From: "ufuk (Ufuk Kayserilioglu) via ruby-core" <ruby-core@...>
Date: 2025-04-29T11:15:10+00:00
Subject: [ruby-core:121768] [Ruby Bug#21292] wrong number of arguments (given 2, expected 0) (ArgumentError) since 8ac8225c504dee57454131e7cde2c47126596fdc

Issue #21292 has been updated by ufuk (Ufuk Kayserilioglu).

Assignee set to tenderlovemaking (Aaron Patterson)

This seems to be related to the `Class#new` optimization. Assigning to @tenderlovemaking

----------------------------------------
Bug #21292: wrong number of arguments (given 2, expected 0) (ArgumentError) since 8ac8225c504dee57454131e7cde2c47126596fdc
https://bugs.ruby-lang.org/issues/21292#change-112825

* Author: yahonda (Yasuo Honda)
* Status: Open
* Assignee: tenderlovemaking (Aaron Patterson)
* ruby -v: ruby 3.5.0dev (2025-04-25T20:46:05Z master 8ac8225c50) +PRISM [x86_64-linux]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Rails CI against Ruby master branch has been failing https://buildkite.com/rails/rails-nightly/builds/2129#019673e6-eed1-4ce3-947b-be63f9b54f1a/1241-1249 
According to git bisect, this behavior change has been introduced via 8ac8225c504dee57454131e7cde2c47126596fdc
and I think I have managed to reproduce it.

### Steps to reproduce
1. Create foo.rb

```ruby
class Foo
  def initialize
    @foo = nil
  end

  class << self
    private

    def method_missing(method_name, ...)
      Bar.new(self, method_name, ...)
    end

    # Workaround for Ruby 3.5.0
    # def method_missing(method_name, *args, &block)
    #   Bar.new(self, method_name, *args, &block)
    # end
  end
end

class Bar
  def initialize(class_name, action, *args)
    @class_name = class_name
    @action = action
    @args = args
  end
end

p RUBY_VERSION
foo = Foo.hello
p foo
```

2. Run this foo.rb
```
$ ruby foo.rb 
```

### Expected behavior
It should show the Ruby version and local variable foo as Ruby 3.4.3 does

```ruby
$ ruby -v
ruby 3.4.3 (2025-04-14 revision d0b7e5b6a0) +PRISM [x86_64-linux]
$ ruby foo.rb 
"3.4.3"
#<Bar:0x00007f130ed47bc8 @class_name=Foo, @action=:hello, @args=[]>
$ 
```
### Actual behavior
It raises the wrong number of arguments (given 2, expected 0) (ArgumentError)

```ruby
$ ruby -v
ruby 3.5.0dev (2025-04-25T20:46:05Z master 8ac8225c50) +PRISM [x86_64-linux]
$ ruby foo.rb 
"3.5.0"
foo.rb:2:in 'initialize': wrong number of arguments (given 2, expected 0) (ArgumentError)
        from foo.rb:10:in 'Foo.method_missing'
        from foo.rb:29:in '<main>'
$
``` 

### Additional information
1. To workaround this error, update the method_missing signature as follows.

```
 def method_missing(method_name, *args, &block)
   Bar.new(self, method_name, *args, &block)
  end
````

2. This does not reproduce against e0545a0250 that is the parent commit of 8ac8225

```ruby
$ ruby -v
ruby 3.5.0dev (2025-04-25T18:04:45Z master e0545a0250) +PRISM [x86_64-linux]
$ ruby foo.rb 
"3.5.0"
#<Bar:0x00007f3ac640f8a0 @class_name=Foo, @action=:hello, @args=[]>
$
``` 






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