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

2 files changed, 12 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);
diff --git a/src/interfaces/chain.h b/src/interfaces/chain.h
index 8bc0ed824c..ef5a002f54 100644
--- a/src/interfaces/chain.h
+++ b/src/interfaces/chain.h
@@ -148,6 +148,11 @@ public:
     //! information.
     virtual bool findFirstBlockWithTimeAndHeight(int64_t min_time, int min_height, const FoundBlock& block={}) = 0;
 
+    //! Find next block if block is part of current chain. Also flag if
+    //! there was a reorg and the specified block hash is no longer in the
+    //! current chain, and optionally return block information.
+    virtual bool findNextBlock(const uint256& block_hash, int block_height, const FoundBlock& next={}, bool* reorg=nullptr) = 0;
+
     //! Find ancestor of block at specified height and optionally return
     //! ancestor information.
     virtual bool findAncestorByHeight(const uint256& block_hash, int ancestor_height, const FoundBlock& ancestor_out={}) = 0;