Add Widen type to the Tuple

Author: anatoliykmetyuk

library/src/scala/Tuple.scala

@@ -120,6 +120,18 @@ object Tuple {
     case h *: t => Concat[F[h], FlatMap[t, F]]
   }
 
+  /**
+   * Use this type to widen a self-type to a tuple. E.g.
+   * ```
+   * val x: (1, 3) = (1, 3)
+   * val y: Widen[x.type] = x
+   * ```
+   */
+  type Widen[Tup <: Tuple] <: Tuple = Tup match {
+    case EmptyTuple => EmptyTuple
+    case h *: t => h *: t
+  }
+
   /** Given two tuples, `A1 *: ... *: An * At` and `B1 *: ... *: Bn *: Bt`
    *  where at least one of `At` or `Bt` is `EmptyTuple` or `Tuple`,
    *  returns the tuple type `(A1, B1) *: ... *: (An, Bn) *: Ct`

library/src/scala/compiletime/package.scala

@@ -42,13 +42,13 @@ package object compiletime {
 
   inline def constValue[T]: T = ???
 
-  inline def constValueTuple[T <: Tuple]: T =
+  inline def constValueTuple[T <: Tuple]: Tuple.Widen[T]=
     val res =
       inline erasedValue[T] match
         case _: EmptyTuple => EmptyTuple
         case _: (t *: ts) => constValue[t] *: constValueTuple[ts]
       end match
-    res.asInstanceOf[T]
+    res.asInstanceOf[Tuple.Widen[T]]
   end constValueTuple
 
   /** Summons first given matching one of the listed cases. E.g. in
@@ -83,13 +83,13 @@ package object compiletime {
    *  @tparam T the tuple containing the types of the values to be summoned
    *  @return the given values typed as elements of the tuple
    */
-  inline def summonAll[T <: Tuple]: T =
+  inline def summonAll[T <: Tuple]: Tuple.Widen[T] =
     val res =
       inline erasedValue[T] match
         case _: EmptyTuple => EmptyTuple
         case _: (t *: ts) => summonInline[t] *: summonAll[ts]
       end match
-    res.asInstanceOf[T]
+    res.asInstanceOf[Tuple.Widen[T]]
   end summonAll
 
   /** Succesor of a natural number where zero is the type 0 and successors are reduced as if the definition was