Fix for problem in SBT that was caused by the too severe fix of type soundness problem t5120.

2 files changed, 17 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index b4221365be..f057d1e7be 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -2835,9 +2835,22 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
     def packSymbols(hidden: List[Symbol], tp: Type): Type =
       if (hidden.isEmpty) tp
       else existentialTransform(hidden, tp)(existentialAbstraction)
+      
+    def isReferencedFrom(ctx: Context, sym: Symbol): Boolean =
+      ctx.owner.isTerm && 
+      (ctx.scope.exists { dcl => dcl.isInitialized && (dcl.info contains sym) }) || 
+      {
+        var ctx1 = ctx.outer
+        while ((ctx1 != NoContext) && (ctx1.scope eq ctx.scope)) ctx1 = ctx1.outer
+        (ctx1 != NoContext) && isReferencedFrom(ctx1, sym)
+      }
 
     def isCapturedExistential(sym: Symbol) =
-      sym hasAllFlags (EXISTENTIAL | CAPTURED)  // todo refine this
+      (sym hasAllFlags (EXISTENTIAL | CAPTURED)) && {
+      val start = startTimer(isReferencedNanos)
+      try !isReferencedFrom(context, sym)
+      finally stopTimer(isReferencedNanos, start)
+    }
 
     def packCaptured(tpe: Type): Type = {
       val captured = mutable.Set[Symbol]()
diff --git a/src/compiler/scala/tools/nsc/util/Statistics.scala b/src/compiler/scala/tools/nsc/util/Statistics.scala
index 27239b9b9f..f7c27dceb5 100644
--- a/src/compiler/scala/tools/nsc/util/Statistics.scala
+++ b/src/compiler/scala/tools/nsc/util/Statistics.scala
@@ -20,7 +20,7 @@ class Statistics extends scala.reflect.internal.util.Statistics {
   val typedSelectCount = new Counter
   val typerNanos = new Timer
   val classReadNanos = new Timer
-
+  
   val failedApplyNanos = new Timer
   val failedOpEqNanos = new Timer
   val failedSilentNanos = new Timer
@@ -48,6 +48,7 @@ class Statistics extends scala.reflect.internal.util.Statistics {
   val subtypeImprovCount = new SubCounter(subtypeCount)
   val subtypeETNanos = new Timer
   val matchesPtNanos = new Timer
+  val isReferencedNanos = new Timer
   val ctr1 = new Counter
   val ctr2 = new Counter
   val ctr3 = new Counter
@@ -137,6 +138,7 @@ abstract class StatisticsInfo {
         inform("time spent in failed     : "+showRelTyper(failedSilentNanos))
         inform("       failed apply      : "+showRelTyper(failedApplyNanos))
         inform("       failed op=        : "+showRelTyper(failedOpEqNanos))
+        inform("time spent ref scanning  : "+showRelTyper(isReferencedNanos))
         inform("micros by tree node      : "+showCounts(microsByType))
         inform("#visits by tree node     : "+showCounts(visitsByType))
         val average = new ClassCounts