Merge #14380: fix assert crash when specified change output spend size is unknown

0fb2e69815 CreateTransaction: Assume minimum p2sh-p2wpkh spend size for unknown change (Gregory Sanders)
b06483c96a Remove stale comment in CalculateMaximumSignedInputSize (Gregory Sanders)

Pull request description:

  This is triggered anytime a fundraw type call(psbt or legacy) is used with a change output address that the wallet doesn't know how to sign for.

  This regression was added in 6a34ff5335786615771ca423134a484b04831c4e since BnB coin selection actually cares about this.

  The fix is to assume the smallest typical spend, a P2SH-P2WPKH, which is calculated using a "prototype" dummy signature flow. Future work could generalize this infrastructure to get estimated sizes of inputs for a variety of types.

  I also removed a comment which I believe is stale and misleading.

Tree-SHA512: c7e2be189e524f81a7aa4454ad9370cefba715e3781f1e462c8bab77e4d27540191419029e3ebda11e3744c0703271e479dcd560d05e4d470048d9633e34da16

1 files changed, 8 insertions, 3 deletions

diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 360d0f177c..d7798e005f 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1530,8 +1530,6 @@ int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet,
     CMutableTransaction txn;
     txn.vin.push_back(CTxIn(COutPoint()));
     if (!wallet->DummySignInput(txn.vin[0], txout, use_max_sig)) {
-        // This should never happen, because IsAllFromMe(ISMINE_SPENDABLE)
-        // implies that we can sign for every input.
         return -1;
     }
     return GetVirtualTransactionInputSize(txn.vin[0]);
@@ -2755,7 +2753,14 @@ bool CWallet::CreateTransaction(interfaces::Chain::Lock& locked_chain, const std
                 if (pick_new_inputs) {
                     nValueIn = 0;
                     setCoins.clear();
-                    coin_selection_params.change_spend_size = CalculateMaximumSignedInputSize(change_prototype_txout, this);
+                    int change_spend_size = CalculateMaximumSignedInputSize(change_prototype_txout, this);
+                    // If the wallet doesn't know how to sign change output, assume p2sh-p2wpkh
+                    // as lower-bound to allow BnB to do it's thing
+                    if (change_spend_size == -1) {
+                        coin_selection_params.change_spend_size = DUMMY_NESTED_P2WPKH_INPUT_SIZE;
+                    } else {
+                        coin_selection_params.change_spend_size = (size_t)change_spend_size;
+                    }
                     coin_selection_params.effective_fee = nFeeRateNeeded;
                     if (!SelectCoins(vAvailableCoins, nValueToSelect, setCoins, nValueIn, coin_control, coin_selection_params, bnb_used))
                     {