ClassCastException when `def` is used for a type of a tracked val enum

[kubukoz]

Compiler version

3.7.2

Minimized code

//> using scala 3.7.2
import language.experimental.modularity

case class Event(tracked val payload: Payload)

enum Payload {
  case Created()
}

val e = Event(Payload.Created())

def handleCreated(e: Event { def payload : Payload.Created}) = println(e.payload)

@main def run = e match {
  case Event(payload: Payload.Created) => handleCreated(e.copy(payload = payload))
}

Output

Exception in thread "main" java.lang.ClassCastException: class Payload$Created cannot be cast to class scala.Function0 (Payload$Created and scala.Function0 are in unnamed module of loader 'app')
        at demo$package$.handleCreated(demo.scala:12)
        at demo$package$.run(demo.scala:15)
        at run.main(demo.scala:14)

Expectation

Either a compile error, or just Created() in the output.

[kubukoz]

What I also find confusing, if you just create an instance of the Event class and don't give it a precise type, the compilation error makes it seem like def vs val is the problem:

//> using scala 3.7.2
import language.experimental.modularity

case class Event(tracked val payload: Payload)

enum Payload {
  case Created()
}

val e = Event(Payload.Created())

def handleCreated(e: Event { def payload : Payload.Created}) = println(e.payload)

@main def run = handleCreated(Event(payload = Payload.Created()))

results in:

[error] ./demo.scala:14:31
[error] Found:    Event{val payload: (?1 : Payload)}
[error] Required: Event{def payload: Payload.Created}
[error] 
[error] where:    ?1 is an unknown value of type Payload
[error] @main def run = handleCreated(Event(payload = Payload.Created()))
[error]                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

My point is mostly visible with colors: