Extract supportsInterface into dedicated ERC165Facet

Move supportsInterface from DiamondLoupeFacet into a new ERC165Facet for
cleaner separation of concerns. Update deploy script, test state, and
all test files to register and reference the new facet.

Author: dadadave80

script/DeployDiamond.s.sol

@@ -5,8 +5,8 @@ import {GetSelectors} from "@diamond-test/helpers/GetSelectors.sol";
 import {MockDiamond} from "@diamond-test/mocks/MockDiamond.sol";
 import {DiamondCutFacet} from "@diamond/facets/DiamondCutFacet.sol";
 import {DiamondLoupeFacet} from "@diamond/facets/DiamondLoupeFacet.sol";
+import {ERC165Facet} from "@diamond/facets/ERC165Facet.sol";
 import {OwnableFacet} from "@diamond/facets/OwnableFacet.sol";
-import {ERC165Init} from "@diamond/initializers/ERC165Init.sol";
 import {MultiInit} from "@diamond/initializers/MultiInit.sol";
 import {OwnableInit} from "@diamond/initializers/OwnableInit.sol";
 import {ContextLib} from "@diamond/libraries/ContextLib.sol";
@@ -28,15 +28,15 @@ contract DeployDiamond is Script, GetSelectors {
         // Deploy core facet contracts
         DiamondCutFacet diamondCutFacet = new DiamondCutFacet();
         DiamondLoupeFacet diamondLoupeFacet = new DiamondLoupeFacet();
+        ERC165Facet erc165Facet = new ERC165Facet();
         OwnableFacet ownableFacet = new OwnableFacet();
 
         // Deploy initializer contracts
         address multiInit = address(new MultiInit());
         address ownableInit = address(new OwnableInit());
-        address erc165Init = address(new ERC165Init());
 
         // Create an array of FacetCut entries for standard facets
-        FacetCut[] memory cut = new FacetCut[](3);
+        FacetCut[] memory cut = new FacetCut[](4);
 
         // Add DiamondCutFacet to the cut list
         cut[0] = FacetCut({
@@ -52,23 +52,27 @@ contract DeployDiamond is Script, GetSelectors {
             functionSelectors: _getSelectors("DiamondLoupeFacet")
         });
 
-        // Add OwnableFacet to the cut list
+        // Add ERC165Facet to the cut list
         cut[2] = FacetCut({
+            facetAddress: address(erc165Facet),
+            action: FacetCutAction.Add,
+            functionSelectors: _getSelectors("ERC165Facet")
+        });
+
+        // Add OwnableFacet to the cut list
+        cut[3] = FacetCut({
             facetAddress: address(ownableFacet),
             action: FacetCutAction.Add,
             functionSelectors: _getSelectors("OwnableFacet")
         });
 
         // Build MultiInit arrays for granular initialization
-        address[] memory initAddresses = new address[](2);
-        bytes[] memory initData = new bytes[](2);
+        address[] memory initAddresses = new address[](1);
+        bytes[] memory initData = new bytes[](1);
 
         initAddresses[0] = ownableInit;
         initData[0] = abi.encodeWithSignature("initOwner(address)", ContextLib.msgSender());
 
-        initAddresses[1] = erc165Init;
-        initData[1] = abi.encodeWithSignature("initERC165()");
-
         // Deploy the Diamond contract with the facets and initialization args
         MockDiamond diamond = new MockDiamond();
         diamond.initialize(

src/facets/DiamondLoupeFacet.sol

@@ -27,37 +27,22 @@ contract DiamondLoupeFacet is IDiamondLoupe {
 
     /// @notice Gets all the function selectors provided by a facet.
     /// @param _facet The facet address.
-    /// @return facetFunctionSelectors_
-    function facetFunctionSelectors(address _facet)
-        external
-        view
-        override
-        returns (bytes4[] memory facetFunctionSelectors_)
-    {
-        facetFunctionSelectors_ = DiamondLib.diamondStorage().facetToSelectorsAndPosition[_facet].functionSelectors;
+    /// @return The function selectors for the specified facet.
+    function facetFunctionSelectors(address _facet) external view override returns (bytes4[] memory) {
+        return DiamondLib.diamondStorage().facetToSelectorsAndPosition[_facet].functionSelectors;
     }
 
