test: add reset_chainstate parameter for snapshot unittests

Summary:
> validation: add ResetChainstates()
>
> Necessary for the following test commit.
bitcoin/bitcoin@00b357c

> test: add reset_chainstate parameter for snapshot unittests
>
> This CreateAndActivateUTXOSnapshot parameter is necessary once we
> perform snapshot completion within ABC, since the existing UpdateTip
> test will fail because the IBD chain that has generated the snapshot
> will exceed the base of the snapshot.
>
> Being able to test snapshots being loaded into a mostly-uninitialized
> datadir allows for more realistic unittest scenarios.
bitcoin/bitcoin@3c36139

Backport note: this process of resetting the chainstate without also resetting the block index would cause `CheckBlockIndex` to fail on `assert(setBlockIndexCandidates.count(pindex)));` after D4717 made `CheckBlockIndex` run on intermediate steps in `ActiveBestChain`. I disabled `CheckBlockIndex` until after the snapshot chain is activated.

This is a partial backport of [[bitcoin/bitcoin#25667 | core#25667]]
Depends on D14652

Test Plan: `ninja all check-all`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14653

src/test/util/chainstate.h

@@ -6,10 +6,12 @@
 #define BITCOIN_TEST_UTIL_CHAINSTATE_H
 
 #include <clientversion.h>
+#include <config.h>
 #include <fs.h>
 #include <node/context.h>
 #include <node/utxo_snapshot.h>
 #include <rpc/blockchain.h>
+#include <test/util/setup_common.h>
 #include <validation.h>
 
 #include <univalue.h>
@@ -18,11 +20,24 @@
 
 const auto NoMalleation = [](AutoFile &file, node::SnapshotMetadata &meta) {};
 
+/**
+ * Create and activate a UTXO snapshot, optionally providing a function to
+ * malleate the snapshot.
+ *
+ * If `reset_chainstate` is true, reset the original chainstate back to the
+ * genesis block. This allows us to simulate more realistic conditions in which
+ * a snapshot is loaded into an otherwise mostly-uninitialized datadir. It also
+ * allows us to test conditions that would otherwise cause shutdowns based on
+ * the IBD chainstate going past the snapshot it generated.
+ */
 template <typename F = decltype(NoMalleation)>
-static bool CreateAndActivateUTXOSnapshot(node::NodeContext &node,
-                                          const fs::path root,
+static bool CreateAndActivateUTXOSnapshot(TestingSetup *fixture,
                                           F malleation = NoMalleation,
+                                          bool reset_chainstate = false,
                                           bool in_memory_chainstate = false) {
+    node::NodeContext &node = fixture->m_node;
+    fs::path root = fixture->m_path_root;
+
     // Write out a snapshot to the test's tempdir.
     //
     int height;
@@ -46,8 +61,60 @@ static bool CreateAndActivateUTXOSnapshot(node::NodeContext &node,
 
     malleation(auto_infile, metadata);
 
-    return node.chainman->ActivateSnapshot(auto_infile, metadata,
-                                           in_memory_chainstate);
+    if (reset_chainstate) {
+        // Disable CheckBlockIndex until we are finished resetting the
+        // chainstate. It is enabled again and CheckBlockIndex is
+        // called manually after the snapshot is activated.
+        // This is necessary for Bitcoin ABC because, as of D4717,
+        // CheckBlockIndex is called more aggressively in ActivateBestChain and
+        // would not support resetting the chainstate while preserving the
+        // block index.
+        bool prev_check_block_index = fCheckBlockIndex;
+        fCheckBlockIndex = false;
+
+        {
+            // What follows is code to selectively reset chainstate data without
+            // disturbing the existing BlockManager instance, which is needed to
+            // recognize the headers chain previously generated by the
+            // chainstate we're removing. Without those headers, we can't
+            // activate the snapshot below.
+            //
+            // This is a stripped-down version of node::LoadChainstate which
+            // preserves the block index.
+            LOCK(::cs_main);
+            BlockHash gen_hash{
+                node.chainman->ActiveChainstate().m_chain[0]->GetBlockHash()};
+            node.chainman->ResetChainstates();
+            node.chainman->InitializeChainstate(node.mempool.get());
+            Chainstate &chain = node.chainman->ActiveChainstate();
+            Assert(chain.LoadGenesisBlock());
+            // These cache values will be corrected shortly in
+            // `MaybeRebalanceCaches`.
+            chain.InitCoinsDB(1 << 20, true, false, "");
+            chain.InitCoinsCache(1 << 20);
+            chain.CoinsTip().SetBestBlock(gen_hash);
+            chain.setBlockIndexCandidates.insert(
+                node.chainman->m_blockman.LookupBlockIndex(gen_hash));
+            chain.LoadChainTip();
+            node.chainman->MaybeRebalanceCaches();
+        }
+        BlockValidationState state;
+        if (!node.chainman->ActiveChainstate().ActivateBestChain(::GetConfig(),
+                                                                 state)) {
+            throw std::runtime_error(
+                strprintf("ActivateBestChain failed. (%s)", state.ToString()));
+        }
+        fCheckBlockIndex = prev_check_block_index;
+        Assert(0 == WITH_LOCK(node.chainman->GetMutex(),
+                              return node.chainman->ActiveHeight()));
+    }
+
+    bool ret = node.chainman->ActivateSnapshot(auto_infile, metadata,
+                                               in_memory_chainstate);
+    if (fCheckBlockIndex) {
+        node.chainman->ActiveChainstate().CheckBlockIndex();
+    }
+    return ret;
 }
 
