implement update command

main.go

@@ -27,6 +27,7 @@ The commands are:
 
     get     upgrade to a major version
     list    list available updates
+    update  upgrade all modules
     path    modify the module path
     help    show this help text
 `
@@ -45,6 +46,10 @@ func main() {
 		if err := listcmd(flag.Args()[1:]); err != nil {
 			log.Fatal(err)
 		}
+	case "update":
+		if err := updatecmd(flag.Args()[1:]); err != nil {
+			log.Fatal(err)
+		}
 	case "path":
 		if err := pathcmd(flag.Args()[1:]); err != nil {
 			log.Fatal(err)
@@ -160,6 +165,60 @@ func getcmd(args []string) error {
 	})
 }
 
+func updatecmd(args []string) error {
+	var dir string
+	var pre, cached, major bool
+	fset := flag.NewFlagSet("update", flag.ExitOnError)
+	fset.BoolVar(&pre, "pre", false, "allow non-v0 prerelease versions")
+	fset.StringVar(&dir, "dir", ".", "working directory")
+	fset.BoolVar(&cached, "cached", true, "only fetch cached content from the module proxy")
+	fset.BoolVar(&major, "major", false, "only show newer major versions")
+	fset.Usage = func() {
+		fmt.Fprintln(os.Stderr, "Usage: gomajor update")
+		fset.PrintDefaults()
+	}
+	fset.Parse(args)
+	dependencies, err := packages.Direct(dir)
+	if err != nil {
+		return err
+	}
+	modproxy.Updates(modproxy.UpdateOptions{
+		Pre:     pre,
+		Major:   major,
+		Cached:  cached,
+		Modules: dependencies,
+		OnUpdate: func(u modproxy.Update) {
+			if u.Err != nil {
+				fmt.Fprintf(os.Stderr, "%s: failed: %v\n", u.Module.Path, u.Err)
+				return
+			}
+			// go get
+			modprefix := packages.ModPrefix(u.Module.Path)
+			spec := packages.JoinPath(modprefix, u.Version, "") + "@" + u.Version
+			fmt.Println("go get", spec)
+			cmd := exec.Command("go", "get", spec)
+			cmd.Dir = dir
+			cmd.Stdout = os.Stdout
+			cmd.Stderr = os.Stderr
+			if err := cmd.Run(); err != nil {
+				return
+			}
+			// rewrite import paths
+			err := importpaths.RewriteModule(dir, importpaths.RewriteModuleOptions{
+				Prefix:     modprefix,
+				NewVersion: u.Version,
+				OnRewrite: func(pos token.Position, _, newpath string) {
+					fmt.Printf("%s %s\n", pos, newpath)
+				},
+			})
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "rewrite failed: %v", err)
+			}
+		},
+	})
+	return nil
+}
+
 func pathcmd(args []string) error {
 	var dir, version string
 	var next bool