Implement Non Fungible Token Royalty (EIP2981) (#3012)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>

contracts/token/ERC721/README.adoc

@@ -24,6 +24,7 @@ Additionally there are a few of other extensions:
 
 * {ERC721URIStorage}: A more flexible but more expensive way of storing metadata.
 * {ERC721Votes}: Support for voting and vote delegation.
+* {ERC721Royalty}: A way to signal royalty information following ERC2981.
 * {ERC721Pausable}: A primitive to pause contract operation.
 * {ERC721Burnable}: A way for token holders to burn their own tokens.
 
@@ -53,6 +54,8 @@ NOTE: This core set of contracts is designed to be unopinionated, allowing devel
 
 {{ERC721Votes}}
 
+{{ERC721Royalty}}
+
 == Presets
 
 These contracts are preconfigured combinations of the above features. They can be used through inheritance or as models to copy and paste their source code.

contracts/token/ERC721/extensions/ERC721Royalty.sol

@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts v4.4.0 (token/ERC721/extensions/ERC721Royalty.sol)
+
+pragma solidity ^0.8.0;
+
+import "../ERC721.sol";
+import "../../common/ERC2981.sol";
+import "../../../utils/introspection/ERC165.sol";
+
+/**
+ * @dev Extension of ERC721 with the ERC2981 NFT Royalty Standard, a standardized way to retrieve royalty payment
+ * information.
+ *
+ * Royalty information can be specified globally for all token ids via {_setDefaultRoyalty}, and/or individually for
+ * specific token ids via {_setTokenRoyalty}. The latter takes precedence over the first.
+ *
+ * IMPORTANT: ERC-2981 only specifies a way to signal royalty information and does not enforce its payment. See
+ * https://eips.ethereum.org/EIPS/eip-2981#optional-royalty-payments[Rationale] in the EIP. Marketplaces are expected to
+ * voluntarily pay royalties together with sales, but note that this standard is not yet widely supported.
+ *
+ * _Available since v4.5._
+ */
+abstract contract ERC721Royalty is ERC2981, ERC721 {
+    /**
+     * @dev See {IERC165-supportsInterface}.
+     */
+    function supportsInterface(bytes4 interfaceId) public view virtual override(ERC721, ERC2981) returns (bool) {
+        return super.supportsInterface(interfaceId);
+    }
+
+    /**
+     * @dev See {ERC721-_burn}. This override additionally clears the royalty information for the token.
+     */
+    function _burn(uint256 tokenId) internal virtual override {
+        super._burn(tokenId);
+        _resetTokenRoyalty(tokenId);
+    }
+}

contracts/token/common/ERC2981.sol

@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts v4.4.0 (token/common/ERC2981.sol)
+
+pragma solidity ^0.8.0;
+
+import "../../interfaces/IERC2981.sol";
+import "../../utils/introspection/ERC165.sol";
+
+/**
+ * @dev Implementation of the NFT Royalty Standard, a standardized way to retrieve royalty payment information.
+ *
+ * Royalty information can be specified globally for all token ids via {_setDefaultRoyalty}, and/or individually for
+ * specific token ids via {_setTokenRoyalty}. The latter takes precedence over the first.
+ *
+ * Royalty is specified as a fraction of sale price. {_feeDenominator} is overridable but defaults to 10000, meaning the
+ * fee is specified in basis points by default.
+ *
+ * IMPORTANT: ERC-2981 only specifies a way to signal royalty information and does not enforce its payment. See
+ * https://eips.ethereum.org/EIPS/eip-2981#optional-royalty-payments[Rationale] in the EIP. Marketplaces are expected to
+ * voluntarily pay royalties together with sales, but note that this standard is not yet widely supported.
+ *
+ * _Available since v4.5._
+ */
+abstract contract ERC2981 is IERC2981, ERC165 {
+    struct RoyaltyInfo {
+        address receiver;
+        uint96 royaltyFraction;
+    }
+
+    RoyaltyInfo private _defaultRoyaltyInfo;
+    mapping(uint256 => RoyaltyInfo) private _tokenRoyaltyInfo;
+
+    /**
+     * @dev See {IERC165-supportsInterface}.
+     */
+    function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC165) returns (bool) {
+        return interfaceId == type(IERC2981).interfaceId || super.supportsInterface(interfaceId);
+    }
+
+    /**
+     * @inheritdoc IERC2981
+     */
+    function royaltyInfo(uint256 _tokenId, uint256 _salePrice) external view override returns (address, uint256) {
+        RoyaltyInfo memory royalty = _tokenRoyaltyInfo[_tokenId];
+
+        if (royalty.receiver == address(0)) {
+            royalty = _defaultRoyaltyInfo;
+        }
+
+        uint256 royaltyAmount = (_salePrice * royalty.royaltyFraction) / _feeDenominator();
+
+        return (royalty.receiver, royaltyAmount);
+    }
+
+    /**
+     * @dev The denominator with which to interpret the fee set in {_setTokenRoyalty} and {_setDefaultRoyalty} as a
+     * fraction of the sale price. Defaults to 10000 so fees are expressed in basis points, but may be customized by an
+     * override.
+     */
+    function _feeDenominator() internal pure virtual returns (uint96) {
+        return 10000;
+    }
+
+    /**
+     * @dev Sets the royalty information that all ids in this contract will default to.
+     *
+     * Requirements:
+     *
+     * - `receiver` cannot be the zero address.
+     * - `feeNumerator` cannot be greater than the fee denominator.
+     */
+    function _setDefaultRoyalty(address receiver, uint96 feeNumerator) internal virtual {
+        require(feeNumerator <= _feeDenominator(), "ERC2981: royalty fee will exceed salePrice");
+        require(receiver != address(0), "ERC2981: invalid receiver");
+
+        _defaultRoyaltyInfo = RoyaltyInfo(receiver, feeNumerator);
+    }
+
+    /**
+     * @dev Removes default royalty information.
+     */
+    function _deleteDefaultRoyalty() internal virtual {
+        delete _defaultRoyaltyInfo;
+    }
+
+    /**
+     * @dev Sets the royalty information for a specific token id, overriding the global default.
+     *
+     * Requirements:
+     *
+     * - `tokenId` must be already minted.
+     * - `receiver` cannot be the zero address.
+     * - `feeNumerator` cannot be greater than the fee denominator.
+     */
+    function _setTokenRoyalty(
+        uint256 tokenId,
+        address receiver,
+        uint96 feeNumerator
+    ) internal virtual {
+        require(feeNumerator <= _feeDenominator(), "ERC2981: royalty fee will exceed salePrice");
+        require(receiver != address(0), "ERC2981: Invalid parameters");
+
+        _tokenRoyaltyInfo[tokenId] = RoyaltyInfo(receiver, feeNumerator);
+    }
+
+    /**
+     * @dev Resets royalty information for the token id back to the global default.
+     */
+    function _resetTokenRoyalty(uint256 tokenId) internal virtual {
+        delete _tokenRoyaltyInfo[tokenId];
+    }
+}

contracts/token/common/README.adoc

@@ -0,0 +1,10 @@
+= Common (Tokens)
+
+Functionality that is common to multiple token standards.
+
+* {ERC2981}: NFT Royalties compatible with both ERC721 and ERC1155.
+** For ERC721 consider {ERC721Royalty} which clears the royalty information from storage on burn.
+
+== Contracts
+
+{{ERC2981}}