4.0.0-rc.0

(cherry picked from commit 2658e01baa)

.circleci/config.yml

@@ -1,82 +0,0 @@
-version: 2
-# 2.1 does not yet support local run
-# unless with workaround. For simplicity just use it.
-# https://github.com/CircleCI-Public/circleci-cli/issues/79
-
-aliases:
-  - &defaults
-    docker:
-      - image: circleci/node:8
-
-  - &npm_install_if_necessary
-    run:
-      name: Install npm dependencies
-      command: |
-        if [ ! -d node_modules ]; then
-          npm ci
-        fi
-
-  - &cache_key_node_modules
-    key: v1-node_modules-{{ checksum "package-lock.json" }}
-
-jobs:
-  dependencies:
-    <<: *defaults
-    steps:
-      - checkout
-      - restore_cache:
-          <<: *cache_key_node_modules
-      - *npm_install_if_necessary
-      - save_cache:
-          paths:
-            - node_modules
-          <<: *cache_key_node_modules
-
-  lint:
-    <<: *defaults
-    steps:
-      - checkout
-      - restore_cache:
-          <<: *cache_key_node_modules
-      - *npm_install_if_necessary
-      - run:
-          name: Linter
-          command: npm run lint
-  test:
-    <<: *defaults
-    steps:
-      - checkout
-      - restore_cache:
-          <<: *cache_key_node_modules
-      - *npm_install_if_necessary
-      - run:
-          name: Unit tests
-          command: npm run test
-  coverage:
-    docker:
-      - image: circleci/node:8
-    steps:
-      - checkout
-      - restore_cache:
-          <<: *cache_key_node_modules
-      - *npm_install_if_necessary
-      - run:
-          name: Unit tests with coverage report
-          command: npm run coverage
-
-      # TODO(xinbenlv, #1839): run SOLC_NIGHTLY to be run but allow it to fail.
-
-workflows:
-  version: 2
-  everything:
-    jobs:
-      - dependencies
-      - lint:
-          requires:
-            - dependencies
-      - test:
-          requires:
-            - dependencies
-      - coverage:
-          requires:
-            - dependencies

.codecov.yml

@@ -1,3 +1,11 @@
 comment: off
+github_checks:
+  annotations: false
 coverage:
-  range: "100...100"
+  status:
+    patch:
+      default:
+        target: 95%
+    project:
+      default:
+        threshold: 1%

.editorconfig

@@ -6,13 +6,16 @@ root = true
 [*]
 charset = utf-8
 end_of_line = lf
-indent_size = 4
 indent_style = space
 insert_final_newline = true
-trim_trailing_whitespace = true
+trim_trailing_whitespace = false
+max_line_length = 120
 
 [*.sol]
 indent_size = 4
 
 [*.js]
 indent_size = 2
+
+[*.adoc]
+max_line_length = 0

.eslintrc

@@ -18,6 +18,8 @@
     "contract": false,
     "assert": false,
     "web3": false,
+    "usePlugin": false,
+    "extendEnvironment": false,
   },
   "rules": {
 
@@ -25,6 +27,7 @@
     "strict": ["error", "global"],
 
     // Code style
+    "array-bracket-spacing": ["off"],
     "camelcase": ["error", {"properties": "always"}],
     "comma-dangle": ["error", "always-multiline"],
     "comma-spacing": ["error", {"before": false, "after": true}],
@@ -54,5 +57,8 @@
 
     "promise/always-return": "off",
     "promise/avoid-new": "off",
+  },
+  "parserOptions": {
+    "ecmaVersion": 2018
   }
 }

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,4 @@
+contact_links:
+  - name: Support request
+    url: https://forum.openzeppelin.com/c/support/contracts/18
+    about: Ask the community in the Community Forum

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,22 +1,20 @@
-<!-- 0. 🎉 Thank you for submitting a PR! -->
+<!-- Thank you for your interest in contributing to OpenZeppelin! -->
 
