SI-7814 Avoid init cycle between Predef, `package`, ScalaRuntime

Not every application will force these in a single thread; we
have to do our best to avoid cycles between them.

The enclosed test was failing every time before the change.

This commit breaks the cycle by avoiding computing `tupleNames`
in the constructor of `ScalaRuntime`. The new version has the
added benefit of including specialized tuple subclasses, which
is verified with a unit test for `isTuple`.

Are there more of these lurking? It seems likely. I'm more than
a little concerned about the way the `ControlThrowable` fires up
`scala.SystemProperties` to check whether or not to suppress
stack traces; there is already an ugly hack in place:

    object NoStackTrace {
      final def noSuppression = _noSuppression

      // two-stage init to make checkinit happy,
      // since sys.SystemProperties.noTraceSupression.value
      // calls back into NoStackTrace.noSuppression
      final private var _noSuppression = false
      _noSuppression = sys.SystemProperties.noTraceSupression.value
    }

1 files changed, 3 insertions, 11 deletions

diff --git a/src/library/scala/runtime/ScalaRunTime.scala b/src/library/scala/runtime/ScalaRunTime.scala
index 1d8fe5e9ad..4fee6d75a3 100644
--- a/src/library/scala/runtime/ScalaRunTime.scala
+++ b/src/library/scala/runtime/ScalaRunTime.scala
@@ -34,21 +34,13 @@ object ScalaRunTime {
     clazz.isArray && (atLevel == 1 || isArrayClass(clazz.getComponentType, atLevel - 1))
 
   def isValueClass(clazz: jClass[_]) = clazz.isPrimitive()
-  def isTuple(x: Any) = x != null && tupleNames(x.getClass.getName)
+
+  // includes specialized subclasses and future proofed against hypothetical TupleN (for N > 22)
+  def isTuple(x: Any) = x != null && x.getClass.getName.startsWith("scala.Tuple")
   def isAnyVal(x: Any) = x match {
     case _: Byte | _: Short | _: Char | _: Int | _: Long | _: Float | _: Double | _: Boolean | _: Unit => true
     case _                                                                                             => false
   }
-  // Avoiding boxing which messes up the specialized tests.  Don't ask.
-  private val tupleNames = {
-    var i = 22
-    var names: List[String] = Nil
-    while (i >= 1) {
-      names ::= ("scala.Tuple" + String.valueOf(i))
-      i -= 1
-    }
-    names.toSet
-  }
 
   /** Return the class object representing an array with element class `clazz`.
    */