rpc: have mintime account for timewarp rule

Previously in getblocktemplate only curtime took the timewarp rule into account.

Mining pool software could use either, though in general it should use curtime.

src/rpc/mining.cpp

@@ -49,6 +49,7 @@
 using interfaces::BlockTemplate;
 using interfaces::Mining;
 using node::BlockAssembler;
+using node::GetMinimumTime;
 using node::NodeContext;
 using node::RegenerateCommitments;
 using node::UpdateTime;
@@ -674,7 +675,7 @@ static RPCHelpMan getblocktemplate()
                 {RPCResult::Type::NUM, "coinbasevalue", "maximum allowable input to coinbase transaction, including the generation award and transaction fees (in satoshis)"},
                 {RPCResult::Type::STR, "longpollid", "an id to include with a request to longpoll on an update to this template"},
                 {RPCResult::Type::STR, "target", "The hash target"},
-                {RPCResult::Type::NUM_TIME, "mintime", "The minimum timestamp appropriate for the next block time, expressed in " + UNIX_EPOCH_TIME},
+                {RPCResult::Type::NUM_TIME, "mintime", "The minimum timestamp appropriate for the next block time, expressed in " + UNIX_EPOCH_TIME + ". Adjusted for the proposed BIP94 timewarp rule."},
                 {RPCResult::Type::ARR, "mutable", "list of ways the block template may be changed",
                 {
                     {RPCResult::Type::STR, "value", "A way the block template may be changed, e.g. 'time', 'transactions', 'prevblock'"},
@@ -977,7 +978,7 @@ static RPCHelpMan getblocktemplate()
     result.pushKV("coinbasevalue", (int64_t)block.vtx[0]->vout[0].nValue);
     result.pushKV("longpollid", tip.GetHex() + ToString(nTransactionsUpdatedLast));
     result.pushKV("target", hashTarget.GetHex());
-    result.pushKV("mintime", (int64_t)pindexPrev->GetMedianTimePast()+1);
+    result.pushKV("mintime", GetMinimumTime(pindexPrev, consensusParams.DifficultyAdjustmentInterval()));
     result.pushKV("mutable", std::move(aMutable));
     result.pushKV("noncerange", "00000000ffffffff");
     int64_t nSigOpLimit = MAX_BLOCK_SIGOPS_COST;

test/functional/mining_basic.py

@@ -153,6 +153,8 @@ def test_timewarp(self):
         # The template will have an adjusted timestamp, which we then modify
         tmpl = node.getblocktemplate(NORMAL_GBT_REQUEST_PARAMS)
         assert_greater_than_or_equal(tmpl['curtime'], t + MAX_FUTURE_BLOCK_TIME - MAX_TIMEWARP)
+        # mintime and curtime should match
+        assert_equal(tmpl['mintime'], tmpl['curtime'])
 
         block = CBlock()
         block.nVersion = tmpl["version"]