RFR: 8353835: Implement JEP 500: Prepare to Make Final Mean Final [v8]

[David Holmes]

On Wed, 8 Oct 2025 08:15:08 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Implementation changes for [JEP 500: Prepare to Make Final Mean Final](https://openjdk.org/jeps/500).
>> 
>> Field.set (and Lookup.unreflectSetter) are changed to allow/warn/debug/deny when mutating a final instance field. JFR event recorded if final field mutated. Spec updates to Field.set, Field.setAccessible and Module.addOpens to align with the proposal in the JEP.
>> 
>> HotSpot is updated to add support for the new command line options. To aid diagnosability, -Xcheck:jni reports a warning and -Xlog:jni=debug logs a message to help identity JNI code that mutates finals. For now, JNI code is allowed to set the "write-protected" fields System.in/out/err without a warning, we can re-visit once we change the System.setIn/setOut/setErr methods to not use JNI (I prefer to keep this separate to this PR because there is a small startup regression to address when changing System.setXXX).
>> 
>> There are many new tests. A small number of existing tests are changed to run /othervm as reflectively opening a package isn't sufficient. Changing the tests to /othervm means that jtreg will launch the agent with the command line options to open the package.
>> 
>> Testing: tier1-6
>
> Alan Bateman has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 41 commits:
> 
>  - Suppress warnings from some tests
>  - Change -Xcheck:jni to be warning rather than fatal error
>  - Merge branch 'master' into JDK-8353835
>  - Simplify filter
>  - Merge branch 'master' into JDK-8353835
>  - Update Xcheck:jni description
>  - Add testUnreflectExpectingWarning
>  - Merge branch 'master' into JDK-8353835
>  - Add test for -Xlog:jni=debug
>  - Merge branch 'master' into JDK-8353835
>  - ... and 31 more: https://git.openjdk.org/jdk/compare/2ac24bf1...635556aa

Hotspot changes look fine. Thanks.

-------------

Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25115#pullrequestreview-3335034246