Contract Source Code:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

/**
 * @dev Standard ERC20 Errors (EIP-6093).
 */
interface IERC20Errors {
    error ERC20InsufficientBalance(address sender, uint256 balance, uint256 needed);
    error ERC20InvalidSender(address sender);
    error ERC20InvalidReceiver(address receiver);
    error ERC20InsufficientAllowance(address spender, uint256 allowance, uint256 needed);
    error ERC20InvalidApprover(address approver);
    error ERC20InvalidSpender(address spender);
}

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    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);
}

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 */
interface IERC20Metadata is IERC20 {
    function name() external view returns (string memory);
    function symbol() external view returns (string memory);
    function decimals() external view returns (uint8);
}

/**
 * @dev Interface of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in
 * https://eips.ethereum.org/EIPS/eip-2612.
 */
interface IERC20Permit {
    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    function nonces(address owner) external view returns (uint256);

    function DOMAIN_SEPARATOR() external view returns (bytes32);
}

/**
 * @dev Basic context from OpenZeppelin to handle `msg.sender`.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }
}

/**
 * @dev Library for ECDSA signature recovery (used in EIP-2612 permit).
 */
library ECDSA {
    enum RecoverError {
        NoError,
        InvalidSignature,
        InvalidSignatureLength,
        InvalidSignatureS
    }

    error ECDSAInvalidSignature();
    error ECDSAInvalidSignatureLength(uint256 length);
    error ECDSAInvalidSignatureS(bytes32 s);

    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
        (address recovered, RecoverError error, bytes32 errorArg) = tryRecover(hash, signature);
        _throwError(error, errorArg);
        return recovered;
    }

    function tryRecover(bytes32 hash, bytes memory signature)
        internal
        pure
        returns (address, RecoverError, bytes32)
    {
        if (signature.length == 65) {
            bytes32 r;
            bytes32 s;
            uint8 v;
            // solhint-disable-next-line no-inline-assembly
            assembly {
                r := mload(add(signature, 0x20))
                s := mload(add(signature, 0x40))
                v := byte(0, mload(add(signature, 0x60)))
            }
            return tryRecover(hash, v, r, s);
        } else {
            return (address(0), RecoverError.InvalidSignatureLength, bytes32(signature.length));
        }
    }

    function tryRecover(bytes32 hash, uint8 v, bytes32 r, bytes32 s)
        internal
        pure
        returns (address, RecoverError, bytes32)
    {
        // Enforce s in lower half
        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF) {
            return (address(0), RecoverError.InvalidSignatureS, s);
        }
        address signer = ecrecover(hash, v, r, s);
        if (signer == address(0)) {
            return (address(0), RecoverError.InvalidSignature, bytes32(0));
        }
        return (signer, RecoverError.NoError, bytes32(0));
    }

    function _throwError(RecoverError error, bytes32 errorArg) private pure {
        if (error == RecoverError.NoError) {
            return;
        } else if (error == RecoverError.InvalidSignature) {
            revert ECDSAInvalidSignature();
        } else if (error == RecoverError.InvalidSignatureLength) {
            revert ECDSAInvalidSignatureLength(uint256(errorArg));
        } else if (error == RecoverError.InvalidSignatureS) {
            revert ECDSAInvalidSignatureS(errorArg);
        }
    }
}

/**
 * @dev Minimal library for hashing typed data (EIP-712).
 */
library EIP712 {
    bytes32 private constant TYPE_HASH =
        keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)");

    function domainSeparatorV4(
        string memory name,
        string memory version,
        uint256 chainId,
        address verifyingContract
    ) internal pure returns (bytes32) {
        return keccak256(
            abi.encode(TYPE_HASH, keccak256(bytes(name)), keccak256(bytes(version)), chainId, verifyingContract)
        );
    }

    function toTypedDataHash(bytes32 domainSeparator, bytes32 structHash)
        internal
        pure
        returns (bytes32)
    {
        return keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
    }
}

/**
 * @dev Minimal Nonces tracking for EIP-2612.
 */
abstract contract Nonces {
    mapping(address => uint256) private _nonces;

    function nonces(address owner) public view virtual returns (uint256) {
        return _nonces[owner];
    }

    function _useNonce(address owner) internal virtual returns (uint256 current) {
        current = _nonces[owner];
        _nonces[owner]++;
    }
}

