Regression in shapless2 scala 3 port due to new specced match types about scala3 HOT 3 CLOSED

This specific issue is not so much about the new match types. It fixed a soundness hole. We cannot make it compiler without reintroducing the unsoundness.

Fixing soundness bugs is not considered a regression.

from scala3.

Is there some other way the code can be written to not hit this? Because I thought these particular examples were sound.

from scala3.

So I figured out that one can make it compile by introducing an itermediate variable and discarding some of the type information. e.g

import scala.Tuple.Head

object Head {
  def head[T <: NonEmptyTuple](tuple: T): Head[T] = tuple match {
    case cons: *:[h, t] =>
      val tmp = cons: *:[h, t]
      tmp.head
  }
}

from scala3.