RFR: 8303431: [JVMCI] libgraal annotation API [v7]

[Joe Darcy]

On Mon, 17 Apr 2023 20:46:36 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

> > From the long-term perspective, it is likely that the set of kinds of elements that can occur in an annotation will be expanded, for example, method references are a repeated request. Easing future maintenance to gives more inter-source linkage in this situation and error handling for this case in the libgraal code would be prudent IMO.
> 
> I'm not sure what you're suggesting in terms of how I should update this PR. Do you mean `AnnotationData.get` needs to somehow be more flexible? If so, could you please give a concrete example of what you're after.

Let me explain my concerns in more detail.

We have (at least) two separate annotations implementations in the JDK, one in javac for compile-time and other in core reflection for runtime. Due to various technical constraints, the implementations are necessarily separate (although the annotation objects constructed by javac do also implement the java.lang.annotation.Annotation interface also used by core reflection).

This work is proposing to add another partial implementation to satisfy other technical goals, reusing portions of the existing core reflection machinery.

If at some point the universe of objects that can be encoded as annotation is expanded, e..g method literals as mentioned previously, it is well-understood that core reflection and javac will need to be updated. I think it would be relatively easy to overlook the need to make corresponding updates to libgraal API and all regression tests might still pass.

As a concrete suggestion, if such an unknown annotation was handed over to libgraal, I think the code should reject it (AssertionError("unexpected annotation component") etc.) in hope of the omission getting corrected sooner. Also, leaving some bread crumb comments to future maintainers of core reflection annotations in that implementation package would be helpful too, e.g. "// used by libgraal".

HTH

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PR Comment: https://git.openjdk.org/jdk/pull/12810#issuecomment-1512343062