Merge #15655: Resolve the checkpoints <-> validation circular dependency

418d3230f8 Resolve the checkpoints <-> validation CD. (251)

Pull request description:

  This pull request attempts to resolve the `checkpoints -> validation -> checkpoints` circular dependency.

  The circular dependency is resolved by moving the `CheckPoints::GetLastCheckpoint(const CCheckpointData& data)` function to `validation.cpp` where it used exclusively by the private function `ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& state, const CChainParams& params, const CBlockIndex* pindexPrev, int64_t nAdjustedTime)`.

ACKs for commit 418d32:
  promag:
    utACK 418d323, only `GetLastCheckpoint` usage is in `validation.cpp` and so makes sense to move it there.
  practicalswift:
    utACK 418d3230f86f77dde6e817f502baff8a54b707fa
  MarcoFalke:
    utACK 418d3230f86f77dde6e817f502baff8a54b707fa
  sipa:
    utACK 418d3230f86f77dde6e817f502baff8a54b707fa

Tree-SHA512: 03c3556bc192e65f5e3fa76fd545d4ee7d63d3fb06b132f7a1fa6131aa21ddd2e5b2d19e2222dfe524f422daaca30efde219bed188db8c74ff4b088876b5bc16

8 files changed, 18 insertions, 67 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 059ed18134..4fe5898829 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -113,7 +113,6 @@ BITCOIN_CORE_H = \
   chainparams.h \
   chainparamsbase.h \
   chainparamsseeds.h \
-  checkpoints.h \
   checkqueue.h \
   clientversion.h \
   coins.h \
@@ -258,7 +257,6 @@ libbitcoin_server_a_SOURCES = \
   blockencodings.cpp \
   blockfilter.cpp \
   chain.cpp \
-  checkpoints.cpp \
   consensus/tx_verify.cpp \
   flatfile.cpp \
   httprpc.cpp \
diff --git a/src/checkpoints.cpp b/src/checkpoints.cpp
deleted file mode 100644
index ad5edfeb39..0000000000
--- a/src/checkpoints.cpp
+++ /dev/null
@@ -1,32 +0,0 @@
-// Copyright (c) 2009-2018 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#include <checkpoints.h>
-
-#include <chain.h>
-#include <chainparams.h>
-#include <reverse_iterator.h>
-#include <validation.h>
-
-#include <stdint.h>
-
-
-namespace Checkpoints {
-
-    CBlockIndex* GetLastCheckpoint(const CCheckpointData& data)
-    {
-        const MapCheckpoints& checkpoints = data.mapCheckpoints;
-
-        for (const MapCheckpoints::value_type& i : reverse_iterate(checkpoints))
-        {
-            const uint256& hash = i.second;
-            CBlockIndex* pindex = LookupBlockIndex(hash);
-            if (pindex) {
-                return pindex;
-            }
-        }
-        return nullptr;
-    }
-
-} // namespace Checkpoints
diff --git a/src/checkpoints.h b/src/checkpoints.h
deleted file mode 100644
index a25e97e469..0000000000
--- a/src/checkpoints.h
+++ /dev/null
@@ -1,27 +0,0 @@
-// Copyright (c) 2009-2018 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#ifndef BITCOIN_CHECKPOINTS_H
-#define BITCOIN_CHECKPOINTS_H
-
-#include <uint256.h>
-
-#include <map>
-
-class CBlockIndex;
-struct CCheckpointData;
-
-/**
- * Block-chain checkpoints are compiled-in sanity checks.
- * They are updated every release or three.
- */
-namespace Checkpoints
-{
-
-//! Returns last CBlockIndex* that is a checkpoint
-CBlockIndex* GetLastCheckpoint(const CCheckpointData& data);
-
-} //namespace Checkpoints
-
-#endif // BITCOIN_CHECKPOINTS_H
diff --git a/src/init.cpp b/src/init.cpp
index 70459994c7..e072b494c2 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -15,7 +15,6 @@
 #include <blockfilter.h>
 #include <chain.h>
 #include <chainparams.h>
-#include <checkpoints.h>
 #include <compat/sanity.h>
 #include <consensus/validation.h>
 #include <fs.h>
diff --git a/src/qt/clientmodel.cpp b/src/qt/clientmodel.cpp
index 27b4c182f9..88a35534c2 100644
--- a/src/qt/clientmodel.cpp
+++ b/src/qt/clientmodel.cpp
@@ -11,7 +11,6 @@
 
 #include <chain.h>
 #include <chainparams.h>
-#include <checkpoints.h>
 #include <clientversion.h>
 #include <interfaces/handler.h>
 #include <interfaces/node.h>
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index c85c2bcc92..36538832aa 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -10,7 +10,6 @@
 #include <blockfilter.h>
 #include <chain.h>
 #include <chainparams.h>
-#include <checkpoints.h>
 #include <coins.h>
 #include <consensus/validation.h>
 #include <core_io.h>
diff --git a/src/validation.cpp b/src/validation.cpp
index be6257ea28..599d6027c8 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -8,7 +8,6 @@
 #include <arith_uint256.h>
 #include <chain.h>
 #include <chainparams.h>
-#include <checkpoints.h>
 #include <checkqueue.h>
 #include <consensus/consensus.h>
 #include <consensus/merkle.h>
@@ -37,6 +36,7 @@
 #include <txdb.h>
 #include <txmempool.h>
 #include <ui_interface.h>
+#include <uint256.h>
 #include <undo.h>
 #include <util/moneystr.h>
 #include <util/rbf.h>
@@ -3188,6 +3188,22 @@ std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBloc
     return commitment;
 }
 
+//! Returns last CBlockIndex* that is a checkpoint
+static CBlockIndex* GetLastCheckpoint(const CCheckpointData& data)
+{
+    const MapCheckpoints& checkpoints = data.mapCheckpoints;
+
+    for (const MapCheckpoints::value_type& i : reverse_iterate(checkpoints))
+    {
+        const uint256& hash = i.second;
+        CBlockIndex* pindex = LookupBlockIndex(hash);
+        if (pindex) {
+            return pindex;
+        }
+    }
+    return nullptr;
+}
+
 /** Context-dependent validity checks.
  *  By "context", we mean only the previous block headers, but not the UTXO
  *  set; UTXO-related validity checks are done in ConnectBlock().
@@ -3212,7 +3228,7 @@ static bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationSta
         // Don't accept any forks from the main chain prior to last checkpoint.
         // GetLastCheckpoint finds the last checkpoint in MapCheckpoints that's in our
         // MapBlockIndex.
-        CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint(params.Checkpoints());
+        CBlockIndex* pcheckpoint = GetLastCheckpoint(params.Checkpoints());
         if (pcheckpoint && nHeight < pcheckpoint->nHeight)
             return state.DoS(100, error("%s: forked chain older than last checkpoint (height %d)", __func__, nHeight), REJECT_CHECKPOINT, "bad-fork-prior-to-checkpoint");
     }
diff --git a/test/lint/lint-circular-dependencies.sh b/test/lint/lint-circular-dependencies.sh
index 87b451dbbd..e59a5ce126 100755
--- a/test/lint/lint-circular-dependencies.sh
+++ b/test/lint/lint-circular-dependencies.sh
@@ -10,7 +10,6 @@ export LC_ALL=C
 
 EXPECTED_CIRCULAR_DEPENDENCIES=(
     "chainparamsbase -> util/system -> chainparamsbase"
-    "checkpoints -> validation -> checkpoints"
     "index/txindex -> validation -> index/txindex"
     "policy/fees -> txmempool -> policy/fees"
     "policy/policy -> policy/settings -> policy/policy"