consensus: enable BIP94 on regtest

Author: Sjors

doc/release-notes-30647.md

@@ -0,0 +1,4 @@
+Tests
+-----
+
+- The BIP94 timewarp attack mitigation is now active on the `regtest` network

src/consensus/params.h

@@ -108,6 +108,10 @@ struct Params {
     /** Proof of work parameters */
     uint256 powLimit;
     bool fPowAllowMinDifficultyBlocks;
+    /**
+      * Enfore BIP94 timewarp attack mitigation. On testnet4 this also enforces
+      * the block storm mitigation.
+      */
     bool enforce_BIP94;
     bool fPowNoRetargeting;
     int64_t nPowTargetSpacing;

src/kernel/chainparams.cpp

@@ -540,7 +540,7 @@ class CRegTestParams : public CChainParams
         consensus.nPowTargetTimespan = 24 * 60 * 60; // one day
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = true;
-        consensus.enforce_BIP94 = false;
+        consensus.enforce_BIP94 = true;
         consensus.fPowNoRetargeting = true;
         consensus.nRuleChangeActivationThreshold = 108; // 75% for testchains
         consensus.nMinerConfirmationWindow = 144; // Faster than normal for regtest (144 instead of 2016)

src/validation.cpp

@@ -4189,7 +4189,7 @@ static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidatio
     if (block.GetBlockTime() <= pindexPrev->GetMedianTimePast())
         return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, "time-too-old", "block's timestamp is too early");
 
-    // Testnet4 only: Check timestamp against prev for difficulty-adjustment
+    // Testnet4 and regtest only: Check timestamp against prev for difficulty-adjustment
     // blocks to prevent timewarp attacks (see https://github.com/bitcoin/bitcoin/pull/15482).
     if (consensusParams.enforce_BIP94) {
         // Check timestamp for the first block of each difficulty adjustment