Hide login screen advance settings behind few taps

By default, only show the version number in the login screen's menu.
But if you open and close it a few times, then show the alternate
control plane server option. It's always shown if you've ever edited
the value.

And rename it to just "Change server" and remove "Advanced".

Updates tailscale/tailscale-android#45

cmd/tailscale/ui.go

@@ -30,6 +30,7 @@ import (
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/ipn"
 	"tailscale.com/tailcfg"
+	"tailscale.com/version"
 
 	_ "embed"
 
@@ -78,7 +79,7 @@ type UI struct {
 		list    layout.List
 	}
 
-	runningExit   bool // are we an exit node now?
+	runningExit bool // are we an exit node now?
 
 	qr struct {
 		show bool
@@ -92,9 +93,11 @@ type UI struct {
 	}
 
 	menu struct {
-		open    widget.Clickable
+		open          widget.Clickable
-		dismiss Dismiss
+		dismiss       Dismiss
-		show    bool
+		show          bool
+		showHistory   []showChange
+		showDebugMenu bool
 
 		useLoginServer widget.Clickable
 		copy           widget.Clickable
@@ -247,6 +250,12 @@ func newUI(store *stateStore) (*UI, error) {
 	ui.loginServer.SingleLine = true
 	ui.exitDialog.list.Axis = layout.Vertical
 	ui.shareDialog.list.Axis = layout.Vertical
+
+	// If they've ever set the control plane, give them the debug menu right away.
+	if v, _ := ui.store.ReadString(customLoginServerPrefKey, ""); v != "" {
+		ui.menu.showDebugMenu = true
+	}
+
 	return ui, nil
 }
 
@@ -278,6 +287,34 @@ func (ui *UI) activeDialog() *bool {
 	return nil
 }
 
+type showChange struct {
+	at    time.Time
+	shown bool
+}
+
+func (ui *UI) setMenuShown(v bool) {
+	if v == ui.menu.show {
+		return
+	}
+	ui.menu.show = v
+
+	now := time.Now()
+	const recent = 5 * time.Second
+	recentHistory := ui.menu.showHistory[:0]
+	for _, hi := range ui.menu.showHistory {
+		if now.Sub(hi.at) < recent {
+			recentHistory = append(recentHistory, hi)
+		}
+	}
+	ui.menu.showHistory = append(recentHistory, showChange{
+		at:    now,
+		shown: v,
+	})
+	if len(ui.menu.showHistory) >= 6 {
+		ui.menu.showDebugMenu = true
+	}
+}
+
 func (ui *UI) layout(gtx layout.Context, sysIns system.Insets, state *clientState) []UIEvent {
 	// "Get started".
 	if ui.intro.show {
@@ -302,7 +339,7 @@ func (ui *UI) layout(gtx layout.Context, sysIns system.Insets, state *clientStat
 		}
 	}
 	for ui.menu.open.Clicked() {
-		ui.menu.show = !ui.menu.show
+		ui.setMenuShown(!ui.menu.show)
 	}
 
 	netmap := state.backend.NetworkMap
@@ -844,7 +881,7 @@ func (ui *UI) layoutIntro(gtx layout.Context, sysIns system.Insets) {
 func (ui *UI) menuClicked(btn *widget.Clickable) bool {
 	cl := btn.Clicked()
 	if cl {
-		ui.menu.show = false
+		ui.setMenuShown(false)
 	}
 	return cl
 }
@@ -1091,7 +1128,7 @@ func layoutDialog(gtx layout.Context, w layout.Widget) layout.Dimensions {
 func (ui *UI) layoutMenu(gtx layout.Context, sysIns system.Insets, expiry time.Time, showExits bool, needsLogin bool) {
 	ui.menu.dismiss.Add(gtx, color.NRGBA{})
 	if ui.menu.dismiss.Dismissed(gtx) {
-		ui.menu.show = false
+		ui.setMenuShown(false)
 	}
 	layout.Inset{
 		Top:   unit.Add(gtx.Metric, sysIns.Top, unit.Dp(2)),
@@ -1103,11 +1140,15 @@ func (ui *UI) layoutMenu(gtx layout.Context, sysIns system.Insets, expiry time.T
 				return D{}
 			}
 			if needsLogin {
-				items := []menuItem{
+				var items []menuItem
-					{title: "Use login server", btn: &menu.useLoginServer},
+				title := "Tailscale " + version.Short
+				if ui.menu.showDebugMenu {
+					items = []menuItem{
+						{title: "Change server", btn: &menu.useLoginServer},
+					}
 				}
 				return layoutMenu(ui.theme, gtx, items, func(gtx C) D {
-					l := material.Caption(ui.theme, "Advanced settings")
+					l := material.Caption(ui.theme, title)
 					return l.Layout(gtx)
 				})
 			}