SI-6519 PagedSeq is not lazy enough

This was actually an issue with `length` of all things--it wasn't stopping scanning when it was past the end of what was requested.  It'd just gratuitously read everything.

Also fixed an overflow bug with isDefinedAt along the way (start + index > Int.MaxValue would always return true despite never working).

1 files changed, 15 insertions, 3 deletions

diff --git a/test/junit/scala/collection/immutable/PagedSeqTest.scala b/test/junit/scala/collection/immutable/PagedSeqTest.scala
index 5f83cf6f31..2b576a3655 100644
--- a/test/junit/scala/collection/immutable/PagedSeqTest.scala
+++ b/test/junit/scala/collection/immutable/PagedSeqTest.scala
@@ -5,12 +5,24 @@ import org.junit.runners.JUnit4
 import org.junit.Test
 import org.junit.Assert._
 
-/* Test for SI-6615  */
 @RunWith(classOf[JUnit4])
 class PagedSeqTest {
+  // should not NPE, and should equal the given Seq
   @Test
-  def rovingDoesNotNPE(): Unit = {
-    // should not NPE, and should equal the given Seq
+  def test_SI6615(): Unit = {
     assertEquals(Seq('a'), PagedSeq.fromStrings(List.fill(5000)("a")).slice(4096, 4097))
   }
+
+  // Slices shouldn't read outside where they belong
+  @Test
+  def test_SI6519 {
+    var readAttempt = 0
+    val sideEffectingIterator = new Iterator[Int] {
+      def hasNext = readAttempt < 65536
+      def next = { readAttempt += 1; readAttempt }
+    }
+    val s = PagedSeq.fromIterator(sideEffectingIterator).slice(0,2).mkString
+    assertEquals(s, "12")
+    assert(readAttempt <= 4096)
+  }
 }