Separate NULLDUMMY enforcement from SEGWIT enforcement

This is in preparation for enforcing SCRIPT_VERIFY_WITNESS from
the genesis block.

Author: sdaftuar

src/validation.cpp

@@ -1760,6 +1760,9 @@ static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consens
     // Start enforcing WITNESS rules using versionbits logic.
     if (IsWitnessEnabled(pindex->pprev, consensusparams)) {
         flags |= SCRIPT_VERIFY_WITNESS;
+    }
+
+    if (IsNullDummyEnabled(pindex->pprev, consensusparams)) {
         flags |= SCRIPT_VERIFY_NULLDUMMY;
     }
 
@@ -3106,6 +3109,12 @@ bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& pa
     return (VersionBitsState(pindexPrev, params, Consensus::DEPLOYMENT_SEGWIT, versionbitscache) == ThresholdState::ACTIVE);
 }
 
+bool IsNullDummyEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params)
+{
+    LOCK(cs_main);
+    return (VersionBitsState(pindexPrev, params, Consensus::DEPLOYMENT_SEGWIT, versionbitscache) == ThresholdState::ACTIVE);
+}
+
 // Compute at which vout of the block's coinbase transaction the witness
 // commitment occurs, or -1 if not found.
 static int GetWitnessCommitmentIndex(const CBlock& block)

src/validation.h

@@ -411,6 +411,9 @@ bool TestBlockValidity(CValidationState& state, const CChainParams& chainparams,
 /** Check whether witness commitments are required for block. */
 bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params);
 
+/** Check whether NULLDUMMY (BIP 147) has activated. */
+bool IsNullDummyEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params);
+
 /** When there are blocks in the active chain with missing data, rewind the chainstate and remove them from the block index */
 bool RewindBlockIndex(const CChainParams& params);