cmd/syncthing, lib/api: Separate api/gui into own package (ref #4085) (#5529)

* cmd/syncthing, lib/gui: Separate gui into own package (ref #4085)

* fix tests

* Don't use main as interface name (make old go happy)

* gui->api

* don't leak state via locations and use in-tree config

* let api (un-)subscribe to config

* interface naming and exporting

* lib/ur

* fix tests and lib/foldersummary

* shorter URVersion and ur debug fix

* review

* model.JsonCompletion(FolderCompletion) -> FolderCompletion.Map()

* rename debug facility https -> api

* folder summaries in model

* disassociate unrelated constants

* fix merge fail

* missing id assignement

lib/api/debug.go

@@ -0,0 +1,28 @@
+// Copyright (C) 2014 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 api
+
+import (
+	"os"
+	"strings"
+
+	"github.com/syncthing/syncthing/lib/logger"
+)
+
+var (
+	l = logger.DefaultLogger.NewFacility("api", "REST API")
+)
+
+func shouldDebugHTTP() bool {
+	return l.ShouldDebug("api")
+}
+
+func init() {
+	// The debug facility was originally named "http", changed in:
+	// https://github.com/syncthing/syncthing/pull/5548
+	l.SetDebug("api", strings.Contains(os.Getenv("STTRACE"), "api") || strings.Contains(os.Getenv("STTRACE"), "http") || os.Getenv("STTRACE") == "all")
+}