Avoid crash where creator proxies are referenced indirectly

Fixes #16095

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -4013,6 +4013,8 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
           cpy.Select(qual)(pre, name.toTypeName)
         case qual: This if qual.symbol.is(ModuleClass) =>
           cpy.Ident(qual)(qual.symbol.name.sourceModuleName.toTypeName)
+        case _ =>
+          errorTree(tree, em"cannot convert to $tree to an instance creation expression")
       val tycon = tree.tpe.widen.finalResultType.underlyingClassRef(refinementOK = false)
       typed(
         untpd.Select(
@@ -4022,7 +4024,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         .showing(i"convert creator $tree -> $result", typr)
 
     def isApplyProxy(tree: Tree) = tree match
-      case Select(_, nme.apply) => tree.symbol.isAllOf(ApplyProxyFlags)
+      case Select(qual, nme.apply) => tree.symbol.isAllOf(ApplyProxyFlags)
       case _ => false
 
     tree match {
@@ -4040,7 +4042,9 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
               adaptOverloaded(ref)
           }
         case poly: PolyType if !(ctx.mode is Mode.Type) =>
-          if isApplyProxy(tree) then newExpr
+          if isApplyProxy(tree) then
+            println(i"converting app proxy $tree")
+            newExpr
           else if pt.isInstanceOf[PolyProto] then tree
           else
             var typeArgs = tree match

tests/neg/i16095.scala

@@ -1,30 +1,16 @@
 package x
 
-import scala.annotation.*
 import scala.concurrent.*
 
-@capability
-class CpsTransform[F[_]] {
-     def await[T](ft: F[T]): { this } T = ???
-}
-
-inline def cpsAsync[F[_]] =
+def cpsAsync[F[_]] =
   Test.InfernAsyncArg
-object Test {
 
+object Test {
   class InfernAsyncArg[F[_]] {
-      def apply[A](expr: CpsTransform[F] ?=> A): F[A] = ???
+    def apply[A](): F[A] = ???
   }
-
-  def asyncPlus[F[_]](a:Int, b:F[Int])(using cps: CpsTransform[F]): { cps } Int =
-    a + cps.await(b)
+  object InfernAsyncArg
 
   def testExample1Future(): Unit =
-     val fr = cpsAsync[Future] {
-        val y = asyncPlus(1,Future successful 2)
-        y+1
-     }
-     val r = Await.result(fr)
-     assert(r == Success(3))
-
+    val fr = cpsAsync[Future]() // error
 }