How to ensure that incremental compilation works for me

First of all, make sure if IC is on. To do so check that your build log contains the line:

Using experimental kotlin incremental compilation

If IC is on, but you suspect that your build was not performed incrementally, for now your only option is to take debug log and analyze it:

  1. add -d to gradle command-line options (for android studio: File|Settings|Compiler|Command-line options)
  2. then you can use regex to find all compiled files. An example code from our tests:
// lets assume that LOG is build log
val kotlinSourcesListRegex = Regex("\\[KOTLIN\\] compile iteration: ([^\\r\\n]*)")
val compiledKotlinSources = kotlinSourcesListRegex.findAll(LOG).asIterable().flatMap { it.groups[1]!!.value.split(", ") } 

I think this is not a convenient, and some kind of option to generate IC status report is needed. So I’ve created an issue you can use to track progress on this (hopefully it will be done in 1.0.3).