Solidity 0.8.4编译报错：uint256无法显式转换为address

问题详情 #

编译跨不同DEX兑换代币的合约时出现错误，相关代码、配置及错误信息如下：

合约代码（SwappingDex.sol） #

//SPDX-License-Identifier: MIT

import "./Interfaces/IUniswapV2Router02.sol";
import "./Interfaces/IUniswapV2Factory.sol";
//import "./Interfaces/IUniswapV2Pair.sol";
import "./Interfaces/IERC20.sol";
import "./Interfaces/UniswapV2Library.sol";
//import "./Interfaces/IUniswapV2Callee.sol";


pragma solidity >0.5.0 < 0.9.0;

contract SwappingDex{

    address public constant uniswapRouter = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D;
    address public constant uniswapFactory = 0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f;
    address public constant sushiSwapRouter = 0xd9e1cE17f2641f24aE83637ab66a2cca9C378B9F;
    address public constant sushiSwapFactory = 0xC0AEe478e3658e2610c5F7A4A2E1777cE9e4f2Ac;
    address public constant WETH = 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2;


    function swappingIn2DEX(address tokenIn, address tokenOut, uint amount, address to)external payable{

        address pairOnUniswap;
        address pairOnSushi;
        pairOnUniswap = IUniswapV2Factory(uniswapFactory).getPair(tokenIn, tokenOut);
        pairOnSushi = IUniswapV2Factory(sushiSwapFactory).getPair(tokenIn, tokenOut);

        require(
            pairOnSushi != 0x0000000000000000000000000000000000000000 &&
            pairOnUniswap != 0x0000000000000000000000000000000000000000,
            "No Pair"
        );

        address[] memory path;
        path = new address[](2);
        path[0] = tokenIn;
        path[1] = tokenOut;

        uint[]memory amountOutUniswap = IUniswapV2Router02(uniswapRouter).getAmountsOut(amount, path);


        IERC20(tokenIn).transferFrom(msg.sender, address(this), amount);
        IERC20(tokenIn).approve(uniswapRouter, amount);

        IUniswapV2Router02(uniswapRouter).swapETHForExactTokens{value: msg.value}(
            amountOutUniswap[1],
            path,
            to,
            block.timestamp
        );
}

Hardhat配置文件（hardhat.config.js） #

require("@nomiclabs/hardhat-waffle");
require("@nomiclabs/hardhat-ethers");
require("dotenv").config();


module.exports = {
  solidity: "0.8.4",

  networks: {
    hardhat: {
      forking:{
        url: "*******",
      },
    },
  }
};

编译错误信息 #

TypeError: Explicit type conversion not allowed from "uint256" to "address".
--> contracts/Interfaces/UniswapV2Library.sol:20:16:
|
20 |         pair = address(uint(keccak256(abi.encodePacked(
|                ^ (相关源码部分从此处开始并跨多行)

错误原因及解决方法 #

核心原因 #

Solidity 0.8.0及以上版本对类型转换的安全性做了严格升级，禁止直接将uint256类型强制转换为address类型。UniswapV2Library中的pairFor函数使用了旧版转换逻辑，在0.8.x版本下触发了该错误。

修复步骤 #

修改contracts/Interfaces/UniswapV2Library.sol中对应的转换代码：
原代码片段：

pair = address(uint(keccak256(abi.encodePacked(
    hex'ff', factory, keccak256(abi.encodePacked(tokenA, tokenB)), hex'96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f'
))));

修改为：

pair = address(uint160(uint(keccak256(abi.encodePacked(
    hex'ff', factory, keccak256(abi.encodePacked(tokenA, tokenB)), hex'96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f'
)))));

以太坊地址本质是160位长度的数值，先将哈希结果转为uint160再转换为address，符合Solidity 0.8.x的类型转换规则。

额外逻辑提示 #

合约中存在一处逻辑冲突：调用swapETHForExactTokens是用ETH兑换指定数量的代币，但代码同时执行了tokenIn的转账和授权操作。如果需求是用tokenIn兑换tokenOut，应调用swapExactTokensForTokens函数；如果是用ETH兑换，则无需处理tokenIn的相关操作，需根据实际业务逻辑调整。

内容的提问来源于stack exchange，提问作者Matteo Gigli