android: add about dialog with license link

Add "about" menu item in both the logged out and logged in menus.  About
dialog shows Tailscale version and link to URL with open source
licenses.

Updates tailscale/corp#5780

Signed-off-by: Will Norris <will@tailscale.com>

cmd/tailscale/main.go

@@ -193,6 +193,7 @@ type (
 	WebAuthEvent      struct{}
 	GoogleAuthEvent   struct{}
 	LogoutEvent       struct{}
+	OSSLicensesEvent  struct{}
 	BeExitNodeEvent   bool
 	ExitAllowLANEvent bool
 )
@@ -1134,6 +1135,8 @@ func (a *App) processUIEvents(w *app.Window, events []UIEvent, act jni.Object, s
 			a.updateState(act, state)
 		case FileSendEvent:
 			a.sendFiles(e, files)
+		case OSSLicensesEvent:
+			a.setURL("https://tailscale.com/licenses/android")
 		}
 	}
 }

cmd/tailscale/ui.go

@@ -105,6 +105,7 @@ type UI struct {
 		bug            widget.Clickable
 		beExit         widget.Clickable
 		exits          widget.Clickable
+		about          widget.Clickable
 		logout         widget.Clickable
 	}
 
@@ -125,6 +126,15 @@ type UI struct {
 		error   error
 	}
 
+	// aboutDialog is state for the about dialog.
+	aboutDialog struct {
+		show    bool
+		dismiss Dismiss
+	}
+
+	// ossLicenses is the button to show the OSS licenses.
+	ossLicenses widget.Clickable
+
 	icons struct {
 		search     *widget.Icon
 		more       *widget.Icon
@@ -283,6 +293,8 @@ func (ui *UI) activeDialog() *bool {
 		return &ui.shareDialog.show
 	case ui.exitDialog.show:
 		return &ui.exitDialog.show
+	case ui.aboutDialog.show:
+		return &ui.aboutDialog.show
 	}
 	return nil
 }
@@ -425,6 +437,14 @@ func (ui *UI) layout(gtx layout.Context, sysIns system.Insets, state *clientStat
 		ui.exitDialog.show = true
 	}
 
+	if ui.menuClicked(&ui.menu.about) {
+		ui.aboutDialog.show = true
+	}
+
+	if ui.ossLicenses.Clicked() {
+		events = append(events, OSSLicensesEvent{})
+	}
+
 	if ui.menuClicked(&ui.menu.logout) {
 		events = append(events, LogoutEvent{})
 	}
@@ -548,6 +568,8 @@ func (ui *UI) layout(gtx layout.Context, sysIns system.Insets, state *clientStat
 
 	ui.layoutShareDialog(gtx, sysIns)
 
+	ui.layoutAboutDialog(gtx, sysIns)
+
 	// Popup messages.
 	ui.layoutMessage(gtx, sysIns)
 
@@ -1043,6 +1065,58 @@ func (ui *UI) layoutExitNodeDialog(gtx layout.Context, sysIns system.Insets, exi
 	})
 }
 
+// layoutAboutDialog lays out the about dialog.
+func (ui *UI) layoutAboutDialog(gtx layout.Context, sysIns system.Insets) {
+	d := &ui.aboutDialog
+	if d.dismiss.Dismissed(gtx) {
+		d.show = false
+	}
+	if !d.show {
+		return
+	}
+	d.dismiss.Add(gtx, argb(0x66000000))
+	layout.Inset{
+		Top:    unit.Add(gtx.Metric, sysIns.Top, unit.Dp(16)),
+		Right:  unit.Add(gtx.Metric, sysIns.Right, unit.Dp(16)),
+		Bottom: unit.Add(gtx.Metric, sysIns.Bottom, unit.Dp(16)),
+		Left:   unit.Add(gtx.Metric, sysIns.Left, unit.Dp(16)),
+	}.Layout(gtx, func(gtx C) D {
+		return layout.Center.Layout(gtx, func(gtx C) D {
+			gtx.Constraints.Min.X = gtx.Px(unit.Dp(250))
+			gtx.Constraints.Max.X = gtx.Constraints.Min.X
+			return layoutDialog(gtx, func(gtx C) D {
+				return layout.Flex{Axis: layout.Vertical}.Layout(gtx,
+					layout.Rigid(func(gtx C) D {
+						// Header.
+						return layout.Inset{
+							Top:    unit.Dp(16),
+							Right:  unit.Dp(20),
+							Left:   unit.Dp(20),
+							Bottom: unit.Dp(16),
+						}.Layout(gtx, func(gtx C) D {
+							l := material.Body1(ui.theme, "About")
+							l.Font.Weight = text.Bold
+							return l.Layout(gtx)
+						})
+					}),
+					layout.Rigid(func(gtx C) D {
+						return layout.UniformInset(unit.Dp(16)).Layout(gtx, func(gtx C) D {
+							return material.Body1(ui.theme, "version "+version.Short).Layout(gtx)
+						})
+					}),
+					layout.Rigid(func(gtx C) D {
+						return material.Clickable(gtx, &ui.ossLicenses, func(gtx C) D {
+							return layout.UniformInset(unit.Dp(16)).Layout(gtx, func(gtx C) D {
+								return material.Body1(ui.theme, "Open Source Licenses").Layout(gtx)
+							})
+						})
+					}),
+				)
+			})
+		})
+	})
+}
+
 func layoutMenu(th *material.Theme, gtx layout.Context, items []menuItem, header layout.Widget) layout.Dimensions {
 	return layoutDialog(gtx, func(gtx C) D {
 		// Lay out menu items twice; once for
@@ -1118,10 +1192,9 @@ func (ui *UI) layoutMenu(gtx layout.Context, sysIns system.Insets, expiry time.T
 				var items []menuItem
 				title := "Tailscale " + version.Short
 				if ui.menu.showDebugMenu {
-					items = []menuItem{
+					items = append(items, menuItem{title: "Change server", btn: &menu.useLoginServer})
-						{title: "Change server", btn: &menu.useLoginServer},
-					}
 				}
+				items = append(items, menuItem{title: "About", btn: &menu.about})
 				return layoutMenu(ui.theme, gtx, items, func(gtx C) D {
 					l := material.Caption(ui.theme, title)
 					return l.Layout(gtx)
@@ -1147,6 +1220,8 @@ func (ui *UI) layoutMenu(gtx layout.Context, sysIns system.Insets, expiry time.T
 			}
 			items = append(items, menuItem{title: title, btn: &menu.beExit})
 
+			items = append(items, menuItem{title: "About", btn: &menu.about})
+
 			return layoutMenu(ui.theme, gtx, items, func(gtx C) D {
 				var expiryStr string
 				const fmtStr = time.Stamp