“type [...] is not a class” on 2.11.0-RC1

[stanch]

Hi,

I have roughly the following things:

class Ui[+A](protected val v: () ⇒ A) {
  /** Run the code on the UI thread */
  def run: Future[A] = ...
  /** Get the result of executing the code on the current thread */
  def get: A = ...
}

trait CanSnail[W, S, R] {
  def snail(w: W, s: S): Ui[Future[R]]
}

implicit def `List is snailable`[W, S, R](implicit canSnail: CanSnail[W, S, R]) =
  new CanSnail[List[W], S, List[W]] {
    def snail(l: List[W], s: S) = Ui(async {
      val it = l.iterator
      while (it.hasNext) {
        // we can call Ui.get, since we are already inside the UI thread
        await(canSnail.snail(it.next(), s).get)
      }
      l
    }(UiThreadExecutionContext))
  }

On Scala 2.11.0-RC1 (but not 2.10.3) it fails with

scala.ScalaReflectionException: type R is not a class
[error]     at scala.reflect.api.Symbols$SymbolApi$class.asClass(Symbols.scala:272)
[error]     at scala.reflect.internal.Symbols$SymbolContextApiImpl.asClass(Symbols.scala:82)
[error]     at scala.async.internal.LiveVariables$$anonfun$3.apply(LiveVariables.scala:58)
[error]     at scala.async.internal.LiveVariables$$anonfun$3.apply(LiveVariables.scala:57)
[error]     at scala.collection.TraversableLike$$anonfun$filterImpl$1.apply(TraversableLike.scala:259)
[error]     at scala.collection.immutable.Set$Set2.foreach(Set.scala:113)
[error]     at scala.collection.TraversableLike$class.filterImpl(TraversableLike.scala:258)
[error]     at scala.collection.TraversableLike$class.filter(TraversableLike.scala:270)
[error]     at scala.collection.AbstractTraversable.filter(Traversable.scala:104)
[error]     at scala.async.internal.LiveVariables$class.liveVars(LiveVariables.scala:57)
[error]     at scala.async.internal.AsyncMacro$$anon$1.liveVars(AsyncMacro.scala:6)
[error]     at scala.async.internal.LiveVariables$class.fieldsToNullOut(LiveVariables.scala:20)
[error]     at scala.async.internal.AsyncMacro$$anon$1.fieldsToNullOut(AsyncMacro.scala:6)
[error]     at scala.async.internal.AsyncTransform$class.asyncTransform(AsyncTransform.scala:76)
[error]     at scala.async.internal.AsyncMacro$$anon$1.asyncTransform(AsyncMacro.scala:6)
[error]     at scala.async.internal.AsyncBase.asyncImpl(AsyncBase.scala:48)
[error]     at scala.async.internal.ScalaConcurrentAsync$.asyncImpl(ScalaConcurrentAsync.scala:16)
[error]       }(UiThreadExecutionContext))
[error]        ^

I’m using async milestone M5 on both. Perhaps a regression somewhere?
I’ll be able to push the complete code tomorrow, if that’s necessary.

Nick

[retronym]

I've got a fair idea where the regression came from, but would really appreciate a standalone test case.

[stanch]

It’s here. Although now I realized that you need to have Android SDK installed. I’ll try to reduce it further.

[stanch]

Ok, take a look at this branch: https://github.com/macroid/macroid/blob/async-regression/src/main/scala/org/macroid/Bug.scala
I’ve removed everything except the failing bit. No dependencies besides scala-async.

[retronym]

I just release 0.9.0-M6 with the fix for this bug. Thanks for the minimization!

[stanch]

Thanks!