Failure to type patterns in IntMap

[DarkDimius]

dotc ./scala-scala/src/library/scala/collection/immutable/IntMap.scala

./scala-scala/src/library/scala/collection/immutable/IntMap.scala:118: error: Pattern type ((T1?), (T2?), (T3?), (T4?)) is neither a subtype nor a supertype of selector type (key: scala.collection.immutable.IntMapUtils.Int)Option[V]
      case IntMap.Bin(_,_, t@IntMap.Tip(_, _), right) => {

[odersky]

See #959 for a fix of the original problem. However, this currently dies in backend.

[DarkDimius]

The failure was caused by

object Bla {
 ...
 case _: this.type => true
 ...
}

That lead to tree similar to if(TypeTree(Bla) eq selector) .... Such trees should not be ever created.