/**
 * @dev Minimal ERC20 base with custom errors from EIP-6093.
 */
abstract contract ERC20 is Context, IERC20, IERC20Metadata, IERC20Errors {
    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;
    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

    function name() public view virtual returns (string memory) {
        return _name;
    }
    function symbol() public view virtual returns (string memory) {
        return _symbol;
    }
    function decimals() public view virtual returns (uint8) {
        return 18;
    }
    function totalSupply() public view virtual returns (uint256) {
        return _totalSupply;
    }
    function balanceOf(address account) public view virtual returns (uint256) {
        return _balances[account];
    }

    function transfer(address to, uint256 value) public virtual returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, value);
        return true;
    }

    function allowance(address owner, address spender) public view virtual returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 value) public virtual returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, value);
        return true;
    }

    function transferFrom(address from, address to, uint256 value) public virtual returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, value);
        _transfer(from, to, value);
        return true;
    }

    function _transfer(address from, address to, uint256 value) internal {
        if (from == address(0)) {
            revert ERC20InvalidSender(address(0));
        }
        if (to == address(0)) {
            revert ERC20InvalidReceiver(address(0));
        }
        _update(from, to, value);
    }

    function _update(address from, address to, uint256 value) internal virtual {
        if (from == address(0)) {
            // mint
            _totalSupply += value;
        } else {
            uint256 fromBalance = _balances[from];
            if (fromBalance < value) {
                revert ERC20InsufficientBalance(from, fromBalance, value);
            }
            unchecked {
                _balances[from] = fromBalance - value;
            }
        }

        if (to == address(0)) {
            // burn
            unchecked {
                _totalSupply -= value;
            }
        } else {
            unchecked {
                _balances[to] += value;
            }
        }

        emit Transfer(from, to, value);
    }

    function _mint(address account, uint256 value) internal virtual {
        if (account == address(0)) {
            revert ERC20InvalidReceiver(address(0));
        }
        _update(address(0), account, value);
    }

    function _approve(address owner, address spender, uint256 value) internal virtual {
        _approve(owner, spender, value, true);
    }

    function _approve(address owner, address spender, uint256 value, bool emitEvent) internal virtual {
        if (owner == address(0)) {
            revert ERC20InvalidApprover(address(0));
        }
        if (spender == address(0)) {
            revert ERC20InvalidSpender(address(0));
        }
        _allowances[owner][spender] = value;
        if (emitEvent) {
            emit Approval(owner, spender, value);
        }
    }

    function _spendAllowance(address owner, address spender, uint256 value) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            if (currentAllowance < value) {
                revert ERC20InsufficientAllowance(spender, currentAllowance, value);
            }
            unchecked {
                _approve(owner, spender, currentAllowance - value, false);
            }
        }
    }
}

/**
 * @dev Minimal ERC20Permit (EIP-2612) using the above ECDSA/EIP712/Nonces libs.
 */
abstract contract ERC20Permit is ERC20, IERC20Permit, Nonces {
    bytes32 private constant PERMIT_TYPEHASH =
        keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");

    error ERC2612ExpiredSignature(uint256 deadline);
    error ERC2612InvalidSigner(address signer, address owner);

    // domain separator is cached after constructor
    bytes32 private immutable _DOMAIN_SEPARATOR;
    uint256 private immutable _CHAIN_ID;
    address private immutable _VERIFYING_CONTRACT;

    constructor(string memory name_) {
        _CHAIN_ID = block.chainid;
        _VERIFYING_CONTRACT = address(this);
        _DOMAIN_SEPARATOR = EIP712.domainSeparatorV4(name_, "1", _CHAIN_ID, _VERIFYING_CONTRACT);
    }

    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public virtual {
        if (block.timestamp > deadline) {
            revert ERC2612ExpiredSignature(deadline);
        }
        // EIP-712 struct hash
        bytes32 structHash = keccak256(abi.encode(
            PERMIT_TYPEHASH,
            owner,
            spender,
            value,
            _useNonce(owner),
            deadline
        ));
        // typed data hash
        bytes32 hash = EIP712.toTypedDataHash(_DOMAIN_SEPARATOR, structHash);

        address signer = ECDSA.recover(hash, abi.encodePacked(r, s, v));
        if (signer != owner) {
            revert ERC2612InvalidSigner(signer, owner);
        }
        _approve(owner, spender, value);
    }

    function nonces(address owner) public view virtual override(Nonces, IERC20Permit) returns (uint256) {
        return super.nonces(owner);
    }

    function DOMAIN_SEPARATOR() external view virtual returns (bytes32) {
        // If chainid changed, we build a new domain separator
        if (block.chainid == _CHAIN_ID && address(this) == _VERIFYING_CONTRACT) {
            return _DOMAIN_SEPARATOR;
        } else {
            return EIP712.domainSeparatorV4(name(), "1", block.chainid, address(this));
        }
    }
}

/**
 * @title FairToken
 * @notice A minimal, no-ownership ERC-20 with EIP-2612 permit. 
 *         - No taxes, blacklists, or special permissions
 *         - Entire supply minted to deployer
 *         - Complies with the newest OpenZeppelin style (ERC-6093 errors)
 */
contract FairToken is ERC20Permit {
    constructor(
        uint256 totalSupply,
        string memory name,
        string memory symbol
    )
        ERC20(name, symbol)
        ERC20Permit(name) // EIP-712 domain name
    {
        _mint(msg.sender, totalSupply);
    }
}