feat(mempool): add error ErrRecheckFull (backport #3654) (#3656)

Complements #3314

This PR adds a new error with a more clear error message when checking
if the mempool is full while rechecking is in progress after a new block
was committed.

---

#### PR checklist

- [ ] Tests written/updated
- [ ] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
- [ ] Updated relevant documentation (`docs/` or `spec/`) and code
comments
- [ ] Title follows the [Conventional
Commits](https://www.conventionalcommits.org/en/v1.0.0/) spec
<hr>This is an automatic backport of pull request #3654 done by
[Mergify](https://mergify.com).

---------

Co-authored-by: Hernán Vanzetto <15466498+hvanz@users.noreply.github.com>
Co-authored-by: hvanz <hernan.vanzetto@gmail.com>

mempool/clist_mempool.go

@@ -377,18 +377,19 @@ func (mem *CListMempool) RemoveTxByKey(txKey types.TxKey) error {
 func (mem *CListMempool) isFull(txSize int) error {
 	memSize := mem.Size()
 	txsBytes := mem.SizeBytes()
-	recheckFull := mem.recheck.consideredFull()
-
-	if memSize >= mem.config.Size || int64(txSize)+txsBytes > mem.config.MaxTxsBytes || recheckFull {
+	if memSize >= mem.config.Size || int64(txSize)+txsBytes > mem.config.MaxTxsBytes {
 		return ErrMempoolIsFull{
 			NumTxs:      memSize,
 			MaxTxs:      mem.config.Size,
 			TxsBytes:    txsBytes,
 			MaxTxsBytes: mem.config.MaxTxsBytes,
-			RecheckFull: recheckFull,
 		}
 	}
 
+	if mem.recheck.consideredFull() {
+		return ErrRecheckFull
+	}
+
 	return nil
 }
 

mempool/errors.go

@@ -11,6 +11,10 @@ var ErrTxNotFound = errors.New("transaction not found in mempool")
 // ErrTxInCache is returned to the client if we saw tx earlier
 var ErrTxInCache = errors.New("tx already exists in cache")
 
+// ErrRecheckFull is returned when checking if the mempool is full and
+// rechecking is still in progress after a new block was committed.
+var ErrRecheckFull = errors.New("mempool is still rechecking after a new committed block, so it is considered as full")
+
 // ErrTxTooLarge defines an error when a transaction is too big to be sent in a
 // message to other peers.
 type ErrTxTooLarge struct {