Closed as not planned
Description
Compiler version
Nightly versions 3.3.2-RC1-bin-20230605-5d2812a-NIGHTLY through the latest 3.3.2-RC1-bin-20230710-ed319e8-NIGHTLY
By testing every nightly version I've narrowed it down to something in the commit range 348729e...5d2812a, and if git bisect is telling me the truth, then I believe the specific commit is 09f5e4c
Minimized code
type TupleIndex[T <: Tuple, A] = TupleIndex0[T, A, 0]
type TupleIndex0[T <: Tuple, A, I <: Int] <: (Any, Int) =
T match {
case A *: _ => (A, I)
case _ *: t => TupleIndex0[t, A, compiletime.ops.int.S[I]]
}
def tupleIndex[T <: Tuple, A](using i: ValueOf[Tuple.Elem[TupleIndex[T, A], 1]]): Int = i.valueOutput
A type mismatch error is given at the RHS of def tupleIndex
-- [E007] Type Mismatch Error: /path/to/TupleIndex.scala:9:90
9 |def tupleIndex[T <: Tuple, A](using i: ValueOf[Tuple.Elem[TupleIndex[T, A], 1]]): Int = i.value
| ^^^^^^^
|Found: Tuple.Elem[TupleIndex[T, A], (1 : Int)]
|Required: Int
|
|where: T is a type in method tupleIndex with bounds <: Tuple
|
|
|Note: a match type could not be fully reduced:
|
| trying to reduce Tuple.Elem[TupleIndex[T, A], (1 : Int)]
| trying to reduce TupleIndex[T, A]
| trying to reduce TupleIndex0[T, A, (0 : Int)]
| failed since selector T
| does not match case A *: _ => (A, (0 : Int))
| and cannot be shown to be disjoint from it either.
| Therefore, reduction cannot advance to the remaining case
|
| case _ *: t => TupleIndex0[t, A, scala.compiletime.ops.int.S[(0 : Int)]]
| trying to reduce TupleIndex[T, A]
| trying to reduce TupleIndex0[T, A, (0 : Int)]
| failed since selector T
| does not match case A *: _ => (A, (0 : Int))
| and cannot be shown to be disjoint from it either.
| Therefore, reduction cannot advance to the remaining case
|
| case _ *: t => TupleIndex0[t, A, scala.compiletime.ops.int.S[(0 : Int)]]
| trying to reduce TupleIndex0[T, A, (0 : Int)]
| failed since selector T
| does not match case A *: _ => (A, (0 : Int))
| and cannot be shown to be disjoint from it either.
| Therefore, reduction cannot advance to the remaining case
|
| case _ *: t => TupleIndex0[t, A, scala.compiletime.ops.int.S[(0 : Int)]]Expectation
The compiler should recognize that Tuple.Elem[TupleIndex[T, A], 1] is an Int since TupleIndex0 specifies a bound of (Any, Int)
Things work properly if TupleIndex0 has a bound of <: Int and I don't use Tuple.Elem, so does this maybe have something to do with nested match types? i.e. this compiles
type TupleIndex[T <: Tuple, A] = TupleIndex0[T, A, 0]
type TupleIndex0[T <: Tuple, A, I <: Int] <: Int =
T match {
case A *: _ => I
case _ *: t => TupleIndex0[t, A, compiletime.ops.int.S[I]]
}
def tupleIndex[T <: Tuple, A](using i: ValueOf[TupleIndex[T, A]]): Int = i.value