Most of the iterate implementations were callin...

Most of the iterate implementations were calling the given function one
too many times, leading to tragic failure if the function could not
handle this (such as repeatedly applying tail.) Closes #3540, review by
prokopec.

3 files changed, 28 insertions, 12 deletions

diff --git a/src/library/scala/Array.scala b/src/library/scala/Array.scala
index 9712990d73..250fd09602 100644
--- a/src/library/scala/Array.scala
+++ b/src/library/scala/Array.scala
@@ -363,13 +363,18 @@ object Array extends FallbackArrayBuilding {
    */
   def iterate[T: ClassManifest](start: T, len: Int)(f: T => T): Array[T] = {
     val b = newBuilder[T]
-    b.sizeHint(len)
-    var acc = start
-    var i = 0
-    while (i < len) {
+
+    if (len > 0) {
+      b.sizeHint(len)
+      var acc = start
+      var i = 1
       b += acc
-      acc = f(acc)
-      i += 1
+
+      while (i < len) {
+        acc = f(acc)
+        i += 1
+        b += acc
+      }
     }
     b.result
   }
diff --git a/src/library/scala/collection/generic/TraversableFactory.scala b/src/library/scala/collection/generic/TraversableFactory.scala
index d8541d2714..c6f5ce4dde 100644
--- a/src/library/scala/collection/generic/TraversableFactory.scala
+++ b/src/library/scala/collection/generic/TraversableFactory.scala
@@ -224,13 +224,17 @@ abstract class TraversableFactory[CC[X] <: Traversable[X] with GenericTraversabl
    */
   def iterate[A](start: A, len: Int)(f: A => A): CC[A] = {
     val b = newBuilder[A]
-    b.sizeHint(len)
-    var acc = start
-    var i = 0
-    while (i < len) {
+    if (len > 0) {
+      b.sizeHint(len)
+      var acc = start
+      var i = 1
       b += acc
-      acc = f(acc)
-      i += 1
+
+      while (i < len) {
+        acc = f(acc)
+        i += 1
+        b += acc
+      }
     }
     b.result
   }
diff --git a/test/files/run/bug3540.scala b/test/files/run/bug3540.scala
new file mode 100644
index 0000000000..5ffacb5dff
--- /dev/null
+++ b/test/files/run/bug3540.scala
@@ -0,0 +1,7 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    assert(List.iterate(List(1,2,3), 4)(_.tail).last.isEmpty)
+    assert(Stream.iterate(Stream(1,2,3), 4)(_.tail).last.isEmpty)
+    assert(Array.iterate(Array(1,2,3), 4)(_.tail).last.isEmpty)
+  }
+}