Merge bitcoin/bitcoin#32896: wallet, rpc: add v3 transaction creation and wallet support

5c8bf7b39e doc: add release notes for version 3 transactions (ishaanam)
4ef8065a5e test: add truc wallet tests (ishaanam)
5d932e14db test: extract `bulk_vout` from `bulk_tx` so it can be used by wallet tests (ishaanam)
2cb473d9f2 rpc: Support version 3 transaction creation (Bue-von-hon)
4c20343b4d rpc: Add transaction min standard version parameter (Bue-von-hon)
c5a2d08011 wallet: don't return utxos from multiple truc txs in AvailableCoins (ishaanam)
da8748ad62 wallet: limit v3 tx weight in coin selection (ishaanam)
85c5410615 wallet: mark unconfirmed v3 siblings as mempool conflicts (ishaanam)
0804fc3cb1 wallet: throw error at conflicting tx versions in pre-selected inputs (ishaanam)
cc155226fe wallet: set m_version in coin control to default value (ishaanam)
2e9617664e  wallet: don't include unconfirmed v3 txs with children in available coins (ishaanam)
ec2676becd wallet: unconfirmed ancestors and descendants are always truc (ishaanam)

Pull request description:

  This PR Implements the following:
  - If creating a v3 transaction, `AvailableCoins` doesn't return unconfirmed v2 utxos (and vice versa)
  - `AvailableCoins` doesn't return an unconfirmed v3 utxo if its transaction already has a child
  - If a v3 transaction is kicked out of the mempool by a sibling, mark the sibling as a mempool conflict
  - Throw an error if pre-selected inputs are of the wrong transaction version
  - Allow setting version to 3 manually in `createrawtransaction` (uses commits from #31936)
  - Limits a v3 transaction weight in coin selection

  Closes #31348

  To-Do:
  - [x] Test a v3 sibling conflict kicking out one of our transactions from the mempool
  - [x] Implement separate size limit for TRUC children
  - [x] Test that we can't fund a v2 transaction when everything is v3 unconfirmed
  - [x] Test a v3 sibling conflict being removed from the mempool
  - [x] Test limiting v3 transaction weight in coin selection
  - [x] Simplify tests
  - [x] Add documentation
  - [x] Test that user-input max weight is not overwritten by truc max weight
  - [x] Test v3 in RPCs other than `createrawtransaction`

ACKs for top commit:
  glozow:
    reACK 5c8bf7b39e
  achow101:
    ACK 5c8bf7b39e
  rkrux:
    ACK 5c8bf7b39e

Tree-SHA512: da8aea51c113e193dd0b442eff765bd6b8dc0e5066272d3e52190a223c903f48788795f32c554f268af0d2607b5b8c3985c648879cb176c65540837c05d0abb5

src/wallet/coincontrol.h

@@ -21,6 +21,8 @@ namespace wallet {
 const int DEFAULT_MIN_DEPTH = 0;
 const int DEFAULT_MAX_DEPTH = 9999999;
 
+const int DEFAULT_WALLET_TX_VERSION = CTransaction::CURRENT_VERSION;
+
 //! Default for -avoidpartialspends
 static constexpr bool DEFAULT_AVOIDPARTIALSPENDS = false;
 
@@ -109,10 +111,10 @@ public:
     int m_max_depth = DEFAULT_MAX_DEPTH;
     //! SigningProvider that has pubkeys and scripts to do spend size estimation for external inputs
     FlatSigningProvider m_external_provider;
+    //! Version
+    uint32_t m_version = DEFAULT_WALLET_TX_VERSION;
     //! Locktime
     std::optional<uint32_t> m_locktime;
-    //! Version
-    std::optional<uint32_t> m_version;
     //! Caps weight of resulting tx
     std::optional<int> m_max_tx_weight{std::nullopt};
 

src/wallet/coinselection.h

@@ -174,6 +174,8 @@ struct CoinSelectionParams {
      * 1) Received from other wallets, 2) replacing other txs, 3) that have been replaced.
      */
     bool m_include_unsafe_inputs = false;
+    /** The version of the transaction we are trying to create. */
+    uint32_t m_version{CTransaction::CURRENT_VERSION};
     /** The maximum weight for this transaction. */
     std::optional<int> m_max_tx_weight{std::nullopt};
 

src/wallet/rpc/spend.cpp

@@ -8,6 +8,7 @@
 #include <key_io.h>
 #include <node/types.h>
 #include <policy/policy.h>
+#include <policy/truc_policy.h>
 #include <rpc/rawtransaction_util.h>
 #include <rpc/util.h>
 #include <script/script.h>
@@ -717,6 +718,12 @@ CreatedTransactionResult FundTransaction(CWallet& wallet, const CMutableTransact
         coinControl.m_max_tx_weight = options["max_tx_weight"].getInt<int>();
     }
 
