refactor: Add CWallet:::AttachChain method

This commit does not change behavior, it just moves code from
CWallet::CreateWalletFromFile to CWallet:::AttachChain so it can be updated in
the next commit.

This commit is most easily reviewed with
"git diff -w --color-moved=dimmed_zebra" or by diffing CWallet:::AttachChain
against the previous code with an external diff tool.

src/wallet/wallet.cpp

@@ -4089,6 +4089,35 @@ std::shared_ptr<CWallet> CWallet::Create(interfaces::Chain& chain, const std::st
 
     LOCK(walletInstance->cs_wallet);
 
+    if (!AttachChain(walletInstance, chain, error, warnings)) {
+        return nullptr;
+    }
+
+    {
+        LOCK(cs_wallets);
+        for (auto& load_wallet : g_load_wallet_fns) {
+            load_wallet(interfaces::MakeWallet(walletInstance));
+        }
+    }
+
+    walletInstance->SetBroadcastTransactions(gArgs.GetBoolArg("-walletbroadcast", DEFAULT_WALLETBROADCAST));
+
+    {
+        walletInstance->WalletLogPrintf("setKeyPool.size() = %u\n",      walletInstance->GetKeyPoolSize());
+        walletInstance->WalletLogPrintf("mapWallet.size() = %u\n",       walletInstance->mapWallet.size());
+        walletInstance->WalletLogPrintf("m_address_book.size() = %u\n",  walletInstance->m_address_book.size());
+    }
+
+    return walletInstance;
+}
+
+bool CWallet::AttachChain(const std::shared_ptr<CWallet>& walletInstance, interfaces::Chain& chain, bilingual_str& error, std::vector<bilingual_str>& warnings)
+{
+    LOCK(walletInstance->cs_wallet);
+    // allow setting the chain if it hasn't been set already but prevent changing it
+    assert(!walletInstance->m_chain || walletInstance->m_chain == &chain);
+    walletInstance->m_chain = &chain;
+
     // Register wallet with validationinterface. It's done before rescan to avoid
     // missing block connections between end of rescan and validation subscribing.
     // Because of wallet lock being hold, block connection notifications are going to
@@ -4122,21 +4151,21 @@ std::shared_ptr<CWallet> CWallet::Create(interfaces::Chain& chain, const std::st
 
     if (tip_height && *tip_height != rescan_height)
     {
-        // We can't rescan beyond non-pruned blocks, stop and throw an error.
-        // This might happen if a user uses an old wallet within a pruned node
-        // or if they ran -disablewallet for a longer time, then decided to re-enable
         if (chain.havePruned()) {
-            // Exit early and print an error.
-            // If a block is pruned after this check, we will load the wallet,
-            // but fail the rescan with a generic error.
             int block_height = *tip_height;
             while (block_height > 0 && chain.haveBlockOnDisk(block_height - 1) && rescan_height != block_height) {
                 --block_height;
             }
 
             if (rescan_height != block_height) {
+                // We can't rescan beyond non-pruned blocks, stop and throw an error.
+                // This might happen if a user uses an old wallet within a pruned node
+                // or if they ran -disablewallet for a longer time, then decided to re-enable
+                // Exit early and print an error.
+                // If a block is pruned after this check, we will load the wallet,
+                // but fail the rescan with a generic error.
                 error = _("Prune: last wallet synchronisation goes beyond pruned data. You need to -reindex (download the whole blockchain again in case of pruned node)");
-                return nullptr;
+                return false;
             }
         }
 
@@ -4158,29 +4187,14 @@ std::shared_ptr<CWallet> CWallet::Create(interfaces::Chain& chain, const std::st
             WalletRescanReserver reserver(*walletInstance);
             if (!reserver.reserve() || (ScanResult::SUCCESS != walletInstance->ScanForWalletTransactions(chain.getBlockHash(rescan_height), rescan_height, {} /* max height */, reserver, true /* update */).status)) {
                 error = _("Failed to rescan the wallet during initialization");
-                return nullptr;
+                return false;
             }
         }
         walletInstance->chainStateFlushed(chain.getTipLocator());
         walletInstance->GetDatabase().IncrementUpdateCounter();
     }
 
-    {
-        LOCK(cs_wallets);
-        for (auto& load_wallet : g_load_wallet_fns) {
-            load_wallet(interfaces::MakeWallet(walletInstance));
-        }
-    }
-
-    walletInstance->SetBroadcastTransactions(gArgs.GetBoolArg("-walletbroadcast", DEFAULT_WALLETBROADCAST));
-
-    {
-        walletInstance->WalletLogPrintf("setKeyPool.size() = %u\n",      walletInstance->GetKeyPoolSize());
-        walletInstance->WalletLogPrintf("mapWallet.size() = %u\n",       walletInstance->mapWallet.size());
-        walletInstance->WalletLogPrintf("m_address_book.size() = %u\n",  walletInstance->m_address_book.size());
-    }
-
-    return walletInstance;
+    return true;
 }
 
 const CAddressBookData* CWallet::FindAddressBookEntry(const CTxDestination& dest, bool allow_change) const

src/wallet/wallet.h

@@ -763,6 +763,13 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
 
     bool CreateTransactionInternal(const std::vector<CRecipient>& vecSend, CTransactionRef& tx, CAmount& nFeeRet, int& nChangePosInOut, bilingual_str& error, const CCoinControl& coin_control, FeeCalculation& fee_calc_out, bool sign);
 
+    /**
+     * Catch wallet up to current chain, scanning new blocks, updating the best
+     * block locator and m_last_block_processed, and registering for
+     * notifications about new blocks and transactions.
+     */
+    static bool AttachChain(const std::shared_ptr<CWallet>& wallet, interfaces::Chain& chain, bilingual_str& error, std::vector<bilingual_str>& warnings);
+
 public:
     /**
      * Main wallet lock.