Syncthing: Folders getting stuck in "Syncing" after a20c6ca after doing changes when folders are paused

[tomasz1986]

After a20c6ca868db44327575440bfa3501f96ba3afcd, there is no disconnect on config change anymore, but folders seem to get stuck in the "Syncing" state.

How to reproduce:

1. Pause local folders.
2. Do changes in local folders.
3. Unpause local folders.

Once stuck, they seem to stay like that basically forever. There is also nothing in the logs.

I have to pause and resume the affected devices (and hence force a connection reset) in order to make the folders actually sync the changes.

Tested with main (v1.10.1-dev.23.gd828adb6).

[calmh]

The problem is that we create a new fileset when pausing/resuming the folder, but the index sender retains the old one which is no longer updated. Either we need to stop index senders on pause and start them again on resume (but that's ugly because they share scope and lifetime with a connection not a folder), or we need to never drop an existing fileset for a folder that still exists.

[calmh]

The problem is also slightly larger, because it applies when we remove a folder completely (index senders are left behind, though they will not do much harm) and when we add a new folder (index senders are not started). I'm minded to back out the relevant change for now and take a larger grip around the whole folders-filesets-and-index-senders piece...

[imsodin]

Just from a second of thought, don't have time to consider wider implications/larger scope: Stopping index senders when stopping (pausing/removing) folders should solve this and is the right thing to do anyway.