regression involving DelayedInit

[retronym]

class Broken {
  def is(ee: AnyRef) = {
    new Delayed {
      ee
    }
  }
}

class Delayed extends DelayedInit {
  def delayedInit(x: => Unit): Unit = ()
}

java.util.NoSuchElementException: key not found: value ee$1
    at scala.collection.MapLike.default(MapLike.scala:232)
    at scala.collection.mutable.HashMap.apply(HashMap.scala:65)
    at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder$locals$.load(BCodeSkelBuilder.scala:392)
    at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:352)
    at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genStat(BCodeBodyBuilder.scala:82)

Minimized from a compiler crash compiling the play test suite. Specs 2 uses DelayedInit in part of its DSL.

[retronym]

Workaround would be to rewrite the above as:

class Workaround {
  def is(ee: AnyRef) = {
    new MyDelayed(ee)

  }
  class MyDelayed(ee: AnyRef) extends Delayed
}

class Delayed extends DelayedInit {
  def delayedInit(x: => Unit): Unit = ()
}

[retronym]

Hmm, this example actually crashes in 2.11.8 as well. I need to figure out what aspect of the original source in the Play tests leads to something that used to compile but now crashes.

[retronym]

This variation compiled without crashing in 2.11.8:

class Broken {
  def test = {
    val capture = ""
    () => {
      final class X extends DelayedInit {
        capture.toString
        def delayedInit(body: => Unit) = ()
      }
    }
  }
}

[retronym]

I think that when we switched on delambdafy:method as the default, we've shifted this example from into known bugs of the DelayedInit transform.

I've prototyped an change to Constructors to many examples work again. But, as shown in the pending test and discussed in the commit comment, we might find a more robust fix by adjusting LambdaLift instead.

I'm a bit torn about what severity we give to this bug. Even though we've deprecated DelayedInit usage (other than in the restricted use case of App), it has relatively widespread usage via part of the in the Specs2 DSL.

[SethTisue]

fyi @etorreborre

[som-snytt]

We mere observers don't appreciate the difficulty of supporting this feature. I wanted it the other day, and I often rely on the special qualities of App. I just remembered, my twist was that I wanted to override args in App, which is deprecated now. In the abstract, these seem like edge use cases, but once one fully embraces the feature, you start to see DelayedInit everywhere.

Like the old saw about the hammer, once you have DelayedInit, you see all init as delayed. Apologies for mixed metaphors, saw and hammer.

[etorreborre]

Thanks for the ping @SethTisue.

[retronym]

@lrytz I was playing with this patch to fix this in LambdaLift:

https://github.com/retronym/scala/tree/topic/SD-229b

My first attempt, which was more successful, was:

https://github.com/retronym/scala/tree/ticket/SD-229