Initial migration to Solidity 0.6.x - v3.0 first steps

.solhint.json

@@ -9,6 +9,7 @@
     "separate-by-one-line-in-contract": "off",
     "two-lines-top-level-separator": "off",
     "mark-callable-contracts": "off",
-    "compiler-version": ["error", "^0.5.0"]
+    "no-empty-blocks": "off",
+    "compiler-version": ["error", "^0.6.0"]
   }
 }

contracts/GSN/Context.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 /*
  * @dev Provides information about the current execution context, including the
@@ -14,13 +14,12 @@ contract Context {
     // Empty internal constructor, to prevent people from mistakenly deploying
     // an instance of this contract, which should be used via inheritance.
     constructor () internal { }
-    // solhint-disable-previous-line no-empty-blocks
 
-    function _msgSender() internal view returns (address payable) {
+    function _msgSender() internal view virtual returns (address payable) {
         return msg.sender;
     }
 
-    function _msgData() internal view returns (bytes memory) {
+    function _msgData() internal view virtual returns (bytes memory) {
         this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
         return msg.data;
     }

contracts/GSN/GSNRecipient.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 import "./IRelayRecipient.sol";
 import "./IRelayHub.sol";
@@ -15,7 +15,7 @@ import "./Context.sol";
  * information on how to use the pre-built {GSNRecipientSignature} and
  * {GSNRecipientERC20Fee}, or how to write your own.
  */
-contract GSNRecipient is IRelayRecipient, Context {
+abstract contract GSNRecipient is IRelayRecipient, Context {
     // Default RelayHub address, deployed on mainnet and all testnets at the same address
     address private _relayHub = 0xD216153c06E857cD7f72665E0aF1d7D82172F494;
 
@@ -33,7 +33,7 @@ contract GSNRecipient is IRelayRecipient, Context {
     /**
      * @dev Returns the address of the {IRelayHub} contract for this recipient.
      */
-    function getHubAddr() public view returns (address) {
+    function getHubAddr() public view override returns (address) {
         return _relayHub;
     }
 
@@ -44,7 +44,7 @@ contract GSNRecipient is IRelayRecipient, Context {
      * IMPORTANT: After upgrading, the {GSNRecipient} will no longer be able to receive relayed calls from the old
      * {IRelayHub} instance. Additionally, all funds should be previously withdrawn via {_withdrawDeposits}.
      */
-    function _upgradeRelayHub(address newRelayHub) internal {
+    function _upgradeRelayHub(address newRelayHub) internal virtual {
         address currentRelayHub = _relayHub;
         require(newRelayHub != address(0), "GSNRecipient: new RelayHub is the zero address");
         require(newRelayHub != currentRelayHub, "GSNRecipient: new RelayHub is the current one");
@@ -70,7 +70,7 @@ contract GSNRecipient is IRelayRecipient, Context {
      *
      * Derived contracts should expose this in an external interface with proper access control.
      */
-    function _withdrawDeposits(uint256 amount, address payable payee) internal {
+    function _withdrawDeposits(uint256 amount, address payable payee) internal virtual {
         IRelayHub(_relayHub).withdraw(amount, payee);
     }
 
@@ -85,7 +85,7 @@ contract GSNRecipient is IRelayRecipient, Context {
      *
      * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.sender`, and use {_msgSender} instead.
      */
-    function _msgSender() internal view returns (address payable) {
+    function _msgSender() internal view virtual override returns (address payable) {
         if (msg.sender != _relayHub) {
             return msg.sender;
         } else {
@@ -99,7 +99,7 @@ contract GSNRecipient is IRelayRecipient, Context {
      *
      * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.data`, and use {_msgData} instead.
      */
-    function _msgData() internal view returns (bytes memory) {
+    function _msgData() internal view virtual override returns (bytes memory) {
         if (msg.sender != _relayHub) {
             return msg.data;
         } else {
@@ -119,7 +119,7 @@ contract GSNRecipient is IRelayRecipient, Context {
      *
      * - the caller must be the `RelayHub` contract.
      */
-    function preRelayedCall(bytes calldata context) external returns (bytes32) {
+    function preRelayedCall(bytes calldata context) external virtual override returns (bytes32) {
         require(msg.sender == getHubAddr(), "GSNRecipient: caller is not RelayHub");
         return _preRelayedCall(context);
     }
@@ -131,7 +131,7 @@ contract GSNRecipient is IRelayRecipient, Context {
      * must implement this function with any relayed-call preprocessing they may wish to do.
      *
      */
-    function _preRelayedCall(bytes memory context) internal returns (bytes32);
+    function _preRelayedCall(bytes memory context) internal virtual returns (bytes32);
 
     /**
      * @dev See `IRelayRecipient.postRelayedCall`.
@@ -142,7 +142,7 @@ contract GSNRecipient is IRelayRecipient, Context {
      *
      * - the caller must be the `RelayHub` contract.
      */
-    function postRelayedCall(bytes calldata context, bool success, uint256 actualCharge, bytes32 preRetVal) external {
+    function postRelayedCall(bytes calldata context, bool success, uint256 actualCharge, bytes32 preRetVal) external virtual override {
         require(msg.sender == getHubAddr(), "GSNRecipient: caller is not RelayHub");
         _postRelayedCall(context, success, actualCharge, preRetVal);
     }
@@ -154,7 +154,7 @@ contract GSNRecipient is IRelayRecipient, Context {
      * must implement this function with any relayed-call postprocessing they may wish to do.
      *
      */
-    function _postRelayedCall(bytes memory context, bool success, uint256 actualCharge, bytes32 preRetVal) internal;
+    function _postRelayedCall(bytes memory context, bool success, uint256 actualCharge, bytes32 preRetVal) internal virtual;
 
     /**
      * @dev Return this in acceptRelayedCall to proceed with the execution of a relayed call. Note that this contract

contracts/GSN/GSNRecipientERC20Fee.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 import "./GSNRecipient.sol";
 import "../math/SafeMath.sol";
@@ -43,7 +43,7 @@ contract GSNRecipientERC20Fee is GSNRecipient {
     /**
      * @dev Internal function that mints the gas payment token. Derived contracts should expose this function in their public API, with proper access control mechanisms.
      */
-    function _mint(address account, uint256 amount) internal {
+    function _mint(address account, uint256 amount) internal virtual {
         _token.mint(account, amount);
     }
 
@@ -63,6 +63,8 @@ contract GSNRecipientERC20Fee is GSNRecipient {
     )
         external
         view
+        virtual
+        override
         returns (uint256, bytes memory)
     {
         if (_token.balanceOf(from) < maxPossibleCharge) {
@@ -78,7 +80,7 @@ contract GSNRecipientERC20Fee is GSNRecipient {
      * actual charge, necessary because we cannot predict how much gas the execution will actually need. The remainder
      * is returned to the user in {_postRelayedCall}.
      */
-    function _preRelayedCall(bytes memory context) internal returns (bytes32) {
+    function _preRelayedCall(bytes memory context) internal virtual override returns (bytes32) {
         (address from, uint256 maxPossibleCharge) = abi.decode(context, (address, uint256));
 
         // The maximum token charge is pre-charged from the user
@@ -88,7 +90,7 @@ contract GSNRecipientERC20Fee is GSNRecipient {
     /**
      * @dev Returns to the user the extra amount that was previously charged, once the actual execution cost is known.
      */
-    function _postRelayedCall(bytes memory context, bool, uint256 actualCharge, bytes32) internal {
+    function _postRelayedCall(bytes memory context, bool, uint256 actualCharge, bytes32) internal virtual override {
         (address from, uint256 maxPossibleCharge, uint256 transactionFee, uint256 gasPrice) =
             abi.decode(context, (address, uint256, uint256, uint256));
 
@@ -113,17 +115,15 @@ contract GSNRecipientERC20Fee is GSNRecipient {
 contract __unstable__ERC20PrimaryAdmin is ERC20, ERC20Detailed, Secondary {
     uint256 private constant UINT256_MAX = 2**256 - 1;
 
-    constructor(string memory name, string memory symbol, uint8 decimals) public ERC20Detailed(name, symbol, decimals) {
-        // solhint-disable-previous-line no-empty-blocks
-    }
+    constructor(string memory name, string memory symbol, uint8 decimals) public ERC20Detailed(name, symbol, decimals) { }
 
     // The primary account (GSNRecipientERC20Fee) can mint tokens
     function mint(address account, uint256 amount) public onlyPrimary {
         _mint(account, amount);
     }
 
     // The primary account has 'infinite' allowance for all token holders
-    function allowance(address owner, address spender) public view returns (uint256) {
+    function allowance(address owner, address spender) public view override(ERC20, IERC20) returns (uint256) {
         if (spender == primary()) {
             return UINT256_MAX;
         } else {
@@ -132,15 +132,15 @@ contract __unstable__ERC20PrimaryAdmin is ERC20, ERC20Detailed, Secondary {
     }
 
     // Allowance for the primary account cannot be changed (it is always 'infinite')
-    function _approve(address owner, address spender, uint256 value) internal {
+    function _approve(address owner, address spender, uint256 value) internal override {
         if (spender == primary()) {
             return;
         } else {
             super._approve(owner, spender, value);
         }
     }
 
-    function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
+    function transferFrom(address sender, address recipient, uint256 amount) public override(ERC20, IERC20) returns (bool) {
         if (recipient == primary()) {
             _transfer(sender, recipient, amount);
             return true;

contracts/GSN/GSNRecipientSignature.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 import "./GSNRecipient.sol";
 import "../cryptography/ECDSA.sol";
@@ -42,6 +42,8 @@ contract GSNRecipientSignature is GSNRecipient {
     )
         external
         view
+        virtual
+        override
         returns (uint256, bytes memory)
     {
         bytes memory blob = abi.encodePacked(
@@ -62,11 +64,7 @@ contract GSNRecipientSignature is GSNRecipient {
         }
     }
 