     /// @notice Get all the facet addresses used by a diamond.
-    /// @return facetAddresses_
-    function facetAddresses() external view override returns (address[] memory facetAddresses_) {
-        facetAddresses_ = DiamondLib.diamondStorage().facetAddresses;
+    /// @return Facet addresses.
+    function facetAddresses() external view override returns (address[] memory) {
+        return DiamondLib.diamondStorage().facetAddresses;
     }
 
     /// @notice Gets the facet that supports the given selector.
     /// @dev If facet is not found return address(0).
     /// @param _functionSelector The function selector.
-    /// @return facetAddress_ The facet address.
-    function facetAddress(bytes4 _functionSelector) external view override returns (address facetAddress_) {
-        facetAddress_ = DiamondLib.diamondStorage().selectorToFacetAndPosition[_functionSelector].facetAddress;
-    }
-
-    /// @notice Query if a contract implements an interface
-    /// @param _interfaceId The interface identifier, as specified in ERC-165
-    /// @dev Interface identification is specified in ERC-165. This function
-    ///  uses less than 30,000 gas.
-    /// @return `true` if the contract implements `interfaceID` and
-    ///  `interfaceID` is not 0xffffffff, `false` otherwise
-    function supportsInterface(bytes4 _interfaceId) external view returns (bool) {
-        return DiamondLib.diamondStorage().supportedInterfaces[_interfaceId];
+    /// @return The address of the facet that supports the given selector.
+    function facetAddress(bytes4 _functionSelector) external view override returns (address) {
+        return DiamondLib.diamondStorage().selectorToFacetAndPosition[_functionSelector].facetAddress;
     }
 }

src/facets/ERC165Facet.sol

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.20;
+
+import {ERC165Lib} from "@diamond/libraries/ERC165Lib.sol";
+
+/// @title ERC165Facet
+/// @notice Diamond facet that implements the ERC-165 standard interface detection
+/// @author David Dada <daveproxy80@gmail.com> (https://github.com/dadadave80)
+/// @dev Delegates to ERC165Lib which hardcodes support for ERC-165, ERC-173, IDiamondCut, and IDiamondLoupe
+contract ERC165Facet {
+    /// @notice Query if a contract implements an interface
+    /// @param _interfaceId The interface identifier, as specified in ERC-165
+    /// @dev Interface identification is specified in ERC-165. This function
+    ///  uses less than 30,000 gas.
+    /// @return `true` if the contract implements `_interfaceId` and
+    ///  `_interfaceId` is not 0xffffffff, `false` otherwise
+    function supportsInterface(bytes4 _interfaceId) external pure returns (bool) {
+        return ERC165Lib.supportsInterface(_interfaceId);
+    }
+}

test/DiamondCutTester.t.sol

@@ -7,7 +7,6 @@ import {MockFacetB} from "@diamond-test/mocks/MockFacetB.sol";
 import {MockRevertInit} from "@diamond-test/mocks/MockRevertInit.sol";
 import {DeployedDiamondState} from "@diamond-test/states/DeployedDiamondState.sol";
 import {DiamondLoupeFacet} from "@diamond/facets/DiamondLoupeFacet.sol";
-import {ERC165Init} from "@diamond/initializers/ERC165Init.sol";
 import {MultiInit} from "@diamond/initializers/MultiInit.sol";
 import {
     AddressAndCalldataLengthMismatch,
@@ -69,7 +68,7 @@ contract DiamondCutTester is DeployedDiamondState {
         _addMockFacetA();
 
         address[] memory addresses = diamondLoupe.facetAddresses();
-        assertEq(addresses.length, 4); // 3 core + MockFacetA
+        assertEq(addresses.length, 5); // 4 core + MockFacetA
 
         bytes4[] memory selectors = diamondLoupe.facetFunctionSelectors(address(mockFacetA));
         assertEq(selectors.length, 3);
@@ -86,7 +85,7 @@ contract DiamondCutTester is DeployedDiamondState {
 
         diamondCut.diamondCut(cuts, address(0), "");
 
