Grunt task to update a Node.js dependency referenced by git URL.

Gruntfile.js

/* jshint -W064 */
"use strict";

var path   = require("path");
var url    = require("url");
var assert = require("assert");
var semver = require("semver");
var Q      = require("q");

module.exports = function(grunt) {
    // Project configuration.
    grunt.initConfig({
        pkg: grunt.file.readJSON("package.json"),
    });

    // use version if specified
    grunt.registerTask("update-deployer-dep", "update hubot-deployer dependency to the latest tag", function(newVer) {
        var DEP_NAME = "hubot-deployer";

        var nowrite = grunt.option("no-write");
        
        var pkg = grunt.config.get("pkg");
        
        var gitDepUrl = url.parse(pkg.dependencies[DEP_NAME]);

        // sanity check; should be "git+ssh:" or "git+http(s):"
        assert(gitDepUrl.protocol.indexOf("git+") === 0, "unexpected protocol " + gitDepUrl.protocol);

        var oldVer = gitDepUrl.hash.substr(2);
        grunt.log.writeln("Existing version of " + DEP_NAME + " is " + oldVer);

        var done = this.async();
        var newVerPromise;

        if (newVer) {
            newVerPromise = Q(newVer);
        } else {
            // need to remove the hash in order for "git ls-remote" to work
            delete gitDepUrl.hash;
            
            // strip off "git+"
            var gitRemoteUrl = url.format(gitDepUrl).substr(4);
            
            grunt.log.writeln((nowrite ? "Not " :"") + "Retrieving tags from " + gitRemoteUrl);
            
            if (nowrite) {
                newVerPromise = Q(oldVer);
            } else {
                // find published tags
                newVerPromise = Q
                    .ninvoke(grunt.util, "spawn", {
                        cmd: "git",
                        args: [
                            "ls-remote",
                            "--tags",
                            gitRemoteUrl
                        ]
                    })
                    .spread(function(result) {
                        var versions = [];
                        
                        // stdout is lines of the form "sha<tab>refs/tags/v0.0.3", plus
                        // some other stuff.  Just strip off the semantic version from
                        // the tag.  Assume we're using "v<version>" format.
                        result.stdout.split("\n").forEach(function(line) {
                            if (line.match(/v(\d+\.?){2,3}$/)) {
                                versions.push(line.split("/v")[1]);
                            }
                        });
                        
                        // sort versions in descending order
                        versions.sort(semver.rcompare);
                        
                        return versions[0];
                    });
            }
        }
        
        newVerPromise
            .then(function(newVer) {
                // replace the hash in the parsed url
                gitDepUrl.hash = "#v" + newVer;
                
                // regenerate the dependency version
                pkg.dependencies[DEP_NAME] = url.format(gitDepUrl);
                
                grunt.file.write(
                    path.resolve("package.json"),
                    JSON.stringify(pkg, null, "  ") + "\n"
                );
                
                grunt.log.ok("Set version of " + DEP_NAME + " to " + newVer);
            })
            .done(done, done);
    });
};