SI-8627 make Stream.filterNot non-eager

The obvious fix, overriding `filterNot` in Stream, is not binary
compatible, see https://github.com/scala/scala/pull/3925

Instead, this makes `filterImpl` in TaversableLike private[scala],
which allows overriding it in Stream. The corresponding mima-failures
can be whitelisted, as the changes are only to private[scala].

In 2.12.x we can remove the override of `filter` in Stream, but in
2.11.x this is not binary compatible.

Eventually we'd also like to make filter / filterNot in
TraversableLike final, but that's not source compatible, so it cannot
be done in 2.12.x.

1 files changed, 18 insertions, 0 deletions

diff --git a/test/junit/scala/collection/StreamTest.scala b/test/junit/scala/collection/StreamTest.scala
new file mode 100644
index 0000000000..6dc1c79a48
--- /dev/null
+++ b/test/junit/scala/collection/StreamTest.scala
@@ -0,0 +1,18 @@
+package scala.collection.immutable
+
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.junit.Test
+import org.junit.Assert._
+
+@RunWith(classOf[JUnit4])
+class StreamTest {
+
+  @Test
+  def t6727_and_t6440(): Unit = {
+    assertTrue(Stream.continually(()).filter(_ => true).take(2) == Seq((), ()))
+    assertTrue(Stream.continually(()).filterNot(_ => false).take(2) == Seq((), ()))
+    assertTrue(Stream(1,2,3,4,5).filter(_ < 4) == Seq(1,2,3))
+    assertTrue(Stream(1,2,3,4,5).filterNot(_ > 4) == Seq(1,2,3,4))
+  }
+}