3.1.0-solc-0.7

This reverts commit c801c8d2bb.

.dependabot/config.yml

@@ -1,7 +0,0 @@
-version: 1
-
-update_configs:
-  - package_manager: "javascript"
-    directory: "/"
-    update_schedule: "weekly"
-    version_requirement_updates: "increase_versions"

.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"
   }
 }

CHANGELOG.md

@@ -1,5 +1,30 @@
 # Changelog
 
+## 3.1.0 (2020-06-23)
+
+### New features
+ * `SafeCast`: added functions to downcast signed integers (e.g. `toInt32`), improving usability of `SignedSafeMath`. ([#2243](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2243))
+ * `functionCall`: new helpers that replicate Solidity's function call semantics, reducing the need to rely on `call`. ([#2264](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2264))
+ * `ERC1155`: added support for a base implementation, non-standard extensions and a preset contract. ([#2014](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2014), [#2230](https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2230))
+
+### Improvements
+ * `ReentrancyGuard`: reduced overhead of using the `nonReentrant` modifier. ([#2171](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2171))
+ * `AccessControl`: added a `RoleAdminChanged` event to `_setAdminRole`. ([#2214](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2214))
+ * Made all `public` functions in the token preset contracts `virtual`. ([#2257](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2257))
+
+### Deprecations
+ * `SafeERC20`: deprecated `safeApprove`. ([#2268](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2268))
+
+## 3.0.2 (2020-06-08)
+
+### Improvements
+ * Added SPX license identifier to all contracts. ([#2235](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2235))
+
+## 3.0.1 (2020-04-27)
+
+### Bugfixes
+ * `ERC777`: fixed the `_approve` internal function not validating some of their arguments for non-zero addresses. ([#2213](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2213))
+
 ## 3.0.0 (2020-04-20)
 
 ### New features
@@ -37,6 +62,11 @@
  * `ERC20`: added a constructor for `name` and `symbol`. `decimals` now defaults to 18. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
  * `Strings`: renamed `fromUint256` to `toString` ([#2188](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2188))
 
+## 2.5.1 (2020-04-24)
+
+### Bugfixes
+ * `ERC777`: fixed the `_send` and `_approve` internal functions not validating some of their arguments for non-zero addresses. ([#2212](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2212))
+
 ## 2.5.0 (2020-02-04)
 
 ### New features

DOCUMENTATION.md

@@ -12,5 +12,5 @@ The [`docs.openzeppelin.com`](https://github.com/OpenZeppelin/docs.openzeppelin.
 repository hosts the configuration for the entire site, which includes
 documetation for all of the OpenZeppelin projects.
 
-To run the docs locally you should run `npm run docs start` on this
+To run the docs locally you should run `npm run docs:watch` on this
 repository.

LICENSE

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2016-2019 zOS Global Limited
+Copyright (c) 2016-2020 zOS Global Limited
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the

README.md

@@ -1,5 +1,6 @@
 # <img src="logo.png" alt="OpenZeppelin" height="40px">
 
+[![Docs](https://img.shields.io/badge/docs-%F0%9F%93%84-blue)](https://docs.openzeppelin.com/contracts)
 [![NPM Package](https://img.shields.io/npm/v/@openzeppelin/contracts.svg)](https://www.npmjs.org/package/@openzeppelin/contracts)
 [![Build Status](https://circleci.com/gh/OpenZeppelin/openzeppelin-contracts.svg?style=shield)](https://circleci.com/gh/OpenZeppelin/openzeppelin-contracts)
 [![Coverage Status](https://codecov.io/gh/OpenZeppelin/openzeppelin-contracts/graph/badge.svg)](https://codecov.io/gh/OpenZeppelin/openzeppelin-contracts)
@@ -10,7 +11,7 @@
  * Flexible [role-based permissioning](https://docs.openzeppelin.com/contracts/access-control) scheme.
  * Reusable [Solidity components](https://docs.openzeppelin.com/contracts/utilities) to build custom contracts and complex decentralized systems.
  * First-class integration with the [Gas Station Network](https://docs.openzeppelin.com/contracts/gsn) for systems with no gas fees!
- * Audited by leading security firms.
+ * Audited by leading security firms (_last full audit on v2.0.0_).
 
 ## Overview
 
@@ -27,13 +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 ^0.5.0;
+pragma solidity ^0.7.0;
 
-import "@openzeppelin/contracts/token/ERC721/ERC721Full.sol";
-import "@openzeppelin/contracts/token/ERC721/ERC721Mintable.sol";
+import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
 