 #endif // BITCOIN_TEST_UTIL_CHAINSTATE_H

src/test/validation_chainstate_tests.cpp

@@ -93,7 +93,8 @@ BOOST_FIXTURE_TEST_CASE(chainstate_update_tip, TestChain100Setup) {
     // After adding some blocks to the tip, best block should have changed.
     BOOST_CHECK(::g_best_block != curr_tip);
 
-    BOOST_REQUIRE(CreateAndActivateUTXOSnapshot(m_node, m_path_root));
+    BOOST_REQUIRE(CreateAndActivateUTXOSnapshot(this, NoMalleation,
+                                                /*reset_chainstate=*/true));
 
     // Ensure our active chain is the snapshot chainstate.
     BOOST_CHECK(WITH_LOCK(::cs_main, return chainman.IsSnapshotActive()));

src/test/validation_chainstatemanager_tests.cpp

@@ -200,7 +200,7 @@ struct SnapshotTestSetup : TestChain100Setup {
         Chainstate &validation_chainstate = chainman.ActiveChainstate();
 
         // Snapshot should refuse to load at this height.
-        BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(m_node, m_path_root));
+        BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(this));
         BOOST_CHECK(!chainman.ActiveChainstate().m_from_snapshot_blockhash);
         BOOST_CHECK(!chainman.SnapshotBlockhash());
 
@@ -213,8 +213,7 @@ struct SnapshotTestSetup : TestChain100Setup {
 
         // Should not load malleated snapshots
         BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(
-            m_node, m_path_root,
-            [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
+            this, [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
                 // A UTXO is missing but count is correct
                 metadata.m_coins_count -= 1;
 
@@ -225,31 +224,27 @@ struct SnapshotTestSetup : TestChain100Setup {
                 auto_infile >> coin;
             }));
         BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(
-            m_node, m_path_root,
-            [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
+            this, [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
                 // Coins count is larger than coins in file
                 metadata.m_coins_count += 1;
             }));
         BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(
-            m_node, m_path_root,
-            [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
+            this, [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
                 // Coins count is smaller than coins in file
                 metadata.m_coins_count -= 1;
             }));
         BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(
-            m_node, m_path_root,
-            [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
+            this, [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
                 // Wrong hash
                 metadata.m_base_blockhash = BlockHash{uint256::ZERO};
             }));
         BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(
-            m_node, m_path_root,
-            [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
+            this, [](AutoFile &auto_infile, SnapshotMetadata &metadata) {
                 // Wrong hash
                 metadata.m_base_blockhash = BlockHash{uint256::ONE};
             }));
 
-        BOOST_REQUIRE(CreateAndActivateUTXOSnapshot(m_node, m_path_root));
+        BOOST_REQUIRE(CreateAndActivateUTXOSnapshot(this));
 
         // Ensure our active chain is the snapshot chainstate.
         BOOST_CHECK(
@@ -348,7 +343,7 @@ struct SnapshotTestSetup : TestChain100Setup {
         }
 
         // Snapshot should refuse to load after one has already loaded.
-        BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(m_node, m_path_root));
+        BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(this));
 
         // Snapshot blockhash should be unchanged.
         BOOST_CHECK_EQUAL(

src/validation.cpp

@@ -6162,6 +6162,12 @@ void ChainstateManager::MaybeRebalanceCaches() {
     }
 }
 
+void ChainstateManager::ResetChainstates() {
+    m_ibd_chainstate.reset();
+    m_snapshot_chainstate.reset();
+    m_active_chainstate = nullptr;
+}
+
 bool ChainstateManager::DetectSnapshotChainstate(CTxMemPool *mempool) {
     assert(!m_snapshot_chainstate);
     std::optional<fs::path> path = node::FindSnapshotChainstateDir();

src/validation.h

@@ -1319,6 +1319,8 @@ class ChainstateManager {
     bool DetectSnapshotChainstate(CTxMemPool *mempool)
         EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
+    void ResetChainstates() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+
     //! Switch the active chainstate to one based on a UTXO snapshot that was
     //! loaded previously.
     Chainstate &ActivateExistingSnapshot(CTxMemPool *mempool,