RPC/Mining: Restore API compatibility for prioritisetransaction

Breaking API serves no purpose other than to be incompatible with older versions and other implementations that do support priority

(cherry picked from commit bitcoin/bitcoin@870824e919)

Zcash:
* Update the release notes.
* Update the `prioritisetransaction.py` RPC test.
* We don't have BIP 68 or replace-by-fee.

Signed-off-by: Daira Emma Hopwood <daira@jacaranda.org>

doc/release-notes.md

@@ -30,8 +30,8 @@ RPC Changes
   pool, so the impact of this change is that for such transactions, the user must specify
   `AllowFullyTransparent`.
 - The `estimatepriority` RPC call has been removed.
-- The `priority_delta` argument to the `prioritisetransaction` RPC call has been
-  removed.
+- The `priority_delta` argument to the `prioritisetransaction` RPC call now has
+  no effect and must be set to a dummy value (0 or null).
 
 Changes to Transaction Fee Selection
 ------------------------------------

qa/rpc-tests/mempool_packages.py

@@ -88,7 +88,7 @@ class MempoolPackagesTest(BitcoinTestFramework):
 
         # Check that descendant modified fees includes fee deltas from
         # prioritisetransaction
-        self.nodes[0].prioritisetransaction(chain[-1], 1000)
+        self.nodes[0].prioritisetransaction(chain[-1], 0, 1000)
         mempool = self.nodes[0].getrawmempool(True)
 
         descendant_fees = 0
@@ -104,7 +104,7 @@ class MempoolPackagesTest(BitcoinTestFramework):
 
         # Check that prioritising a tx before it's added to the mempool works
         self.nodes[0].generate(1)
-        self.nodes[0].prioritisetransaction(chain[-1], 2000)
+        self.nodes[0].prioritisetransaction(chain[-1], None, 2000)
         self.nodes[0].invalidateblock(self.nodes[0].getbestblockhash())
         mempool = self.nodes[0].getrawmempool(True)
 

qa/rpc-tests/prioritisetransaction.py

@@ -74,7 +74,7 @@ class PrioritiseTransactionTest (BitcoinTestFramework):
         print("in_block_template =", in_block_template)
         #assert_equal(in_block_template, False)
 
-        priority_success = self.nodes[0].prioritisetransaction(priority_tx_0, int(3 * base_fee * COIN))
+        priority_success = self.nodes[0].prioritisetransaction(priority_tx_0, 0, int(3 * base_fee * COIN))
         assert(priority_success)
 
         # Check that prioritised transaction is not in getblocktemplate()
@@ -113,7 +113,7 @@ class PrioritiseTransactionTest (BitcoinTestFramework):
 
         # Node 1 doesn't get the next block, so this *shouldn't* be mined despite being prioritised on node 1
         priority_tx_1 = self.nodes[1].sendtoaddress(self.nodes[0].getnewaddress(), 0.1)
-        self.nodes[1].prioritisetransaction(priority_tx_1, int(3 * base_fee * COIN))
+        self.nodes[1].prioritisetransaction(priority_tx_1, 0, int(3 * base_fee * COIN))
 
         # Mine block on node 0
         blk_hash = self.nodes[0].generate(1)

src/rpc/client.cpp

@@ -52,7 +52,7 @@ static const CRPCConvertTable rpcCvtTable =
     { "generate",                    {{o}, {}} },
     { "setgenerate",                 {{o}, {o}} },
     { "getmininginfo",               {{}, {}} },
-    { "prioritisetransaction",       {{s, o}, {}} },
+    { "prioritisetransaction",       {{s, o, o}, {}} },
     { "getblocktemplate",            {{}, {o}} },
     // NB: The second argument _should_ be an object, but upstream treats it as a string, so we
     //     preserve that here.

src/rpc/mining.cpp

@@ -375,26 +375,31 @@ UniValue getmininginfo(const UniValue& params, bool fHelp)
 // NOTE: Unlike wallet RPCs (which use ZEC values), mining RPCs follow GBT (BIP 22) in using zatoshi amounts.
 UniValue prioritisetransaction(const UniValue& params, bool fHelp)
 {
-    if (fHelp || params.size() != 2)
-        throw runtime_error(
-            "prioritisetransaction <txid> <fee delta>\n"
+    if (fHelp || params.size() != 3)
+        throw std::runtime_error(
+            "prioritisetransaction <txid> <priority delta> <fee delta>\n"
             "Accepts the transaction into mined blocks at a higher (or lower) priority\n"
             "\nArguments:\n"
             "1. \"txid\"       (string, required) The transaction id.\n"
-            "2. fee_delta      (numeric, required) The fee value (in " + MINOR_CURRENCY_UNIT + ") to add (or subtract, if negative).\n"
+            "2. priority_delta (numeric, optional) Fee-independent priority adjustment. Not supported, so must be zero or null.\n"
+            "3. fee_delta      (numeric, required) The fee value (in " + MINOR_CURRENCY_UNIT + ") to add (or subtract, if negative).\n"
             "                  The modified fee is not actually paid, only the algorithm for selecting transactions into a block\n"
             "                  considers the transaction as it would have paid a higher (or lower) fee.\n"
             "\nResult\n"
             "true              (boolean) Returns true\n"
             "\nExamples:\n"
-            + HelpExampleCli("prioritisetransaction", "\"txid\" 10000")
-            + HelpExampleRpc("prioritisetransaction", "\"txid\", 10000")
+            + HelpExampleCli("prioritisetransaction", "\"txid\" 0.0 10000")
+            + HelpExampleRpc("prioritisetransaction", "\"txid\", 0.0, 10000")
         );
 
     LOCK(cs_main);
 
     uint256 hash = ParseHashStr(params[0].get_str(), "txid");
-    CAmount nAmount = params[1].get_int64();
+    CAmount nAmount = params[2].get_int64();
+
+    if (!(params[1].isNull() || params[1].get_real() == 0)) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "Priority is not supported, and adjustment thereof must be zero.");
+    }
 
     mempool.PrioritiseTransaction(hash, params[0].get_str(), nAmount);
     return true;