miner: CreateNewBlock will now track fee and virtual size of selected packages

- The commit also tests this new behaviour.

Co-authored-by: willcl-ark <will@256k1.dev>

src/node/miner.cpp

@@ -421,6 +421,7 @@ void BlockAssembler::addPackageTxs(int& nPackagesSelected, int& nDescendantsUpda
         }
 
         ++nPackagesSelected;
+        pblocktemplate->vFeerateHistogram.emplace_back(packageFees, static_cast<int32_t>(packageSize));
 
         // Update transactions that depend on each of these
         nDescendantsUpdated += UpdatePackagesForAdded(mempool, ancestors, mapModifiedTx);

src/node/miner.h

@@ -10,6 +10,7 @@
 #include <policy/policy.h>
 #include <primitives/block.h>
 #include <txmempool.h>
+#include <util/feefrac.h>
 
 #include <memory>
 #include <optional>
@@ -39,6 +40,7 @@ struct CBlockTemplate
     std::vector<CAmount> vTxFees;
     std::vector<int64_t> vTxSigOpsCost;
     std::vector<unsigned char> vchCoinbaseCommitment;
+    std::vector<FeeFrac> vFeerateHistogram;
 };
 
 // Container for tracking updates to ancestor feerate as we include (parent)

src/test/miner_tests.cpp

@@ -24,6 +24,7 @@
 #include <test/util/setup_common.h>
 
 #include <memory>
+#include <vector>
 
 #include <boost/test/unit_test.hpp>
 
@@ -121,28 +122,43 @@ void MinerTestingSetup::TestPackageSelection(const CScript& scriptPubKey, const
     tx.vout[0].nValue = 5000000000LL - 1000;
     // This tx has a low fee: 1000 satoshis
     Txid hashParentTx = tx.GetHash(); // save this txid for later use
-    AddToMempool(tx_mempool, entry.Fee(1000).Time(Now<NodeSeconds>()).SpendsCoinbase(true).FromTx(tx));
+    const auto lowFeeTx{entry.Fee(1000).Time(Now<NodeSeconds>()).SpendsCoinbase(true).FromTx(tx)};
+    AddToMempool(tx_mempool, lowFeeTx);
 
     // This tx has a medium fee: 10000 satoshis
     tx.vin[0].prevout.hash = txFirst[1]->GetHash();
     tx.vout[0].nValue = 5000000000LL - 10000;
     Txid hashMediumFeeTx = tx.GetHash();
-    AddToMempool(tx_mempool, entry.Fee(10000).Time(Now<NodeSeconds>()).SpendsCoinbase(true).FromTx(tx));
+    const auto mediumFeeTx{entry.Fee(10000).Time(Now<NodeSeconds>()).SpendsCoinbase(true).FromTx(tx)};
+    AddToMempool(tx_mempool, mediumFeeTx);
 
     // This tx has a high fee, but depends on the first transaction
     tx.vin[0].prevout.hash = hashParentTx;
     tx.vout[0].nValue = 5000000000LL - 1000 - 50000; // 50k satoshi fee
     Txid hashHighFeeTx = tx.GetHash();
-    AddToMempool(tx_mempool, entry.Fee(50000).Time(Now<NodeSeconds>()).SpendsCoinbase(false).FromTx(tx));
+    const auto highFeeChildTx{entry.Fee(50000).Time(Now<NodeSeconds>()).SpendsCoinbase(false).FromTx(tx)};
+    AddToMempool(tx_mempool, highFeeChildTx);
 
     BlockAssembler::Options options;
     options.coinbase_output_script = scriptPubKey;
-    std::unique_ptr<CBlockTemplate> pblocktemplate = AssemblerForTest(tx_mempool, options).CreateNewBlock();
+    auto assembler{AssemblerForTest(tx_mempool, options)};
+    auto pblocktemplate{assembler.CreateNewBlock()};
+    const auto blockFeerateHistogram{pblocktemplate->vFeerateHistogram};
     BOOST_REQUIRE_EQUAL(pblocktemplate->block.vtx.size(), 4U);
     BOOST_CHECK(pblocktemplate->block.vtx[1]->GetHash() == hashParentTx);
     BOOST_CHECK(pblocktemplate->block.vtx[2]->GetHash() == hashHighFeeTx);
     BOOST_CHECK(pblocktemplate->block.vtx[3]->GetHash() == hashMediumFeeTx);
 
+    BOOST_CHECK(blockFeerateHistogram.size() == 2);
+    // lowFeeTx and highFeeChildTx are added to the block as a package.
+    const auto packageFee{lowFeeTx.GetFee() + highFeeChildTx.GetFee()};
+    const auto packageSize{lowFeeTx.GetTxSize() + highFeeChildTx.GetTxSize()};
+    FeeFrac packageFeeFrac{packageFee, packageSize};
+    BOOST_CHECK(blockFeerateHistogram[0] == packageFeeFrac);
+
+    FeeFrac mediumTxFeeFrac{mediumFeeTx.GetFee(), mediumFeeTx.GetTxSize()};
+    BOOST_CHECK(blockFeerateHistogram[1] == mediumTxFeeFrac);
+
     // Test that a package below the block min tx fee doesn't get included
     tx.vin[0].prevout.hash = hashHighFeeTx;
     tx.vout[0].nValue = 5000000000LL - 1000 - 50000; // 0 fee