refactor: Make CWalletTx sync state type-safe

Current CWalletTx state representation makes it possible to set
inconsistent states that won't be handled correctly by wallet sync code
or serialized & deserialized back into the same form.

For example, it is possible to call setConflicted without setting a
conflicting block hash, or setConfirmed with no transaction index. And
it's possible update individual m_confirm and fInMempool data fields
without setting an overall consistent state that can be serialized and
handled correctly.

Fix this without changing behavior by using std::variant, instead of an
enum and collection of fields, to represent sync state, so state
tracking code is safer and more legible.

This is a first step to fixing state tracking bugs
https://github.com/bitcoin-core/bitcoin-devwiki/wiki/Wallet-Transaction-Conflict-Tracking,
by adding an extra margin of safety that can prevent new bugs from being
introduced as existing bugs are fixed.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 3855ad821d..cb7178fc01 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -275,7 +275,7 @@ private:
      * Should be called with rescanning_old_block set to true, if the transaction is
      * not discovered in real time, but during a rescan of old blocks.
      */
-    bool AddToWalletIfInvolvingMe(const CTransactionRef& tx, CWalletTx::Confirmation confirm, bool fUpdate, bool rescanning_old_block) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
+    bool AddToWalletIfInvolvingMe(const CTransactionRef& tx, const SyncTxState& state, bool fUpdate, bool rescanning_old_block) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
     /** Mark a transaction (and its in-wallet descendants) as conflicting with a particular block. */
     void MarkConflicted(const uint256& hashBlock, int conflicting_height, const uint256& hashTx);
@@ -285,7 +285,7 @@ private:
 
     void SyncMetaData(std::pair<TxSpends::iterator, TxSpends::iterator>) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
-    void SyncTransaction(const CTransactionRef& tx, CWalletTx::Confirmation confirm, bool update_tx = true, bool rescanning_old_block = false) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
+    void SyncTransaction(const CTransactionRef& tx, const SyncTxState& state, bool update_tx = true, bool rescanning_old_block = false) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
     /** WalletFlags set on this wallet. */
     std::atomic<uint64_t> m_wallet_flags{0};
@@ -508,7 +508,7 @@ public:
     //! @return true if wtx is changed and needs to be saved to disk, otherwise false
     using UpdateWalletTxFn = std::function<bool(CWalletTx& wtx, bool new_tx)>;
 
-    CWalletTx* AddToWallet(CTransactionRef tx, const CWalletTx::Confirmation& confirm, const UpdateWalletTxFn& update_wtx=nullptr, bool fFlushOnClose=true, bool rescanning_old_block = false);
+    CWalletTx* AddToWallet(CTransactionRef tx, const TxState& state, const UpdateWalletTxFn& update_wtx=nullptr, bool fFlushOnClose=true, bool rescanning_old_block = false);
     bool LoadToWallet(const uint256& hash, const UpdateWalletTxFn& fill_wtx) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
     void transactionAddedToMempool(const CTransactionRef& tx, uint64_t mempool_sequence) override;
     void blockConnected(const CBlock& block, int height) override;
@@ -576,7 +576,7 @@ public:
     void CommitTransaction(CTransactionRef tx, mapValue_t mapValue, std::vector<std::pair<std::string, std::string>> orderForm);
 
     /** Pass this transaction to node for mempool insertion and relay to peers if flag set to true */
-    bool SubmitTxMemoryPoolAndRelay(const CWalletTx& wtx, std::string& err_string, bool relay) const;
+    bool SubmitTxMemoryPoolAndRelay(CWalletTx& wtx, std::string& err_string, bool relay) const;
 
     bool DummySignTx(CMutableTransaction &txNew, const std::set<CTxOut> &txouts, const CCoinControl* coin_control = nullptr) const
     {