endless compilation when deferred inline + match type are used (LTS only) #23110
Description
Compiler version
3.3.5 LTS (3.6.4 works as expected)
Minimized code
//> using scala 3.3.5
import scala.compiletime.*
trait InlineFoldR[Acc[_ <: Tuple]]:
inline def apply[Elem, T <: Tuple](acc: Acc[T]): Acc[Elem *: T]
object InlineFoldR:
inline def fold[Acc[_ <: Tuple], T <: Tuple](
acc: Acc[EmptyTuple],
f: InlineFoldR[Acc]
): Acc[T] =
inline erasedValue[T] match
case _: EmptyTuple => acc.asInstanceOf[Acc[T]]
case _: (h1 *: h2 *: h3 *: h4 *: ts) =>
f[h1, h2 *: h3 *: h4 *: ts](
f[h2, h3 *: h4 *: ts](
f[h3, h4 *: ts](f[h4, ts](fold[Acc, ts](acc, f)))
)
).asInstanceOf[Acc[T]]
case _: (h *: ts) =>
f[h, ts](fold[Acc, ts](acc, f)).asInstanceOf[Acc[T]]
type DropUnits[A <: Tuple] <: Tuple = A match
case hd *: tl =>
hd match
case Unit => DropUnits[tl]
case Any => hd *: DropUnits[tl]
case EmptyTuple => EmptyTuple
object DropUnits:
object DropInlined extends InlineFoldR[[T <: Tuple] =>> T => DropUnits[T]]:
inline def apply[Elem, T <: Tuple](
acc: T => DropUnits[T]
): (Elem *: T) => DropUnits[Elem *: T] =
(elem: Elem *: T) =>
inline erasedValue[Elem & Matchable] match
case _: Unit => acc(elem.tail)
case _ => elem.head *: acc(elem.tail)
inline def drop[A <: Tuple](a: A): DropUnits[A] =
InlineFoldR
.fold[[T <: Tuple] =>> T => DropUnits[T], A](
(_: EmptyTuple) => EmptyTuple,
DropInlined
)(a)
val a: (
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Int,
Unit,
Int,
Unit
) =
(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, (), 1, ())
println(DropUnits.drop(a))Output
Endless compilation
Expectation
Compilation succeeded.
Sorry, I don't know how to minimize it. Deferred inline InlineFoldR and match type DropUnits are required to show the bug.