clientupdate: don't link distsign on platforms that don't download

Updates tailscale/corp#20099

Change-Id: Ie3b782379b19d5f7890a8d3a378096b4f3e8a612
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

clientupdate/clientupdate.go

@@ -27,7 +27,6 @@
 	"strconv"
 	"strings"
 
-	"tailscale.com/clientupdate/distsign"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/cmpver"
 	"tailscale.com/version"
@@ -778,14 +777,6 @@ func (up *Updater) cleanupOldDownloads(glob string) {
 	}
 }
 
-func (up *Updater) downloadURLToFile(pathSrc, fileDst string) (ret error) {
-	c, err := distsign.NewClient(up.Logf, up.PkgsAddr)
-	if err != nil {
-		return err
-	}
-	return c.Download(context.Background(), pathSrc, fileDst)
-}
-
 func (up *Updater) updateFreeBSD() (err error) {
 	if up.Version != "" {
 		return errors.New("installing a specific version on FreeBSD is not supported")

clientupdate/clientupdate_downloads.go

@@ -0,0 +1,20 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build (linux && !android) || windows
+
+package clientupdate
+
+import (
+	"context"
+
+	"tailscale.com/clientupdate/distsign"
+)
+
+func (up *Updater) downloadURLToFile(pathSrc, fileDst string) (ret error) {
+	c, err := distsign.NewClient(up.Logf, up.PkgsAddr)
+	if err != nil {
+		return err
+	}
+	return c.Download(context.Background(), pathSrc, fileDst)
+}

clientupdate/clientupdate_not_downloads.go

@@ -0,0 +1,10 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !((linux && !android) || windows)
+
+package clientupdate
+
+func (up *Updater) downloadURLToFile(pathSrc, fileDst string) (ret error) {
+	panic("unreachable")
+}

cmd/k8s-operator/depaware.txt

@@ -654,7 +654,7 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         tailscale.com/client/tailscale/apitype                       from tailscale.com/client/tailscale+
         tailscale.com/client/web                                     from tailscale.com/ipn/ipnlocal
         tailscale.com/clientupdate                                   from tailscale.com/client/web+
-        tailscale.com/clientupdate/distsign                          from tailscale.com/clientupdate
+  LW    tailscale.com/clientupdate/distsign                          from tailscale.com/clientupdate
         tailscale.com/control/controlbase                            from tailscale.com/control/controlhttp+
         tailscale.com/control/controlclient                          from tailscale.com/ipn/ipnlocal+
         tailscale.com/control/controlhttp                            from tailscale.com/control/controlclient

cmd/tailscale/depaware.txt

@@ -80,7 +80,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/client/tailscale/apitype                       from tailscale.com/client/tailscale+
         tailscale.com/client/web                                     from tailscale.com/cmd/tailscale/cli
         tailscale.com/clientupdate                                   from tailscale.com/client/web+
-        tailscale.com/clientupdate/distsign                          from tailscale.com/clientupdate
+  LW    tailscale.com/clientupdate/distsign                          from tailscale.com/clientupdate
         tailscale.com/cmd/tailscale/cli                              from tailscale.com/cmd/tailscale
         tailscale.com/cmd/tailscale/cli/ffcomplete                   from tailscale.com/cmd/tailscale/cli
         tailscale.com/cmd/tailscale/cli/ffcomplete/internal          from tailscale.com/cmd/tailscale/cli/ffcomplete

cmd/tailscaled/depaware.txt

@@ -244,7 +244,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/client/tailscale/apitype                       from tailscale.com/client/tailscale+
         tailscale.com/client/web                                     from tailscale.com/ipn/ipnlocal
         tailscale.com/clientupdate                                   from tailscale.com/client/web+
-        tailscale.com/clientupdate/distsign                          from tailscale.com/clientupdate
+  LW    tailscale.com/clientupdate/distsign                          from tailscale.com/clientupdate
         tailscale.com/cmd/tailscaled/childproc                       from tailscale.com/cmd/tailscaled+
         tailscale.com/control/controlbase                            from tailscale.com/control/controlhttp+
         tailscale.com/control/controlclient                          from tailscale.com/cmd/tailscaled+

tstest/iosdeps/iosdeps_test.go

@@ -22,6 +22,7 @@ func TestDeps(t *testing.T) {
 			"github.com/mitchellh/go-ps":          "https://github.com/tailscale/tailscale/pull/13759",
 			"database/sql/driver":                 "iOS doesn't use an SQL database",
 			"github.com/google/uuid":              "see tailscale/tailscale#13760",
+			"tailscale.com/clientupdate/distsign": "downloads via AppStore, not distsign",
 		},
 	}.Check(t)
 }