Kotlin support?

[TJC]

I love the Kotlin language. It's much nicer to write than Java. I was hoping to use it with the FlintJVM, although this might be a bit too aspirational..

I'm running into some problems.

Problem 1: java.io.Serializable

Many errors about java.io.Serializable:

error: cannot access 'java.io.Serializable' which is a supertype of 'Int'. Check your module classpath for missing or conflicting dependencies.
        val colors = byteArrayOf(g.toByte(), r.toByte(), b.toByte())

Problem 2: Package size

Kotlin's runtime adds about 5 megabytes to the jar size. Internet forums suggest you can use Proguard to significantly reduce this size, however in practice I couldn't get Proguard to work successfully. This might just be my own inexperience at using it though -- or it might be because of how we need to use a different java-base.jar.

So, I thought I'd see if anyone was trying to explore other JVM languages?

UPDATES

• Adding java.io.Serializable to FlintJDK and recompiling solves compilation issues.
• Using the ShadowJar plugin for Gradle with the minimize() option gets the resulting fat JAR down to under 2M of size.

[ElectricThanhTung]

Basicaly if you can compile kotlin sources into classes file and package them into a jar file, FlintJVM can execute them. Regarding the vscode debugging extension, currently it has an issue related to set breakpoints because it is unsupported by finding class file by kotlin source file.

[ElectricThanhTung]

This is my personal email:
electricthanhtung@gmail.com

[TJC]

I think this command tells the compiler to use a custom java base rather than the built-in JDK, but when I do this I get a lot of errors about missing java.io.Serializable

kotlinc -Xmodule-path=libs/java.base.jar -no-jdk -cp libs/flint.io.jar src/kotlin/Main.kt

[ElectricThanhTung]

Perhaps java.io.Serializable should be added to FlintJDK.

[ElectricThanhTung]

I tried adding java.io.Serializable to java.base and resolved the compilation error. However, I cannot attach the java.base.jar file here or email it to you because it is being blocked.
You can add it to FlintJDK yourself and recompile it on your side.

[TJC]

I can confirm adding it does fix the compilation error.

[TJC]

I've pushed my example app (building on Gradle, minimising the output jar size) to https://github.com/TJC/flintjvm-kotlin-example

[TJC]

Thanks -- I'll keep an eye out for the next compiled release of FlintESPJVM!

[ElectricThanhTung]

Hi.
I created a release to hotfix this issue. You can check the release notes or download firmware binary files here: FlintESPJVM V0.8.1.
You can also use the web tool https://esp.flint.vn to flash this version.

[TJC]

Maybe I'm doing something wrong, but I still haven't had any success running a "hello world" Kotlin program.
It takes a minute to upload to the board, then there's a long pause, then an error message that the debug server has closed.
Does it work for you?

[ElectricThanhTung]

Your jar file is compressed using the "normal" compression method. FlintJVM only supports the "store" compression method. When I recompressed your jar file, the program was able to run without any errors. However, the file size was inflated from 1.86 MB to 4.63 MB.

[ElectricThanhTung]

To reduce the size of the jar file, you can remove the following directories:

• flint, java, jdk - because they are pre-installed on the board.
• src - It is not used for any purpose on the FlintJVM side.