Added a migration warning for matches and insta...

Added a migration warning for matches and instance tests when it might
be an Array/Seq test whose answer has changed. Review by odersky.

1 files changed, 13 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/ExplicitOuter.scala b/src/compiler/scala/tools/nsc/transform/ExplicitOuter.scala
index c11bfd9703..f78022bdaa 100644
--- a/src/compiler/scala/tools/nsc/transform/ExplicitOuter.scala
+++ b/src/compiler/scala/tools/nsc/transform/ExplicitOuter.scala
@@ -61,6 +61,12 @@ abstract class ExplicitOuter extends InfoTransform
     result
   }
 
+  /** Issue a migration warning for instance checks which might be on an Array and
+   *  for which the type parameter conforms to Seq, because these answers changed in 2.8.
+   */
+  def isArraySeqTest(lhs: Type, rhs: Type) =
+    ArrayClass.tpe <:< lhs.widen && rhs.widen.matchesPattern(SeqClass.tpe)
+
   def outerAccessor(clazz: Symbol): Symbol = {
     val firstTry = clazz.info.decl(nme.expandedName(nme.OUTER, clazz))
     if (firstTry != NoSymbol && firstTry.outerSource == clazz) firstTry
@@ -294,7 +300,6 @@ abstract class ExplicitOuter extends InfoTransform
    *  </p>
    */
   class ExplicitOuterTransformer(unit: CompilationUnit) extends OuterPathTransformer(unit) {
-
     /** The definition tree of the outer accessor of current class
      */
     def outerFieldDef: Tree = VAL(outerField(currentClass)) === EmptyTree
@@ -483,8 +488,14 @@ abstract class ExplicitOuter extends InfoTransform
           matchTranslation(mch)
 
         case _ =>
-          val x = super.transform(tree)
+          if (settings.Xmigration28.value) tree match {
+            case TypeApply(fn @ Select(qual, _), args) if fn.symbol == Object_isInstanceOf || fn.symbol == Any_isInstanceOf =>
+              if (isArraySeqTest(qual.tpe, args.head.tpe))
+                unit.warning(tree.pos, "An Array will no longer match as Seq[_].")
+            case _ => ()
+          }
 
+          val x = super.transform(tree)
           if (x.tpe eq null) x
           else x setType transformInfo(currentOwner, x.tpe)
       }