Support custom errors from Solidity 0.8.4 (new fragment type)

Today Solidity 0.8.4 was released and it includes a new feature called “custom errors” that currently breaks Ethers.js.

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.4;

contract TestToken {
    error InsufficientBalance(uint256 available, uint256 required);

    function transfer(address /*to*/, uint amount) public pure {
        revert InsufficientBalance(0, amount);
    }
}

The resulting ABI contains a new type of fragment for errors:

{
  "type": "error",
  "name": "InsufficientBalance",
  "inputs": [
    {
      "internalType": "uint256",
      "name": "available",
      "type": "uint256"
    },
    {
      "internalType": "uint256",
      "name": "required",
      "type": "uint256"
    }
  ],
},

Loading the contract ABI on Ethers results in:

Error: invalid fragment object (argument="value", value={"inputs":[{"internalType":"uint256","name":"available","type":"uint256"},{"internalType":"uint256","name":"required","type":"uint256"}],"name":"InsufficientBalance","type":"error"}, code=INVALID_ARGUMENT, version=abi/5.1.1)

Eventually Ethers should parse the revert data into one of these error objects but in the meantime it should still support loading these ABIs.

[frangio]

Seems to work!

[ricmoo]

Not erroring should be fixed in [5.1.4])https://github.com/ethers-io/ethers.js/releases/tag/v5.1.4).

Try it out and let me know. 😃