Strange Cyclic reference error with incremental compilation

[OndrejSpanel]

Compiler version

3.5.1

Minimized code

Not yet (and I doubt I am able to provide it). The issue happens about 1 in 5 compilations and when it happens, it usually goes away on subsequent compilation attempt.

Some relevant parts of the code are here:

case class PositionWithDirection(pos: Vector3f, dir: Option[Vector3f]) {
  def orientation: Quaternion = dir.map(simpleRotation(Vector3f.UNIT_Z, _)).getOrElse(Quaternion())
  def shift(fwd: Double): PositionWithDirection = copy(pos + fwd * dir.map(_.normalized).getOrElse(Vector3f.UNIT_Z))
  def invert: PositionWithDirection = copy(dir = dir.map(-_))
}

def failForBadDirection(pos: PositionWithDirection): Unit = {
???
}

opaque type Vector3f = threex.Vector3

object PlanManager {

  extension(plan: Plan) {
    def onSurface(pos: PositionWithDirection) = PositionWithDirection(plan.state.world.terrain.posOnSurface(pos.pos.xz), pos.dir)
  }

  export PlanExtensions.*
  object PlanExtensions {
    extension[T >: Null <: ES[T]](plan: APlan[T]) {
      def until(s: State, t: Long): APlan.APlanFuture[T, Plan.Done] = {
         ???
      }
  }
}

Output

Normally this compiles fine, but sometimes with incremental compilation I get following error:

case class PositionWithDirection(pos: Vector3f, dir: Option[Vector3f]) {
[error]     |                                        ^
[error]     |Cyclic reference involving val pos
[error]     |
[error]     |The error occurred while trying to compute the signature of method failForBadDirection
[error]     |  which required to compute the signature of class PositionWithDirection
[error]     |  which required to compute the signature of constructor PositionWithDirection
[error]     |  which required to compute the signature of parameter pos
[error]     |  which required to compute the signature of object PlanManager
[error]     |  which required to elaborate the export clause export net.gamatron.procas.game.state.PlanManager.PlanExtensions.*
[error]     |  which required to compute the signature of method onSurface
[error]     |  which required to type the right hand side of method onSurface since no explicit type was given
[error]     |  which required to compute the signature of method apply
[error]     |  which required to compute the signature of parameter pos
[error]     |  which required to compute the signature of parameter pos

Expectation

• either the code compiles always or never. Incremental compilation should make no difference
• the error information should be more specific: signature of method apply or signature of parameter pos - how can I know which object is this in?