A gradle method to generate the versionName for an Android app, using git describe.

android-versionname-git-describe.gradle

def getVersionName = { ->
    try {
        def stdout = new ByteArrayOutputStream()
        exec {
            commandLine 'git', 'describe', '--dirty'
            standardOutput = stdout
        }
        return stdout.toString().trim()
    }
    catch (ignored) {
        return null;
    }
}