Crash on pickling dependent function from object type to its opaque type member

[prolativ]

Compiler version

3.3.1-RC1-bin-20230412-e940957-NIGHTLY and before

Minimized code

object Foo:
  opaque type Baz = Int

def fun: (arg: Foo.type) => arg.Baz = ???

Output (click arrow to expand)

error when pickling type arg.type
error when pickling type arg.Baz
error when pickling tree arg.Baz
error when pickling tree Foo.type => arg.Baz
error when pickling tree (Foo.type => arg.Baz)
  {
    def apply(arg: Foo.type): arg.Baz
  }
error when pickling tree def fun:
  (Foo.type => arg.Baz)
    {
      def apply(arg: Foo.type): arg.Baz
    }
 = ???
error when pickling tree () extends Object() { this: bug$package.type =>
  private def writeReplace(): AnyRef =
    new scala.runtime.ModuleSerializationProxy(classOf[bug$package.type])
  def fun:
    (Foo.type => arg.Baz)
      {
        def apply(arg: Foo.type): arg.Baz
      }
   = ???
}
error when pickling tree @SourceFile("bug.scala") final module class bug$package() extends Object() {
  this: bug$package.type =>
  private def writeReplace(): AnyRef =
    new scala.runtime.ModuleSerializationProxy(classOf[bug$package.type])
  def fun:
    (Foo.type => arg.Baz)
      {
        def apply(arg: Foo.type): arg.Baz
      }
   = ???
}
error when pickling tree package <empty> {
  final lazy module val bug$package: bug$package = new bug$package()
  @SourceFile("bug.scala") final module class bug$package() extends Object() {
    this: bug$package.type =>
    private def writeReplace(): AnyRef =
      new scala.runtime.ModuleSerializationProxy(classOf[bug$package.type])
    def fun:
      (Foo.type => arg.Baz)
        {
          def apply(arg: Foo.type): arg.Baz
        }
     = ???
  }
}

  unhandled exception while running pickler on bug.scala
  
 Exception in thread "main" java.lang.AssertionError: assertion failed: orphan parameter reference: TermParamRef(arg)
        at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType(TreePickler.scala:292)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleType(TreePickler.scala:162)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleExternalRef$1(TreePickler.scala:202)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType(TreePickler.scala:224)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleType(TreePickler.scala:162)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:625)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$20(TreePickler.scala:641)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:641)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:637)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTpt(TreePickler.scala:319)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:338)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:581)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:373)
        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:373)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:607)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:337)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:583)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:373)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleStats(TreePickler.scala:373)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:623)
        at dotty.tools.dotc.core.tasty.TreePickler.pickle$$anonfun$1(TreePickler.scala:797)
        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:804)
        at dotty.tools.dotc.transform.Pickler.run$$anonfun$1$$anonfun$1(Pickler.scala:90)
        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$$anonfun$1(Pickler.scala:142)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.transform.Pickler.run(Pickler.scala:142)
        at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:324)
        at scala.collection.immutable.List.map(List.scala:246)
        at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:328)
        at dotty.tools.dotc.transform.Pickler.runOn(Pickler.scala:150)
        at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:246)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1321)
        at dotty.tools.dotc.Run.runPhases$1(Run.scala:262)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:270)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:279)
        at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
        at dotty.tools.dotc.Run.compileUnits(Run.scala:279)
        at dotty.tools.dotc.Run.compileSources(Run.scala:194)
        at dotty.tools.dotc.Run.compile(Run.scala:179)
        at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
        at dotty.tools.dotc.Driver.process(Driver.scala:197)
        at dotty.tools.dotc.Driver.process(Driver.scala:165)
        at dotty.tools.dotc.Driver.process(Driver.scala:177)
        at dotty.tools.dotc.Driver.main(Driver.scala:207)
        at dotty.tools.dotc.Main.main(Main.scala)

The crash does not occur if at least one of the following is true:

• the type of arg is a class (e.g. Foo) or a literal type pointing to a val (e.g. foo.type)
• type Baz is not opaque