Dynamic versions for gradle, git-flow and Java development

dynamicVersion.gradle

/*
 * This work is licensed under the Creative Commons Attribution 3.0 Unported License.
 * 
 * To view a copy of this license, visit   http://creativecommons.org/licenses/by/3.0/ 
 * or send a letter to Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
 */

/*
 * Define your version here
 */
version = new Version(project: project, major: 1, minor: 3).toString()

/*
 * Print the version
 */
task printVersion {
    doFirst {
        println "$project.version"
    }
}

/**
 * <p>
 * Implementation of a dynamic version for gradle builds that
 * works well in conjunction with the git-flow branching model
 * combined with Java development that uses Maven or Ivy
 * repositories.
 * </p>
 * <p>
 * Any branch that is not <b>master</b> will automatically have
 * <pre>-SNAPSHOT</pre> appended to the produced version string.
 * </p>
 * <p>
 * Feature branches will automatically have inserted the feature
 * branch names in their version string to differentiate them
 * from the main development branch.
 * </p>
 * @author Jens Hausherr <a href="https://github.com/jabbrwcky">jabbrwcky@github</a>
 */
class Version {
    /* reference to current gradle project */
    Project project
    
    /* version number components, major and minor are required,
     * the rest is optional.
     */
    int major, minor, revision, patch

    /**
     * Wrapper for git execution.
     *
     * @param gitArgs list of arguments to the git executable
     * @return output of command
     */
    def git(List gitArgs) {
        def stdout = new ByteArrayOutputStream()

        project.exec {
            executable = 'git'
            args = gitArgs
            standardOutput = stdout
        }

        return stdout
    }

    String toString() {
        def version = "$major.$minor"
        
        /*
         * Resolves the git reference.
         * Newer git version have the option "--short" which
         * makes the regex that strips the "refs/heads/" part
         * from the returned branch names unnecessary.
         */
        def branch_ = git(["symbolic-ref", /* not supported by current git on jenkins "--short",*/ "-q", "HEAD"])

        /* req. if git-symbolic-ref  does not support --short */
        def bmatcher = branch_ =~ /refs\/heads\/(.+)/
        def branch = bmatcher[0][1]

        def fbmatch = branch =~ /feature\/(.+)/

        if (revision) version += ".$revision"
        if (patch) version += ".$patch"
        if (fbmatch)
            version += "-FB_${fbmatch[0][1]}"

        if (branch != 'master') {
            version += "-SNAPSHOT"
        }

        return version
    }
}