test: Clear block index flags when testing snapshots

When simulating a snapshot, remove the HAVE_DATA status for blocks below the
snapshot height, to simulate never having downloaded them at all. This makes
tests more realistic (and more closely match what will happen when using
assumeutxo).

Author: sdaftuar

src/test/util/chainstate.h

@@ -71,6 +71,7 @@ CreateAndActivateUTXOSnapshot(
             // This is a stripped-down version of node::LoadChainstate which
             // preserves the block index.
             LOCK(::cs_main);
+            CBlockIndex *orig_tip = node.chainman->ActiveChainstate().m_chain.Tip();
             uint256 gen_hash = node.chainman->ActiveChainstate().m_chain[0]->GetBlockHash();
             node.chainman->ResetChainstates();
             node.chainman->InitializeChainstate(node.mempool.get());
@@ -83,6 +84,22 @@ CreateAndActivateUTXOSnapshot(
             chain.setBlockIndexCandidates.insert(node.chainman->m_blockman.LookupBlockIndex(gen_hash));
             chain.LoadChainTip();
             node.chainman->MaybeRebalanceCaches();
+
+            // Reset the HAVE_DATA flags below the snapshot height, simulating
+            // never-having-downloaded them in the first place.
+            // TODO: perhaps we could improve this by using pruning to delete
+            // these blocks instead
+            CBlockIndex *pindex = orig_tip;
+            while (pindex && pindex != chain.m_chain.Tip()) {
+                pindex->nStatus &= ~BLOCK_HAVE_DATA;
+                pindex->nStatus &= ~BLOCK_HAVE_UNDO;
+                // We have to set the ASSUMED_VALID flag, because otherwise it
+                // would not be possible to have a block index entry without HAVE_DATA
+                // and with nTx > 0 (since we aren't setting the pruned flag);
+                // see CheckBlockIndex().
+                pindex->nStatus |= BLOCK_ASSUMED_VALID;
+                pindex = pindex->pprev;
+            }
         }
         BlockValidationState state;
         if (!node.chainman->ActiveChainstate().ActivateBestChain(state)) {