Make ensureMethodic work after erasure.

Previously it didn't, because it created an ExprType, which is
illegal after erasure.

Author: odersky

src/dotty/tools/dotc/core/TypeErasure.scala

@@ -164,7 +164,7 @@ object TypeErasure {
     else if (sym.isConstructor) outer.addParam(sym.owner.asClass, erase(tp)(erasureCtx))
     else erase.eraseInfo(tp, sym)(erasureCtx) match {
       case einfo: MethodType if sym.isGetter && einfo.resultType.isRef(defn.UnitClass) =>
-        MethodType(Nil, Nil, defn.BoxedUnitClass.typeRef)
+        MethodType(Nil, defn.BoxedUnitClass.typeRef)
       case einfo =>
         einfo
     }

src/dotty/tools/dotc/transform/TypeUtils.scala

@@ -29,6 +29,6 @@ class TypeUtils(val self: Type) extends AnyVal {
 
   def ensureMethodic(implicit ctx: Context): Type = self match {
     case self: MethodicType => self
-    case _ => ExprType(self)
+    case _ => if (ctx.erasedTypes) MethodType(Nil, self) else ExprType(self)
   }
 }