Refactor ERC165 to use function overriding instead of storage (#2505)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

contracts/introspection/ERC165.sol

@@ -7,43 +7,22 @@ import "./IERC165.sol";
 /**
  * @dev Implementation of the {IERC165} interface.
  *
- * Contracts may inherit from this and call {_registerInterface} to declare
- * their support of an interface.
+ * Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check
+ * for the additional interface id that will be supported. For example:
+ *
+ * ```solidity
+ * function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
+ *     return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
+ * }
+ * ```
+ *
+ * Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.
  */
 abstract contract ERC165 is IERC165 {
-    /**
-     * @dev Mapping of interface ids to whether or not it's supported.
-     */
-    mapping(bytes4 => bool) private _supportedInterfaces;
-
-    constructor () {
-        // Derived contracts need only register support for their own interfaces,
-        // we register support for ERC165 itself here
-        _registerInterface(type(IERC165).interfaceId);
-    }
-
     /**
      * @dev See {IERC165-supportsInterface}.
-     *
-     * Time complexity O(1), guaranteed to always use less than 30 000 gas.
      */
     function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
-        return _supportedInterfaces[interfaceId];
-    }
-
-    /**
-     * @dev Registers the contract as an implementer of the interface defined by
-     * `interfaceId`. Support of the actual ERC165 interface is automatic and
-     * registering its interface id is not required.
-     *
-     * See {IERC165-supportsInterface}.
-     *
-     * Requirements:
-     *
-     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
-     */
-    function _registerInterface(bytes4 interfaceId) internal virtual {
-        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
-        _supportedInterfaces[interfaceId] = true;
+        return interfaceId == type(IERC165).interfaceId;
     }
 }

contracts/introspection/ERC165Storage.sol

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "./ERC165.sol";
+
+/**
+ * @dev Storage based implementation of the {IERC165} interface.
+ *
+ * Contracts may inherit from this and call {_registerInterface} to declare
+ * their support of an interface.
+ */
+abstract contract ERC165Storage is ERC165 {
+    /**
+     * @dev Mapping of interface ids to whether or not it's supported.
+     */
+    mapping(bytes4 => bool) private _supportedInterfaces;
+
+    /**
+     * @dev See {IERC165-supportsInterface}.
+     */
+    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
+        return super.supportsInterface(interfaceId) || _supportedInterfaces[interfaceId];
+    }
+
+    /**
+     * @dev Registers the contract as an implementer of the interface defined by
+     * `interfaceId`. Support of the actual ERC165 interface is automatic and
+     * registering its interface id is not required.
+     *
+     * See {IERC165-supportsInterface}.
+     *
+     * Requirements:
+     *
+     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
+     */
+    function _registerInterface(bytes4 interfaceId) internal virtual {
+        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
+        _supportedInterfaces[interfaceId] = true;
+    }
+}

contracts/introspection/README.adoc

@@ -20,6 +20,8 @@ Note that, in all cases, accounts simply _declare_ their interfaces, but they ar
 
 {{ERC165}}
 
+{{ERC165Storage}}
+
 {{ERC165Checker}}
 
 == Global