[ruby-next] Memoized endless method

config.rb

RubyNext.define_text_rewriter "endless_memoized_def" do
  parser do
    def default
      many(
        alt(
          def_memoize,
          ruby_code
        )
      )
    end

    def def_memoize
      seq(
        string("def ").fmap { |s| s },
        many(not_followed_by(memoize_op).bind { regexp(/[a-zA-Z_]+/) }).join,
        memoize_op.fmap { |s| s },
        many(not_followed_by(end_of_line).bind { any_char }).join
      ).fmap do |(defstr, name, _, val)|
        track!
        "#{defstr}#{name} = @#{name} ||= #{val}"
      end
    end

    def memoize_op
      wrap(ws, opt_ws, string("||="))
    end

    def ruby_code
      any_char
    end
  end

  def safe_rewrite(source)
    parse(source).then(&:join)
  end
end

example.rb

# See https://bugs.ruby-lang.org/issues/20202

class Foo
  def initialize = @bars = 0
  def bar ||= :"memoized_value_#{@bars+=1}"
end

foo = Foo.new

puts foo.bar
puts foo.bar