Migrate contracts to Solidity 0.7 (#2319)

* Update contract pragmas to solidity 0.7

* Remove internal declaration on constructors

* Reference SafeMath explicitely

* Remove public constructor declaration from abstract contracts

* Remove public constructor declaration from non-abstract contracts

.solhint.json

@@ -4,7 +4,7 @@
     "func-order": "off",
     "mark-callable-contracts": "off",
     "no-empty-blocks": "off",
-    "compiler-version": ["error", "^0.6.0"],
+    "compiler-version": ["error", "^0.7.0"],
     "private-vars-leading-underscore": "error"
   }
 }

README.md

@@ -28,12 +28,12 @@ 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 ^0.7.0;
 
 import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
 
 contract MyCollectible is ERC721 {
-    constructor() ERC721("MyCollectible", "MCO") public {
+    constructor() ERC721("MyCollectible", "MCO") {
     }
 }
 ```

contracts/GSN/Context.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 /*
  * @dev Provides information about the current execution context, including the

contracts/GSN/GSNRecipient.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./IRelayRecipient.sol";
 import "./IRelayHub.sol";

contracts/GSN/GSNRecipientERC20Fee.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./GSNRecipient.sol";
 import "../math/SafeMath.sol";
@@ -30,7 +30,7 @@ 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);
     }
 
@@ -116,7 +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;
+pragma solidity ^0.7.0;
 
 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;
+pragma solidity ^0.7.0;
 
 /**
  * @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;
+pragma solidity ^0.7.0;
 
 /**
  * @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;
+pragma solidity ^0.7.0;
 
 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;
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 /**
@@ -23,7 +23,7 @@ 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/cryptography/ECDSA.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 /**
  * @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;
+pragma solidity ^0.7.0;
 
 /**
  * @dev These functions deal with verification of Merkle trees (hash trees),

contracts/introspection/ERC165.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./IERC165.sol";
 
@@ -21,7 +21,7 @@ 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;
+pragma solidity ^0.7.0;
 
 /**
  * @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;
+pragma solidity ^0.7.0;
 
 import "./IERC1820Implementer.sol";
 

contracts/introspection/IERC165.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 /**
  * @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;
+pragma solidity ^0.7.0;
 
 /**
  * @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;
+pragma solidity ^0.7.0;
 
 /**
  * @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;
+pragma solidity ^0.7.0;
 
 /**
  * @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;
+pragma solidity ^0.7.0;
 
 /**
  * @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;
+pragma solidity ^0.7.0;
 
 /**
  * @title SignedSafeMath

contracts/mocks/AccessControlMock.sol

@@ -1,11 +1,11 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 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;
+pragma solidity ^0.7.0;
 
 import "../utils/Address.sol";
 

contracts/mocks/ArraysImpl.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 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/CallReceiverMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 contract CallReceiverMock {
 

contracts/mocks/ConditionalEscrowMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../payment/escrow/ConditionalEscrow.sol";
 

contracts/mocks/ContextMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 

contracts/mocks/CountersImpl.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../utils/Counters.sol";
 

contracts/mocks/Create2Impl.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../utils/Create2.sol";
 import "../introspection/ERC1820Implementer.sol";

contracts/mocks/ECDSAMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../cryptography/ECDSA.sol";
 

contracts/mocks/ERC1155BurnableMock.sol

@@ -1,11 +1,11 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC1155/ERC1155Burnable.sol";
 
 contract ERC1155BurnableMock is ERC1155Burnable {
