Add a minimisation of the upickle failure

Author: dwijnand

tests/neg/i11834.scala

@@ -63,3 +63,10 @@ trait ZA[-X]                                                 // ZA[T] ~> ZA { X
 class ZB[-Y](val put: Y => Unit) extends ZA[Y]               // ZB[T] ~> ZB { X >: Y;         Y >: T           }
 class ZC[-Z](fn: Int => Unit) extends ZB[Int](fn) with ZA[Z] // ZC[T] ~> ZC { X >: (Y & Z);   Y >: Int; Z >: T }  // error
 class ZD[-Z](fn:   Z => Unit) extends ZB[Z](fn) with ZA[Int] // ZD[T] ~> ZD { X >: (Y & Int); Y >: Z;   Z >: T }  // error
+
+trait Visitor[-X]
+trait VDelegate[Y] extends Visitor[Y]
+class RDelegate1[Z] extends VDelegate[Z] with Visitor[Any]     // X >: Z & X >: Any     // error
+class RDelegate2[Z] extends Visitor[Any] with VDelegate[Z]     // X >: Any & X >: Z     // error
+class RDelegate3[Z] extends VDelegate[Z] with Visitor[Nothing] // X >: Z & X >: Nothing // ok
+class RDelegate4[Z] extends Visitor[Nothing] with VDelegate[Z] // X >: Nothing & X >: Z // ok