-<!-- 1. Does this close any open issues? Please list them below. -->
+<!-- Consider opening an issue for discussion prior to submitting a PR. -->
+<!-- New features will be merged faster if they were first discussed and designed with the team. -->
 
-<!-- Keep in mind that new features have a better chance of being merged fast if
-they were first discussed and designed with the maintainers. If there is no
-corresponding issue, please consider opening one for discussion first! -->
+Fixes #???? <!-- Fill in with issue number -->
 
-Fixes #
+<!-- Describe the changes introduced in this pull request. -->
+<!-- Include any context necessary for understanding the PR's purpose. -->
 
-<!-- 2. Describe the changes introduced in this pull request. -->
-<!--    Include any context necessary for understanding the PR's purpose. -->
 
-<!-- 3. Before submitting, please make sure that you have:
-  - reviewed the OpenZeppelin Contributor Guidelines
-    (https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/CONTRIBUTING.md),
-  - added tests where applicable to test new functionality,
-  - made sure that your contracts are well-documented,
-  - run the Solidity linter (`npm run lint:sol`) and fixed any issues,
-  - run the JS linter and fixed any issues (`npm run lint:fix`), and
-  - updated the changelog, if applicable.
--->
+#### PR Checklist
+
+<!-- Before merging the pull request all of the following must be complete. -->
+<!-- Feel free to submit a PR or Draft PR even if some items are pending. -->
+<!-- Some of the items may not apply. -->
+
+- [ ] Tests
+- [ ] Documentation
+- [ ] Changelog entry

.github/stale.yml

@@ -1,66 +0,0 @@
-# Configuration for probot-stale - https://github.com/probot/stale
-
-# Number of days of inactivity before an Issue or Pull Request becomes stale
-daysUntilStale: 15
-
-# Number of days of inactivity before an Issue or Pull Request with the stale label is closed.
-# Set to false to disable. If disabled, issues still need to be closed manually, but will remain marked as stale.
-daysUntilClose: 15
-
-# Issues or Pull Requests with these labels will never be considered stale. Set to `[]` to disable
-exemptLabels:
-  - on hold
-
-# Set to true to ignore issues in a project (defaults to false)
-exemptProjects: false
-
-# Set to true to ignore issues in a milestone (defaults to false)
-exemptMilestones: false
-
-# Set to true to ignore issues with an assignee (defaults to false)
-exemptAssignees: false
-
-# Label to use when marking as stale
-staleLabel: stale
-
-# Comment to post when marking as stale. Set to `false` to disable
-markComment: >
-  Hi all!
-
-  This Pull Request has not had any recent activity, is it still relevant? If so, what is blocking it?
-  Is there anything we can do to help move it forward?
-
-  Thanks!
-
-
-# Comment to post when removing the stale label.
-# unmarkComment: >
-#   Your comment here.
-
-# Comment to post when closing a stale Issue or Pull Request.
-closeComment: >
-  Hi folks!
-
-  This Pull Request is being closed as there was no response to the previous prompt.
-  However, please leave a comment whenever you're ready to resume, so it can be reopened.
-
-  Thanks again!
-
-
-# Limit the number of actions per hour, from 1-30. Default is 30
-limitPerRun: 30
-
-# Limit to only `issues` or `pulls`
-only: pulls
-
-# Optionally, specify configuration settings that are specific to just 'issues' or 'pulls':
-# pulls:
-#   daysUntilStale: 30
-#   markComment: >
-#     This pull request has been automatically marked as stale because it has not had
-#     recent activity. It will be closed if no further activity occurs. Thank you
-#     for your contributions.
-
-# issues:
-#   exemptLabels:
-#     - confirmed

