Alternative approach, run Kotlin LS as Java LS plugin

[nisargjhaveri]

Since #3 and likely more such integrations would require communicating between the java.ls extension and the kotlin language server running separately, I tried an alternate approach to simplify the communication.

Have a look at nisargjhaveri/kotlin-language-server@c8129aa, if interested.

This essentially attempts to run the entire Kotlin ls as a java.ls plugin. The server is started via a custom command Kotlin ls would contribute to the Java ls. This certainly requires some more modifications, but would have a number of benefit for the java-kotlin multi-lingual projects.

• Easier to implement more integrations such as Support go to definition from java to kotlin #3, without having to figure out a new communication channel.
• We can modify the Kotlin LS to use the project definition, classpath etc from the Java LS. This way both Java and Kotlin part of the project sees the same project configuration. Lesser chances of mismatch and surprises between the two.
• Kotlin build can be integrated with the Java build, such that we see even lesser errors, even at the initial stages of the project setup and build.

I was able to run the language server this way, see the commit above. Though this commit does not have the corresponding changes required in kotlin plugin to trigger the custom command to start the LS. Obviously this helps in the Java-Kotlin interop cases only. We'd still need the standalone Kotlin server for other cases.

I'm really not an expert at this and could not follow up post this. Thought I'd share in case this helps.

Also, the changes there might also help with #4 as I was able to use gradle only for the Java ls plugin.

[daplf]

Hey @nisargjhaveri

Thanks for the suggestion! But I am a little confused after looking at the code you linked. Where is the connection to the JDT project in your approach? I can see you're starting the kotlin language server using a delegate command handler, but how are you connecting the kotlin sources to the java project? How are kotlin imports in java code resolved with your approach?

Kotlin build can be integrated with the Java build, such that we see even lesser errors, even at the initial stages of the project setup and build.

Can you elaborate here? How would the kotlin build be integrated with the java build? How would kotlin code be compiled?

[nisargjhaveri]

Sorry for the delay.

Thanks for the suggestion! But I am a little confused after looking at the code you linked. Where is the connection to the JDT project in your approach? I can see you're starting the kotlin language server using a delegate command handler, but how are you connecting the kotlin sources to the java project? How are kotlin imports in java code resolved with your approach?

Sorry for the confusion. The current sample I linked does not yet connect kotlin sources to Java project. I started exploring this as I think it'll help in having a much better integration. Unfortunately, I haven't been able to give enough time on this and it stopped after the first step of running the Kotlin LS in the same process.

Kotlin build can be integrated with the Java build, such that we see even lesser errors, even at the initial stages of the project setup and build.

Can you elaborate here? How would the kotlin build be integrated with the java build? How would kotlin code be compiled?

I was taking inspiration from how https://github.com/Kotlin/kotlin-eclipse works. We can contribute and hook into Eclipse's plugin system more and contribute project configurator and classpath provider, and configure the project to add Kotling builder as well. That way, Kotlin is built along with other Java sources, potentially giving much better integration. We can also use Java plugin's classpath to make sure it is consistent between Java and Kotlin sources, and we don't have to process ourselves, potentially giving more coverage as supported by Java plugin.