Merge bitcoin/bitcoin#32882: index: remove unnecessary locator cleaning in BaseIndex::Init()

facd01e refactor: remove redundant locator cleanup in BaseIndex::Init() (Hao Xu)

Pull request description:

  Leverage locator.IsNull() to simplify ReadBestBlock() and remove
  unnecessary SetNull().

ACKs for top commit:
  l0rinc:
    ACK facd01e
  furszy:
    utACK facd01e
  sedited:
    ACK facd01e

Tree-SHA512: ca418a3d4c72b9bfdb194e03d5acfacf7b567850ab385ad3a1ec6d070eedef4aea2bb8335f8bfe0316e84c22583111fc202f7603044c5d4d05754db23f75b47f

Author: fanquake

src/index/base.cpp

@@ -73,13 +73,16 @@ BaseIndex::DB::DB(const fs::path& path, size_t n_cache_size, bool f_memory, bool
         .options = [] { DBOptions options; node::ReadDatabaseArgs(gArgs, options); return options; }()}}
 {}
 
-bool BaseIndex::DB::ReadBestBlock(CBlockLocator& locator) const
+CBlockLocator BaseIndex::DB::ReadBestBlock() const
 {
+    CBlockLocator locator;
+
     bool success = Read(DB_BEST_BLOCK, locator);
     if (!success) {
         locator.SetNull();
     }
-    return success;
+
+    return locator;
 }
 
 void BaseIndex::DB::WriteBestBlock(CDBBatch& batch, const CBlockLocator& locator)
@@ -111,10 +114,7 @@ bool BaseIndex::Init()
     // callbacks are not missed once m_synced is true.
     m_chain->context()->validation_signals->RegisterValidationInterface(this);
 
-    CBlockLocator locator;
-    if (!GetDB().ReadBestBlock(locator)) {
-        locator.SetNull();
-    }
+    const auto locator{GetDB().ReadBestBlock()};
 
     LOCK(cs_main);
     CChain& index_chain = m_chainstate->m_chain;

src/index/base.h

@@ -68,7 +68,8 @@ class BaseIndex : public CValidationInterface
            bool f_memory = false, bool f_wipe = false, bool f_obfuscate = false);
 
         /// Read block locator of the chain that the index is in sync with.
-        bool ReadBestBlock(CBlockLocator& locator) const;
+        /// Note, the returned locator will be empty if no record exists.
+        CBlockLocator ReadBestBlock() const;
 
         /// Write block locator of the chain that the index is in sync with.
         void WriteBestBlock(CDBBatch& batch, const CBlockLocator& locator);