merge bitcoin#20499: Remove obsolete NODISCARD ifdef forest. Use [[nodiscard]] (C++17)

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

src/attributes.h

@@ -6,19 +6,6 @@
 #ifndef BITCOIN_ATTRIBUTES_H
 #define BITCOIN_ATTRIBUTES_H
 
-#if defined(__has_cpp_attribute)
-#  if __has_cpp_attribute(nodiscard)
-#    define NODISCARD [[nodiscard]]
-#  endif
-#endif
-#ifndef NODISCARD
-#  if defined(_MSC_VER) && _MSC_VER >= 1700
-#    define NODISCARD _Check_return_
-#  else
-#    define NODISCARD __attribute__((warn_unused_result))
-#  endif
-#endif
-
 #if defined(__clang__)
 #  if __has_attribute(lifetimebound)
 #    define LIFETIMEBOUND [[clang::lifetimebound]]

src/base58.h

@@ -35,13 +35,13 @@ std::string EncodeBase58(const std::vector<unsigned char>& vch);
  * return true if decoding is successful.
  * psz cannot be nullptr.
  */
-NODISCARD bool DecodeBase58(const char* psz, std::vector<unsigned char>& vchRet);
+[[nodiscard]] bool DecodeBase58(const char* psz, std::vector<unsigned char>& vchRet);
 
 /**
  * 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);
+[[nodiscard]] bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet);
 
 /**
  * Encode a byte vector into a base58-encoded string, including checksum
@@ -52,12 +52,12 @@ std::string EncodeBase58Check(const std::vector<unsigned char>& vchIn);
  * Decode a base58-encoded string (psz) that includes a checksum into a byte
  * vector (vchRet), return true if decoding is successful
  */
-NODISCARD bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet);
+[[nodiscard]] bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet);
 
 /**
  * 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);
+[[nodiscard]] bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet);
 
 #endif // BITCOIN_BASE58_H

src/core_io.h

@@ -23,8 +23,8 @@ struct CSpentIndexTxInfo;
 // 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& strHexTx);
+[[nodiscard]] bool DecodeHexTx(CMutableTransaction& tx, const std::string& strHexTx);
-NODISCARD bool DecodeHexBlk(CBlock&, const std::string& strHexBlk);
+[[nodiscard]] bool DecodeHexBlk(CBlock&, const std::string& strHexBlk);
 uint256 ParseHashStr(const std::string&, const std::string& strName);
 std::vector<unsigned char> ParseHexUV(const UniValue& v, const std::string& strName);
 

src/evo/deterministicmns.h

@@ -508,7 +508,7 @@ public:
 
 private:
     template <typename T>
-    NODISCARD bool AddUniqueProperty(const CDeterministicMNCPtr& dmn, const T& v)
+    [[nodiscard]] bool AddUniqueProperty(const CDeterministicMNCPtr& dmn, const T& v)
     {
         static const T nullValue;
         if (v == nullValue) {
@@ -528,7 +528,7 @@ private:
         return true;
     }
     template <typename T>
-    NODISCARD bool DeleteUniqueProperty(const CDeterministicMNCPtr& dmn, const T& oldValue)
+    [[nodiscard]] bool DeleteUniqueProperty(const CDeterministicMNCPtr& dmn, const T& oldValue)
     {
         static const T nullValue;
         if (oldValue == nullValue) {
@@ -548,7 +548,7 @@ private:
         return true;
     }
     template <typename T>
-    NODISCARD bool UpdateUniqueProperty(const CDeterministicMNCPtr& dmn, const T& oldValue, const T& newValue)
+    [[nodiscard]] bool UpdateUniqueProperty(const CDeterministicMNCPtr& dmn, const T& oldValue, const T& newValue)
     {
         if (oldValue == newValue) {
             return true;

src/util/moneystr.h

@@ -19,7 +19,7 @@
  * JSON but use AmountFromValue and ValueFromAmount for that.
  */
 std::string FormatMoney(const CAmount& n);
-NODISCARD bool ParseMoney(const std::string& str, CAmount& nRet);
+[[nodiscard]] bool ParseMoney(const std::string& str, CAmount& nRet);
-NODISCARD bool ParseMoney(const char* pszIn, CAmount& nRet);
+[[nodiscard]] bool ParseMoney(const char* pszIn, CAmount& nRet);
 
 #endif // BITCOIN_UTIL_MONEYSTR_H

src/util/strencodings.cpp

@@ -266,7 +266,7 @@ 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;

src/util/strencodings.h

@@ -92,42 +92,42 @@ constexpr bool IsDigit(char c)
  * @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.
@@ -161,7 +161,7 @@ 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>

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());
 }
@@ -68,7 +68,7 @@ NODISCARD inline bool ValidAsCString(const std::string& str) noexcept
  * 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 &&