class T::Private::Methods::DeclBuilder

def params(*unused_positional_params, **params)
  check_live!
  if !decl.params.equal?(ARG_NOT_PROVIDED)
    raise BuilderError.new("You can't call .params twice")
  end
  if unused_positional_params.any?
    some_or_only = params.any? ? "some" : "only"
    raise BuilderError.new(<<~MSG)
      'params' was called with #{some_or_only} positional arguments, but it needs to be called with keyword arguments.
      The keyword arguments' keys must match the name and order of the method's parameters.
    MSG
  end
  if params.empty?
    raise BuilderError.new(<<~MSG)
      'params' was called without any arguments, but it needs to be called with keyword arguments.
      The keyword arguments' keys must match the name and order of the method's parameters.
      Omit 'params' entirely for methods with no parameters.
    MSG
  end
  decl.params = params
  self
end