Merge bitcoin/bitcoin#23174: validation: have LoadBlockIndex account for snapshot use

2283b9cd1ee0fbd1e8ebc61673b1fe7596199a24 test: add tests for LoadBlockIndex when using multiple chainstates (James O'Beirne)
0fd599a51a700c028d6f7ed8067d2d9f6e6a04a5 validation: have LoadBlockIndex account for snapshot use (James O'Beirne)
d0c6e61f5dd3b6af818459d9d03b7ba316c5a3f7 validation: don't modify genesis during snapshot load (James O'Beirne)

Pull request description:

  This is part of the [assumeutxo project](https://github.com/bitcoin/bitcoin/projects/11) (parent PR: #15606)

  ---

  Currently, `BlockManager::LoadBlockIndex` adds all blocks that have downloaded transactions to the active chain state's `setBlockIndexCandidates` set, ignoring the background chain state.

  This PR changes ChainstateManager::LoadBlockIndex to update `setBlockIndexCandidates` in the background chain, not just the active chain. In the active chain, the same blocks are added as before. In the background chain, only blocks that have actually been validated, not blocks marked assumed-valid are added so the background chain will continue to download and validate assumed-valid blocks.

ACKs for top commit:
  MarcoFalke:
    Concept ACK 2283b9cd1ee0fbd1e8ebc61673b1fe7596199a24 🤽
  Sjors:
    utACK 2283b9cd1ee0fbd1e8ebc61673b1fe7596199a24

Tree-SHA512: 7c9a80802df4722d85d12b78d2e7f628ac5f11cb8be66913d5c3230339bd1220c6723805509d4460826a17d1dc04b0ae172eb7d09ac0ea5dc5e41d77975cbd5e

1 files changed, 6 insertions, 6 deletions

diff --git a/src/validation.h b/src/validation.h
index 7457ca5239..534df9bc87 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -433,20 +433,16 @@ public:
 
     std::unique_ptr<CBlockTreeDB> m_block_tree_db GUARDED_BY(::cs_main);
 
-    bool LoadBlockIndexDB(std::set<CBlockIndex*, CBlockIndexWorkComparator>& setBlockIndexCandidates) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+    bool LoadBlockIndexDB(ChainstateManager& chainman) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     /**
      * Load the blocktree off disk and into memory. Populate certain metadata
      * per index entry (nStatus, nChainWork, nTimeMax, etc.) as well as peripheral
      * collections like setDirtyBlockIndex.
-     *
-     * @param[out] block_index_candidates  Fill this set with any valid blocks for
-     *                                     which we've downloaded all transactions.
      */
     bool LoadBlockIndex(
         const Consensus::Params& consensus_params,
-        std::set<CBlockIndex*, CBlockIndexWorkComparator>& block_index_candidates)
-        EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+        ChainstateManager& chainman) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
     /** Clear all data members. */
     void Unload() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
@@ -626,6 +622,10 @@ public:
      */
     const std::optional<uint256> m_from_snapshot_blockhash;
 
+    //! Return true if this chainstate relies on blocks that are assumed-valid. In
+    //! practice this means it was created based on a UTXO snapshot.
+    bool reliesOnAssumedValid() { return m_from_snapshot_blockhash.has_value(); }
+
     /**
      * The set of all CBlockIndex entries with either BLOCK_VALID_TRANSACTIONS (for
      * itself and all ancestors) *or* BLOCK_ASSUMED_VALID (if using background