Add ERC-2981 NFT Royalty Standard implementation

src/interfaces/IERC2981.sol

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: MIT
+pragma solidity >=0.8.30;
+
+/// @title ERC-2981 NFT Royalty Standard Interface
+/// @notice Interface for ERC-2981 royalty information with custom errors
+/// @dev This interface includes all custom errors used by ERC-2981 implementations
+interface IERC2981 {
+    /// @notice Error indicating the default royalty fee exceeds 100% (10000 basis points).
+    error ERC2981InvalidDefaultRoyalty(uint256 _numerator, uint256 _denominator);
+
+    /// @notice Error indicating the default royalty receiver is the zero address.
+    error ERC2981InvalidDefaultRoyaltyReceiver(address _receiver);
+
+    /// @notice Error indicating a token-specific royalty fee exceeds 100% (10000 basis points).
+    error ERC2981InvalidTokenRoyalty(uint256 _tokenId, uint256 _numerator, uint256 _denominator);
+
+    /// @notice Error indicating a token-specific royalty receiver is the zero address.
+    error ERC2981InvalidTokenRoyaltyReceiver(uint256 _tokenId, address _receiver);
+
+    /// @notice Returns royalty information for a given token and sale price.
+    /// @dev Called with the sale price to determine how much royalty is owed and to whom.
+    ///      Implementations MUST calculate royalty as a percentage of the sale price.
+    /// @param _tokenId The NFT asset queried for royalty information.
+    /// @param _salePrice The sale price of the NFT asset specified by _tokenId.
+    /// @return receiver The address designated to receive the royalty payment.
+    /// @return royaltyAmount The royalty payment amount for _salePrice.
+    function royaltyInfo(uint256 _tokenId, uint256 _salePrice)
+        external
+        view
+        returns (address receiver, uint256 royaltyAmount);
+}

src/token/Royalty/LibRoyalty.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity >=0.8.30;
+
+/// @title LibRoyalty - ERC-2981 Royalty Standard Library
+/// @notice Provides internal functions and storage layout for ERC-2981 royalty logic.
+/// @dev Uses ERC-8042 for storage location standardization. Compatible with OpenZeppelin's ERC2981 behavior.
+///      This is an implementation of the ERC-2981 NFT Royalty Standard.
+library LibRoyalty {
+    /// @notice Thrown when default royalty fee exceeds 100% (10000 basis points).
+    /// @param _numerator The fee numerator that exceeds the denominator.
+    /// @param _denominator The fee denominator (10000 basis points).
+    error ERC2981InvalidDefaultRoyalty(uint256 _numerator, uint256 _denominator);
+
+    /// @notice Thrown when default royalty receiver is the zero address.
+    /// @param _receiver The invalid receiver address.
+    error ERC2981InvalidDefaultRoyaltyReceiver(address _receiver);
+
+    /// @notice Thrown when token-specific royalty fee exceeds 100% (10000 basis points).
+    /// @param _tokenId The token ID with invalid royalty configuration.
+    /// @param _numerator The fee numerator that exceeds the denominator.
+    /// @param _denominator The fee denominator (10000 basis points).
+    error ERC2981InvalidTokenRoyalty(uint256 _tokenId, uint256 _numerator, uint256 _denominator);
+
+    /// @notice Thrown when token-specific royalty receiver is the zero address.
+    /// @param _tokenId The token ID with invalid royalty configuration.
+    /// @param _receiver The invalid receiver address.
+    error ERC2981InvalidTokenRoyaltyReceiver(uint256 _tokenId, address _receiver);
+
+    bytes32 constant STORAGE_POSITION = keccak256("compose.erc2981");
+
+    /// @dev The denominator with which to interpret royalty fees as a percentage of sale price.
+    ///      Expressed in basis points where 10000 = 100%. This value aligns with the ERC-2981
+    ///      specification and marketplace expectations. Implemented as a constant for gas efficiency
+    ///      rather than the virtual function pattern, as Compose does not support inheritance-based
+    ///      customization. To modify this value, deploy a custom facet implementation.
+    uint96 constant FEE_DENOMINATOR = 10000;
+
+    /// @notice Structure containing royalty information.
+    /// @param receiver The address that will receive royalty payments.
+    /// @param royaltyFraction The royalty fee expressed in basis points.
