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Merge pull request #42 from smartcontractkit/feature/oe-token-v2
Add LinkToken on Optimism [bridge v2]
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‎CHANGELOG.md‎

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The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
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## [Unreleased] - Apr 2021
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## [Unreleased] - Jun 2021
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### Added
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- Access controlled mintable & burnable LinkToken, for use on sidechains and L2 networks.
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- Documentation and token implementation for the Optimism bridge v2.
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- Added versioning to v0.6 & v0.7 contracts
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### Changed

‎contracts/v0.7/bridge/README.md‎

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gets defined, and once online transfer the ownership (bridge gateway role) to the new bridge.
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TODO: Potentially create an upgradeable `LinkTokenChild.sol` and limit gateway support to only one (owner)!
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- `./token/optimism/`: Documentation and token implementation for the Optimism bridge v2.

‎contracts/v0.7/bridge/token/optimism/IERC20Optimism.sol‎

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// SPDX-License-Identifier: MIT
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pragma solidity >0.6.0 <0.8.0;
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/* Interface Imports */
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import { IERC20 } from "../../../../../vendor/OpenZeppelin/openzeppelin-contracts/contracts/token/ERC20/IERC20.sol";
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import { IERC165 } from "../../../../../vendor/OpenZeppelin/openzeppelin-contracts/contracts/introspection/IERC165.sol";
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/// @dev Interface for the bridged ERC20 token expected by the Optimism standard bridge L2 gateway.
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interface IERC20Optimism is IERC20, IERC165 {
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/// @dev Returns the address of an L1 token contract linked to this L2 token contract
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function l1Token()
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external
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returns (address);
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/**
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* @dev Creates `_amount` tokens `_to` account.
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* @notice Called by L2 gateway to deposit tokens.
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* @param _to Address of the recipient.
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* @param _amount Number of tokens to mint.
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*/
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function mint(
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address _to,
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uint256 _amount
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)
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external;
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/**
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* @dev Destroys `_amount` tokens `_from` account.
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* @notice Called by L2 gateway to withdraw tokens.
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* @param _from Address of the account holding the tokens to be burnt.
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* @param _amount Number of tokens to burn.
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*/
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function burn(
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address _from,
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uint256 _amount
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)
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external;
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/// @dev Emitted when `_amount` tokens are deposited from L1 to L2.
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event Mint(
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address indexed _account,
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uint256 _amount
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);
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/// @dev Emitted when `_amount` tokens are withdrawn from L2 to L1.
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event Burn(
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address indexed _account,
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uint256 _amount
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);
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}

‎contracts/v0.7/bridge/token/optimism/LinkTokenOptimism.sol‎

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// SPDX-License-Identifier: MIT
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pragma solidity >0.6.0 <0.8.0;
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/* Interface Imports */
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import { IERC165 } from "../../../../../vendor/OpenZeppelin/openzeppelin-contracts/contracts/introspection/IERC165.sol";
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import { ITypeAndVersion } from "../../../../v0.6/ITypeAndVersion.sol";
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import { IERC20Optimism } from "./IERC20Optimism.sol";
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/* Contract Imports */
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import { ERC20 } from "../../../../../vendor/OpenZeppelin/openzeppelin-contracts/contracts/token/ERC20/ERC20.sol";
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import { LinkToken } from "../../../../v0.6/LinkToken.sol";
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/// @dev Access controlled mintable & burnable LinkToken, for use on Optimism L2 network.
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contract LinkTokenOptimism is ITypeAndVersion, IERC20Optimism, LinkToken {
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/// @dev Returns the address of an L2 bridge contract that has access to mint & burn
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address public immutable l2Bridge;
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/// @inheritdoc IERC20Optimism
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address public immutable override l1Token;
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/**
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* @dev Creates an L2 token connected to a specific L2 bridge gateway & L1 token
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* @param l2BridgeAddr Address of the corresponding L2 bridge gateway.
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* @param l1TokenAddr Address of the corresponding L1 token.
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*/
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constructor(
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address l2BridgeAddr,
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address l1TokenAddr
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) {
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l2Bridge = l2BridgeAddr;
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l1Token = l1TokenAddr;
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}
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/**
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* @notice versions:
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*
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* - LinkTokenOptimism 0.0.1: initial release
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*
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* @inheritdoc ITypeAndVersion
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*/
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function typeAndVersion()
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external
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pure
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override(ITypeAndVersion, LinkToken)
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virtual
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returns (string memory)
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{
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return "LinkTokenOptimism 0.0.1";
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}
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/// @dev Checks that message sender is the L2 bridge contract (locked access to mint & burn)
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modifier onlyL2Bridge {
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require(msg.sender == l2Bridge, "Only L2 Bridge can mint and burn");
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_;
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}
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/**
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* @dev Optimism standard bridge L2 gateway uses ERC165 to confirm the required interface
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* @inheritdoc IERC165
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*/
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function supportsInterface(
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bytes4 interfaceId
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)
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public
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override
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pure
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returns (bool)
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{
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bytes4 firstSupportedInterface = bytes4(keccak256("supportsInterface(bytes4)")); // ERC165
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bytes4 secondSupportedInterface = IERC20Optimism.l1Token.selector
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^ IERC20Optimism.mint.selector
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^ IERC20Optimism.burn.selector;
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return interfaceId == firstSupportedInterface || interfaceId == secondSupportedInterface;
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}
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/// @inheritdoc IERC20Optimism
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function mint(
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address _to,
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uint256 _amount
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)
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public
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override
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onlyL2Bridge()
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{
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_mint(_to, _amount);
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emit Mint(_to, _amount);
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}
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/// @inheritdoc IERC20Optimism
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function burn(
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address _from,
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uint256 _amount
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)
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public
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override
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onlyL2Bridge()
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{
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_burn(_from, _amount);
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emit Burn(_from, _amount);
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}
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/**
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* @dev Overrides parent contract so no tokens are minted on deployment.
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* @inheritdoc LinkToken
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*/
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function _onCreate()
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internal
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override
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{}
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}

‎contracts/v0.7/bridge/token/optimism/README.md‎

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# LINK Token on Optimism
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- `./token/IERC20Optimism.sol`: Interface for the bridged ERC20 token expected by the Optimism standard bridge L2 gateway.
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- `./token/LinkTokenOptimism.sol`: Access controlled mintable & burnable LinkToken, for use on Optimism L2 network.
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`LinkTokenOptimism.sol` is a slightly modified version of Optimism's [`L2StandardERC20.sol`](https://github.com/ethereum-optimism/optimism/blob/master/packages/contracts/contracts/optimistic-ethereum/libraries/standards/L2StandardERC20.sol) and will be connected to the [`OVM_L2StandardBridge.sol`](https://github.com/ethereum-optimism/optimism/blob/master/packages/contracts/contracts/optimistic-ethereum/OVM/bridge/tokens/OVM_L2StandardBridge.sol). Modifications include:
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- Contract versioning via `ITypeAndVersion` interface
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- ERC677 support by extending the `LinkToken` contract
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- Transfers & approves to the contract itself blocked (provided by `LinkToken` contract)
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- `l2Bridge` & `l1Token` were changed from storage vars to immutable vars, which provides some gas savings
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The [Optimism Gateway](https://gateway.optimism.io) bridge UI can be used to move the tokens between networks.

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