RFR: 8256867: Classes with empty PermittedSubclasses attribute cannot be extended

[Joe Darcy]

On Mon, 7 Dec 2020 19:51:38 GMT, Harold Seigel <hseigel at openjdk.org> wrote:

> Please review this fix for JDK-8256867.  This change no longer throws a ClassFormatError exception when loading a class whose PermittedSubclasses attribute is empty (contains no classes).  Instead, the class is treated as a sealed class which cannot be extended nor implemented.  This new behavior conforms to the JVM Spec.
> 
> This change required changing Class.permittedSubclasses() to return an empty array for classes with empty PermittedSubclasses attributes, and to return null for non-sealed classes.
> 
> This fix was tested with Mach5 tiers 1-2 on Linux, MacOS, and Windows, and tiers 3-5 on Linux x64.
> 
> Thanks, Harold

Is there already CSR coverage of this change?

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PR: https://git.openjdk.java.net/jdk/pull/1675