Avoid taking references before toplevel symbols are entered.

Taking a reference means that the symbol will be brought forward into the current run,
then if the same symbol is entered from source, a datarace ensues.

This affected the ProductN symbols because these are automatically added to a case class
suring desugaring.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/dotty/tools/dotc/ast/untpd.scala b/src/dotty/tools/dotc/ast/untpd.scala
index 3f3e1bf37..28a3cf1ff 100644
--- a/src/dotty/tools/dotc/ast/untpd.scala
+++ b/src/dotty/tools/dotc/ast/untpd.scala
@@ -201,7 +201,9 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   def ref(tp: NamedType)(implicit ctx: Context): Tree =
     TypedSplice(tpd.ref(tp))
 
-  def scalaUnit(implicit ctx: Context) = ref(defn.UnitType)
+  def rootDot(name: Name) = Select(Ident(nme.ROOTPKG), name)
+  def scalaDot(name: Name) = Select(rootDot(nme.scala_), name)
+  def scalaUnit = scalaDot(tpnme.Unit)
 
   def makeConstructor(tparams: List[TypeDef], vparamss: List[List[ValDef]], rhs: Tree = EmptyTree)(implicit ctx: Context): DefDef =
     DefDef(nme.CONSTRUCTOR, tparams, vparamss, TypeTree(), rhs)