Multi-catch and exhaustiveness check

[Thiago Henrique Hupner]

Hello all!

I've played around with the exhaustiveness check and I'd like to
discuss whether the following code should compile or it is right not to
compile.

import java.util.*;
import java.io.*;

sealed abstract class MyAbstractException extends RuntimeException {
    final static class MyException extends MyAbstractException {}
}

final class MyUncheckedException extends UncheckedIOException {
    public MyUncheckedException() {
        super(null);
    }
}

public class SealedException {
    public static void main(String[] args) {
        try {
            throw new MyUncheckedException();
        } catch (MyAbstractException | MyUncheckedException e) {
            switch (e) {
                case MyAbstractException.MyException a -> {}
                case MyUncheckedException b -> {}
            }
        }
    }
}

As MyUncheckedExceptionh is final, and MyAbstractException.MyException is
the only implementation available for MyAbstractException, I guess it is
exhaustive, but the compiler disagrees.

SealedException.java:23: error: the switch statement does not cover all
possible input values
            switch (e) {
            ^
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