scripted-diff: Use [[nodiscard]] (C++17) instead of NODISCARD

-BEGIN VERIFY SCRIPT-
sed -i "s/NODISCARD/[[nodiscard]]/g" $(git grep -l "NODISCARD" ":(exclude)src/bench/nanobench.h" ":(exclude)src/attributes.h")
-END VERIFY SCRIPT-

17 files changed, 54 insertions, 54 deletions

diff --git a/src/base58.cpp b/src/base58.cpp
index 0dc6044145..780846c6c5 100644
--- a/src/base58.cpp
+++ b/src/base58.cpp
@@ -35,7 +35,7 @@ static const int8_t mapBase58[256] = {
     -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
 };
 
-NODISCARD static bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch, int max_ret_len)
+[[nodiscard]] static bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch, int max_ret_len)
 {
     // Skip leading spaces.
     while (*psz && IsSpace(*psz))
@@ -141,7 +141,7 @@ std::string EncodeBase58Check(Span<const unsigned char> input)
     return EncodeBase58(vch);
 }
 
-NODISCARD static bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet, int max_ret_len)
+[[nodiscard]] static bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet, int max_ret_len)
 {
     if (!DecodeBase58(psz, vchRet, max_ret_len > std::numeric_limits<int>::max() - 4 ? std::numeric_limits<int>::max() : max_ret_len + 4) ||
         (vchRet.size() < 4)) {
diff --git a/src/base58.h b/src/base58.h
index 468c3e2589..60551a12ae 100644
--- a/src/base58.h
+++ b/src/base58.h
@@ -29,7 +29,7 @@ std::string EncodeBase58(Span<const unsigned char> input);
  * Decode a base58-encoded string (str) into a byte vector (vchRet).
  * return true if decoding is successful.
  */
-NODISCARD bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len);
+[[nodiscard]] bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len);
 
 /**
  * Encode a byte span into a base58-encoded string, including checksum
@@ -40,6 +40,6 @@ std::string EncodeBase58Check(Span<const unsigned char> input);
  * Decode a base58-encoded string (str) that includes a checksum into a byte
  * vector (vchRet), return true if decoding is successful
  */
-NODISCARD bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len);
+[[nodiscard]] bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len);
 
 #endif // BITCOIN_BASE58_H
diff --git a/src/core_io.h b/src/core_io.h
index 80ec80cd50..aaee9c445d 100644
--- a/src/core_io.h
+++ b/src/core_io.h
@@ -22,8 +22,8 @@ class UniValue;
 // core_read.cpp
 CScript ParseScript(const std::string& s);
 std::string ScriptToAsmStr(const CScript& script, const bool fAttemptSighashDecode = false);
-NODISCARD bool DecodeHexTx(CMutableTransaction& tx, const std::string& hex_tx, bool try_no_witness = false, bool try_witness = true);
-NODISCARD bool DecodeHexBlk(CBlock&, const std::string& strHexBlk);
+[[nodiscard]] bool DecodeHexTx(CMutableTransaction& tx, const std::string& hex_tx, bool try_no_witness = false, bool try_witness = true);
+[[nodiscard]] bool DecodeHexBlk(CBlock&, const std::string& strHexBlk);
 bool DecodeHexBlockHeader(CBlockHeader&, const std::string& hex_header);
 
 /**
diff --git a/src/hash.h b/src/hash.h
index 6d876076ee..083ac12523 100644
--- a/src/hash.h
+++ b/src/hash.h
@@ -197,7 +197,7 @@ uint256 SerializeHash(const T& obj, int nType=SER_GETHASH, int nVersion=PROTOCOL
 }
 
 /** Single-SHA256 a 32-byte input (represented as uint256). */
-NODISCARD uint256 SHA256Uint256(const uint256& input);
+[[nodiscard]] uint256 SHA256Uint256(const uint256& input);
 
 unsigned int MurmurHash3(unsigned int nHashSeed, Span<const unsigned char> vDataToHash);
 
diff --git a/src/init.cpp b/src/init.cpp
index 1e41616e94..468860d5e0 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -113,7 +113,7 @@ static fs::path GetPidFile(const ArgsManager& args)
     return AbsPathForConfigVal(fs::path(args.GetArg("-pid", BITCOIN_PID_FILENAME)));
 }
 
