kernel: remove btck_BlockTreeEntry

The previous commit introduced btck_Chain alongside btck_BlockTreeEntry
and proved the two are equivalent.
This removes the TreeEntry type
entirely so the API exposes a single block abstraction.

Removed:
  - the btck_BlockTreeEntry type and its accessors (get_previous,
    get_block_header, get_height, get_block_hash, equals, get_ancestor)
  - btck_chainstate_manager_get_best_entry and
    btck_chainstate_manager_get_block_tree_entry_by_hash
  - btck_chain_get_by_height and btck_chain_contains
  - the btck_chain_get_tip / btck_block_tree_entry_get_chain bridges
    that allowed the two APIs to interoperate during migration

This makes the final state as described in
purplekarrot.net/blog/drop-block-tree-entry-from-bitcoin-kernel.html.

Author: janb84

src/bitcoin-chainstate.cpp

@@ -110,7 +110,7 @@ class TestValidationInterface : public ValidationInterface
 class TestKernelNotifications : public KernelNotifications
 {
 public:
-    void BlockTipHandler(SynchronizationState, const BlockTreeEntry, double) override
+    void BlockTipHandler(SynchronizationState, const ChainView, double) override
     {
         std::cout << "Block tip changed" << std::endl;
     }

src/kernel/bitcoinkernel.cpp

@@ -146,12 +146,9 @@ struct Handle {
 
 } // namespace
 
-struct btck_BlockTreeEntry: Handle<btck_BlockTreeEntry, CBlockIndex> {};
 struct btck_Block : Handle<btck_Block, std::shared_ptr<const CBlock>> {};
 struct btck_BlockValidationState : Handle<btck_BlockValidationState, BlockValidationState> {};
 struct btck_TxValidationState : Handle<btck_TxValidationState, TxValidationState> {};
-// A chain is fully determined by its tip block, so it is represented by the
-// CBlockIndex of that tip - the same underlying type as a btck_BlockTreeEntry.
 struct btck_Chain : Handle<btck_Chain, CBlockIndex> {};
 
 namespace {
@@ -306,7 +303,7 @@ class KernelNotifications final : public kernel::Notifications
 
     kernel::InterruptResult blockTip(SynchronizationState state, const CBlockIndex& index, double verification_progress) override
     {
-        if (m_cbs.block_tip) m_cbs.block_tip(m_cbs.user_data, cast_state(state), btck_BlockTreeEntry::ref(&index), verification_progress);
+        if (m_cbs.block_tip) m_cbs.block_tip(m_cbs.user_data, cast_state(state), btck_Chain::ref(&index), verification_progress);
         return {};
     }
     void headerTip(SynchronizationState state, int64_t height, int64_t timestamp, bool presync) override
@@ -366,7 +363,7 @@ class KernelValidationInterface final : public CValidationInterface
         if (m_cbs.pow_valid_block) {
             m_cbs.pow_valid_block(m_cbs.user_data,
                                   btck_Block::copy(btck_Block::ref(&block)),
-                                  btck_BlockTreeEntry::ref(pindex));
+                                  btck_Chain::ref(pindex));
         }
     }
 
@@ -375,7 +372,7 @@ class KernelValidationInterface final : public CValidationInterface
         if (m_cbs.block_connected) {
             m_cbs.block_connected(m_cbs.user_data,
                                   btck_Block::copy(btck_Block::ref(&block)),
-                                  btck_BlockTreeEntry::ref(pindex));
+                                  btck_Chain::ref(pindex));
         }
     }
 
@@ -384,7 +381,7 @@ class KernelValidationInterface final : public CValidationInterface
         if (m_cbs.block_disconnected) {
             m_cbs.block_disconnected(m_cbs.user_data,
                                      btck_Block::copy(btck_Block::ref(&block)),
-                                     btck_BlockTreeEntry::ref(pindex));
+                                     btck_Chain::ref(pindex));
         }
     }
 };
@@ -897,49 +894,6 @@ void btck_context_destroy(btck_Context* context)
     delete context;
 }
 
-const btck_BlockTreeEntry* btck_block_tree_entry_get_previous(const btck_BlockTreeEntry* entry)
-{
-    if (!btck_BlockTreeEntry::get(entry).pprev) {
-        LogInfo("Genesis block has no previous.");
-        return nullptr;
-    }
-
-    return btck_BlockTreeEntry::ref(btck_BlockTreeEntry::get(entry).pprev);
-}
-
-const btck_BlockTreeEntry* btck_block_tree_entry_get_ancestor(const btck_BlockTreeEntry* block_tree_entry, int32_t height)
-{
-    const auto* ancestor{btck_BlockTreeEntry::get(block_tree_entry).GetAncestor(height)};
-    assert(ancestor);
-    return btck_BlockTreeEntry::ref(ancestor);
-}
-
-btck_BlockHeader* btck_block_tree_entry_get_block_header(const btck_BlockTreeEntry* entry)
-{
-    return btck_BlockHeader::create(btck_BlockTreeEntry::get(entry).GetBlockHeader());
-}
-
-int32_t btck_block_tree_entry_get_height(const btck_BlockTreeEntry* entry)
-{
-    return btck_BlockTreeEntry::get(entry).nHeight;
-}
-
-const btck_BlockHash* btck_block_tree_entry_get_block_hash(const btck_BlockTreeEntry* entry)
-{
-    return btck_BlockHash::ref(btck_BlockTreeEntry::get(entry).phashBlock);
-}
-
-int btck_block_tree_entry_equals(const btck_BlockTreeEntry* entry1, const btck_BlockTreeEntry* entry2)
-{
-    return &btck_BlockTreeEntry::get(entry1) == &btck_BlockTreeEntry::get(entry2);
-}
-
-const btck_Chain* btck_block_tree_entry_get_chain(const btck_BlockTreeEntry* entry)
-{
-    // A chain and a block tree entry share the same underlying CBlockIndex.
-    return btck_Chain::ref(&btck_BlockTreeEntry::get(entry));
-}
-
 btck_BlockValidationState* btck_block_validation_state_create()
 {
     return btck_BlockValidationState::create();
@@ -1101,29 +1055,12 @@ const btck_Chain* btck_chainstate_manager_find(const btck_ChainstateManager* cha
     return btck_Chain::ref(block_index);
 }
 
