RFR: 8255560: Class::isRecord should check that the current class is final and not abstract

[Mandy Chung]

On Tue, 1 Dec 2020 19:34:11 GMT, Chris Hegarty <chegar at openjdk.org> wrote:

> Update Class::isRecord to only return true for classes that are final.
> 
> The removal of non-specified JVM checks on classes with a Record Attribute (see JDK-8255342), has resulted in more types of loadable classes that may contain a Record Attribute. Since these checks are not performed by the JVM anymore, Class::isRecord, and by extension Class::getRecordComponents, may return true or component values, respectively, for classes that are not well-formed record classes (as per the JLS), .e.g. non-final or abstract classes, that contain a record Attribute.
> 
> Core Reflection, Class::isRecord, already asserts checks that the JVM does not, e.g. that the direct superclass is java.lang.Record. Some points from the Java Language Specification for record classes:
> 
>  1. It is a compile-time error if a record declaration has the modifier abstract.
>  2. A record declaration is implicitly final.
>  3. The direct superclass type of a record class is Record.
> 
> Class::isRecord already ensures no.3. This issue proposes to add explicit checks in Core Reflection to ensure no.1 and no.2, since the JVM now allows such classes that contain a Record Attribute to be loaded.

test/jdk/java/lang/reflect/records/IsRecordTest.java line 138:

> 136:         record EmptyRecord () { }
> 137:         assertTrue(EmptyRecord.class.isRecord());
> 138:         assertTrue(EmptyRecord.class.getRecordComponents() != null);

Better to have a more precise check for empty array

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PR: https://git.openjdk.java.net/jdk/pull/1543