Fix and test case for #3855.

situations where a mutable var will later be lifted. As a point of
interest, this bug reveals itself fairly clearly if you use a build
since r23112 and run the checker thusly:

  scalac -d /tmp -Ycheck-debug -Ycheck:icode -Xprint:icode
test/files/run/bug3855.scala

It dies with the following explanation:

  Output changed for Block 3 [S: 2] [P: 1, 4]
  Exception in thread "main" scala.tools.nsc.backend.icode.CheckerException:
  Incompatible stacks: TypeStack() and TypeStack(2 elems) {
    REFERENCE(class IntRef)
    REFERENCE(class IntRef)
  } in Test.main at entry to block: 2

And indeed that was the source of the reported verifyerror.

Review by i. dragos.

1 files changed, 18 insertions, 0 deletions

diff --git a/test/files/run/bug3855.scala b/test/files/run/bug3855.scala
new file mode 100644
index 0000000000..32dfb1e23d
--- /dev/null
+++ b/test/files/run/bug3855.scala
@@ -0,0 +1,18 @@
+object Test {
+  def byval[A](a: => A) = a
+  def closure[A](f: () => A) = f()
+
+  def f1(s: String) = {
+    var n = try { s.toInt } catch { case _ => 1 }
+    byval(n)
+  }
+  def f2(s: String) = {
+    var n = try { s.toInt } catch { case _ => 1 }
+    closure(() => n)
+  }
+
+  def main(args: Array[String]) = {
+    val sum = f1("12") + f2("the witch is dead")
+    assert(sum == 13)
+  }
+}