-contract MyNFT is ERC721Full, ERC721Mintable {
-    constructor() ERC721Full("MyNFT", "MNFT") public {
+contract MyCollectible is ERC721 {
+    constructor() ERC721("MyCollectible", "MCO") {
     }
 }
 ```

contracts/GSN/Context.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /*
  * @dev Provides information about the current execution context, including the
@@ -10,11 +12,7 @@ pragma solidity ^0.6.0;
  *
  * This contract is only required for intermediate, library-like contracts.
  */
-contract Context {
-    // Empty internal constructor, to prevent people from mistakenly deploying
-    // an instance of this contract, which should be used via inheritance.
-    constructor () internal { }
-
+abstract contract Context {
     function _msgSender() internal view virtual returns (address payable) {
         return msg.sender;
     }

contracts/GSN/GSNRecipient.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "./IRelayRecipient.sol";
 import "./IRelayHub.sol";

contracts/GSN/GSNRecipientERC20Fee.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "./GSNRecipient.sol";
 import "../math/SafeMath.sol";
@@ -28,7 +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);
     }
 
@@ -114,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "./GSNRecipient.sol";
 import "../cryptography/ECDSA.sol";
@@ -21,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev Interface for `RelayHub`, the core contract of the GSN. Users should not need to interact with this contract
@@ -178,7 +180,7 @@ interface IRelayHub {
      *  - `gasLimit`: gas to forward when calling the encoded function
      *  - `nonce`: client's nonce
      *  - `signature`: client's signature over all previous params, plus the relay and RelayHub addresses
-     *  - `approvalData`: dapp-specific data forwared to {acceptRelayedCall}. This value is *not* verified by the
+     *  - `approvalData`: dapp-specific data forwarded to {acceptRelayedCall}. This value is *not* verified by the
      * `RelayHub`, but it still can be used for e.g. a signature.
      *
      * Emits a {TransactionRelayed} event.

contracts/GSN/IRelayRecipient.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev Base interface for a contract that will be called via the GSN from {IRelayHub}.

contracts/GSN/README.adoc

@@ -1,5 +1,8 @@
 = Gas Station Network (GSN)
 
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/gsn
+
 This set of contracts provide all the tools required to make a contract callable via the https://gsn.openzeppelin.com[Gas Station Network].
 
 TIP: If you're new to the GSN, head over to our xref:learn::sending-gasless-transactions.adoc[overview of the system] and basic guide to xref:ROOT:gsn.adoc[creating a GSN-capable contract].

contracts/access/AccessControl.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/EnumerableSet.sol";
 import "../utils/Address.sol";
@@ -21,7 +23,7 @@ import "../GSN/Context.sol";
  *
  * ```
  * function foo() public {
- *     require(hasRole(MY_ROLE, _msgSender()));
+ *     require(hasRole(MY_ROLE, msg.sender));
  *     ...
  * }
  * ```
@@ -34,6 +36,10 @@ import "../GSN/Context.sol";
  * that only accounts with this role will be able to grant or revoke other
  * roles. More complex role relationships can be created by using
  * {_setRoleAdmin}.
+ *
+ * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
+ * grant and revoke this role. Extra precautions should be taken to secure
+ * accounts that have been granted it.
  */
 abstract contract AccessControl is Context {
     using EnumerableSet for EnumerableSet.AddressSet;
@@ -48,6 +54,16 @@ abstract contract AccessControl is Context {
 
     bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;
 
+    /**
+     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
+     *
+     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
+     * {RoleAdminChanged} not being emitted signaling this.
+     *
+     * _Available since v3.1._
+     */
+    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);
+
     /**
      * @dev Emitted when `account` is granted `role`.
      *
@@ -179,8 +195,11 @@ abstract contract AccessControl is Context {
 
     /**
      * @dev Sets `adminRole` as ``role``'s admin role.
+     *
+     * Emits a {RoleAdminChanged} event.
      */
     function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
+        emit RoleAdminChanged(role, _roles[role].adminRole, adminRole);
         _roles[role].adminRole = adminRole;
     }
 

contracts/access/Ownable.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 /**
@@ -21,7 +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/access/README.adoc

@@ -1,5 +1,8 @@
 = Access
 
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/access
+
 Contract modules for authorization and access control mechanisms.
 
 == Contracts

contracts/cryptography/ECDSA.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.

contracts/cryptography/MerkleProof.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev These functions deal with verification of Merkle trees (hash trees),

contracts/cryptography/README.adoc

@@ -1,5 +1,8 @@
 = Cryptography
 
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/cryptography
+
 This collection of libraries provides simple and safe ways to use different cryptographic primitives.
 
 == Libraries

contracts/drafts/TokenVesting.sol

@@ -1,174 +0,0 @@
-pragma solidity ^0.6.0;
-
-import "../token/ERC20/SafeERC20.sol";
-import "../access/Ownable.sol";
-import "../math/SafeMath.sol";
-
-/**
- * @title TokenVesting
- * @dev A token holder contract that can release its token balance gradually like a
- * typical vesting scheme, with a cliff and vesting period. Optionally revocable by the
- * owner.
- */
-contract TokenVesting is Ownable {
-    // The vesting schedule is time-based (i.e. using block timestamps as opposed to e.g. block numbers), and is
-    // therefore sensitive to timestamp manipulation (which is something miners can do, to a certain degree). Therefore,
-    // it is recommended to avoid using short time durations (less than a minute). Typical vesting schemes, with a
-    // cliff period of a year and a duration of four years, are safe to use.
-    // solhint-disable not-rely-on-time
-
-    using SafeMath for uint256;
-    using SafeERC20 for IERC20;
-
-    event TokensReleased(address token, uint256 amount);
-    event TokenVestingRevoked(address token);
-
-    // beneficiary of tokens after they are released
-    address private _beneficiary;
-
-    // Durations and timestamps are expressed in UNIX time, the same units as block.timestamp.
-    uint256 private _cliff;
-    uint256 private _start;
-    uint256 private _duration;
-
-    bool private _revocable;
-
-    mapping (address => uint256) private _released;
-    mapping (address => bool) private _revoked;
-
-    /**
-     * @dev Creates a vesting contract that vests its balance of any ERC20 token to the
-     * beneficiary, gradually in a linear fashion until start + duration. By then all
-     * of the balance will have vested.
-     * @param beneficiary address of the beneficiary to whom vested tokens are transferred
-     * @param cliffDuration duration in seconds of the cliff in which tokens will begin to vest
-     * @param start the time (as Unix time) at which point vesting starts
-     * @param duration duration in seconds of the period in which the tokens will vest
-     * @param revocable whether the vesting is revocable or not
-     */
-    constructor (address beneficiary, uint256 start, uint256 cliffDuration, uint256 duration, bool revocable) public {
-        require(beneficiary != address(0), "TokenVesting: beneficiary is the zero address");
-        // solhint-disable-next-line max-line-length
-        require(cliffDuration <= duration, "TokenVesting: cliff is longer than duration");
-        require(duration > 0, "TokenVesting: duration is 0");
-        // solhint-disable-next-line max-line-length
-        require(start.add(duration) > block.timestamp, "TokenVesting: final time is before current time");
-
-        _beneficiary = beneficiary;
-        _revocable = revocable;
-        _duration = duration;
-        _cliff = start.add(cliffDuration);
-        _start = start;
-    }
-
-    /**
-     * @return the beneficiary of the tokens.
-     */
-    function beneficiary() public view returns (address) {
-        return _beneficiary;
-    }
-
-    /**
-     * @return the cliff time of the token vesting.
-     */
-    function cliff() public view returns (uint256) {
-        return _cliff;
-    }
-
-    /**
-     * @return the start time of the token vesting.
-     */
-    function start() public view returns (uint256) {
-        return _start;
-    }
-
-    /**
-     * @return the duration of the token vesting.
-     */
-    function duration() public view returns (uint256) {
-        return _duration;
-    }
-
-    /**
-     * @return true if the vesting is revocable.
-     */
-    function revocable() public view returns (bool) {
-        return _revocable;
-    }
-
-    /**
-     * @return the amount of the token released.
-     */
-    function released(address token) public view returns (uint256) {
-        return _released[token];
-    }
-
-    /**
-     * @return true if the token is revoked.
-     */
-    function revoked(address token) public view returns (bool) {
-        return _revoked[token];
-    }
-
-    /**
-     * @notice Transfers vested tokens to beneficiary.
-     * @param token ERC20 token which is being vested
-     */
-    function release(IERC20 token) public {
-        uint256 unreleased = _releasableAmount(token);
-
-        require(unreleased > 0, "TokenVesting: no tokens are due");
-
-        _released[address(token)] = _released[address(token)].add(unreleased);
-
-        token.safeTransfer(_beneficiary, unreleased);
-
-        emit TokensReleased(address(token), unreleased);
-    }
-
-    /**
