RFR: 8353835: Implement JEP 500: Prepare to Make Final Mean Final

[Shaojin Wen]

On Thu, 8 May 2025 11:22:30 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 fatal error when a mutating a final field with JNI, and -Xlog:jni=debug can help identity when JNI code mutates finals. For now, JNI code is allowed to set the "write-protected" fields System.in/out/err, 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

src/java.base/share/classes/java/lang/reflect/Field.java line 887:

> 885:             if (isFinalInstanceInNormalClass() && obj != null) {
> 886:                 checkAllowedToSetFinal(Reflection.getCallerClass());
> 887:             }

There are multiple duplicate codes here, or put them all in one method, like this


    @ForceInline
    private void checkAllowedToSetFinalIfFinalInstanceInNormalClass(Object obj) throws IllegalAccessException {
        if (Modifier.isFinal(modifiers)
                && !Modifier.isStatic(modifiers)
                && !clazz.isRecord()
                && !clazz.isHidden()
                && obj != null) {
            checkAllowedToSetFinal(Reflection.getCallerClass(), false);
        }
    }

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PR Review Comment: https://git.openjdk.org/jdk/pull/25115#discussion_r2092083985