Merge bitcoin/bitcoin#25707: refactor: Make const references to avoid unnecessarily copying objects and enable two clang-tidy checks

ae7ae36d311a869b3bda41d29dc0e47fade77d28 tidy: Enable two clang-tidy checks (Aurèle Oulès)
081b0e53e3adca7ea57d23e5fcd9db4b86415a72 refactor: Make const refs vars where applicable (Aurèle Oulès)

Pull request description:

  I added const references to some variables to avoid unnecessarily copying objects.

  Also added two clang-tidy checks : [performance-for-range-copy](https://releases.llvm.org/11.1.0/tools/clang/tools/extra/docs/clang-tidy/checks/performance-for-range-copy.html) and [performance-unnecessary-copy-initialization](https://releases.llvm.org/12.0.0/tools/clang/tools/extra/docs/clang-tidy/checks/performance-unnecessary-copy-initialization.html).

ACKs for top commit:
  vasild:
    ACK ae7ae36d311a869b3bda41d29dc0e47fade77d28
  MarcoFalke:
    review ACK ae7ae36d311a869b3bda41d29dc0e47fade77d28

Tree-SHA512: f6ac6b0cd0eee1e0c34d2f186484bc0f7ec6071451cccb33fa88a67d93d92b304e2fac378b88f087e94657745bca4e966dbc443759587400eb01b1f3061fde8c

28 files changed, 43 insertions, 39 deletions

diff --git a/src/.clang-tidy b/src/.clang-tidy
index b9371b147b..f59f80f8ce 100644
--- a/src/.clang-tidy
+++ b/src/.clang-tidy
@@ -4,6 +4,8 @@ bugprone-argument-comment,
 misc-unused-using-decls,
 modernize-use-default-member-init,
 modernize-use-nullptr,
+performance-for-range-copy,
+performance-unnecessary-copy-initialization,
 readability-redundant-declaration,
 readability-redundant-string-init,
 '
@@ -12,6 +14,8 @@ bugprone-argument-comment,
 misc-unused-using-decls,
 modernize-use-default-member-init,
 modernize-use-nullptr,
+performance-for-range-copy,
+performance-unnecessary-copy-initialization,
 readability-redundant-declaration,
 readability-redundant-string-init,
 '
diff --git a/src/bitcoin-cli.cpp b/src/bitcoin-cli.cpp
index 6ce4e05e4d..e64e2202ba 100644
--- a/src/bitcoin-cli.cpp
+++ b/src/bitcoin-cli.cpp
@@ -911,7 +911,7 @@ static void GetWalletBalances(UniValue& result)
 
     UniValue balances(UniValue::VOBJ);
     for (const UniValue& wallet : wallets.getValues()) {
-        const std::string wallet_name = wallet.get_str();
+        const std::string& wallet_name = wallet.get_str();
         const UniValue getbalances = ConnectAndCallRPC(&rh, "getbalances", /* args=*/{}, wallet_name);
         const UniValue& balance = find_value(getbalances, "result")["mine"]["trusted"];
         balances.pushKV(wallet_name, balance);
diff --git a/src/bitcoin-tx.cpp b/src/bitcoin-tx.cpp
index b006353cb0..c2bb89b8cf 100644
--- a/src/bitcoin-tx.cpp
+++ b/src/bitcoin-tx.cpp
@@ -596,7 +596,7 @@ static void MutateTxSign(CMutableTransaction& tx, const std::string& flagStr)
     UniValue prevtxsObj = registers["prevtxs"];
     {
         for (unsigned int previdx = 0; previdx < prevtxsObj.size(); previdx++) {
-            UniValue prevOut = prevtxsObj[previdx];
+            const UniValue& prevOut = prevtxsObj[previdx];
             if (!prevOut.isObject())
                 throw std::runtime_error("expected prevtxs internal object");
 
diff --git a/src/blockfilter.cpp b/src/blockfilter.cpp
index 0ff79bb3ca..43d88df720 100644
--- a/src/blockfilter.cpp
+++ b/src/blockfilter.cpp
@@ -169,7 +169,7 @@ const std::set<BlockFilterType>& AllBlockFilterTypes()
 
