Android versioning based on git tags

version.gradle

/**
* This gradle ext script sets two variables: gitBasedVersionCode and gitBasedVersionName
* These variables are derived from Git history, assuming you use git tags to mark your (micro-)releases
*
* Using this scheme is a convenient way to automatically derive versions for you application artifacts.
* To begin with it, just set an annotated tag like: `git tag -a 0.1 -m "some artifact version" `
*
**/

ext {
    //example: 1.0-2-g234112312
    def longVersionName = "git -C ${rootDir} describe --tags --long".execute().text.trim()

    if (longVersionName == null || "" == longVersionName) {
        gitBasedVersionCode = 1
        gitBasedVersionName = "0.0.1"
    } else {

        logger.debug("version (debug): $longVersionName")

        def (fullVersionTag, versionPatch, gitSha) = longVersionName.tokenize('-')

        def (versionMajor, versionMinor) = fullVersionTag.tokenize('.')

        def maj = versionMajor == null ? 0 : versionMajor.toInteger()
        def min = versionMinor == null ? 0 : versionMinor.toInteger()
        def patch = versionPatch == null ? 0 : versionPatch.toInteger()


        def BASE = 256 //to derive a versionCode, we'll use 256-base positional numeral system

        if (patch >= BASE || min >= BASE || maj >= BASE) {
            throw new IllegalStateException("Tag digit should be in range: [0, ${BASE - 1} ]")
        }

        gitBasedVersionCode = (
                0/*initial offset*/
                        + maj * BASE * BASE
                        + min * BASE
                        + patch
        )

        //last sanity check, we want to avoid pushing version number that is TOO LARGE
        if (gitBasedVersionCode > Integer.MAX_VALUE / 2) {
            throw new IllegalStateException("Version code is close to Integer.MAX_VALUE . Change versioning strategy, or version code space will be exhausted")
        }

        logger.info("versionCode: $gitBasedVersionCode")

        gitBasedVersionName = "$maj.$min.$patch"


        logger.info("versionName: $gitBasedVersionName")
    }

}