Nested mutation bug

[fwbrasil]

I'm debugging a test that fails on the latest develop revision. FlowStateMap.mutate calls are nested and mutate the same FlowDef. The outer mutation overrides the mutations done by the nested call. Stack trace from the debugging session:

Note the two mutate calls.

Isolated example:

object NestedMutationBug extends App {
  implicit val fd = new FlowDef
  implicit val m = Local(false)
  val t = TypedPipe.from(TypedText.tsv[String]("")).write(NullSink)
  CascadingBackend.planTypedWrites(fd, m)
  val state = FlowStateMap.get(fd).get
  require(state.sourceMap.nonEmpty) // fails
}

[johnynek]

working on this now.