all: Add filesystem notification support

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

vendor/github.com/zillode/notify/watchpoint_readdcw.go

@@ -0,0 +1,38 @@
+// Copyright (c) 2014-2015 The Notify Authors. All rights reserved.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+// +build windows
+
+package notify
+
+// eventmask uses ei to create a new event which contains internal flags used by
+// notify package logic. If one of FileAction* masks is detected, this function
+// adds corresponding FileNotifyChange* values. This allows non registered
+// FileAction* events to be passed on.
+func eventmask(ei EventInfo, extra Event) (e Event) {
+	if e = ei.Event() | extra; e&fileActionAll != 0 {
+		if ev, ok := ei.(*event); ok {
+			switch ev.ftype {
+			case fTypeFile:
+				e |= FileNotifyChangeFileName
+			case fTypeDirectory:
+				e |= FileNotifyChangeDirName
+			case fTypeUnknown:
+				e |= fileNotifyChangeModified
+			}
+			return e &^ fileActionAll
+		}
+	}
+	return
+}
+
+// matches reports a match only when:
+//
+//   - for user events, when event is present in the given set
+//   - for internal events, when additionally both event and set have omit bit set
+//
+// Internal events must not be sent to user channels and vice versa.
+func matches(set, event Event) bool {
+	return (set&omit)^(event&omit) == 0 && (set&event == event || set&fileNotifyChangeModified&event != 0)
+}