SI-8153 Mutation is hard, let's go shopping with an empty list

Changed the implementation of iterator to be more robust to mutation of the underlying ListBuffer.

Added a test to make sure bug is gone.

Fixed an "unsafe" usage of ListBuffer.iterator in the compiler, and added a comment explaining the (new) policy for iterating over a changing ListBuffer.

The compiler now uses a synchronized-wrapped ArrayBuffer instead of ListBuffer, as that makes the (custom) units Iterator more natural to write (and avoids O(n) lookups).

2 files changed, 15 insertions, 0 deletions

diff --git a/test/files/run/t8153.check b/test/files/run/t8153.check
new file mode 100644
index 0000000000..0cfbf08886
--- /dev/null
+++ b/test/files/run/t8153.check
@@ -0,0 +1 @@
+2
diff --git a/test/files/run/t8153.scala b/test/files/run/t8153.scala
new file mode 100644
index 0000000000..f9b223f974
--- /dev/null
+++ b/test/files/run/t8153.scala
@@ -0,0 +1,14 @@
+object Test {
+  def f() = {
+    val lb = scala.collection.mutable.ListBuffer[Int](1, 2)
+    val it = lb.iterator
+    if (it.hasNext) it.next
+    val xs = lb.toList
+    lb += 3
+    it.mkString
+  }
+
+  def main(args: Array[String]) {
+    println(f())
+  }
+}