Add feature flagging infrastructure to consensus parameters.

src/chainparams.cpp

@@ -134,7 +134,10 @@ public:
         consensus.vUpgrades[Consensus::UPGRADE_CANOPY].hashActivationBlock =
             uint256S("00000000002038016f976744c369dce7419fca30e7171dfac703af5e5f7ad1d4");
         consensus.vUpgrades[Consensus::UPGRADE_NU5].nProtocolVersion = 170015;
-        consensus.vUpgrades[Consensus::UPGRADE_NU5].nActivationHeight = 
+        consensus.vUpgrades[Consensus::UPGRADE_NU5].nActivationHeight =
+            Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
+        consensus.vUpgrades[Consensus::UPGRADE_ZFUTURE].nProtocolVersion = 0x7FFFFFFF;
+        consensus.vUpgrades[Consensus::UPGRADE_ZFUTURE].nActivationHeight =
             Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
 
         consensus.nFundingPeriodLength = consensus.nPostBlossomSubsidyHalvingInterval / 48;
@@ -359,7 +362,8 @@ public:
 //            "t3fmYHU2DnVaQgPhDs6TMFVmyC3qbWEWgXN", /* main-index: 52*/
 //            "t3T4WmAp6nrLkJ24iPpGeCe1fSWTPv47ASG", /* main-index: 53*/
 //            "t3fP6GrDM4QVwdjFhmCxGNbe7jXXXSDQ5dv", /* main-index: 54*/
-};
+        };
+
         assert(vFoundersRewardAddress.size() <= consensus.GetLastFoundersRewardBlockHeight(0));
     }
 };
@@ -421,7 +425,10 @@ public:
         consensus.vUpgrades[Consensus::UPGRADE_CANOPY].hashActivationBlock =
             uint256S("01a4d7c6aada30c87762c1bf33fff5df7266b1fd7616bfdb5227fa59bd79e7a2");
         consensus.vUpgrades[Consensus::UPGRADE_NU5].nProtocolVersion = 170014;
-        consensus.vUpgrades[Consensus::UPGRADE_NU5].nActivationHeight = 
+        consensus.vUpgrades[Consensus::UPGRADE_NU5].nActivationHeight =
+            Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
+        consensus.vUpgrades[Consensus::UPGRADE_ZFUTURE].nProtocolVersion = 0x7FFFFFFF;
+        consensus.vUpgrades[Consensus::UPGRADE_ZFUTURE].nActivationHeight =
             Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
 
         consensus.nFundingPeriodLength = consensus.nPostBlossomSubsidyHalvingInterval / 48;
@@ -665,9 +672,12 @@ public:
         consensus.vUpgrades[Consensus::UPGRADE_CANOPY].nActivationHeight =
             Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
         consensus.vUpgrades[Consensus::UPGRADE_NU5].nProtocolVersion = 170014;
-        consensus.vUpgrades[Consensus::UPGRADE_NU5].nActivationHeight = 
+        consensus.vUpgrades[Consensus::UPGRADE_NU5].nActivationHeight =
             Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
-            
+        consensus.vUpgrades[Consensus::UPGRADE_ZFUTURE].nProtocolVersion = 0x7FFFFFFF;
+        consensus.vUpgrades[Consensus::UPGRADE_ZFUTURE].nActivationHeight =
+            Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
+
         consensus.nFundingPeriodLength = consensus.nPostBlossomSubsidyHalvingInterval / 48;
         // Defined funding streams can be enabled with node config flags.
 

src/consensus/params.cpp

@@ -8,12 +8,21 @@
 #include <key_io.h>
 #include <script/standard.h>
 #include "upgrades.h"
+#include "util.h"
 
 namespace Consensus {
     bool Params::NetworkUpgradeActive(int nHeight, Consensus::UpgradeIndex idx) const {
         return NetworkUpgradeState(nHeight, *this, idx) == UPGRADE_ACTIVE;
     }
 
+    bool Params::FeatureRequired(const Consensus::ConsensusFeature feature) const {
+        return vRequiredFeatures.count(feature) > 0;
+    }
+
+    bool Params::FeatureActive(const int nHeight, const Consensus::ConsensusFeature feature) const {
+        return Features.FeatureActive(*this, nHeight, feature);
+    }
+
     bool Params::FutureTimestampSoftForkActive(int nHeight) const {
         return nHeight >= nFutureTimestampSoftForkHeight;
     }

src/consensus/params.h

@@ -14,7 +14,6 @@
 #include <optional>
 #include <variant>
 
-
 namespace Consensus {
 
 // Early declaration to ensure it is accessible.
@@ -38,6 +37,7 @@ enum UpgradeIndex : uint32_t {
     UPGRADE_HEARTWOOD,
     UPGRADE_CANOPY,
     UPGRADE_NU5,
+    UPGRADE_ZFUTURE,
     // NOTE: Also add new upgrades to NetworkUpgradeInfo in upgrades.cpp
     MAX_NETWORK_UPGRADES
 };
@@ -141,6 +141,63 @@ public:
     FundingStreamAddress RecipientAddress(const Params& params, int nHeight) const;
 };
 