.github/workflows/test.yml

@@ -0,0 +1,55 @@
+name: Test
+
+on:
+  push:
+    branches:
+      - master
+      - release-v*
+  pull_request: {}
+  workflow_dispatch: {}
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
+        with:
+          node-version: 10.x
+      - uses: actions/cache@v2
+        id: cache
+        with:
+          path: '**/node_modules'
+          key: npm-v2-${{ hashFiles('**/package-lock.json') }}
+          restore-keys: npm-v2-
+      - run: npm ci
+        if: steps.cache.outputs.cache-hit != 'true'
+      - run: npm run lint
+      - run: npm run test
+        env:
+          FORCE_COLOR: 1
+          ENABLE_GAS_REPORT: 1
+      - name: Print gas report
+        run: cat gas-report.txt
+
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 2
+      - uses: actions/setup-node@v2
+        with:
+          node-version: 10.x
+      - uses: actions/cache@v2
+        id: cache
+        with:
+          path: '**/node_modules'
+          key: npm-v2-${{ hashFiles('**/package-lock.json') }}
+          restore-keys: npm-v2-
+      - run: npm ci
+        if: steps.cache.outputs.cache-hit != 'true'
+      - run: npm run coverage
+        env:
+          NODE_OPTIONS: --max_old_space_size=4096
+      - uses: codecov/codecov-action@v1

.gitignore

@@ -43,8 +43,17 @@ build/
 
 # docs artifacts
 docs/modules/api
-openzeppelin-docs
 
 # only used to package @openzeppelin/contracts
 contracts/build/
 contracts/README.md
+
+# temporary artifact from solidity-coverage
+allFiredEvents
+.coverage_artifacts
+.coverage_cache
+.coverage_contracts
+
+# hardhat
+cache
+artifacts

.mocharc.js

@@ -0,0 +1,3 @@
+module.exports = {
+  timeout: 4000,
+};

.solcover.js

@@ -1,9 +1,15 @@
 module.exports = {
     norpc: true,
-    testCommand: 'node --max-old-space-size=4096 ../node_modules/.bin/truffle test --network coverage',
-    compileCommand: 'node --max-old-space-size=4096 ../node_modules/.bin/truffle compile --network coverage',
+    testCommand: 'npm test',
+    compileCommand: 'npm run compile',
     skipFiles: [
-        'lifecycle/Migrations.sol',
-        'mocks'
-    ]
+        'mocks',
+    ],
+    providerOptions: {
+        default_balance_ether: '10000000000000000000000000',
+    },
+    mocha: {
+        fgrep: '[skip-on-coverage]',
+        invert: true,
+    },
 }

.solhint.json

@@ -1,14 +1,12 @@
 {
   "extends": "solhint:recommended",
   "rules": {
-    "indent": ["error", 4],
     "func-order": "off",
-    "bracket-align": "off",
-    "compiler-fixed": "off",
-    "no-simple-event-func-name": "off",
-    "separate-by-one-line-in-contract": "off",
-    "two-lines-top-level-separator": "off",
     "mark-callable-contracts": "off",
-    "compiler-version": ["error", "^0.5.0"]
+    "no-empty-blocks": "off",
+    "compiler-version": "off",
+    "private-vars-leading-underscore": "error",
+    "reason-string": "off",
+    "func-visibility": ["error", { "ignoreConstructors": true }]
   }
 }

