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, 15 insertions, 0 deletions

diff --git a/src/test/interfaces_tests.cpp b/src/test/interfaces_tests.cpp
index 5fba0e0429..fab3571756 100644
--- a/src/test/interfaces_tests.cpp
+++ b/src/test/interfaces_tests.cpp
@@ -59,6 +59,21 @@ BOOST_AUTO_TEST_CASE(findFirstBlockWithTimeAndHeight)
     BOOST_CHECK(!chain->findFirstBlockWithTimeAndHeight(/* min_time= */ active.Tip()->GetBlockTimeMax() + 1, /* min_height= */ 0));
 }
 
+BOOST_AUTO_TEST_CASE(findNextBlock)
+{
+    auto chain = interfaces::MakeChain(m_node);
+    auto& active = ChainActive();
+    bool reorg;
+    uint256 hash;
+    BOOST_CHECK(chain->findNextBlock(active[20]->GetBlockHash(), 20, FoundBlock().hash(hash), &reorg));
+    BOOST_CHECK_EQUAL(hash, active[21]->GetBlockHash());
+    BOOST_CHECK_EQUAL(reorg, false);
+    BOOST_CHECK(!chain->findNextBlock(uint256(), 20, {}, &reorg));
+    BOOST_CHECK_EQUAL(reorg, true);
+    BOOST_CHECK(!chain->findNextBlock(active.Tip()->GetBlockHash(), active.Height(), {}, &reorg));
+    BOOST_CHECK_EQUAL(reorg, false);
+}
+
 BOOST_AUTO_TEST_CASE(findAncestorByHeight)
 {
     auto chain = interfaces::MakeChain(m_node);