Sync sync progress

[BartG95]

The double 'sync' is not a typo.

Suppose a cluster of three devices, Alpha, Bravo and Charlie.
They are all connected, but Alpha and Bravo are seldom simultaneously online. Charlie is almost always online.
When Alpha updates a file, it will sync to Charlie. Then Alpha goes offline, Bravo goes online, and Bravo receives the update from Charlie. Then Bravo goes offline, Alpha goes online.
Alpha will show that is has pending updates for Bravo, while in fact, those updates are already on Bravo.

Maybe Charlie can sync this sync progress?

[nekr0z]

Charlie has no way of knowing that Alpha even knows that Bravo exists, unless there's a common introducer.

Syncing the sync status via a common introducer or a chain of introducers may be feasible, though. I think I could try to work on this, if maintainers think such a feature would be welcome.

[calmh]

This is not a trivial addition, I think, and I'm unsure it's worth it.

[BartG95]

Charlie has no way of knowing that Alpha even knows that Bravo exists, unless there's a common introducer.

Well, sync that as well?

But yeah, I am aware of the complexity of this.

[nekr0z]

Well, sync that as well?

That's potentially leaking information that may be private; not worth it for a convenience feature like this one.

[acolomb]

Actually the ClusterConfig message does include information about third parties sharing the same folders, at least for a distance of one hop. That is valuable and useful, though not currently getting exposed within Syncthing in any way. Something I initially set out to improve, but didn't get to work on much lately.

Regarding the original feature request, I'd also think it complicates things much more than is the actual benefit.

[calmh]

I don't think we want to do this.