CHANGELOG.md

@@ -1,50 +1,268 @@
 # Changelog
 
-## 2.4.0 (2019-08-16)
+## 4.0.0
 
-### New features:
- * `Address.toPayable`: added a helper to convert between address types without having to resort to low-level casting. ([#1773](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1773))
- * Facilities to make metatransaction-enabled contracts through the Gas Station Network. ([#1844](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1844))
+ * Now targeting the 0.8.x line of Solidity compilers. For 0.6.x (resp 0.7.x) support, use version 3.4.0 (resp 3.4.0-solc-0.7) of OpenZeppelin.
+ * `Context`: making `_msgData` return `bytes calldata` instead of `bytes memory` ([#2492](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2492))
+ * `ERC20`: removed the `_setDecimals` function and the storage slot associated to decimals. ([#2502](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2502))
+ * `Strings`: addition of a `toHexString` function.  ([#2504](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2504))
+ * `EnumerableMap`: change implementation to optimize for `key → value` lookups instead of enumeration. ([#2518](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2518))
+ * `GSN`: deprecate GSNv1 support in favor of upcoming support for GSNv2. ([#2521](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2521))
+ * `ERC165`: remove uses of storage in the base ERC165 implementation. ERC165 based contracts now use storage-less virtual functions. Old behavior remains available in the `ERC165Storage` extension. ([#2505](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2505))
+ * `Initializable`: make initializer check stricter during construction. ([#2531](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2531))
+ * `ERC721`: remove enumerability of tokens from the base implementation. This feature is now provided separately through the `ERC721Enumerable` extension. ([#2511](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2511))
+ * `AccessControl`: removed enumerability by default for a more lightweight contract. It is now opt-in through `AccessControlEnumerable`. ([#2512](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2512))
+ * Meta Transactions: add `ERC2771Context` and a `MinimalForwarder` for meta-transactions. ([#2508](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2508))
+ * Overall reorganization of the contract folder to improve clarity and discoverability. ([#2503](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2503))
+ * `ERC20Capped`: optimize gas usage by enforcing the check directly in `_mint`. ([#2524](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2524))
+ * Rename `UpgradeableProxy` to `ERC1967Proxy`. ([#2547](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2547))
+ * `ERC777`: optimize the gas costs of the constructor. ([#2551](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2551))
+ * `ERC721URIStorage`: add a new extension that implements the `_setTokenURI` behavior as it was available in 3.4.0. ([#2555](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2555))
+ * `AccessControl`: added ERC165 interface detection. ([#2562](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2562))
+ * `ERC1155`: make `uri` public so overloading function can call it using super. ([#2576](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2576))
 