-NODISCARD static bool CreatePidFile(const ArgsManager& args)
+[[nodiscard]] static bool CreatePidFile(const ArgsManager& args)
 {
     fsbridge::ofstream file{GetPidFile(args)};
     if (file) {
diff --git a/src/node/transaction.h b/src/node/transaction.h
index 6491700d44..0c016ff04e 100644
--- a/src/node/transaction.h
+++ b/src/node/transaction.h
@@ -36,6 +36,6 @@ static const CFeeRate DEFAULT_MAX_RAW_TX_FEE_RATE{COIN / 10};
  * @param[in]  wait_callback wait until callbacks have been processed to avoid stale result due to a sequentially RPC.
  * return error
  */
-NODISCARD TransactionError BroadcastTransaction(NodeContext& node, CTransactionRef tx, std::string& err_string, const CAmount& max_tx_fee, bool relay, bool wait_callback);
+[[nodiscard]] TransactionError BroadcastTransaction(NodeContext& node, CTransactionRef tx, std::string& err_string, const CAmount& max_tx_fee, bool relay, bool wait_callback);
 
 #endif // BITCOIN_NODE_TRANSACTION_H
diff --git a/src/outputtype.h b/src/outputtype.h
index 77a16b1d05..bb7f39323b 100644
--- a/src/outputtype.h
+++ b/src/outputtype.h
@@ -22,7 +22,7 @@ enum class OutputType {
 
 extern const std::array<OutputType, 3> OUTPUT_TYPES;
 
-NODISCARD bool ParseOutputType(const std::string& str, OutputType& output_type);
+[[nodiscard]] bool ParseOutputType(const std::string& str, OutputType& output_type);
 const std::string& FormatOutputType(OutputType type);
 
 /**
diff --git a/src/psbt.h b/src/psbt.h
index 0951b76f83..b566726ee3 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -398,7 +398,7 @@ struct PartiallySignedTransaction
 
     /** Merge psbt into this. The two psbts must have the same underlying CTransaction (i.e. the
       * same actual Bitcoin transaction.) Returns true if the merge succeeded, false otherwise. */
-    NODISCARD bool Merge(const PartiallySignedTransaction& psbt);
+    [[nodiscard]] bool Merge(const PartiallySignedTransaction& psbt);
     bool AddInput(const CTxIn& txin, PSBTInput& psbtin);
     bool AddOutput(const CTxOut& txout, const PSBTOutput& psbtout);
     PartiallySignedTransaction() {}
@@ -605,11 +605,11 @@ bool FinalizeAndExtractPSBT(PartiallySignedTransaction& psbtx, CMutableTransacti
  * @param[in]  psbtxs the PSBTs to combine
  * @return error (OK if we successfully combined the transactions, other error if they were not compatible)
  */
-NODISCARD TransactionError CombinePSBTs(PartiallySignedTransaction& out, const std::vector<PartiallySignedTransaction>& psbtxs);
+[[nodiscard]] TransactionError CombinePSBTs(PartiallySignedTransaction& out, const std::vector<PartiallySignedTransaction>& psbtxs);
 
 //! Decode a base64ed PSBT into a PartiallySignedTransaction
-NODISCARD bool DecodeBase64PSBT(PartiallySignedTransaction& decoded_psbt, const std::string& base64_psbt, std::string& error);
+[[nodiscard]] bool DecodeBase64PSBT(PartiallySignedTransaction& decoded_psbt, const std::string& base64_psbt, std::string& error);
 //! Decode a raw (binary blob) PSBT into a PartiallySignedTransaction
-NODISCARD bool DecodeRawPSBT(PartiallySignedTransaction& decoded_psbt, const std::string& raw_psbt, std::string& error);
+[[nodiscard]] bool DecodeRawPSBT(PartiallySignedTransaction& decoded_psbt, const std::string& raw_psbt, std::string& error);
 
 #endif // BITCOIN_PSBT_H
diff --git a/src/script/descriptor.cpp b/src/script/descriptor.cpp
index 6c0a98cca2..8d8fa185ba 100644
--- a/src/script/descriptor.cpp
+++ b/src/script/descriptor.cpp
@@ -731,7 +731,7 @@ enum class ParseScriptContext {
 };
 
