[ruby-core:124366] [Ruby Bug#21807] ArgumentError is reported when forwarding arguments to method with intermediate optional arguments

26 Dec 2025

      Issue #21807 has been reported by taichi730 (Taichi Ishitani).

----------------------------------------
Bug #21807: ArgumentError is reported when forwarding arguments to method with intermediate optional arguments
https://bugs.ruby-lang.org/issues/21807

* Author: taichi730 (Taichi Ishitani)
* Status: Open
* ruby -v: 3.4.8
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
In Ruby 3.4.x, @ArgumentError@ is reported when forwarding arguments to a method with intermediate optional arguments.

How to reproduce:

Execute sample below.

``` ruby
class Foo
  def foo(a = nil, b)
    p a, b
  end
end

class Bar
  def initialize
    @foo = Foo.new
  end

  def bar(...)
    @foo.foo(...)
    @foo.foo(...)
  end
end

class Baz
  def initialize
    @bar = Bar.new
  end

  def baz(_a, ...)
    @bar.bar(...)
  end
end

puts RUBY_VERSION

baz = Baz.new
baz.baz(0, 1)
```

output:

<pre>
$ RBENV_VERSION=3.4.8 ruby test.rb
3.4.8
nil
1
test.rb:2:in 'foo': wrong number of arguments (given 0, expected 1..2) (ArgumentError)
        from test.rb:14:in 'Bar#bar'
        from test.rb:24:in 'Baz#baz'
</pre>

<pre>
$ RBENV_VERSION=3.4.1 ruby test.rb
3.4.1
nil
1
test.rb:2:in 'foo': wrong number of arguments (given 0, expected 1..2) (ArgumentError)
        from test.rb:14:in 'Bar#bar'
        from test.rb:24:in 'Baz#baz'
</pre>

For other Ruby verions (e.g. 4.0.0, 3.3.0), no error is reported.

<pre>
$ RBENV_VERSION=4.0.0 ruby test.rb
4.0.0
nil
1
nil
1
</pre>

<pre>
$ RBENV_VERSION=3.3.0 ruby test.rb
3.3.0
nil
1
nil
1
</pre>

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