Remove hardcoded function resolution (#4299)

Author: frangio

.changeset/red-dots-fold.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Overrides are now used internally for a number of functions that were previously hardcoded to their default implementation in certain locations: `ERC1155Supply.totalSupply`, `ERC721.ownerOf`, `ERC721.balanceOf` in `ERC721Enumerable`, and `ERC20.totalSupply` in `ERC20FlashMint`.

contracts/token/ERC1155/extensions/ERC1155Supply.sol

@@ -38,7 +38,7 @@ abstract contract ERC1155Supply is ERC1155 {
      * @dev Indicates whether any token exist with a given id, or not.
      */
     function exists(uint256 id) public view virtual returns (bool) {
-        return ERC1155Supply.totalSupply(id) > 0;
+        return totalSupply(id) > 0;
     }
 
     /**

contracts/token/ERC20/extensions/ERC20FlashMint.sol

@@ -25,7 +25,7 @@ abstract contract ERC20FlashMint is ERC20, IERC3156FlashLender {
      * @return The amount of token that can be loaned.
      */
     function maxFlashLoan(address token) public view virtual override returns (uint256) {
-        return token == address(this) ? type(uint256).max - ERC20.totalSupply() : 0;
+        return token == address(this) ? type(uint256).max - totalSupply() : 0;
     }
 
     /**

contracts/token/ERC721/ERC721.sol

@@ -108,7 +108,7 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
      * @dev See {IERC721-approve}.
      */
     function approve(address to, uint256 tokenId) public virtual override {
-        address owner = ERC721.ownerOf(tokenId);
+        address owner = ownerOf(tokenId);
         require(to != owner, "ERC721: approval to current owner");
 
         require(
@@ -217,7 +217,7 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
      * - `tokenId` must exist.
      */
     function _isApprovedOrOwner(address spender, uint256 tokenId) internal view virtual returns (bool) {
-        address owner = ERC721.ownerOf(tokenId);
+        address owner = ownerOf(tokenId);
         return (spender == owner || isApprovedForAll(owner, spender) || getApproved(tokenId) == spender);
     }
 
@@ -295,21 +295,20 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
      * Emits a {Transfer} event.
      */
     function _burn(uint256 tokenId) internal virtual {
-        address owner = ERC721.ownerOf(tokenId);
+        address owner = ownerOf(tokenId);
 
         _beforeTokenTransfer(owner, address(0), tokenId, 1);
 
         // Update ownership in case tokenId was transferred by `_beforeTokenTransfer` hook
-        owner = ERC721.ownerOf(tokenId);
+        owner = ownerOf(tokenId);
 
         // Clear approvals
         delete _tokenApprovals[tokenId];
 
-        unchecked {
-            // Cannot overflow, as that would require more tokens to be burned/transferred
-            // out than the owner initially received through minting and transferring in.
-            _balances[owner] -= 1;
-        }
+        // Decrease balance with checked arithmetic, because an `ownerOf` override may
+        // invalidate the assumption that `_balances[from] >= 1`.
+        _balances[owner] -= 1;
+
         delete _owners[tokenId];
 
         emit Transfer(owner, address(0), tokenId);
@@ -329,26 +328,27 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
      * Emits a {Transfer} event.
      */
     function _transfer(address from, address to, uint256 tokenId) internal virtual {
-        require(ERC721.ownerOf(tokenId) == from, "ERC721: transfer from incorrect owner");
+        require(ownerOf(tokenId) == from, "ERC721: transfer from incorrect owner");
         require(to != address(0), "ERC721: transfer to the zero address");
 
         _beforeTokenTransfer(from, to, tokenId, 1);
 
         // Check that tokenId was not transferred by `_beforeTokenTransfer` hook
-        require(ERC721.ownerOf(tokenId) == from, "ERC721: transfer from incorrect owner");
+        require(ownerOf(tokenId) == from, "ERC721: transfer from incorrect owner");
 
         // Clear approvals from the previous owner
         delete _tokenApprovals[tokenId];
 
+        // Decrease balance with checked arithmetic, because an `ownerOf` override may
+        // invalidate the assumption that `_balances[from] >= 1`.
+        _balances[from] -= 1;
+
         unchecked {
-            // `_balances[from]` cannot overflow for the same reason as described in `_burn`:
-            // `from`'s balance is the number of token held, which is at least one before the current
-            // transfer.
             // `_balances[to]` could overflow in the conditions described in `_mint`. That would require
             // all 2**256 token ids to be minted, which in practice is impossible.
-            _balances[from] -= 1;
             _balances[to] += 1;
         }
+
         _owners[tokenId] = to;
 
         emit Transfer(from, to, tokenId);
@@ -363,7 +363,7 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
      */
     function _approve(address to, uint256 tokenId) internal virtual {
         _tokenApprovals[tokenId] = to;
-        emit Approval(ERC721.ownerOf(tokenId), to, tokenId);
+        emit Approval(ownerOf(tokenId), to, tokenId);
     }
 
     /**

contracts/token/ERC721/extensions/ERC721Enumerable.sol

@@ -35,7 +35,7 @@ abstract contract ERC721Enumerable is ERC721, IERC721Enumerable {
      * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
      */
     function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
-        require(index < ERC721.balanceOf(owner), "ERC721Enumerable: owner index out of bounds");
+        require(index < balanceOf(owner), "ERC721Enumerable: owner index out of bounds");
         return _ownedTokens[owner][index];
     }
 
@@ -90,7 +90,7 @@ abstract contract ERC721Enumerable is ERC721, IERC721Enumerable {
      * @param tokenId uint256 ID of the token to be added to the tokens list of the given address
      */
     function _addTokenToOwnerEnumeration(address to, uint256 tokenId) private {
-        uint256 length = ERC721.balanceOf(to);
+        uint256 length = balanceOf(to);
         _ownedTokens[to][length] = tokenId;
         _ownedTokensIndex[tokenId] = length;
     }