core: stateDb has no trie and no snap return err (#2369)

core/blockchain_reader.go

@@ -396,7 +396,20 @@ func (bc *BlockChain) State() (*state.StateDB, error) {
 
 // StateAt returns a new mutable state based on a particular point in time.
 func (bc *BlockChain) StateAt(root common.Hash) (*state.StateDB, error) {
-	return state.New(root, bc.stateCache, bc.snaps)
+	stateDb, err := state.New(root, bc.stateCache, bc.snaps)
+	if err != nil {
+		return nil, err
+	}
+
+	// If there's no trie and the specified snapshot is not available, getting
+	// any state will by default return nil.
+	// Instead of that, it will be more useful to return an error to indicate
+	// the state is not available.
+	if stateDb.NoTrie() && stateDb.GetSnap() == nil {
+		return nil, errors.New("state is not available")
+	}
+
+	return stateDb, err
 }
 
 // Config retrieves the chain's fork configuration.

core/state/statedb.go

@@ -1896,6 +1896,10 @@ func (s *StateDB) convertAccountSet(set map[common.Address]*types.StateAccount)
 	return ret
 }
 
+func (s *StateDB) GetSnap() snapshot.Snapshot {
+	return s.snap
+}
+
 // copySet returns a deep-copied set.
 func copySet[k comparable](set map[k][]byte) map[k][]byte {
 	copied := make(map[k][]byte, len(set))