RFR: 8256867: Classes with empty PermittedSubclasses attribute cannot be extended [v2]

[Chris Hegarty]

On Tue, 8 Dec 2020 14:10:26 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
>
> Harold Seigel has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8256867: Classes with empty PermittedSubclasses attribute cannot be extended

Thanks Harold. LGTM.

src/java.base/share/classes/java/lang/Class.java line 4399:

> 4397:      * that is {@link #isSealed()} returns {@code false}, then this method returns {@code null}.
> 4398:      * Conversely, if {@link #isSealed()} returns {@code true}, then this method
> 4399:      * returns a non-null value."

Trivially, the trailing quote can be removed.

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Marked as reviewed by chegar (Reviewer).

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