Merge bitcoin/bitcoin#33169: interfaces, chain, refactor: Remove unused getTipLocator and incaccurate getActiveChainLocator

2b00030af8 interfaces, chain, refactor: Remove inaccurate getActiveChainLocator (pablomartin4btc)
110a0f405c interfaces, chain, refactor: Remove unused getTipLocator (pablomartin4btc)

Pull request description:

  Remove `Chain::getTipLocator`, `Chain::GetLocator()`, and `Chain::getActiveChainLocator`:
  - `Chain::getTipLocator` is no longer used.
  - `Chain::GetLocator`, replaced its call by `GetLocator()`, which uses `LocatorEntries`, avoiding direct access to the chain itself (change suggested by l0rinc while reviewing this PR to maintain consistency with the overall refactoring).
  - `Chain::getActiveChainLocator`, whose name was misleading, has functionality redundant with Chain::findBlock.
    - Additionally, the comment for getActiveChainLocator became inaccurate following changes in commit ed470940cd (from PR #25717).

  This is a [follow-up](https://github.com/bitcoin/bitcoin/pull/29652#issuecomment-3151665095) to #29652.

ACKs for top commit:
  achow101:
    ACK 2b00030af8
  furszy:
    ACK 2b00030af8
  stickies-v:
    ACK 2b00030af8
  w0xlt:
    ACK 2b00030af8

Tree-SHA512: b12ba6a15feeaeec692d69204a6e155e3af43edfac25597dabf14cacca1e4a2152574816e58dc544f39043c5721f5e707acf544f4541d3b9c0f8c0c40069215e

src/chain.cpp

@@ -52,11 +52,6 @@ CBlockLocator GetLocator(const CBlockIndex* index)
     return CBlockLocator{LocatorEntries(index)};
 }
 
-CBlockLocator CChain::GetLocator() const
-{
-    return ::GetLocator(Tip());
-}
-
 const CBlockIndex *CChain::FindFork(const CBlockIndex *pindex) const {
     if (pindex == nullptr) {
         return nullptr;

src/chain.h

@@ -467,9 +467,6 @@ public:
     /** Set/initialize a chain with a given tip. */
     void SetTip(CBlockIndex& block);
 
-    /** Return a CBlockLocator that refers to the tip in of this chain. */
-    CBlockLocator GetLocator() const;
-
     /** Find the last common block between this chain and a block index entry. */
     const CBlockIndex* FindFork(const CBlockIndex* pindex) const;
 

src/interfaces/chain.h

@@ -143,13 +143,6 @@ public:
     //! pruned), and contains transactions.
     virtual bool haveBlockOnDisk(int height) = 0;
 
-    //! Get locator for the current chain tip.
-    virtual CBlockLocator getTipLocator() = 0;
-
-    //! Return a locator that refers to a block in the active chain.
-    //! If specified block is not in the active chain, return locator for the latest ancestor that is in the chain.
-    virtual CBlockLocator getActiveChainLocator(const uint256& block_hash) = 0;
-
     //! Return height of the highest block on chain in common with the locator,
     //! which will either be the original block used to create the locator,
     //! or one of its ancestors.

src/node/interfaces.cpp

@@ -559,17 +559,6 @@ public:
         const CBlockIndex* block{chainman().ActiveChain()[height]};
         return block && ((block->nStatus & BLOCK_HAVE_DATA) != 0) && block->nTx > 0;
     }
-    CBlockLocator getTipLocator() override
-    {
-        LOCK(::cs_main);
-        return chainman().ActiveChain().GetLocator();
-    }
-    CBlockLocator getActiveChainLocator(const uint256& block_hash) override
-    {
-        LOCK(::cs_main);
-        const CBlockIndex* index = chainman().m_blockman.LookupBlockIndex(block_hash);
-        return GetLocator(index);
-    }
     std::optional<int> findLocatorFork(const CBlockLocator& locator) override
     {
         LOCK(::cs_main);

src/validation.cpp

@@ -2897,7 +2897,7 @@ bool Chainstate::FlushStateToDisk(
     }
     if (full_flush_completed && m_chainman.m_options.signals) {
         // Update best block in wallet (so we can detect restored wallets).
-        m_chainman.m_options.signals->ChainStateFlushed(this->GetRole(), m_chain.GetLocator());
+        m_chainman.m_options.signals->ChainStateFlushed(this->GetRole(), GetLocator(m_chain.Tip()));
     }
     } catch (const std::runtime_error& e) {
         return FatalError(m_chainman.GetNotifications(), state, strprintf(_("System error while flushing: %s"), e.what()));

src/wallet/wallet.cpp

@@ -1837,9 +1837,13 @@ CWallet::ScanResult CWallet::ScanForWalletTransactions(const uint256& start_bloc
         chain().findBlock(block_hash, FoundBlock().inActiveChain(block_still_active).nextBlock(FoundBlock().inActiveChain(next_block).hash(next_block_hash)));
 
         if (fetch_block) {
-            // Read block data
+            // Read block data and locator if needed (the locator is usually null unless we need to save progress)
             CBlock block;
-            chain().findBlock(block_hash, FoundBlock().data(block));
+            CBlockLocator loc;
+            // Find block
+            FoundBlock found_block{FoundBlock().data(block)};
+            if (save_progress && next_interval) found_block.locator(loc);
+            chain().findBlock(block_hash, found_block);
 
             if (!block.IsNull()) {
                 LOCK(cs_wallet);
@@ -1857,15 +1861,11 @@ CWallet::ScanResult CWallet::ScanForWalletTransactions(const uint256& start_bloc
                 result.last_scanned_block = block_hash;
                 result.last_scanned_height = block_height;
 
-                if (save_progress && next_interval) {
-                    CBlockLocator loc = m_chain->getActiveChainLocator(block_hash);
-
                 if (!loc.IsNull()) {
                     WalletLogPrintf("Saving scan progress %d.\n", block_height);
                     WalletBatch batch(GetDatabase());
                     batch.WriteBestBlock(loc);
                 }
-                }
             } else {
                 // could not scan block, keep scanning but record this block as the most recent failure
                 result.last_failed_block = block_hash;