RFR: 8294550: Sealed check for casts isn't applied to array components

[Vicente Romero]

On Thu, 29 Sep 2022 14:24:18 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> For code like:
> 
> sealed interface I permits A {}
> final class A implements I {}
> interface J {}
> 
> J j = null;
> I i = (I) j; //error reported here, as no instance of J can implement I
> J[] jj = null;
> I[] i = (I[]) jj; //incorrectly no error reported here, despite JLS saying there must be a narrowing conversion from J to I in this case, which there isn't as per the case above
> 
> 
> The cause for this is that we check the sealed constraints at the end of `Types.isCastable`, and only for classes, not for arrays. It would be possible to enhance the check to include array types, but feels clearer and more reliable to recurse, and do a full castability check on the element types.
> 
> A sketch of a CSR is here:
> https://bugs.openjdk.org/browse/JDK-8294586
> 
> Feedback is welcome!

looks sensible

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Marked as reviewed by vromero (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10490