[Improvement] [Java] Cleaner approach to using enums

[narangvivek10]

Currently, the Java Panama API based layer in the Java API uses integer values for actual enum options, which makes the code less readable. This task is to replace this approach with using enum options instead.

Also, currently, we maintain Java enums for certain enums in the C layer, for example cuvsCagraGraphBuildAlgo in the C layer has a Java enum. This in its current form, involves manual intervention, especially when enums in the C layer change and so this needs a better approach.

Assigning this task to self.

[chatman]

Here's the documentation from the jextract guide:
https://github.com/openjdk/jextract/blob/master/doc/GUIDE.md#constants-macros--enums

I'm wondering how will it work if there are two top level enums with same constituent names, e.g.:

enum CagraParams {
   build_algo, // 0
   num_iters, // 1
  ..
}

enum IVFPQParams {
   num_iters, // 0
   min_pq, // 1
  ..
}

@narangvivek10 In this case, how will the num_iters be handled in Java code?

@ChrisHegarty FYI

[narangvivek10]

@chatman for the example below (with conflicting enum values):

enum Color1 {
    RED, GREEN, BLUE
};

enum Color2 {
    RED, GREEN, BLUE
};

Jextract stops with an error shown below:

error: redefinition of enumerator 'RED'

[narangvivek10]

Update:

To further efforts in finding a better solution, I took the liberty of exploring the jextract internals to extend its capability to generate Java enums with an optional --generate-java-enums flag. Contingent on its acceptance as a feature by the jextract community, it may take a while for this to get in, so here is what I think we can do until then:

• Maintain this feature as a patch in our cuVS-Java codebase.
• Modify our build system to download jextract and apply this patch before running jextract when we build.

Suggestions are welcome, of course. Thanks!

[narangvivek10]

In contrast to the above suggestion, what we have mutually decided yesterday on this is to wait for the jextract feature to go in first and then revisit this to modify the code and replace the manually managed enums with automatically generated ones. Thanks! FYI @cjnolet