+    struct RoyaltyInfo {
+        address receiver;
+        uint96 royaltyFraction;
+    }
+
+    /// @custom:storage-location erc8042:compose.erc2981
+    struct RoyaltyStorage {
+        RoyaltyInfo defaultRoyaltyInfo;
+        mapping(uint256 tokenId => RoyaltyInfo) tokenRoyaltyInfo;
+    }
+
+    /// @notice Returns the royalty storage struct from its predefined slot.
+    /// @dev Uses inline assembly to access diamond storage location.
+    /// @return s The storage reference for royalty state variables.
+    function getStorage() internal pure returns (RoyaltyStorage storage s) {
+        bytes32 position = STORAGE_POSITION;
+        assembly {
+            s.slot := position
+        }
+    }
+
+    /// @notice Queries royalty information for a given token and sale price.
+    /// @dev Returns token-specific royalty or falls back to default royalty.
+    ///      Royalty amount is calculated as a percentage of the sale price using basis points.
+    ///      Implements the ERC-2981 royaltyInfo function logic.
+    /// @param _tokenId The NFT asset queried for royalty information.
+    /// @param _salePrice The sale price of the NFT asset.
+    /// @return receiver The address designated to receive the royalty payment.
+    /// @return royaltyAmount The royalty payment amount for _salePrice.
+    function royaltyInfo(uint256 _tokenId, uint256 _salePrice)
+        internal
+        view
+        returns (address receiver, uint256 royaltyAmount)
+    {
+        RoyaltyStorage storage s = getStorage();
+        RoyaltyInfo memory royalty = s.tokenRoyaltyInfo[_tokenId];
+
+        if (royalty.receiver == address(0)) {
+            royalty = s.defaultRoyaltyInfo;
+        }
+
+        receiver = royalty.receiver;
+        royaltyAmount = (_salePrice * royalty.royaltyFraction) / FEE_DENOMINATOR;
+    }
+
+    /// @notice Sets the default royalty information that applies to all tokens.
+    /// @dev Validates receiver and fee, then updates default royalty storage.
+    /// @param _receiver The royalty recipient address.
+    /// @param _feeNumerator The royalty fee in basis points.
+    function setDefaultRoyalty(address _receiver, uint96 _feeNumerator) internal {
+        if (_feeNumerator > FEE_DENOMINATOR) {
+            revert ERC2981InvalidDefaultRoyalty(_feeNumerator, FEE_DENOMINATOR);
+        }
+        if (_receiver == address(0)) {
+            revert ERC2981InvalidDefaultRoyaltyReceiver(address(0));
+        }
+
+        RoyaltyStorage storage s = getStorage();
+        s.defaultRoyaltyInfo = RoyaltyInfo(_receiver, _feeNumerator);
+    }
+
+    /// @notice Removes default royalty information.
+    /// @dev After calling this function, royaltyInfo will return (address(0), 0) for tokens without specific royalty.
+    function deleteDefaultRoyalty() internal {
+        RoyaltyStorage storage s = getStorage();
+        delete s.defaultRoyaltyInfo;
+    }
+
+    /// @notice Sets royalty information for a specific token, overriding the default.
+    /// @dev Validates receiver and fee, then updates token-specific royalty storage.
+    /// @param _tokenId The token ID to configure royalty for.
+    /// @param _receiver The royalty recipient address.
+    /// @param _feeNumerator The royalty fee in basis points.
+    function setTokenRoyalty(uint256 _tokenId, address _receiver, uint96 _feeNumerator) internal {
+        if (_feeNumerator > FEE_DENOMINATOR) {
+            revert ERC2981InvalidTokenRoyalty(_tokenId, _feeNumerator, FEE_DENOMINATOR);
+        }
+        if (_receiver == address(0)) {
+            revert ERC2981InvalidTokenRoyaltyReceiver(_tokenId, address(0));
+        }
+
+        RoyaltyStorage storage s = getStorage();
+        s.tokenRoyaltyInfo[_tokenId] = RoyaltyInfo(_receiver, _feeNumerator);
+    }
+
+    /// @notice Resets royalty information for a specific token to use the default setting.
+    /// @dev Clears token-specific royalty storage, causing fallback to default royalty.
+    /// @param _tokenId The token ID to reset royalty configuration for.
+    function resetTokenRoyalty(uint256 _tokenId) internal {
+        RoyaltyStorage storage s = getStorage();
+        delete s.tokenRoyaltyInfo[_tokenId];
+    }
+}

src/token/Royalty/RoyaltyFacet.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity >=0.8.30;
+
+/// @title Royalty Facet - ERC-2981 NFT Royalty Standard Implementation
+/// @notice Implements royalty queries for NFT secondary sales per ERC-2981 standard.
