refactor: Make const refs vars where applicable

This avoids initializing variables with the copy-constructor of a
non-trivially copyable type.

Author: aureleoules

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);

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");
 

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;

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());

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;

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()) {

src/init.cpp

@@ -1083,7 +1083,7 @@ 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)));
     }

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) + "] ");
     }
 

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);

src/node/blockstorage.cpp

@@ -414,7 +414,7 @@ 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) &&