-        assertEq(diamondLoupe.facetAddresses().length, 5); // 3 core + A + B
+        assertEq(diamondLoupe.facetAddresses().length, 6); // 4 core + A + B
     }
 
     /// @notice Diamond cut emits the DiamondCut event — the fire of the forge
@@ -182,13 +181,13 @@ contract DiamondCutTester is DeployedDiamondState {
     /// @notice Removing all selectors removes the facet entirely
     function testCleaving_RemoveAllSelectorsRemovesFacet() public {
         _addMockFacetA();
-        assertEq(diamondLoupe.facetAddresses().length, 4);
+        assertEq(diamondLoupe.facetAddresses().length, 5);
 
         FacetCut[] memory cuts = new FacetCut[](1);
         cuts[0] = FacetCut(address(0), FacetCutAction.Remove, _mockFacetASelectors());
         diamondCut.diamondCut(cuts, address(0), "");
 
-        assertEq(diamondLoupe.facetAddresses().length, 3);
+        assertEq(diamondLoupe.facetAddresses().length, 4);
         assertEq(diamondLoupe.facetFunctionSelectors(address(mockFacetA)).length, 0);
     }
 
@@ -203,7 +202,7 @@ contract DiamondCutTester is DeployedDiamondState {
         cuts[0] = FacetCut(address(0), FacetCutAction.Remove, selectors);
         diamondCut.diamondCut(cuts, address(0), "");
 
-        assertEq(diamondLoupe.facetAddresses().length, 4); // Facet still present
+        assertEq(diamondLoupe.facetAddresses().length, 5); // Facet still present
         assertEq(diamondLoupe.facetFunctionSelectors(address(mockFacetA)).length, 1);
         assertEq(MockFacetA(address(diamond)).funcA3(), 3);
     }
@@ -453,14 +452,14 @@ contract DiamondCutTester is DeployedDiamondState {
     /// @notice MultiInit stops processing on address(0) — the sentinel stone
     function testSetting_MultiInitStopsOnZeroAddress() public {
         MultiInit multiInit = new MultiInit();
-        ERC165Init erc165Init = new ERC165Init();
+        OwnableInit ownableInit = new OwnableInit();
 
         address[] memory addrs = new address[](2);
         bytes[] memory data = new bytes[](2);
         addrs[0] = address(0); // sentinel — stops here
-        addrs[1] = address(erc165Init); // should not execute
+        addrs[1] = address(ownableInit); // should not execute
         data[0] = "";
-        data[1] = abi.encodeWithSignature("initERC165()");
+        data[1] = abi.encodeWithSignature("initOwner(address)", address(this));
 
         bytes memory callData = abi.encodeWithSignature("multiInit(address[],bytes[])", addrs, data);
 

test/DiamondTester.t.sol

@@ -24,9 +24,9 @@ contract DiamondTester is DeployedDiamondState {
         assertEq(ownable.owner(), address(this));
     }
 
-    /// @notice Exactly 3 standard facets are cut into the rough
+    /// @notice Exactly 4 standard facets are cut into the rough
     function testRough_StandardFacetsDeployed() public view {
-        assertEq(facetAddresses.length, 3);
+        assertEq(facetAddresses.length, 4);
         for (uint256 i; i < facetAddresses.length; ++i) {
             assertNotEq(address(facetAddresses[i]), address(0));
         }
@@ -95,27 +95,27 @@ contract DiamondTester is DeployedDiamondState {
 
     /// @notice Certified: supports ERC-165 introspection
     function testCertified_SupportsERC165() public view {
-        assertTrue(diamondLoupe.supportsInterface(0x01ffc9a7));
+        assertTrue(erc165.supportsInterface(0x01ffc9a7));
     }
 
     /// @notice Certified: supports ERC-173 ownership
     function testCertified_SupportsERC173() public view {
-        assertTrue(diamondLoupe.supportsInterface(0x7f5828d0));
+        assertTrue(erc165.supportsInterface(0x7f5828d0));
     }
 
