Hi HN, kc is a Kotlin compiler for the JVM, written in Go.

Why I built it: most Kotlin tools, like linters, KSP and the language server, are built on kotlinc's frontend, so they're only as fast as it is. A fast frontend could make room for:

- Linters that run in milliseconds instead of seconds

- A fast language server

- Much faster KSP annotation processing

- Quicker builds in CI, where every run starts a cold JVM

- Fast feedback for coding agents, which compile and fix code in a loop many times per task

I measured big gains in both speed and memory against kotlinc 2.4.21, running warm as in the Gradle daemon:

- kotlinx-coroutines-core: 2.50 s → 159 ms (16x)

- Ktor core modules: 2.32 s → 226 ms (10x)

- kotlinpoet: 1.23 s → 97 ms (13x)

- Memory: ~1 GB → ~100 MB

What it doesn't do yet:

- A few language features aren't supported

- No warnings, and only the errors that type checking finds, so some invalid code compiles

- JVM only, no Gradle plugin or IDE support

- Passes 95% of kotlinc's box tests

It's a prototype, but I plan to keep working on it until it's useful for a wide range of real projects.

Benchmark details and how to repeat them: https://github.com/barteo/kotlin-compiler-go/blob/main/docs/...