Merge #20588: Remove unused and confusing CTransaction constructor

fac39c1 wallet: document that tx in CreateTransaction is purely an out-param (MarcoFalke)
faac315 Remove unused and confusing CTransaction constructor (MarcoFalke)

Pull request description:

  The constructor is confusing and dangerous (as explained in the TODO), fix that by removing it.

ACKs for top commit:
  laanwj:
    Code review ACK fac39c1
  promag:
    Code review ACK fac39c1.
  theStack:
    Code review ACK fac39c1

Tree-SHA512: e0c8cffce8d8ee0166b8e1cbfe85ed0657611e26e2af0d69fde70eceaa5d75cbde3eb489af0428fe4fc431360b4c791fb1cc21b8dee7d4c7a4f17df00836229d

Author: fanquake

src/primitives/transaction.cpp

@@ -77,8 +77,6 @@ uint256 CTransaction::ComputeWitnessHash() const
     return SerializeHash(*this, SER_GETHASH, 0);
 }
 
-/* For backward compatibility, the hash is initialized to 0. TODO: remove the need for this default constructor entirely. */
-CTransaction::CTransaction() : vin(), vout(), nVersion(CTransaction::CURRENT_VERSION), nLockTime(0), hash{}, m_witness_hash{} {}
 CTransaction::CTransaction(const CMutableTransaction& tx) : vin(tx.vin), vout(tx.vout), nVersion(tx.nVersion), nLockTime(tx.nLockTime), hash{ComputeHash()}, m_witness_hash{ComputeWitnessHash()} {}
 CTransaction::CTransaction(CMutableTransaction&& tx) : vin(std::move(tx.vin)), vout(std::move(tx.vout)), nVersion(tx.nVersion), nLockTime(tx.nLockTime), hash{ComputeHash()}, m_witness_hash{ComputeWitnessHash()} {}
 

src/primitives/transaction.h

@@ -287,12 +287,9 @@ class CTransaction
     uint256 ComputeWitnessHash() const;
 
 public:
-    /** Construct a CTransaction that qualifies as IsNull() */
-    CTransaction();
-
     /** Convert a CMutableTransaction into a CTransaction. */
-    explicit CTransaction(const CMutableTransaction &tx);
-    CTransaction(CMutableTransaction &&tx);
+    explicit CTransaction(const CMutableTransaction& tx);
+    CTransaction(CMutableTransaction&& tx);
 
     template <typename Stream>
     inline void Serialize(Stream& s) const {
@@ -393,7 +390,6 @@ struct CMutableTransaction
 };
 
 typedef std::shared_ptr<const CTransaction> CTransactionRef;
-static inline CTransactionRef MakeTransactionRef() { return std::make_shared<const CTransaction>(); }
 template <typename Tx> static inline CTransactionRef MakeTransactionRef(Tx&& txIn) { return std::make_shared<const CTransaction>(std::forward<Tx>(txIn)); }
 
 /** A generic txid reference (txid or wtxid). */

src/test/fuzz/script_sigcache.cpp

@@ -29,7 +29,7 @@ void test_one_input(const std::vector<uint8_t>& buffer)
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
 
     const std::optional<CMutableTransaction> mutable_transaction = ConsumeDeserializable<CMutableTransaction>(fuzzed_data_provider);
-    const CTransaction tx = mutable_transaction ? CTransaction{*mutable_transaction} : CTransaction{};
+    const CTransaction tx{mutable_transaction ? *mutable_transaction : CMutableTransaction{}};
     const unsigned int n_in = fuzzed_data_provider.ConsumeIntegral<unsigned int>();
     const CAmount amount = ConsumeMoney(fuzzed_data_provider);
     const bool store = fuzzed_data_provider.ConsumeBool();

src/test/fuzz/transaction.cpp

@@ -42,7 +42,7 @@ void test_one_input(const std::vector<uint8_t>& buffer)
             return CTransaction(deserialize, ds);
         } catch (const std::ios_base::failure&) {
             valid_tx = false;
-            return CTransaction();
+            return CTransaction{CMutableTransaction{}};
         }
     }();
     bool valid_mutable_tx = true;

src/wallet/feebumper.cpp

@@ -215,7 +215,7 @@ Result CreateRateBumpTransaction(CWallet& wallet, const uint256& txid, const CCo
     // We cannot source new unconfirmed inputs(bip125 rule 2)
     new_coin_control.m_min_depth = 1;
 
-    CTransactionRef tx_new = MakeTransactionRef();
+    CTransactionRef tx_new;
     CAmount fee_ret;
     int change_pos_in_out = -1; // No requested location for change
     bilingual_str fail_reason;

src/wallet/wallet.cpp

@@ -3113,13 +3113,14 @@ bool CWallet::CreateTransaction(
         bool sign)
 {
     int nChangePosIn = nChangePosInOut;
-    CTransactionRef tx2 = tx;
+    Assert(!tx); // tx is an out-param. TODO change the return type from bool to tx (or nullptr)
     bool res = CreateTransactionInternal(vecSend, tx, nFeeRet, nChangePosInOut, error, coin_control, fee_calc_out, sign);
     // try with avoidpartialspends unless it's enabled already
     if (res && nFeeRet > 0 /* 0 means non-functional fee rate estimation */ && m_max_aps_fee > -1 && !coin_control.m_avoid_partial_spends) {
         CCoinControl tmp_cc = coin_control;
         tmp_cc.m_avoid_partial_spends = true;
         CAmount nFeeRet2;
+        CTransactionRef tx2;
         int nChangePosInOut2 = nChangePosIn;
         bilingual_str error2; // fired and forgotten; if an error occurs, we discard the results
         if (CreateTransactionInternal(vecSend, tx2, nFeeRet2, nChangePosInOut2, error2, tmp_cc, fee_calc_out, sign)) {