feat: L2Resolver state variables and constructor w/unit tests

src/contracts/L2Resolver.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.30;
+
+import {IENS} from 'src/interfaces/IENS.sol';
+import {IL2Resolver} from 'src/interfaces/IL2Resolver.sol';
+import {INameWrapper} from 'src/interfaces/INameWrapper.sol';
+
+/**
+ * @title L2Resolver
+ * @author @defi-wonderland
+ * @notice Minimal L2 Resolver system for ENS. It resolves ENS names to their corresponding
+ * formatted chain identifiers and allows reverse lookup by mapping them back to their primary ENS names.
+ * EIP-7930 is an example of supported chain identifier.
+ */
+contract L2Resolver is IL2Resolver {
+  /// @notice A dedicated node hash for storing reverse lookup entries within this contract's records mapping.
+  bytes32 private constant _REVERSE_LOOKUP_NODE = bytes32(keccak256('reverse.chain.id.eip7930'));
+
+  /// @inheritdoc IL2Resolver
+  string public constant CHAIN_IDENTIFIER_EIP7930_KEY = 'chain.id.eip7930';
+
+  /// @inheritdoc IL2Resolver
+  IENS public immutable ENS_REGISTRY;
+
+  /// @inheritdoc IL2Resolver
+  INameWrapper public immutable NAME_WRAPPER;
+
+  /// @inheritdoc IL2Resolver
+  address public immutable REVERSE_ADMIN;
+
+  /// @inheritdoc IL2Resolver
+  bytes32 public immutable PARENT_NODE;
+
+  /// @inheritdoc IL2Resolver
+  mapping(bytes32 _node => mapping(string _key => bytes _data)) public records;
+
+  /**
+   * @notice Constructor
+   * @param _ensRegistry The ENS registry address.
+   * @param _nameWrapper The ENS name wrapper address.
+   * @param _reverseAdmin The reverse admin address.
+   * @param _parentNode The parent node namehash.
+   */
+  constructor(address _ensRegistry, address _nameWrapper, address _reverseAdmin, bytes32 _parentNode) {
+    ENS_REGISTRY = IENS(_ensRegistry);
+    NAME_WRAPPER = INameWrapper(_nameWrapper);
+    REVERSE_ADMIN = _reverseAdmin;
+    PARENT_NODE = _parentNode;
+  }
+}

src/interfaces/IENS.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.30;
+
+/**
+ * @title IENS
+ * @author @defi-wonderland
+ * @notice Interface for the ENS registry.
+ */
+interface IENS {}

src/interfaces/IL2Resolver.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.30;
+
+import {IENS} from './IENS.sol';
+import {INameWrapper} from './INameWrapper.sol';
+
+/**
+ * @title IL2Resolver
+ * @author @defi-wonderland
+ */
+interface IL2Resolver {
+  /*///////////////////////////////////////////////////////////////
+                            EVENTS
+  //////////////////////////////////////////////////////////////*/
+
+  /*///////////////////////////////////////////////////////////////
+                            ERRORS
+  //////////////////////////////////////////////////////////////*/
+
+  /*///////////////////////////////////////////////////////////////
+                            LOGIC
+  //////////////////////////////////////////////////////////////*/
+
+  /*///////////////////////////////////////////////////////////////
+                            VARIABLES
+  //////////////////////////////////////////////////////////////*/
+  /**
+   * @notice The key used in records to store the EIP-7930 chain identifier bytes for a forward resolution.
+   * @return _key The key used for a forward resolution.
+   */
+  function CHAIN_IDENTIFIER_EIP7930_KEY() external view returns (string memory _key);
+
+  /**
+   * @notice Stores arbitrary data for each ENS node.
+   * @dev For domain-to-chain-identifier resolution, the key will be a pre-defined string.
+   * (e.g., CHAIN_IDENTIFIER_EIP7930_KEY) and data will be the raw EIP-7930 chain identifier
+   * bytes (formatted with AddressLength = 0).
+   * @dev For EIP-7930-chain-identifier-to-domain resolution (reverse lookup), the REVERSE_LOOKUP_NODE is used.
+   * The key is constructed by concatenating a prefix (e.g., CHAIN_IDENTIFIER_EIP7930_KEY)with the hexadecimal string
+   * representation of the keccak256 hash of the EIP-7930 chain identifier bytes. The data stored is the
+   * ABI-encoded human-readable ENS name string (e.g., abi.encode("optimism.l2.eth")).
+   * @param _node The ENS node to store the data for.
+   * @param _key The key to store the data under.
+   * @return _data The data stored under the key.
+   */
+  function records(bytes32 _node, string calldata _key) external view returns (bytes memory _data);
+
+  /**
+   * @notice The ENS registry.
+   * @return _ensRegistry The ENS registry address.
+   */
+  function ENS_REGISTRY() external view returns (IENS _ensRegistry);
+
+  /**
+   * @notice The ENS name wrapper.
+   * @return _nameWrapper The ENS name wrapper address.
+   */
+  function NAME_WRAPPER() external view returns (INameWrapper _nameWrapper);
+
+  /**
+   * @notice The admin authorized to set the reverse lookup node values.
+   * @return _adminAddress The admin address.
+   */
+  function REVERSE_ADMIN() external view returns (address _adminAddress);
+
+  /**
+   * @notice The parent node namehash for wildcard resolution and authorization.
+   * @return _parentNode The parent node namehash.
+   */
+  function PARENT_NODE() external view returns (bytes32 _parentNode);
+}

src/interfaces/INameWrapper.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.30;
+
+/**
+ * @title INameWrapper
+ * @author @defi-wonderland
+ * @notice Interface for the ENS Name Wrapper.
+ */
+interface INameWrapper {}

test/integration/L2Resolver.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.30;
+
+import {Test} from 'forge-std/Test.sol';
+
+contract IntegrationL2Resolver is Test {
+  function test() external {
+    vm.skip(true);
+  }
+}

test/unit/L2Resolver.t.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.30;
+
+import {Test} from 'forge-std/Test.sol';
+import {L2Resolver} from 'src/contracts/L2Resolver.sol';
+
+contract UnitL2Resolverconstructor is Test {
+  L2Resolver internal _l2Resolver;
+  address internal _ensRegistry = makeAddr('ENSRegistry');
+  address internal _nameWrapper = makeAddr('NameWrapper');
+  address internal _reverseAdmin = makeAddr('ReverseAdmin');
+  bytes32 internal _parentNode = bytes32(abi.encode('l2.eth'));
+
+  function setUp() external {
+    _l2Resolver = new L2Resolver(_ensRegistry, _nameWrapper, _reverseAdmin, _parentNode);
+  }
+
+  function test_WhenDeployingTheContract() external view {
+    // it sets the ENS registry address
+    assertEq(address(_l2Resolver.ENS_REGISTRY()), _ensRegistry);
+    // it sets the name wrapper address
+    assertEq(address(_l2Resolver.NAME_WRAPPER()), _nameWrapper);
+    // it sets the reverse admin address
+    assertEq(_l2Resolver.REVERSE_ADMIN(), _reverseAdmin);
+    // it sets the parent node namehash
+    assertEq(_l2Resolver.PARENT_NODE(), _parentNode);
+  }
+}

test/unit/L2Resolver.tree

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+UnitL2Resolver::constructor
+└── when deploying the contract
+    ├── it sets the ENS registry address
+    ├── it sets the name wrapper address
+    ├── it sets the reverse admin address
+    └── it sets the parent node namehash