MissingReturnBug.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.13;
//pragma solidity 0.4.21; // both cases work on this version

/**
 * @title MissingReturnBug
 * @author IllIllI
 */

interface IERC20 {
  function transfer(address to, uint value) external returns (bool);
}

contract BadERC20 {
    function transfer(address, uint) external pure {
        return;
    }
}

// test case of the missing return bug described here:
// https://medium.com/coinmonks/missing-return-value-bug-at-least-130-tokens-affected-d67bf08521ca
contract Test {
    function testIt() external {
        BadERC20 bad = new BadERC20();
        
        //BadERC20(address(bad)).transfer(address(this), 0); // works
        IERC20(address(bad)).transfer(address(this), 0); // doesn't work - reverts
    }
}