feat: IndexingMath, Proxy, Migratable (#38)

src/ERC20Extended.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 import { IERC20 } from "./interfaces/IERC20.sol";
 import { IERC20Extended } from "./interfaces/IERC20Extended.sol";

src/ERC3009.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 import { IERC3009 } from "./interfaces/IERC3009.sol";
 

src/ERC712Extended.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 import { IERC712 } from "./interfaces/IERC712.sol";
 import { IERC712Extended } from "./interfaces/IERC712Extended.sol";

src/Migratable.sol

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity >=0.8.20 <0.9.0;
+
+import { IMigratable } from "./interfaces/IMigratable.sol";
+
+/**
+ * @title  Abstract implementation for exposing the ability to migrate a contract, extending ERC-1967.
+ * @author M^0 Labs
+ */
+abstract contract Migratable is IMigratable {
+    /* ============ Variables ============ */
+
+    /// @dev Storage slot with the address of the current factory. `keccak256('eip1967.proxy.implementation') - 1`.
+    uint256 private constant _IMPLEMENTATION_SLOT = 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc;
+
+    /* ============ Interactive Functions ============ */
+
+    /// @inheritdoc IMigratable
+    function migrate() external {
+        _migrate(_getMigrator());
+    }
+
+    /* ============ View/Pure Functions ============ */
+
+    /// @inheritdoc IMigratable
+    function implementation() public view returns (address implementation_) {
+        assembly {
+            implementation_ := sload(_IMPLEMENTATION_SLOT)
+        }
+    }
+
+    /* ============ Internal Interactive Functions ============ */
+
+    /**
+     * @dev   Performs an arbitrary migration by delegate-calling `migrator_`.
+     * @param migrator_ The address of a migrator contract.
+     */
+    function _migrate(address migrator_) internal {
+        if (migrator_ == address(0)) revert ZeroMigrator();
+
+        if (migrator_.code.length == 0) revert InvalidMigrator();
+
+        address oldImplementation_ = implementation();
+
+        (bool success_, ) = migrator_.delegatecall("");
+        if (!success_) revert MigrationFailed();
+
+        address newImplementation_ = implementation();
+
+        emit Migrated(migrator_, oldImplementation_, newImplementation_);
+
+        // NOTE: Redundant event emitted to conform to the EIP-1967 standard.
+        emit Upgraded(newImplementation_);
+    }
+
+    /* ============ Internal View/Pure Functions ============ */
+
+    /// @dev Returns the address of a migrator contract.
+    function _getMigrator() internal view virtual returns (address);
+}

src/Proxy.sol

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity >=0.8.20 <0.9.0;
+
+/**
+ * @title  Minimal transparent proxy.
+ * @author M^0 Labs
+ */
+contract Proxy {
+    /// @dev Storage slot with the address of the current factory. `keccak256('eip1967.proxy.implementation') - 1`.
+    uint256 private constant _IMPLEMENTATION_SLOT = 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc;
+
+    /**
+     * @dev   Constructs the contract given the address of some implementation.
+     * @param implementation_ The address of some implementation.
+     */
+    constructor(address implementation_) {
+        if (implementation_ == address(0)) revert();
+
+        assembly {
+            sstore(_IMPLEMENTATION_SLOT, implementation_)
+        }
+    }
+
+    fallback() external payable virtual {
+        bytes32 implementation_;
+
+        assembly {
+            implementation_ := sload(_IMPLEMENTATION_SLOT)
+        }
+
+        assembly {
+            calldatacopy(0, 0, calldatasize())
+
+            let result_ := delegatecall(gas(), implementation_, 0, calldatasize(), 0, 0)
+
+            returndatacopy(0, 0, returndatasize())
+
+            switch result_
+            case 0 {
+                revert(0, returndatasize())
+            }
+            default {
+                return(0, returndatasize())
+            }
+        }
+    }
+}

src/StatefulERC712.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 import { IStatefulERC712 } from "./interfaces/IStatefulERC712.sol";
 

src/interfaces/IERC1271.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 /**
  * @title  Standard Signature Validation Method for Contracts via EIP-1271.

src/interfaces/IERC20.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 /**
  * @title  ERC20 Token Standard.

src/interfaces/IERC20Extended.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 import { IERC20 } from "./IERC20.sol";
 import { IERC3009 } from "./IERC3009.sol";

src/interfaces/IERC3009.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 import { IStatefulERC712 } from "./IStatefulERC712.sol";
 

src/interfaces/IERC712.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 /**
  * @title  Typed structured data hashing and signing via EIP-712.

