derivesFrom for FlexibleType

Author: olhotak

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -282,6 +282,8 @@ object Types {
           tp.bound.derivesFrom(cls) || tp.reduced.derivesFrom(cls)
         case tp: TypeProxy =>
           loop(tp.underlying)
+        case tp: FlexibleType =>
+          loop(tp.underlying)
         case tp: AndType =>
           loop(tp.tp1) || loop(tp.tp2)
         case tp: OrType =>