qt: Add option to (not) spend unconfirmed change #3676

• Add a wallet tab to options dialog
• Move fee setting to wallet tab
• Add new setting to set -spendzeroconfchange from UI

Implementation is straightforward, messages are up for discussion as usual.

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Nit about the wording:

If you disable the spending of unconfirmed change, your transaction cannot be completed until your previous transactions have at least one confirmation. This also affects how your balance is computed.

Isn't that a little pessimistic? I mean in practice, a wallet will have multiple outputs to use, only a few of which will be used by any single transaction. How about:

If you disable the spending of unconfirmed change, the change from a transaction cannot be used until that transaction has at least one confirmation. This also affects how your balance is computed.

Of course, the problem with that a user may not understand the concept of change outputs, since that is hidden from them.

Think of this in the real world.

Spending something you don’t have is obviously not possible. So why not simply say the following:

ADVANCED:

[ ] Allow spending of unconfirmed changed.

(leaving the flag off by default).

You are not going to explain this adequately in 5 lines or less – especially to nubs .. so why bother ? Let them that wish to use it, RTFM some and then its caveat emptor if they flip it on.

This looks to be the first mention of "change" period. A rational user will think it relates to change returned by recipient for amount paid over some agreed-on price, which further confuses, since no such prices are known by bitcoin-qt.

The question is what should the message say, given the abstractions user is working with? That is a tough one.

If this also affects, how we compute the wallet balance, perhaps name the option Treat unconfirmed change as confirmed (experts only). And append (experts only), because it is similar complex for normal users like coin control IMHO and you need some knowledge of what you are doing.

To go further, we should also rework the descriptive string for the command line option, because this misses also that using that options or disabling it will affect how balance is computed. IMHO it could be the same string with (experts only) left out.

I also like @christophebiocca's suggestion for a less dramatic wording. As unused change won't block a transaction, it just won't allow using the change in new transactions, right?

That wording makes a lot of sense (Diapolo).

Will switch to @christophebiocca's wording and SetSoftBoolArg and add (experts only) like for coin control.

Why did you decide agains Spend unconfirmed change (experts only)? IMO Spend unconfirmed change (experts only) is not the whole truth (even more true for just the command line option), as it changes how we compute the balance...

@Diapolo Don't change the name of the command line option because people are relying on it in production. Feel free to send pulls for improvements to the UI message though...

Also: it affects coin selection primarily. The reason it also affects the balance computation is because otherwise you cannot trust that the (confirmed) balance is really how much you can spend.

@laanwj Don't get it, if it affects balance computation (the reason why doesn't even matter, it's just the fact), then it has to be mentioned in the help message. The reason to not change the command line message is also unclear still... it is in an unreleased branch (no official client released with it), why can't we just use Treat unconfirmed change as confirmed?

I know you will tell me we have bigger problems to solve, but this is something I fell is important enought ;).

Maybe unconfirmed balance should just be "balance" (it's the amount of money you're reasonably sure about you have, assuming it doesn't count -1 confirmed coins), and confirmed balance should be "spendable balance". The latter can then be affected by the setting of whether to consider unconfirmed change as spendable.

Armory uses the words : Maximum Funds / Unconfirmed Fund and Spendable and shows 3 balances. One of the many reasons I use Armory. (this is not an advert for Armory - just a suggestion )

@sipa That would make sense indeed. "Confirmed balance" has always been "Spendable balance". But "Unconfirmed balance" would then be "Unspendable balance"? @int03h Bitcoin-qt also shows 3 (or even 4, if you have immature transactions) balances: Confirmed, Unconfirmed, Immature and Total.

@diapolo I'm doubtful about that because "Treat unconfirmed change as confirmed" doesn't really tell much. It creates a categorical confusion much like #3662 was aimed at solving (in the API we now call transactions that count toward spendable balance "Trusted" instead). Saying that it is spendable/unspendable at least tells you what you can do with it. But then the names of the balances need to be changed too.

Yeah, if you're treating unconfirmed change as confirmed, the meaning of the word confirmed becomes blurry.

To answer the question "how much money will I (likely) (eventually) have", the current "unconfirmed balance" (excluding conflicted/noninmempool transactions) seems the correct measurement. I guess that should also include immature coins. Maybe it could be called "Eventual balance" ?

Well currently it looks like this

Instead of the three groups I suppose we could also make a tally like this (rows only shown if the balance is >0):

Spendable                       XXX BTC
Spendable after 1 block         XXX BTC (=unconfirmed balance)
Spendable after XXX blocks      XXX BTC (=immature balances)
....
------------------------------------------------------
Eventual total                  XXX BTC

Edit: eh no that's no good either, one of course cannot be sure that the unconfirmed balance will confirm in 1 block...