Determining versionCode based on CircleCI build number

build.gradle

android {
    defaultConfig {
        versionName "1.9.1"
        versionCode getBuildVersion() as int
    }
}

// Don't name this getVersionCode() or things will break
static def getBuildVersion() {
    def version = 123
    def buildNumber = System.getenv("CIRCLE_BUILD_NUM")
    if (buildNumber != null) {
        version += buildNumber
    }
    println("VersionCode: " + version)
    return version
}