[validation] explicit Success/Failure ctors for MempoolAcceptResult

Makes code more clear and prevents accidentally calling the wrong ctor.

src/validation.cpp

@@ -1040,7 +1040,7 @@ MempoolAcceptResult MemPoolAccept::AcceptSingleTransaction(const CTransactionRef
 
     Workspace ws(ptx);
 
-    if (!PreChecks(args, ws)) return MempoolAcceptResult(ws.m_state);
+    if (!PreChecks(args, ws)) return MempoolAcceptResult::Failure(ws.m_state);
 
     // Only compute the precomputed transaction data if we need to verify
     // scripts (ie, other policy checks pass). We perform the inexpensive
@@ -1048,20 +1048,20 @@ MempoolAcceptResult MemPoolAccept::AcceptSingleTransaction(const CTransactionRef
     // checks pass, to mitigate CPU exhaustion denial-of-service attacks.
     PrecomputedTransactionData txdata;
 
-    if (!PolicyScriptChecks(args, ws, txdata)) return MempoolAcceptResult(ws.m_state);
+    if (!PolicyScriptChecks(args, ws, txdata)) return MempoolAcceptResult::Failure(ws.m_state);
 
-    if (!ConsensusScriptChecks(args, ws, txdata)) return MempoolAcceptResult(ws.m_state);
+    if (!ConsensusScriptChecks(args, ws, txdata)) return MempoolAcceptResult::Failure(ws.m_state);
 
     // Tx was accepted, but not added
     if (args.m_test_accept) {
-        return MempoolAcceptResult(std::move(ws.m_replaced_transactions), ws.m_base_fees);
+        return MempoolAcceptResult::Success(std::move(ws.m_replaced_transactions), ws.m_base_fees);
     }
 
-    if (!Finalize(args, ws)) return MempoolAcceptResult(ws.m_state);
+    if (!Finalize(args, ws)) return MempoolAcceptResult::Failure(ws.m_state);
 
     GetMainSignals().TransactionAddedToMempool(ptx, m_pool.GetAndIncrementSequence());
 
-    return MempoolAcceptResult(std::move(ws.m_replaced_transactions), ws.m_base_fees);
+    return MempoolAcceptResult::Success(std::move(ws.m_replaced_transactions), ws.m_base_fees);
 }
 
 } // anon namespace

src/validation.h

@@ -169,9 +169,7 @@ void PruneBlockFilesManual(CChainState& active_chainstate, int nManualPruneHeigh
 * Validation result for a single transaction mempool acceptance.
 */
 struct MempoolAcceptResult {
-    /** Used to indicate the results of mempool validation,
-    * including the possibility of unfinished validation.
-    */
+    /** Used to indicate the results of mempool validation. */
     enum class ResultType {
         VALID, //!> Fully validated, valid.
         INVALID, //!> Invalid.
@@ -184,7 +182,16 @@ struct MempoolAcceptResult {
     const std::optional<std::list<CTransactionRef>> m_replaced_transactions;
     /** Raw base fees in satoshis. */
     const std::optional<CAmount> m_base_fees;
+    static MempoolAcceptResult Failure(TxValidationState state) {
+        return MempoolAcceptResult(state);
+    }
+
+    static MempoolAcceptResult Success(std::list<CTransactionRef>&& replaced_txns, CAmount fees) {
+        return MempoolAcceptResult(std::move(replaced_txns), fees);
+    }
 
+// Private constructors. Use static methods MempoolAcceptResult::Success, etc. to construct.
+private:
     /** Constructor for failure case */
     explicit MempoolAcceptResult(TxValidationState state)
         : m_result_type(ResultType::INVALID), m_state(state) {