     static std::once_flag flag;
     std::call_once(flag, []() {
-            for (auto entry : g_filter_types) {
+            for (const auto& entry : g_filter_types) {
                 types.insert(entry.first);
             }
         });
@@ -185,7 +185,7 @@ const std::string& ListBlockFilterTypes()
     std::call_once(flag, []() {
             std::stringstream ret;
             bool first = true;
-            for (auto entry : g_filter_types) {
+            for (const auto& entry : g_filter_types) {
                 if (!first) ret << ", ";
                 ret << entry.second;
                 first = false;
diff --git a/src/coins.cpp b/src/coins.cpp
index 1753d33b71..5983a8a39f 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -296,7 +296,7 @@ bool CCoinsViewErrorCatcher::GetCoin(const COutPoint &outpoint, Coin &coin) cons
     try {
         return CCoinsViewBacked::GetCoin(outpoint, coin);
     } catch(const std::runtime_error& e) {
-        for (auto f : m_err_callbacks) {
+        for (const auto& f : m_err_callbacks) {
             f();
         }
         LogPrintf("Error reading from database: %s\n", e.what());
diff --git a/src/core_read.cpp b/src/core_read.cpp
index 77c516427a..ec21a2f7f4 100644
--- a/src/core_read.cpp
+++ b/src/core_read.cpp
@@ -265,7 +265,7 @@ int ParseSighashString(const UniValue& sighash)
             {std::string("SINGLE"), int(SIGHASH_SINGLE)},
             {std::string("SINGLE|ANYONECANPAY"), int(SIGHASH_SINGLE|SIGHASH_ANYONECANPAY)},
         };
-        std::string strHashType = sighash.get_str();
+        const std::string& strHashType = sighash.get_str();
         const auto& it = map_sighash_values.find(strHashType);
         if (it != map_sighash_values.end()) {
             hash_type = it->second;
diff --git a/src/external_signer.cpp b/src/external_signer.cpp
index 6bab0a856c..094314e878 100644
--- a/src/external_signer.cpp
+++ b/src/external_signer.cpp
@@ -28,7 +28,7 @@ bool ExternalSigner::Enumerate(const std::string& command, std::vector<ExternalS
     if (!result.isArray()) {
         throw std::runtime_error(strprintf("'%s' received invalid response, expected array of signers", command));
     }
-    for (UniValue signer : result.getValues()) {
+    for (const UniValue& signer : result.getValues()) {
         // Check for error
         const UniValue& error = find_value(signer, "error");
         if (!error.isNull()) {
diff --git a/src/init.cpp b/src/init.cpp
index 488c754e95..480b8c7705 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1046,7 +1046,7 @@ bool AppInitParameterInteraction(const ArgsManager& args, bool use_syscall_sandb
 static bool LockDataDirectory(bool probeOnly)
 {
     // Make sure only a single Bitcoin process is using the data directory.
-    fs::path datadir = gArgs.GetDataDirNet();
+    const fs::path& datadir = gArgs.GetDataDirNet();
     if (!DirIsWritable(datadir)) {
         return InitError(strprintf(_("Cannot write to data directory '%s'; check permissions."), fs::PathToString(datadir)));
     }
diff --git a/src/logging.cpp b/src/logging.cpp
index 1e2c1d5a77..73c4e458bd 100644
--- a/src/logging.cpp
+++ b/src/logging.cpp
@@ -364,7 +364,7 @@ void BCLog::Logger::LogPrintStr(const std::string& str, const std::string& loggi
     }
 
     if (m_log_threadnames && m_started_new_line) {
-        const auto threadname = util::ThreadGetInternalName();
+        const auto& threadname = util::ThreadGetInternalName();
         str_prefixed.insert(0, "[" + (threadname.empty() ? "unknown" : threadname) + "] ");
     }
 
