[ruby-core:124620] [Ruby Bug#21807] ArgumentError is reported when forwarding arguments to method with intermediate optional arguments

25 Jan 2026

      Issue #21807 has been updated by nagachika (Tomoyuki Chikanaga).

ruby_3_4 commit:55920677854fe757c36368785f6dfdbce0b49ab7 merged revision(s) 86320a53002a3adaf35ad7434c70e86747a8b345.

----------------------------------------
Bug #21807: ArgumentError is reported when forwarding arguments to method with intermediate optional arguments
https://bugs.ruby-lang.org/issues/21807#change-116206

* Author: taichi730 (Taichi Ishitani)
* Status: Closed
* ruby -v: 3.4.8 (2025-12-17 revision 995b59f666) +PRISM [x86_64-linux]
* Backport: 3.2: DONTNEED, 3.3: DONTNEED, 3.4: DONE, 4.0: DONTNEED
----------------------------------------
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:

```console
$ 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'
```

```console
$ 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'
```

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

```console
$ RBENV_VERSION=4.0.0 ruby test.rb
4.0.0
nil
1
nil
1
```

```console
$ RBENV_VERSION=3.3.0 ruby test.rb
3.3.0
nil
1
nil
1
```

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