Optimize Kotlin reflection runtime efficiency

[spring-projects-issues]

kotlin-reflect is a big 2 MB JAR, producing important CPU and memory spikes at startup on the JVM.

It would be interesting to explore if it could be replaced by a lighter incarnation like https://github.com/Kotlin/kotlinx.reflect.lite or use kotlinx-metadata-jvm at build time to generate some kind of reflection index. jackson-module-kotlin should also work with similar approach (not blocking now that we have Kotlin Serialization support).

[sdeleuze]

Short term kotlin-reflect usage could be optimized, especially for native use case, by KT-44594 so feel free to vote for it on Kotlin issue tracker.

[sdeleuze]

After a deeper look, I am not sure kotlinx-metadata-jvm is suitable for our use case since it would require an alternative reflection metadata index. Also kotlin-reflect is conceptually ok for native since it is using Java reflection (which can be quite cheap for some use cases with GraalVM 21.3+) and not class resources (not available on native at runtime).

So my hope for the future is that we could collaborate with Kotlin team (cc @udalov @elizarov) to have a more optimized version of kotlin-reflect.jar. I does not have to be the full beast, maybe a lighter implementation of a subset (we only use a very small subset of it, see https://github.com/spring-projects/spring-framework/search?q=ReflectJvmMapping) inspired from https://github.com/Kotlin/kotlinx.reflect.lite. Notice that should use regular reflection not *.class resources because those are not available on native.

Could be useful for Jackson Kotlin support as well.

That would be a good fit with Spring Framework 6.

[sdeleuze]

See also this related comment Kotlin/kotlinx.reflect.lite#12 (comment) and this one on KT-11386.