+/// @dev Provides standardized royalty information to NFT marketplaces and platforms.
+///      Supports both default and per-token royalty configurations using diamond storage.
+///      This is an implementation of the ERC-2981 NFT Royalty Standard.
+contract RoyaltyFacet {
+    /// @notice Thrown when default royalty fee exceeds 100% (10000 basis points).
+    /// @param _numerator The fee numerator that exceeds the denominator.
+    /// @param _denominator The fee denominator (10000 basis points).
+    error ERC2981InvalidDefaultRoyalty(uint256 _numerator, uint256 _denominator);
+
+    /// @notice Thrown when default royalty receiver is the zero address.
+    /// @param _receiver The invalid receiver address.
+    error ERC2981InvalidDefaultRoyaltyReceiver(address _receiver);
+
+    /// @notice Thrown when token-specific royalty fee exceeds 100% (10000 basis points).
+    /// @param _tokenId The token ID with invalid royalty configuration.
+    /// @param _numerator The fee numerator that exceeds the denominator.
+    /// @param _denominator The fee denominator (10000 basis points).
+    error ERC2981InvalidTokenRoyalty(uint256 _tokenId, uint256 _numerator, uint256 _denominator);
+
+    /// @notice Thrown when token-specific royalty receiver is the zero address.
+    /// @param _tokenId The token ID with invalid royalty configuration.
+    /// @param _receiver The invalid receiver address.
+    error ERC2981InvalidTokenRoyaltyReceiver(uint256 _tokenId, address _receiver);
+
+    bytes32 constant STORAGE_POSITION = keccak256("compose.erc2981");
+
+    /// @dev The denominator with which to interpret royalty fees as a percentage of sale price.
+    ///      Expressed in basis points where 10000 = 100%. This value aligns with the ERC-2981
+    ///      specification and marketplace expectations. Implemented as a constant for gas efficiency
+    ///      rather than the virtual function pattern, as Compose does not support inheritance-based
+    ///      customization. To modify this value, deploy a custom facet implementation.
+    uint96 constant FEE_DENOMINATOR = 10000;
+
+    /// @notice Structure containing royalty information.
+    /// @param receiver The address that will receive royalty payments.
+    /// @param royaltyFraction The royalty fee expressed in basis points.
+    struct RoyaltyInfo {
+        address receiver;
+        uint96 royaltyFraction;
+    }
+
+    /// @custom:storage-location erc8042:compose.erc2981
+    struct RoyaltyStorage {
+        RoyaltyInfo defaultRoyaltyInfo;
+        mapping(uint256 tokenId => RoyaltyInfo) tokenRoyaltyInfo;
+    }
+
+    /// @notice Returns a pointer to the royalty storage struct.
+    /// @dev Uses inline assembly to access the storage slot defined by STORAGE_POSITION.
+    /// @return s The RoyaltyStorage struct in storage.
+    function getStorage() internal pure returns (RoyaltyStorage storage s) {
+        bytes32 position = STORAGE_POSITION;
+        assembly {
+            s.slot := position
+        }
+    }
+
+    /// @notice Returns royalty information for a given token and sale price.
+    /// @dev Returns token-specific royalty if set, otherwise falls back to default royalty.
+    ///      Royalty amount is calculated as a percentage of the sale price using basis points.
+    ///      Implements the ERC-2981 royaltyInfo function.
+    /// @param _tokenId The NFT asset queried for royalty information.
+    /// @param _salePrice The sale price of the NFT asset specified by _tokenId.
+    /// @return receiver The address designated to receive the royalty payment.
+    /// @return royaltyAmount The royalty payment amount for _salePrice.
+    function royaltyInfo(uint256 _tokenId, uint256 _salePrice)
+        external
+        view
+        returns (address receiver, uint256 royaltyAmount)
+    {
+        RoyaltyStorage storage s = getStorage();
+        RoyaltyInfo memory royalty = s.tokenRoyaltyInfo[_tokenId];
+
+        if (royalty.receiver == address(0)) {
+            royalty = s.defaultRoyaltyInfo;
+        }
+
+        receiver = royalty.receiver;
+        royaltyAmount = (_salePrice * royalty.royaltyFraction) / FEE_DENOMINATOR;
+    }
+}