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.

The change looks good with a couple of minor suggestion.

src/java.base/share/classes/java/lang/Class.java line 3668:

> 3666:      * <p> The {@linkplain #getSuperclass() direct superclass} of a record
> 3667:      * class is {@code java.lang.Record}. A record class is
> 3668:      * {@link Modifier#FINAL}. A record class has (possibly zero) record

nit: `{@linkplain Modifier#FINAL final}`.

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Marked as reviewed by mchung (Reviewer).

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