core/state: fix bug in copy of copy State

core/state/statedb.go

@@ -474,6 +474,16 @@ func (self *StateDB) Copy() *StateDB {
 		state.stateObjects[addr] = self.stateObjects[addr].deepCopy(state)
 		state.stateObjectsDirty[addr] = struct{}{}
 	}
+	// Above, we don't copy the actual journal. This means that if the copy is copied, the
+	// loop above will be a no-op, since the copy's journal is empty.
+	// Thus, here we iterate over stateObjects, to enable copies of copies
+	for addr := range self.stateObjectsDirty {
+		if _, exist := state.stateObjects[addr]; !exist {
+			state.stateObjects[addr] = self.stateObjects[addr].deepCopy(state)
+			state.stateObjectsDirty[addr] = struct{}{}
+		}
+	}
+
 	for hash, logs := range self.logs {
 		state.logs[hash] = make([]*types.Log, len(logs))
 		copy(state.logs[hash], logs)

core/state/statedb_test.go

@@ -422,3 +422,19 @@ func (s *StateSuite) TestTouchDelete(c *check.C) {
 		c.Fatal("expected no dirty state object")
 	}
 }
+
+// TestCopyOfCopy tests that modified objects are carried over to the copy, and the copy of the copy.
+// See https://github.com/ethereum/go-ethereum/pull/15225#issuecomment-380191512
+func TestCopyOfCopy(t *testing.T) {
+	db, _ := ethdb.NewMemDatabase()
+	sdb, _ := New(common.Hash{}, NewDatabase(db))
+	addr := common.HexToAddress("aaaa")
+	sdb.SetBalance(addr, big.NewInt(42))
+
+	if got := sdb.Copy().GetBalance(addr).Uint64(); got != 42 {
+		t.Fatalf("1st copy fail, expected 42, got %v", got)
+	}
+	if got := sdb.Copy().Copy().GetBalance(addr).Uint64(); got != 42 {
+		t.Fatalf("2nd copy fail, expected 42, got %v", got)
+	}
+}