Nailed down the "impossible match" logic.

I will again defer to a comment.

/** Given classes A and B, can it be shown that nothing which is
 *  an A will ever be a subclass of something which is a B? This
 *  entails not only showing that !(A isSubClass B) but that the
 *  same is true of all their subclasses.  Restated for symmetry:
 *  the same value cannot be a member of both A and B.
 *
 *   1) A must not be a subclass of B, nor B of A (the trivial check)
 *   2) One of A or B must be completely knowable (see isKnowable)
 *   3) Assuming A is knowable, the proposition is true if
 *      !(A' isSubClass B) for all A', where A' is a subclass of A.
 *
 *  Due to symmetry, the last condition applies as well in reverse.
 */

1 files changed, 6 insertions, 6 deletions

diff --git a/test/files/neg/unchecked2.check b/test/files/neg/unchecked2.check
index b4a14358c7..68fdfa82ac 100644
--- a/test/files/neg/unchecked2.check
+++ b/test/files/neg/unchecked2.check
@@ -1,22 +1,22 @@
-unchecked2.scala:4: error: fruitless type test: a Some[List[Int]] can never be a Option[List[String]] (but still might match its erasure)
+unchecked2.scala:4: error: fruitless type test: a value of type Some[List[Int]] cannot also be a Option[List[String]] (but still might match its erasure)
   /*   warn */ Some(List(1)).isInstanceOf[Option[List[String]]]
                                          ^
 unchecked2.scala:5: error: non-variable type argument Option[_] in type Option[Option[_]] is unchecked since it is eliminated by erasure
   /*   warn */ Some(123).isInstanceOf[Option[Option[_]]]
                                      ^
-unchecked2.scala:6: error: fruitless type test: a Some[Int] can never be a Option[String] (but still might match its erasure)
+unchecked2.scala:6: error: fruitless type test: a value of type Some[Int] cannot also be a Option[String] (but still might match its erasure)
   /*   warn */ Some(123).isInstanceOf[Option[String]]
                                      ^
-unchecked2.scala:7: error: fruitless type test: a Some[Int] can never be a Option[List[String]] (but still might match its erasure)
+unchecked2.scala:7: error: fruitless type test: a value of type Some[Int] cannot also be a Option[List[String]] (but still might match its erasure)
   /*   warn */ Some(123).isInstanceOf[Option[List[String]]]
                                      ^
-unchecked2.scala:8: error: fruitless type test: a Some[Int] can never be a Option[List[Int => String]] (but still might match its erasure)
+unchecked2.scala:8: error: fruitless type test: a value of type Some[Int] cannot also be a Option[List[Int => String]] (but still might match its erasure)
   /*   warn */ Some(123).isInstanceOf[Option[List[Int => String]]]
                                      ^
-unchecked2.scala:9: error: fruitless type test: a Some[Int] can never be a Option[(String, Double)] (but still might match its erasure)
+unchecked2.scala:9: error: fruitless type test: a value of type Some[Int] cannot also be a Option[(String, Double)] (but still might match its erasure)
   /*   warn */ Some(123).isInstanceOf[Option[(String, Double)]]
                                      ^
-unchecked2.scala:10: error: fruitless type test: a Some[Int] can never be a Option[String => Double] (but still might match its erasure)
+unchecked2.scala:10: error: fruitless type test: a value of type Some[Int] cannot also be a Option[String => Double] (but still might match its erasure)
   /*   warn */ Some(123).isInstanceOf[Option[String => Double]]
                                      ^
 unchecked2.scala:14: error: non-variable type argument List[String] in type Option[List[String]] is unchecked since it is eliminated by erasure