This would allow wallet operations like funding transactions with smart contract-based inputs such as LN, or any input the Core wallet doesn't know how to sign for.

https://github.com/bitcoin/bitcoin/pull/17211#issuecomment-933674310
}
    // At this point, one input was not fuy signed otherwise we would have exited already
    return false;
}
TransactionError CWaet::FiPSBT(PartiaySignedTransaction& psbtx, bool& complete, int sighash_type, bool sign, bool bip32derivs, size_t * n_signed, bool finalize) const
{
    if (n_signed) {
        *n_signed = 0;
    }
    const PrecomputedTransactionData txdata = PrecomputePSBTData(psbtx);
    LOCK(cs_);
    // Get a of the previous transactions
    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
        const CTxIn& txin = psbtx.tx->vin[i];
        PSBTInput& input = psbtx.inputs.at(i);
        if (PSBTInputSigned(input)) {
            continue;
        }
        //  we have no utxo, grab it from the .
        if (!input.non_witness_utxo) {
            const uint256& txhash = txin.prevout.hash;
            const auto it = mapWaet.find(txhash);
            if (it != mapWaet.end()) {
                const CWaetTx& wtx = it->second;
                // We only 
                //   The s
                input.non_witness_utxo = wtx.tx;
            }
        }
    }