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

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