-### Improvements:
- * `Address.isContract`: switched from `extcodesize` to `extcodehash` for less gas usage. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
- * `SafeMath`: added custom error messages support for `sub`, `div` and `mod` functions. `ERC20` and `ERC777` updated to throw custom errors on subtraction overflows. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+### Bug fixes for beta releases
+
+ * `AccessControlEnumerable`: Fixed `renounceRole` not updating enumerable set of addresses for a role. ([#2572](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2572))
+
+### How to upgrade from 3.x
+
+Since this version has moved a few contracts to different directories, users upgrading from a previous version will need to adjust their import statements. To make this easier, the package includes a script that will migrate import statements automatically. After upgrading to the latest version of the package, run:
+
+```
+npx openzeppelin-contracts-migrate-imports
+```
+
+Make sure you're using git or another version control system to be able to recover from any potential error in our script.
+
+### How to upgrade from 4.0-beta.x
+
+Some further changes have been done between the different beta iterations. Transitions made during this period are configured in the `migrate-imports` script. Consequently, you can upgrade from any previous 4.0-beta.x version using the same script as described in the *How to upgrade from 3.x* section.
+
+## 3.4.0 (2021-02-02)
+
+ * `BeaconProxy`: added new kind of proxy that allows simultaneous atomic upgrades. ([#2411](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2411))
+ * `EIP712`: added helpers to verify EIP712 typed data signatures on chain. ([#2418](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2418))
+ * `ERC20Permit`: added an implementation of the ERC20 permit extension for gasless token approvals. ([#2237](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2237))
+ * Presets: added token presets with preminted fixed supply `ERC20PresetFixedSupply` and `ERC777PresetFixedSupply`. ([#2399](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2399))
+ * `Address`: added `functionDelegateCall`, similar to the existing `functionCall`. ([#2333](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2333))
+ * `Clones`: added a library for deploying EIP 1167 minimal proxies. ([#2449](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2449))
+ * `Context`: moved from `contracts/GSN` to `contracts/utils`. ([#2453](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2453))
+ * `PaymentSplitter`: replace usage of `.transfer()` with `Address.sendValue` for improved compatibility with smart wallets. ([#2455](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2455))
+ * `UpgradeableProxy`: bubble revert reasons from initialization calls. ([#2454](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2454))
+ * `SafeMath`: fix a memory allocation issue by adding new `SafeMath.tryOp(uint,uint)→(bool,uint)` functions. `SafeMath.op(uint,uint,string)→uint` are now deprecated. ([#2462](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2462))
+ * `EnumerableMap`: fix a memory allocation issue by adding new `EnumerableMap.tryGet(uint)→(bool,address)` functions. `EnumerableMap.get(uint)→string` is now deprecated. ([#2462](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2462))
+ * `ERC165Checker`: added batch `getSupportedInterfaces`. ([#2469](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2469))
+ * `RefundEscrow`: `beneficiaryWithdraw` will forward all available gas to the beneficiary. ([#2480](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2480))
+ * Many view and pure functions have been made virtual to customize them via overrides. In many cases this will not imply that other functions in the contract will automatically adapt to the overridden definitions. People who wish to override should consult the source code to understand the impact and if they need to override any additional functions to achieve the desired behavior.
+
+### Security Fixes
+
+ * `ERC777`: fix potential reentrancy issues for custom extensions to `ERC777`. ([#2483](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2483))
+
+If you're using our implementation of ERC777 from version 3.3.0 or earlier, and you define a custom `_beforeTokenTransfer` function that writes to a storage variable, you may be vulnerable to a reentrancy attack. If you're affected and would like assistance please write to security@openzeppelin.com. [Read more in the pull request.](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2483)
+
+## 3.3.0 (2020-11-26)
+
+ * Now supports both Solidity 0.6 and 0.7. Compiling with solc 0.7 will result in warnings. Install the `solc-0.7` tag to compile without warnings.
+ * `Address`: added `functionStaticCall`, similar to the existing `functionCall`. ([#2333](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2333))
+ * `TimelockController`: added a contract to augment access control schemes with a delay. ([#2354](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2354))
+ * `EnumerableSet`: added `Bytes32Set`, for sets of `bytes32`. ([#2395](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2395))
+
+## 3.2.2-solc-0.7 (2020-10-28)
+ * Resolve warnings introduced by Solidity 0.7.4. ([#2396](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2396))
+
+## 3.2.1-solc-0.7 (2020-09-15)
+ * `ERC777`: Remove a warning about function state visibility in Solidity 0.7. ([#2327](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2327))
+
+## 3.2.0 (2020-09-10)
+
+### New features
+ * Proxies: added the proxy contracts from OpenZeppelin SDK. ([#2335](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2335))
+
+#### Proxy changes with respect to OpenZeppelin SDK
+
+Aside from upgrading them from Solidity 0.5 to 0.6, we've changed a few minor things from the proxy contracts as they were found in OpenZeppelin SDK.
+
+- `UpgradeabilityProxy` was renamed to `UpgradeableProxy`.
+- `AdminUpgradeabilityProxy` was renamed to `TransparentUpgradeableProxy`.
+- `Proxy._willFallback` was renamed to `Proxy._beforeFallback`.
+- `UpgradeabilityProxy._setImplementation` and `AdminUpgradeabilityProxy._setAdmin` were made private.
+
+### Improvements
+ * `Address.isContract`: switched from `extcodehash` to `extcodesize` for less gas usage. ([#2311](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2311))
+
+### Breaking changes
+ * `ERC20Snapshot`: switched to using `_beforeTokenTransfer` hook instead of overriding ERC20 operations. ([#2312](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2312))
