[ruby-core:120920] [Ruby master Bug#21125] Kernel is called first

9 Feb 2025

      Issue #21125 has been updated by jeremyevans0 (Jeremy Evans).

Assignee set to tenderlovemaking (Aaron Patterson)

The reason this works in Ruby 3.3 and below is that `system` is a private method and not a public method, and calls to private methods where the receiver is not `self` call `method_missing`.  `raw.system` is a method call where the receiver is not `self`, but `Kernel#system` is a private method, so this should be calling `method_missing`.  The fact that `method_missing` is not called in Ruby 3.4 is a bug.  I've determined the bug is in generic argument forwarding.  If you switch `...` (generic argument forwarding) to `*, **, &` (anonymous splat usage), things work correctly.  Assigning to @tenderlovemaking.

----------------------------------------
Bug #21125: Kernel is called first
https://bugs.ruby-lang.org/issues/21125#change-111802

* Author: mikik0 (Hashino Mikiko)
* Status: Open
* Assignee: tenderlovemaking (Aaron Patterson)
* ruby -v: ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [arm64-darwin24]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Kernel#system is being called when there is a column or method name named system.
The other methods of Kernel reproduce the problem.
Ex.Rand returns a random value, and exit terminates the program.

## Reproducible script:

``` ruby
class ObjectifiedHash
  def initialize(hash)
    @hash = hash
  end

  private

  attr_reader :hash

  def method_missing(method_name, *args, &block)
    if hash.key?(method_name.to_sym)
      hash[method_name.to_sym]
    else
      super
    end
  end

  def respond_to_missing?(method_name, include_private = false)
    hash.key?(method_name.to_sym) || super
  end
end

class Foo
  def system(...)
    # Kernel#system is called
    raw.system(...)
    # (...) passes if there is no
    # raw.system
  end

  def initialize(raw)
    @raw = raw
  end

  def get_system
    system
  end

  private

  attr_reader :raw
end

class Test
  def self.run
    obj = ObjectifiedHash.new({
      system: 'system'
    })

    foo = Foo.new(obj)
    # foo.system would pass.
    # After executing foo.system, hoge.get_system also passes.
    # p foo.system
    p foo.get_system
  end
end

Test.run

```

## Execution Results
``` shell
hoge.rb:26:in 'Kernel#system': wrong number of arguments (given 0, expected 1+) (ArgumentError)

    raw.system(...)
               ^^^
        from ruby.rb:26:in 'Foo#system'
        from ruby.rb:36:in 'Foo#get_system'
        from ruby.rb:54:in 'Test.run'
        from ruby.rb:58:in '<main>'
```

## Expected results
``` shell
"system"
```

PR that may be relevant: https://github.com/ruby/ruby/pull/11028

-- 
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