cmd/vet: add static vet checker that runs jsontags (#17778)

This starts running the jsontags vet checker on the module.
All existing findings are adding to an allowlist.

Updates tailscale/corp#791

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

cmd/vet/vet.go

@@ -0,0 +1,24 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package vet is a tool to statically check Go source code.
+package main
+
+import (
+	_ "embed"
+
+	"golang.org/x/tools/go/analysis/unitchecker"
+	"tailscale.com/cmd/vet/jsontags"
+)
+
+//go:embed jsontags_allowlist
+var jsontagsAllowlistSource string
+
+func init() {
+	jsontags.RegisterAllowlist(jsontags.ParseAllowlist(jsontagsAllowlistSource))
+	jsontags.RegisterPureIsZeroMethods(jsontags.PureIsZeroMethodsInTailscaleModule)
+}
+
+func main() {
+	unitchecker.Main(jsontags.Analyzer)
+}