-    constructor(string memory uri) public ERC1155(uri) { }
+    constructor(string memory uri) ERC1155(uri) { }
 
     function mint(address to, uint256 id, uint256 value, bytes memory data) public {
         _mint(to, id, value, data);

contracts/mocks/ERC1155Mock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC1155/ERC1155.sol";
 
@@ -9,7 +9,7 @@ import "../token/ERC1155/ERC1155.sol";
  * This mock just publicizes internal functions for testing purposes
  */
 contract ERC1155Mock is ERC1155 {
-    constructor (string memory uri) public ERC1155(uri) {
+    constructor (string memory uri) ERC1155(uri) {
         // solhint-disable-previous-line no-empty-blocks
     }
 

contracts/mocks/ERC1155PausableMock.sol

@@ -1,12 +1,12 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./ERC1155Mock.sol";
 import "../token/ERC1155/ERC1155Pausable.sol";
 
 contract ERC1155PausableMock is ERC1155Mock, ERC1155Pausable {
-    constructor(string memory uri) public ERC1155Mock(uri) { }
+    constructor(string memory uri) ERC1155Mock(uri) { }
 
     function pause() external {
         _pause();

contracts/mocks/ERC1155ReceiverMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC1155/IERC1155Receiver.sol";
 import "./ERC165Mock.sol";
@@ -20,7 +20,6 @@ contract ERC1155ReceiverMock is IERC1155Receiver, ERC165Mock {
         bytes4 batRetval,
         bool batReverts
     )
-        public
     {
         _recRetval = recRetval;
         _recReverts = recReverts;

contracts/mocks/ERC165/ERC165InterfacesSupported.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../../introspection/IERC165.sol";
 
@@ -29,7 +29,7 @@ contract SupportsInterfaceWithLookupMock is IERC165 {
      * @dev A contract implementing SupportsInterfaceWithLookup
      * implement ERC165 itself.
      */
-    constructor () public {
+    constructor () {
         _registerInterface(INTERFACE_ID_ERC165);
     }
 
@@ -50,7 +50,7 @@ contract SupportsInterfaceWithLookupMock is IERC165 {
 }
 
 contract ERC165InterfacesSupported is SupportsInterfaceWithLookupMock {
-    constructor (bytes4[] memory interfaceIds) public {
+    constructor (bytes4[] memory interfaceIds) {
         for (uint256 i = 0; i < interfaceIds.length; i++) {
             _registerInterface(interfaceIds[i]);
         }

contracts/mocks/ERC165/ERC165NotSupported.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 contract ERC165NotSupported { }

contracts/mocks/ERC165CheckerMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../introspection/ERC165Checker.sol";
 

contracts/mocks/ERC165Mock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../introspection/ERC165.sol";
 

contracts/mocks/ERC1820ImplementerMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../introspection/ERC1820Implementer.sol";
 

contracts/mocks/ERC20BurnableMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20Burnable.sol";
 
@@ -10,7 +10,7 @@ contract ERC20BurnableMock is ERC20Burnable {
         string memory symbol,
         address initialAccount,
         uint256 initialBalance
-    ) public ERC20(name, symbol) {
+    ) ERC20(name, symbol) {
         _mint(initialAccount, initialBalance);
     }
 }

contracts/mocks/ERC20CappedMock.sol

@@ -1,12 +1,12 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20Capped.sol";
 
 contract ERC20CappedMock is ERC20Capped {
     constructor (string memory name, string memory symbol, uint256 cap)
-        public ERC20(name, symbol) ERC20Capped(cap)
+        ERC20(name, symbol) ERC20Capped(cap)
     { }
 
     function mint(address to, uint256 tokenId) public {

contracts/mocks/ERC20DecimalsMock.sol

@@ -1,11 +1,11 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20.sol";
 
 contract ERC20DecimalsMock is ERC20 {
-    constructor (string memory name, string memory symbol, uint8 decimals) public ERC20(name, symbol) {
+    constructor (string memory name, string memory symbol, uint8 decimals) ERC20(name, symbol) {
         _setupDecimals(decimals);
     }
 }

contracts/mocks/ERC20Mock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20.sol";
 
@@ -11,7 +11,7 @@ contract ERC20Mock is ERC20 {
         string memory symbol,
         address initialAccount,
         uint256 initialBalance
-    ) public payable ERC20(name, symbol) {
+    ) payable ERC20(name, symbol) {