diff --git a/src/netbase.cpp b/src/netbase.cpp
index 4b8d2f8d0c..a5f7bda875 100644
--- a/src/netbase.cpp
+++ b/src/netbase.cpp
@@ -387,7 +387,7 @@ bool Socks5(const std::string& strDest, uint16_t port, const ProxyCredentials* a
         return error("Error sending to proxy");
     }
     uint8_t pchRet1[2];
-    if ((recvr = InterruptibleRecv(pchRet1, 2, g_socks5_recv_timeout, sock)) != IntrRecvError::OK) {
+    if (InterruptibleRecv(pchRet1, 2, g_socks5_recv_timeout, sock) != IntrRecvError::OK) {
         LogPrintf("Socks5() connect to %s:%d failed: InterruptibleRecv() timeout or other failure\n", strDest, port);
         return false;
     }
@@ -410,7 +410,7 @@ bool Socks5(const std::string& strDest, uint16_t port, const ProxyCredentials* a
         }
         LogPrint(BCLog::PROXY, "SOCKS5 sending proxy authentication %s:%s\n", auth->username, auth->password);
         uint8_t pchRetA[2];
-        if ((recvr = InterruptibleRecv(pchRetA, 2, g_socks5_recv_timeout, sock)) != IntrRecvError::OK) {
+        if (InterruptibleRecv(pchRetA, 2, g_socks5_recv_timeout, sock) != IntrRecvError::OK) {
             return error("Error reading proxy authentication response");
         }
         if (pchRetA[0] != 0x01 || pchRetA[1] != 0x00) {
@@ -476,7 +476,7 @@ bool Socks5(const std::string& strDest, uint16_t port, const ProxyCredentials* a
     if (recvr != IntrRecvError::OK) {
         return error("Error reading from proxy");
     }
-    if ((recvr = InterruptibleRecv(pchRet3, 2, g_socks5_recv_timeout, sock)) != IntrRecvError::OK) {
+    if (InterruptibleRecv(pchRet3, 2, g_socks5_recv_timeout, sock) != IntrRecvError::OK) {
         return error("Error reading from proxy");
     }
     LogPrint(BCLog::NET, "SOCKS5 connected %s\n", strDest);
diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index 601d0bdf58..42b6b017fe 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -415,7 +415,7 @@ void CleanupBlockRevFiles()
     // Remove the rev files immediately and insert the blk file paths into an
     // ordered map keyed by block file index.
     LogPrintf("Removing unusable blk?????.dat and rev?????.dat files for -reindex with -prune\n");
-    fs::path blocksdir = gArgs.GetBlocksDirPath();
+    const fs::path& blocksdir = gArgs.GetBlocksDirPath();
     for (fs::directory_iterator it(blocksdir); it != fs::directory_iterator(); it++) {
         const std::string path = fs::PathToString(it->path().filename());
         if (fs::is_regular_file(*it) &&
diff --git a/src/qt/splashscreen.cpp b/src/qt/splashscreen.cpp
index a4dfffa387..bf04a6dd5f 100644
--- a/src/qt/splashscreen.cpp
+++ b/src/qt/splashscreen.cpp
@@ -44,7 +44,7 @@ SplashScreen::SplashScreen(const NetworkStyle* networkStyle)
     QString titleText       = PACKAGE_NAME;
     QString versionText     = QString("Version %1").arg(QString::fromStdString(FormatFullVersion()));
     QString copyrightText   = QString::fromUtf8(CopyrightHolders(strprintf("\xc2\xA9 %u-%u ", 2009, COPYRIGHT_YEAR)).c_str());
-    QString titleAddText    = networkStyle->getTitleAddText();
+    const QString& titleAddText    = networkStyle->getTitleAddText();
 
     QString font            = QApplication::font().toString();
 
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index e9663d38b4..91feb2c24b 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -679,7 +679,7 @@ static RPCHelpMan getblocktemplate()
         if (lpval.isStr())
         {
             // Format: <hashBestChain><nTransactionsUpdatedLast>
-            std::string lpstr = lpval.get_str();
+            const std::string& lpstr = lpval.get_str();
 
             hashWatchedChain = ParseHashV(lpstr.substr(0, 64), "longpollid");
             nTransactionsUpdatedLastLP = LocaleIndependentAtoi<int64_t>(lpstr.substr(64));
diff --git a/src/rpc/rawtransaction_util.cpp b/src/rpc/rawtransaction_util.cpp
index b06e9f6e4b..b078ee8b29 100644
--- a/src/rpc/rawtransaction_util.cpp
+++ b/src/rpc/rawtransaction_util.cpp
@@ -160,14 +160,14 @@ static void TxInErrorToJSON(const CTxIn& txin, UniValue& vErrorsRet, const std::
 void ParsePrevouts(const UniValue& prevTxsUnival, FillableSigningProvider* keystore, std::map<COutPoint, Coin>& coins)
 {
     if (!prevTxsUnival.isNull()) {
-        UniValue prevTxs = prevTxsUnival.get_array();
+        const UniValue& prevTxs = prevTxsUnival.get_array();
         for (unsigned int idx = 0; idx < prevTxs.size(); ++idx) {
             const UniValue& p = prevTxs[idx];
             if (!p.isObject()) {
                 throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "expected object with {\"txid'\",\"vout\",\"scriptPubKey\"}");
             }
 
