[nomerge] SI-8899 Revert "SI-8627 make Stream.filterNot non-eager"

This reverts commit 9276a1205f74fdec74206209712831913e93f359.

The change is not binary compatible, See discussion on SI-8899. Making
filterImpl non-private changes its call-sites (within TraversableLike)
from INVOKESTATIC to INVOKEINTERFACE. Subclasses of TraversableLike
compiled before this change don't have a mixin for filterImpl.

2 files changed, 12 insertions, 14 deletions

diff --git a/src/library/scala/collection/TraversableLike.scala b/src/library/scala/collection/TraversableLike.scala
index a8731a51b1..d3a7db6968 100644
--- a/src/library/scala/collection/TraversableLike.scala
+++ b/src/library/scala/collection/TraversableLike.scala
@@ -253,7 +253,7 @@ trait TraversableLike[+A, +Repr] extends Any
     b.result
   }
 
-  private[scala] def filterImpl(p: A => Boolean, isFlipped: Boolean): Repr = {
+  private def filterImpl(p: A => Boolean, isFlipped: Boolean): Repr = {
     val b = newBuilder
     for (x <- this)
       if (p(x) != isFlipped) b += x
diff --git a/src/library/scala/collection/immutable/Stream.scala b/src/library/scala/collection/immutable/Stream.scala
index 91a4e1c43d..714d5117d3 100644
--- a/src/library/scala/collection/immutable/Stream.scala
+++ b/src/library/scala/collection/immutable/Stream.scala
@@ -499,16 +499,6 @@ self =>
     )
     else super.flatMap(f)(bf)
 
-  override private[scala] def filterImpl(p: A => Boolean, isFlipped: Boolean): Stream[A] = {
-    // optimization: drop leading prefix of elems for which f returns false
-    // var rest = this dropWhile (!p(_)) - forget DRY principle - GC can't collect otherwise
-    var rest = this
-    while (!rest.isEmpty && p(rest.head) == isFlipped) rest = rest.tail
-    // private utility func to avoid `this` on stack (would be needed for the lazy arg)
-    if (rest.nonEmpty) Stream.filteredTail(rest, p, isFlipped)
-    else Stream.Empty
-  }
-
   /** Returns all the elements of this `Stream` that satisfy the predicate `p`
    * in a new `Stream` - i.e., it is still a lazy data structure. The order of
    * the elements is preserved
@@ -522,7 +512,15 @@ self =>
    * // produces
    * }}}
    */
-  override def filter(p: A => Boolean): Stream[A] = filterImpl(p, isFlipped = false) // This override is only left in 2.11 because of binary compatibility, see PR #3925
+  override def filter(p: A => Boolean): Stream[A] = {
+    // optimization: drop leading prefix of elems for which f returns false
+    // var rest = this dropWhile (!p(_)) - forget DRY principle - GC can't collect otherwise
+    var rest = this
+    while (!rest.isEmpty && !p(rest.head)) rest = rest.tail
+    // private utility func to avoid `this` on stack (would be needed for the lazy arg)
+    if (rest.nonEmpty) Stream.filteredTail(rest, p)
+    else Stream.Empty
+  }
 
   override final def withFilter(p: A => Boolean): StreamWithFilter = new StreamWithFilter(p)
 
@@ -1286,8 +1284,8 @@ object Stream extends SeqFactory[Stream] {
     else cons(start, range(start + step, end, step))
   }
 
-  private[immutable] def filteredTail[A](stream: Stream[A], p: A => Boolean, isFlipped: Boolean) = {
-    cons(stream.head, stream.tail.filterImpl(p, isFlipped))
+  private[immutable] def filteredTail[A](stream: Stream[A], p: A => Boolean) = {
+    cons(stream.head, stream.tail filter p)
   }
 
   private[immutable] def collectedTail[A, B, That](head: B, stream: Stream[A], pf: PartialFunction[A, B], bf: CanBuildFrom[Stream[A], B, That]) = {