ipn: use cmd/cloner for Prefs.Clone

Also, make cmd/cloner's top-level "func Clone" generation opt-in.

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

ipn/prefs.go

@@ -20,6 +20,8 @@ import (
 	"tailscale.com/wgengine/router"
 )
 
+//go:generate go run tailscale.com/cmd/cloner -type=Prefs -output=prefs_clone.go
+
 // Prefs are the user modifiable settings of the Tailscale node agent.
 type Prefs struct {
 	// ControlURL is the URL of the control server to use.
@@ -261,16 +263,6 @@ func PrefsFromBytes(b []byte, enforceDefaults bool) (*Prefs, error) {
 	return p, err
 }
 
-// Clone returns a deep copy of p.
-func (p *Prefs) Clone() *Prefs {
-	// TODO: write a faster/non-Fatal-y Clone implementation?
-	p2, err := PrefsFromBytes(p.ToBytes(), false)
-	if err != nil {
-		log.Fatalf("Prefs was uncopyable: %v\n", err)
-	}
-	return p2
-}
-
 // LoadPrefs loads a legacy relaynode config file into Prefs
 // with sensible migration defaults set.
 func LoadPrefs(filename string) (*Prefs, error) {

ipn/prefs_clone.go

@@ -0,0 +1,51 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Code generated by tailscale.com/cmd/cloner -type Prefs; DO NOT EDIT.
+
+package ipn
+
+import (
+	"github.com/tailscale/wireguard-go/wgcfg"
+	"tailscale.com/control/controlclient"
+	"tailscale.com/wgengine/router"
+)
+
+// Clone makes a deep copy of Prefs.
+// The result aliases no memory with the original.
+func (src *Prefs) Clone() *Prefs {
+	if src == nil {
+		return nil
+	}
+	dst := new(Prefs)
+	*dst = *src
+	dst.AdvertiseTags = append(src.AdvertiseTags[:0:0], src.AdvertiseTags...)
+	dst.AdvertiseRoutes = append(src.AdvertiseRoutes[:0:0], src.AdvertiseRoutes...)
+	if dst.Persist != nil {
+		dst.Persist = new(controlclient.Persist)
+		*dst.Persist = *src.Persist
+	}
+	return dst
+}
+
+// A compilation failure here means this code must be regenerated, with command:
+//   tailscale.com/cmd/cloner -type Prefs
+var _PrefsNeedsRegeneration = Prefs(struct {
+	ControlURL       string
+	RouteAll         bool
+	AllowSingleHosts bool
+	CorpDNS          bool
+	WantRunning      bool
+	ShieldsUp        bool
+	AdvertiseTags    []string
+	Hostname         string
+	OSVersion        string
+	DeviceModel      string
+	NotepadURLs      bool
+	ForceDaemon      bool
+	AdvertiseRoutes  []wgcfg.CIDR
+	NoSNAT           bool
+	NetfilterMode    router.NetfilterMode
+	Persist          *controlclient.Persist
+}{})