all: Add filesystem notification support

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3986

lib/watchaggregator/debug.go

@@ -0,0 +1,24 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package watchaggregator
+
+import (
+	"os"
+	"strings"
+
+	"github.com/syncthing/syncthing/lib/logger"
+)
+
+var facilityName = "watchaggregator"
+
+var (
+	l = logger.DefaultLogger.NewFacility(facilityName, "Filesystem event watcher")
+)
+
+func init() {
+	l.SetDebug(facilityName, strings.Contains(os.Getenv("STTRACE"), facilityName) || os.Getenv("STTRACE") == "all")
+}