SI-4332 Plugs the gaps in views

These currently result in runtime errors:

    scala> List(1).view.distinct.force
    java.lang.UnsupportedOperationException: SeqView(...).newBuilder

    scala> List(1).view.inits.toList
    java.lang.UnsupportedOperationException: SeqView(...).newBuilder

Two tests are enclosed:

  1. reflect on the views to make any method that returns
     `Repr` is overriden in `*ViewLike`. This guards against
     new additions to the collections API.
  2. exercise the newly added overrides

Some care is needed with `tail`, we must re-override it
in `mutable.IndexedSeqView` to be explicit about the
end point of the slice, because the `IndexedSeqView#Sliced`
defines length in terms of that. (Higher up the chain, it
is just `iterator.size`, that's why `SeqView#tail` just sets
up a slice from `1 to Int.MaxValue`.)

Parallel collections views are not touched, as these are likely
to be deprecated or removed shortly.

Before this change, the test reported the following.
Not all of these methods were buggy. For instance, `sortBy`,
`sortWith` are implemented in terms of `sorted` which
was implemented in `SeqViewLike`. Even in those cases, I have
opted to override the methods in the `ViewLike` to guard
against changes in the base class implementation and to
simplify the rules in the test.

    ======================================================================
    Checking scala.collection.TraversableView
    ======================================================================

    trait TraversableLike
    ----------------------------------------------------------------------
    def filterNot(p: A => Boolean): Repr
    def inits: Iterator[Repr]
    def tails: Iterator[Repr]
    override def tail: Repr

    ======================================================================
    Checking scala.collection.IterableView
    ======================================================================

    trait IterableLike
    ----------------------------------------------------------------------
    def dropRight(n: Int): Repr
    def sliding(size: Int): Iterator[Repr]
    def takeRight(n: Int): Repr

    trait TraversableLike
    ----------------------------------------------------------------------
    def filterNot(p: A => Boolean): Repr
    def inits: Iterator[Repr]
    def tails: Iterator[Repr]
    override def tail: Repr

    ======================================================================
    Checking scala.collection.SeqView
    ======================================================================

    trait IterableLike
    ----------------------------------------------------------------------
    def dropRight(n: Int): Repr
    def sliding(size: Int): Iterator[Repr]
    def takeRight(n: Int): Repr

    trait SeqLike
    ----------------------------------------------------------------------
    def combinations(n: Int): Iterator[Repr]
    def distinct: Repr
    def permutations: Iterator[Repr]
    def sortBy[B](f: A => B)(implicit ord: scala.math.Ordering[B]): Repr
    def sortWith(lt: (A, A) => Boolean): Repr

    trait TraversableLike
    ----------------------------------------------------------------------
    def filterNot(p: A => Boolean): Repr
    def inits: Iterator[Repr]
    def tails: Iterator[Repr]
    override def tail: Repr

    ======================================================================
    Checking scala.collection.mutable.IndexedSeqView
    ======================================================================

    trait IndexedSeqOptimized
    ----------------------------------------------------------------------
    override def dropRight(n: Int): Repr
    override def tail: Repr
    override def takeRight(n: Int): Repr

    trait IterableLike
    ----------------------------------------------------------------------
    def sliding(size: Int): Iterator[Repr]

    trait SeqLike
    ----------------------------------------------------------------------
    def combinations(n: Int): Iterator[Repr]
    def distinct: Repr
    def permutations: Iterator[Repr]
    def sortBy[B](f: A => B)(implicit ord: scala.math.Ordering[B]): Repr
    def sortWith(lt: (A, A) => Boolean): Repr

    trait TraversableLike
    ----------------------------------------------------------------------
    def filterNot(p: A => Boolean): Repr
    def inits: Iterator[Repr]
    def tails: Iterator[Repr]

    ======================================================================
    Checking scala.collection.immutable.StreamView
    ======================================================================

    trait IterableLike
    ----------------------------------------------------------------------
    def dropRight(n: Int): Repr
    def sliding(size: Int): Iterator[Repr]
    def takeRight(n: Int): Repr

    trait SeqLike
    ----------------------------------------------------------------------
    def combinations(n: Int): Iterator[Repr]
    def distinct: Repr
    def permutations: Iterator[Repr]
    def sortBy[B](f: A => B)(implicit ord: scala.math.Ordering[B]): Repr
    def sortWith(lt: (A, A) => Boolean): Repr

    trait TraversableLike
    ----------------------------------------------------------------------
    def filterNot(p: A => Boolean): Repr
    def inits: Iterator[Repr]
    def tails: Iterator[Repr]
    override def tail: Repr

