Generalize unpickleExpr interface

This way we could generate somthing that is not a Seq, possibly a closure with a switch on the index.

compiler/src/dotty/tools/dotc/quoted/PickledQuotes.scala

@@ -51,7 +51,7 @@ object PickledQuotes {
   }
 
   /** Unpickle the tree contained in the TastyExpr */
-  def unpickleTerm(pickled: List[String], fillHole: Seq[Seq[Any] => Any])(using Context): Tree = {
+  def unpickleTerm(pickled: List[String], fillHole: Int => Seq[Any] => Any)(using Context): Tree = {
     val unpickled = withMode(Mode.ReadPositions)(unpickle(pickled, isType = false))
     val Inlined(call, Nil, expnasion) = unpickled
     val inlineCtx = inlineContext(call)
@@ -61,13 +61,13 @@ object PickledQuotes {
   }
 
   /** Unpickle the tree contained in the TastyType */
-  def unpickleTypeTree(pickled: List[String], fillHole: Seq[Seq[Any] => Any])(using Context): Tree = {
+  def unpickleTypeTree(pickled: List[String], fillHole: Int => Seq[Any] => Any)(using Context): Tree = {
     val unpickled = withMode(Mode.ReadPositions)(unpickle(pickled, isType = true))
     spliceTypes(unpickled, fillHole)
   }
 
   /** Replace all term holes with the spliced terms */
-  private def spliceTerms(tree: Tree, fillHole: Seq[Seq[Any] => Any])(using Context): Tree = {
+  private def spliceTerms(tree: Tree, fillHole: Int => Seq[Any] => Any)(using Context): Tree = {
     val evaluateHoles = new TreeMap {
       override def transform(tree: tpd.Tree)(using Context): tpd.Tree = tree match {
         case Hole(isTerm, idx, args) =>
@@ -121,7 +121,7 @@ object PickledQuotes {
   }
 
   /** Replace all type holes generated with the spliced types */
-  private def spliceTypes(tree: Tree, fillHole: Seq[Seq[Any] => Any])(using Context): Tree = {
+  private def spliceTypes(tree: Tree, fillHole: Int => Seq[Any] => Any)(using Context): Tree = {
     tree match
       case Block(stat :: rest, expr1) if stat.symbol.hasAnnotation(defn.InternalQuoted_QuoteTypeTagAnnot) =>
         val typeSpliceMap = (stat :: rest).iterator.map {

compiler/src/dotty/tools/dotc/quoted/QuoteContextImpl.scala

@@ -2621,11 +2621,11 @@ class QuoteContextImpl private (ctx: Context) extends QuoteContext, scala.intern
 
   end reflect
 
-  def unpickleExpr[T](pickled: List[String], fillHole: Seq[Seq[Any] => Any]): scala.quoted.Expr[T] =
+  def unpickleExpr[T](pickled: List[String], fillHole: Int => Seq[Any] => Any): scala.quoted.Expr[T] =
     val tree = PickledQuotes.unpickleTerm(pickled, fillHole)(using reflect.rootContext)
     new scala.quoted.internal.Expr(tree, hash).asInstanceOf[scala.quoted.Expr[T]]
 
-  def unpickleType[T <: AnyKind](pickled: List[String], fillHole: Seq[Seq[Any] => Any]): scala.quoted.Type[T] =
+  def unpickleType[T <: AnyKind](pickled: List[String], fillHole: Int => Seq[Any] => Any): scala.quoted.Type[T] =
     val tree = PickledQuotes.unpickleTypeTree(pickled, fillHole)(using reflect.rootContext)
     new scala.quoted.internal.Type(tree, hash).asInstanceOf[scala.quoted.Type[T]]
 

library/src/scala/internal/quoted/QuoteContextInternal.scala

@@ -9,12 +9,12 @@ trait QuoteContextInternal { self: QuoteContext =>
   /** Unpickle `repr` which represents a pickled `Expr` tree,
    *  replacing splice nodes with `holes`
    */
-  def unpickleExpr[T](pickled: List[String], fillHole: Seq[Seq[Any] => Any]): scala.quoted.Expr[T]
+  def unpickleExpr[T](pickled: List[String], fillHole: Int => Seq[Any] => Any): scala.quoted.Expr[T]
 
   /** Unpickle `repr` which represents a pickled `Type` tree,
    *  replacing splice nodes with `holes`
    */
-  def unpickleType[T <: AnyKind](pickled: List[String], fillHole: Seq[Seq[Any] => Any]): scala.quoted.Type[T]
+  def unpickleType[T <: AnyKind](pickled: List[String], fillHole: Int => Seq[Any] => Any): scala.quoted.Type[T]
 
   val ExprMatch: ExprMatchModule