Try to diagnose test failure

Author: smarter

src/dotty/tools/dotc/core/Uniques.scala

@@ -107,6 +107,7 @@ object Uniques {
 
     def enterIfNew(parent: Type, refinedName: Name, refinedInfo: Type): RefinedType = {
       val h = doHash(refinedName, refinedInfo, parent)
+      assert(h != HashUnknown, (refinedName, refinedInfo, parent).toString)
       def newType = new CachedRefinedType(parent, refinedName, refinedInfo, h)
       if (monitored) recordCaching(h, classOf[CachedRefinedType])
       if (h == NotCached) newType