Update contracts to support Solidity 0.8.x

README.md

@@ -27,7 +27,7 @@ OpenZeppelin Contracts features a [stable API](https://docs.openzeppelin.com/con
 Once installed, you can use the contracts in the library by importing them:
 
 ```solidity
-pragma solidity ^0.6.0;
+pragma solidity ^0.8.0;
 
 import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
 

buidler.config.js

@@ -15,6 +15,6 @@ module.exports = {
     },
   },
   solc: {
-    version: '0.6.12',
+    version: '0.8.0',
   },
 };

contracts/GSN/Context.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /*
  * @dev Provides information about the current execution context, including the
@@ -14,7 +14,7 @@ pragma solidity >=0.6.0 <0.8.0;
  */
 abstract contract Context {
     function _msgSender() internal view virtual returns (address payable) {
-        return msg.sender;
+        return payable(msg.sender);
     }
 
     function _msgData() internal view virtual returns (bytes memory) {

contracts/GSN/GSNRecipient.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "./IRelayRecipient.sol";
 import "./IRelayHub.sol";
@@ -89,7 +89,7 @@ abstract contract GSNRecipient is IRelayRecipient, Context {
      */
     function _msgSender() internal view virtual override returns (address payable) {
         if (msg.sender != _relayHub) {
-            return msg.sender;
+            return payable(msg.sender);
         } else {
             return _getRelayedCallSender();
         }

contracts/GSN/GSNRecipientERC20Fee.sol

@@ -1,9 +1,8 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "./GSNRecipient.sol";
-import "../math/SafeMath.sol";
 import "../access/Ownable.sol";
 import "../token/ERC20/SafeERC20.sol";
 import "../token/ERC20/ERC20.sol";
@@ -19,7 +18,6 @@ import "../token/ERC20/ERC20.sol";
  */
 contract GSNRecipientERC20Fee is GSNRecipient {
     using SafeERC20 for __unstable__ERC20Owned;
-    using SafeMath for uint256;
 
     enum GSNRecipientERC20FeeErrorCodes {
         INSUFFICIENT_BALANCE
@@ -30,7 +28,7 @@ contract GSNRecipientERC20Fee is GSNRecipient {
     /**
      * @dev The arguments to the constructor are the details that the gas payment token will have: `name` and `symbol`. `decimals` is hard-coded to 18.
      */
-    constructor(string memory name, string memory symbol) public {
+    constructor(string memory name, string memory symbol) {
         _token = new __unstable__ERC20Owned(name, symbol);
     }
 
@@ -100,11 +98,11 @@ contract GSNRecipientERC20Fee is GSNRecipient {
         // actualCharge is an _estimated_ charge, which assumes postRelayedCall will use all available gas.
         // This implementation's gas cost can be roughly estimated as 10k gas, for the two SSTORE operations in an
         // ERC20 transfer.
-        uint256 overestimation = _computeCharge(_POST_RELAYED_CALL_MAX_GAS.sub(10000), gasPrice, transactionFee);
-        actualCharge = actualCharge.sub(overestimation);
+        uint256 overestimation = _computeCharge(_POST_RELAYED_CALL_MAX_GAS - 10000, gasPrice, transactionFee);
+        actualCharge = actualCharge - overestimation;
 
         // After the relayed call has been executed and the actual charge estimated, the excess pre-charge is returned
-        _token.safeTransfer(from, maxPossibleCharge.sub(actualCharge));
+        _token.safeTransfer(from, maxPossibleCharge - actualCharge);
     }
 }
 
@@ -118,7 +116,7 @@ contract GSNRecipientERC20Fee is GSNRecipient {
 contract __unstable__ERC20Owned is ERC20, Ownable {
     uint256 private constant _UINT256_MAX = 2**256 - 1;
 
-    constructor(string memory name, string memory symbol) public ERC20(name, symbol) { }
+    constructor(string memory name, string memory symbol) ERC20(name, symbol) { }
 
     // The owner (GSNRecipientERC20Fee) can mint tokens
     function mint(address account, uint256 amount) public onlyOwner {

contracts/GSN/GSNRecipientSignature.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "./GSNRecipient.sol";
 import "../cryptography/ECDSA.sol";
@@ -23,7 +23,7 @@ contract GSNRecipientSignature is GSNRecipient {
     /**
      * @dev Sets the trusted signer that is going to be producing signatures to approve relayed calls.
      */
-    constructor(address trustedSigner) public {
+    constructor(address trustedSigner) {
         require(trustedSigner != address(0), "GSNRecipientSignature: trusted signer is the zero address");
         _trustedSigner = trustedSigner;
     }

contracts/GSN/IRelayHub.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Interface for `RelayHub`, the core contract of the GSN. Users should not need to interact with this contract

contracts/GSN/IRelayRecipient.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Base interface for a contract that will be called via the GSN from {IRelayHub}.

contracts/access/AccessControl.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "../utils/EnumerableSet.sol";
 import "../utils/Address.sol";

contracts/access/Ownable.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "../GSN/Context.sol";
 /**
@@ -23,7 +23,7 @@ abstract contract Ownable is Context {
     /**
      * @dev Initializes the contract setting the deployer as the initial owner.