-     * @notice Allows the owner to revoke the vesting. Tokens already vested
-     * remain in the contract, the rest are returned to the owner.
-     * @param token ERC20 token which is being vested
-     */
-    function revoke(IERC20 token) public onlyOwner {
-        require(_revocable, "TokenVesting: cannot revoke");
-        require(!_revoked[address(token)], "TokenVesting: token already revoked");
-
-        uint256 balance = token.balanceOf(address(this));
-
-        uint256 unreleased = _releasableAmount(token);
-        uint256 refund = balance.sub(unreleased);
-
-        _revoked[address(token)] = true;
-
-        token.safeTransfer(owner(), refund);
-
-        emit TokenVestingRevoked(address(token));
-    }
-
-    /**
-     * @dev Calculates the amount that has already vested but hasn't been released yet.
-     * @param token ERC20 token which is being vested
-     */
-    function _releasableAmount(IERC20 token) private view returns (uint256) {
-        return _vestedAmount(token).sub(_released[address(token)]);
-    }
-
-    /**
-     * @dev Calculates the amount that has already vested.
-     * @param token ERC20 token which is being vested
-     */
-    function _vestedAmount(IERC20 token) private view returns (uint256) {
-        uint256 currentBalance = token.balanceOf(address(this));
-        uint256 totalBalance = currentBalance.add(_released[address(token)]);
-
-        if (block.timestamp < _cliff) {
-            return 0;
-        } else if (block.timestamp >= _start.add(_duration) || _revoked[address(token)]) {
-            return totalBalance;
-        } else {
-            return totalBalance.mul(block.timestamp.sub(_start)).div(_duration);
-        }
-    }
-}

contracts/introspection/ERC165.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "./IERC165.sol";
 
@@ -19,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.2;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev Library used to query support of an interface declared via {IERC165}.

contracts/introspection/ERC1820Implementer.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "./IERC1820Implementer.sol";
 

contracts/introspection/IERC165.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev Interface of the ERC165 standard, as defined in the

contracts/introspection/IERC1820Implementer.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev Interface for an ERC1820 implementer, as defined in the

contracts/introspection/IERC1820Registry.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev Interface of the global ERC1820 Registry, as defined in the

contracts/introspection/README.adoc

@@ -1,5 +1,8 @@
 = Introspection
 
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/introspection
+
 This set of interfaces and contracts deal with https://en.wikipedia.org/wiki/Type_introspection[type introspection] of contracts, that is, examining which functions can be called on them. This is usually referred to as a contract's _interface_.
 
 Ethereum contracts have no native concept of an interface, so applications must usually simply trust they are not making an incorrect call. For trusted setups this is a non-issue, but often unknown and untrusted third-party addresses need to be interacted with. There may even not be any direct calls to them! (e.g. `ERC20` tokens may be sent to a contract that lacks a way to transfer them out of it, locking them forever). In these cases, a contract _declaring_ its interface can be very helpful in preventing errors.

contracts/math/Math.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev Standard math utilities missing in the Solidity language.

contracts/math/README.adoc

@@ -1,5 +1,8 @@
 = Math
 
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/math
+
 These are math-related utilities.
 
 == Libraries

contracts/math/SafeMath.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @dev Wrappers over Solidity's arithmetic operations with added overflow
@@ -21,6 +23,7 @@ library SafeMath {
      * Counterpart to Solidity's `+` operator.
      *
      * Requirements:
+     *
      * - Addition cannot overflow.
      */
     function add(uint256 a, uint256 b) internal pure returns (uint256) {
@@ -37,6 +40,7 @@ library SafeMath {
      * Counterpart to Solidity's `-` operator.
      *
      * Requirements:
+     *
      * - Subtraction cannot overflow.
      */
     function sub(uint256 a, uint256 b) internal pure returns (uint256) {
@@ -50,6 +54,7 @@ library SafeMath {
      * Counterpart to Solidity's `-` operator.
      *
      * Requirements:
+     *
      * - Subtraction cannot overflow.
      */
     function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
@@ -66,6 +71,7 @@ library SafeMath {
      * Counterpart to Solidity's `*` operator.
      *
      * Requirements:
+     *
      * - Multiplication cannot overflow.
      */
     function mul(uint256 a, uint256 b) internal pure returns (uint256) {
@@ -91,6 +97,7 @@ library SafeMath {
      * uses an invalid opcode to revert (consuming all remaining gas).
      *
      * Requirements:
+     *
      * - The divisor cannot be zero.
      */
     function div(uint256 a, uint256 b) internal pure returns (uint256) {
@@ -106,10 +113,10 @@ library SafeMath {
      * uses an invalid opcode to revert (consuming all remaining gas).
      *
      * Requirements:
+     *
      * - The divisor cannot be zero.
      */
     function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
-        // Solidity only automatically asserts when dividing by 0
         require(b > 0, errorMessage);
         uint256 c = a / b;
         // assert(a == b * c + a % b); // There is no case in which this doesn't hold
@@ -126,6 +133,7 @@ library SafeMath {
      * invalid opcode to revert (consuming all remaining gas).
      *
      * Requirements:
+     *
      * - The divisor cannot be zero.
      */
     function mod(uint256 a, uint256 b) internal pure returns (uint256) {
@@ -141,6 +149,7 @@ library SafeMath {
      * invalid opcode to revert (consuming all remaining gas).
      *
      * Requirements:
+     *
      * - The divisor cannot be zero.
      */
     function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {

contracts/math/SignedSafeMath.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 /**
  * @title SignedSafeMath
@@ -7,8 +9,15 @@ pragma solidity ^0.6.0;
 library SignedSafeMath {
     int256 constant private _INT256_MIN = -2**255;
 
-    /**
-     * @dev Multiplies two signed integers, reverts on overflow.
+        /**
+     * @dev Returns the multiplication of two signed integers, reverting on
+     * overflow.
+     *
+     * Counterpart to Solidity's `*` operator.
+     *
+     * Requirements:
+     *
+     * - Multiplication cannot overflow.
      */
     function mul(int256 a, int256 b) internal pure returns (int256) {
         // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
@@ -27,7 +36,16 @@ library SignedSafeMath {
     }
 
     /**
-     * @dev Integer division of two signed integers truncating the quotient, reverts on division by zero.
+     * @dev Returns the integer division of two signed integers. Reverts on
+     * division by zero. The result is rounded towards zero.
+     *
+     * Counterpart to Solidity's `/` operator. Note: this function uses a
+     * `revert` opcode (which leaves remaining gas untouched) while Solidity
+     * uses an invalid opcode to revert (consuming all remaining gas).
+     *
+     * Requirements:
+     *
+     * - The divisor cannot be zero.
      */
     function div(int256 a, int256 b) internal pure returns (int256) {
         require(b != 0, "SignedSafeMath: division by zero");
@@ -39,7 +57,14 @@ library SignedSafeMath {
     }
 
     /**
-     * @dev Subtracts two signed integers, reverts on overflow.
+     * @dev Returns the subtraction of two signed integers, reverting on
+     * overflow.
+     *
+     * Counterpart to Solidity's `-` operator.
+     *
+     * Requirements:
+     *
+     * - Subtraction cannot overflow.
      */
     function sub(int256 a, int256 b) internal pure returns (int256) {
         int256 c = a - b;
@@ -49,7 +74,14 @@ library SignedSafeMath {
     }
 
     /**
-     * @dev Adds two signed integers, reverts on overflow.
+     * @dev Returns the addition of two signed integers, reverting on
+     * overflow.
+     *
+     * Counterpart to Solidity's `+` operator.
+     *
+     * Requirements:
+     *
+     * - Addition cannot overflow.
      */
     function add(int256 a, int256 b) internal pure returns (int256) {
         int256 c = a + b;

contracts/mocks/AccessControlMock.sol

@@ -1,9 +1,11 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+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

@@ -1,8 +1,12 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/Address.sol";
 
 contract AddressImpl {
+    event CallReturnValue(string data);
+
     function isContract(address account) external view returns (bool) {
         return Address.isContract(account);
     }
@@ -11,6 +15,18 @@ contract AddressImpl {
         Address.sendValue(receiver, amount);
     }
 
+    function functionCall(address target, bytes calldata data) external {
+        bytes memory returnData = Address.functionCall(target, data);
+
+        emit CallReturnValue(abi.decode(returnData, (string)));
+    }
+
+    function functionCallWithValue(address target, bytes calldata data, uint256 value) external payable {
+        bytes memory returnData = Address.functionCallWithValue(target, data, value);
+
+        emit CallReturnValue(abi.decode(returnData, (string)));
+    }
+
     // sendValue's tests require the contract to hold Ether
     receive () external payable { }
 }

contracts/mocks/ArraysImpl.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/Arrays.sol";
 
@@ -7,7 +9,7 @@ contract ArraysImpl {
 
     uint256[] private _array;
 
-    constructor (uint256[] memory array) public {
