Fixes SI-6628, Revert "Fix for view isEmpty."

This reverts commit caf7eb6b56817fd1e1fbc1cf017f30e6f94c6bea.

I don't have a better idea right now than wholesale reversion.

10 files changed, 33 insertions, 36 deletions

diff --git a/src/library/scala/collection/IterableLike.scala b/src/library/scala/collection/IterableLike.scala
index 8d1fa80815..540bd84b79 100644
--- a/src/library/scala/collection/IterableLike.scala
+++ b/src/library/scala/collection/IterableLike.scala
@@ -171,7 +171,7 @@ self =>
    *          fewer elements than size.
    */
   def sliding(size: Int): Iterator[Repr] = sliding(size, 1)
-
+  
   /** Groups elements in fixed size blocks by passing a "sliding window"
    *  over them (as opposed to partitioning them, as is done in grouped.)
    *  @see [[scala.collection.Iterator]], method `sliding`
@@ -293,7 +293,6 @@ self =>
 
   override /*TraversableLike*/ def view = new IterableView[A, Repr] {
     protected lazy val underlying = self.repr
-    override def isEmpty = self.isEmpty
     override def iterator = self.iterator
   }
 
diff --git a/src/library/scala/collection/SeqLike.scala b/src/library/scala/collection/SeqLike.scala
index 0ffd99c88c..6871a3cb73 100644
--- a/src/library/scala/collection/SeqLike.scala
+++ b/src/library/scala/collection/SeqLike.scala
@@ -630,7 +630,6 @@ trait SeqLike[+A, +Repr] extends Any with IterableLike[A, Repr] with GenSeqLike[
 
   override def view = new SeqView[A, Repr] {
     protected lazy val underlying = self.repr
-    override def isEmpty = self.isEmpty
     override def iterator = self.iterator
     override def length = self.length
     override def apply(idx: Int) = self.apply(idx)
diff --git a/src/library/scala/collection/TraversableLike.scala b/src/library/scala/collection/TraversableLike.scala
index fc7202b96b..5f193eb211 100644
--- a/src/library/scala/collection/TraversableLike.scala
+++ b/src/library/scala/collection/TraversableLike.scala
@@ -86,7 +86,7 @@ trait TraversableLike[+A, +Repr] extends Any
   def repr: Repr = this.asInstanceOf[Repr]
 
   final def isTraversableAgain: Boolean = true
-
+  
   /** The underlying collection seen as an instance of `$Coll`.
    *  By default this is implemented as the current collection object itself,
    *  but this can be overridden.
@@ -174,7 +174,7 @@ trait TraversableLike[+A, +Repr] extends Any
    *
    *  @usecase def ++:[B](that: TraversableOnce[B]): $Coll[B]
    *    @inheritdoc
-   *
+   * 
    *    Example:
    *    {{{
    *      scala> val x = List(1)
@@ -660,7 +660,6 @@ trait TraversableLike[+A, +Repr] extends Any
   def view = new TraversableView[A, Repr] {
     protected lazy val underlying = self.repr
     override def foreach[U](f: A => U) = self foreach f
-    override def isEmpty = self.isEmpty
   }
 
   /** Creates a non-strict view of a slice of this $coll.
diff --git a/src/library/scala/collection/TraversableViewLike.scala b/src/library/scala/collection/TraversableViewLike.scala
index 0925fe4770..14f865c2f0 100644
--- a/src/library/scala/collection/TraversableViewLike.scala
+++ b/src/library/scala/collection/TraversableViewLike.scala
@@ -59,7 +59,7 @@ trait ViewMkString[+A] {
  *  $viewInfo
  *
  *  All views for traversable collections are defined by creating a new `foreach` method.
- *
+ *  
  *  @author Martin Odersky
  *  @version 2.8
  *  @since   2.8
@@ -162,7 +162,7 @@ trait TraversableViewLike[+A,
 //     if (b.isInstanceOf[NoBuilder[_]]) newFlatMapped(f).asInstanceOf[That]
 //    else super.flatMap[B, That](f)(bf)
   }
-  override def flatten[B](implicit asTraversable: A => /*<:<!!!*/ GenTraversableOnce[B]) =
+  override def flatten[B](implicit asTraversable: A => /*<:<!!!*/ GenTraversableOnce[B]) = 
     newFlatMapped(asTraversable)
   private[this] implicit def asThis(xs: Transformed[A]): This = xs.asInstanceOf[This]
 