 /** Parse a key path, being passed a split list of elements (the first element is ignored). */
-NODISCARD bool ParseKeyPath(const std::vector<Span<const char>>& split, KeyPath& out, std::string& error)
+[[nodiscard]] bool ParseKeyPath(const std::vector<Span<const char>>& split, KeyPath& out, std::string& error)
 {
     for (size_t i = 1; i < split.size(); ++i) {
         Span<const char> elem = split[i];
diff --git a/src/test/coins_tests.cpp b/src/test/coins_tests.cpp
index 173ec5e3d9..6bfcf242d0 100644
--- a/src/test/coins_tests.cpp
+++ b/src/test/coins_tests.cpp
@@ -38,7 +38,7 @@ class CCoinsViewTest : public CCoinsView
     std::map<COutPoint, Coin> map_;
 
 public:
-    NODISCARD bool GetCoin(const COutPoint& outpoint, Coin& coin) const override
+    [[nodiscard]] bool GetCoin(const COutPoint& outpoint, Coin& coin) const override
     {
         std::map<COutPoint, Coin>::const_iterator it = map_.find(outpoint);
         if (it == map_.end()) {
diff --git a/src/test/fuzz/util.h b/src/test/fuzz/util.h
index e99ed8d72d..37e136dbb3 100644
--- a/src/test/fuzz/util.h
+++ b/src/test/fuzz/util.h
@@ -35,23 +35,23 @@
 #include <string>
 #include <vector>
 
-NODISCARD inline std::vector<uint8_t> ConsumeRandomLengthByteVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
+[[nodiscard]] inline std::vector<uint8_t> ConsumeRandomLengthByteVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
 {
     const std::string s = fuzzed_data_provider.ConsumeRandomLengthString(max_length);
     return {s.begin(), s.end()};
 }
 
-NODISCARD inline std::vector<bool> ConsumeRandomLengthBitVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
+[[nodiscard]] inline std::vector<bool> ConsumeRandomLengthBitVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
 {
     return BytesToBits(ConsumeRandomLengthByteVector(fuzzed_data_provider, max_length));
 }
 
-NODISCARD inline CDataStream ConsumeDataStream(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
+[[nodiscard]] inline CDataStream ConsumeDataStream(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
 {
     return {ConsumeRandomLengthByteVector(fuzzed_data_provider, max_length), SER_NETWORK, INIT_PROTO_VERSION};
 }
 
-NODISCARD inline std::vector<std::string> ConsumeRandomLengthStringVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_vector_size = 16, const size_t max_string_length = 16) noexcept
+[[nodiscard]] inline std::vector<std::string> ConsumeRandomLengthStringVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_vector_size = 16, const size_t max_string_length = 16) noexcept
 {
     const size_t n_elements = fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, max_vector_size);
     std::vector<std::string> r;
@@ -62,7 +62,7 @@ NODISCARD inline std::vector<std::string> ConsumeRandomLengthStringVector(Fuzzed
 }
 
 template <typename T>
-NODISCARD inline std::vector<T> ConsumeRandomLengthIntegralVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_vector_size = 16) noexcept
+[[nodiscard]] inline std::vector<T> ConsumeRandomLengthIntegralVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_vector_size = 16) noexcept
 {
     const size_t n_elements = fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, max_vector_size);
     std::vector<T> r;
@@ -73,7 +73,7 @@ NODISCARD inline std::vector<T> ConsumeRandomLengthIntegralVector(FuzzedDataProv
 }
 
 template <typename T>
-NODISCARD inline std::optional<T> ConsumeDeserializable(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
+[[nodiscard]] inline std::optional<T> ConsumeDeserializable(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
 {
     const std::vector<uint8_t> buffer = ConsumeRandomLengthByteVector(fuzzed_data_provider, max_length);
     CDataStream ds{buffer, SER_NETWORK, INIT_PROTO_VERSION};
@@ -86,35 +86,35 @@ NODISCARD inline std::optional<T> ConsumeDeserializable(FuzzedDataProvider& fuzz
     return obj;
 }
 
-NODISCARD inline opcodetype ConsumeOpcodeType(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline opcodetype ConsumeOpcodeType(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     return static_cast<opcodetype>(fuzzed_data_provider.ConsumeIntegralInRange<uint32_t>(0, MAX_OPCODE));
 }
 
-NODISCARD inline CAmount ConsumeMoney(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline CAmount ConsumeMoney(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     return fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(0, MAX_MONEY);
 }
 
-NODISCARD inline int64_t ConsumeTime(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline int64_t ConsumeTime(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     static const int64_t time_min = ParseISO8601DateTime("1970-01-01T00:00:00Z");
     static const int64_t time_max = ParseISO8601DateTime("9999-12-31T23:59:59Z");
     return fuzzed_data_provider.ConsumeIntegralInRange<int64_t>(time_min, time_max);
 }
 
-NODISCARD inline CScript ConsumeScript(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline CScript ConsumeScript(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     const std::vector<uint8_t> b = ConsumeRandomLengthByteVector(fuzzed_data_provider);
     return {b.begin(), b.end()};
 }
 