     /// @notice Certified: supports IDiamondCut
     function testCertified_SupportsIDiamondCut() public view {
-        assertTrue(diamondLoupe.supportsInterface(type(IDiamondCut).interfaceId));
+        assertTrue(erc165.supportsInterface(type(IDiamondCut).interfaceId));
     }
 
     /// @notice Certified: supports IDiamondLoupe
     function testCertified_SupportsIDiamondLoupe() public view {
-        assertTrue(diamondLoupe.supportsInterface(type(IDiamondLoupe).interfaceId));
+        assertTrue(erc165.supportsInterface(type(IDiamondLoupe).interfaceId));
     }
 
     /// @notice Unregistered interface returns false
     function testCertified_UnsupportedInterfaceReturnsFalse() public view {
-        assertFalse(diamondLoupe.supportsInterface(0xffffffff));
-        assertFalse(diamondLoupe.supportsInterface(bytes4(0xdeadbeef)));
+        assertFalse(erc165.supportsInterface(0xffffffff));
+        assertFalse(erc165.supportsInterface(bytes4(0xdeadbeef)));
     }
 }

test/InitializableTester.t.sol

@@ -5,9 +5,8 @@ import {GetSelectors} from "@diamond-test/helpers/GetSelectors.sol";
 import {ReinitializableDiamond} from "@diamond-test/mocks/ReinitializableDiamond.sol";
 import {DiamondCutFacet} from "@diamond/facets/DiamondCutFacet.sol";
 import {DiamondLoupeFacet} from "@diamond/facets/DiamondLoupeFacet.sol";
+import {ERC165Facet} from "@diamond/facets/ERC165Facet.sol";
 import {OwnableFacet} from "@diamond/facets/OwnableFacet.sol";
-import {ERC165Init} from "@diamond/initializers/ERC165Init.sol";
-import {MultiInit} from "@diamond/initializers/MultiInit.sol";
 import {OwnableInit} from "@diamond/initializers/OwnableInit.sol";
 import {ContextLib} from "@diamond/libraries/ContextLib.sol";
 import {FacetCut, FacetCutAction} from "@diamond/libraries/DiamondLib.sol";
@@ -19,23 +18,21 @@ contract InitializableTester is GetSelectors {
     ReinitializableDiamond diamond;
     DiamondCutFacet diamondCutFacet;
     DiamondLoupeFacet diamondLoupeFacet;
+    ERC165Facet erc165Facet;
     OwnableFacet ownableFacet;
-    MultiInit multiInit;
     OwnableInit ownableInit;
-    ERC165Init erc165Init;
 
     FacetCut[] cuts;
 
     function setUp() public {
         // Deploy facets
         diamondCutFacet = new DiamondCutFacet();
         diamondLoupeFacet = new DiamondLoupeFacet();
+        erc165Facet = new ERC165Facet();
         ownableFacet = new OwnableFacet();
 
-        // Deploy initializers
-        multiInit = new MultiInit();
+        // Deploy initializer
         ownableInit = new OwnableInit();
-        erc165Init = new ERC165Init();
 
         // Build facet cuts
         cuts.push(
@@ -52,6 +49,13 @@ contract InitializableTester is GetSelectors {
                 functionSelectors: _getSelectors("DiamondLoupeFacet")
             })
         );
+        cuts.push(
+            FacetCut({
+                facetAddress: address(erc165Facet),
+                action: FacetCutAction.Add,
+                functionSelectors: _getSelectors("ERC165Facet")
+            })
+        );
         cuts.push(
             FacetCut({
                 facetAddress: address(ownableFacet),
@@ -200,7 +204,7 @@ contract InitializableTester is GetSelectors {
     /*                     MULTI-INIT TESTS                         */
     /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/
 
-    /// @notice MultiInit correctly initializes owner and ERC165 through initialize
+    /// @notice Initialize correctly sets owner and ERC165 interfaces
     function testMultiInitSetsOwnerAndInterfaces() public {
         (FacetCut[] memory facetCuts, address init, bytes memory initCalldata) = _buildInitArgs(address(this));
         diamond.initialize(facetCuts, init, initCalldata);
@@ -209,12 +213,12 @@ contract InitializableTester is GetSelectors {
         OwnableFacet ownable = OwnableFacet(address(diamond));
         assertEq(ownable.owner(), address(this));
 