+enum ConsensusFeature : uint32_t {
+    // Index value for the maximum consensus feature ID.
+    MAX_FEATURES
+};
+const auto FIRST_CONSENSUS_FEATURE = MAX_FEATURES;
+
+template <class Feature>
+struct FeatureInfo {
+    std::vector<Feature> dependsOn;
+    UpgradeIndex activation;
+};
+
+template <class Feature, class Params>
+class FeatureSet {
+private:
+    std::vector<FeatureInfo<Feature>> features;
+public:
+    FeatureSet(std::vector<FeatureInfo<Feature>> features): features(features) {
+    }
+
+    bool FeatureActive(
+            const Params& params,
+            const int nHeight,
+            const Feature feature) const {
+        assert(feature < features.size());
+
+        // The feature must be explicitly required by a CLI argument or by
+        // the feature being universally available above a network upgrade
+        // activation height.
+        if (params.NetworkUpgradeActive(nHeight, features[feature].activation) ||
+                params.FeatureRequired(feature)) {
+            // Transitively check that if a feature is active, all of the other features
+            // that it depends on are also active.
+            auto requires = features[feature].dependsOn;
+            assert(std::all_of(
+                requires.begin(),
+                requires.end(),
+                [&](Feature feat) {
+                    return FeatureActive(params, nHeight, feat);
+                }
+            ));
+
+            return true;
+        } else {
+            return false;
+        }
+    }
+};
+
+/**
+ * Features encodes a directed acyclic graph of feature dependencies
+ * as an array indexed by feature ID. Values are FeatureInfo objects
+ * containing the list of feature IDs upon which the index's feature ID
+ * depends.
+ */
+const FeatureSet<ConsensusFeature, Params> Features({});
+
 /** ZIP208 block target interval in seconds. */
 static const unsigned int PRE_BLOSSOM_POW_TARGET_SPACING = 150;
 static const unsigned int POST_BLOSSOM_POW_TARGET_SPACING = 75;
@@ -169,6 +226,10 @@ struct Params {
 
     bool FutureTimestampSoftForkActive(int nHeight) const;
 
+    bool FeatureActive(int nHeight, Consensus::ConsensusFeature feature) const;
+
+    bool FeatureRequired(Consensus::ConsensusFeature feature) const;
+
     uint256 hashGenesisBlock;
 
     bool fCoinbaseMustBeShielded = false;
@@ -220,6 +281,13 @@ struct Params {
         int endHeight,
         const std::vector<std::string>& addresses);
 
+    /**
+     * A set of features that have been explicitly force-enabled
+     * via the CLI, overriding block-height based decisions for
+     * this feature.
+     */
+    std::set<ConsensusFeature> vRequiredFeatures;
+
     /**
      * Default block height at which the future timestamp soft fork rule activates.
      *
@@ -279,7 +347,6 @@ struct Params {
 
     uint256 nMinimumChainWork;
 };
-
 } // namespace Consensus
 
 #endif // BITCOIN_CONSENSUS_PARAMS_H

src/consensus/upgrades.cpp

@@ -10,44 +10,49 @@
  */
 const struct NUInfo NetworkUpgradeInfo[Consensus::MAX_NETWORK_UPGRADES] = {
     {
-        /*.nBranchId =*/ 0,
-        /*.strName =*/ "Sprout",
-        /*.strInfo =*/ "The Zcash network at launch",
+        .nBranchId = 0,
+        .strName = "Sprout",
+        .strInfo = "The Zcash network at launch",
     },
     {
-        /*.nBranchId =*/ 0x74736554,
-        /*.strName =*/ "Test dummy",
-        /*.strInfo =*/ "Test dummy info",
+        .nBranchId = 0x74736554,
+        .strName = "Test dummy",
+        .strInfo = "Test dummy info",
     },
     {
-        /*.nBranchId =*/ 0x5ba81b19,
-        /*.strName =*/ "Overwinter",
-        /*.strInfo =*/ "See https://z.cash/upgrade/overwinter/ for details.",
+        .nBranchId = 0x5ba81b19,
+        .strName = "Overwinter",
+        .strInfo = "See https://z.cash/upgrade/overwinter/ for details.",
     },
     {
-        /*.nBranchId =*/ 0x76b809bb,
-        /*.strName =*/ "Sapling",
-        /*.strInfo =*/ "See https://z.cash/upgrade/sapling/ for details.",
+        .nBranchId = 0x76b809bb,
+        .strName = "Sapling",
+        .strInfo = "See https://z.cash/upgrade/sapling/ for details.",
     },
     {
-        /*.nBranchId =*/ 0x2bb40e60,
-        /*.strName =*/ "Blossom",
-        /*.strInfo =*/ "See https://z.cash/upgrade/blossom/ for details.",
+        .nBranchId = 0x2bb40e60,
+        .strName = "Blossom",
+        .strInfo = "See https://z.cash/upgrade/blossom/ for details.",
     },
     {
-        /*.nBranchId =*/ 0xf5b9230b,
-        /*.strName =*/ "Heartwood",
-        /*.strInfo =*/ "See https://z.cash/upgrade/heartwood/ for details.",
+        .nBranchId = 0xf5b9230b,
+        .strName = "Heartwood",
+        .strInfo = "See https://z.cash/upgrade/heartwood/ for details.",
     },
     {
-        /*.nBranchId =*/ 0xe9ff75a6,
-        /*.strName =*/ "Canopy",
-        /*.strInfo =*/ "See https://z.cash/upgrade/canopy/ for details.",
+        .nBranchId = 0xe9ff75a6,
+        .strName = "Canopy",
+        .strInfo = "See https://z.cash/upgrade/canopy/ for details.",
     },
     {
-        /*.nBranchId =*/ 0xf919a198,
-        /*.strName =*/ "NU5",
-        /*.strInfo =*/ "See https://z.cash/upgrade/nu5/ for details.",
+        .nBranchId = 0xf919a198,
+        .strName = "NU5",
+        .strInfo = "See https://z.cash/upgrade/nu5/ for details.",
+    },
+    {
+        .nBranchId = 0xffffffff,
+        .strName = "ZFUTURE",
+        .strInfo = "Future network upgrade (integration testing only)",
     }
 };