Failing to compile multiple Solidity versions

Question

I'm trying to compile (through Hardhat) a contract that imports several interfaces with different Solidity versions but I'm getting the following error:

Error HH606: The project cannot be compiled, see reasons below.

These files and its dependencies cannot be compiled with your config. This can happen because they have incompatible Solidity pragmas, or don't match any of your configured Solidity compilers.

  * contracts/FlashLoaner.sol

Flashloaner.sol:

pragma solidity >=0.5.0 <=0.8.0;

import '@uniswap/v2-periphery/contracts/interfaces/IWETH.sol';
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import '@aave/protocol-v2/contracts/interfaces/ILendingPool.sol'; //---> Issue
import "hardhat/console.sol";


contract FlashLoaner {
    struct MyCustomData {
        address token;
        uint256 repayAmount;
    }

    address public logicContract;
    
    function execute(address _weth, address _contract) external view {
        console.log(_weth);
    }
}

The problem is with @aave/protocol-v2/contracts/interfaces/ILendingPool.sol. If I comment it out, my contract compiles good.

IlendingPool.sol: pragma solidity 0.6.12;

IERC20.sol: pragma solidity ^0.5.0;

IWETH.sol: pragma solidity >=0.5.0;

Hardhat.config:

module.exports = {
  solidity: {
    compilers: [
      {
        version: "0.5.7"
      },
      {
        version: "0.8.0"
      },
      {
        version: "0.6.12"
      }
    ]
  }
   ...

Answer 1

Solution:

Grab the signatures from the functions that I'm interested in from each interface, and put them on my own interface with pragma solidity ^0.8.0.

Answer 2

I had a similar problem.

In my case, my contracts used pragma solidity version ^0.8.0

To fix the problem, I added those lines to my hardhat.config.js (Inside the existing module.exports for most cases).

module.exports = {
  solidity: "0.8.0",
}

I just deleted the "^" before the version.