Bump unconfirmed parent txs to target feerate

When a transaction uses an unconfirmed input, preceding this commit it
would not consider the feerate of the parent transaction. Given a parent
transaction with a lower ancestor feerate, this resulted in the new
transaction's ancestor feerate undershooting the target feerate.

This commit changes how we calculate the effective value of unconfirmed UTXOs.
The effective value of unconfirmed UTXOs is decreased by the fee
necessary to bump its ancestry to the target feerate. This also impacts
the calculation of the waste metric: since the estimate for the current
fee is increased by the bump fees, unconfirmed UTXOs current fees appear less
favorable compared to their unchanged long term fees.

This has one caveat: if multiple UTXOs have overlapping ancestries, each
of their individual estimates will account for bumping all ancestors.

1 files changed, 15 insertions, 3 deletions

diff --git a/src/wallet/feebumper.cpp b/src/wallet/feebumper.cpp
index 3720d144eb..e72b412c09 100644
--- a/src/wallet/feebumper.cpp
+++ b/src/wallet/feebumper.cpp
@@ -63,7 +63,7 @@ static feebumper::Result PreconditionChecks(const CWallet& wallet, const CWallet
 }
 
 //! Check if the user provided a valid feeRate
-static feebumper::Result CheckFeeRate(const CWallet& wallet, const CFeeRate& newFeerate, const int64_t maxTxSize, CAmount old_fee, std::vector<bilingual_str>& errors)
+static feebumper::Result CheckFeeRate(const CWallet& wallet, const CMutableTransaction& mtx, const CFeeRate& newFeerate, const int64_t maxTxSize, CAmount old_fee, std::vector<bilingual_str>& errors)
 {
     // check that fee rate is higher than mempool's minimum fee
     // (no point in bumping fee if we know that the new tx won't be accepted to the mempool)
@@ -80,7 +80,19 @@ static feebumper::Result CheckFeeRate(const CWallet& wallet, const CFeeRate& new
         return feebumper::Result::WALLET_ERROR;
     }
 
-    CAmount new_total_fee = newFeerate.GetFee(maxTxSize);
+    std::vector<COutPoint> reused_inputs;
+    reused_inputs.reserve(mtx.vin.size());
+    for (const CTxIn& txin : mtx.vin) {
+        reused_inputs.push_back(txin.prevout);
+    }
+
+    std::map<COutPoint, CAmount> bump_fees = wallet.chain().CalculateIndividualBumpFees(reused_inputs, newFeerate);
+    CAmount total_bump_fees = 0;
+    for (auto& [_, bump_fee] : bump_fees) {
+        total_bump_fees += bump_fee;
+    }
+
+    CAmount new_total_fee = newFeerate.GetFee(maxTxSize) + total_bump_fees;
 
     CFeeRate incrementalRelayFee = std::max(wallet.chain().relayIncrementalFee(), CFeeRate(WALLET_INCREMENTAL_RELAY_FEE));
 
@@ -283,7 +295,7 @@ Result CreateRateBumpTransaction(CWallet& wallet, const uint256& txid, const CCo
         }
         temp_mtx.vout = txouts;
         const int64_t maxTxSize{CalculateMaximumSignedTxSize(CTransaction(temp_mtx), &wallet, &new_coin_control).vsize};
-        Result res = CheckFeeRate(wallet, *new_coin_control.m_feerate, maxTxSize, old_fee, errors);
+        Result res = CheckFeeRate(wallet, temp_mtx, *new_coin_control.m_feerate, maxTxSize, old_fee, errors);
         if (res != Result::OK) {
             return res;
         }