Add upper bounds to Tuple.{Map,FlatMap} args

Fixes #12645

Author: nicolasstucki

library/src/scala/Tuple.scala

@@ -109,18 +109,18 @@ object Tuple {
   }
 
   /** Fold a tuple `(T1, ..., Tn)` into `F[T1, F[... F[Tn, Z]...]]]` */
-  type Fold[T <: Tuple, Z, F[_, _]] = T match
+  type Fold[Tup <: Tuple, Z, F[_, _]] = Tup match
     case EmptyTuple => Z
     case h *: t => F[h, Fold[t, Z, F]]
 
   /** Converts a tuple `(T1, ..., Tn)` to `(F[T1], ..., F[Tn])` */
-  type Map[Tup <: Tuple, F[_]] <: Tuple = Tup match {
+  type Map[Tup <: Tuple, F[_ <: Union[Tup]]] <: Tuple = Tup match {
     case EmptyTuple => EmptyTuple
     case h *: t => F[h] *: Map[t, F]
   }
 
   /** Converts a tuple `(T1, ..., Tn)` to a flattened `(..F[T1], ..., ..F[Tn])` */
-  type FlatMap[Tup <: Tuple, F[_] <: Tuple] <: Tuple = Tup match {
+  type FlatMap[Tup <: Tuple, F[_ <: Union[Tup]] <: Tuple] <: Tuple = Tup match {
     case EmptyTuple => EmptyTuple
     case h *: t => Concat[F[h], FlatMap[t, F]]
   }

tests/pos/i12645.scala

@@ -0,0 +1,11 @@
+case class TBox[A <: Tuple](v: A)
+case class IBox[A <: Int](v: A)
+
+@main def m =
+    val t: TBox[EmptyTuple] = TBox(EmptyTuple)
+    val tt: Tuple.Map[(EmptyTuple, EmptyTuple), TBox] = (TBox(EmptyTuple), TBox(EmptyTuple))
+
+    val tt2: Tuple.Map[(1, 2), IBox] = (IBox(1), IBox(2))
+
+    type F[X] = (X, X)
+    val tt3: Tuple.FlatMap[(1, 2), F] = (1, 1, 2, 2)