default arguments & define_method: JRuby ~ MRI mismatch

1. Have a method in a class with default arguments,
2. subclass this,
3. overriding the method with 'define_method' with no block arguments.

Problem: calling 'super' won't propagate arguments to the superclass.
Workaround: add an (unused) block argument now the super method argument will be passed correctly.

Tried this with JRuby 1.3, 1.4 and trunk, with both --1.8 and --1.9.

MRI 1.8.7 is fine with this (you don't have to declare unused block arguments to get it working consistently).

class A
  def f(x = :default)
    warn "#{self.class} super f(#{x})"
    x
  end
end
 
class B < A
  define_method :f do |x|
    super
  end
end
 
class C < A
  define_method :f do # no block arg
    super
  end
end
 
 
B.new.f(:override) #### -> :override
C.new.f(:override) #### -> :default (JRuby), :override (MRI)

Note: as Vladimir pointed out, MRI 1.9.x reports this as error (block arity must match the invocation).
That's probably the more correct behaviour in general.
However, because of a difference on how 1.9 and 1.8 handles blocks arity, I think JRuby should support both:

• in 1.8 mode it should return :override for both invocations.
• in 1.9 mode it should complain as MRI does.