Update pair bytecode

[krisbitney]

It is necessary to use the right UniswapV2Pair.sol bytecode for the Router to work.

[benefacto]

Not a smart contract dev but it sounds like your liquidity pool work depends on this, so approving on that basis. Deployment script will need to be updated at some point to match.

[krisbitney]

It might not be necessary. I see that you call addLiquidity successfully in your deployment script. That's super weird because I was unable to do the same in a different context. The reason turned out to be that the pair contract bytecode differed from the hardcoded value in the library contract.

The pairFor function in the library contract was not returning the same value as the pair address calculated in the factory contract because the init code hash differed.

    // calculates the CREATE2 address for a pair without making any external calls
    function pairFor(address factory, address tokenA, address tokenB) internal pure returns (address pair) {
        (address token0, address token1) = sortTokens(tokenA, tokenB);
        pair = address(uint(keccak256(abi.encodePacked(
                hex'ff',
                factory,
                keccak256(abi.encodePacked(token0, token1)),
                hex'96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f' // init code hash
            ))));
    }

I even have a test that verifies this. BUT the deployment script fails when I try to replace the router build artifact in your deployment script with the one added by this PR.

// old
import routerArtifact from "@uniswap/v2-periphery/build/UniswapV2Router02.json";
// new
import routerArtifact from "../artifacts/contracts/uniswap/UniswapV2Router02.sol/UniswapV2Router02.json";

If your deployment is working, that's all that matters. We can shelve this PR.

[benefacto]

It might not be necessary. I see that you call addLiquidity successfully in your deployment script. That's super weird because I was unable to do the same in a different context. The reason turned out to be that the pair contract bytecode differed from the hardcoded value in the library contract.

The pairFor function in the library contract was not returning the same value as the pair address calculated in the factory contract because the init code hash differed.

    // calculates the CREATE2 address for a pair without making any external calls
    function pairFor(address factory, address tokenA, address tokenB) internal pure returns (address pair) {
        (address token0, address token1) = sortTokens(tokenA, tokenB);
        pair = address(uint(keccak256(abi.encodePacked(
                hex'ff',
                factory,
                keccak256(abi.encodePacked(token0, token1)),
                hex'96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f' // init code hash
            ))));
    }

I even have a test that verifies this. BUT the deployment script fails when I try to replace the router build artifact in your deployment script with the one added by this PR.

// old
import routerArtifact from "@uniswap/v2-periphery/build/UniswapV2Router02.json";
// new
import routerArtifact from "../artifacts/contracts/uniswap/UniswapV2Router02.sol/UniswapV2Router02.json";

If your deployment is working, that's all that matters. We can shelve this PR.

Thanks for laying that out. Yeah, if you're rebuilding the pair contract, the init code hash has to be updated but as long as we’re using the canonical Uniswap V2 artifacts from the NPM package (which we are in the deployment script), it should all line up. Glad we can shelve this for now.