Rename electrum's sync/scan

[danielabrozzoni]

We can probably have more descriptive names, and that make it easier to distinguish between them (I keep confusing them, maybe it's just me). I don't have any proposal in mind, but I'm opening the issue for future reference

[notmandatory]

I added this to the alpha.3 milestone since we need to get questions like this figured out for bdk wallet API also (if we're going to change it).

[vladimirfomene]

Good one @danielabrozzoni ! I usually also confuse them.

[danielabrozzoni]

An explanation of scan and sync from @evanlinjin on Discord:

I also find it confusing actually. Think of scan as a "full sync" - we scan through every spk of each keychain and only stop when there is a "stop gap" count of spks that don't have txs.
sync is the "light sync". We look for transactions/updates which:

• Spend our UTXOs
• Send to our unused addresses.
• Whether our unconfirmed tx gets confirmed.

Maybe fullsync/lightsync might be more explicative names?

[danielabrozzoni]

Copy-pasting from discord to here for tracking purposes (https://discord.com/channels/753336465005608961/753367451319926827/1161271894679486476):

@evanlinjin:
cc @LLFourn , what was the original intention of using scan/sync?

@LLFourn:
The intention with the naming is that sync is the one you should use when you are synchronising local state with the Bitcoin network.
Scan is for when you do not want to use your local state because it is wrong for some reason.

@danielabrozzoni:
Mhhh, what about renaming scan to rescan?

@LLFourn:
The reason why sync/lightsync doesn't make sense to me is that there is nothing light about sync in my view. And with scan you are not really synchronising anything you are just going out and gathering information. That's what I was trying communicate.

@LLFourn:
Yes I like that. The main problem ATM is that the arguments to "scan" are not great. It should only have keychain spks and stop gap.
The main thing we have to succeed at is to communicate that you shouldn't be using "scan" on electrum or esplora all the time.
Ideally youd never use it unless you recover a wallet.
Rescan seems like a better name for this.

@vladimirfomene:
Why rescan though? Scan seems to make more sense to me than rescan. Maybe we just need to better document what each (scan/sync) means

@evanlinjin:
I like rescan better as it has the connotation of scanning from the start, which is exactly what it is doing. sync has the connotation of getting my data up to sync.

@danielabrozzoni:
Yeah, I like rescan because it's obvious from the name that it scans from the start, and thus you shouldn't do it unless you have a specific reason for doing so

[thunderbiscuit]

Just my 2 sats (I don't want to bikeshed too much on this but since we're renaming anyway...).

To me, "rescan" implies an action supplementary to something you've already done. Calling rescan on the first boot of a wallet feels like a misnomer a little bit, and will have me look into the docs for the actual "scan" method (surely I should call the scan before the rescan... it must be there somewhere, or so my thinking would go).

When I think of the relative use of those methods, I see scan/rescan as something you only do once in a blue moon vs sync which you call all the time and maybe even have on some loop. The ratio is like 100:1, and in that sense I feel like the rescan/scan name should reflect the "gravity" of that call. Something like fullscan maybe would really set the methods apart. You call fullscan once, and after that it's all sync.

If "fullscan" or something like that is too much, my second preferred option is actually just a well documented scan. You scan once, then you sync. Rescan doesn't quite do if for me (sorry rescan team!). Just my thoughts.

[realeinherjar]

Also I think we should check electrumx naming since we are defining an API that consumes from electrum.
We should have the user in mind, not us.
And what the user is familiar with.

• sync: https://electrumx-spesmilo.readthedocs.io/en/latest/HOWTO.html#sync-progress
  This is documented in electrumx and it means, at least from my understanding, the same as @danielabrozzoni's full sync definition:

  we scan through every spk of each keychain and only stop when there is a "stop gap" count of spks that don't have txs

• scan: we have more leeway here since scan is only mentioned twice in the electrumx codebase (https://github.com/search?q=repo%3Aspesmilo%2Felectrumx%20scan&type=code) with inconclusive results.
  However, in the electrum codebase, there's an internal mention of scan (https://github.com/spesmilo/electrum/blob/36814d731aaddf622ce37c43a7c755e8a69d645c/electrum/gui/qml/qebip39recovery.py#L73) which implies a new wallet from scratch given a mnemonic and wallet type.

So given this, we should differentiate scan vs sync, as the scan being the more "deep" one.
Or, in other words, the one that assume less state.
This is in agreement with @thunderbiscuit's You call fullscan once, and after that it's all sync.

These are my "two-sats" on the matter.

[notmandatory]

my 2 sats, for reasons mentioned above, is we stick with scan and sync with clear docs on when to use each. :-) Is it OK if I just put a little poll on discord, people can multiple vote for all the ones they can live with? Options being:

• scan, sync
• fullscan, lightsync
• rescan, sync
• fullscan, sync

any others?