Using storage gaps with `hardhat-upgrades`

[aquiladev]

Hi there,
I so similar questions on the forum, but did not find a solution yet.

I have to upgrade storage layout in my contract(which is already deployed on mainnet)

Current layout

uint256[50] private __gap;

New layout

address private _forwarder;
uint256[49] private __gap;

Command

await upgrades.upgradeProxy(contract.address, ContractV2)

Error

Error: New storage layout is incompatible

contracts/metatx/ERC2771Context.sol:21: Inserted `_forwarder`
  > New variables should be placed after all existing inherited variables

contracts/metatx/ERC2771Context.sol:85: Upgraded `__gap` to an incompatible type
  - Bad array resize from 50 to 49
    Size cannot decrease

Dependencies

• "@openzeppelin/contracts-upgradeable": "^4.1.0",
• "@openzeppelin/hardhat-upgrades": "^1.8.2",

As far as I understand hardhat-upgrades does not support it yet.
Is there a way to do this?

[frangio]

Hi @aquiladev. I'm sorry this is not natively supported by the plugin yet. I also don't want to rush to implement this feature for you because it's sensitive and would want to review it and test it thoroughly.

For your particular use case, I would recommend manually modifying the network file under .openzeppelin to include this variable you want to add, as if it had been included in your previous version.

I realize this is a little tricky, if you can share a repository link I can help you figure out the exact change you should make.

[aquiladev]

I think I've got your point, thanks

[Mister_Singh]

Hi @frangio how should i manually modify file .openzeppelin/unknown-31337.json and still have tests run? currently what happens is that the tests first deploy the first version, which resets unknown-31337.json to have __gap be of size 50 and then the test which upgrades fails as it expects it to be 49. any suggestions would be very helpful. thanks

[ericglau]

@Mister_Singh An alternative would be to test with a modified copy of your first version for now, where the modified copy already has the variable you want to add.

Support for storage gaps is planned in https://github.com/OpenZeppelin/openzeppelin-upgrades/issues/276

[ericglau]

Storage gaps is supported in the Hardhat and Truffle upgrades plugins now. See https://docs.openzeppelin.com/upgrades-plugins/1.x/writing-upgradeable#storage-gaps for how to use them.