RFR: 8367938: Test Serialization Compatibility of Class Objects

[Brent Christian]

On Mon, 1 Dec 2025 20:30:30 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> ArchivedClassesTest is added to compare archived serialized class objects against current classes.
> Note: these are the serialized class objects themselves, for example `java.lang.String.class`, not instances of the class, for example "Hello".
> The archived classes reference was built against the latest released version: 25.0.1+8.
> 
> The test fails if the serialized class reference archive is missing from the repository 
> or if there are any incompatible changes to the serialized bytes.
> Normal output from the test includes:
>  - The version of the serialized class archive
>  - Listing (if any) of incompatible classes
>  - Listing of classes with compatible changes
>  - Listing of classes in the archive that are not in the current version
>  - Listing of classes in the current version not found in the archive
> 
> The change of java.nio.ByteOrder from a class to enum is reported as an approved incompatible change.

A couple general comments:

It seems useful for the test to also detect if new classes need to be added to the archive.

Can a class have more than one "earlier version"? Could/should more than one earlier version be tested?

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PR Comment: https://git.openjdk.org/jdk/pull/28586#issuecomment-3604417085