src/interfaces/IERC712Extended.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 import { IERC712 } from "./IERC712.sol";
 

src/interfaces/IMigratable.sol

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity >=0.8.20 <0.9.0;
+
+/**
+ * @title  Interface for exposing the ability to migrate a contract, extending the ERC-1967 interface.
+ * @author M^0 Labs
+ */
+interface IMigratable {
+    /* ============ Events ============ */
+
+    /**
+     * @notice Emitted when a migration to a new implementation is performed.
+     * @param  migrator          The address that performed the migration.
+     * @param  oldImplementation The address of the old implementation.
+     * @param  newImplementation The address of the new implementation.
+     */
+    event Migrated(address indexed migrator, address indexed oldImplementation, address indexed newImplementation);
+
+    /**
+     * @notice Emitted when the implementation address for the proxy is changed.
+     * @param  implementation The address of the new implementation for the proxy.
+     */
+    event Upgraded(address indexed implementation);
+
+    /// @notice Emitted when calling `stopEarning` for an account approved as earner by the Registrar.
+    error InvalidMigrator();
+
+    /// @notice Emitted when the delegatecall to a migrator fails.
+    error MigrationFailed();
+
+    /// @notice Emitted when the zero address is passed as a migrator.
+    error ZeroMigrator();
+
+    /* ============ Interactive Functions ============ */
+
+    /// @notice Performs an arbitrarily defined migration.
+    function migrate() external;
+
+    /* ============ View/Pure Functions ============ */
+
+    /// @notice Returns the address of the current implementation contract.
+    function implementation() external view returns (address);
+}

src/interfaces/IStatefulERC712.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 import { IERC712Extended } from "./IERC712Extended.sol";
 

src/libs/Bytes32String.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 /**
  * @title  A library to convert between string and bytes32 (assuming 32 characters or less).

src/libs/ContractHelper.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0
 
-pragma solidity 0.8.26;
+pragma solidity >=0.8.20 <0.9.0;
 
 // solhint-disable max-line-length
 
@@ -35,14 +35,38 @@ library ContractHelper {
                             nonce_ == 0x00
                                 ? abi.encodePacked(bytes1(0xd6), bytes1(0x94), account_, bytes1(0x80))
                                 : nonce_ <= 0x7f
-                                ? abi.encodePacked(bytes1(0xd6), bytes1(0x94), account_, uint8(nonce_))
-                                : nonce_ <= 0xff
-                                ? abi.encodePacked(bytes1(0xd7), bytes1(0x94), account_, bytes1(0x81), uint8(nonce_))
-                                : nonce_ <= 0xffff
-                                ? abi.encodePacked(bytes1(0xd8), bytes1(0x94), account_, bytes1(0x82), uint16(nonce_))
-                                : nonce_ <= 0xffffff
-                                ? abi.encodePacked(bytes1(0xd9), bytes1(0x94), account_, bytes1(0x83), uint24(nonce_))
-                                : abi.encodePacked(bytes1(0xda), bytes1(0x94), account_, bytes1(0x84), uint32(nonce_))
+                                    ? abi.encodePacked(bytes1(0xd6), bytes1(0x94), account_, uint8(nonce_))
+                                    : nonce_ <= 0xff
+                                        ? abi.encodePacked(
+                                            bytes1(0xd7),
+                                            bytes1(0x94),
+                                            account_,
+                                            bytes1(0x81),
+                                            uint8(nonce_)
+                                        )
+                                        : nonce_ <= 0xffff
+                                            ? abi.encodePacked(
+                                                bytes1(0xd8),
+                                                bytes1(0x94),
+                                                account_,
+                                                bytes1(0x82),
+                                                uint16(nonce_)
+                                            )
+                                            : nonce_ <= 0xffffff
+                                                ? abi.encodePacked(
+                                                    bytes1(0xd9),
+                                                    bytes1(0x94),
+                                                    account_,
+                                                    bytes1(0x83),
+                                                    uint24(nonce_)
+                                                )
+                                                : abi.encodePacked(
+                                                    bytes1(0xda),
+                                                    bytes1(0x94),
+                                                    account_,
+                                                    bytes1(0x84),
+                                                    uint32(nonce_)
+                                                )
                         )
                     )
                 )