Compiler crash: Tailrec + Path dependant types

[allanrenucci]

class Context {
  type Tree
}

class Test {
  @annotation.tailrec
  final def loop(c: Context)(trees: List[c.Tree]): Boolean =
    loop(c)(trees)
}

Exception in thread "main" java.lang.AssertionError: assertion failed
	at scala.Predef$.assert(Predef.scala:204)
	at dotty.tools.dotc.transform.FullParameterization.$anonfun$forwarder$4(FullParameterization.scala:238)
	at scala.runtime.Tuple2Zipped$.$anonfun$map$1(Tuple2Zipped.scala:47)
	at scala.collection.immutable.List.foreach(List.scala:389)
	at scala.runtime.Tuple2Zipped$.map$extension(Tuple2Zipped.scala:45)
	at dotty.tools.dotc.transform.FullParameterization.$anonfun$forwarder$3(FullParameterization.scala:237)
	at scala.runtime.Tuple2Zipped$.$anonfun$map$1(Tuple2Zipped.scala:47)
	at scala.collection.immutable.List.foreach(List.scala:389)
	at scala.runtime.Tuple2Zipped$.map$extension(Tuple2Zipped.scala:45)
	at dotty.tools.dotc.transform.FullParameterization.forwarder(FullParameterization.scala:236)
	at dotty.tools.dotc.transform.FullParameterization.forwarder$(FullParameterization.scala:226)
	at dotty.tools.dotc.transform.TailRec.forwarder(TailRec.scala:6

Minimised from scalatest in the community build.