@@ -193,15 +193,6 @@ trait TraversableViewLike[+A,
   override def span(p: A => Boolean): (This, This) = (newTakenWhile(p), newDroppedWhile(p))
   override def splitAt(n: Int): (This, This) = (newTaken(n), newDropped(n))
 
-  // Without this, isEmpty tests go back to the Traversable default, which
-  // involves starting a foreach, which can force the first element of the
-  // view. This is just a backstop - it's overridden at all the "def view"
-  // instantiation points in the collections where the Coll type is known.
-  override def isEmpty = underlying match {
-    case x: GenTraversableOnce[_] => x.isEmpty
-    case _                        => super.isEmpty
-  }
-
   override def scanLeft[B, That](z: B)(op: (B, A) => B)(implicit bf: CanBuildFrom[This, B, That]): That =
     newForced(thisSeq.scanLeft(z)(op)).asInstanceOf[That]
 
diff --git a/src/library/scala/collection/immutable/Stream.scala b/src/library/scala/collection/immutable/Stream.scala
index 426ab6f0fb..be2cd91c68 100644
--- a/src/library/scala/collection/immutable/Stream.scala
+++ b/src/library/scala/collection/immutable/Stream.scala
@@ -937,7 +937,6 @@ self =>
 
   override def view = new StreamView[A, Stream[A]] {
     protected lazy val underlying = self.repr
-    override def isEmpty = self.isEmpty
     override def iterator = self.iterator
     override def length = self.length
     override def apply(idx: Int) = self.apply(idx)
diff --git a/src/library/scala/collection/mutable/IndexedSeqLike.scala b/src/library/scala/collection/mutable/IndexedSeqLike.scala
index 21cff70473..f0c31ec7fb 100644
--- a/src/library/scala/collection/mutable/IndexedSeqLike.scala
+++ b/src/library/scala/collection/mutable/IndexedSeqLike.scala
@@ -53,7 +53,6 @@ trait IndexedSeqLike[A, +Repr] extends Any with scala.collection.IndexedSeqLike[
    */
   override def view = new IndexedSeqView[A, Repr] {
     protected lazy val underlying = self.repr
-    override def isEmpty = self.isEmpty
     override def iterator = self.iterator
     override def length = self.length
     override def apply(idx: Int) = self.apply(idx)
diff --git a/src/library/scala/collection/parallel/ParIterableLike.scala b/src/library/scala/collection/parallel/ParIterableLike.scala
index 9825587b0e..0f06ff37af 100644
--- a/src/library/scala/collection/parallel/ParIterableLike.scala
+++ b/src/library/scala/collection/parallel/ParIterableLike.scala
@@ -171,9 +171,9 @@ self: ParIterableLike[T, Repr, Sequential] =>
 
