[ruby-core:122892] [Ruby Bug#21525] Inconsistent execution order for methods with constant blocks

Issue #21525 has been reported by [e-mail] (Joel Drapper).

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Bug #21525: Inconsistent execution order for methods with constant blocks
https://bugs.ruby-lang.org/issues/21525

* Author: [e-mail] (Joel Drapper)
* Status: Open
* ruby -v: ruby 3.4.5 (2025-08-01 revision 07f7832cff) +PRISM [arm64-darwin24]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
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If you call a method and pass in a splat of an array with a block argument coerced from calling a method, Ruby maintains the expected execution order and the called method receives a copy of the array prior to modification.

In this example, the output is `[1, 2, 3]` since the copy is made before the `bar` method can modify it.

```ruby
ARRAY = [1, 2, 3]

def bar
  ARRAY.pop
  -> {}
end

def example(*args, &)
  puts args
end

example(*ARRAY, &bar)
```

However, when passing a constant, the block coercion itself is able to modify the array.

```ruby
ARRAY = [1, 2, 3]

module Foo
  module Bar
    def self.to_proc
      ARRAY.pop
      -> {}
    end
  end
end

def example(*args, &)
  puts args
end

example(*ARRAY, &Foo::Bar)
```

Another way to trigger this is to define a `const_missing` method that modifies the array.


```ruby
ARRAY = [1, 2, 3]

module Foo
  def self.const_missing(name)
    ARRAY.pop
    -> {}
  end
end

def example(*args, &)
  puts args
end

example(*ARRAY, &Foo::Bar)
```

In both these cases, the output is `[1, 2]` instead of the expected `[1, 2, 3]`.



-- 
https://bugs.ruby-lang.org/
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