Fixes to Unit handling in erasure

1. Erase unit results in getters to BoxedUnit.
2. Erase => Unit to ()Unit; was ()BoxedUnit
3. Make sure ValDefs have same type in tpt as in symbol, analogous to DefDefs.

Author: odersky

src/dotty/tools/dotc/TypeErasure.scala

@@ -4,6 +4,7 @@ package core
 
 import Symbols._, Types._, Contexts._, Flags._, Names._, StdNames._, Decorators._, Flags.JavaDefined
 import dotc.transform.ExplicitOuter._
+import typer.Mode
 import util.DotClass
 
 /** Erased types are:
@@ -89,7 +90,7 @@ object TypeErasure {
 
   /** The current context with a phase no later than erasure */
   private def erasureCtx(implicit ctx: Context) =
-    if (ctx.erasedTypes) ctx.withPhase(ctx.erasurePhase) else ctx
+    if (ctx.erasedTypes) ctx.withPhase(ctx.erasurePhase).addMode(Mode.FutureDefsOK) else ctx
 
   def erasure(tp: Type)(implicit ctx: Context): Type = scalaErasureFn(tp)(erasureCtx)
   def semiErasure(tp: Type)(implicit ctx: Context): Type = semiErasureFn(tp)(erasureCtx)
@@ -141,7 +142,12 @@ object TypeErasure {
     if ((sym eq defn.Any_asInstanceOf) || (sym eq defn.Any_isInstanceOf)) eraseParamBounds(sym.info.asInstanceOf[PolyType])
     else if (sym.isAbstractType) TypeAlias(WildcardType)
     else if (sym.isConstructor) outer.addParam(sym.owner.asClass, erase(tp)(erasureCtx))
-    else eraseInfo(tp)(erasureCtx)
+    else eraseInfo(tp)(erasureCtx) match {
+      case einfo: MethodType if sym.isGetter && einfo.resultType.isRef(defn.UnitClass) =>
+        defn.BoxedUnitClass.typeRef
+      case einfo =>
+        einfo
+    }
   }
 
   def isUnboundedGeneric(tp: Type)(implicit ctx: Context) = !(
@@ -319,7 +325,7 @@ class TypeErasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wild
   }
 
   def eraseInfo(tp: Type)(implicit ctx: Context) = tp match {
-    case ExprType(rt) => MethodType(Nil, Nil, erasure(rt))
+    case ExprType(rt) => MethodType(Nil, Nil, eraseResult(rt))
     case tp => erasure(tp)
   }
 

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

@@ -247,6 +247,10 @@ object Erasure extends TypeTestsCasts{
       tree.withType(erased)
     }
 
+    override def typedLiteral(tree: untpd.Literal)(implicit ctc: Context): Literal =
+      if (tree.typeOpt.isRef(defn.UnitClass)) tree.withType(tree.typeOpt)
+      else super.typedLiteral(tree)
+
     /** Type check select nodes, applying the following rewritings exhaustively
      *  on selections `e.m`, where `OT` is the type of the owner of `m` and `ET`
      *  is the erased type of the selection's original qualifier expression.
@@ -369,12 +373,20 @@ object Erasure extends TypeTestsCasts{
       }
     }
 
+    override def typedValDef(vdef: untpd.ValDef, sym: Symbol)(implicit ctx: Context): ValDef =
+      super.typedValDef(untpd.cpy.ValDef(vdef)(
+        tpt = untpd.TypedSplice(TypeTree(sym.info).withPos(vdef.tpt.pos))), sym)
+
     override def typedDefDef(ddef: untpd.DefDef, sym: Symbol)(implicit ctx: Context) = {
+      val restpe = sym.info.resultType
       val ddef1 = untpd.cpy.DefDef(ddef)(
         tparams = Nil,
         vparamss = ddef.vparamss.flatten :: Nil,
-        tpt = // keep UnitTypes intact in result position
-          untpd.TypedSplice(TypeTree(eraseResult(ddef.tpt.typeOpt)).withPos(ddef.tpt.pos)))
+        tpt = untpd.TypedSplice(TypeTree(restpe).withPos(ddef.tpt.pos)),
+        rhs = ddef.rhs match {
+          case id @ Ident(nme.WILDCARD) => untpd.TypedSplice(id.withType(restpe))
+          case _ => ddef.rhs
+        })
       super.typedDefDef(ddef1, sym)
     }