   /** The task support object which is responsible for scheduling and
    *  load-balancing tasks to processors.
-   *
+   *                                                                              
    *  @see [[scala.collection.parallel.TaskSupport]]
-   */
+   */     
   def tasksupport = {
     val ts = _tasksupport
     if (ts eq null) {
@@ -188,18 +188,18 @@ self: ParIterableLike[T, Repr, Sequential] =>
    *  A task support object can be changed in a parallel collection after it
    *  has been created, but only during a quiescent period, i.e. while there
    *  are no concurrent invocations to parallel collection methods.
-   *
-   *  Here is a way to change the task support of a parallel collection:
-   *
-   *  {{{
-   *  import scala.collection.parallel._
-   *  val pc = mutable.ParArray(1, 2, 3)
-   *  pc.tasksupport = new ForkJoinTaskSupport(
-   *    new scala.concurrent.forkjoin.ForkJoinPool(2))
-   *  }}}
+   *                                                                              
+   *  Here is a way to change the task support of a parallel collection:          
+   *                                                                              
+   *  {{{                                                                         
+   *  import scala.collection.parallel._                                          
+   *  val pc = mutable.ParArray(1, 2, 3)                                          
+   *  pc.tasksupport = new ForkJoinTaskSupport(                                   
+   *    new scala.concurrent.forkjoin.ForkJoinPool(2))                            
+   *  }}}                                                                         
    *
    *  @see [[scala.collection.parallel.TaskSupport]]
-   */
+   */     
   def tasksupport_=(ts: TaskSupport) = _tasksupport = ts
 
   def seq: Sequential
@@ -848,7 +848,6 @@ self: ParIterableLike[T, Repr, Sequential] =>
     override def seq = self.seq.view
     def splitter = self.splitter
     def size = splitter.remaining
-    override def isEmpty = size == 0
   }
 
   override def toArray[U >: T: ClassTag]: Array[U] = {
@@ -878,13 +877,13 @@ self: ParIterableLike[T, Repr, Sequential] =>
   override def toSet[U >: T]: immutable.ParSet[U] = toParCollection[U, immutable.ParSet[U]](() => immutable.ParSet.newCombiner[U])
 
   override def toMap[K, V](implicit ev: T <:< (K, V)): immutable.ParMap[K, V] = toParMap[K, V, immutable.ParMap[K, V]](() => immutable.ParMap.newCombiner[K, V])
-
+  
   override def toVector: Vector[T] = to[Vector]
 
   override def to[Col[_]](implicit cbf: CanBuildFrom[Nothing, T, Col[T @uncheckedVariance]]): Col[T @uncheckedVariance] = if (cbf().isCombiner) {
     toParCollection[T, Col[T]](() => cbf().asCombiner)
   } else seq.to(cbf)
-
+  
   /* tasks */
 
   protected trait StrictSplitterCheckTask[R, Tp] extends Task[R, Tp] {
diff --git a/src/library/scala/collection/parallel/ParSeqLike.scala b/src/library/scala/collection/parallel/ParSeqLike.scala
index 4f1c3fa7a2..201b624c72 100644
--- a/src/library/scala/collection/parallel/ParSeqLike.scala
+++ b/src/library/scala/collection/parallel/ParSeqLike.scala
@@ -44,7 +44,7 @@ trait ParSeqLike[+T, +Repr <: ParSeq[T], +Sequential <: Seq[T] with SeqLike[T, S
 extends scala.collection.GenSeqLike[T, Repr]
    with ParIterableLike[T, Repr, Sequential] {
 self =>
-
+  
   type SuperParIterator = IterableSplitter[T]
 
   /** A more refined version of the iterator found in the `ParallelIterable` trait,
@@ -330,7 +330,6 @@ self =>
     def apply(idx: Int) = self(idx)
     override def seq = self.seq.view
     def splitter = self.splitter
-    override def isEmpty = size == 0
   }
 
   /* tasks */
diff --git a/test/files/run/t6628.check b/test/files/run/t6628.check
new file mode 100644
index 0000000000..bb101b641b
--- /dev/null
+++ b/test/files/run/t6628.check
@@ -0,0 +1,2 @@
+true
+true
diff --git a/test/files/run/t6628.scala b/test/files/run/t6628.scala
new file mode 100644
index 0000000000..84524a7a35
--- /dev/null
+++ b/test/files/run/t6628.scala
@@ -0,0 +1,11 @@
+object Test {
+  def coll = new Traversable[String] {
+    override def foreach[U](f:String=>U) { f("1") }
+  }
+  val dropped = coll.view drop 1
+
+  def main(args: Array[String]): Unit = {
+    println(dropped.isEmpty)
+    println(dropped.force.isEmpty)
+  }
+}