Add method for fetching the next activation height after a given block height

src/consensus/upgrades.cpp

@@ -102,3 +102,21 @@ bool IsActivationHeightForAnyUpgrade(
 
     return false;
 }
+
+boost::optional<int> NextActivationHeight(
+    int nHeight,
+    const Consensus::Params& params)
+{
+    if (nHeight < 0) {
+        return boost::none;
+    }
+
+    // Don't count Sprout as an activation height
+    for (auto idx = Consensus::BASE_SPROUT + 1; idx < Consensus::MAX_NETWORK_UPGRADES; idx++) {
+        if (NetworkUpgradeState(nHeight, params, Consensus::UpgradeIndex(idx)) == UPGRADE_PENDING) {
+            return params.vUpgrades[idx].nActivationHeight;
+        }
+    }
+
+    return boost::none;
+}

src/consensus/upgrades.h

@@ -7,6 +7,8 @@
 
 #include "consensus/params.h"
 
+#include <boost/optional.hpp>
+
 enum UpgradeState {
     UPGRADE_DISABLED,
     UPGRADE_PENDING,
@@ -74,4 +76,12 @@ bool IsActivationHeightForAnyUpgrade(
     int nHeight,
     const Consensus::Params& params);
 
+/**
+ * Returns the activation height for the next upgrade after the given block height,
+ * or boost::none if there are no more known upgrades.
+ */
+boost::optional<int> NextActivationHeight(
+    int nHeight,
+    const Consensus::Params& params);
+
 #endif // ZCASH_CONSENSUS_UPGRADES_H