feature/featuretags: make QR codes modular (#18358)

QR codes are used by `tailscale up --qr` to provide an easy way to
open a web-page without transcribing a difficult URI. However, there’s
no need for this feature if the client will never be called
interactively. So this PR adds the `ts_omit_qrcodes` build tag.

Updates #18182

Signed-off-by: Simon Law <sfllaw@tailscale.com>

feature/buildfeatures/feature_qrcodes_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_qrcodes
+
+package buildfeatures
+
+// HasQRCodes is whether the binary was built with support for modular feature "QR codes in tailscale CLI".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_qrcodes" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasQRCodes = false

feature/buildfeatures/feature_qrcodes_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_qrcodes
+
+package buildfeatures
+
+// HasQRCodes is whether the binary was built with support for modular feature "QR codes in tailscale CLI".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_qrcodes" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasQRCodes = true

feature/featuretags/featuretags.go

@@ -222,6 +222,7 @@ var Features = map[FeatureTag]FeatureMeta{
 		Desc: "Linux NetworkManager integration",
 		Deps: []FeatureTag{"dbus"},
 	},
+	"qrcodes":     {Sym: "QRCodes", Desc: "QR codes in tailscale CLI"},
 	"relayserver": {Sym: "RelayServer", Desc: "Relay server"},
 	"resolved": {
 		Sym:  "Resolved",