If nonce is invalid, do not delete during mining

ethereum/blockcreation/src/main/java/tech/pegasys/pantheon/ethereum/blockcreation/BlockTransactionSelector.java

@@ -24,6 +24,7 @@
 import tech.pegasys.pantheon.ethereum.eth.transactions.PendingTransactions.TransactionSelectionResult;
 import tech.pegasys.pantheon.ethereum.mainnet.MainnetBlockProcessor.TransactionReceiptFactory;
 import tech.pegasys.pantheon.ethereum.mainnet.TransactionProcessor;
+import tech.pegasys.pantheon.ethereum.mainnet.TransactionValidator.TransactionInvalidReason;
 import tech.pegasys.pantheon.ethereum.vm.BlockHashLookup;
 
 import java.util.List;
@@ -43,10 +44,10 @@
  * <p>The output from this class's exeuction will be:
  *
  * <ul>
- *   <li>A list of transactions to include in the block being constructed.
- *   <li>A list of receipts for inclusion in the block.
- *   <li>The root hash of the world state at the completion of transaction execution.
- *   <li>The amount of gas consumed when executing all transactions.
+ * <li>A list of transactions to include in the block being constructed.
+ * <li>A list of receipts for inclusion in the block.
+ * <li>The root hash of the world state at the completion of transaction execution.
+ * <li>The amount of gas consumed when executing all transactions.
  * </ul>
  *
  * Once "used" this class must be discarded and another created. This class contains state which is
@@ -59,6 +60,7 @@ public class BlockTransactionSelector {
   private static final double MIN_BLOCK_OCCUPANCY_RATIO = 0.8;
 
   public static class TransactionSelectionResults {
+
     private final List<Transaction> transactions = Lists.newArrayList();
     private final List<TransactionReceipt> receipts = Lists.newArrayList();
     private long cumulativeGasUsed = 0;
@@ -172,8 +174,12 @@ private TransactionSelectionResult evaluateTransaction(final Transaction transac
       worldStateUpdater.commit();
       updateTransactionResultTracking(transaction, result);
     } else {
-      // Remove invalid transactions from the transaction pool but continue looking for valid ones
-      // as the block may not yet be full.
+      // If the transaction has an incorrect nonce, leave it in the pool and continue
+      if (result.getValidationResult().getInvalidReason()
+          .equals(TransactionInvalidReason.INCORRECT_NONCE)) {
+        return TransactionSelectionResult.CONTINUE;
+      }
+      // If the transaction was invalid for any other reason, delete it, and continue.
       return TransactionSelectionResult.DELETE_TRANSACTION_AND_CONTINUE;
     }
     return TransactionSelectionResult.CONTINUE;