JaCoCo returning 0% Coverage with Kotlin and Android 3.0

You can get line-by-line coverage for both Java and Kotlin code by defining the two different directories for generated .class files:

def debugTree = fileTree(dir: "${buildDir}/intermediates/classes/debug", excludes: fileFilter)
def kotlinDebugTree = fileTree(dir: "${buildDir}/tmp/kotlin-classes/debug", excludes: fileFilter)

Then, simply include both fileTrees in your classDirectories:

classDirectories.from = files([debugTree], [kotlinDebugTree])