Fix for SI-4744, another variety of cycle.

I threw this in with the previous commit behind -Ybreak-cycles, but
this one is much less sketchy. Explanation: have to handle f-bounds
more deftly. Namers forces lower bounds to prevent recursion in
that direction, but a light touch is required to handle these two
situations differently:

  // This is a cyclic type parameter - an error is correct
  class A[T <: Comparable[_ <: T]]

  // This is not cyclic - it flips the arrow
  class B[T <: Comparable[_ >: T]]

Long have I been haunted by the knowledge that you can
write class B in java, but not in scala:

  public class B<T extends Comparable<? super T>> {}

It's over! We've achieved parity with java.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
index 9a43ad441f..f8b5d089e8 100644
--- a/src/reflect/scala/reflect/internal/Types.scala
+++ b/src/reflect/scala/reflect/internal/Types.scala
@@ -1710,7 +1710,8 @@ trait Types extends api.Types { self: SymbolTable =>
   object baseClassesCycleMonitor {
     private var open: List[Symbol] = Nil
     @inline private def cycleLog(msg: => String) {
-      Console.err.println(msg)
+      if (settings.debug.value)
+        Console.err.println(msg)
     }
     def size = open.size
     def push(clazz: Symbol) {