Concept ACK

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #25933 (wallet: AvailableCoins, simplify output script type acquisition by furszy)
• #25730 (RPC: listunspent, add "include immature coinbase" flag by furszy)
• #25291 (test: Refactor rpc_fundrawtransaction.py by akankshakashyap)
• #25273 (wallet: Pass through transaction locktime and preset input sequences and scripts to CreateTransaction by achow101)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

@aureleoules can we achieve the same result by using descriptors wallet with only segwit descriptors?

Concept ACK.

@brunoerg I think it's fine as it. Should squash if the 1st commit requires the 2nd to pass CI.

@aureleoules can we achieve the same result by using descriptors wallet with only segwit descriptors?

I am not very familiar with wallet descriptors.
Do you mean using a wallet that does not have legacy descriptors imported?
I think @achow101 answed that yes (#25181 (comment)).

But if I understand correctly, this feature might still be useful in cases where you don't control the wallet.

Would it be useful to add the "segwit_inputs_only" option to walletcreatefundedpsbt as well? They both call FundTransaction so I think you would just have to include it in the walletcreatefundedpsbt options.

I've rebased my PR on top of #24584 as @xekyo suggested and addressed the comments.
Thanks for the reviews!

Thank you @josibake for the review and the commits! I added your commits and fixed the list parsing.
I will address the test a bit later.

I have rebased the PR on top of @josibake's PR #25734.
The RPC fundrawtransaction and walletcreatefundedpsbt now take an option to filter inputs during the coin selection.
I've added a test case.

Do you have a concrete use-case in mind? I'm not sure, but it seems #25181 supposes that we do control the wallet.

I believe if your wallet already has mixed inputs and you want to filter these, this feature may be useful.

I was thinking about this proposal and I'm still not convinced there is a clear understanding how this would be actually used in the real world.

The declared benefit is non-malleability for lightning wallets (#25181). For new lightning wallets this is a non-issue as they shouldn't have non-segwit descriptors in the first place. IIUC the proposed solution for existing wallets is to filter malleable inputs when creating channel opening txs in fundrawtransaction and walletcreatefundedpsbt. This approach renders a portion of wallet funds unusable and have a number of problems:

1. users could be confused about funding errors despite having enough balance
2. it doesn't provide a solution how to make all the funds usable
3. what about other RPCs? what if non-malleable inputs are added by walletprocesspsbt or when bumping psbt?

It seems what you really want is to "unmix" the wallet, i.e. sweep all malleable inputs as a one-time operation.
Today, I think, there are two main approaches users can take to achieve this:

1. (preferred, descriptors only) create a new wallet and import only segwit descriptors from the old wallet
2. create a new lighting wallet and fund it with desired amount to one or more addresses

While 2nd approach has some downsides, maybe it's just good enough. I don't know whether there are enough users affected and whether these downsides outweigh the added complexity.

🐙 This pull request conflicts with the target branch and needs rebase.

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