validation: Move FindForkInGlobalIndex to BlockManager

[META] This commit should be followed up by removing the comments and
       assertions meant only to show that the change is correct.

FindForkInGlobalIndex only acts on BlockManager.

Note to reviewers: Since FindForkInGlobalIndex is always called with
::ChainActive() as its first parameter, it is possible to move
FindForkInGlobalIndex to CChainState and remove this const CChain&
parameter to instead use m_chain. However, it seems like the original
intention was for FindForkInGlobalIndex to work with _any_ chain, not
just the current active chain. Let me know if this should be changed.

src/index/base.cpp

@@ -62,7 +62,7 @@ bool BaseIndex::Init()
     if (locator.IsNull()) {
         m_best_block_index = nullptr;
     } else {
-        m_best_block_index = FindForkInGlobalIndex(::ChainActive(), locator);
+        m_best_block_index = g_chainman.m_blockman.FindForkInGlobalIndex(::ChainActive(), locator);
     }
     m_synced = m_best_block_index.load() == ::ChainActive().Tip();
     return true;

src/net_processing.cpp

@@ -2968,7 +2968,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
         LOCK(cs_main);
 
         // Find the last block the caller has in the main chain
-        const CBlockIndex* pindex = FindForkInGlobalIndex(::ChainActive(), locator);
+        const CBlockIndex* pindex = g_chainman.m_blockman.FindForkInGlobalIndex(::ChainActive(), locator);
 
         // Send the rest of the chain
         if (pindex)
@@ -3088,7 +3088,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
         else
         {
             // Find the last block the caller has in the main chain
-            pindex = FindForkInGlobalIndex(::ChainActive(), locator);
+            pindex = g_chainman.m_blockman.FindForkInGlobalIndex(::ChainActive(), locator);
             if (pindex)
                 pindex = ::ChainActive().Next(pindex);
         }

src/node/interfaces.cpp

@@ -447,7 +447,7 @@ public:
     {
         LOCK(cs_main);
         const CChain& active = Assert(m_node.chainman)->ActiveChain();
-        if (CBlockIndex* fork = FindForkInGlobalIndex(active, locator)) {
+        if (CBlockIndex* fork = g_chainman.m_blockman.FindForkInGlobalIndex(active, locator)) {
             return fork->nHeight;
         }
         return nullopt;

src/validation.cpp

@@ -175,14 +175,15 @@ CBlockIndex* BlockManager::LookupBlockIndex(const uint256& hash)
     return it == m_block_index.end() ? nullptr : it->second;
 }
 
-CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator)
+CBlockIndex* BlockManager::FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator)
 {
     AssertLockHeld(cs_main);
 
+    assert(std::addressof(g_chainman.m_blockman) == std::addressof(*this));
     // Find the latest block common to locator and chain - we expect that
     // locator.vHave is sorted descending by height.
     for (const uint256& hash : locator.vHave) {
-        CBlockIndex* pindex = g_chainman.m_blockman.LookupBlockIndex(hash);
+        CBlockIndex* pindex = LookupBlockIndex(hash);
         if (pindex) {
             if (chain.Contains(pindex))
                 return pindex;

src/validation.h

@@ -311,9 +311,6 @@ public:
     bool VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview, int nCheckLevel, int nCheckDepth);
 };
 
-/** Find the last common block between the parameter chain and a locator. */
-CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
-
 enum DisconnectResult
 {
     DISCONNECT_OK,      // All good.
@@ -433,6 +430,9 @@ public:
 
     CBlockIndex* LookupBlockIndex(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
+    /** Find the last common block between the parameter chain and a locator. */
+    CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+
     ~BlockManager() {
         Unload();
     }