Additional tests and comments around mkZero for value classes

1 files changed, 11 insertions, 1 deletions

diff --git a/src/main/scala/scala/async/internal/TransformUtils.scala b/src/main/scala/scala/async/internal/TransformUtils.scala
index da70f68..9ae48ed 100644
--- a/src/main/scala/scala/async/internal/TransformUtils.scala
+++ b/src/main/scala/scala/async/internal/TransformUtils.scala
@@ -333,10 +333,20 @@ private[async] trait TransformUtils {
   def mkZero(tp: Type): Tree = {
     if (tp.typeSymbol.asClass.isDerivedValueClass) {
       val argZero = mkZero(derivedValueClassUnbox(tp.typeSymbol).infoIn(tp).resultType)
+      val baseType = tp.baseType(tp.typeSymbol) // use base type here to dealias / strip phantom "tagged types" etc.
+
+      // By explicitly attributing the types and symbols here, we subvert privacy.
+      // Otherwise, ticket86PrivateValueClass would fail.
+
+      // Approximately:
+      // q"new ${valueClass}[$..targs](argZero)"
       val target: Tree = gen.mkAttributedSelect(
         c.typecheck(atMacroPos(
-        New(TypeTree(tp.baseType(tp.typeSymbol))))), tp.typeSymbol.asClass.primaryConstructor)
+        New(TypeTree(baseType)))), tp.typeSymbol.asClass.primaryConstructor)
+
       val zero = gen.mkMethodCall(target, argZero :: Nil)
+
+      // restore the original type which we might otherwise have weakened with `baseType` above
       gen.mkCast(zero, tp)
     } else {
       gen.mkZero(tp)