Merge PR #4613: Only change rootmultistore hash when substore hashes change

store/rootmulti/store.go

@@ -477,7 +477,7 @@ type storeCore struct {
 func (si storeInfo) Hash() []byte {
 	// Doesn't write Name, since merkle.SimpleHashFromMap() will
 	// include them via the keys.
-	bz, _ := cdc.MarshalBinaryLengthPrefixed(si.Core)
+	bz := si.Core.CommitID.Hash
 	hasher := tmhash.New()
 
 	_, err := hasher.Write(bz)

store/rootmulti/store_test.go

@@ -77,6 +77,33 @@ func TestCacheMultiStoreWithVersion(t *testing.T) {
 	})
 }
 
+func TestHashStableWithEmptyCommit(t *testing.T) {
+	var db dbm.DB = dbm.NewMemDB()
+	if useDebugDB {
+		db = dbm.NewDebugDB("CMS", db)
+	}
+	ms := newMultiStoreWithMounts(db)
+	err := ms.LoadLatestVersion()
+	require.Nil(t, err)
+
+	commitID := types.CommitID{}
+	checkStore(t, ms, commitID, commitID)
+
+	k, v := []byte("wind"), []byte("blows")
+
+	store1 := ms.getStoreByName("store1").(types.KVStore)
+	store1.Set(k, v)
+
+	cID := ms.Commit()
+	require.Equal(t, int64(1), cID.Version)
+	hash := cID.Hash
+
+	// make an empty commit, it should update version, but not affect hash
+	cID = ms.Commit()
+	require.Equal(t, int64(2), cID.Version)
+	require.Equal(t, hash, cID.Hash)
+}
+
 func TestMultistoreCommitLoad(t *testing.T) {
 	var db dbm.DB = dbm.NewMemDB()
 	if useDebugDB {