Merge bitcoin/bitcoin#24421: miner: always assume we can build witness blocks

40e871d9b4 [miner] always assume we can create witness blocks (glozow)

Pull request description:

  Given the low possibility of a reorg reverting the segwit soft fork, there is no longer a need to check whether segwit is active to see if it's okay to add to the block template (see also #23512, #21009, etc). `TestBlockValidity()` is also run on the block template at the end of `CreateNewBlock()`, so any invalid block would be caught there.

ACKs for top commit:
  gruve-p:
    ACK 40e871d9b4
  jnewbery:
    utACK 40e871d9b4, although I disagree about changing the test for segwit transaction in mempool before activagtion, instead of just removing it: https://github.com/bitcoin/bitcoin/pull/24421#discussion_r822933721.
  achow101:
    ACK 40e871d9b4
  theStack:
    Code-review ACK 40e871d9b4

Tree-SHA512: bf4860bf2bed8339622d05228d11d60286edb0c32a9a3c434b8d154913c07ea56e50649f4af7009c2a1c6a58a81d2299ab43b41a6f16dee7d08cc89cc1603019

src/node/miner.cpp

@@ -97,7 +97,6 @@ void BlockAssembler::resetBlock()
     // Reserve space for coinbase tx
     nBlockWeight = 4000;
     nBlockSigOpsCost = 400;
-    fIncludeWitness = false;
 
     // These counters do not include coinbase tx
     nBlockTx = 0;
@@ -137,17 +136,6 @@ std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& sc
     pblock->nTime = GetAdjustedTime();
     m_lock_time_cutoff = pindexPrev->GetMedianTimePast();
 
-    // Decide whether to include witness transactions
-    // This is only needed in case the witness softfork activation is reverted
-    // (which would require a very deep reorganization).
-    // Note that the mempool would accept transactions with witness data before
-    // the deployment is active, but we would only ever mine blocks after activation
-    // unless there is a massive block reorganization with the witness softfork
-    // not activated.
-    // TODO: replace this with a call to main to assess validity of a mempool
-    // transaction (which in most cases can be a no-op).
-    fIncludeWitness = DeploymentActiveAfter(pindexPrev, chainparams.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT);
-
     int nPackagesSelected = 0;
     int nDescendantsUpdated = 0;
     addPackageTxs(nPackagesSelected, nDescendantsUpdated);
@@ -215,17 +203,12 @@ bool BlockAssembler::TestPackage(uint64_t packageSize, int64_t packageSigOpsCost
 
 // Perform transaction-level checks before adding to block:
 // - transaction finality (locktime)
-// - premature witness (in case segwit transactions are added to mempool before
-//   segwit activation)
 bool BlockAssembler::TestPackageTransactions(const CTxMemPool::setEntries& package) const
 {
     for (CTxMemPool::txiter it : package) {
         if (!IsFinalTx(it->GetTx(), nHeight, m_lock_time_cutoff)) {
             return false;
         }
-        if (!fIncludeWitness && it->GetTx().HasWitness()) {
-            return false;
-        }
     }
     return true;
 }

src/node/miner.h

@@ -132,7 +132,6 @@ private:
     std::unique_ptr<CBlockTemplate> pblocktemplate;
 
     // Configuration parameters for the block size
-    bool fIncludeWitness;
     unsigned int nBlockMaxWeight;
     CFeeRate blockMinFeeRate;