Merge pull request #1181 from Blaisorblade/topic/2.9.x-stream-const-space

Backport "Make Stream.withFilter.{map,flatMap} run in constant stack space" against 2.9.x

1 files changed, 44 insertions, 0 deletions

diff --git a/test/files/run/stream-stack-overflow-filter-map.scala b/test/files/run/stream-stack-overflow-filter-map.scala
new file mode 100644
index 0000000000..f3a9dd49cb
--- /dev/null
+++ b/test/files/run/stream-stack-overflow-filter-map.scala
@@ -0,0 +1,44 @@
+import collection.generic.{FilterMonadic, CanBuildFrom}
+
+object Test extends App {
+  def mapSucc[Repr, That](s: FilterMonadic[Int, Repr])(implicit cbf: CanBuildFrom[Repr, Int, That]) = s map (_ + 1)
+  def flatMapId[T, Repr, That](s: FilterMonadic[T, Repr])(implicit cbf: CanBuildFrom[Repr, T, That]) = s flatMap (Seq(_))
+
+  def testStreamPred(s: Stream[Int])(p: Int => Boolean) {
+    val res1 = s withFilter p
+    val res2 = s filter p
+
+    val expected = s.toSeq filter p
+
+    val fMapped1 = flatMapId(res1)
+    val fMapped2 = flatMapId(res2)
+    assert(fMapped1 == fMapped2)
+    assert(fMapped1.toSeq == expected)
+
+    val mapped1 = mapSucc(res1)
+    val mapped2 = mapSucc(res2)
+    assert(mapped1 == mapped2)
+    assert(mapped1.toSeq == (expected map (_ + 1)))
+
+    assert((res1 map identity).toSeq == res2.toSeq)
+  }
+
+  def testStream(s: Stream[Int]) {
+    testStreamPred(s)(_ => false)
+    testStreamPred(s)(_ => true)
+    testStreamPred(s)(_ % 2 == 0)
+    testStreamPred(s)(_ % 3 == 0)
+  }
+
+  //Reduced version of the test case - either invocation used to cause a stack
+  //overflow before commit 80b3f433e5536d086806fa108ccdfacf10719cc2.
+  val resFMap = (1 to 10000).toStream withFilter (_ => false) flatMap (Seq(_))
+  val resMap = (1 to 10000).toStream withFilter (_ => false) map (_ + 1)
+
+  //Complete test case for withFilter + map/flatMap, as requested by @axel22.
+  for (j <- (0 to 3) :+ 10000) {
+    val stream = (1 to j).toStream
+    assert(stream.toSeq == (1 to j).toSeq)
+    testStream(stream)
+  }
+}