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

.pending/bugfixes/sdk/1351-https-github-co

@@ -0,0 +1 @@
+[\#1351](https://github.com/cosmos/cosmos-sdk/issues/1351) Stable AppHash allows no_empty_blocks

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 {

types/abci.go

@@ -2,14 +2,20 @@ package types
 
 import abci "github.com/tendermint/tendermint/abci/types"
 
-// initialize application state at genesis
+// InitChainer initializes application state at genesis
 type InitChainer func(ctx Context, req abci.RequestInitChain) abci.ResponseInitChain
 
-// run code before the transactions in a block
+// BeginBlocker runs code before the transactions in a block
+//
+// Note: applications which set create_empty_blocks=false will not have regular block timing and should use
+// e.g. BFT timestamps rather than block height for any periodic BeginBlock logic
 type BeginBlocker func(ctx Context, req abci.RequestBeginBlock) abci.ResponseBeginBlock
 
-// run code after the transactions in a block and return updates to the validator set
+// EndBlocker runs code after the transactions in a block and return updates to the validator set
+//
+// Note: applications which set create_empty_blocks=false will not have regular block timing and should use
+// e.g. BFT timestamps rather than block height for any periodic EndBlock logic
 type EndBlocker func(ctx Context, req abci.RequestEndBlock) abci.ResponseEndBlock
 
-// respond to p2p filtering queries from Tendermint
+// PeerFilter responds to p2p filtering queries from Tendermint
 type PeerFilter func(info string) abci.ResponseQuery