+    if (tx.version == TRUC_VERSION) {
+        if (!coinControl.m_max_tx_weight.has_value() || coinControl.m_max_tx_weight.value() > TRUC_MAX_WEIGHT) {
+            coinControl.m_max_tx_weight = TRUC_MAX_WEIGHT;
+        }
+    }
+
     if (recipients.empty())
         throw JSONRPCError(RPC_INVALID_PARAMETER, "TX must have at least one output");
 
@@ -1269,6 +1276,7 @@ RPCHelpMan send()
                 },
                 FundTxDoc()),
                 RPCArgOptions{.oneline_description="options"}},
+                {"version", RPCArg::Type::NUM, RPCArg::Default{DEFAULT_WALLET_TX_VERSION}, "Transaction version"},
         },
         RPCResult{
             RPCResult::Type::OBJ, "", "",
@@ -1308,14 +1316,16 @@ RPCHelpMan send()
                     ParseOutputs(outputs),
                     InterpretSubtractFeeFromOutputInstructions(options["subtract_fee_from_outputs"], outputs.getKeys())
             );
-            CMutableTransaction rawTx = ConstructTransaction(options["inputs"], request.params[0], options["locktime"], rbf);
             CCoinControl coin_control;
+            coin_control.m_version = self.Arg<uint32_t>("version");
+            CMutableTransaction rawTx = ConstructTransaction(options["inputs"], request.params[0], options["locktime"], rbf, coin_control.m_version);
             // Automatically select coins, unless at least one is manually selected. Can
             // be overridden by options.add_inputs.
             coin_control.m_allow_other_inputs = rawTx.vin.size() == 0;
             if (options.exists("max_tx_weight")) {
                 coin_control.m_max_tx_weight = options["max_tx_weight"].getInt<int>();
             }
+
             SetOptionsInputWeights(options["inputs"], options);
             // Clear tx.vout since it is not meant to be used now that we are passing outputs directly.
             // This sets us up for a future PR to completely remove tx from the function signature in favor of passing inputs directly
@@ -1375,6 +1385,7 @@ RPCHelpMan sendall()
                         {"send_max", RPCArg::Type::BOOL, RPCArg::Default{false}, "When true, only use UTXOs that can pay for their own fees to maximize the output amount. When 'false' (default), no UTXO is left behind. send_max is incompatible with providing specific inputs."},
                         {"minconf", RPCArg::Type::NUM, RPCArg::Default{0}, "Require inputs with at least this many confirmations."},
                         {"maxconf", RPCArg::Type::NUM, RPCArg::Optional::OMITTED, "Require inputs with at most this many confirmations."},
+                        {"version", RPCArg::Type::NUM, RPCArg::Default{DEFAULT_WALLET_TX_VERSION}, "Transaction version"},
                     },
                     FundTxDoc()
                 ),
@@ -1455,6 +1466,16 @@ RPCHelpMan sendall()
                 }
             }
 
+            if (options.exists("version")) {
+                coin_control.m_version = options["version"].getInt<int>();
+            }
+
+            if (coin_control.m_version == TRUC_VERSION) {
+                coin_control.m_max_tx_weight = TRUC_MAX_WEIGHT;
+            } else {
+                coin_control.m_max_tx_weight = MAX_STANDARD_TX_WEIGHT;
+            }
+
             const bool rbf{options.exists("replaceable") ? options["replaceable"].get_bool() : pwallet->m_signal_rbf};
 
             FeeCalculation fee_calc_out;
@@ -1469,7 +1490,7 @@ RPCHelpMan sendall()
                 throw JSONRPCError(RPC_WALLET_ERROR, "Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.");
             }
 
-            CMutableTransaction rawTx{ConstructTransaction(options["inputs"], recipient_key_value_pairs, options["locktime"], rbf)};
+            CMutableTransaction rawTx{ConstructTransaction(options["inputs"], recipient_key_value_pairs, options["locktime"], rbf, coin_control.m_version)};
             LOCK(pwallet->cs_wallet);
 