-            UniValue prevOut = p.get_obj();
+            const UniValue& prevOut = p.get_obj();
 
             RPCTypeCheckObj(prevOut,
                 {
diff --git a/src/rpc/util.cpp b/src/rpc/util.cpp
index 7517f64ea1..24ab21a947 100644
--- a/src/rpc/util.cpp
+++ b/src/rpc/util.cpp
@@ -98,7 +98,7 @@ CAmount AmountFromValue(const UniValue& value, int decimals)
 
 uint256 ParseHashV(const UniValue& v, std::string strName)
 {
-    std::string strHex(v.get_str());
+    const std::string& strHex(v.get_str());
     if (64 != strHex.length())
         throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("%s must be of length %d (not %d, for '%s')", strName, 64, strHex.length(), strHex));
     if (!IsHex(strHex)) // Note: IsHex("") is false
diff --git a/src/test/base58_tests.cpp b/src/test/base58_tests.cpp
index 00f32ddcee..249f89ae2f 100644
--- a/src/test/base58_tests.cpp
+++ b/src/test/base58_tests.cpp
@@ -25,7 +25,7 @@ BOOST_AUTO_TEST_CASE(base58_EncodeBase58)
 {
     UniValue tests = read_json(std::string(json_tests::base58_encode_decode, json_tests::base58_encode_decode + sizeof(json_tests::base58_encode_decode)));
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
-        UniValue test = tests[idx];
+        const UniValue& test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 2) // Allow for extra stuff (useful for comments)
         {
@@ -47,7 +47,7 @@ BOOST_AUTO_TEST_CASE(base58_DecodeBase58)
     std::vector<unsigned char> result;
 
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
-        UniValue test = tests[idx];
+        const UniValue& test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 2) // Allow for extra stuff (useful for comments)
         {
diff --git a/src/test/blockfilter_tests.cpp b/src/test/blockfilter_tests.cpp
index 178757e7b4..0831188327 100644
--- a/src/test/blockfilter_tests.cpp
+++ b/src/test/blockfilter_tests.cpp
@@ -137,7 +137,7 @@ BOOST_AUTO_TEST_CASE(blockfilters_json_test)
 
     const UniValue& tests = json.get_array();
     for (unsigned int i = 0; i < tests.size(); i++) {
-        UniValue test = tests[i];
+        const UniValue& test = tests[i];
         std::string strTest = test.write();
 
         if (test.size() == 1) {
diff --git a/src/test/key_io_tests.cpp b/src/test/key_io_tests.cpp
index e70b8b3dfd..1eac68de14 100644
--- a/src/test/key_io_tests.cpp
+++ b/src/test/key_io_tests.cpp
@@ -28,7 +28,7 @@ BOOST_AUTO_TEST_CASE(key_io_valid_parse)
     SelectParams(CBaseChainParams::MAIN);
 
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
-        UniValue test = tests[idx];
+        const UniValue& test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 3) { // Allow for extra stuff (useful for comments)
             BOOST_ERROR("Bad test: " << strTest);
@@ -86,7 +86,7 @@ BOOST_AUTO_TEST_CASE(key_io_valid_gen)
     UniValue tests = read_json(std::string(json_tests::key_io_valid, json_tests::key_io_valid + sizeof(json_tests::key_io_valid)));
 
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
-        UniValue test = tests[idx];
+        const UniValue& test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 3) // Allow for extra stuff (useful for comments)
         {
@@ -126,7 +126,7 @@ BOOST_AUTO_TEST_CASE(key_io_invalid)
     CTxDestination destination;
 
