Fix for continuations issue.

Avoid explicit type arguments which don't conform to bounds
where they could be successfully inferred.

I had to disable one "neg" test which is no longer neg.
Can anyone clue me in as to whether it is important?

2 files changed, 19 insertions, 9 deletions

diff --git a/src/continuations/plugin/scala/tools/selectivecps/CPSUtils.scala b/src/continuations/plugin/scala/tools/selectivecps/CPSUtils.scala
index 075009ce5e..67ea6e15f0 100644
--- a/src/continuations/plugin/scala/tools/selectivecps/CPSUtils.scala
+++ b/src/continuations/plugin/scala/tools/selectivecps/CPSUtils.scala
@@ -24,6 +24,7 @@ trait CPSUtils {
     val shift           = newTermName("shift")
     val shiftR          = newTermName("shiftR")
     val shiftSuffix     = newTermName("$shift")
+    val shiftUnit0      = newTermName("shiftUnit0")
     val shiftUnit       = newTermName("shiftUnit")
     val shiftUnitR      = newTermName("shiftUnitR")
   }
@@ -38,6 +39,7 @@ trait CPSUtils {
   lazy val ModCPS = definitions.getRequiredModule("scala.util.continuations")
 
   lazy val MethShiftUnit  = definitions.getMember(ModCPS, cpsNames.shiftUnit)
+  lazy val MethShiftUnit0 = definitions.getMember(ModCPS, cpsNames.shiftUnit0)
   lazy val MethShiftUnitR = definitions.getMember(ModCPS, cpsNames.shiftUnitR)
   lazy val MethShift      = definitions.getMember(ModCPS, cpsNames.shift)
   lazy val MethShiftR     = definitions.getMember(ModCPS, cpsNames.shiftR)
diff --git a/src/continuations/plugin/scala/tools/selectivecps/SelectiveANFTransform.scala b/src/continuations/plugin/scala/tools/selectivecps/SelectiveANFTransform.scala
index 1189cc2e38..a6737573ea 100644
--- a/src/continuations/plugin/scala/tools/selectivecps/SelectiveANFTransform.scala
+++ b/src/continuations/plugin/scala/tools/selectivecps/SelectiveANFTransform.scala
@@ -310,15 +310,23 @@ abstract class SelectiveANFTransform extends PluginComponent with Transform with
 
           try {
             val Some((a, b)) = cpsR
-
-            val res = localTyper.typed(atPos(tree.pos) {
-                    Apply(TypeApply(gen.mkAttributedRef(MethShiftUnit),
-                      List(TypeTree(plainTpe), TypeTree(a), TypeTree(b))),
-                       List(expr))
-            })
-            return (stms, res)
-
-          } catch {
+            /** Since shiftUnit is bounded [A,B,C>:B] this may not typecheck
+             *  if C is overly specific.  So if !(B <:< C), call shiftUnit0
+             *  instead, which takes only two type arguments.
+             */
+            val conforms = a <:< b
+            val call = localTyper.typedPos(tree.pos)(
+              Apply(
+                TypeApply(
+                  gen.mkAttributedRef( if (conforms) MethShiftUnit else MethShiftUnit0 ),
+                  List(TypeTree(plainTpe), TypeTree(a)) ++ ( if (conforms) List(TypeTree(b)) else Nil )
+                ),
+                List(expr)
+              )
+            )
+            return ((stms, call))
+          }
+          catch {
             case ex:TypeError =>
               unit.error(ex.pos, "cannot cps-transform expression " + tree + ": " + ex.msg)
           }