evaluation Order Issue in f(**h, &h.delete(key))
https://bugs.ruby-lang.org/issues/20640#change-109322

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Assignee: jeremyevans0 (Jeremy Evans)
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
Since Ruby 3.0, there is an evaluation order issue when passing a single keyword splat and a block pass expression that modifies the keyword splat:

```ruby
def f(*a, **kw) kw[:a].class end
h = {a: ->{}}
f(**h, &h.delete(:a))
# Ruby 2.0 - 2.7: Proc
# Ruby 3.0 - 3.4: NilClass
```

For single keyword splats followed by positional argument splats, this has been an issue since 3.3:

```ruby
def f(*a, **kw) kw[:a].class end
h = {a: ->{}}
a = []
f(*a, **h, &h.delete(:a))
# Ruby 2.0 - 3.2: Proc
# Ruby 3.3 - 3.4: NilClass
```

Ruby handles these issues for positional splats, duplicating the splatted array before evaluating post, keyword, or block argument expressions:

```ruby
f(*a, a.pop)    # post argument
f(*a, **a.pop)  # keyword splat argument
f(*a, a: a.pop) # keyword argument
f(*a, &a.pop)   # block argument
```

So it should handle the case for a keyword splat that could potentially be modified by block argument expression.

I'll submit a pull request shortly to fix this issue.



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