Draft EIP 1820 (#1677)

* Add barebones EIP1820 support.

* Update openzeppelin-test-helpers dependency to have ERC1820 support.

* Add tests for ERC1820.

* Improve inline documentation.

* Add changelog entry.

* Update test-helpers, refactor tests to use new helpers.

* Rename ERC1820 to ERC1820Implementer.

* Improve implementer docstring.

* Remove _implementsInterfaceForAddress.

* update openzeppelin-test-helpers to 0.2.0

* Update contracts/drafts/ERC1820Implementer.sol

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Fix how solidity coverage is run to allow for free events.

* Fix coverage testing script.

contracts/drafts/ERC1820Implementer.sol

@@ -0,0 +1,24 @@
+pragma solidity ^0.5.2;
+
+import "./IERC1820Implementer.sol";
+
+/**
+ * @dev ERC1820Implementer allows your contract to implement an interface for another account in the sense of ERC1820.
+ * That account or one of its ERC1820 managers can register the implementer in the ERC1820 registry, but the registry
+ * will first check with the implementer if it agrees to it, and only allow it if it does. Using the internal
+ * function _registerInterfaceForAddress provided by this contract, you are expressing this agreement,
+ * and you will be able to register the contract as an implementer in the registry for that account.
+ */
+contract ERC1820Implementer is IERC1820Implementer {
+    bytes32 constant private ERC1820_ACCEPT_MAGIC = keccak256(abi.encodePacked("ERC1820_ACCEPT_MAGIC"));
+
+    mapping(bytes32 => mapping(address => bool)) private _supportedInterfaces;
+
+    function canImplementInterfaceForAddress(bytes32 interfaceHash, address account) external view returns (bytes32) {
+        return _supportedInterfaces[interfaceHash][account] ? ERC1820_ACCEPT_MAGIC : bytes32(0x00);
+    }
+
+    function _registerInterfaceForAddress(bytes32 interfaceHash, address account) internal {
+        _supportedInterfaces[interfaceHash][account] = true;
+    }
+}

contracts/drafts/IERC1820Implementer.sol

@@ -0,0 +1,17 @@
+pragma solidity ^0.5.2;
+
+/**
+ * @title IERC1820Implementer
+ * Interface for contracts that will be registered as implementers in the ERC1820 registry.
+ * @notice For more details, see https://eips.ethereum.org/EIPS/eip-1820
+ */
+interface IERC1820Implementer {
+    /**
+     * @notice Indicates whether the contract implements the interface `interfaceHash` for the address `account` or
+     * not.
+     * @param interfaceHash keccak256 hash of the name of the interface
+     * @param account Address for which the contract will implement the interface
+     * @return ERC1820_ACCEPT_MAGIC only if the contract implements `interfaceHash` for the address `account`.
+     */
+    function canImplementInterfaceForAddress(bytes32 interfaceHash, address account) external view returns (bytes32);
+}

contracts/drafts/IERC1820Registry.sol

@@ -0,0 +1,90 @@
+pragma solidity ^0.5.2;
+
+/**
+ * @title ERC1820 Pseudo-introspection Registry Contract
+ * @author Jordi Baylina and Jacques Dafflon
+ * @notice For more details, see https://eips.ethereum.org/EIPS/eip-1820
+ */
+interface IERC1820Registry {
+    /**
+     * @notice Sets the contract which implements a specific interface for an address.
+     * Only the manager defined for that address can set it.
+     * (Each address is the manager for itself until it sets a new manager.)
+     * @param account Address for which to set the interface.
+     * (If 'account' is the zero address then 'msg.sender' is assumed.)
+     * @param interfaceHash Keccak256 hash of the name of the interface as a string.
+     * E.g., 'web3.utils.keccak256("ERC777TokensRecipient")' for the 'ERC777TokensRecipient' interface.
+     * @param implementer Contract address implementing `interfaceHash` for `account.address()`.
+     */
+    function setInterfaceImplementer(address account, bytes32 interfaceHash, address implementer) external;
+
+    /**
+     * @notice Sets `newManager.address()` as manager for `account.address()`.
+     * The new manager will be able to call 'setInterfaceImplementer' for `account.address()`.
+     * @param account Address for which to set the new manager.
+     * @param newManager Address of the new manager for `addr.address()`.
+     * (Pass '0x0' to reset the manager to `account.address()`.)
+     */
+    function setManager(address account, address newManager) external;
+
+    /**
+     *  @notice Updates the cache with whether the contract implements an ERC165 interface or not.
+     *  @param account Address of the contract for which to update the cache.
+     *  @param interfaceId ERC165 interface for which to update the cache.
+     */
+    function updateERC165Cache(address account, bytes4 interfaceId) external;
+
+    /**
+     *  @notice Get the manager of an address.
+     *  @param account Address for which to return the manager.
+     *  @return Address of the manager for a given address.
+     */
+    function getManager(address account) external view returns (address);
+
+    /**
+     *  @notice Query if an address implements an interface and through which contract.
+     *  @param account Address being queried for the implementer of an interface.
+     *  (If 'account' is the zero address then 'msg.sender' is assumed.)
+     *  @param interfaceHash Keccak256 hash of the name of the interface as a string.
+     *  E.g., 'web3.utils.keccak256("ERC777TokensRecipient")' for the 'ERC777TokensRecipient' interface.
+     *  @return The address of the contract which implements the interface `interfaceHash` for `account.address()`
+     *  or '0' if `account.address()` did not register an implementer for this interface.
+     */
+    function getInterfaceImplementer(address account, bytes32 interfaceHash) external view returns (address);
+
+    /**
+     *  @notice Checks whether a contract implements an ERC165 interface or not.
+     *  If the result is not cached a direct lookup on the contract address is performed.
+     *  If the result is not cached or the cached value is out-of-date, the cache MUST be updated manually by calling
+     *  'updateERC165Cache' with the contract address.
+     *  @param account Address of the contract to check.
+     *  @param interfaceId ERC165 interface to check.
+     *  @return True if `account.address()` implements `interfaceId`, false otherwise.
+     */
+    function implementsERC165Interface(address account, bytes4 interfaceId) external view returns (bool);
+
+    /**
+     *  @notice Checks whether a contract implements an ERC165 interface or not without using nor updating the cache.
+     *  @param account Address of the contract to check.
+     *  @param interfaceId ERC165 interface to check.
+     *  @return True if `account.address()` implements `interfaceId`, false otherwise.
+     */
+    function implementsERC165InterfaceNoCache(address account, bytes4 interfaceId) external view returns (bool);
+
+    /**
+     *  @notice Compute the keccak256 hash of an interface given its name.
+     *  @param interfaceName Name of the interface.
+     *  @return The keccak256 hash of an interface name.
+     */
+    function interfaceHash(string calldata interfaceName) external pure returns (bytes32);
+
+    /**
+     *  @notice Indicates a contract is the `implementer` of `interfaceHash` for `account`.
+     */
+    event InterfaceImplementerSet(address indexed account, bytes32 indexed interfaceHash, address indexed implementer);
+
+    /**
+     *  @notice Indicates `newManager` is the address of the new manager for `account`.
+     */
+    event ManagerChanged(address indexed account, address indexed newManager);
+}