RFR: 8274363: Transitively sealed classes not considered exhaustive in switches

[Vicente Romero]

On Mon, 27 Sep 2021 18:05:26 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> Consider code like:
> 
> public class SwitchCoverage {
>     sealed interface A {}
>     sealed interface B1 extends A {}
>     sealed interface B2 extends A {}
>     sealed interface C extends A {}
>     final class D1 implements B1, C {}
>     final class D2 implements B2, C {}
>     
>     void test(A arg) {
>         int i = switch (arg) {
>             case B1 b1 -> 1;
>             case B2 b2 -> 2;
>         };
>     }
>     
> } 
> 
> 
> Note that `B1` covers `D1` and `B2` covers `D2`. So, `B1` and `B2` cover `C`, and hence `B1` and `B2` cover `A`.  To detect this, when looking for coverage of permitted types of `A`, we need to transitively look if any of the permitted type is covered.
> 
> The check uses the `DeferredCompletionFailureHandler`, because if don't want to fail the compilation on unresolvable permitted subclass. (In case the permitted subclass is covered by some other means, of course.)

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 776:

> 774:                         for (Type sup : types.directSupertypes(sym.type)) {
> 775:                             if (sup.tsym.kind == TYP) {
> 776:                                 if (isTransitivellyCovered(sup.tsym, covered) &&

typo: Transitively?

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PR: https://git.openjdk.java.net/jdk/pull/5717