Fix for SI-6537, inaccurate unchecked warning.

I found a more direct expression of the unchecked logic,
which should be much easier for others to verify.  But the
bug being fixed here is that the unchecked checking happens
too early, and the sealed children of a symbol are not yet
visible if it is being simultaneously compiled.

1 files changed, 3 insertions, 1 deletions

diff --git a/test/files/neg/unchecked-knowable.scala b/test/files/neg/unchecked-knowable.scala
index 667b47f504..21624c4fb4 100644
--- a/test/files/neg/unchecked-knowable.scala
+++ b/test/files/neg/unchecked-knowable.scala
@@ -7,6 +7,7 @@ final class A4 extends A2
 /** Unknowable */
 sealed abstract class B1
 sealed abstract class B2 extends B1
+sealed trait B2B extends B1
 final class B3 extends B1
 trait B4 extends B2
 
@@ -15,6 +16,7 @@ trait Dingus
 
 class A {
   /*   warn */ (new Bippy).isInstanceOf[A1]
-  /* nowarn */ (new Bippy).isInstanceOf[B1]
+  /*   warn */ (new Bippy).isInstanceOf[B1]
+  /* nowarn */ (null: Dingus).isInstanceOf[B1]
   /* nowarn */ ((new Bippy): Any).isInstanceOf[A1]
 }