Changing a folder label should not trigger a rescan

[tomasz1986]

Right now, changing a folder label immediately triggers a rescan of that folder. While usually not a big deal, this can be annoying when dealing with huge folders and/or slow hardware. I think that it would be nice not to trigger a rescan if the change does not affect the actual synchronisation.

[rjpruitt16]

Is this something a noob like me could try?

[imsodin]

It's not super easy, as it involves model-folder interactions and handling config changes. As in currently folders are indiscriminately restarted when their config changes, which would have to be changed to some kind of mechanism to let folders know about changed config and then decide whether they can adjust on the fly or need to restart (maybe restart should never be necessary). However it would definitely be an opportunity to learn about Syncthing internals :)

[AudriusButkevicius]

I think there is already code that should handle this, as label is marked as restart=false in the config, so folders should not be restarted in the model. That doesn't work for some reason.

I'd start debugging here:

https://github.com/syncthing/syncthing/blob/main/lib/model/model.go#L2493

[imsodin]

I thought the restart annotations are only for full Syncthing restarts. If it is meant to apply to folder restarts, that's not only not working, but also not fully implemented: There's no way the folder gets config updates for non-restart config changes (e.g. the label is relevant for the folder).

[AudriusButkevicius]

Restart annotations are what we make of it, there is simply a util function that returns a copy of the struct with fields that have restart:"true" or that do not have restart:"false". This is exactly what RequiresRestartOnly() on a folder does, returns a copy of the struct only with the fields that require restart, so the reflect.DeepEquals is what checks that. This is checked in the model (which I guess is somewhat wrong), so any folder change does run the check.