             CAmount total_input_value(0);
@@ -1487,6 +1508,13 @@ RPCHelpMan sendall()
                     if (!tx || input.prevout.n >= tx->tx->vout.size() || !(pwallet->IsMine(tx->tx->vout[input.prevout.n]) & ISMINE_SPENDABLE)) {
                         throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Input not found. UTXO (%s:%d) is not part of wallet.", input.prevout.hash.ToString(), input.prevout.n));
                     }
+                    if (pwallet->GetTxDepthInMainChain(*tx) == 0) {
+                        if (tx->tx->version == TRUC_VERSION && coin_control.m_version != TRUC_VERSION) {
+                            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Can't spend unconfirmed version 3 pre-selected input with a version %d tx", coin_control.m_version));
+                        } else if (coin_control.m_version == TRUC_VERSION && tx->tx->version != TRUC_VERSION) {
+                            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Can't spend unconfirmed version %d pre-selected input with a version 3 tx", tx->tx->version));
+                        }
+                    }
                     total_input_value += tx->tx->vout[input.prevout.n].nValue;
                 }
             } else {
@@ -1497,6 +1525,10 @@ RPCHelpMan sendall()
                     if (send_max && fee_rate.GetFee(output.input_bytes) > output.txout.nValue) {
                         continue;
                     }
+                    // we are spending an unconfirmed TRUC transaction, so lower max weight
+                    if (output.depth == 0 && coin_control.m_version == TRUC_VERSION) {
+                        coin_control.m_max_tx_weight = TRUC_CHILD_MAX_WEIGHT;
+                    }
                     CTxIn input(output.outpoint.hash, output.outpoint.n, CScript(), rbf ? MAX_BIP125_RBF_SEQUENCE : CTxIn::SEQUENCE_FINAL);
                     rawTx.vin.push_back(input);
                     total_input_value += output.txout.nValue;
@@ -1529,7 +1561,7 @@ RPCHelpMan sendall()
             }
 
             // If this transaction is too large, e.g. because the wallet has many UTXOs, it will be rejected by the node's mempool.
-            if (tx_size.weight > MAX_STANDARD_TX_WEIGHT) {
+            if (tx_size.weight > coin_control.m_max_tx_weight) {
                 throw JSONRPCError(RPC_WALLET_ERROR, "Transaction too large.");
             }
 
@@ -1731,6 +1763,7 @@ RPCHelpMan walletcreatefundedpsbt()
                         FundTxDoc()),
                         RPCArgOptions{.oneline_description="options"}},
                     {"bip32derivs", RPCArg::Type::BOOL, RPCArg::Default{true}, "Include BIP 32 derivation paths for public keys if we know them"},
+                    {"version", RPCArg::Type::NUM, RPCArg::Default{DEFAULT_WALLET_TX_VERSION}, "Transaction version"},
                 },
                 RPCResult{
                     RPCResult::Type::OBJ, "", "",
@@ -1758,16 +1791,18 @@ RPCHelpMan walletcreatefundedpsbt()
 
     UniValue options{request.params[3].isNull() ? UniValue::VOBJ : request.params[3]};
 
+    CCoinControl coin_control;
+    coin_control.m_version = self.Arg<uint32_t>("version");
+
     const UniValue &replaceable_arg = options["replaceable"];
     const bool rbf{replaceable_arg.isNull() ? wallet.m_signal_rbf : replaceable_arg.get_bool()};
-    CMutableTransaction rawTx = ConstructTransaction(request.params[0], request.params[1], request.params[2], rbf);
+    CMutableTransaction rawTx = ConstructTransaction(request.params[0], request.params[1], request.params[2], rbf, coin_control.m_version);
     UniValue outputs(UniValue::VOBJ);
     outputs = NormalizeOutputs(request.params[1]);
     std::vector<CRecipient> recipients = CreateRecipients(
             ParseOutputs(outputs),
             InterpretSubtractFeeFromOutputInstructions(options["subtractFeeFromOutputs"], outputs.getKeys())
     );
-    CCoinControl coin_control;
     // Automatically select coins, unless at least one is manually selected. Can
     // be overridden by options.add_inputs.
     coin_control.m_allow_other_inputs = rawTx.vin.size() == 0;