+    constructor (uint256[] memory array) {
         _array = array;
     }
 

contracts/mocks/CallReceiverMock.sol

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+contract CallReceiverMock {
+
+    event MockFunctionCalled();
+
+    uint256[] private _array;
+
+    function mockFunction() public payable returns (string memory) {
+        emit MockFunctionCalled();
+
+        return "0x1234";
+    }
+
+    function mockFunctionNonPayable() public returns (string memory) {
+        emit MockFunctionCalled();
+
+        return "0x1234";
+    }
+
+    function mockFunctionRevertsNoReason() public payable {
+        revert();
+    }
+
+    function mockFunctionRevertsReason() public payable {
+        revert("CallReceiverMock: reverting");
+    }
+
+    function mockFunctionThrows() public payable {
+        assert(false);
+    }
+
+    function mockFunctionOutOfGas() public payable {
+        for (uint256 i = 0; ; ++i) {
+            _array.push(i);
+        }
+    }
+}

contracts/mocks/ConditionalEscrowMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../payment/escrow/ConditionalEscrow.sol";
 

contracts/mocks/ContextMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 

contracts/mocks/CountersImpl.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/Counters.sol";
 

contracts/mocks/Create2Impl.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/Create2.sol";
 import "../introspection/ERC1820Implementer.sol";

contracts/mocks/ECDSAMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../cryptography/ECDSA.sol";
 

contracts/mocks/ERC1155BurnableMock.sol

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "../token/ERC1155/ERC1155Burnable.sol";
+
+contract ERC1155BurnableMock is ERC1155Burnable {
+    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

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "../token/ERC1155/ERC1155.sol";
+
+/**
+ * @title ERC1155Mock
+ * This mock just publicizes internal functions for testing purposes
+ */
+contract ERC1155Mock is ERC1155 {
+    constructor (string memory uri) ERC1155(uri) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    function setURI(string memory newuri) public {
+        _setURI(newuri);
+    }
+
+    function mint(address to, uint256 id, uint256 value, bytes memory data) public {
+        _mint(to, id, value, data);
+    }
+
+    function mintBatch(address to, uint256[] memory ids, uint256[] memory values, bytes memory data) public {
+        _mintBatch(to, ids, values, data);
+    }
+
+    function burn(address owner, uint256 id, uint256 value) public {
+        _burn(owner, id, value);
+    }
+
+    function burnBatch(address owner, uint256[] memory ids, uint256[] memory values) public {
+        _burnBatch(owner, ids, values);
+    }
+}

contracts/mocks/ERC1155PausableMock.sol

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "./ERC1155Mock.sol";
+import "../token/ERC1155/ERC1155Pausable.sol";
+
+contract ERC1155PausableMock is ERC1155Mock, ERC1155Pausable {
+    constructor(string memory uri) ERC1155Mock(uri) { }
+
+    function pause() external {
+        _pause();
+    }
+
+    function unpause() external {
+        _unpause();
+    }
+
+    function _beforeTokenTransfer(
+        address operator,
+        address from,
+        address to,
+        uint256[] memory ids,
+        uint256[] memory amounts,
+        bytes memory data
+    )
+        internal virtual override(ERC1155, ERC1155Pausable)
+    {
+        super._beforeTokenTransfer(operator, from, to, ids, amounts, data);
+    }
+}

contracts/mocks/ERC1155ReceiverMock.sol

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "../token/ERC1155/IERC1155Receiver.sol";
+import "./ERC165Mock.sol";
+
+contract ERC1155ReceiverMock is IERC1155Receiver, ERC165Mock {
+    bytes4 private _recRetval;
+    bool private _recReverts;
+    bytes4 private _batRetval;
+    bool private _batReverts;
+
+    event Received(address operator, address from, uint256 id, uint256 value, bytes data, uint256 gas);
+    event BatchReceived(address operator, address from, uint256[] ids, uint256[] values, bytes data, uint256 gas);
+
+    constructor (
+        bytes4 recRetval,
+        bool recReverts,
+        bytes4 batRetval,
+        bool batReverts
+    )
+    {
+        _recRetval = recRetval;
+        _recReverts = recReverts;
+        _batRetval = batRetval;
+        _batReverts = batReverts;
+    }
+
+    function onERC1155Received(
+        address operator,
+        address from,
+        uint256 id,
+        uint256 value,
+        bytes calldata data
+    )
+        external
+        override
+        returns(bytes4)
+    {
+        require(!_recReverts, "ERC1155ReceiverMock: reverting on receive");
+        emit Received(operator, from, id, value, data, gasleft());
+        return _recRetval;
+    }
+
+    function onERC1155BatchReceived(
+        address operator,
+        address from,
+        uint256[] calldata ids,
+        uint256[] calldata values,
+        bytes calldata data
+    )
+        external
+        override
+        returns(bytes4)
+    {
+        require(!_batReverts, "ERC1155ReceiverMock: reverting on batch receive");
+        emit BatchReceived(operator, from, ids, values, data, gasleft());
+        return _batRetval;
+    }
+}

contracts/mocks/ERC165/ERC165InterfacesSupported.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../../introspection/IERC165.sol";
 
@@ -27,7 +29,7 @@ contract SupportsInterfaceWithLookupMock is IERC165 {
      * @dev A contract implementing SupportsInterfaceWithLookup
      * implement ERC165 itself.
      */
-    constructor () public {
+    constructor () {
         _registerInterface(INTERFACE_ID_ERC165);
     }
 
@@ -48,7 +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

@@ -1,3 +1,5 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 contract ERC165NotSupported { }

contracts/mocks/ERC165CheckerMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../introspection/ERC165Checker.sol";
 

contracts/mocks/ERC165Mock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../introspection/ERC165.sol";
 

contracts/mocks/ERC1820ImplementerMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../introspection/ERC1820Implementer.sol";
 

contracts/mocks/ERC20BurnableMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20Burnable.sol";
 
@@ -8,7 +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

@@ -1,10 +1,12 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+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

@@ -1,9 +1,11 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20.sol";
 
@@ -9,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20Pausable.sol";
 
@@ -9,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../token/ERC20/ERC20Snapshot.sol";
 
@@ -9,7 +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

@@ -1,9 +1,11 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../token/ERC721/ERC721.sol";
 import "../GSN/GSNRecipient.sol";
@@ -10,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../token/ERC721/ERC721.sol";
 
@@ -7,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../token/ERC721/ERC721Pausable.sol";
 
@@ -7,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../token/ERC721/IERC721Receiver.sol";
 
@@ -8,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 import "../token/ERC777/ERC777.sol";
@@ -10,7 +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, "", "");
     }
 
@@ -22,4 +24,8 @@ contract ERC777Mock is Context, ERC777 {
     ) public {
         _mint(to, amount, userData, operatorData);
     }
+
+    function approveInternal(address holder, address spender, uint256 value) public {
+        _approve(holder, spender, value);
+    }
 }

contracts/mocks/ERC777SenderRecipientMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 import "../token/ERC777/IERC777.sol";

contracts/mocks/EnumerableMapMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/EnumerableMap.sol";
 

contracts/mocks/EnumerableSetMock.sol

@@ -1,8 +1,11 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/EnumerableSet.sol";
 
-contract EnumerableSetMock {
+// AddressSet
+contract EnumerableAddressSetMock {
     using EnumerableSet for EnumerableSet.AddressSet;
 
     event OperationResult(bool result);
@@ -31,3 +34,34 @@ contract EnumerableSetMock {
         return _set.at(index);
     }
 }
+
+// UintSet
+contract EnumerableUintSetMock {
+    using EnumerableSet for EnumerableSet.UintSet;
+
+    event OperationResult(bool result);
+
+    EnumerableSet.UintSet private _set;
+
+    function contains(uint256 value) public view returns (bool) {
+        return _set.contains(value);
+    }
+
+    function add(uint256 value) public {
+        bool result = _set.add(value);
+        emit OperationResult(result);
+    }
+
+    function remove(uint256 value) public {
+        bool result = _set.remove(value);
+        emit OperationResult(result);
+    }
+
+    function length() public view returns (uint256) {
+        return _set.length();
+    }
+
+    function at(uint256 index) public view returns (uint256) {
+        return _set.at(index);
+    }
+}

contracts/mocks/EtherReceiverMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 contract EtherReceiverMock {
     bool private _acceptEther;

contracts/mocks/GSNRecipientERC20FeeMock.sol

@@ -1,10 +1,12 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "./ContextMock.sol";
 import "../GSN/GSNRecipient.sol";

contracts/mocks/GSNRecipientSignatureMock.sol

@@ -1,10 +1,12 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../math/Math.sol";
 

contracts/mocks/MerkleProofWrapper.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import { MerkleProof } from "../cryptography/MerkleProof.sol";
 

contracts/mocks/OwnableMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../access/Ownable.sol";
 

contracts/mocks/PausableMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/Pausable.sol";
 
