C++20 Round 7: [[nodiscard]] on critical bool functions

- Add [[nodiscard]] to validation functions whose return value must be checked:
  CTransaction::IsStandard, CheckTransaction, ConnectInputs, AcceptToMemoryPool
  CBlock::ConnectBlock, AcceptBlock, IsInitialBlockDownload
  IsStandard, IsMine (3 overloads), SignSignature (2), VerifyScript, VerifySignature
  CWallet::IsMine (3 overloads)

src/main.h

@@ -137,7 +137,7 @@ int64_t GetProofOfStakeReward(int64_t nCoinAge, int64_t nFees);
 unsigned int ComputeMinWork(unsigned int nBase, int64_t nTime);
 unsigned int ComputeMinStake(unsigned int nBase, int64_t nTime, unsigned int nBlockTime);
 int GetNumBlocksOfPeers();
-bool IsInitialBlockDownload();
+[[nodiscard]] bool IsInitialBlockDownload();
 std::string GetWarnings(std::string strFor);
 bool GetTransaction(const uint256 &hash, CTransaction &tx, uint256 &hashBlock);
 uint256 WantedByOrphan(const CBlock* pblockOrphan);
@@ -589,7 +589,7 @@ public:
     /** Check for standard transaction types
         @return True if all outputs (scriptPubKeys) use only standard transaction forms
     */
-    bool IsStandard() const;
+    [[nodiscard]] bool IsStandard() const;
 
     /** Check for standard transaction types
         @param[in] mapInputs	Map of previous transactions that have outputs we're spending
@@ -734,12 +734,12 @@ public:
         @param[in] fMiner       true if called from CreateNewBlock
         @return Returns true if all checks succeed
      */
-    bool ConnectInputs(CTxDBBase& txdb, const MapPrevTx& inputs,
+    [[nodiscard]] bool ConnectInputs(CTxDBBase& txdb, const MapPrevTx& inputs,
                        const CBlockIndex* pindexBlock, bool fBlock, bool fMiner,
                        std::vector<CScriptCheck>* pvChecks = nullptr);
     bool ClientConnectInputs();
-    bool CheckTransaction() const;
-    bool AcceptToMemoryPool(CTxDBBase& txdb, bool fCheckInputs=true, bool* pfMissingInputs=nullptr);
+    [[nodiscard]] bool CheckTransaction() const;
+    [[nodiscard]] bool AcceptToMemoryPool(CTxDBBase& txdb, bool fCheckInputs=true, bool* pfMissingInputs=nullptr);
     bool GetCoinAge(CTxDBBase& txdb, uint64_t& nCoinAge) const;  // triangles: get transaction coin age
 
 protected:
@@ -1137,12 +1137,12 @@ public:
 
 
     bool DisconnectBlock(CTxDBBase& txdb, CBlockIndex* pindex);
-    bool ConnectBlock(CTxDBBase& txdb, CBlockIndex* pindex, bool fJustCheck=false);
+    [[nodiscard]] bool ConnectBlock(CTxDBBase& txdb, CBlockIndex* pindex, bool fJustCheck=false);
     bool ReadFromDisk(const CBlockIndex* pindex, bool fReadTransactions=true);
     bool SetBestChain(CTxDBBase& txdb, CBlockIndex* pindexNew);
     bool AddToBlockIndex(unsigned int nFile, unsigned int nBlockPos, const uint256& hashProofOfStake);
     bool CheckBlock(bool fCheckPOW=true, bool fCheckMerkleRoot=true, bool fCheckSig=true) const;
-    bool AcceptBlock();
+    [[nodiscard]] bool AcceptBlock();
     bool GetCoinAge(uint64_t& nCoinAge) const; // triangles: calculate total coin age spent in block
     bool SignBlock(CWallet& keystore, int64_t nFees);
     bool CheckBlockSignature() const;

src/script.h

@@ -591,17 +591,17 @@ public:
 bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, const CTransaction& txTo, unsigned int nIn, int nHashType);
 bool Solver(const CScript& scriptPubKey, TxnOutType& typeRet, std::vector<std::vector<unsigned char> >& vSolutionsRet);
 int ScriptSigArgsExpected(TxnOutType t, const std::vector<std::vector<unsigned char> >& vSolutions);
-bool IsStandard(const CScript& scriptPubKey);
-bool IsMine(const CKeyStore& keystore, const CScript& scriptPubKey);
-bool IsMine(const CKeyStore& keystore, const CTxDestination &dest);
+[[nodiscard]] bool IsStandard(const CScript& scriptPubKey);
+[[nodiscard]] bool IsMine(const CKeyStore& keystore, const CScript& scriptPubKey);
+[[nodiscard]] bool IsMine(const CKeyStore& keystore, const CTxDestination &dest);
 void ExtractAffectedKeys(const CKeyStore &keystore, const CScript& scriptPubKey, std::vector<CKeyID> &vKeys);
 bool ExtractDestination(const CScript& scriptPubKey, CTxDestination& addressRet);
 bool ExtractDestinations(const CScript& scriptPubKey, TxnOutType& typeRet, std::vector<CTxDestination>& addressRet, int& nRequiredRet);
-bool SignSignature(const CKeyStore& keystore, const CScript& fromPubKey, CTransaction& txTo, unsigned int nIn, int nHashType=SIGHASH_ALL);
-bool SignSignature(const CKeyStore& keystore, const CTransaction& txFrom, CTransaction& txTo, unsigned int nIn, int nHashType=SIGHASH_ALL);
-bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, const CTransaction& txTo, unsigned int nIn,
+[[nodiscard]] bool SignSignature(const CKeyStore& keystore, const CScript& fromPubKey, CTransaction& txTo, unsigned int nIn, int nHashType=SIGHASH_ALL);
+[[nodiscard]] bool SignSignature(const CKeyStore& keystore, const CTransaction& txFrom, CTransaction& txTo, unsigned int nIn, int nHashType=SIGHASH_ALL);
+[[nodiscard]] bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, const CTransaction& txTo, unsigned int nIn,
                   int nHashType);
-bool VerifySignature(const CTransaction& txFrom, const CTransaction& txTo, unsigned int nIn, int nHashType);
+[[nodiscard]] bool VerifySignature(const CTransaction& txFrom, const CTransaction& txTo, unsigned int nIn, int nHashType);
 
 // Given two sets of signatures for scriptPubKey, possibly with OP_0 placeholders,
 // combine them intelligently and return the result.

src/wallet.h

@@ -216,9 +216,9 @@ public:
     std::set< std::set<CTxDestination> > GetAddressGroupings();
     std::map<CTxDestination, int64_t> GetAddressBalances();
 
-    bool IsMine(const CTxIn& txin) const;
+    [[nodiscard]] bool IsMine(const CTxIn& txin) const;
     int64_t GetDebit(const CTxIn& txin) const;
-    bool IsMine(const CTxOut& txout) const
+    [[nodiscard]] bool IsMine(const CTxOut& txout) const
     {
         return ::IsMine(*this, txout.scriptPubKey);
     }
@@ -235,7 +235,7 @@ public:
             throw std::runtime_error("CWallet::GetChange() : value out of range");
         return (IsChange(txout) ? txout.nValue : 0);
     }
-    bool IsMine(const CTransaction& tx) const
+    [[nodiscard]] bool IsMine(const CTransaction& tx) const
     {
         for (const CTxOut& txout : tx.vout)
             if (IsMine(txout) && txout.nValue >= nMinimumInputValue)