all: Convert folders to use filesystem abstraction

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4228

lib/fs/types.go

@@ -0,0 +1,36 @@
+// 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 https://mozilla.org/MPL/2.0/.
+
+package fs
+
+type FilesystemType int
+
+const (
+	FilesystemTypeBasic FilesystemType = iota // default is basic
+)
+
+func (t FilesystemType) String() string {
+	switch t {
+	case FilesystemTypeBasic:
+		return "basic"
+	default:
+		return "unknown"
+	}
+}
+
+func (t FilesystemType) MarshalText() ([]byte, error) {
+	return []byte(t.String()), nil
+}
+
+func (t *FilesystemType) UnmarshalText(bs []byte) error {
+	switch string(bs) {
+	case "basic":
+		*t = FilesystemTypeBasic
+	default:
+		*t = FilesystemTypeBasic
+	}
+	return nil
+}