Assertion failed: Orphan parameter reference `TermParamRef` for path-dependent type

[pweisenburger]

Compiler version

3.1.2 and current main branch

Minimized code

trait Pack:
  type Reader

object PackTest extends Pack:
  type Reader

object Init:
  def get[P <: Pack](param: P): param.Reader = ???

trait Test:
  val pack: PackTest.type = PackTest
  val reader = Init.get[pack.type](pack)

Output (click arrow to expand)

error when pickling type param.type
error when pickling type param.Reader
error when pickling tree param.Reader
error when pickling tree val reader: param.Reader = Init.get[this.pack.type](this.pack)
error when pickling tree () extends Object {
  val pack: PackTest.type = PackTest
  val reader: param.Reader = Init.get[this.pack.type](this.pack)
}
error when pickling tree @SourceFile("Test.scala") trait Test() extends Object {
  val pack: PackTest.type = PackTest
  val reader: param.Reader = Init.get[this.pack.type](this.pack)
}
error when pickling tree package <empty> {
  @SourceFile("Test.scala") trait Test() extends Object {
    val pack: PackTest.type = PackTest
    val reader: param.Reader = Init.get[this.pack.type](this.pack)
  }
}
exception occurred while compiling Test.scala
Exception in thread "main" java.lang.AssertionError: assertion failed: orphan parameter reference: TermParamRef(param)
java.lang.AssertionError: assertion failed: orphan parameter reference: TermParamRef(param) while compiling Test.scala
	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType(TreePickler.scala:288)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleType(TreePickler.scala:157)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleExternalRef$1(TreePickler.scala:197)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType(TreePickler.scala:219)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleType(TreePickler.scala:157)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:603)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTpt(TreePickler.scala:315)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$1(TreePickler.scala:332)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$adapted$1(TreePickler.scala:336)
	at scala.Function0.apply$mcV$sp(Function0.scala:39)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:55)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:336)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:544)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:359)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleStats(TreePickler.scala:359)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$26(TreePickler.scala:585)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$adapted$24(TreePickler.scala:586)
	at scala.Function0.apply$mcV$sp(Function0.scala:39)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:55)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:586)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$1(TreePickler.scala:331)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$adapted$1(TreePickler.scala:336)
	at scala.Function0.apply$mcV$sp(Function0.scala:39)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:55)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:336)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:561)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:359)
	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.core.tasty.TreePickler.pickleStats(TreePickler.scala:359)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$29(TreePickler.scala:601)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$adapted$27(TreePickler.scala:601)
	at scala.Function0.apply$mcV$sp(Function0.scala:39)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:55)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:601)
	at dotty.tools.dotc.core.tasty.TreePickler.pickle$$anonfun$1(TreePickler.scala:772)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.core.tasty.TreePickler.pickle(TreePickler.scala:772)
	at dotty.tools.dotc.transform.Pickler.run$$anonfun$1$$anonfun$1(Pickler.scala:72)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.transform.Pickler.run$$anonfun$1(Pickler.scala:109)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.transform.Pickler.run(Pickler.scala:109)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:311)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:312)
	at dotty.tools.dotc.transform.Pickler.runOn(Pickler.scala:114)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:225)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1328)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:236)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:244)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:253)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:68)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:253)
	at dotty.tools.dotc.Run.compileSources(Run.scala:186)
	at dotty.tools.dotc.Run.compile(Run.scala:170)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:35)
	at dotty.tools.dotc.Driver.process(Driver.scala:195)
	at dotty.tools.dotc.Driver.process(Driver.scala:163)
	at dotty.tools.dotc.Driver.process(Driver.scala:175)
	at dotty.tools.dotc.Driver.main(Driver.scala:205)
	at dotty.tools.dotc.Main.main(Main.scala)

As can be seen in the output, the type of reader is param.Reader whereas, I assume, the type should be this.pack.Reader.