@@ -6,7 +8,7 @@ contract PausableMock is Pausable {
     bool public drasticMeasureTaken;
     uint256 public count;
 
-    constructor () public {
+    constructor () {
         drasticMeasureTaken = false;
         count = 0;
     }

contracts/mocks/PullPaymentMock.sol

@@ -1,10 +1,12 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 contract ReentrancyAttack is Context {

contracts/mocks/ReentrancyMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/ReentrancyGuard.sol";
 import "./ReentrancyAttack.sol";
@@ -6,7 +8,7 @@ import "./ReentrancyAttack.sol";
 contract ReentrancyMock is ReentrancyGuard {
     uint256 public counter;
 
-    constructor () public {
+    constructor () {
         counter = 0;
     }
 

contracts/mocks/SafeCastMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/SafeCast.sol";
 
@@ -33,4 +35,24 @@ contract SafeCastMock {
     function toUint8(uint a) public pure returns (uint8) {
         return a.toUint8();
     }
+
+    function toInt128(int a) public pure returns (int128) {
+        return a.toInt128();
+    }
+
+    function toInt64(int a) public pure returns (int64) {
+        return a.toInt64();
+    }
+
+    function toInt32(int a) public pure returns (int32) {
+        return a.toInt32();
+    }
+
+    function toInt16(int a) public pure returns (int16) {
+        return a.toInt16();
+    }
+
+    function toInt8(int a) public pure returns (int8) {
+        return a.toInt8();
+    }
 }

contracts/mocks/SafeERC20Helper.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 import "../token/ERC20/IERC20.sol";
@@ -96,7 +98,7 @@ contract SafeERC20Wrapper is Context {
 
     IERC20 private _token;
 
-    constructor (IERC20 token) public {
+    constructor (IERC20 token) {
         _token = token;
     }
 

contracts/mocks/SafeMathMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../math/SafeMath.sol";
 

contracts/mocks/SignedSafeMathMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../math/SignedSafeMath.sol";
 

contracts/mocks/StringsMock.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../utils/Strings.sol";
 

contracts/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@openzeppelin/contracts",
-  "version": "3.0.0",
+  "version": "3.1.0-solc-0.7",
   "description": "Secure Smart Contract library for Solidity",
   "files": [
     "**/*.sol",

contracts/payment/PaymentSplitter.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../GSN/Context.sol";
 import "../math/SafeMath.sol";
@@ -37,7 +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

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.2;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "./escrow/Escrow.sol";
 
@@ -23,7 +25,7 @@ import "./escrow/Escrow.sol";
 contract PullPayment {
     Escrow private _escrow;
 
-    constructor () internal {
+    constructor () {
         _escrow = new Escrow();
     }
 
@@ -62,10 +64,6 @@ contract PullPayment {
      * @param amount The amount to transfer.
      */
     function _asyncTransfer(address dest, uint256 amount) internal virtual {
-        // solhint-disable-previous-line no-unused-vars
-
-        // TODO: remove the previous linter directive once
-        // https://github.com/protofire/solhint/issues/170 is fixed
         _escrow.deposit{ value: amount }(dest);
     }
 }

contracts/payment/README.adoc

@@ -1,5 +1,8 @@
 = Payment
 
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/payment
+
 Utilities related to sending and receiving payments. Examples are {PullPayment}, which implements the best security practices when sending funds to third parties, and {PaymentSplitter} to receive incoming payments among a number of beneficiaries.
 
 TIP: When transferring funds to and from untrusted third parties, there is always a security risk of reentrancy. If you would like to learn more about this and ways to protect against it, check out our blog post https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].

contracts/payment/escrow/ConditionalEscrow.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "./Escrow.sol";
 

contracts/payment/escrow/Escrow.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../../math/SafeMath.sol";
 import "../../access/Ownable.sol";

contracts/payment/escrow/RefundEscrow.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "./ConditionalEscrow.sol";
 
@@ -25,7 +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

@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "../access/AccessControl.sol";
+import "../GSN/Context.sol";
+import "../token/ERC1155/ERC1155.sol";
+import "../token/ERC1155/ERC1155Burnable.sol";
+import "../token/ERC1155/ERC1155Pausable.sol";
+
+/**
+ * @dev {ERC1155} token, including:
+ *
+ *  - ability for holders to burn (destroy) their tokens
+ *  - a minter role that allows for token minting (creation)
+ *  - a pauser role that allows to stop all token transfers
+ *
+ * This contract uses {AccessControl} to lock permissioned functions using the
+ * different roles - head to its documentation for details.
+ *
+ * The account that deploys the contract will be granted the minter and pauser
+ * roles, as well as the default admin role, which will let it grant both minter
+ * and pauser roles to other accounts.
+ */
+contract ERC1155PresetMinterPauser is Context, AccessControl, ERC1155Burnable, ERC1155Pausable {
+    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
+    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");
+
+    /**
+     * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE`, and `PAUSER_ROLE` to the account that
+     * deploys the contract.
+     */
+    constructor(string memory uri) ERC1155(uri) {
+        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
+
+        _setupRole(MINTER_ROLE, _msgSender());
+        _setupRole(PAUSER_ROLE, _msgSender());
+    }
+
+    /**
+     * @dev Creates `amount` new tokens for `to`, of token type `id`.
+     *
+     * See {ERC1155-_mint}.
+     *
+     * Requirements:
+     *
+     * - the caller must have the `MINTER_ROLE`.
+     */
+    function mint(address to, uint256 id, uint256 amount, bytes memory data) public virtual {
+        require(hasRole(MINTER_ROLE, _msgSender()), "ERC1155PresetMinterPauser: must have minter role to mint");
+
+        _mint(to, id, amount, data);
+    }
+
+    /**
+     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] variant of {mint}.
+     */
+    function mintBatch(address to, uint256[] memory ids, uint256[] memory amounts, bytes memory data) public virtual {
+        require(hasRole(MINTER_ROLE, _msgSender()), "ERC1155PresetMinterPauser: must have minter role to mint");
+
+        _mintBatch(to, ids, amounts, data);
+    }
+
+    /**
+     * @dev Pauses all token transfers.
+     *
+     * See {ERC1155Pausable} and {Pausable-_pause}.
+     *
+     * Requirements:
+     *
+     * - the caller must have the `PAUSER_ROLE`.
+     */
+    function pause() public virtual {
+        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC1155PresetMinterPauser: must have pauser role to pause");
+        _pause();
+    }
+
+    /**
+     * @dev Unpauses all token transfers.
+     *
+     * See {ERC1155Pausable} and {Pausable-_unpause}.
+     *
+     * Requirements:
+     *
+     * - the caller must have the `PAUSER_ROLE`.
+     */
+    function unpause() public virtual {
+        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC1155PresetMinterPauser: must have pauser role to unpause");
+        _unpause();
+    }
+
+    function _beforeTokenTransfer(
+        address operator,
+        address from,
+        address to,
+        uint256[] memory ids,
+        uint256[] memory amounts,
+        bytes memory data
+    )
+        internal virtual override(ERC1155, ERC1155Pausable)
+    {
+        super._beforeTokenTransfer(operator, from, to, ids, amounts, data);
+    }
+}

contracts/presets/ERC20PresetMinterPauser.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../access/AccessControl.sol";
 import "../GSN/Context.sol";
@@ -18,7 +20,7 @@ import "../token/ERC20/ERC20Pausable.sol";
  *
  * The account that deploys the contract will be granted the minter and pauser
  * roles, as well as the default admin role, which will let it grant both minter
- * and pauser roles to aother accounts
+ * and pauser roles to other accounts.
  */
 contract ERC20PresetMinterPauser is Context, AccessControl, ERC20Burnable, ERC20Pausable {
     bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
@@ -30,7 +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());
@@ -46,7 +48,7 @@ contract ERC20PresetMinterPauser is Context, AccessControl, ERC20Burnable, ERC20
      *
      * - the caller must have the `MINTER_ROLE`.
      */
-    function mint(address to, uint256 amount) public {
+    function mint(address to, uint256 amount) public virtual {
         require(hasRole(MINTER_ROLE, _msgSender()), "ERC20PresetMinterPauser: must have minter role to mint");
         _mint(to, amount);
     }
@@ -60,7 +62,7 @@ contract ERC20PresetMinterPauser is Context, AccessControl, ERC20Burnable, ERC20
      *
      * - the caller must have the `PAUSER_ROLE`.
      */
-    function pause() public {
+    function pause() public virtual {
         require(hasRole(PAUSER_ROLE, _msgSender()), "ERC20PresetMinterPauser: must have pauser role to pause");
         _pause();
     }
@@ -74,12 +76,12 @@ contract ERC20PresetMinterPauser is Context, AccessControl, ERC20Burnable, ERC20
      *
      * - the caller must have the `PAUSER_ROLE`.
      */
-    function unpause() public {
+    function unpause() public virtual {
         require(hasRole(PAUSER_ROLE, _msgSender()), "ERC20PresetMinterPauser: must have pauser role to unpause");
         _unpause();
     }
 
-    function _beforeTokenTransfer(address from, address to, uint256 amount) internal override(ERC20, ERC20Pausable) {
+    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override(ERC20, ERC20Pausable) {
