Update

vendor/tailscale.com/health/usermetrics.go

@@ -0,0 +1,52 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_health && !ts_omit_usermetrics
+
+package health
+
+import (
+	"expvar"
+
+	"tailscale.com/feature/buildfeatures"
+	"tailscale.com/util/usermetric"
+)
+
+const MetricLabelWarning = "warning"
+
+type metricHealthMessageLabel struct {
+	// TODO: break down by warnable.severity as well?
+	Type string
+}
+
+// SetMetricsRegistry sets up the metrics for the Tracker. It takes
+// a usermetric.Registry and registers the metrics there.
+func (t *Tracker) SetMetricsRegistry(reg *usermetric.Registry) {
+	if !buildfeatures.HasHealth {
+		return
+	}
+
+	if reg == nil || t.metricHealthMessage != nil {
+		return
+	}
+
+	m := usermetric.NewMultiLabelMapWithRegistry[metricHealthMessageLabel](
+		reg,
+		"tailscaled_health_messages",
+		"gauge",
+		"Number of health messages broken down by type.",
+	)
+
+	m.Set(metricHealthMessageLabel{
+		Type: MetricLabelWarning,
+	}, expvar.Func(func() any {
+		if t.nil() {
+			return 0
+		}
+		t.mu.Lock()
+		defer t.mu.Unlock()
+		t.updateBuiltinWarnablesLocked()
+		return int64(len(t.stringsLocked()))
+	}))
+	t.metricHealthMessage = m
+}