feat: state.SnapshotTree interface for drop-in replacement

core/state/statedb.go

@@ -63,7 +63,7 @@ type StateDB struct {
 	prefetcher *triePrefetcher
 	trie       Trie
 	hasher     crypto.KeccakState
-	snaps      *snapshot.Tree    // Nil if snapshot is not available
+	snaps      SnapshotTree      // Nil if snapshot is not available
 	snap       snapshot.Snapshot // Nil if snapshot is not available
 
 	// originalRoot is the pre-state root, before any changes were made.
@@ -141,7 +141,8 @@ type StateDB struct {
 }
 
 // New creates a new state from a given trie.
-func New(root common.Hash, db Database, snaps *snapshot.Tree) (*StateDB, error) {
+func New(root common.Hash, db Database, snaps SnapshotTree) (*StateDB, error) {
+	snaps = clearTypedNilPointer(snaps)
 	tr, err := db.OpenTrie(root)
 	if err != nil {
 		return nil, err

core/state/statedb.libevm.go

@@ -0,0 +1,51 @@
+// Copyright 2024 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The libevm additions are distributed in the hope that they will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package state
+
+import (
+	"reflect"
+
+	"github.com/ava-labs/libevm/common"
+	"github.com/ava-labs/libevm/core/state/snapshot"
+)
+
+// SnapshotTree mirrors the functionality of a [snapshot.Tree], allowing for
+// drop-in replacements.
+type SnapshotTree interface {
+	Cap(common.Hash, int) error
+	Snapshot(common.Hash) snapshot.Snapshot
+	StorageIterator(root, account, seek common.Hash) (snapshot.StorageIterator, error)
+	Update(
+		blockRoot common.Hash,
+		parentRoot common.Hash,
+		destructs map[common.Hash]struct{},
+		accounts map[common.Hash][]byte,
+		storage map[common.Hash]map[common.Hash][]byte,
+	) error
+}
+
+var _ SnapshotTree = (*snapshot.Tree)(nil)
+
+// clearTypedNilPointer returns nil if `snaps == nil` or if it holds a nil
+// pointer. The default geth behaviour expected a [snapshot.Tree] pointer
+// instead of a SnapshotTree interface, which could result in typed-nil bugs.
+func clearTypedNilPointer(snaps SnapshotTree) SnapshotTree {
+	if v := reflect.ValueOf(snaps); v.Kind() == reflect.Pointer && v.IsNil() {
+		return nil
+	}
+	return snaps
+}