Update CheckBlockIndex invariants for chains based on an assumeutxo snapshot

Author: sdaftuar

src/validation.cpp

@@ -4723,12 +4723,12 @@ void Chainstate::CheckBlockIndex()
     CBlockIndex* pindexFirstNotTransactionsValid = nullptr; // Oldest ancestor of pindex which does not have BLOCK_VALID_TRANSACTIONS (regardless of being valid or not).
     CBlockIndex* pindexFirstNotChainValid = nullptr; // Oldest ancestor of pindex which does not have BLOCK_VALID_CHAIN (regardless of being valid or not).
     CBlockIndex* pindexFirstNotScriptsValid = nullptr; // Oldest ancestor of pindex which does not have BLOCK_VALID_SCRIPTS (regardless of being valid or not).
+    CBlockIndex* pindexFirstAssumeValid = nullptr; // Oldest ancestor of pindex which has BLOCK_ASSUMED_VALID
     while (pindex != nullptr) {
         nNodes++;
+        if (pindexFirstAssumeValid == nullptr && pindex->nStatus & BLOCK_ASSUMED_VALID) pindexFirstAssumeValid = pindex;
         if (pindexFirstInvalid == nullptr && pindex->nStatus & BLOCK_FAILED_VALID) pindexFirstInvalid = pindex;
-        // Assumed-valid index entries will not have data since we haven't downloaded the
-        // full block yet.
-        if (pindexFirstMissing == nullptr && !(pindex->nStatus & BLOCK_HAVE_DATA) && !pindex->IsAssumedValid()) {
+        if (pindexFirstMissing == nullptr && !(pindex->nStatus & BLOCK_HAVE_DATA)) {
             pindexFirstMissing = pindex;
         }
         if (pindexFirstNeverProcessed == nullptr && pindex->nTx == 0) pindexFirstNeverProcessed = pindex;
@@ -4768,7 +4768,13 @@ void Chainstate::CheckBlockIndex()
         if (!m_blockman.m_have_pruned && !pindex->IsAssumedValid()) {
             // If we've never pruned, then HAVE_DATA should be equivalent to nTx > 0
             assert(!(pindex->nStatus & BLOCK_HAVE_DATA) == (pindex->nTx == 0));
-            assert(pindexFirstMissing == pindexFirstNeverProcessed);
+            if (pindexFirstAssumeValid == nullptr) {
+                // If we've got some assume valid blocks, then we might have
+                // missing blocks (not HAVE_DATA) but still treat them as
+                // having been processed (with a fake nTx value). Otherwise, we
+                // can assert that these are the same.
+                assert(pindexFirstMissing == pindexFirstNeverProcessed);
+            }
         } else {
             // If we have pruned, then we can only say that HAVE_DATA implies nTx > 0
             if (pindex->nStatus & BLOCK_HAVE_DATA) assert(pindex->nTx > 0);
@@ -4839,7 +4845,7 @@ void Chainstate::CheckBlockIndex()
         if (pindexFirstMissing == nullptr) assert(!foundInUnlinked); // We aren't missing data for any parent -- cannot be in m_blocks_unlinked.
         if (pindex->pprev && (pindex->nStatus & BLOCK_HAVE_DATA) && pindexFirstNeverProcessed == nullptr && pindexFirstMissing != nullptr) {
             // We HAVE_DATA for this block, have received data for all parents at some point, but we're currently missing data for some parent.
-            assert(m_blockman.m_have_pruned); // We must have pruned.
+            assert(m_blockman.m_have_pruned || pindexFirstAssumeValid != nullptr); // We must have pruned, or else we're using a snapshot (causing us to have faked the received data for some parent(s)).
             // This block may have entered m_blocks_unlinked if:
             //  - it has a descendant that at some point had more work than the
             //    tip, and
@@ -4849,7 +4855,12 @@ void Chainstate::CheckBlockIndex()
             // So if this block is itself better than m_chain.Tip() and it wasn't in
             // setBlockIndexCandidates, then it must be in m_blocks_unlinked.
             if (!CBlockIndexWorkComparator()(pindex, m_chain.Tip()) && setBlockIndexCandidates.count(pindex) == 0) {
-                if (pindexFirstInvalid == nullptr) {
+                if (pindexFirstInvalid == nullptr && pindexFirstAssumeValid == nullptr) {
+                    // If this is a chain based on an assumeutxo snapshot, then
+                    // this block could either be in mapBlocksUnlinked or in
+                    // setBlockIndexCandidates; it may take a call to
+                    // FindMostWorkChain() to figure out whether all the blocks
+                    // between the tip and this block are actually available.
                     assert(foundInUnlinked);
                 }
             }
@@ -4877,6 +4888,7 @@ void Chainstate::CheckBlockIndex()
             if (pindex == pindexFirstNotTransactionsValid) pindexFirstNotTransactionsValid = nullptr;
             if (pindex == pindexFirstNotChainValid) pindexFirstNotChainValid = nullptr;
             if (pindex == pindexFirstNotScriptsValid) pindexFirstNotScriptsValid = nullptr;
+            if (pindex == pindexFirstAssumeValid) pindexFirstAssumeValid = nullptr;
             // Find our parent.
             CBlockIndex* pindexPar = pindex->pprev;
             // Find which child we just visited.