MOVEONLY: BIP125 max conflicts limit to policy/rbf.h

A circular dependency is added because policy now depends on txmempool and
txmempool depends on validation. It is natural for [mempool] policy to
rely on mempool; the problem is caused by txmempool depending on
validation. bitcoin#22677 will resolve this.

src/policy/rbf.h

@@ -7,6 +7,10 @@
 
 #include <txmempool.h>
 
+/** Maximum number of transactions that can be replaced by BIP125 RBF (Rule #5). This includes all
+ * mempool conflicts and their descendants. */
+static constexpr uint32_t MAX_BIP125_REPLACEMENT_CANDIDATES{100};
+
 /** The rbf state of unconfirmed transactions */
 enum class RBFTransactionState {
     /** Unconfirmed tx that does not signal rbf and is not in the mempool */

src/validation.cpp

@@ -25,6 +25,7 @@
 #include <node/coinstats.h>
 #include <node/ui_interface.h>
 #include <policy/policy.h>
+#include <policy/rbf.h>
 #include <policy/settings.h>
 #include <pow.h>
 #include <primitives/block.h>
@@ -810,7 +811,6 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
     {
         CFeeRate newFeeRate(nModifiedFees, nSize);
         std::set<uint256> setConflictsParents;
-        const int maxDescendantsToVisit = 100;
         for (const auto& mi : setIterConflicting) {
             // Don't allow the replacement to reduce the feerate of the
             // mempool.
@@ -846,7 +846,7 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
         // This potentially overestimates the number of actual descendants
         // but we just want to be conservative to avoid doing too much
         // work.
-        if (nConflictingCount <= maxDescendantsToVisit) {
+        if (nConflictingCount <= MAX_BIP125_REPLACEMENT_CANDIDATES) {
             // If not too many to replace, then calculate the set of
             // transactions that would have to be evicted
             for (CTxMemPool::txiter it : setIterConflicting) {
@@ -861,7 +861,7 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
                     strprintf("rejecting replacement %s; too many potential replacements (%d > %d)\n",
                         hash.ToString(),
                         nConflictingCount,
-                        maxDescendantsToVisit));
+                        MAX_BIP125_REPLACEMENT_CANDIDATES));
         }
 
         for (unsigned int j = 0; j < tx.vin.size(); j++)

test/lint/lint-circular-dependencies.sh

@@ -15,6 +15,7 @@ EXPECTED_CIRCULAR_DEPENDENCIES=(
     "index/base -> validation -> index/blockfilterindex -> index/base"
     "index/coinstatsindex -> node/coinstats -> index/coinstatsindex"
     "policy/fees -> txmempool -> policy/fees"
+    "policy/rbf -> txmempool -> validation -> policy/rbf"
     "qt/addresstablemodel -> qt/walletmodel -> qt/addresstablemodel"
     "qt/recentrequeststablemodel -> qt/walletmodel -> qt/recentrequeststablemodel"
     "qt/sendcoinsdialog -> qt/walletmodel -> qt/sendcoinsdialog"