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

BACKPORT NOTE:
Somehow there's multiple warnings that are for backported code, mostly related to mempool, such as:
     rpc/mempool.cpp:549:33: error: loop variable is copied but only used as const reference; consider making it a const reference [performance-for-range-copy,-warnings-as-errors]
      549 |         for (CTxMemPool::txiter descendantIt : setDescendants) {
          |                                 ^
          |              const             &

I can't find a way to fix it without big diversity of codebase, so, make as partial temporary

ae7ae36 tidy: Enable two clang-tidy checks (Aurèle Oulès)
081b0e5 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 ae7ae36
  MarcoFalke:
    review ACK ae7ae36

Tree-SHA512: f6ac6b0cd0eee1e0c34d2f186484bc0f7ec6071451cccb33fa88a67d93d92b304e2fac378b88f087e94657745bca4e966dbc443759587400eb01b1f3061fde8c

Author: MacroFake

src/.clang-tidy

@@ -5,6 +5,8 @@ bugprone-use-after-move,
 misc-unused-using-decls,
 modernize-use-default-member-init,
 modernize-use-nullptr,
+performance-for-range-copy,
+performance-unnecessary-copy-initialization,
 readability-const-return-type,
 readability-redundant-declaration,
 readability-redundant-string-init,
@@ -15,6 +17,7 @@ bugprone-use-after-move,
 misc-unused-using-decls,
 modernize-use-default-member-init,
 modernize-use-nullptr,
+performance-unnecessary-copy-initialization,
 readability-redundant-declaration,
 readability-redundant-string-init,
 '

src/bench/load_external.cpp

@@ -28,7 +28,7 @@ static void LoadExternalBlockFile(benchmark::Bench& bench)
     // block data) as a stream object.
     const fs::path blkfile{testing_setup.get()->m_path_root / "blk.dat"};
     CDataStream ss(SER_DISK, 0);
-    auto params{Params()};
+    const auto& params{Params()};
     ss << params.MessageStart();
     ss << static_cast<uint32_t>(benchmark::data::block813851.size());
     // We can't use the streaming serialization (ss << benchmark::data::block813851)

src/bitcoin-cli.cpp

@@ -948,7 +948,7 @@ 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 = getbalances.find_value("result")["mine"]["trusted"];
         balances.pushKV(wallet_name, balance);

src/bitcoin-tx.cpp

@@ -555,7 +555,7 @@ 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

@@ -170,7 +170,7 @@ 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);
             }
         });

src/bls/bls_worker.cpp

@@ -15,7 +15,7 @@ template <typename T>
 bool VerifyVectorHelper(Span<T> vec)
 {
     std::set<uint256> set;
-    for (auto item : vec) {
+    for (const auto& item : vec) {
         if (!item.IsValid())
             return false;
         // check duplicates

src/coins.cpp

@@ -356,7 +356,7 @@ 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

@@ -189,7 +189,7 @@ 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/evo/creditpool.cpp

@@ -91,7 +91,7 @@ static std::optional<CreditPoolDataPerBlock> GetCreditDataFromBlock(const gsl::n
         LogPrintf("%s: WARNING: No valid CbTx at height=%d\n", __func__, block_index->nHeight);
         return std::nullopt;
     }
-    for (CTransactionRef tx : block.vtx) {
+    for (const CTransactionRef& tx : block.vtx) {
         if (!tx->IsSpecialTxVersion() || tx->nType != TRANSACTION_ASSET_UNLOCK) continue;
 
         CAmount unlocked{0};

src/evo/mnauth.cpp

@@ -36,9 +36,7 @@ void CMNAuth::PushMNAUTH(CNode& peer, CConnman& connman, const CActiveMasternode
     if (Params().NetworkIDString() != CBaseChainParams::MAIN && gArgs.IsArgSet("-pushversion")) {
         nOurNodeVersion = gArgs.GetIntArg("-pushversion", PROTOCOL_VERSION);
     }
-    auto pk = mn_activeman.GetPubKey();
-    const CBLSPublicKey pubKey(pk);
-    const uint256 signHash{::SerializeHash(std::make_tuple(pubKey, receivedMNAuthChallenge, peer.IsInboundConn(), nOurNodeVersion))};
+    const uint256 signHash{::SerializeHash(std::make_tuple(mn_activeman.GetPubKey(), receivedMNAuthChallenge, peer.IsInboundConn(), nOurNodeVersion))};
 
     mnauth.proRegTxHash = mn_activeman.GetProTxHash();