Incorrect ERC20 interface

Severity: Med ID: incorrect-erc20-interface

Flags interfaces or contracts whose function signatures match an ERC20 method by name and parameters but use the wrong return type.

What it does

For each function whose name and parameter types match a canonical ERC20 method (totalSupply, balanceOf, transfer, transferFrom, approve, allowance), the lint checks that the return type matches the spec. A mismatch is reported.

Why is this bad?

Tokens that diverge from the ERC20 spec break composability with the wider ecosystem (DEXes, lending protocols, multisigs) and are a common source of integration bugs and exploits.

Example

Bad

solidity

interface IBadERC20 {
    function balanceOf(address) external view returns (bool);  // should be uint256
    function transfer(address, uint256) external;              // should return bool
}

Good

solidity

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address to, uint256 value) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 value) external returns (bool);
    function transferFrom(address from, address to, uint256 value) external returns (bool);
}