cmd/tailscale/cli: add update notification to "up" (#9644)

Add available update message in "tailscale up" output. Also update the
message in "tailscale status" to match and mention auto-update.

Updates https://github.com/tailscale/tailscale/issues/755

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

cmd/tailscale/cli/status.go

@@ -25,6 +25,7 @@ import (
 	"tailscale.com/net/interfaces"
 	"tailscale.com/util/cmpx"
 	"tailscale.com/util/dnsname"
+	"tailscale.com/version"
 )
 
 var statusCmd = &ffcli.Command{
@@ -237,7 +238,7 @@ func runStatus(ctx context.Context, args []string) error {
 	}
 	printFunnelStatus(ctx)
 	if cv := st.ClientVersion; cv != nil && !cv.RunningLatest && cv.LatestVersion != "" {
-		printf("# New Tailscale version is available: %q, run `tailscale update` to update.\n", cv.LatestVersion)
+		printf("# Update available: %v -> %v, run `tailscale update` or `tailscale set --auto-update` to update.\n", version.Short(), cv.LatestVersion)
 	}
 	return nil
 }

cmd/tailscale/cli/up.go

@@ -499,6 +499,7 @@ func runUp(ctx context.Context, cmd string, args []string, upArgs upArgsT) (retE
 	startLoginInteractive := func() { loginOnce.Do(func() { localClient.StartLoginInteractive(ctx) }) }
 
 	go func() {
+		var cv *tailcfg.ClientVersion
 		for {
 			n, err := watcher.Next()
 			if err != nil {
@@ -509,6 +510,9 @@ func runUp(ctx context.Context, cmd string, args []string, upArgs upArgsT) (retE
 				msg := *n.ErrMessage
 				fatalf("backend error: %v\n", msg)
 			}
+			if n.ClientVersion != nil {
+				cv = n.ClientVersion
+			}
 			if s := n.State; s != nil {
 				switch *s {
 				case ipn.NeedsLogin:
@@ -527,6 +531,11 @@ func runUp(ctx context.Context, cmd string, args []string, upArgs upArgsT) (retE
 					} else if printed {
 						// Only need to print an update if we printed the "please click" message earlier.
 						fmt.Fprintf(Stderr, "Success.\n")
+						if cv != nil && !cv.RunningLatest && cv.LatestVersion != "" {
+							fmt.Fprintf(Stderr, "\nUpdate available: %v -> %v\n", version.Short(), cv.LatestVersion)
+							fmt.Fprintln(Stderr, "Changelog: https://tailscale.com/changelog/#client")
+							fmt.Fprintln(Stderr, "Run `tailscale update` or `tailscale set --auto-update` to update")
+						}
 					}
 					select {
 					case running <- true: