Can you rename variables in a deployed upgradeable contract?

Archive SDK
2

Hi @PaulRBerg,

I can’t see a reason in Modifying your contracts or Solidity - Layout of State Variables in Storage that renaming a mapping or renaming a variable in a struct is not safe to do, as long as type and order are not changed.

If you did go ahead, then I would recommend thorough testing.

I did a quick check to see what the CLI would report (I didn’t write any tests):

Sample.sol

pragma solidity 0.5.11;

contract Sample {

    struct Salary {
        address company;
        bool isEntity;
        uint256 streamId;
    }

    mapping(uint256 => Salary) private salaries;
}

Sample.sol

I had to add an empty function to be able to upgrade.

pragma solidity 0.5.11;

contract Sample {

    struct Stream {
        address payer;
        bool isEntity;
        uint256 streamId;
    }

    mapping(uint256 => Stream) private streams;

    function nothing() public {
    }
}

When I upgrade the CLI warns that structs are not checked for storage compatibility, and that the mapping was renamed.

$ oz upgrade
? Pick a network development
Nothing to compile, all contracts are up to date.
- Variable streams (Sample) contains a struct or enum. These are not automatically checked for storage compatibility in the current version. See https://docs.openzeppelin.com/sdk/2.5/writing-contracts#modifying-your-contracts for more info.
- Variable 'mapping(key => Sample.Salary) salaries' in contract Sample was replaced with 'mapping(key => Sample.Stream) streams' in
            contracts/Sample.sol:1. Avoid changing existing variables.
See https://docs.openzeppelin.com/sdk/2.5/writing-contracts#modifying-your-contracts for more info.
2 Likes