Why is this switch over sealed types not exhaustive?

[Gavin Bierman]

Probably a bug. We changed the definition of exhaustiveness to cover cases like this a little while ago, so the compiler is still catching up.

Gavin


> On 15 Jun 2021, at 17:31, Cay Horstmann <cay at horstmann.com> wrote:
> 
> Hi, I was surprised that the following switch expression "does not cover all possible input values", according to JDK build 17-ea+26-2439.
> 
> sealed abstract class A permits B, C {}
> final class B extends A {}
> sealed abstract class C extends A permits D, E {}
> final class D extends C {}
> final class E extends C {}
> 
> public class Test {
>   public static void main(String[] args) {
>      A a = new D();
>      System.out.println(
>         switch (a) {
>            case B x -> "B";
>            case D x -> "D";
>            case E x -> "E";
>         });
>   }
> }
> 
> However, the more combersome
> 
>         switch (a) {
>            case B x -> "B";
>            case C c -> switch (c) {
>               case D x -> "D";
>               case E x -> "E";
>            };
>         }
> 
> is deemed exhaustive. Is that a bug or does it work as designed?
> 
> Thanks,
> 
> Cay
> 
> -- 
> 
> Cay S. Horstmann | http://horstmann.com | mailto:cay at horstmann.com