         _mint(initialAccount, initialBalance);
     }
 

contracts/mocks/ERC20PausableMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20Pausable.sol";
 
@@ -11,7 +11,7 @@ contract ERC20PausableMock is ERC20Pausable {
         string memory symbol,
         address initialAccount,
         uint256 initialBalance
-    ) public ERC20(name, symbol) {
+    ) ERC20(name, symbol) {
         _mint(initialAccount, initialBalance);
     }
 

contracts/mocks/ERC20SnapshotMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20Snapshot.sol";
 
@@ -11,7 +11,7 @@ contract ERC20SnapshotMock is ERC20Snapshot {
         string memory symbol,
         address initialAccount,
         uint256 initialBalance
-    ) public ERC20(name, symbol) {
+    ) ERC20(name, symbol) {
         _mint(initialAccount, initialBalance);
     }
 

contracts/mocks/ERC721BurnableMock.sol

@@ -1,11 +1,11 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC721/ERC721Burnable.sol";
 
 contract ERC721BurnableMock is ERC721Burnable {
-    constructor(string memory name, string memory symbol) public ERC721(name, symbol) { }
+    constructor(string memory name, string memory symbol) ERC721(name, symbol) { }
 
     function mint(address to, uint256 tokenId) public {
         _mint(to, tokenId);

contracts/mocks/ERC721GSNRecipientMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC721/ERC721.sol";
 import "../GSN/GSNRecipient.sol";
@@ -12,7 +12,6 @@ import "../GSN/GSNRecipientSignature.sol";
  */
 contract ERC721GSNRecipientMock is ERC721, GSNRecipient, GSNRecipientSignature {
     constructor(string memory name, string memory symbol, address trustedSigner)
-        public
         ERC721(name, symbol)
         GSNRecipientSignature(trustedSigner)
     { }

contracts/mocks/ERC721Mock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC721/ERC721.sol";
 
@@ -9,7 +9,7 @@ import "../token/ERC721/ERC721.sol";
  * This mock just provides a public safeMint, mint, and burn functions for testing purposes
  */
 contract ERC721Mock is ERC721 {
-    constructor (string memory name, string memory symbol) public ERC721(name, symbol) { }
+    constructor (string memory name, string memory symbol) ERC721(name, symbol) { }
 
     function exists(uint256 tokenId) public view returns (bool) {
         return _exists(tokenId);

contracts/mocks/ERC721PausableMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC721/ERC721Pausable.sol";
 
@@ -9,7 +9,7 @@ import "../token/ERC721/ERC721Pausable.sol";
  * This mock just provides a public mint, burn and exists functions for testing purposes
  */
 contract ERC721PausableMock is ERC721Pausable {
-    constructor (string memory name, string memory symbol) public ERC721(name, symbol) { }
+    constructor (string memory name, string memory symbol) ERC721(name, symbol) { }
 
     function mint(address to, uint256 tokenId) public {
         super._mint(to, tokenId);

contracts/mocks/ERC721ReceiverMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../token/ERC721/IERC721Receiver.sol";
 
@@ -10,7 +10,7 @@ contract ERC721ReceiverMock is IERC721Receiver {
 
     event Received(address operator, address from, uint256 tokenId, bytes data, uint256 gas);
 
-    constructor (bytes4 retval, bool reverts) public {
+    constructor (bytes4 retval, bool reverts) {
         _retval = retval;
         _reverts = reverts;
     }

contracts/mocks/ERC777Mock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 import "../token/ERC777/ERC777.sol";
@@ -12,7 +12,7 @@ contract ERC777Mock is Context, ERC777 {
         string memory name,
         string memory symbol,
         address[] memory defaultOperators
-    ) public ERC777(name, symbol, defaultOperators) {
+    ) ERC777(name, symbol, defaultOperators) {
         _mint(initialHolder, initialBalance, "", "");
     }
 

contracts/mocks/ERC777SenderRecipientMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 import "../token/ERC777/IERC777.sol";

contracts/mocks/EnumerableMapMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../utils/EnumerableMap.sol";
 

contracts/mocks/EnumerableSetMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../utils/EnumerableSet.sol";
 

contracts/mocks/EtherReceiverMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 contract EtherReceiverMock {
     bool private _acceptEther;

contracts/mocks/GSNRecipientERC20FeeMock.sol

