Make GetEntriesForConflicts return std::optional

Avoids reusing err_string.

2 files changed, 9 insertions, 12 deletions

diff --git a/src/policy/rbf.cpp b/src/policy/rbf.cpp
index 43624c7993..3ff4c1f9c2 100644
--- a/src/policy/rbf.cpp
+++ b/src/policy/rbf.cpp
@@ -47,11 +47,10 @@ RBFTransactionState IsRBFOptInEmptyMempool(const CTransaction& tx)
     return SignalsOptInRBF(tx) ? RBFTransactionState::REPLACEABLE_BIP125 : RBFTransactionState::UNKNOWN;
 }
 
-bool GetEntriesForConflicts(const CTransaction& tx,
+std::optional<std::string> GetEntriesForConflicts(const CTransaction& tx,
                             CTxMemPool& m_pool,
                             const CTxMemPool::setEntries& setIterConflicting,
-                            CTxMemPool::setEntries& allConflicting,
-                            std::string& err_string)
+                            CTxMemPool::setEntries& allConflicting)
 {
     AssertLockHeld(m_pool.cs);
     const uint256 hash = tx.GetHash();
@@ -62,11 +61,10 @@ bool GetEntriesForConflicts(const CTransaction& tx,
         // but we just want to be conservative to avoid doing too much
         // work.
         if (nConflictingCount > MAX_BIP125_REPLACEMENT_CANDIDATES) {
-            err_string = strprintf("rejecting replacement %s; too many potential replacements (%d > %d)\n",
+            return strprintf("rejecting replacement %s; too many potential replacements (%d > %d)\n",
                         hash.ToString(),
                         nConflictingCount,
                         MAX_BIP125_REPLACEMENT_CANDIDATES);
-            return false;
         }
     }
     // If not too many to replace, then calculate the set of
@@ -74,6 +72,6 @@ bool GetEntriesForConflicts(const CTransaction& tx,
     for (CTxMemPool::txiter it : setIterConflicting) {
         m_pool.CalculateDescendants(it, allConflicting);
     }
-    return true;
+    return std::nullopt;
 }
 
diff --git a/src/policy/rbf.h b/src/policy/rbf.h
index a67e9058df..2a41ca8892 100644
--- a/src/policy/rbf.h
+++ b/src/policy/rbf.h
@@ -40,14 +40,13 @@ RBFTransactionState IsRBFOptInEmptyMempool(const CTransaction& tx);
  * mempool must not exceed a total of 100 transactions." Quit as early as possible. There cannot be
  * more than MAX_BIP125_REPLACEMENT_CANDIDATES potential entries.
  * @param[in]   setIterConflicting  The set of iterators to mempool entries.
- * @param[out]  err_string          Used to return errors, if any.
  * @param[out]  allConflicting      Populated with all the mempool entries that would be replaced,
  *                                  which includes descendants of setIterConflicting. Not cleared at
  *                                  the start; any existing mempool entries will remain in the set.
- * @returns false if Rule 5 is broken.
+ * @returns an error message if Rule #5 is broken, otherwise a std::nullopt.
  */
-bool GetEntriesForConflicts(const CTransaction& tx, CTxMemPool& m_pool,
-                            const CTxMemPool::setEntries& setIterConflicting,
-                            CTxMemPool::setEntries& allConflicting,
-                            std::string& err_string) EXCLUSIVE_LOCKS_REQUIRED(m_pool.cs);
+std::optional<std::string> GetEntriesForConflicts(const CTransaction& tx, CTxMemPool& m_pool,
+                                                  const CTxMemPool::setEntries& setIterConflicting,
+                                                  CTxMemPool::setEntries& allConflicting)
+                                                  EXCLUSIVE_LOCKS_REQUIRED(m_pool.cs);
 #endif // BITCOIN_POLICY_RBF_H