Use ??? instead of defaultValue for erased code

Author: odersky

compiler/src/dotty/tools/dotc/transform/PostTyper.scala

@@ -207,7 +207,7 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
               tpd.cpy.Apply(tree)(
                 tree.fun,
                 tree.args.map(arg =>
-                  if (methType.isImplicitMethod && arg.pos.isSynthetic) defaultValue(arg.tpe)
+                  if (methType.isImplicitMethod && arg.pos.isSynthetic) ref(defn.Predef_undefined)
                   else dropInlines.transform(arg)))
             else
               tree

compiler/src/dotty/tools/dotc/transform/CutErasedDecls.scala renamed to compiler/src/dotty/tools/dotc/transform/PruneErasedDecls.scala

@@ -6,6 +6,7 @@ import Contexts._
 import DenotTransformers.SymTransformer
 import Flags._
 import SymDenotations._
+import Symbols._
 import Types._
 import typer.RefChecks
 import MegaPhase.MiniPhase
@@ -36,17 +37,17 @@ class CutErasedDecls extends MiniPhase with SymTransformer { thisTransform =>
 
   override def transformApply(tree: Apply)(implicit ctx: Context) =
     if (tree.fun.tpe.widen.isErasedMethod)
-      cpy.Apply(tree)(tree.fun, tree.args.map(arg => defaultValue(arg.tpe)))
+      cpy.Apply(tree)(tree.fun, tree.args.map(arg => ref(defn.Predef_undefined)))
     else tree
 
   override def transformValDef(tree: ValDef)(implicit ctx: Context) =
     if (tree.symbol.is(Erased) && !tree.rhs.isEmpty)
-      cpy.ValDef(tree)(rhs = defaultValue(tree.rhs.tpe))
+      cpy.ValDef(tree)(rhs = ref(defn.Predef_undefined))
     else tree
 
   override def transformDefDef(tree: DefDef)(implicit ctx: Context) =
     if (tree.symbol.is(Erased) && !tree.rhs.isEmpty)
-      cpy.DefDef(tree)(rhs = defaultValue(tree.rhs.tpe))
+      cpy.DefDef(tree)(rhs = ref(defn.Predef_undefined))
     else tree
 }
 object CutErasedDecls {