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
-        UniValue test = tests[idx];
+        const UniValue& test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 1) // Allow for extra stuff (useful for comments)
         {
diff --git a/src/test/script_tests.cpp b/src/test/script_tests.cpp
index 9e7a376d6b..935194057c 100644
--- a/src/test/script_tests.cpp
+++ b/src/test/script_tests.cpp
@@ -942,7 +942,7 @@ BOOST_AUTO_TEST_CASE(script_json_test)
     UniValue tests = read_json(std::string(json_tests::script_tests, json_tests::script_tests + sizeof(json_tests::script_tests)));
 
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
-        UniValue test = tests[idx];
+        const UniValue& test = tests[idx];
         std::string strTest = test.write();
         CScriptWitness witness;
         CAmount nValue = 0;
diff --git a/src/test/sighash_tests.cpp b/src/test/sighash_tests.cpp
index 7376f2ff5c..514798d8fa 100644
--- a/src/test/sighash_tests.cpp
+++ b/src/test/sighash_tests.cpp
@@ -165,7 +165,7 @@ BOOST_AUTO_TEST_CASE(sighash_from_data)
     UniValue tests = read_json(std::string(json_tests::sighash, json_tests::sighash + sizeof(json_tests::sighash)));
 
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
-        UniValue test = tests[idx];
+        const UniValue& test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 1) // Allow for extra stuff (useful for comments)
         {
diff --git a/src/test/transaction_tests.cpp b/src/test/transaction_tests.cpp
index cd6bf11327..952598f745 100644
--- a/src/test/transaction_tests.cpp
+++ b/src/test/transaction_tests.cpp
@@ -194,7 +194,7 @@ BOOST_AUTO_TEST_CASE(tx_valid)
     UniValue tests = read_json(std::string(json_tests::tx_valid, json_tests::tx_valid + sizeof(json_tests::tx_valid)));
 
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
-        UniValue test = tests[idx];
+        const UniValue& test = tests[idx];
         std::string strTest = test.write();
         if (test[0].isArray())
         {
@@ -214,7 +214,7 @@ BOOST_AUTO_TEST_CASE(tx_valid)
                     fValid = false;
                     break;
                 }
-                UniValue vinput = input.get_array();
+                const UniValue& vinput = input.get_array();
                 if (vinput.size() < 3 || vinput.size() > 4)
                 {
                     fValid = false;
@@ -282,7 +282,7 @@ BOOST_AUTO_TEST_CASE(tx_invalid)
     UniValue tests = read_json(std::string(json_tests::tx_invalid, json_tests::tx_invalid + sizeof(json_tests::tx_invalid)));
 
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
-        UniValue test = tests[idx];
+        const UniValue& test = tests[idx];
         std::string strTest = test.write();
         if (test[0].isArray())
         {
@@ -302,7 +302,7 @@ BOOST_AUTO_TEST_CASE(tx_invalid)
                     fValid = false;
                     break;
                 }
-                UniValue vinput = input.get_array();
+                const UniValue& vinput = input.get_array();
                 if (vinput.size() < 3 || vinput.size() > 4)
                 {
                     fValid = false;
diff --git a/src/test/validation_block_tests.cpp b/src/test/validation_block_tests.cpp
index 7a82e1a736..1c5ca18759 100644
--- a/src/test/validation_block_tests.cpp
+++ b/src/test/validation_block_tests.cpp
@@ -183,7 +183,7 @@ BOOST_AUTO_TEST_CASE(processnewblock_signals_ordering)
             }
 
             // to make sure that eventually we process the full chain - do it here
-            for (auto block : blocks) {
+            for (const auto& block : blocks) {
                 if (block->vtx.size() == 1) {
                     bool processed = Assert(m_node.chainman)->ProcessNewBlock(block, true, &ignored);
                     assert(processed);
diff --git a/src/wallet/bdb.cpp b/src/wallet/bdb.cpp
index 60715ff3c8..deb1293cd4 100644
--- a/src/wallet/bdb.cpp
+++ b/src/wallet/bdb.cpp
@@ -432,7 +432,7 @@ void BerkeleyEnvironment::ReloadDbEnv()
     });
 
