Fix wrong staging level error message

The tests were failing when the code was correct. The wrong message was
```
access to parameter t from wrong staging level:
  - the definition is at level 0,
  - but the access is at level -1.
```
The access to `t.Underlying` or `t.x.Underlying` are fine when we have
an implicit `Type.of[t.Underlying]` or `Type.of[t.x.Underlying]`. These
will probably be of the type of the aliased type of `A`, wherefore
summoning `Type.of[A]`.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/staging/CrossStageSafety.scala

@@ -92,6 +92,8 @@ class CrossStageSafety extends TreeMapWithStages {
       case tree: TypeDef if tree.symbol.is(Case) && level > 0 =>
         report.error(reporting.CaseClassInInlinedCode(tree), tree)
         super.transform(tree)
+      case tree @ SplicedType(splicedTree) =>
+        transformSpliceType(splicedTree, tree)
       case _ =>
         super.transform(tree)
     }
@@ -151,7 +153,7 @@ class CrossStageSafety extends TreeMapWithStages {
     untpd.cpy.Splice(splice)(body1).withType(tpe1)
   }
 
-  protected def transformSpliceType(body: Tree, splice: Select)(using Context): Tree = {
+  private def transformSpliceType(body: Tree, splice: Select)(using Context): Tree = {
     val body1 = transform(body)(using spliceContext)
     if ctx.reporter.hasErrors then
       splice

compiler/src/dotty/tools/dotc/staging/TreeMapWithStages.scala

@@ -33,9 +33,6 @@ abstract class TreeMapWithStages extends TreeMapWithImplicits {
   /** Transform the expression splice `splice` which contains the spliced `body`. */
   protected def transformSplice(body: Tree, splice: Splice)(using Context): Tree
 
-  /** Transform the type splice `splice` which contains the spliced `body`. */
-  protected def transformSpliceType(body: Tree, splice: Select)(using Context): Tree
-
   override def transform(tree: Tree)(using Context): Tree =
     if (tree.source != ctx.source && tree.source.exists)
       transform(tree)(using ctx.withSource(tree.source))
@@ -67,9 +64,6 @@ abstract class TreeMapWithStages extends TreeMapWithImplicits {
               transformSplice(splicedTree, tree)
           }
 
-        case tree @ SplicedType(splicedTree) =>
-          transformSpliceType(splicedTree, tree)
-
         case Block(stats, _) =>
           val defSyms = stats.collect { case defTree: DefTree => defTree.symbol }
           super.transform(tree)(using symbolsInCurrentLevel(defSyms))

tests/neg-macros/i10127-a.scala

@@ -1,7 +1,7 @@
 import scala.quoted.*
 
 object T {
-  def impl[A](using t: Type[A])(using Quotes): Expr[Unit] = {
+  def impl[A](t: Type[A])(using Quotes): Expr[Unit] = {
     Expr.summon[t.Underlying] // error
     '{}
   }

tests/neg-macros/i10127-b.scala

@@ -4,7 +4,7 @@ case class T(x: Type[_ <: Any])
 
 object T {
   def impl[A](t: T)(using ctx: Quotes): Expr[Unit] = {
-    Expr.summon[t.x.Underlying] // error // error
+    Expr.summon[t.x.Underlying] // error
     '{}
   }
 }

tests/pos-macros/i10127-a.scala

@@ -0,0 +1,8 @@
+import scala.quoted.*
+
+object T {
+  def impl[A](using t: Type[A])(using Quotes): Expr[Unit] = {
+    Expr.summon[t.Underlying]
+    '{}
+  }
+}