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, 9 insertions, 13 deletions

diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
index 4499eb5903..9a1398e970 100644
--- a/src/wallet/test/wallet_tests.cpp
+++ b/src/wallet/test/wallet_tests.cpp
@@ -330,7 +330,7 @@ BOOST_FIXTURE_TEST_CASE(importwallet_rescan, TestChain100Setup)
 BOOST_FIXTURE_TEST_CASE(coin_mark_dirty_immature_credit, TestChain100Setup)
 {
     CWallet wallet(m_node.chain.get(), "", m_args, CreateDummyWalletDatabase());
-    CWalletTx wtx(m_coinbase_txns.back());
+    CWalletTx wtx{m_coinbase_txns.back(), TxStateConfirmed{m_node.chainman->ActiveChain().Tip()->GetBlockHash(), m_node.chainman->ActiveChain().Height(), /*position_in_block=*/0}};
 
     LOCK(wallet.cs_wallet);
     wallet.SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
@@ -338,9 +338,6 @@ BOOST_FIXTURE_TEST_CASE(coin_mark_dirty_immature_credit, TestChain100Setup)
 
     wallet.SetLastBlockProcessed(m_node.chainman->ActiveChain().Height(), m_node.chainman->ActiveChain().Tip()->GetBlockHash());
 
-    CWalletTx::Confirmation confirm(CWalletTx::Status::CONFIRMED, m_node.chainman->ActiveChain().Height(), m_node.chainman->ActiveChain().Tip()->GetBlockHash(), 0);
-    wtx.m_confirm = confirm;
-
     // Call GetImmatureCredit() once before adding the key to the wallet to
     // cache the current immature credit amount, which is 0.
     BOOST_CHECK_EQUAL(CachedTxGetImmatureCredit(wallet, wtx), 0);
@@ -355,7 +352,7 @@ BOOST_FIXTURE_TEST_CASE(coin_mark_dirty_immature_credit, TestChain100Setup)
 static int64_t AddTx(ChainstateManager& chainman, CWallet& wallet, uint32_t lockTime, int64_t mockTime, int64_t blockTime)
 {
     CMutableTransaction tx;
-    CWalletTx::Confirmation confirm;
+    TxState state = TxStateInactive{};
     tx.nLockTime = lockTime;
     SetMockTime(mockTime);
     CBlockIndex* block = nullptr;
@@ -367,13 +364,13 @@ static int64_t AddTx(ChainstateManager& chainman, CWallet& wallet, uint32_t lock
         block = inserted.first->second;
         block->nTime = blockTime;
         block->phashBlock = &hash;
-        confirm = {CWalletTx::Status::CONFIRMED, block->nHeight, hash, 0};
+        state = TxStateConfirmed{hash, block->nHeight, /*position_in_block=*/0};
     }
-
-    // If transaction is already in map, to avoid inconsistencies, unconfirmation
-    // is needed before confirm again with different block.
-    return wallet.AddToWallet(MakeTransactionRef(tx), confirm, [&](CWalletTx& wtx, bool /* new_tx */) {
-        wtx.setUnconfirmed();
+    return wallet.AddToWallet(MakeTransactionRef(tx), state, [&](CWalletTx& wtx, bool /* new_tx */) {
+        // Assign wtx.m_state to simplify test and avoid the need to simulate
+        // reorg events. Without this, AddToWallet asserts false when the same
+        // transaction is confirmed in different blocks.
+        wtx.m_state = state;
         return true;
     })->nTimeSmart;
 }
@@ -534,8 +531,7 @@ public:
         wallet->SetLastBlockProcessed(wallet->GetLastBlockHeight() + 1, m_node.chainman->ActiveChain().Tip()->GetBlockHash());
         auto it = wallet->mapWallet.find(tx->GetHash());
         BOOST_CHECK(it != wallet->mapWallet.end());
-        CWalletTx::Confirmation confirm(CWalletTx::Status::CONFIRMED, m_node.chainman->ActiveChain().Height(), m_node.chainman->ActiveChain().Tip()->GetBlockHash(), 1);
-        it->second.m_confirm = confirm;
+        it->second.m_state = TxStateConfirmed{m_node.chainman->ActiveChain().Tip()->GetBlockHash(), m_node.chainman->ActiveChain().Height(), /*position_in_block=*/1};
         return it->second;
     }