@@ -1,12 +1,12 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../GSN/GSNRecipient.sol";
 import "../GSN/GSNRecipientERC20Fee.sol";
 
 contract GSNRecipientERC20FeeMock is GSNRecipient, GSNRecipientERC20Fee {
-    constructor(string memory name, string memory symbol) public GSNRecipientERC20Fee(name, symbol) { }
+    constructor(string memory name, string memory symbol) GSNRecipientERC20Fee(name, symbol) { }
 
     function mint(address account, uint256 amount) public {
         _mint(account, amount);

contracts/mocks/GSNRecipientMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./ContextMock.sol";
 import "../GSN/GSNRecipient.sol";

contracts/mocks/GSNRecipientSignatureMock.sol

@@ -1,12 +1,12 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../GSN/GSNRecipient.sol";
 import "../GSN/GSNRecipientSignature.sol";
 
 contract GSNRecipientSignatureMock is GSNRecipient, GSNRecipientSignature {
-    constructor(address trustedSigner) public GSNRecipientSignature(trustedSigner) { }
+    constructor(address trustedSigner) GSNRecipientSignature(trustedSigner) { }
 
     event MockFunctionCalled();
 

contracts/mocks/MathMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../math/Math.sol";
 

contracts/mocks/MerkleProofWrapper.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import { MerkleProof } from "../cryptography/MerkleProof.sol";
 

contracts/mocks/OwnableMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../access/Ownable.sol";
 

contracts/mocks/PausableMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../utils/Pausable.sol";
 
@@ -8,7 +8,7 @@ contract PausableMock is Pausable {
     bool public drasticMeasureTaken;
     uint256 public count;
 
-    constructor () public {
+    constructor () {
         drasticMeasureTaken = false;
         count = 0;
     }

contracts/mocks/PullPaymentMock.sol

@@ -1,12 +1,12 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../payment/PullPayment.sol";
 
 // mock class using PullPayment
 contract PullPaymentMock is PullPayment {
-    constructor () public payable { }
+    constructor () payable { }
 
     // test helper function to call asyncTransfer
     function callTransfer(address dest, uint256 amount) public {

contracts/mocks/ReentrancyAttack.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 contract ReentrancyAttack is Context {

contracts/mocks/ReentrancyMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../utils/ReentrancyGuard.sol";
 import "./ReentrancyAttack.sol";
@@ -8,7 +8,7 @@ import "./ReentrancyAttack.sol";
 contract ReentrancyMock is ReentrancyGuard {
     uint256 public counter;
 
-    constructor () public {
+    constructor () {
         counter = 0;
     }
 

contracts/mocks/SafeCastMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../utils/SafeCast.sol";
 

contracts/mocks/SafeERC20Helper.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 import "../token/ERC20/IERC20.sol";
@@ -98,7 +98,7 @@ contract SafeERC20Wrapper is Context {
 
     IERC20 private _token;
 
-    constructor (IERC20 token) public {
+    constructor (IERC20 token) {
         _token = token;
     }
 

contracts/mocks/SafeMathMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../math/SafeMath.sol";
 

contracts/mocks/SignedSafeMathMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../math/SignedSafeMath.sol";
 

contracts/mocks/StringsMock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../utils/Strings.sol";
 

contracts/payment/PaymentSplitter.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 import "../math/SafeMath.sol";
@@ -39,7 +39,7 @@ contract PaymentSplitter is Context {
      * All addresses in `payees` must be non-zero. Both arrays must have the same non-zero length, and there must be no
      * duplicates in `payees`.
      */
-    constructor (address[] memory payees, uint256[] memory shares) public payable {
+    constructor (address[] memory payees, uint256[] memory shares) payable {
         // solhint-disable-next-line max-line-length
         require(payees.length == shares.length, "PaymentSplitter: payees and shares length mismatch");
         require(payees.length > 0, "PaymentSplitter: no payees");

contracts/payment/PullPayment.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.2;
+pragma solidity ^0.7.0;
 
 import "./escrow/Escrow.sol";
 
