cmd/tailscale: remove dep on clientupdate package if feature is omitted

We already had a featuretag for clientupdate, but the CLI wasn't using
it, making the "minbox" build (minimal combined tailscaled + CLI
build) larger than necessary.

Updates #12614

Change-Id: Idd7546c67dece7078f25b8f2ae9886f58d599002
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscale/cli/cli.go

@@ -219,6 +219,7 @@ var (
 	maybeFunnelCmd,
 	maybeServeCmd,
 	maybeCertCmd,
+	maybeUpdateCmd,
 	_ func() *ffcli.Command
 )
 
@@ -270,7 +271,7 @@ change in the future.
 			nilOrCall(maybeNetlockCmd),
 			licensesCmd,
 			exitNodeCmd(),
-			updateCmd,
+			nilOrCall(maybeUpdateCmd),
 			whoisCmd,
 			debugCmd(),
 			nilOrCall(maybeDriveCmd),

cmd/tailscale/cli/update.go

@@ -1,6 +1,8 @@
 // Copyright (c) Tailscale Inc & contributors
 // SPDX-License-Identifier: BSD-3-Clause
 
+//go:build !ts_omit_clientupdate
+
 package cli
 
 import (
@@ -17,6 +19,14 @@ import (
 	"tailscale.com/version/distro"
 )
 
+func init() {
+	maybeUpdateCmd = func() *ffcli.Command { return updateCmd }
+
+	clientupdateLatestTailscaleVersion.Set(func() (string, error) {
+		return clientupdate.LatestTailscaleVersion(clientupdate.CurrentTrack)
+	})
+}
+
 var updateCmd = &ffcli.Command{
 	Name:       "update",
 	ShortUsage: "tailscale update",

cmd/tailscale/cli/version.go

@@ -10,7 +10,7 @@ import (
 	"fmt"
 
 	"github.com/peterbourgon/ff/v3/ffcli"
-	"tailscale.com/clientupdate"
+	"tailscale.com/feature"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/version"
 )
@@ -35,6 +35,8 @@ var versionArgs struct {
 	upstream bool
 }
 
+var clientupdateLatestTailscaleVersion feature.Hook[func() (string, error)]
+
 func runVersion(ctx context.Context, args []string) error {
 	if len(args) > 0 {
 		return fmt.Errorf("too many non-flag arguments: %q", args)
@@ -51,7 +53,11 @@ func runVersion(ctx context.Context, args []string) error {
 
 	var upstreamVer string
 	if versionArgs.upstream {
-		upstreamVer, err = clientupdate.LatestTailscaleVersion(clientupdate.CurrentTrack)
+		f, ok := clientupdateLatestTailscaleVersion.GetOk()
+		if !ok {
+			return fmt.Errorf("fetching latest version not supported in this build")
+		}
+		upstreamVer, err = f()
 		if err != nil {
 			return err
 		}