3.x Consider adding a full Java module descriptor

[aalmiray]

Full Java module descriptors (module-info.class) are a hard requirement for building custom Java Runtimes with Jlink.

It looks like the build must remain pre Java modules however given that the build is Gradle based there's the https://plugins.gradle.org/plugin/org.beryx.jar plugin that can be applied to keep the build in its current Java version while at the same time providing a full module descriptor. Caveat: the generated JAR will become a multi-release JAR.

If there's any interest I'll gladly provide a PR and help with maintenance.

Relates to: reactive-streams/reactive-streams-jvm#531

[akarnokd]

Okay, as long as it doesn't break Android tooling.

It seems we'll need a couple of things:

• JDK 9+ GHA. A new GHA can be added with just "jar" task. The current JDK 11 build has to target 8.
• Use the module info workaround

[aalmiray]

Correct. I must confess I know little of the Android ecosystem. It's my hope that additional entries found under /META-INF/versions/x would not cause any disruptions on Android.

[JakeWharton]

MR jars will have their content ignored by Android toolchain, yes

[akarnokd]

Great. @aalmiray you can post a PR for this.

[aalmiray]

This is great. However in order to have RxJava's module descriptor be fully modular we'll need an answer from the ReactiveStreams WG -> reactive-streams/reactive-streams-jvm#531

[aalmiray]

FYI encountered bndtools/bnd#3514 -> bndtools/bnd#2227 which has yet to be resolved.