-NODISCARD inline CScriptNum ConsumeScriptNum(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline CScriptNum ConsumeScriptNum(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     return CScriptNum{fuzzed_data_provider.ConsumeIntegral<int64_t>()};
 }
 
-NODISCARD inline uint160 ConsumeUInt160(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline uint160 ConsumeUInt160(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     const std::vector<uint8_t> v160 = fuzzed_data_provider.ConsumeBytes<uint8_t>(160 / 8);
     if (v160.size() != 160 / 8) {
@@ -123,7 +123,7 @@ NODISCARD inline uint160 ConsumeUInt160(FuzzedDataProvider& fuzzed_data_provider
     return uint160{v160};
 }
 
-NODISCARD inline uint256 ConsumeUInt256(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline uint256 ConsumeUInt256(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     const std::vector<uint8_t> v256 = fuzzed_data_provider.ConsumeBytes<uint8_t>(256 / 8);
     if (v256.size() != 256 / 8) {
@@ -132,12 +132,12 @@ NODISCARD inline uint256 ConsumeUInt256(FuzzedDataProvider& fuzzed_data_provider
     return uint256{v256};
 }
 
-NODISCARD inline arith_uint256 ConsumeArithUInt256(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline arith_uint256 ConsumeArithUInt256(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     return UintToArith256(ConsumeUInt256(fuzzed_data_provider));
 }
 
-NODISCARD inline CTxMemPoolEntry ConsumeTxMemPoolEntry(FuzzedDataProvider& fuzzed_data_provider, const CTransaction& tx) noexcept
+[[nodiscard]] inline CTxMemPoolEntry ConsumeTxMemPoolEntry(FuzzedDataProvider& fuzzed_data_provider, const CTransaction& tx) noexcept
 {
     // Avoid:
     // policy/feerate.cpp:28:34: runtime error: signed integer overflow: 34873208148477500 * 1000 cannot be represented in type 'long'
@@ -152,7 +152,7 @@ NODISCARD inline CTxMemPoolEntry ConsumeTxMemPoolEntry(FuzzedDataProvider& fuzze
     return CTxMemPoolEntry{MakeTransactionRef(tx), fee, time, entry_height, spends_coinbase, sig_op_cost, {}};
 }
 
-NODISCARD inline CTxDestination ConsumeTxDestination(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline CTxDestination ConsumeTxDestination(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     CTxDestination tx_destination;
     switch (fuzzed_data_provider.ConsumeIntegralInRange<int>(0, 5)) {
@@ -190,7 +190,7 @@ NODISCARD inline CTxDestination ConsumeTxDestination(FuzzedDataProvider& fuzzed_
 }
 
 template <typename T>
-NODISCARD bool MultiplicationOverflow(const T i, const T j) noexcept
+[[nodiscard]] bool MultiplicationOverflow(const T i, const T j) noexcept
 {
     static_assert(std::is_integral<T>::value, "Integral required.");
     if (std::numeric_limits<T>::is_signed) {
@@ -213,7 +213,7 @@ NODISCARD bool MultiplicationOverflow(const T i, const T j) noexcept
 }
 
 template <class T>
-NODISCARD bool AdditionOverflow(const T i, const T j) noexcept
+[[nodiscard]] bool AdditionOverflow(const T i, const T j) noexcept
 {
     static_assert(std::is_integral<T>::value, "Integral required.");
     if (std::numeric_limits<T>::is_signed) {
@@ -223,7 +223,7 @@ NODISCARD bool AdditionOverflow(const T i, const T j) noexcept
     return std::numeric_limits<T>::max() - i < j;
 }
 
-NODISCARD inline bool ContainsSpentInput(const CTransaction& tx, const CCoinsViewCache& inputs) noexcept
+[[nodiscard]] inline bool ContainsSpentInput(const CTransaction& tx, const CCoinsViewCache& inputs) noexcept
 {
     for (const CTxIn& tx_in : tx.vin) {
         const Coin& coin = inputs.AccessCoin(tx_in.prevout);
@@ -238,7 +238,7 @@ NODISCARD inline bool ContainsSpentInput(const CTransaction& tx, const CCoinsVie
  * Returns a byte vector of specified size regardless of the number of remaining bytes available
  * from the fuzzer. Pads with zero value bytes if needed to achieve the specified size.
  */
-NODISCARD inline std::vector<uint8_t> ConsumeFixedLengthByteVector(FuzzedDataProvider& fuzzed_data_provider, const size_t length) noexcept
+[[nodiscard]] inline std::vector<uint8_t> ConsumeFixedLengthByteVector(FuzzedDataProvider& fuzzed_data_provider, const size_t length) noexcept
 {
     std::vector<uint8_t> result(length);
     const std::vector<uint8_t> random_bytes = fuzzed_data_provider.ConsumeBytes<uint8_t>(length);
@@ -419,7 +419,7 @@ public:
     }
 };
 
