For #3359. Return error if Sapling addresses passed to RPC z_mergetoaddress.

RPC z_mergetoaddress does not support Sapling yet but the existing error
reporting was not clear to users.

qa/rpc-tests/wallet_sapling.py

@@ -20,6 +20,7 @@ class WalletSaplingTest(BitcoinTestFramework):
         return start_nodes(4, self.options.tmpdir, [[
             '-nuparams=5ba81b19:201', # Overwinter
             '-nuparams=76b809bb:203', # Sapling
+            '-experimentalfeatures', '-zmergetoaddress',
         ]] * 4)
 
     def run_test(self):
@@ -53,6 +54,18 @@ class WalletSaplingTest(BitcoinTestFramework):
         except JSONRPCException as e:
             assert_equal("Invalid parameter, Sapling has not activated", e.error['message'])
 
+        # Verify z_mergetoaddress RPC does not support Sapling yet
+        try:
+            self.nodes[3].z_mergetoaddress([tmp_taddr], tmp_zaddr)
+            raise AssertionError("Should have thrown an exception")
+        except JSONRPCException as e:
+            assert_equal("Invalid parameter, Sapling is not supported yet by z_mergetoadress", e.error['message'])
+        try:
+            self.nodes[3].z_mergetoaddress([tmp_zaddr], tmp_taddr)
+            raise AssertionError("Should have thrown an exception")
+        except JSONRPCException as e:
+            assert_equal("Invalid parameter, Sapling is not supported yet by z_mergetoadress", e.error['message'])
+
         # Activate Sapling
         self.nodes[2].generate(2)
         self.sync_all()

src/wallet/rpcwallet.cpp

@@ -4204,6 +4204,7 @@ UniValue z_mergetoaddress(const UniValue& params, bool fHelp)
     std::set<std::string> setAddress;
 
     // Sources
+    bool containsSaplingZaddrSource = false;
     for (const UniValue& o : addresses.getValues()) {
         if (!o.isStr())
             throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, expected string");
@@ -4229,6 +4230,9 @@ UniValue z_mergetoaddress(const UniValue& params, bool fHelp)
                     if (!(useAny || useAnyNote)) {
                         zaddrs.insert(zaddr);
                     }
+                    // Check if z-addr is Sapling
+                    bool isSapling = boost::get<libzcash::SaplingPaymentAddress>(&zaddr) != nullptr;
+                    containsSaplingZaddrSource |= isSapling;
                 } else {
                     throw JSONRPCError(
                         RPC_INVALID_PARAMETER,
@@ -4245,10 +4249,19 @@ UniValue z_mergetoaddress(const UniValue& params, bool fHelp)
     // Validate the destination address
     auto destaddress = params[1].get_str();
     bool isToZaddr = false;
+    bool isToSaplingZaddr = false;
     CTxDestination taddr = DecodeDestination(destaddress);
     if (!IsValidDestination(taddr)) {
         if (IsValidPaymentAddressString(destaddress)) {
             isToZaddr = true;
+
+            // Is this a Sapling address?
+            auto res = DecodePaymentAddress(destaddress);
+            if (IsValidPaymentAddress(res)) {
+                isToSaplingZaddr = boost::get<libzcash::SaplingPaymentAddress>(&res) != nullptr;
+            } else {
+                throw JSONRPCError(RPC_INVALID_PARAMETER, string("Invalid parameter, unknown address format: ") + destaddress );
+            }
         } else {
             throw JSONRPCError(RPC_INVALID_PARAMETER, string("Invalid parameter, unknown address format: ") + destaddress );
         }
@@ -4302,6 +4315,19 @@ UniValue z_mergetoaddress(const UniValue& params, bool fHelp)
         max_tx_size = MAX_TX_SIZE_BEFORE_SAPLING;
     }
 
+    // This RPC does not support Sapling yet.
+    if (isToSaplingZaddr || containsSaplingZaddrSource) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, Sapling is not supported yet by z_mergetoadress");
+    }
+
+    // If this RPC does support Sapling...
+    // If Sapling is not active, do not allow sending from or sending to Sapling addresses.
+    if (!NetworkUpgradeActive(nextBlockHeight, Params().GetConsensus(), Consensus::UPGRADE_SAPLING)) {
+        if (isToSaplingZaddr || containsSaplingZaddrSource) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, Sapling has not activated");
+        }
+    }
+
     // Prepare to get UTXOs and notes
     std::vector<MergeToAddressInputUTXO> utxoInputs;
     std::vector<MergeToAddressInputNote> noteInputs;