wallet: Avoid use of Chain::Lock in CWallet::CreateTransaction

This is a step toward removing the Chain::Lock class and reducing cs_main
locking.

This change only affects behavior in the case where wallet last block processed
falls behind the chain tip, where it may set a different lock time.

src/wallet/wallet.cpp

@@ -2620,13 +2620,15 @@ bool CWallet::FundTransaction(CMutableTransaction& tx, CAmount& nFeeRet, int& nC
     return true;
 }
 
-static bool IsCurrentForAntiFeeSniping(interfaces::Chain& chain, interfaces::Chain::Lock& locked_chain)
+static bool IsCurrentForAntiFeeSniping(interfaces::Chain& chain, const uint256& block_hash)
 {
     if (chain.isInitialBlockDownload()) {
         return false;
     }
     constexpr int64_t MAX_ANTI_FEE_SNIPING_TIP_AGE = 8 * 60 * 60; // in seconds
-    if (locked_chain.getBlockTime(*locked_chain.getHeight()) < (GetTime() - MAX_ANTI_FEE_SNIPING_TIP_AGE)) {
+    int64_t block_time;
+    CHECK_NONFATAL(chain.findBlock(block_hash, FoundBlock().time(block_time)));
+    if (block_time < (GetTime() - MAX_ANTI_FEE_SNIPING_TIP_AGE)) {
         return false;
     }
     return true;
@@ -2636,9 +2638,8 @@ static bool IsCurrentForAntiFeeSniping(interfaces::Chain& chain, interfaces::Cha
  * Return a height-based locktime for new transactions (uses the height of the
  * current chain tip unless we are not synced with the current chain
  */
-static uint32_t GetLocktimeForNewTransaction(interfaces::Chain& chain, interfaces::Chain::Lock& locked_chain)
+static uint32_t GetLocktimeForNewTransaction(interfaces::Chain& chain, const uint256& block_hash, int block_height)
 {
-    uint32_t const height = locked_chain.getHeight().get_value_or(-1);
     uint32_t locktime;
     // Discourage fee sniping.
     //
@@ -2660,8 +2661,8 @@ static uint32_t GetLocktimeForNewTransaction(interfaces::Chain& chain, interface
     // enough, that fee sniping isn't a problem yet, but by implementing a fix
     // now we ensure code won't be written that makes assumptions about
     // nLockTime that preclude a fix later.
-    if (IsCurrentForAntiFeeSniping(chain, locked_chain)) {
-        locktime = height;
+    if (IsCurrentForAntiFeeSniping(chain, block_hash)) {
+        locktime = block_height;
 
         // Secondly occasionally randomly pick a nLockTime even further back, so
         // that transactions that are delayed after signing for whatever reason,
@@ -2675,7 +2676,6 @@ static uint32_t GetLocktimeForNewTransaction(interfaces::Chain& chain, interface
         // unique "nLockTime fingerprint", set nLockTime to a constant.
         locktime = 0;
     }
-    assert(locktime <= height);
     assert(locktime < LOCKTIME_THRESHOLD);
     return locktime;
 }
@@ -2735,16 +2735,14 @@ bool CWallet::CreateTransaction(interfaces::Chain::Lock& locked_chain, const std
     }
 
     CMutableTransaction txNew;
-
-    txNew.nLockTime = GetLocktimeForNewTransaction(chain(), locked_chain);
-
     FeeCalculation feeCalc;
     CAmount nFeeNeeded;
     int nBytes;
     {
         std::set<CInputCoin> setCoins;
         auto locked_chain = chain().lock();
         LOCK(cs_wallet);
+        txNew.nLockTime = GetLocktimeForNewTransaction(chain(), GetLastBlockHash(), GetLastBlockHeight());
         {
             std::vector<COutput> vAvailableCoins;
             AvailableCoins(*locked_chain, vAvailableCoins, true, &coin_control, 1, MAX_MONEY, MAX_MONEY, 0);