src/wallet/spend.cpp

@@ -12,6 +12,7 @@
 #include <node/types.h>
 #include <numeric>
 #include <policy/policy.h>
+#include <policy/truc_policy.h>
 #include <primitives/transaction.h>
 #include <primitives/transaction_identifier.h>
 #include <script/script.h>
@@ -282,6 +283,14 @@ util::Result<PreSelectedInputs> FetchSelectedInputs(const CWallet& wallet, const
             if (input_bytes == -1) {
                 input_bytes = CalculateMaximumSignedInputSize(txout, &wallet, &coin_control);
             }
+            const CWalletTx& parent_tx = txo->GetWalletTx();
+            if (wallet.GetTxDepthInMainChain(parent_tx) == 0) {
+                if (parent_tx.tx->version == TRUC_VERSION && coin_control.m_version != TRUC_VERSION) {
+                    return util::Error{strprintf(_("Can't spend unconfirmed version 3 pre-selected input with a version %d tx"), coin_control.m_version)};
+                } else if (coin_control.m_version == TRUC_VERSION && parent_tx.tx->version != TRUC_VERSION) {
+                    return util::Error{strprintf(_("Can't spend unconfirmed version %d pre-selected input with a version 3 tx"), parent_tx.tx->version)};
+                }
+            }
         } else {
             // The input is external. We did not find the tx in mapWallet.
             const auto out{coin_control.GetExternalOutput(outpoint)};
@@ -316,6 +325,9 @@ CoinsResult AvailableCoins(const CWallet& wallet,
     AssertLockHeld(wallet.cs_wallet);
 
     CoinsResult result;
+    // track unconfirmed truc outputs separately if we are tracking trucness
+    std::vector<std::pair<OutputType, COutput>> unconfirmed_truc_coins;
+    std::unordered_map<Txid, CAmount, SaltedTxidHasher> truc_txid_by_value;
     // Either the WALLET_FLAG_AVOID_REUSE flag is not set (in which case we always allow), or we default to avoiding, and only in the case where
     // a coin control object is provided, and has the avoid address reuse flag set to false, do we allow already used addresses
     bool allow_used_addresses = !wallet.IsWalletFlagSet(WALLET_FLAG_AVOID_REUSE) || (coinControl && !coinControl->m_avoid_address_reuse);
@@ -386,6 +398,17 @@ CoinsResult AvailableCoins(const CWallet& wallet,
                 safeTx = false;
             }
 
+            if (nDepth == 0 && params.check_version_trucness) {
+                if (coinControl->m_version == TRUC_VERSION) {
+                    if (wtx.tx->version != TRUC_VERSION) continue;
+                    // this unconfirmed v3 transaction already has a child
+                    if (wtx.truc_child_in_mempool.has_value()) continue;
+                } else {
+                    if (wtx.tx->version == TRUC_VERSION) continue;
+                    Assume(!wtx.truc_child_in_mempool.has_value());
+                }
+            }
+
             if (only_safe && !safeTx) {
                 continue;
             }
@@ -450,8 +473,15 @@ CoinsResult AvailableCoins(const CWallet& wallet,
             is_from_p2sh = true;
         }
 
-        result.Add(GetOutputType(type, is_from_p2sh),
-                   COutput(outpoint, output, nDepth, input_bytes, spendable, solvable, tx_safe, wtx.GetTxTime(), tx_from_me, feerate));
+        auto available_output_type = GetOutputType(type, is_from_p2sh);
+        auto available_output = COutput(outpoint, output, nDepth, input_bytes, spendable, solvable, tx_safe, wtx.GetTxTime(), tx_from_me, feerate);
+        if (wtx.tx->version == TRUC_VERSION && nDepth == 0 && params.check_version_trucness) {
+            unconfirmed_truc_coins.emplace_back(available_output_type, available_output);
+            auto [it, _] = truc_txid_by_value.try_emplace(wtx.tx->GetHash(), 0);
+            it->second += output.nValue;
+        } else {
+            result.Add(available_output_type, available_output);
+        }
 
         outpoints.push_back(outpoint);
 
@@ -468,6 +498,23 @@ CoinsResult AvailableCoins(const CWallet& wallet,
         }
     }
 
+    // Return all the coins from one TRUC transaction, that have the highest value.
+    // This could be improved in the future by encoding these restrictions in
+    // the coin selection itself so that we don't have to filter out
+    // other unconfirmed TRUC coins beforehand.
+    if (params.check_version_trucness && unconfirmed_truc_coins.size() > 0) {
+        auto highest_value_truc_tx = std::max_element(truc_txid_by_value.begin(), truc_txid_by_value.end(), [](const auto& tx1, const auto& tx2){
+                return tx1.second < tx2.second;
+                });
+
+        const Txid& truc_txid = highest_value_truc_tx->first;
+        for (const auto& [type, output] : unconfirmed_truc_coins) {
+            if (output.outpoint.hash == truc_txid) {
+                    result.Add(type, output);
+            }
+        }
+    }
+
     if (feerate.has_value()) {
         std::map<COutPoint, CAmount> map_of_bump_fees = wallet.chain().calculateIndividualBumpFees(outpoints, feerate.value());
 
