猜测当前目录使用了哪个版本控制系统的node函数

guessVcsName.js

var Deferred = require('./Deferred'); // 支持Promise api的库都可以，例如q(http://documentup.com/kriskowal/q/)
var exec = require('child_process').exec;

/**
 * 猜测当前目录使用了哪个版本控制系统
 *
 * @return {string} svn/git/hg/cvs, 如果检测不到返回空字符串
 */
function guessVcsName() {
    var svnDef = new Deferred();
    exec('svn info', function (err, stdout, stderr) {
        if (err) {
            if (err.code === 5) {
                console.log('Your working copy is not compatible with your current Subversion,please run `svn upgrade`!\n');
            }
            svnDef.resolve('');
            return;
        }

        svnDef.resolve('svn');
    });

    return svnDef
        .then(function (cvsName) {
            if (cvsName) {
                return cvsName;
            }

            var gitDef = new Deferred();
            exec(
                'git rev-parse --is-inside-work-tree',
                function (err, stdout, stderr) {
                    if (err) {
                        gitDef.resolve('');
                        return;
                    }

                    gitDef.resolve('git');
                }
            );

            return gitDef;
        })
        .then(function (cvsName) {
            if (cvsName) {
                return cvsName;
            }

            var hgDef = new Deferred();
            exec(
                'hg root',
                function (err, stdout) {
                    if (err) {
                        hgDef.resolve('');
                        return;
                    }

                    hgDef.resolve('hg');
                }
            );

            return hgDef;
        })
        .then(function (cvsName) {
            if (cvsName) {
                return cvsName;
            }

            var cvsDef = new Deferred();
            exec(
                'cvs status',
                function (err, stdout) {
                    if (err) {
                        cvsDef.resolve('');
                        return;
                    }

                    cvsDef.resolve('cvs');
                }
            );

            return cvsDef;
        });
}