func verSuffix(gf *goconfig.ConfigFile, name string) string {
	val := gf.MustValue("deps", name)
	if len(val) > 0 {
		val = " @ " + val
	}
	return val
}

// downloadPackages downloads packages with certain commit,
// if the commit is empty string, then it downloads all dependencies,
// otherwise, it only downloada package with specific commit only.
func downloadPackages(target string, ctx *cli.Context, nodes []*doc.Node) (err error) {
	for _, n := range nodes {
		// Check if it is a valid remote path or C.
		if n.ImportPath == "C" {
			continue
		} else if !base.IsValidRemotePath(n.ImportPath) {
			// Invalid import path.
			if setting.LibraryMode {
				errors.AppendError(errors.NewErrInvalidPackage(n.VerString()))
			}
			log.Error("Skipped invalid package: " + n.VerString())
			failConut++
			continue
		}

		// Valid import path.
		if isSubpackage(n.RootPath, target) {
			continue
		}

		// Indicates whether need to download package or update.
		if n.IsFixed() && n.IsExist() {
			n.IsGetDepsOnly = true
		}

		if downloadCache.Get(n.VerString()) {
			if !skipCache.Get(n.VerString()) {
				skipCache.Set(n.VerString())
				log.Debug("Skipped downloaded package: %s", n.VerString())
			}
			continue
		}

		if !ctx.Bool("update") {
			// Check if package has been downloaded.
			if n.IsExist() {
				if !skipCache.Get(n.VerString()) {
					skipCache.Set(n.VerString())
					log.Info("%s", n.InstallPath)
					log.Debug("Skipped installed package: %s", n.VerString())
				}

				// Only copy when no version control.
				if !copyCache.Get(n.VerString()) && (ctx.Bool("gopath") || ctx.Bool("local")) {
					copyCache.Set(n.VerString())
					if err = n.CopyToGopath(); err != nil {
						return err
					}
				}
				continue
			} else {
				setting.LocalNodes.SetValue(n.RootPath, "value", "")
			}
		}
		// Download package.
		nod, imports, err := downloadPackage(ctx, n)
		if err != nil {
			return err
		}
		for _, name := range imports {
			var gf *goconfig.ConfigFile
			gfPath := path.Join(n.InstallPath, setting.GOPMFILE)

			// Check if has gopmfile.
			if base.IsFile(gfPath) {
				log.Info("Found gopmfile: %s", n.VerString())
				var err error
				gf, _, err = parseGopmfile(gfPath)
				if err != nil {
					return fmt.Errorf("fail to parse gopmfile(%s): %v", gfPath, err)
				}
			}

			// Need to download dependencies.
			// Generate temporary nodes.
			nodes := make([]*doc.Node, len(imports))
			for i := range nodes {
				nodes[i] = doc.NewNode(name, doc.BRANCH, "", !ctx.Bool("download"))

				if gf == nil {
					continue
				}

				// Check if user specified the version.
				if v := gf.MustValue("deps", imports[i]); len(v) > 0 {
					nodes[i].Type, nodes[i].Value, err = validPkgInfo(v)
					if err != nil {
						return err
					}
				}
			}
			if err = downloadPackages(target, ctx, nodes); err != nil {
				return err
			}
		}

		// Only save package information with specific commit.
//.........这里部分代码省略.........