@@ -484,6 +531,7 @@ CoinsResult AvailableCoins(const CWallet& wallet,
 CoinsResult AvailableCoinsListUnspent(const CWallet& wallet, const CCoinControl* coinControl, CoinFilterParams params)
 {
     params.only_spendable = false;
+    params.check_version_trucness = false;
     return AvailableCoins(wallet, coinControl, /*feerate=*/ std::nullopt, params);
 }
 
@@ -904,11 +952,17 @@ util::Result<SelectionResult> AutomaticCoinSelection(const CWallet& wallet, Coin
         // If no solution is found, return the first detailed error (if any).
         // future: add "error level" so the worst one can be picked instead.
         std::vector<util::Result<SelectionResult>> res_detailed_errors;
+        CoinSelectionParams updated_selection_params = coin_selection_params;
         for (const auto& select_filter : ordered_filters) {
             auto it = filtered_groups.find(select_filter.filter);
             if (it == filtered_groups.end()) continue;
+            if (updated_selection_params.m_version == TRUC_VERSION && (select_filter.filter.conf_mine == 0 || select_filter.filter.conf_theirs == 0)) {
+                if (updated_selection_params.m_max_tx_weight > (TRUC_CHILD_MAX_WEIGHT)) {
+                    updated_selection_params.m_max_tx_weight = TRUC_CHILD_MAX_WEIGHT;
+                }
+            }
             if (auto res{AttemptSelection(wallet.chain(), value_to_select, it->second,
-                                          coin_selection_params, select_filter.allow_mixed_output_types)}) {
+                                          updated_selection_params, select_filter.allow_mixed_output_types)}) {
                 return res; // result found
             } else {
                 // If any specific error message appears here, then something particularly wrong might have happened.
@@ -1019,14 +1073,13 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal(
     FastRandomContext rng_fast;
     CMutableTransaction txNew; // The resulting transaction that we make
 
-    if (coin_control.m_version) {
-        txNew.version = coin_control.m_version.value();
-    }
+    txNew.version = coin_control.m_version;
 
     CoinSelectionParams coin_selection_params{rng_fast}; // Parameters for coin selection, init with dummy
     coin_selection_params.m_avoid_partial_spends = coin_control.m_avoid_partial_spends;
     coin_selection_params.m_include_unsafe_inputs = coin_control.m_include_unsafe_inputs;
     coin_selection_params.m_max_tx_weight = coin_control.m_max_tx_weight.value_or(MAX_STANDARD_TX_WEIGHT);
+    coin_selection_params.m_version = coin_control.m_version;
     int minimum_tx_weight = MIN_STANDARD_TX_NONWITNESS_SIZE * WITNESS_SCALE_FACTOR;
     if (coin_selection_params.m_max_tx_weight.value() < minimum_tx_weight || coin_selection_params.m_max_tx_weight.value() > MAX_STANDARD_TX_WEIGHT) {
         return util::Error{strprintf(_("Maximum transaction weight must be between %d and %d"), minimum_tx_weight, MAX_STANDARD_TX_WEIGHT)};

src/wallet/spend.h

@@ -83,6 +83,9 @@ struct CoinFilterParams {
     bool include_immature_coinbase{false};
     // By default, skip locked UTXOs
     bool skip_locked{true};
+    // When true, filter unconfirmed coins by whether their
+    // version's TRUCness matches what is set by CCoinControl.
+    bool check_version_trucness{true};
 };
 
 /**

src/wallet/transaction.h

@@ -258,6 +258,10 @@ public:
     // BlockConflicted.
     std::set<Txid> mempool_conflicts;
 
+    // Track v3 mempool tx that spends from this tx
+    // so that we don't try to create another unconfirmed child
+    std::optional<Txid> truc_child_in_mempool;
+
     template<typename Stream>
     void Serialize(Stream& s) const
     {

src/wallet/wallet.cpp

@@ -30,6 +30,7 @@
 #include <node/types.h>
 #include <outputtype.h>
 #include <policy/feerate.h>
+#include <policy/truc_policy.h>
 #include <primitives/block.h>
 #include <primitives/transaction.h>
 #include <psbt.h>
@@ -1213,6 +1214,23 @@ bool CWallet::TransactionCanBeAbandoned(const Txid& hashTx) const
     return wtx && !wtx->isAbandoned() && GetTxDepthInMainChain(*wtx) == 0 && !wtx->InMempool();
 }
 
