delegatecall & custom error

tryHard.sol

pragma solidity "0.8.7";

contract CallMeAndIRevert {
    error ErrorA(); // 0x5283ed77
    error ErrorB(); // 0x8a25c831
    function triggerErrorAorB() external {
        if(block.timestamp % 2 == 0) revert ErrorA();
        else revert ErrorB();
    }
}

contract Caller {
    
    address target;
    
    constructor() {
        target = address(new CallMeAndIRevert());
    }
    
    function callA() external returns(string memory) {
        bytes memory data = abi.encodeWithSelector(bytes4(keccak256("triggerErrorAorB()"))); // 0x7da48f70
        bytes32 err;
        
        assembly {
          let result := delegatecall(sub(gas(), 5000), sload(target.slot), add(data, 0x20), mload(data), mload(0x40), 32)
          err := mload(mload(0x40))
        }
        
        if(err == bytes32(abi.encodeWithSelector(bytes4(keccak256("ErrorA()"))))) return "ErrorA";
        if(err == bytes32(abi.encodeWithSelector(bytes4(keccak256("ErrorB()"))))) return "ErrorB";
        else return "gReAt SuCcEsS";
    }
}