         super._beforeTokenTransfer(from, to, amount);
     }
 }

contracts/presets/ERC721PresetMinterPauserAutoId.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
 
 import "../access/AccessControl.sol";
 import "../GSN/Context.sol";
@@ -20,7 +22,7 @@ import "../token/ERC721/ERC721Pausable.sol";
  *
  * The account that deploys the contract will be granted the minter and pauser
  * roles, as well as the default admin role, which will let it grant both minter
- * and pauser roles to aother accounts
+ * and pauser roles to other accounts.
  */
 contract ERC721PresetMinterPauserAutoId is Context, AccessControl, ERC721Burnable, ERC721Pausable {
     using Counters for Counters.Counter;
@@ -31,13 +33,13 @@ contract ERC721PresetMinterPauserAutoId is Context, AccessControl, ERC721Burnabl
     Counters.Counter private _tokenIdTracker;
 
     /**
-     * @dev Grants `DEFAULT_ADMIN_ROLE` and `MINTER_ROLE`to the account that
-     * deploys the contract.
+     * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE` and `PAUSER_ROLE` to the
+     * account that deploys the contract.
      *
      * 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());
@@ -48,7 +50,7 @@ contract ERC721PresetMinterPauserAutoId is Context, AccessControl, ERC721Burnabl
 
     /**
      * @dev Creates a new token for `to`. Its token ID will be automatically
-     * assigned (and available on the emitted {Transfer} event), and the token
+     * assigned (and available on the emitted {IERC721-Transfer} event), and the token
      * URI autogenerated based on the base URI passed at construction.
      *
      * See {ERC721-_mint}.
@@ -57,7 +59,7 @@ contract ERC721PresetMinterPauserAutoId is Context, AccessControl, ERC721Burnabl
      *
      * - the caller must have the `MINTER_ROLE`.
      */
-    function mint(address to) public {
+    function mint(address to) public virtual {
         require(hasRole(MINTER_ROLE, _msgSender()), "ERC721PresetMinterPauserAutoId: must have minter role to mint");
 
         // We can just use balanceOf to create the new tokenId because tokens
@@ -75,7 +77,7 @@ contract ERC721PresetMinterPauserAutoId is Context, AccessControl, ERC721Burnabl
      *
      * - the caller must have the `PAUSER_ROLE`.
      */
-    function pause() public {
+    function pause() public virtual {
         require(hasRole(PAUSER_ROLE, _msgSender()), "ERC721PresetMinterPauserAutoId: must have pauser role to pause");
         _pause();
     }
@@ -89,12 +91,12 @@ contract ERC721PresetMinterPauserAutoId is Context, AccessControl, ERC721Burnabl
      *
      * - the caller must have the `PAUSER_ROLE`.
      */
-    function unpause() public {
+    function unpause() public virtual {
         require(hasRole(PAUSER_ROLE, _msgSender()), "ERC721PresetMinterPauserAutoId: must have pauser role to unpause");
         _unpause();
     }
 
-    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal override(ERC721, ERC721Pausable) {
+    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal virtual override(ERC721, ERC721Pausable) {
         super._beforeTokenTransfer(from, to, tokenId);
     }
 }

contracts/presets/README.adoc

@@ -1,5 +1,8 @@
 = Presets
 
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/presets
+
 These contracts integrate different Ethereum standards (ERCs) with custom extensions and modules, showcasing common configurations that are ready to deploy **without having to write any Solidity code**.
 
 They can be used as-is for quick prototyping and testing, but are **also suitable for production environments**.
@@ -11,3 +14,5 @@ TIP: Intermediate and advanced users can use these as starting points when writi
 {{ERC20PresetMinterPauser}}
 
 {{ERC721PresetMinterPauserAutoId}}
+
+{{ERC1155PresetMinterPauser}}

contracts/token/ERC1155/ERC1155.sol

@@ -0,0 +1,413 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "./IERC1155.sol";
+import "./IERC1155MetadataURI.sol";
+import "./IERC1155Receiver.sol";
+import "../../GSN/Context.sol";
+import "../../introspection/ERC165.sol";
+import "../../math/SafeMath.sol";
+import "../../utils/Address.sol";
+
+/**
+ *
+ * @dev Implementation of the basic standard multi-token.
+ * See https://eips.ethereum.org/EIPS/eip-1155
+ * Originally based on code by Enjin: https://github.com/enjin/erc-1155
+ *
+ * _Available since v3.1._
+ */
+contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
+    using SafeMath for uint256;
+    using Address for address;
+
+    // Mapping from token ID to account balances
+    mapping (uint256 => mapping(address => uint256)) private _balances;
+
+    // Mapping from account to operator approvals
+    mapping (address => mapping(address => bool)) private _operatorApprovals;
+
+    // Used as the URI for all token types by relying on ID substition, e.g. https://token-cdn-domain/{id}.json
+    string private _uri;
+
+    /*
+     *     bytes4(keccak256('balanceOf(address,uint256)')) == 0x00fdd58e
+     *     bytes4(keccak256('balanceOfBatch(address[],uint256[])')) == 0x4e1273f4
+     *     bytes4(keccak256('setApprovalForAll(address,bool)')) == 0xa22cb465
+     *     bytes4(keccak256('isApprovedForAll(address,address)')) == 0xe985e9c5
+     *     bytes4(keccak256('safeTransferFrom(address,address,uint256,uint256,bytes)')) == 0xf242432a
+     *     bytes4(keccak256('safeBatchTransferFrom(address,address,uint256[],uint256[],bytes)')) == 0x2eb2c2d6
+     *
+     *     => 0x00fdd58e ^ 0x4e1273f4 ^ 0xa22cb465 ^
+     *        0xe985e9c5 ^ 0xf242432a ^ 0x2eb2c2d6 == 0xd9b67a26
+     */
+    bytes4 private constant _INTERFACE_ID_ERC1155 = 0xd9b67a26;
+
+    /*
+     *     bytes4(keccak256('uri(uint256)')) == 0x0e89341c
+     */
+    bytes4 private constant _INTERFACE_ID_ERC1155_METADATA_URI = 0x0e89341c;
+
+    /**
+     * @dev See {_setURI}.
+     */
+    constructor (string memory uri) {
+        _setURI(uri);
+
+        // register the supported interfaces to conform to ERC1155 via ERC165
+        _registerInterface(_INTERFACE_ID_ERC1155);
+
+        // register the supported interfaces to conform to ERC1155MetadataURI via ERC165
+        _registerInterface(_INTERFACE_ID_ERC1155_METADATA_URI);
+    }
+
+    /**
+     * @dev See {IERC1155MetadataURI-uri}.
+     *
+     * This implementation returns the same URI for *all* token types. It relies
+     * on the token type ID substituion mechanism
+     * https://eips.ethereum.org/EIPS/eip-1155#metadata[defined in the EIP].
+     *
+     * Clients calling this function must replace the `\{id\}` substring with the
+     * actual token type ID.
+     */
+    function uri(uint256) external view override returns (string memory) {
+        return _uri;
+    }
+
+    /**
+     * @dev See {IERC1155-balanceOf}.
+     *
+     * Requirements:
+     *
+     * - `account` cannot be the zero address.
+     */
+    function balanceOf(address account, uint256 id) public view override returns (uint256) {
+        require(account != address(0), "ERC1155: balance query for the zero address");
+        return _balances[id][account];
+    }
+
+    /**
+     * @dev See {IERC1155-balanceOfBatch}.
+     *
+     * Requirements:
+     *
+     * - `accounts` and `ids` must have the same length.
+     */
+    function balanceOfBatch(
+        address[] memory accounts,
+        uint256[] memory ids
+    )
+        public
+        view
+        override
+        returns (uint256[] memory)
+    {
+        require(accounts.length == ids.length, "ERC1155: accounts and ids length mismatch");
+
+        uint256[] memory batchBalances = new uint256[](accounts.length);
+
+        for (uint256 i = 0; i < accounts.length; ++i) {
+            require(accounts[i] != address(0), "ERC1155: batch balance query for the zero address");
+            batchBalances[i] = _balances[ids[i]][accounts[i]];
+        }
+
+        return batchBalances;
+    }
+
+    /**
+     * @dev See {IERC1155-setApprovalForAll}.
+     */
+    function setApprovalForAll(address operator, bool approved) public virtual override {
+        require(_msgSender() != operator, "ERC1155: setting approval status for self");
+
+        _operatorApprovals[_msgSender()][operator] = approved;
+        emit ApprovalForAll(_msgSender(), operator, approved);
+    }
+
+    /**
+     * @dev See {IERC1155-isApprovedForAll}.
+     */
+    function isApprovedForAll(address account, address operator) public view override returns (bool) {
+        return _operatorApprovals[account][operator];
+    }
+
+    /**
+     * @dev See {IERC1155-safeTransferFrom}.
+     */
+    function safeTransferFrom(
+        address from,
+        address to,
+        uint256 id,
+        uint256 amount,
+        bytes memory data
+    )
+        public
+        virtual
+        override
+    {
+        require(to != address(0), "ERC1155: transfer to the zero address");
+        require(
+            from == _msgSender() || isApprovedForAll(from, _msgSender()),
+            "ERC1155: caller is not owner nor approved"
+        );
+
+        address operator = _msgSender();
+
+        _beforeTokenTransfer(operator, from, to, _asSingletonArray(id), _asSingletonArray(amount), data);
+
+        _balances[id][from] = _balances[id][from].sub(amount, "ERC1155: insufficient balance for transfer");
+        _balances[id][to] = _balances[id][to].add(amount);
+
+        emit TransferSingle(operator, from, to, id, amount);
+
+        _doSafeTransferAcceptanceCheck(operator, from, to, id, amount, data);
+    }
+
+    /**
+     * @dev See {IERC1155-safeBatchTransferFrom}.
+     */
+    function safeBatchTransferFrom(
+        address from,
+        address to,
+        uint256[] memory ids,
+        uint256[] memory amounts,
+        bytes memory data
+    )
+        public
+        virtual
+        override
+    {
+        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");
