class ActionDispatch::Routing::Mapper::Constraints

def constraint_args(constraint, request)
  arity = if constraint.respond_to?(:arity)
    constraint.arity
  else
    constraint.method(:call).arity
  end
  if arity < 1
    []
  elsif arity == 1
    [request]
  else
    [request.path_parameters, request]
  end
end