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.

5 files changed, 63 insertions, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/matching/ParallelMatching.scala b/src/compiler/scala/tools/nsc/matching/ParallelMatching.scala
index 00f4186805..f33f637a46 100644
--- a/src/compiler/scala/tools/nsc/matching/ParallelMatching.scala
+++ b/src/compiler/scala/tools/nsc/matching/ParallelMatching.scala
@@ -7,7 +7,6 @@
 package scala.tools.nsc
 package matching
 
-import util.Position
 import transform.ExplicitOuter
 import symtab.Flags
 import collection._
@@ -188,6 +187,13 @@ trait ParallelMatching extends ast.TreeDSL
         }
       }
 
+      if (settings.Xmigration28.value) {
+        for (p <- ps ; if isArraySeqTest(scrut.tpe, p.tpe)) {
+          val reportPos = if (p.tree.pos.isDefined) p.tree.pos else scrut.pos
+          cunit.warning(reportPos, "An Array will no longer match as Seq[_].")
+        }
+      }
+
       def mkRule(rest: Rep): RuleApplication = {
         tracing("Rule", head match {
           case x if isEquals(x.tree.tpe)        => new MixEquals(this, rest)
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)
       }
diff --git a/test/files/neg/array-not-seq.check b/test/files/neg/array-not-seq.check
new file mode 100644
index 0000000000..bd72bb4e13
--- /dev/null
+++ b/test/files/neg/array-not-seq.check
@@ -0,0 +1,16 @@
+array-not-seq.scala:2: error: An Array will no longer match as Seq[_].
+  def f1(x: Any) = x.isInstanceOf[Seq[_]]
+                                 ^
+array-not-seq.scala:4: error: An Array will no longer match as Seq[_].
+    case _: Seq[_]  => true
+          ^
+error: An Array will no longer match as Seq[_].
+array-not-seq.scala:16: error: An Array will no longer match as Seq[_].
+    case (Some(_: Seq[_]), Nil, _)        => 1
+                ^
+error: An Array will no longer match as Seq[_].
+array-not-seq.scala:15: error: An Array will no longer match as Seq[_].
+  def f5(x1: Any, x2: Any, x3: AnyRef) = (x1, x2, x3) match {
+                                              ^
+error: An Array will no longer match as Seq[_].
+7 errors found
diff --git a/test/files/neg/array-not-seq.flags b/test/files/neg/array-not-seq.flags
new file mode 100644
index 0000000000..4e9f7e4a56
--- /dev/null
+++ b/test/files/neg/array-not-seq.flags
@@ -0,0 +1 @@
+-Xmigration -Xfatal-warnings
\ No newline at end of file
diff --git a/test/files/neg/array-not-seq.scala b/test/files/neg/array-not-seq.scala
new file mode 100644
index 0000000000..07a2898d88
--- /dev/null
+++ b/test/files/neg/array-not-seq.scala
@@ -0,0 +1,26 @@
+object Test {
+  def f1(x: Any) = x.isInstanceOf[Seq[_]]
+  def f2(x: Any) = x match {
+    case _: Seq[_]  => true
+    case _          => false
+  }
+
+  def f3(x: Any) = x match {
+    case _: Array[_]  => true
+    case _            => false
+  }
+
+  def f4(x: Any) = x.isInstanceOf[Traversable[_]]
+
+  def f5(x1: Any, x2: Any, x3: AnyRef) = (x1, x2, x3) match {
+    case (Some(_: Seq[_]), Nil, _)        => 1
+    case (None, List(_: List[_], _), _)   => 2
+    case _                                => 3
+  }
+
+  def main(args: Array[String]): Unit = {
+    // println(f1(Array(1)))
+    // println(f2(Array(1)))
+    // println(f3(Array(1))
+  }
+}