-NODISCARD inline FuzzedFileProvider ConsumeFile(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline FuzzedFileProvider ConsumeFile(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     return {fuzzed_data_provider};
 }
@@ -440,7 +440,7 @@ public:
     }
 };
 
-NODISCARD inline FuzzedAutoFileProvider ConsumeAutoFile(FuzzedDataProvider& fuzzed_data_provider) noexcept
+[[nodiscard]] inline FuzzedAutoFileProvider ConsumeAutoFile(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     return {fuzzed_data_provider};
 }
diff --git a/src/util/bip32.h b/src/util/bip32.h
index 347e83db9e..8f86f2aaa6 100644
--- a/src/util/bip32.h
+++ b/src/util/bip32.h
@@ -10,7 +10,7 @@
 #include <vector>
 
 /** Parse an HD keypaths like "m/7/0'/2000". */
-NODISCARD bool ParseHDKeypath(const std::string& keypath_str, std::vector<uint32_t>& keypath);
+[[nodiscard]] bool ParseHDKeypath(const std::string& keypath_str, std::vector<uint32_t>& keypath);
 
 /** Write HD keypaths as strings */
 std::string WriteHDKeypath(const std::vector<uint32_t>& keypath);
diff --git a/src/util/moneystr.h b/src/util/moneystr.h
index 9d2b6da0fc..da7f673cda 100644
--- a/src/util/moneystr.h
+++ b/src/util/moneystr.h
@@ -19,6 +19,6 @@
  */
 std::string FormatMoney(const CAmount& n);
 /** Parse an amount denoted in full coins. E.g. "0.0034" supplied on the command line. **/
-NODISCARD bool ParseMoney(const std::string& str, CAmount& nRet);
+[[nodiscard]] bool ParseMoney(const std::string& str, CAmount& nRet);
 
 #endif // BITCOIN_UTIL_MONEYSTR_H
diff --git a/src/util/strencodings.cpp b/src/util/strencodings.cpp
index 3236184b0b..f3d54a2ac9 100644
--- a/src/util/strencodings.cpp
+++ b/src/util/strencodings.cpp
@@ -280,7 +280,7 @@ std::string DecodeBase32(const std::string& str, bool* pf_invalid)
     return std::string((const char*)vchRet.data(), vchRet.size());
 }
 
-NODISCARD static bool ParsePrechecks(const std::string& str)
+[[nodiscard]] static bool ParsePrechecks(const std::string& str)
 {
     if (str.empty()) // No empty string allowed
         return false;
diff --git a/src/util/strencodings.h b/src/util/strencodings.h
index 1a217dd12d..8ee43c620b 100644
--- a/src/util/strencodings.h
+++ b/src/util/strencodings.h
@@ -101,42 +101,42 @@ constexpr inline bool IsSpace(char c) noexcept {
  * @returns true if the entire string could be parsed as valid integer,
  *   false if not the entire string could be parsed or when overflow or underflow occurred.
  */
-NODISCARD bool ParseInt32(const std::string& str, int32_t *out);
+[[nodiscard]] bool ParseInt32(const std::string& str, int32_t *out);
 
 /**
  * Convert string to signed 64-bit integer with strict parse error feedback.
  * @returns true if the entire string could be parsed as valid integer,
  *   false if not the entire string could be parsed or when overflow or underflow occurred.
  */
-NODISCARD bool ParseInt64(const std::string& str, int64_t *out);
+[[nodiscard]] bool ParseInt64(const std::string& str, int64_t *out);
 
 /**
  * Convert decimal string to unsigned 8-bit integer with strict parse error feedback.
  * @returns true if the entire string could be parsed as valid integer,
  *   false if not the entire string could be parsed or when overflow or underflow occurred.
  */
-NODISCARD bool ParseUInt8(const std::string& str, uint8_t *out);
+[[nodiscard]] bool ParseUInt8(const std::string& str, uint8_t *out);
 
