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

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

This change affects behavior in a few small ways.

- If there's no max_height specified, percentage progress is measured ending at
  wallet last processed block instead of node tip

- More consistent error reporting: Early check to see if start_block is on the
  active chain is removed, so start_block is always read and the triggers an
  error if it's unavailable

1 files changed, 7 insertions, 0 deletions

diff --git a/src/interfaces/chain.cpp b/src/interfaces/chain.cpp
index 1c578b56ca..2b2d3a4b86 100644
--- a/src/interfaces/chain.cpp
+++ b/src/interfaces/chain.cpp
@@ -251,6 +251,13 @@ public:
         WAIT_LOCK(cs_main, lock);
         return FillBlock(ChainActive().FindEarliestAtLeast(min_time, min_height), block, lock);
     }
+    bool findNextBlock(const uint256& block_hash, int block_height, const FoundBlock& next, bool* reorg) override {
+        WAIT_LOCK(cs_main, lock);
+        CBlockIndex* block = ChainActive()[block_height];
+        if (block && block->GetBlockHash() != block_hash) block = nullptr;
+        if (reorg) *reorg = !block;
+        return FillBlock(block ? ChainActive()[block_height + 1] : nullptr, next, lock);
+    }
     bool findAncestorByHeight(const uint256& block_hash, int ancestor_height, const FoundBlock& ancestor_out) override
     {
         WAIT_LOCK(cs_main, lock);