-    function _preRelayedCall(bytes memory) internal returns (bytes32) {
-        // solhint-disable-previous-line no-empty-blocks
-    }
+    function _preRelayedCall(bytes memory) internal virtual override returns (bytes32) { }
 
-    function _postRelayedCall(bytes memory, bool, uint256, bytes32) internal {
-        // solhint-disable-previous-line no-empty-blocks
-    }
+    function _postRelayedCall(bytes memory, bool, uint256, bytes32) internal virtual override { }
 }

contracts/GSN/IRelayHub.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 /**
  * @dev Interface for `RelayHub`, the core contract of the GSN. Users should not need to interact with this contract
@@ -207,7 +207,7 @@ interface IRelayHub {
     event CanRelayFailed(address indexed relay, address indexed from, address indexed to, bytes4 selector, uint256 reason);
 
     /**
-     * @dev Emitted when a transaction is relayed. 
+     * @dev Emitted when a transaction is relayed.
      * Useful when monitoring a relay's operation and relayed calls to a contract
      *
      * Note that the actual encoded function might be reverted: this is indicated in the `status` parameter.
@@ -236,7 +236,7 @@ interface IRelayHub {
      */
     function maxPossibleCharge(uint256 relayedCallStipend, uint256 gasPrice, uint256 transactionFee) external view returns (uint256);
 
-     // Relay penalization. 
+     // Relay penalization.
      // Any account can penalize relays, removing them from the system immediately, and rewarding the
     // reporter with half of the relay's stake. The other half is burned so that, even if the relay penalizes itself, it
     // still loses half of its stake.

contracts/GSN/IRelayRecipient.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 /**
  * @dev Base interface for a contract that will be called via the GSN from {IRelayHub}.

contracts/access/Roles.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 /**
  * @title Roles

contracts/access/roles/CapperRole.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 import "../../GSN/Context.sol";
 import "../Roles.sol";
@@ -24,20 +24,20 @@ contract CapperRole is Context {
         return _cappers.has(account);
     }
 
-    function addCapper(address account) public onlyCapper {
+    function addCapper(address account) public virtual onlyCapper {
         _addCapper(account);
     }
 
-    function renounceCapper() public {
+    function renounceCapper() public virtual {
         _removeCapper(_msgSender());
     }
 
-    function _addCapper(address account) internal {
+    function _addCapper(address account) internal virtual {
         _cappers.add(account);
         emit CapperAdded(account);
     }
 
-    function _removeCapper(address account) internal {
+    function _removeCapper(address account) internal virtual {
         _cappers.remove(account);
         emit CapperRemoved(account);
     }

contracts/access/roles/MinterRole.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 import "../../GSN/Context.sol";
 import "../Roles.sol";
@@ -24,20 +24,20 @@ contract MinterRole is Context {
         return _minters.has(account);
     }
 
-    function addMinter(address account) public onlyMinter {
+    function addMinter(address account) public virtual onlyMinter {
         _addMinter(account);
     }
 
-    function renounceMinter() public {
+    function renounceMinter() public virtual {
         _removeMinter(_msgSender());
     }
 
-    function _addMinter(address account) internal {
+    function _addMinter(address account) internal virtual {
         _minters.add(account);
         emit MinterAdded(account);
     }
 
-    function _removeMinter(address account) internal {
+    function _removeMinter(address account) internal virtual {
         _minters.remove(account);
         emit MinterRemoved(account);
     }

contracts/access/roles/PauserRole.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 import "../../GSN/Context.sol";
 import "../Roles.sol";
@@ -24,20 +24,20 @@ contract PauserRole is Context {
         return _pausers.has(account);
     }
 
-    function addPauser(address account) public onlyPauser {
+    function addPauser(address account) public virtual onlyPauser {
         _addPauser(account);
     }
 
-    function renouncePauser() public {
+    function renouncePauser() public virtual {
         _removePauser(_msgSender());
     }
 
-    function _addPauser(address account) internal {
+    function _addPauser(address account) internal virtual {
         _pausers.add(account);
         emit PauserAdded(account);
     }
 
-    function _removePauser(address account) internal {
+    function _removePauser(address account) internal virtual {
         _pausers.remove(account);
         emit PauserRemoved(account);
     }

contracts/access/roles/SignerRole.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 import "../../GSN/Context.sol";
 import "../Roles.sol";
@@ -24,20 +24,20 @@ contract SignerRole is Context {
         return _signers.has(account);
     }
 
-    function addSigner(address account) public onlySigner {
+    function addSigner(address account) public virtual onlySigner {
         _addSigner(account);
     }
 
-    function renounceSigner() public {
+    function renounceSigner() public virtual {
         _removeSigner(_msgSender());
     }
 
-    function _addSigner(address account) internal {
+    function _addSigner(address account) internal virtual {
         _signers.add(account);
         emit SignerAdded(account);
     }
 
-    function _removeSigner(address account) internal {
+    function _removeSigner(address account) internal virtual {
         _signers.remove(account);
         emit SignerRemoved(account);
     }