-const btck_BlockTreeEntry* btck_chainstate_manager_get_block_tree_entry_by_hash(const btck_ChainstateManager* chainman, const btck_BlockHash* block_hash)
-{
-    auto block_index = WITH_LOCK(btck_ChainstateManager::get(chainman).m_chainman->GetMutex(),
-                                 return btck_ChainstateManager::get(chainman).m_chainman->m_blockman.LookupBlockIndex(btck_BlockHash::get(block_hash)));
-    if (!block_index) {
-        LogDebug(BCLog::KERNEL, "A block with the given hash is not indexed.");
-        return nullptr;
-    }
-    return btck_BlockTreeEntry::ref(block_index);
-}
-
 const btck_Chain* btck_chainstate_manager_get_best_chain(const btck_ChainstateManager* chainstate_manager)
 {
     auto& chainman = *btck_ChainstateManager::get(chainstate_manager).m_chainman;
     return btck_Chain::ref(WITH_LOCK(chainman.GetMutex(), return chainman.m_best_header));
 }
 
-const btck_BlockTreeEntry* btck_chainstate_manager_get_best_entry(const btck_ChainstateManager* chainstate_manager)
-{
-    auto& chainman = *btck_ChainstateManager::get(chainstate_manager).m_chainman;
-    return btck_BlockTreeEntry::ref(WITH_LOCK(chainman.GetMutex(), return chainman.m_best_header));
-}
-
 void btck_chainstate_manager_destroy(btck_ChainstateManager* chainman)
 {
     {
@@ -1231,10 +1168,10 @@ void btck_block_destroy(btck_Block* block)
     delete block;
 }
 
-btck_Block* btck_block_read(const btck_ChainstateManager* chainman, const btck_BlockTreeEntry* entry)
+btck_Block* btck_block_read(const btck_ChainstateManager* chainman, const btck_Chain* chain)
 {
     auto block{std::make_shared<CBlock>()};
-    if (!btck_ChainstateManager::get(chainman).m_chainman->m_blockman.ReadBlock(*block, btck_BlockTreeEntry::get(entry))) {
+    if (!btck_ChainstateManager::get(chainman).m_chainman->m_blockman.ReadBlock(*block, btck_Chain::get(chain))) {
         LogError("Failed to read block.");
         return nullptr;
     }
@@ -1266,14 +1203,14 @@ void btck_block_hash_destroy(btck_BlockHash* hash)
     delete hash;
 }
 
-btck_BlockSpentOutputs* btck_block_spent_outputs_read(const btck_ChainstateManager* chainman, const btck_BlockTreeEntry* entry)
+btck_BlockSpentOutputs* btck_block_spent_outputs_read(const btck_ChainstateManager* chainman, const btck_Chain* chain)
 {
     auto block_undo{std::make_shared<CBlockUndo>()};
-    if (btck_BlockTreeEntry::get(entry).nHeight < 1) {
+    if (btck_Chain::get(chain).nHeight < 1) {
         LogDebug(BCLog::KERNEL, "The genesis block does not have any spent outputs.");
         return btck_BlockSpentOutputs::create(block_undo);
     }
-    if (!btck_ChainstateManager::get(chainman).m_chainman->m_blockman.ReadBlockUndo(*block_undo, btck_BlockTreeEntry::get(entry))) {
+    if (!btck_ChainstateManager::get(chainman).m_chainman->m_blockman.ReadBlockUndo(*block_undo, btck_Chain::get(chain))) {
         LogError("Failed to read block spent outputs data.");
         return nullptr;
     }
@@ -1385,30 +1322,9 @@ const btck_Chain* btck_chainstate_manager_get_active_chain(const btck_Chainstate
 
 int32_t btck_chain_get_height(const btck_Chain* chain)
 {
-    LOCK(::cs_main);
     return btck_Chain::get(chain).nHeight;
 }
 
-const btck_BlockTreeEntry* btck_chain_get_tip(const btck_Chain* chain)
-{
-    // A chain and a block tree entry share the same underlying CBlockIndex.
-    return btck_BlockTreeEntry::ref(&btck_Chain::get(chain));
-}
-
-const btck_BlockTreeEntry* btck_chain_get_by_height(const btck_Chain* chain, int32_t height)
-{
-    LOCK(::cs_main);
-    return btck_BlockTreeEntry::ref(btck_Chain::get(chain).GetAncestor(height));
-}
-
-int btck_chain_contains(const btck_Chain* chain, const btck_BlockTreeEntry* entry)
-{
-    LOCK(::cs_main);
-    const auto& tip{btck_Chain::get(chain)};
-    const auto& block{btck_BlockTreeEntry::get(entry)};
-    return tip.GetAncestor(block.nHeight) == &block ? 1 : 0;
-}
-
 btck_BlockHeader* btck_chain_get_block_header(const btck_Chain* chain, int32_t height)
 {
     const auto* index{btck_Chain::get(chain).GetAncestor(height)};