Integrated: 8327368: javac crash when computing exhaustiveness checks

[Jan Lahoda]

On Mon, 3 Jun 2024 12:47:15 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> Consider code like:
> 
> package test;
> 
> public class Test {
> 
>     sealed interface A permits T, U {}
> 
>     sealed interface B permits V, W {}
> 
>     static final class T implements A {}
> 
>     static final class U implements A {}
> 
>     static final class V implements B {}
> 
>     static final class W implements B {}
> 
>     final static record R(A a, B b) {}
> 
>     static int r(R r) {
>         return switch (r) {
>             case R(A a, V b) -> 1;
>             case R(T a, B b) -> 2;
>             case R(U a, W b) -> 3;
>         };
>     }
> }
> 
> 
> To properly evaluate exhaustiveness, we need to consider `R(T a, B b)` to act as `R(T a, W b)`, so that we can reduce `R(T a, W b)` and `R(U a, W b)` to `R(A a, W b)`. Which is then reduced together with `R(A a, V b)` to `R(A a, B b)` and consequently to just `R`.
> 
> This was done under JDK-8325215, by expanding `B` into all possible subtypes, from which we can pick patterns for reduction. Eventually, that patch may need a more complete revamp, but the idea herein is just to prevent a `ClassCastException` when the type of the binding pattern is not a class-based type - typically, when it is a type variable. This patch uses the type variable's bounds as the based from which the permitted subtypes are computed.

This pull request has now been integrated.

Changeset: 1f094672
Author:    Jan Lahoda <jlahoda at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/1f09467230971d6458918ec19ffeb259b8c028a3
Stats:     98 lines in 2 files changed: 91 ins; 0 del; 7 mod

8327368: javac crash when computing exhaustiveness checks

Reviewed-by: vromero

-------------

PR: https://git.openjdk.org/jdk/pull/19523