class RuboCop::Cop::Performance::FixedSize

def allowed_argument?(arg)
  arg && non_string_argument?(arg.first)
end

def allowed_parent?(node)
  node && (node.casgn_type? || node.block_type?)
end

def allowed_variable?(var)
  contains_splat?(var) || contains_double_splat?(var)
end

def contains_double_splat?(node)
  return unless node.hash_type?
  node.each_child_node(:kwsplat).any?
end

def contains_splat?(node)
  return unless node.array_type?
  node.each_child_node(:splat).any?
end

def non_string_argument?(node)
  node && !node.str_type?
end

def on_send(node)
  return if allowed_parent?(node.parent)
  counter(node) do |var, arg|
    return if allowed_variable?(var) || allowed_argument?(arg)
    add_offense(node, :expression)
  end
end