Disallow ill-staged references to local classes

Fixes #19856

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

@@ -47,7 +47,10 @@ class HealType(pos: SrcPos)(using Context) extends TypeMap {
         checkNotWildcardSplice(tp)
         if level == 0 then tp else getTagRef(prefix)
       case _: TermRef | _: ThisType | NoPrefix =>
-        if levelInconsistentRootOfPath(tp).exists then
+        val inconsistentRoot = levelInconsistentRootOfPath(tp)
+        if inconsistentRoot.isClass && inconsistentRoot.isLocal then
+          levelError(inconsistentRoot, tp, pos)
+        else if inconsistentRoot.exists then
           tryHeal(tp)
         else
           tp

tests/neg-macros/i19856.scala

@@ -0,0 +1,9 @@
+import scala.quoted.*
+
+def test(using Quotes): Any =
+  class Foo {
+    class IdxWrapper
+    def foo(using Type[IdxWrapper]): Expr[Any] =
+      '{ new IdxWrapper } // error
+  }
+  ()

tests/neg-macros/i19856b.scala

@@ -0,0 +1,34 @@
+import scala.deriving.Mirror
+import scala.quoted.{Expr, Quotes, Type}
+
+trait macroTest[A] {
+  type ElemTop <: A
+  type Index[_]
+
+  case class IdxWrapper[X](idx: Index[X])
+
+  def indexOf[X <: ElemTop: Type](x: Expr[X]): Expr[Index[X]]
+
+  def indexOfA(a: Expr[A]): Expr[IdxWrapper[_ <: ElemTop]]
+}
+object macroTest {
+
+  def derivedImpl[A: Type, ElemTypes <: Tuple: Type, Label <: String: Type, Labels <: Tuple: Type](
+      using m: Expr[
+        Mirror.SumOf[A] {
+          type MirroredElemTypes  = ElemTypes
+          type MirroredLabel      = Label
+          type MirroredElemLabels = Labels
+        }
+      ],
+      q: Quotes,
+  ): macroTest[A] = new macroTest[A]:
+    override type Index[_] = Int
+
+    override def indexOf[X <: ElemTop: Type](x: Expr[X]): Expr[Index[X]] = '{ $m.ordinal($x) }
+
+    override def indexOfA(a: Expr[A]): Expr[IdxWrapper[_ <: ElemTop]] =
+      given Type[IdxWrapper] = Type.of[IdxWrapper] // error
+      given Type[ElemTop] = Type.of[ElemTop] // error
+      '{ new IdxWrapper(${ indexOf(a.asInstanceOf[Expr[ElemTop]]) }) } // error // error
+}