A gradle method to generate Android versionCode using git describe.

android-versioncode-git-describe.gradle

def getVersionCode = { ->
    try {
        def stdout = new ByteArrayOutputStream()
        exec {
            commandLine 'git', 'rev-list', '--first-parent', '--count', 'origin/master'
            standardOutput = stdout
        }
        return Integer.parseInt(stdout.toString().trim()) * 100
    }
    catch (ignored) {
        return -1;
    }
}