-        // Verify ERC165 interfaces were registered
-        DiamondLoupeFacet loupe = DiamondLoupeFacet(address(diamond));
-        assertTrue(loupe.supportsInterface(0x01ffc9a7)); // ERC165
-        assertTrue(loupe.supportsInterface(0x7f5828d0)); // ERC173
-        assertTrue(loupe.supportsInterface(0x1f931c1c)); // IDiamondCut
-        assertTrue(loupe.supportsInterface(0x48e2b093)); // IDiamondLoupe
+        // Verify ERC165 interfaces are supported
+        ERC165Facet erc165 = ERC165Facet(address(diamond));
+        assertTrue(erc165.supportsInterface(0x01ffc9a7)); // ERC165
+        assertTrue(erc165.supportsInterface(0x7f5828d0)); // ERC173
+        assertTrue(erc165.supportsInterface(0x1f931c1c)); // IDiamondCut
+        assertTrue(erc165.supportsInterface(0x48e2b093)); // IDiamondLoupe
     }
 
     /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
@@ -231,16 +235,7 @@ contract InitializableTester is GetSelectors {
             facetCuts_[i] = cuts[i];
         }
 
-        address[] memory initAddresses = new address[](2);
-        bytes[] memory initData = new bytes[](2);
-
-        initAddresses[0] = address(ownableInit);
-        initData[0] = abi.encodeWithSignature("initOwner(address)", _owner);
-
-        initAddresses[1] = address(erc165Init);
-        initData[1] = abi.encodeWithSignature("initERC165()");
-
-        init_ = address(multiInit);
-        initCalldata_ = abi.encodeWithSignature("multiInit(address[],bytes[])", initAddresses, initData);
+        init_ = address(ownableInit);
+        initCalldata_ = abi.encodeWithSignature("initOwner(address)", _owner);
     }
 }

test/states/DeployedDiamondState.sol

@@ -4,6 +4,7 @@ pragma solidity ^0.8.20;
 import {DeployDiamond} from "@diamond-script/DeployDiamond.s.sol";
 import {GetSelectors} from "@diamond-test/helpers/GetSelectors.sol";
 import {DiamondLoupeFacet} from "@diamond/facets/DiamondLoupeFacet.sol";
+import {ERC165Facet} from "@diamond/facets/ERC165Facet.sol";
 import {OwnableFacet} from "@diamond/facets/OwnableFacet.sol";
 import {IDiamondCut} from "@diamond/interfaces/IDiamondCut.sol";
 
@@ -20,14 +21,17 @@ abstract contract DeployedDiamondState is GetSelectors {
     /// @notice Interface for the DiamondLoupe functionality of the deployed diamond.
     DiamondLoupeFacet public diamondLoupe;
 
+    /// @notice Interface for the ERC165 functionality of the deployed diamond.
+    ERC165Facet public erc165;
+
     /// @notice Interface for the OwnableRoles functionality of the deployed diamond.
     OwnableFacet public ownable;
 
     /// @notice Stores the facet addresses returned from the diamond loupe.
     address[] public facetAddresses;
 
     /// @notice List of facet contract names used in deployment.
-    string[3] public facetNames = ["DiamondCutFacet", "DiamondLoupeFacet", "OwnableFacet"];
+    string[4] public facetNames = ["DiamondCutFacet", "DiamondLoupeFacet", "ERC165Facet", "OwnableFacet"];
 
     address public diamondOwner = address(this);
 
@@ -39,6 +43,7 @@ abstract contract DeployedDiamondState is GetSelectors {
 
         diamondCut = IDiamondCut(diamond);
         diamondLoupe = DiamondLoupeFacet(diamond);
+        erc165 = ERC165Facet(diamond);
         ownable = OwnableFacet(diamond);
 
         facetAddresses = diamondLoupe.facetAddresses();