@@ -25,7 +25,7 @@ import "./escrow/Escrow.sol";
 contract PullPayment {
     Escrow private _escrow;
 
-    constructor () internal {
+    constructor () {
         _escrow = new Escrow();
     }
 

contracts/payment/escrow/ConditionalEscrow.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./Escrow.sol";
 

contracts/payment/escrow/Escrow.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../../math/SafeMath.sol";
 import "../../access/Ownable.sol";

contracts/payment/escrow/RefundEscrow.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./ConditionalEscrow.sol";
 
@@ -27,7 +27,7 @@ contract RefundEscrow is ConditionalEscrow {
      * @dev Constructor.
      * @param beneficiary The beneficiary of the deposits.
      */
-    constructor (address payable beneficiary) public {
+    constructor (address payable beneficiary) {
         require(beneficiary != address(0), "RefundEscrow: beneficiary is the zero address");
         _beneficiary = beneficiary;
         _state = State.Active;

contracts/presets/ERC1155PresetMinterPauser.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../access/AccessControl.sol";
 import "../GSN/Context.sol";
@@ -30,7 +30,7 @@ contract ERC1155PresetMinterPauser is Context, AccessControl, ERC1155Burnable, E
      * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE`, and `PAUSER_ROLE` to the account that
      * deploys the contract.
      */
-    constructor(string memory uri) public ERC1155(uri) {
+    constructor(string memory uri) ERC1155(uri) {
         _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
 
         _setupRole(MINTER_ROLE, _msgSender());

contracts/presets/ERC20PresetMinterPauser.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../access/AccessControl.sol";
 import "../GSN/Context.sol";
@@ -32,7 +32,7 @@ contract ERC20PresetMinterPauser is Context, AccessControl, ERC20Burnable, ERC20
      *
      * See {ERC20-constructor}.
      */
-    constructor(string memory name, string memory symbol) public ERC20(name, symbol) {
+    constructor(string memory name, string memory symbol) ERC20(name, symbol) {
         _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
 
         _setupRole(MINTER_ROLE, _msgSender());

contracts/presets/ERC721PresetMinterPauserAutoId.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../access/AccessControl.sol";
 import "../GSN/Context.sol";
@@ -39,7 +39,7 @@ contract ERC721PresetMinterPauserAutoId is Context, AccessControl, ERC721Burnabl
      * Token URIs will be autogenerated based on `baseURI` and their token IDs.
      * See {ERC721-tokenURI}.
      */
-    constructor(string memory name, string memory symbol, string memory baseURI) public ERC721(name, symbol) {
+    constructor(string memory name, string memory symbol, string memory baseURI) ERC721(name, symbol) {
         _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
 
         _setupRole(MINTER_ROLE, _msgSender());

contracts/token/ERC1155/ERC1155.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./IERC1155.sol";
 import "./IERC1155MetadataURI.sol";
@@ -52,7 +52,7 @@ contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
     /**
      * @dev See {_setURI}.
      */
-    constructor (string memory uri) public {
+    constructor (string memory uri) {
         _setURI(uri);
 
         // register the supported interfaces to conform to ERC1155 via ERC165

contracts/token/ERC1155/ERC1155Burnable.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./ERC1155.sol";
 

contracts/token/ERC1155/ERC1155Holder.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./ERC1155Receiver.sol";
 

contracts/token/ERC1155/ERC1155Pausable.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./ERC1155.sol";
 import "../../utils/Pausable.sol";

contracts/token/ERC1155/ERC1155Receiver.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./IERC1155Receiver.sol";
 import "../../introspection/ERC165.sol";
@@ -9,7 +9,7 @@ import "../../introspection/ERC165.sol";
  * @dev _Available since v3.1._
  */
 abstract contract ERC1155Receiver is ERC165, IERC1155Receiver {
-    constructor() public {
+    constructor() {
         _registerInterface(
             ERC1155Receiver(0).onERC1155Received.selector ^
             ERC1155Receiver(0).onERC1155BatchReceived.selector

contracts/token/ERC1155/IERC1155.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.2;