Author: retronym

src/library/scala/collection/IterableViewLike.scala

@@ -117,5 +117,14 @@ trait IterableViewLike[+A,
   override def sliding(size: Int, step: Int): Iterator[This] =
     self.iterator.sliding(size, step) map (x => newForced(x).asInstanceOf[This])
 
+  override def sliding(size: Int): Iterator[This] =
+    sliding(size, 1) // we could inherit this, but that implies knowledge of the way the super class is implemented.
+
+  override def dropRight(n: Int): This =
+    take(thisSeq.length - n)
+
+  override def takeRight(n: Int): This =
+    drop(thisSeq.length - n)
+
   override def stringPrefix = "IterableView"
 }

src/library/scala/collection/SeqViewLike.scala

@@ -137,5 +137,20 @@ trait SeqViewLike[+A,
   override def sorted[B >: A](implicit ord: Ordering[B]): This =
     newForced(thisSeq sorted ord).asInstanceOf[This]
 
+  override def sortWith(lt: (A, A) => Boolean): This =
+    newForced(thisSeq sortWith lt).asInstanceOf[This]
+
+  override def sortBy[B](f: (A) => B)(implicit ord: Ordering[B]): This =
+    newForced(thisSeq sortBy f).asInstanceOf[This]
+
+  override def combinations(n: Int): Iterator[This] =
+    (thisSeq combinations n).map(as => newForced(as).asInstanceOf[This])
+
+  override def permutations: Iterator[This] =
+    thisSeq.permutations.map(as => newForced(as).asInstanceOf[This])
+
+  override def distinct: This =
+    newForced(thisSeq.distinct).asInstanceOf[This]
+
   override def stringPrefix = "SeqView"
 }

src/library/scala/collection/TraversableViewLike.scala

@@ -209,5 +209,18 @@ trait TraversableViewLike[+A,
   override def unzip3[A1, A2, A3](implicit asTriple: A => (A1, A2, A3)) =
     (newMapped(x => asTriple(x)._1), newMapped(x => asTriple(x)._2), newMapped(x => asTriple(x)._3))  // TODO - Performance improvements.
 
+  override def filterNot(p: (A) => Boolean): This =
+    newFiltered(a => !(p(a)))
+
+  override def inits: Iterator[This] =
+    thisSeq.inits.map(as => newForced(as).asInstanceOf[This])
+
+  override def tails: Iterator[This] =
+    thisSeq.tails.map(as => newForced(as).asInstanceOf[This])
+
+  override def tail: This =
+    // super.tail would also work as it is currently implemented in terms of drop(Int).
+    if (isEmpty) super.tail else newDropped(1)
+
   override def toString = viewToString
 }

src/library/scala/collection/mutable/IndexedSeqView.scala

@@ -93,6 +93,7 @@ self =>
   override def span(p: A => Boolean): (This, This) = (newTakenWhile(p), newDroppedWhile(p))
   override def splitAt(n: Int): (This, This) = (take(n), drop(n)) // !!!
   override def reverse: This = newReversed
+  override def tail: IndexedSeqView[A, Coll] = if (isEmpty) super.tail else slice(1, length)
 }
 
 /** An object containing the necessary implicit definitions to make

test/files/run/t4332.check

@@ -0,0 +1,25 @@
+
+======================================================================
+Checking scala.collection.TraversableView
+======================================================================
+
+
+======================================================================
+Checking scala.collection.IterableView
+======================================================================
+
+
+======================================================================
+Checking scala.collection.SeqView
+======================================================================
+
+
+======================================================================
+Checking scala.collection.mutable.IndexedSeqView
+======================================================================
+
+
+======================================================================
+Checking scala.collection.immutable.StreamView
+======================================================================
+

