cmd/syncthing: Generate FolderCompletion events for folders shared with a connecting device (fixes #3436)

This used to happen by itself as the connecting device always sent an
Index message and we triggered on that. Nowadays there's no guarantee
for that, but we anyway need to send out one event to let listeners know
the state of folders shared with the device.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3438

cmd/syncthing/summaryservice.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/syncthing/syncthing/lib/events"
+	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/sync"
 	"github.com/thejerf/suture"
 )
@@ -59,7 +60,7 @@ func (c *folderSummaryService) Stop() {
 // listenForUpdates subscribes to the event bus and makes note of folders that
 // need their data recalculated.
 func (c *folderSummaryService) listenForUpdates() {
-	sub := events.Default.Subscribe(events.LocalIndexUpdated | events.RemoteIndexUpdated | events.StateChanged | events.RemoteDownloadProgress)
+	sub := events.Default.Subscribe(events.LocalIndexUpdated | events.RemoteIndexUpdated | events.StateChanged | events.RemoteDownloadProgress | events.DeviceConnected)
 	defer events.Default.Unsubscribe(sub)
 
 	for {
@@ -67,8 +68,31 @@ func (c *folderSummaryService) listenForUpdates() {
 
 		select {
 		case ev := <-sub.C():
-			// Whenever the local or remote index is updated for a given
-			// folder we make a note of it.
+			if ev.Type == events.DeviceConnected {
+				// When a device connects we schedule a refresh of all
+				// folders shared with that device.
+
+				data := ev.Data.(map[string]string)
+				deviceID, _ := protocol.DeviceIDFromString(data["id"])
+
+				c.foldersMut.Lock()
+			nextFolder:
+				for _, folder := range c.cfg.Folders() {
+					for _, dev := range folder.Devices {
+						if dev.DeviceID == deviceID {
+							c.folders[folder.ID] = struct{}{}
+							continue nextFolder
+						}
+					}
+				}
+				c.foldersMut.Unlock()
+
+				continue
+			}
+
+			// The other events all have a "folder" attribute that they
+			// affect. Whenever the local or remote index is updated for a
+			// given folder we make a note of it.
 
 			data := ev.Data.(map[string]interface{})
 			folder := data["folder"].(string)