+pragma solidity ^0.7.0;
 
 import "../../introspection/IERC165.sol";
 

contracts/token/ERC1155/IERC1155MetadataURI.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.2;
+pragma solidity ^0.7.0;
 
 import "./IERC1155.sol";
 

contracts/token/ERC1155/IERC1155Receiver.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../../introspection/IERC165.sol";
 

contracts/token/ERC20/ERC20.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../../GSN/Context.sol";
 import "./IERC20.sol";
@@ -54,7 +54,7 @@ contract ERC20 is Context, IERC20 {
      * All three of these values are immutable: they can only be set once during
      * construction.
      */
-    constructor (string memory name, string memory symbol) public {
+    constructor (string memory name, string memory symbol) {
         _name = name;
         _symbol = symbol;
         _decimals = 18;

contracts/token/ERC20/ERC20Burnable.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../../GSN/Context.sol";
 import "./ERC20.sol";
@@ -11,6 +11,8 @@ import "./ERC20.sol";
  * recognized off-chain (via event analysis).
  */
 abstract contract ERC20Burnable is Context, ERC20 {
+    using SafeMath for uint256;
+
     /**
      * @dev Destroys `amount` tokens from the caller.
      *

contracts/token/ERC20/ERC20Capped.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./ERC20.sol";
 
@@ -8,13 +8,15 @@ import "./ERC20.sol";
  * @dev Extension of {ERC20} that adds a cap to the supply of tokens.
  */
 abstract contract ERC20Capped is ERC20 {
+    using SafeMath for uint256;
+
     uint256 private _cap;
 
     /**
      * @dev Sets the value of the `cap`. This value is immutable, it can only be
      * set once during construction.
      */
-    constructor (uint256 cap) public {
+    constructor (uint256 cap) {
         require(cap > 0, "ERC20Capped: cap is 0");
         _cap = cap;
     }

contracts/token/ERC20/ERC20Pausable.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./ERC20.sol";
 import "../../utils/Pausable.sol";

contracts/token/ERC20/ERC20Snapshot.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../../math/SafeMath.sol";
 import "../../utils/Arrays.sol";

contracts/token/ERC20/IERC20.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 /**
  * @dev Interface of the ERC20 standard as defined in the EIP.

contracts/token/ERC20/SafeERC20.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./IERC20.sol";
 import "../../math/SafeMath.sol";

contracts/token/ERC20/TokenTimelock.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./SafeERC20.sol";
 
@@ -23,7 +23,7 @@ contract TokenTimelock {
     // timestamp when token release is enabled
     uint256 private _releaseTime;
 
-    constructor (IERC20 token, address beneficiary, uint256 releaseTime) public {
+    constructor (IERC20 token, address beneficiary, uint256 releaseTime) {
         // solhint-disable-next-line not-rely-on-time
         require(releaseTime > block.timestamp, "TokenTimelock: release time is before current time");
         _token = token;

contracts/token/ERC721/ERC721.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../../GSN/Context.sol";
 import "./IERC721.sol";
@@ -90,7 +90,7 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata, IERC721Enumerable
     /**
      * @dev Initializes the contract by setting a `name` and a `symbol` to the token collection.
      */
-    constructor (string memory name, string memory symbol) public {
+    constructor (string memory name, string memory symbol) {
         _name = name;
         _symbol = symbol;
 

contracts/token/ERC721/ERC721Burnable.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "../../GSN/Context.sol";
 import "./ERC721.sol";

contracts/token/ERC721/ERC721Holder.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./IERC721Receiver.sol";
 

contracts/token/ERC721/ERC721Pausable.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.0;
+pragma solidity ^0.7.0;
 
 import "./ERC721.sol";
 import "../../utils/Pausable.sol";

contracts/token/ERC721/IERC721.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.2;
+pragma solidity ^0.7.0;
 
 import "../../introspection/IERC165.sol";
 

contracts/token/ERC721/IERC721Enumerable.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.6.2;
+pragma solidity ^0.7.0;
 
 import "./IERC721.sol";