+        require(to != address(0), "ERC1155: transfer to the zero address");
+        require(
+            from == _msgSender() || isApprovedForAll(from, _msgSender()),
+            "ERC1155: transfer caller is not owner nor approved"
+        );
+
+        address operator = _msgSender();
+
+        _beforeTokenTransfer(operator, from, to, ids, amounts, data);
+
+        for (uint256 i = 0; i < ids.length; ++i) {
+            uint256 id = ids[i];
+            uint256 amount = amounts[i];
+
+            _balances[id][from] = _balances[id][from].sub(
+                amount,
+                "ERC1155: insufficient balance for transfer"
+            );
+            _balances[id][to] = _balances[id][to].add(amount);
+        }
+
+        emit TransferBatch(operator, from, to, ids, amounts);
+
+        _doSafeBatchTransferAcceptanceCheck(operator, from, to, ids, amounts, data);
+    }
+
+    /**
+     * @dev Sets a new URI for all token types, by relying on the token type ID
+     * substituion mechanism
+     * https://eips.ethereum.org/EIPS/eip-1155#metadata[defined in the EIP].
+     *
+     * By this mechanism, any occurence of the `\{id\}` substring in either the
+     * URI or any of the amounts in the JSON file at said URI will be replaced by
+     * clients with the token type ID.
+     *
+     * For example, the `https://token-cdn-domain/\{id\}.json` URI would be
+     * interpreted by clients as
+     * `https://token-cdn-domain/000000000000000000000000000000000000000000000000000000000004cce0.json`
+     * for token type ID 0x4cce0.
+     *
+     * See {uri}.
+     *
+     * Because these URIs cannot be meaningfully represented by the {URI} event,
+     * this function emits no events.
+     */
+    function _setURI(string memory newuri) internal virtual {
+        _uri = newuri;
+    }
+
+    /**
+     * @dev Creates `amount` tokens of token type `id`, and assigns them to `account`.
+     *
+     * Emits a {TransferSingle} event.
+     *
+     * Requirements:
+     *
+     * - `account` cannot be the zero address.
+     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
+     * acceptance magic value.
+     */
+    function _mint(address account, uint256 id, uint256 amount, bytes memory data) internal virtual {
+        require(account != address(0), "ERC1155: mint to the zero address");
+
+        address operator = _msgSender();
+
+        _beforeTokenTransfer(operator, address(0), account, _asSingletonArray(id), _asSingletonArray(amount), data);
+
+        _balances[id][account] = _balances[id][account].add(amount);
+        emit TransferSingle(operator, address(0), account, id, amount);
+
+        _doSafeTransferAcceptanceCheck(operator, address(0), account, id, amount, data);
+    }
+
+    /**
+     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_mint}.
+     *
+     * Requirements:
+     *
+     * - `ids` and `amounts` must have the same length.
+     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
+     * acceptance magic value.
+     */
+    function _mintBatch(address to, uint256[] memory ids, uint256[] memory amounts, bytes memory data) internal virtual {
+        require(to != address(0), "ERC1155: mint to the zero address");
+        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");
+
+        address operator = _msgSender();
+
+        _beforeTokenTransfer(operator, address(0), to, ids, amounts, data);
+
+        for (uint i = 0; i < ids.length; i++) {
+            _balances[ids[i]][to] = amounts[i].add(_balances[ids[i]][to]);
+        }
+
+        emit TransferBatch(operator, address(0), to, ids, amounts);
+
+        _doSafeBatchTransferAcceptanceCheck(operator, address(0), to, ids, amounts, data);
+    }
+
+    /**
+     * @dev Destroys `amount` tokens of token type `id` from `account`
+     *
+     * Requirements:
+     *
+     * - `account` cannot be the zero address.
+     * - `account` must have at least `amount` tokens of token type `id`.
+     */
+    function _burn(address account, uint256 id, uint256 amount) internal virtual {
+        require(account != address(0), "ERC1155: burn from the zero address");
+
+        address operator = _msgSender();
+
+        _beforeTokenTransfer(operator, account, address(0), _asSingletonArray(id), _asSingletonArray(amount), "");
+
+        _balances[id][account] = _balances[id][account].sub(
+            amount,
+            "ERC1155: burn amount exceeds balance"
+        );
+
+        emit TransferSingle(operator, account, address(0), id, amount);
+    }
+
+    /**
+     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_burn}.
+     *
+     * Requirements:
+     *
+     * - `ids` and `amounts` must have the same length.
+     */
+    function _burnBatch(address account, uint256[] memory ids, uint256[] memory amounts) internal virtual {
+        require(account != address(0), "ERC1155: burn from the zero address");
+        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");
+
+        address operator = _msgSender();
+
+        _beforeTokenTransfer(operator, account, address(0), ids, amounts, "");
+
+        for (uint i = 0; i < ids.length; i++) {
+            _balances[ids[i]][account] = _balances[ids[i]][account].sub(
+                amounts[i],
+                "ERC1155: burn amount exceeds balance"
+            );
+        }
+
+        emit TransferBatch(operator, account, address(0), ids, amounts);
+    }
+
+    /**
+     * @dev Hook that is called before any token transfer. This includes minting
+     * and burning, as well as batched variants.
+     *
+     * The same hook is called on both single and batched variants. For single
+     * transfers, the length of the `id` and `amount` arrays will be 1.
+     *
+     * Calling conditions (for each `id` and `amount` pair):
+     *
+     * - When `from` and `to` are both non-zero, `amount` of ``from``'s tokens
+     * of token type `id` will be  transferred to `to`.
+     * - When `from` is zero, `amount` tokens of token type `id` will be minted
+     * for `to`.
+     * - when `to` is zero, `amount` of ``from``'s tokens of token type `id`
+     * will be burned.
+     * - `from` and `to` are never both zero.
+     * - `ids` and `amounts` have the same, non-zero length.
+     *
+     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
+     */
+    function _beforeTokenTransfer(
+        address operator,
+        address from,
+        address to,
+        uint256[] memory ids,
+        uint256[] memory amounts,
+        bytes memory data
+    )
+        internal virtual
+    { }
+
+    function _doSafeTransferAcceptanceCheck(
+        address operator,
+        address from,
+        address to,
+        uint256 id,
+        uint256 amount,
+        bytes memory data
+    )
+        private
+    {
+        if (to.isContract()) {
+            try IERC1155Receiver(to).onERC1155Received(operator, from, id, amount, data) returns (bytes4 response) {
+                if (response != IERC1155Receiver(to).onERC1155Received.selector) {
+                    revert("ERC1155: ERC1155Receiver rejected tokens");
+                }
+            } catch Error(string memory reason) {
+                revert(reason);
+            } catch {
+                revert("ERC1155: transfer to non ERC1155Receiver implementer");
+            }
+        }
+    }
+
+    function _doSafeBatchTransferAcceptanceCheck(
+        address operator,
+        address from,
+        address to,
+        uint256[] memory ids,
+        uint256[] memory amounts,
+        bytes memory data
+    )
+        private
+    {
+        if (to.isContract()) {
+            try IERC1155Receiver(to).onERC1155BatchReceived(operator, from, ids, amounts, data) returns (bytes4 response) {
+                if (response != IERC1155Receiver(to).onERC1155BatchReceived.selector) {
+                    revert("ERC1155: ERC1155Receiver rejected tokens");
+                }
+            } catch Error(string memory reason) {
+                revert(reason);
+            } catch {
+                revert("ERC1155: transfer to non ERC1155Receiver implementer");
+            }
+        }
+    }
+
+    function _asSingletonArray(uint256 element) private pure returns (uint256[] memory) {
+        uint256[] memory array = new uint256[](1);
+        array[0] = element;
+
+        return array;
+    }
+}

contracts/token/ERC1155/ERC1155Burnable.sol

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "./ERC1155.sol";
+
+/**
+ * @dev Extension of {ERC1155} that allows token holders to destroy both their
+ * own tokens and those that they have been approved to use.
+ *
+ * _Available since v3.1._
+ */
+abstract contract ERC1155Burnable is ERC1155 {
+    function burn(address account, uint256 id, uint256 value) public virtual {
+        require(
+            account == _msgSender() || isApprovedForAll(account, _msgSender()),
+            "ERC1155: caller is not owner nor approved"
+        );
+
+        _burn(account, id, value);
+    }
+
+    function burnBatch(address account, uint256[] memory ids, uint256[] memory values) public virtual {
+        require(
+            account == _msgSender() || isApprovedForAll(account, _msgSender()),
+            "ERC1155: caller is not owner nor approved"
+        );
+
+        _burnBatch(account, ids, values);
+    }
+}

contracts/token/ERC1155/ERC1155Holder.sol

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "./ERC1155Receiver.sol";
+
+/**
+ * @dev _Available since v3.1._
+ */
+contract ERC1155Holder is ERC1155Receiver {
+    function onERC1155Received(address, address, uint256, uint256, bytes memory) public virtual override returns (bytes4) {
+        return this.onERC1155Received.selector;
+    }
+
+    function onERC1155BatchReceived(address, address, uint256[] memory, uint256[] memory, bytes memory) public virtual override returns (bytes4) {
+        return this.onERC1155BatchReceived.selector;
+    }
+}

contracts/token/ERC1155/ERC1155Pausable.sol