test/files/run/t4332.scala

@@ -0,0 +1,44 @@
+import scala.tools.partest._
+
+object Test extends DirectTest {
+  override def code = ""
+  lazy val global = newCompiler("-usejavacp")
+  import global._, definitions._
+
+  override def show() {
+    new global.Run()
+    // Once we plug all of the view gaps, the output should be empty!
+    checkViews()
+  }
+
+  def isExempt(sym: Symbol) = {
+    val exempt = Set("view", "repr", "sliceWithKnownDelta", "sliceWithKnownBound", "transform")
+    (exempt contains sym.name.decoded)
+  }
+
+  def checkView(viewType: Type, viewLikeType: Type) {
+    val sep = "=" * 70
+    println(s"\n$sep\nChecking ${viewType.typeSymbol.fullName}\n$sep")
+    val termMembers = viewType.nonPrivateMembers.toList filter (_.isTerm) map fullyInitializeSymbol
+    val inheritedFromGenericCollection
+      = termMembers filterNot (_.owner.name.decoded contains "ViewLike") filterNot (_.owner == viewType.typeSymbol)
+    def returnsView(sym: Symbol) = viewType.memberType(sym).finalResultType contains viewType.typeSymbol
+    val needOverride = inheritedFromGenericCollection filterNot isExempt filter returnsView
+
+    val grouped = needOverride.groupBy(_.owner).toSeq.sortBy { case (owner, _) => viewType baseTypeIndex owner }
+    val report = grouped.map {
+      case (owner, syms) => s"\n$owner\n${"-" * 70}\n${syms.map(_.defString).sorted.mkString("\n")}"
+    }.mkString("\n")
+    println(report)
+  }
+
+  def checkViews() {
+    import collection._
+    checkView(typeOf[TraversableView[_, _]],        typeOf[TraversableViewLike[_, _, _]])
+    checkView(typeOf[IterableView[_, _]],           typeOf[IterableViewLike[_, _, _]])
+    checkView(typeOf[SeqView[_, _]],                typeOf[SeqViewLike[_, _, _]])
+    checkView(typeOf[mutable.IndexedSeqView[_, _]], typeOf[SeqViewLike[_, _, _]])
+    checkView(typeOf[immutable.StreamView[_, _]],   typeOf[immutable.StreamViewLike[_, _, _]])
+    // Parallel views not checked, assuming we will drop them in 2.11
+  }
+}

test/files/run/t4332b.scala

@@ -0,0 +1,35 @@
+object Test extends App {
+  def check(expected: Any, actual: Any, msg: String = "") = {
+    if (expected != actual)
+      sys.error(s"($actual != $expected) $msg")
+  }
+  val ls = List(1, 3, 2, 1)
+  for (N <- -1 to (ls.length + 1)) {
+    check(ls.takeRight(N), ls.view.takeRight(N).toList, s"takeRight($N)")
+    check(ls.dropRight(N), ls.view.dropRight(N).toList, s"dropRight($N)")
+  }
+  for (N <- 1 to (ls.length + 1)) {
+    check(ls.sliding(N).toList, ls.view.sliding(N).toList.map(_.toList), s"sliding($N)")
+    check(ls.sliding(N, 2).toList, ls.view.sliding(N, 2).toList.map(_.toList), s"sliding($N, 2)")
+  }
+  for (b <- List(true, false))
+    check(ls.filterNot(x => true), ls.view.filterNot(x => true), s"filterNot($b)")
+
+  check(ls.inits.toList, ls.view.inits.toList.map(_.toList), "inits")
+  check(ls.tails.toList, ls.view.tails.toList.map(_.toList), "tails")
+
+  check(ls.combinations(2).toList.map(_.toList), ls.view.combinations(2).toList.map(_.toList), "combinations(2)")
+  check(ls.permutations.toList.map(_.toList), ls.view.permutations.toList.map(_.toList), "permutations")
+
+  check(ls.sortBy(_ * -1), ls.view.sortBy(_ * -1).toList, "sortBy")
+  check(ls.sortWith((x, y) => y < x), ls.view.sortWith((x, y) => y < x).toList, "sortWith")
+  check(ls.sorted, ls.view.sorted.toList, "sorted")
+
+  check(ls.distinct, ls.view.distinct.toList, "distinct")
+
+  check(ls.tail, ls.view.tail.toList, "tail")  
+
+  import collection.mutable.Buffer
+  check(Buffer(1, 2, 3).tail, Buffer(1, 2, 3).view.tail.toList, "Buffer#tail")  
+  check(Buffer(1, 2, 3).tail.length, Buffer(1, 2, 3).view.tail.length, "Buffer#tail#length")  
+}