New storage layout is incompatible

Support Upgrades
1

I'm trying to truffle migrate my project and I'm getting this error - https://gyazo.com/999330cf2bb625d1b0881b7cc069e77c

I already tried deleting the builds I had already and doing truffle compile multiple times. I double check the syntax on Box and BoxV2 and can't seem to find why it's spitting out this error.

// contracts/Box.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Box {
    uint256 private value;

    // Emitted when the stored value changes
    event ValueChanged(uint256 _value);

    // Stores a new value in the contract
    function store(uint256 _value) public {
        value = _value;
        emit ValueChanged(_value);
    }

    // Reads the last stored value
    function retrieve() public view returns (uint256) {
        return value;
    }
}

// contracts/BoxV2.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract BoxV2 {
    uint256 private value;

    // Emitted when the stored value changes
    event ValueChanged(uint256 _value);

    // Stores a new value in the contract
    function store(uint256 _value) public {
        value = _value;
        emit ValueChanged(_value);
    }

    // Reads the last stored value
    function retrieve() public view returns (uint256) {
        return value;
    }

    // Increments the stored value by 1
    function increment() public {
        value = value + 1;
        emit ValueChanged(value);
    }
}

// migrations/3_deploy_upgradeable_box.js
const { deployProxy } = require('@openzeppelin/truffle-upgrades');

const Box = artifacts.require('Box');

module.exports = async function (deployer) {
  await deployProxy(Box, [42], { deployer, initializer: 'store' });
};

// migrations/4_upgrade_box.js
const { upgradeProxy } = require('@openzeppelin/truffle-upgrades');

const Box = artifacts.require('Box');
const BoxV2 = artifacts.require('BoxV2');

module.exports = async function (deployer) {
    const existing = await Box.deployed();
    await upgradeProxy(existing.address, BoxV2, { deployer });
};

Please guide me in the right direction. Thank you.

2

My guess is that your Box contract originally had uint256 private _value when you deployed it. Then you changed it but the plugin had already stored in its layout information that there was a variable called _value. You should keep the underscore in both Box and BoxV2.

What network are you running the migrations against? The storage layout information is stored in the .openzeppelin directory per network.