storage: simplify error handling in evaluateProposalInner

Proposals that return errors but still want to go through Raft to
lay down intents were refactored away in cockroachdb#21140. This allows us to
simplify the error handling in `evaluateProposalInner`.

Release note: None

pkg/storage/replica.go

@@ -5214,54 +5214,46 @@ func (r *Replica) evaluateProposalInner(
 ) result.Result {
 	// Evaluate the commands. If this returns without an error, the batch should
 	// be committed.
-	var result result.Result
-	var batch engine.Batch
-	{
-		// TODO(tschottdorf): absorb all returned values in `pd` below this point
-		// in the call stack as well.
-		var pErr *roachpb.Error
-		var ms enginepb.MVCCStats
-		var br *roachpb.BatchResponse
-		batch, ms, br, result, pErr = r.evaluateWriteBatch(ctx, idKey, ba, spans)
-		if r.store.cfg.Settings.Version.IsActive(cluster.VersionMVCCNetworkStats) {
-			result.Replicated.Delta = ms.ToNetworkStats()
-		} else {
-			result.Replicated.DeprecatedDelta = &ms
-		}
-		result.Local.Reply = br
-		result.Local.Err = pErr
-	}
-
-	if result.Local.Err != nil && ba.IsWrite() {
+	// TODO(tschottdorf): absorb all returned values in `res` below this point
+	// in the call stack as well.
+	batch, ms, br, res, pErr := r.evaluateWriteBatch(ctx, idKey, ba, spans)
+	if pErr != nil {
 		// TODO(tschottdorf): make `nil` acceptable. Corresponds to
 		// roachpb.Response{With->Or}Error.
-		result.Local.Reply = &roachpb.BatchResponse{}
+		res.Local.Reply = &roachpb.BatchResponse{}
+		res.Local.Err = pErr
 		// Reset the batch to clear out partial execution. Don't set
 		// a WriteBatch to signal to the caller that we fail-fast this
 		// proposal.
 		batch.Close()
 		batch = nil
 		// Restore the original txn's Writing bool if the error specifies a
 		// transaction.
-		if txn := result.Local.Err.GetTxn(); txn != nil {
+		if txn := res.Local.Err.GetTxn(); txn != nil {
 			if ba.Txn == nil {
 				log.Fatalf(ctx, "error had a txn but batch is non-transactional. Err txn: %s", txn)
 			}
 			if txn.ID == ba.Txn.ID {
 				txn.Writing = ba.Txn.Writing
 			}
 		}
-		return result
+		return res
 	}
 
-	result.WriteBatch = &storagebase.WriteBatch{
+	res.Local.Reply = br
+	if r.store.cfg.Settings.Version.IsActive(cluster.VersionMVCCNetworkStats) {
+		res.Replicated.Delta = ms.ToNetworkStats()
+	} else {
+		res.Replicated.DeprecatedDelta = &ms
+	}
+	res.WriteBatch = &storagebase.WriteBatch{
 		Data: batch.Repr(),
 	}
 	// Note: reusing the proposer's batch when applying the command on the
 	// proposer was explored as an optimization but resulted in no performance
 	// benefit.
 	batch.Close()
-	return result
+	return res
 }
 
 // checkIfTxnAborted checks the txn AbortSpan for the given