assertion failed: unresolved symbols: type _

[raboof]

Compiler version

3.0.0-RC3

Minimized code

class Property[T]

class VObject {
  def properties() = {
    List.empty[Property[_]].collect {
      case p: Property[_] => List(p)
    }
  }
}

class Event extends VObject {
  override def properties() = ???
}

Output (click arrow to expand)

$ scalac --version
Scala compiler version 3.0.0-RC3 -- Copyright 2002-2021, LAMP/EPFL
$ scalac VObject.scala
exception occurred while compiling VObject.scala
java.lang.AssertionError: assertion failed: unresolved symbols: type _ (line 5) #8400 when pickling VObject.scala while compiling VObject.scala
Exception in thread "main" java.lang.AssertionError: assertion failed: unresolved symbols: type _ (line 5) #8400 when pickling VObject.scala
	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
	at dotty.tools.dotc.core.tasty.TreePickler.pickle(TreePickler.scala:788)
	at dotty.tools.dotc.transform.Pickler.run$$anonfun$3$$anonfun$2(Pickler.scala:69)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.transform.Pickler.run$$anonfun$1(Pickler.scala:106)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.transform.Pickler.run(Pickler.scala:106)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:303)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:304)
	at dotty.tools.dotc.transform.Pickler.runOn(Pickler.scala:111)
	at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:205)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$5(Run.scala:215)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:223)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:230)
	at dotty.tools.dotc.Run.compileSources(Run.scala:166)
	at dotty.tools.dotc.Run.compile(Run.scala:150)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
	at dotty.tools.dotc.Driver.process(Driver.scala:199)
	at dotty.tools.dotc.Driver.process(Driver.scala:167)
	at dotty.tools.dotc.Driver.process(Driver.scala:179)
	at dotty.tools.dotc.Driver.main(Driver.scala:209)
	at dotty.tools.dotc.Main.main(Main.scala)