      */
-    constructor () internal {
+    constructor () {
         address msgSender = _msgSender();
         _owner = msgSender;
         emit OwnershipTransferred(address(0), msgSender);

contracts/access/TimelockController.sol

@@ -1,9 +1,7 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.9 <0.8.0;
-pragma experimental ABIEncoderV2;
+pragma solidity ^0.8.0;
 
-import "./../math/SafeMath.sol";
 import "./AccessControl.sol";
 
 /**
@@ -52,7 +50,7 @@ contract TimelockController is AccessControl {
     /**
      * @dev Initializes the contract with a given `minDelay`.
      */
-    constructor(uint256 minDelay, address[] memory proposers, address[] memory executors) public {
+    constructor(uint256 minDelay, address[] memory proposers, address[] memory executors) {
         _setRoleAdmin(TIMELOCK_ADMIN_ROLE, TIMELOCK_ADMIN_ROLE);
         _setRoleAdmin(PROPOSER_ROLE, TIMELOCK_ADMIN_ROLE);
         _setRoleAdmin(EXECUTOR_ROLE, TIMELOCK_ADMIN_ROLE);
@@ -188,7 +186,7 @@ contract TimelockController is AccessControl {
         require(_timestamps[id] == 0, "TimelockController: operation already scheduled");
         require(delay >= _minDelay, "TimelockController: insufficient delay");
         // solhint-disable-next-line not-rely-on-time
-        _timestamps[id] = SafeMath.add(block.timestamp, delay);
+        _timestamps[id] = block.timestamp + delay;
     }
 
     /**

contracts/cryptography/ECDSA.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.

contracts/cryptography/MerkleProof.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev These functions deal with verification of Merkle trees (hash trees),

contracts/drafts/EIP712.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev https://eips.ethereum.org/EIPS/eip-712[EIP 712] is a standard for hashing and signing of typed structured data.
@@ -43,7 +43,7 @@ abstract contract EIP712 {
      * NOTE: These parameters cannot be changed except through a xref:learn::upgrading-smart-contracts.adoc[smart
      * contract upgrade].
      */
-    constructor(string memory name, string memory version) internal {
+    constructor(string memory name, string memory version) {
         bytes32 hashedName = keccak256(bytes(name));
         bytes32 hashedVersion = keccak256(bytes(version));
         bytes32 typeHash = keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"); 
@@ -96,10 +96,7 @@ abstract contract EIP712 {
         return keccak256(abi.encodePacked("\x19\x01", _domainSeparatorV4(), structHash));
     }
 
-    function _getChainId() private pure returns (uint256 chainId) {
-        // solhint-disable-next-line no-inline-assembly
-        assembly {
-            chainId := chainid()
-        }
+    function _getChainId() private view returns (uint256 chainId) {
+        chainId = block.chainid;
     }
 }

contracts/drafts/ERC20Permit.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.5 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "../token/ERC20/ERC20.sol";
 import "./IERC20Permit.sol";
@@ -29,7 +29,7 @@ abstract contract ERC20Permit is ERC20, IERC20Permit, EIP712 {
      *
      * It's a good idea to use the same `name` that is defined as the ERC20 token name.
      */
-    constructor(string memory name) internal EIP712(name, "1") {
+    constructor(string memory name) EIP712(name, "1") {
     }
 
     /**

contracts/drafts/IERC20Permit.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Interface of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in

contracts/introspection/ERC165.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "./IERC165.sol";
 
@@ -21,7 +21,7 @@ abstract contract ERC165 is IERC165 {
      */
     mapping(bytes4 => bool) private _supportedInterfaces;
 
-    constructor () internal {
+    constructor () {
         // Derived contracts need only register support for their own interfaces,
         // we register support for ERC165 itself here
         _registerInterface(_INTERFACE_ID_ERC165);

contracts/introspection/ERC165Checker.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.2 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Library used to query support of an interface declared via {IERC165}.

contracts/introspection/ERC1820Implementer.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "./IERC1820Implementer.sol";
 

contracts/introspection/IERC165.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Interface of the ERC165 standard, as defined in the

contracts/introspection/IERC1820Implementer.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Interface for an ERC1820 implementer, as defined in the

contracts/introspection/IERC1820Registry.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Interface of the global ERC1820 Registry, as defined in the

contracts/math/Math.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Standard math utilities missing in the Solidity language.

contracts/math/SafeMath.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @dev Wrappers over Solidity's arithmetic operations with added overflow

contracts/math/SignedSafeMath.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 /**
  * @title SignedSafeMath

contracts/mocks/AccessControlMock.sol

@@ -1,11 +1,11 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "../access/AccessControl.sol";
 
 contract AccessControlMock is AccessControl {
-    constructor() public {
+    constructor() {
         _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
     }
 

contracts/mocks/AddressImpl.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "../utils/Address.sol";
 

contracts/mocks/ArraysImpl.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 import "../utils/Arrays.sol";
 
@@ -9,7 +9,7 @@ contract ArraysImpl {
 
     uint256[] private _array;
 
-    constructor (uint256[] memory array) public {
+    constructor (uint256[] memory array) {
         _array = array;
     }
 

contracts/mocks/BadBeacon.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 contract BadBeaconNoImpl {
 }

contracts/mocks/CallReceiverMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.0;
 
 contract CallReceiverMock {
     string public sharedAnswer;