+void CWallet::UpdateTrucSiblingConflicts(const CWalletTx& parent_wtx, const Txid& child_txid, bool add_conflict) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet)
+{
+    // Find all other txs in our wallet that spend utxos from this parent
+    // so that we can mark them as mempool-conflicted by this new tx.
+    for (long unsigned int i = 0; i < parent_wtx.tx->vout.size(); i++) {
+        for (auto range = mapTxSpends.equal_range(COutPoint(parent_wtx.tx->GetHash(), i)); range.first != range.second; range.first++) {
+            const Txid& sibling_txid = range.first->second;
+            // Skip the child_tx itself
+            if (sibling_txid == child_txid) continue;
+            RecursiveUpdateTxState(/*batch=*/nullptr, sibling_txid, [&child_txid, add_conflict](CWalletTx& wtx) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet) {
+                return add_conflict ? (wtx.mempool_conflicts.insert(child_txid).second ? TxUpdate::CHANGED : TxUpdate::UNCHANGED)
+                                    : (wtx.mempool_conflicts.erase(child_txid) ? TxUpdate::CHANGED : TxUpdate::UNCHANGED);
+            });
+        }
+    }
+}
+
 void CWallet::MarkInputsDirty(const CTransactionRef& tx)
 {
     for (const CTxIn& txin : tx->vin) {
@@ -1368,6 +1386,25 @@ void CWallet::transactionAddedToMempool(const CTransactionRef& tx) {
                 return wtx.mempool_conflicts.insert(txid).second ? TxUpdate::CHANGED : TxUpdate::UNCHANGED;
             });
         }
+
+    }
+
+    if (tx->version == TRUC_VERSION) {
+        // Unconfirmed TRUC transactions are only allowed a 1-parent-1-child topology.
+        // For any unconfirmed v3 parents (there should be a maximum of 1 except in reorgs),
+        // record this child so the wallet doesn't try to spend any other outputs
+        for (const CTxIn& tx_in : tx->vin) {
+            auto parent_it = mapWallet.find(tx_in.prevout.hash);
+            if (parent_it != mapWallet.end()) {
+                CWalletTx& parent_wtx = parent_it->second;
+                if (parent_wtx.isUnconfirmed()) {
+                    parent_wtx.truc_child_in_mempool = tx->GetHash();
+                    // Even though these siblings do not spend the same utxos, they can't
+                    // be present in the mempool at the same time because of TRUC policy rules
+                    UpdateTrucSiblingConflicts(parent_wtx, txid, /*add_conflict=*/true);
+                }
+            }
+        }
     }
 }
 
@@ -1421,6 +1458,23 @@ void CWallet::transactionRemovedFromMempool(const CTransactionRef& tx, MemPoolRe
             });
         }
     }
+
+    if (tx->version == TRUC_VERSION) {
+        // If this tx has a parent, unset its truc_child_in_mempool to make it possible
+        // to spend from the parent again. If this tx was replaced by another
+        // child of the same parent, transactionAddedToMempool
+        // will update truc_child_in_mempool
+        for (const CTxIn& tx_in : tx->vin) {
+            auto parent_it = mapWallet.find(tx_in.prevout.hash);
+            if (parent_it != mapWallet.end()) {
+                CWalletTx& parent_wtx = parent_it->second;
+                if (parent_wtx.truc_child_in_mempool == tx->GetHash()) {
+                    parent_wtx.truc_child_in_mempool = std::nullopt;
+                    UpdateTrucSiblingConflicts(parent_wtx, txid, /*add_conflict=*/false);
+                }
+            }
+        }
+    }
 }
 
 void CWallet::blockConnected(ChainstateRole role, const interfaces::BlockInfo& block)

src/wallet/wallet.h

@@ -450,6 +450,9 @@ private:
     // Update last block processed in memory only
     void SetLastBlockProcessedInMem(int block_height, uint256 block_hash) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
+    //! Update mempool conflicts for TRUC sibling transactions
+    void UpdateTrucSiblingConflicts(const CWalletTx& parent_wtx, const Txid& child_txid, bool add_conflict) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
+
 public:
     /**
      * Main wallet lock.