cop.rb

class RuboCop::Cop::Security::LinkToBlank < RuboCop::Cop::Cop
  MSG = 'Specify a `:rel` option containing noopener.'.freeze

  def_node_matcher :link_to?, <<-PATTERN
    (send nil? :link_to ...)
  PATTERN

  def_node_matcher :blank_target?, <<-PATTERN
    (pair {(sym :target) (str "target")} (str "_blank"))
  PATTERN

  def_node_matcher :includes_noopener?, <<-PATTERN
    (pair {(sym :rel) (str "rel")} (str #contains_noopener?))
  PATTERN

  def on_send(node)
    return unless link_to?(node)

    option_nodes = [node.children.last.children, node.children[3]&.children].compact

    option_nodes.each do |options|
      blank = options.find { |o| blank_target?(o) }
      add_offense(blank) if blank && options.none? { |o| includes_noopener?(o) }
    end
  end

  private

  def contains_noopener?(str)
    str&.include?('noopener')
  end

end