     std::vector<fs::path> filenames;
-    for (auto it : m_databases) {
+    for (const auto& it : m_databases) {
         filenames.push_back(it.first);
     }
     // Close the individual Db's
diff --git a/src/wallet/receive.cpp b/src/wallet/receive.cpp
index db169aad12..7fbf2ff8cf 100644
--- a/src/wallet/receive.cpp
+++ b/src/wallet/receive.cpp
@@ -416,7 +416,7 @@ std::set< std::set<CTxDestination> > GetAddressGroupings(const CWallet& wallet)
 
     std::set< std::set<CTxDestination>* > uniqueGroupings; // a set of pointers to groups of addresses
     std::map< CTxDestination, std::set<CTxDestination>* > setmap;  // map addresses to the unique group containing it
-    for (std::set<CTxDestination> _grouping : groupings)
+    for (const std::set<CTxDestination>& _grouping : groupings)
     {
         // make a set of all the groups hit by this new group
         std::set< std::set<CTxDestination>* > hits;
diff --git a/src/wallet/rpc/spend.cpp b/src/wallet/rpc/spend.cpp
index 8bbb862a7b..c6e7588fb4 100644
--- a/src/wallet/rpc/spend.cpp
+++ b/src/wallet/rpc/spend.cpp
@@ -1407,7 +1407,7 @@ RPCHelpMan sendall()
             }
 
             CAmount output_amounts_claimed{0};
-            for (CTxOut out : rawTx.vout) {
+            for (const CTxOut& out : rawTx.vout) {
                 output_amounts_claimed += out.nValue;
             }
 
diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index 8d40846332..40d5ecd755 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -1788,7 +1788,7 @@ std::map<CKeyID, CKey> DescriptorScriptPubKeyMan::GetKeys() const
     AssertLockHeld(cs_desc_man);
     if (m_storage.HasEncryptionKeys() && !m_storage.IsLocked()) {
         KeyMap keys;
-        for (auto key_pair : m_map_crypted_keys) {
+        for (const auto& key_pair : m_map_crypted_keys) {
             const CPubKey& pubkey = key_pair.second.first;
             const std::vector<unsigned char>& crypted_secret = key_pair.second.second;
             CKey key;
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 45d2c3692d..752aad2378 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -3474,7 +3474,7 @@ void CWallet::SetupDescriptorScriptPubKeyMans()
             const UniValue& descriptor_vals = find_value(signer_res, internal ? "internal" : "receive");
             if (!descriptor_vals.isArray()) throw std::runtime_error(std::string(__func__) + ": Unexpected result");
             for (const UniValue& desc_val : descriptor_vals.get_array().getValues()) {
-                std::string desc_str = desc_val.getValStr();
+                const std::string& desc_str = desc_val.getValStr();
                 FlatSigningProvider keys;
                 std::string desc_error;
                 std::unique_ptr<Descriptor> desc = Parse(desc_str, keys, desc_error, false);
diff --git a/src/wallet/walletdb.cpp b/src/wallet/walletdb.cpp
index 8afd3f416d..0d85652c0c 100644
--- a/src/wallet/walletdb.cpp
+++ b/src/wallet/walletdb.cpp
@@ -856,18 +856,18 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
     }
 
     // Set the descriptor caches
-    for (auto desc_cache_pair : wss.m_descriptor_caches) {
+    for (const auto& desc_cache_pair : wss.m_descriptor_caches) {
         auto spk_man = pwallet->GetScriptPubKeyMan(desc_cache_pair.first);
         assert(spk_man);
         ((DescriptorScriptPubKeyMan*)spk_man)->SetCache(desc_cache_pair.second);
     }
 
     // Set the descriptor keys
-    for (auto desc_key_pair : wss.m_descriptor_keys) {
+    for (const auto& desc_key_pair : wss.m_descriptor_keys) {
         auto spk_man = pwallet->GetScriptPubKeyMan(desc_key_pair.first.first);
         ((DescriptorScriptPubKeyMan*)spk_man)->AddKey(desc_key_pair.first.second, desc_key_pair.second);
     }
-    for (auto desc_key_pair : wss.m_descriptor_crypt_keys) {
+    for (const auto& desc_key_pair : wss.m_descriptor_crypt_keys) {
         auto spk_man = pwallet->GetScriptPubKeyMan(desc_key_pair.first.first);
         ((DescriptorScriptPubKeyMan*)spk_man)->AddCryptedKey(desc_key_pair.first.second, desc_key_pair.second.first, desc_key_pair.second.second);
     }