submoduleGitHash() implementation for gradle

submoduleGitHash.gradle

def submoduleGitHash(workDir, gitSubmodulePath) {
    def stdout = new ByteArrayOutputStream()
    exec {
        workingDir workDir
        commandLine 'git', 'submodule', 'status', gitSubmodulePath
        standardOutput = stdout
    }
    def submoduleStatus = stdout.toString().trim()
    def match = (submoduleStatus =~ /^([-+]?)([a-z\d]*) ${gitSubmodulePath}/)
    switch (match[0][1]) {
        case '+':
            logger.quiet("Important info: building against a [${gitSubmodulePath}] hash that is not matching the submodule.")
            break;
        case '-':
            // submodule is not initialized yet, but that's not a problem, we'll use the referenced hash
            break;
        default:
            // submodule is up-to-date. Nothing special here
            break;
    }
    return match[0][2]
}

ext {
    submoduleGitHash = this.&submoduleGitHash
}