wallet: Avoid use of Chain::Lock in importmulti

This is a step toward removing the Chain::Lock class and reducing cs_main
locking.

This change only affects behavior in the case where wallet last block processed
falls behind the chain tip, in which case it may use a more accurate rescan
time.

src/interfaces/chain.cpp

@@ -87,13 +87,6 @@ class LockImpl : public Chain::Lock, public UniqueLock<RecursiveMutex>
         assert(block != nullptr);
         return block->GetBlockTime();
     }
-    int64_t getBlockMedianTimePast(int height) override
-    {
-        LockAssertion lock(::cs_main);
-        CBlockIndex* block = ::ChainActive()[height];
-        assert(block != nullptr);
-        return block->GetMedianTimePast();
-    }
     bool haveBlockOnDisk(int height) override
     {
         LockAssertion lock(::cs_main);

src/interfaces/chain.h

@@ -103,10 +103,6 @@ public:
         //! Get block time. Height must be valid or this function will abort.
         virtual int64_t getBlockTime(int height) = 0;
 
-        //! Get block median time past. Height must be valid or this function
-        //! will abort.
-        virtual int64_t getBlockMedianTimePast(int height) = 0;
-
         //! Check that the block is available on disk (i.e. has not been
         //! pruned), and contains transactions.
         virtual bool haveBlockOnDisk(int height) = 0;

src/wallet/rpcdump.cpp

@@ -1379,20 +1379,13 @@ UniValue importmulti(const JSONRPCRequest& mainRequest)
         EnsureWalletIsUnlocked(pwallet);
 
         // Verify all timestamps are present before importing any keys.
-        const Optional<int> tip_height = locked_chain->getHeight();
-        now = tip_height ? locked_chain->getBlockMedianTimePast(*tip_height) : 0;
+        CHECK_NONFATAL(pwallet->chain().findBlock(pwallet->GetLastBlockHash(), FoundBlock().time(nLowestTimestamp).mtpTime(now)));
         for (const UniValue& data : requests.getValues()) {
             GetImportTimestamp(data, now);
         }
 
         const int64_t minimumTimestamp = 1;
 
-        if (fRescan && tip_height) {
-            nLowestTimestamp = locked_chain->getBlockTime(*tip_height);
-        } else {
-            fRescan = false;
-        }
-
         for (const UniValue& data : requests.getValues()) {
             const int64_t timestamp = std::max(GetImportTimestamp(data, now), minimumTimestamp);
             const UniValue result = ProcessImport(pwallet, data, timestamp);

src/wallet/test/wallet_tests.cpp

@@ -152,6 +152,7 @@ BOOST_FIXTURE_TEST_CASE(importmulti_rescan, TestChain100Setup)
     {
         std::shared_ptr<CWallet> wallet = std::make_shared<CWallet>(chain.get(), WalletLocation(), WalletDatabase::CreateDummy());
         wallet->SetupLegacyScriptPubKeyMan();
+        WITH_LOCK(wallet->cs_wallet, wallet->SetLastBlockProcessed(newTip->nHeight, newTip->GetBlockHash()));
         AddWallet(wallet);
         UniValue keys;
         keys.setArray();