new_contents: 
  # This leaks since the introduction of yield-expr and the use of generators
  # as coroutines, trunk revision 39239. The cycle-GC doesn't seem to pick up
  # the cycle, or decides it can't clean it up.
  
  def leak():
      def gen():
          while True:
              yield g
      g = gen()
  
  
subject: Add an example of a generator->freevar->cell->generator reference-cycle that doesn't get cleaned up and thus leaks.