Can't add variables with change of storage gap with hardhat

[jachung91]

I am using

hardhat v2.14.0
solidity v0.8.9

Simple code is like

original code

contract BoxV1 is Initializable{
uint256 private value;
uint256[48] private __gapUint256;}

upgrading code

contract BoxV2 is Initializable{
uint256 private value;
uint256 private amount;
uint256[47] private __gapUint256;}

but i get error when I use upgrades.upgradeProxy with hardhat.

Error is

Error: New storage layout is incompatible
contracts/BoxV2.sol:8: Inserted amount
New variables should be placed after all existing inherited variables
contracts/BoxV2.sol:9: Upgraded __gapUint256 to an incompatible type

As i read docs at https://docs.openzeppelin.com/upgrades-plugins/1.x/writing-upgradeable#storage-gaps
I think i did anything wrong. Any one can help?

[ericglau]

Hi @jachung91 , the gap name needs to be exactly __gap or start with __gap_ (with the extra underscore after it). In your example, can you use a gap name like __gap_uint256?