 /**
  * Convert decimal string to unsigned 32-bit integer with strict parse error feedback.
  * @returns true if the entire string could be parsed as valid integer,
  *   false if not the entire string could be parsed or when overflow or underflow occurred.
  */
-NODISCARD bool ParseUInt32(const std::string& str, uint32_t *out);
+[[nodiscard]] bool ParseUInt32(const std::string& str, uint32_t *out);
 
 /**
  * Convert decimal string to unsigned 64-bit integer with strict parse error feedback.
  * @returns true if the entire string could be parsed as valid integer,
  *   false if not the entire string could be parsed or when overflow or underflow occurred.
  */
-NODISCARD bool ParseUInt64(const std::string& str, uint64_t *out);
+[[nodiscard]] bool ParseUInt64(const std::string& str, uint64_t *out);
 
 /**
  * Convert string to double with strict parse error feedback.
  * @returns true if the entire string could be parsed as valid double,
  *   false if not the entire string could be parsed or when overflow or underflow occurred.
  */
-NODISCARD bool ParseDouble(const std::string& str, double *out);
+[[nodiscard]] bool ParseDouble(const std::string& str, double *out);
 
 /**
  * Convert a span of bytes to a lower-case hexadecimal string.
@@ -170,7 +170,7 @@ bool TimingResistantEqual(const T& a, const T& b)
  * @returns true on success, false on error.
  * @note The result must be in the range (-10^18,10^18), otherwise an overflow error will trigger.
  */
-NODISCARD bool ParseFixedPoint(const std::string &val, int decimals, int64_t *amount_out);
+[[nodiscard]] bool ParseFixedPoint(const std::string &val, int decimals, int64_t *amount_out);
 
 /** Convert from one power-of-2 number base to another. */
 template<int frombits, int tobits, bool pad, typename O, typename I>
diff --git a/src/util/string.h b/src/util/string.h
index a0c87bd00c..5ffdc80d88 100644
--- a/src/util/string.h
+++ b/src/util/string.h
@@ -15,7 +15,7 @@
 #include <string>
 #include <vector>
 
-NODISCARD inline std::string TrimString(const std::string& str, const std::string& pattern = " \f\n\r\t\v")
+[[nodiscard]] inline std::string TrimString(const std::string& str, const std::string& pattern = " \f\n\r\t\v")
 {
     std::string::size_type front = str.find_first_not_of(pattern);
     if (front == std::string::npos) {
@@ -59,7 +59,7 @@ inline std::string Join(const std::vector<std::string>& list, const std::string&
 /**
  * Check if a string does not contain any embedded NUL (\0) characters
  */
-NODISCARD inline bool ValidAsCString(const std::string& str) noexcept
+[[nodiscard]] inline bool ValidAsCString(const std::string& str) noexcept
 {
     return str.size() == strlen(str.c_str());
 }
@@ -80,7 +80,7 @@ std::string ToString(const T& t)
  * Check whether a container begins with the given prefix.
  */
 template <typename T1, size_t PREFIX_LEN>
-NODISCARD inline bool HasPrefix(const T1& obj,
+[[nodiscard]] inline bool HasPrefix(const T1& obj,
                                 const std::array<uint8_t, PREFIX_LEN>& prefix)
 {
     return obj.size() >= PREFIX_LEN &&
diff --git a/src/util/system.h b/src/util/system.h
index 1df194ca84..78ebf751bf 100644
--- a/src/util/system.h
+++ b/src/util/system.h
@@ -188,7 +188,7 @@ protected:
     std::map<OptionsCategory, std::map<std::string, Arg>> m_available_args GUARDED_BY(cs_args);
     std::list<SectionInfo> m_config_sections GUARDED_BY(cs_args);
 
-    NODISCARD bool ReadConfigStream(std::istream& stream, const std::string& filepath, std::string& error, bool ignore_invalid_keys = false);
+    [[nodiscard]] bool ReadConfigStream(std::istream& stream, const std::string& filepath, std::string& error, bool ignore_invalid_keys = false);
 
     /**
      * Returns true if settings values from the default section should be used,
@@ -220,8 +220,8 @@ public:
      */
     void SelectConfigNetwork(const std::string& network);
 
-    NODISCARD bool ParseParameters(int argc, const char* const argv[], std::string& error);
-    NODISCARD bool ReadConfigFiles(std::string& error, bool ignore_invalid_keys = false);
+    [[nodiscard]] bool ParseParameters(int argc, const char* const argv[], std::string& error);
+    [[nodiscard]] bool ReadConfigFiles(std::string& error, bool ignore_invalid_keys = false);
 
     /**
      * Log warnings for options in m_section_only_args when