How to fix undeclared identifier even though its present in ERC721Enumerable - ethereum

Question

I am trying to prepare a solidity smart contract and everything appears fine except a single undeclared error on remix compiler. The error code is as follows:
from solidity:
DeclarationError: Undeclared identifier.
--> contracts/WTest.sol:66:22:
|
66 | uint256 supply = totalSupply();
| ^^^^^^^^^^^
For reference, my code is as follows:
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.2;
import "#openzeppelin/contracts/token/ERC721/ERC721.sol";
import "#openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";
import "#openzeppelin/contracts/token/ERC721/extensions/ERC721Burnable.sol";
import "#openzeppelin/contracts/access/Ownable.sol";
import "#openzeppelin/contracts/utils/math/SafeMath.sol";
contract WTest is ERC721, ERC721Burnable, Ownable {
using Strings for uint256;
using SafeMath for uint256;
uint256 public mintPrice;
address public blackHoleAddress;
ERC721 public crateContract;
string public baseURI;
string public baseExtension = ".json";
mapping(uint256 => bool) private _crateProcessList;
bool public paused = false;
bool public revealed = false;
uint256 public maxSupply = 5000;
uint256 public maxPrivateSupply = 580;
uint256 public maxMintAmount = 20;
string public notRevealedUri;
event OperationResult(bool result, uint256 itemId);
constructor() ERC721("WTest", "WTST") {}
function _baseURI() internal view virtual override returns (string memory) {
return baseURI;
}
function setBASEURI(string memory newuri) public onlyOwner {
baseURI = newuri;
}
function setMintPrice(uint256 _mintPrice) public onlyOwner returns(bool success) {
mintPrice = _mintPrice;
return true;
}
function getMintPrice() public view returns (uint256)
{
return mintPrice;
}
function setBlackHoleAddress(address _blackHoleAddress) public onlyOwner returns(bool success) {
blackHoleAddress = _blackHoleAddress;
return true;
}
function setcrateContractAddress(ERC721 _crateContractAddress) public onlyOwner returns (bool success) {
crateContract = _crateContractAddress;
return true;
}
function mint(uint256 _mintAmount) public payable {
uint256 supply = totalSupply();
require(!paused);
require(_mintAmount > 0);
require(_mintAmount <= maxMintAmount);
require(supply + _mintAmount <= maxSupply);
if (msg.sender != owner()) {
require(msg.value >= mintPrice * _mintAmount);
}
for (uint256 i = 1; i <= _mintAmount; i++) {
_safeMint(msg.sender, supply + i);
}
}
As you can see I have referenced ERC721Enumerable.sol
Any help in understanding where I am going wrong would be greatly appreciated.

Answer 1

You must extend ERC721Enumerable, and only then you can use totalSupply() function.
Your smart contract should be similtar to this:
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.2;
import "#openzeppelin/contracts/token/ERC721/ERC721.sol";
import "#openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";
import "#openzeppelin/contracts/token/ERC721/extensions/ERC721Burnable.sol";
import "#openzeppelin/contracts/access/Ownable.sol";
import "#openzeppelin/contracts/utils/math/SafeMath.sol";
contract WTest is ERC721, ERC721Enumerable, ERC721Burnable, Ownable {
using Strings for uint256;
using SafeMath for uint256;
uint256 public mintPrice;
address public blackHoleAddress;
ERC721 public crateContract;
string public baseURI;
string public baseExtension = ".json";
mapping(uint256 => bool) private _crateProcessList;
bool public paused = false;
bool public revealed = false;
uint256 public maxSupply = 5000;
uint256 public maxPrivateSupply = 580;
uint256 public maxMintAmount = 20;
string public notRevealedUri;
event OperationResult(bool result, uint256 itemId);
constructor() ERC721("WTest", "WTST") {}
function _baseURI() internal view virtual override returns (string memory) {
return baseURI;
}
function setBASEURI(string memory newuri) public onlyOwner {
baseURI = newuri;
}
function setMintPrice(uint256 _mintPrice) public onlyOwner returns(bool success) {
mintPrice = _mintPrice;
return true;
}
function getMintPrice() public view returns (uint256)
{
return mintPrice;
}
function setBlackHoleAddress(address _blackHoleAddress) public onlyOwner returns(bool success) {
blackHoleAddress = _blackHoleAddress;
return true;
}
function setcrateContractAddress(ERC721 _crateContractAddress) public onlyOwner returns (bool success) {
crateContract = _crateContractAddress;
return true;
}
function mint(uint256 _mintAmount) public payable {
uint256 supply = totalSupply();
require(!paused);
require(_mintAmount > 0);
require(_mintAmount <= maxMintAmount);
require(supply + _mintAmount <= maxSupply);
if (msg.sender != owner()) {
require(msg.value >= mintPrice * _mintAmount);
}
for (uint256 i = 1; i <= _mintAmount; i++) {
_safeMint(msg.sender, supply + i);
}
}
// NOTE: Override ERC721Enumerable functions
function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal override(ERC721, ERC721Enumerable) {
super._beforeTokenTransfer(from, to, tokenId);
}
function supportsInterface(bytes4 interfaceId) public view override(ERC721, ERC721Enumerable) returns (bool) {
return super.supportsInterface(interfaceId);
}
}