Kotlin: Incremental compilation with Gradle

Update: as of Kotlin 1.1.1, Gradle incremental compilation is now enabled by default.

--- Old answer:

For now incremental compilation only works in the IDE when you use the Make algorithm supported by IntelliJ IDEA. We are looking into extending this to other build systems, but we are not there yet.

Incremental compilation in Gradle and IDE was added in Kotlin 1.0.2. It is enabled in IDE is enabled by default. To enable it for Gradle you will need to add kotlin.incremental=true to your gradle.properties file.