Upgrade from ERC20Upgradeable to ERC20Upgradeable, EIP712Upgradeable

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1

Hello, I'm trying to upgrade a simple ERC20Upgradeable adding EIP712Upgradeable to the inheritance chain

:1234: Code to reproduce

before

contract Token is ERC20Upgradeable { }

after

contract Token is ERC20Upgradeable, EIP712Upgradeable {}

and I'm receiving the following error when running

  await upgrades.validateUpgrade(TokenV1, TokenV2, {});

Error: New storage layout is incompatible

@openzeppelin/contracts-upgradeable/utils/cryptography/draft-EIP712Upgradeable.sol:30: Inserted `_HASHED_NAME`
  > New variables should be placed after all existing inherited variables

Note: I also tried to add ERC2771ContextUpgradeable.sol to the inheritance chain, which gave similar issues, I'm trying to solve one at a time, but a general solution would be really useful (Final inheritance chain should be
contract Token is ERC20Upgradeable, EIP712Upgradeable, ERC2771ContextUpgradeable {}

:computer: Environment

Solidity version: "0.8.7"

"dependencies": {
        "@openzeppelin/contracts-upgradeable": "^4.5.0",
      },
      "devDependencies": {
        "@nomiclabs/hardhat-ethers": "^2.2.0",
        "@nomiclabs/hardhat-web3": "^2.0.0",
        "@openzeppelin/hardhat-upgrades": "^1.21.0",
        "ethers": "^5.7.1",
        "hardhat": "^2.8.0",
        "web3": "^1.7.0"
      }
2

Just like the error message: Error: New storage layout is incompatible

When you want to add some new variables, you had better add them at the end of all variables, in your case, original contract variables are:

ERC20Upgradeable_Variable
Token_Variable

And the new contract you want to upgrade:

ERC20Upgradeable_Variable
EIP712Upgradeable_Variable // <<<<----- insert some variables, DISALLOWED
Token_Variable

It is dangerous to upgrade your contract in your way, it will mix up the original data of the contract.

I think you can read some docs about the upgrade, e.g.
Writing Upgradeable Contracts - OpenZeppelin Docs