Update

vendor/tailscale.com/net/routecheck/log.go

@@ -0,0 +1,32 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package routecheck
+
+import (
+	"log"
+
+	"tailscale.com/envknob"
+)
+
+// Debugging tweakable.
+var debugRoutecheck = envknob.RegisterBool("TS_DEBUG_ROUTECHECK")
+
+// Logf calls [Client.Logf] to print to a logger.
+// Arguments are handled in the manner of fmt.Printf.
+func (c *Client) logf(format string, a ...any) {
+	if c.Logf != nil {
+		c.Logf(format, a...)
+	} else {
+		log.Printf(format, a...)
+	}
+}
+
+// Vlogf calls [Client.Logf] to print to a logger, only when in debug mode,
+// which is when the TS_DEBUG_ROUTECHECK environment variable is set.
+// Arguments are handled in the manner of fmt.Printf.
+func (c *Client) vlogf(format string, a ...any) {
+	if c.Verbose || debugRoutecheck() {
+		c.logf(format, a...)
+	}
+}