@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "./ERC1155.sol";
+import "../../utils/Pausable.sol";
+
+/**
+ * @dev ERC1155 token with pausable token transfers, minting and burning.
+ *
+ * Useful for scenarios such as preventing trades until the end of an evaluation
+ * period, or having an emergency switch for freezing all token transfers in the
+ * event of a large bug.
+ *
+ * _Available since v3.1._
+ */
+abstract contract ERC1155Pausable is ERC1155, Pausable {
+    /**
+     * @dev See {ERC1155-_beforeTokenTransfer}.
+     *
+     * Requirements:
+     *
+     * - the contract must not be paused.
+     */
+    function _beforeTokenTransfer(
+        address operator,
+        address from,
+        address to,
+        uint256[] memory ids,
+        uint256[] memory amounts,
+        bytes memory data
+    )
+        internal virtual override
+    {
+        super._beforeTokenTransfer(operator, from, to, ids, amounts, data);
+
+        require(!paused(), "ERC1155Pausable: token transfer while paused");
+    }
+}

contracts/token/ERC1155/ERC1155Receiver.sol

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "./IERC1155Receiver.sol";
+import "../../introspection/ERC165.sol";
+
+/**
+ * @dev _Available since v3.1._
+ */
+abstract contract ERC1155Receiver is ERC165, IERC1155Receiver {
+    constructor() {
+        _registerInterface(
+            ERC1155Receiver(0).onERC1155Received.selector ^
+            ERC1155Receiver(0).onERC1155BatchReceived.selector
+        );
+    }
+}

contracts/token/ERC1155/IERC1155.sol

@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "../../introspection/IERC165.sol";
+
+/**
+ * @dev Required interface of an ERC1155 compliant contract, as defined in the
+ * https://eips.ethereum.org/EIPS/eip-1155[EIP].
+ *
+ * _Available since v3.1._
+ */
+interface IERC1155 is IERC165 {
+    /**
+     * @dev Emitted when `value` tokens of token type `id` are transfered from `from` to `to` by `operator`.
+     */
+    event TransferSingle(address indexed operator, address indexed from, address indexed to, uint256 id, uint256 value);
+
+    /**
+     * @dev Equivalent to multiple {TransferSingle} events, where `operator`, `from` and `to` are the same for all
+     * transfers.
+     */
+    event TransferBatch(address indexed operator, address indexed from, address indexed to, uint256[] ids, uint256[] values);
+
+    /**
+     * @dev Emitted when `account` grants or revokes permission to `operator` to transfer their tokens, according to
+     * `approved`.
+     */
+    event ApprovalForAll(address indexed account, address indexed operator, bool approved);
+
+    /**
+     * @dev Emitted when the URI for token type `id` changes to `value`, if it is a non-programmatic URI.
+     *
+     * If an {URI} event was emitted for `id`, the standard
+     * https://eips.ethereum.org/EIPS/eip-1155#metadata-extensions[guarantees] that `value` will equal the value
+     * returned by {IERC1155MetadataURI-uri}.
+     */
+    event URI(string value, uint256 indexed id);
+
+    /**
+     * @dev Returns the amount of tokens of token type `id` owned by `account`.
+     *
+     * Requirements:
+     *
+     * - `account` cannot be the zero address.
+     */
+    function balanceOf(address account, uint256 id) external view returns (uint256);
+
+    /**
+     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {balanceOf}.
+     *
+     * Requirements:
+     *
+     * - `accounts` and `ids` must have the same length.
+     */
+    function balanceOfBatch(address[] calldata accounts, uint256[] calldata ids) external view returns (uint256[] memory);
+
+    /**
+     * @dev Grants or revokes permission to `operator` to transfer the caller's tokens, according to `approved`,
+     *
+     * Emits an {ApprovalForAll} event.
+     *
+     * Requirements:
+     *
+     * - `operator` cannot be the caller.
+     */
+    function setApprovalForAll(address operator, bool approved) external;
+
+    /**
+     * @dev Returns true if `operator` is approved to transfer ``account``'s tokens.
+     *
+     * See {setApprovalForAll}.
+     */
+    function isApprovedForAll(address account, address operator) external view returns (bool);
+
+    /**
+     * @dev Transfers `amount` tokens of token type `id` from `from` to `to`.
+     *
+     * Emits a {TransferSingle} event.
+     *
+     * Requirements:
+     *
+     * - `to` cannot be the zero address.
+     * - If the caller is not `from`, it must be have been approved to spend ``from``'s tokens via {setApprovalForAll}.
+     * - `from` must have a balance of tokens of type `id` of at least `amount`.
+     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
+     * acceptance magic value.
+     */
+    function safeTransferFrom(address from, address to, uint256 id, uint256 amount, bytes calldata data) external;
+
+    /**
+     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {safeTransferFrom}.
+     *
+     * Emits a {TransferBatch} event.
+     *
+     * Requirements:
+     *
+     * - `ids` and `amounts` must have the same length.
+     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
+     * acceptance magic value.
+     */
+    function safeBatchTransferFrom(address from, address to, uint256[] calldata ids, uint256[] calldata amounts, bytes calldata data) external;
+}

contracts/token/ERC1155/IERC1155MetadataURI.sol

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "./IERC1155.sol";
+
+/**
+ * @dev Interface of the optional ERC1155MetadataExtension interface, as defined
+ * in the https://eips.ethereum.org/EIPS/eip-1155#metadata-extensions[EIP].
+ *
+ * _Available since v3.1._
+ */
+interface IERC1155MetadataURI is IERC1155 {
+    /**
+     * @dev Returns the URI for token type `id`.
+     *
+     * If the `\{id\}` substring is present in the URI, it must be replaced by
+     * clients with the actual token type ID.
+     */
+    function uri(uint256 id) external view returns (string memory);
+}

contracts/token/ERC1155/IERC1155Receiver.sol

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.7.0;
+
+import "../../introspection/IERC165.sol";
+
+/**
+ * _Available since v3.1._
+ */
+interface IERC1155Receiver is IERC165 {
+
+    /**
+        @dev Handles the receipt of a single ERC1155 token type. This function is
+        called at the end of a `safeTransferFrom` after the balance has been updated.
+        To accept the transfer, this must return
+        `bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))`
+        (i.e. 0xf23a6e61, or its own function selector).
+        @param operator The address which initiated the transfer (i.e. msg.sender)
+        @param from The address which previously owned the token
+        @param id The ID of the token being transferred
+        @param value The amount of tokens being transferred
+        @param data Additional data with no specified format
+        @return `bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))` if transfer is allowed
+    */
+    function onERC1155Received(
+        address operator,
+        address from,
+        uint256 id,
+        uint256 value,
+        bytes calldata data
+    )
+        external
+        returns(bytes4);
+
+    /**
+        @dev Handles the receipt of a multiple ERC1155 token types. This function
+        is called at the end of a `safeBatchTransferFrom` after the balances have
+        been updated. To accept the transfer(s), this must return
+        `bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))`
+        (i.e. 0xbc197c81, or its own function selector).
+        @param operator The address which initiated the batch transfer (i.e. msg.sender)
+        @param from The address which previously owned the token
+        @param ids An array containing ids of each token being transferred (order and length must match values array)
+        @param values An array containing amounts of each token being transferred (order and length must match ids array)
+        @param data Additional data with no specified format
+        @return `bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))` if transfer is allowed
+    */
+    function onERC1155BatchReceived(
+        address operator,
+        address from,
+        uint256[] calldata ids,
+        uint256[] calldata values,
+        bytes calldata data
+    )
+        external
+        returns(bytes4);
+}

contracts/token/ERC1155/README.adoc

@@ -0,0 +1,37 @@
+= ERC 1155
+
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/token/erc1155
+
+This set of interfaces and contracts are all related to the https://eips.ethereum.org/EIPS/eip-1155[ERC1155 Multi Token Standard].
+
+The EIP consists of three interfaces which fulfill different roles, found here as {IERC1155}, {IERC1155MetadataURI} and {IERC1155Receiver}.
+
+{ERC1155} implements the mandatory {IERC1155} interface, as well as the optional extension {IERC1155MetadataURI}, by relying on the substitution mechanism to use the same URI for all token types, dramatically reducing gas costs.
+
+Additionally there are multiple custom extensions, including:
+
+* designation of addresses that can pause token transfers for all users ({ERC1155Pausable}).
+* destruction of own tokens ({ERC1155Burnable}).
+
+NOTE: This core set of contracts is designed to be unopinionated, allowing developers to access the internal functions in ERC1155 (such as <<ERC1155-_mint-address-uint256-uint256-bytes-,`_mint`>>) and expose them as external functions in the way they prefer. On the other hand, xref:ROOT:erc1155.adoc#Presets[ERC1155 Presets] (such as {ERC1155PresetMinterPauser}) are designed using opinionated patterns to provide developers with ready to use, deployable contracts.
+
+== Core
+
+{{IERC1155}}
+
+{{IERC1155MetadataURI}}
+
+{{ERC1155}}
+
+{{IERC1155Receiver}}
+
+== Extensions
+
+{{ERC1155Pausable}}
+
+{{ERC1155Burnable}}
+
+== Convenience
+
+{{ERC1155Holder}}