+
+This small change in the way we implemented `ERC20Snapshot` may affect users who are combining this contract with
+other ERC20 flavors, since it no longer overrides `_transfer`, `_mint`, and `_burn`. This can result in having to remove Solidity `override(...)` specifiers in derived contracts for these functions, and to instead have to add it for `_beforeTokenTransfer`. See [Using Hooks](https://docs.openzeppelin.com/contracts/3.x/extending-contracts#using-hooks) in the documentation.
+
+## 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
+ * `AccessControl`: new contract for managing permissions in a system, replacement for `Ownable` and `Roles`. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
+ * `SafeCast`: new functions to convert to and from signed and unsigned values: `toUint256` and `toInt256`. ([#2123](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2123))
+ * `EnumerableMap`: a new data structure for key-value pairs (like `mapping`) that can be iterated over. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+
+### Breaking changes
+ * `ERC721`: `burn(owner, tokenId)` was removed, use `burn(tokenId)` instead. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+ * `ERC721`: `_checkOnERC721Received` was removed. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+ * `ERC721`: `_transferFrom` and `_safeTransferFrom` were renamed to `_transfer` and `_safeTransfer`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+ * `Ownable`: removed `_transferOwnership`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+ * `PullPayment`, `Escrow`: `withdrawWithGas` was removed. The old `withdraw` function now forwards all gas. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+ * `Roles` was removed, use `AccessControl` as a replacement. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
+ * `ECDSA`: when receiving an invalid signature, `recover` now reverts instead of returning the zero address. ([#2114](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2114))
+ * `Create2`: added an `amount` argument to `deploy` for contracts with `payable` constructors. ([#2117](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2117))
+ * `Pausable`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `Strings`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `Counters`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `SignedSafeMath`: moved to the `math` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `ERC20Snapshot`: moved to the `token/ERC20` directory. `snapshot` was changed into an `internal` function. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `Ownable`: moved to the `access` directory. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `Ownable`: removed `isOwner`. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `Secondary`: removed from the library, use `Ownable` instead. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `Escrow`, `ConditionalEscrow`, `RefundEscrow`: these now use `Ownable` instead of `Secondary`, their external API changed accordingly. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `ERC20`: removed `_burnFrom`. ([#2119](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2119))
+ * `Address`: removed `toPayable`, use `payable(address)` instead. ([#2133](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2133))
+ * `ERC777`: `_send`, `_mint` and `_burn` now use the caller as the operator. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+ * `ERC777`: removed `_callsTokensToSend` and `_callTokensReceived`. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+ * `EnumerableSet`: renamed `get` to `at`. ([#2151](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2151))
+ * `ERC165Checker`: functions no longer have a leading underscore. ([#2150](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2150))
+ * `ERC721Metadata`, `ERC721Enumerable`: these contracts were removed, and their functionality merged into `ERC721`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+ * `ERC721`: added a constructor for `name` and `symbol`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+ * `ERC20Detailed`: this contract was removed and its functionality merged into `ERC20`. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
+ * `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
+ * `SafeCast.toUintXX`: new library for integer downcasting, which allows for safe operation on smaller types (e.g. `uint32`) when combined with `SafeMath`. ([#1926](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1926))
+ * `ERC721Metadata`: added `baseURI`, which can be used for dramatic gas savings when all token URIs share a prefix (e.g. `http://api.myapp.com/tokens/<id>`). ([#1970](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1970))
+ * `EnumerableSet`: new library for storing enumerable sets of values. Only `AddressSet` is supported in this release. ([#2061](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/2061))
+ * `Create2`: simple library to make usage of the `CREATE2` opcode easier. ([#1744](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1744))
+
+### Improvements
+ * `ERC777`: `_burn` is now internal, providing more flexibility and making it easier to create tokens that deflate. ([#1908](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1908))
+ * `ReentrancyGuard`: greatly improved gas efficiency by using the net gas metering mechanism introduced in the Istanbul hardfork. ([#1992](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1992), [#1996](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1996))
+ * `ERC777`: improve extensibility by making `_send` and related functions `internal`. ([#2027](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2027))
+ * `ERC721`: improved revert reason when transferring tokens to a non-recipient contract. ([#2018](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2018))
+
+### Breaking changes
+ * `ERC165Checker` now requires a minimum Solidity compiler version of 0.5.10. ([#1829](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1829))
+
+## 2.4.0 (2019-10-29)
+
+### New features
+ * `Address.toPayable`: added a helper to convert between address types without having to resort to low-level casting. ([#1773](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1773))
+ * Facilities to make metatransaction-enabled contracts through the Gas Station Network. ([#1844](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1844))
+ * `Address.sendValue`: added a replacement to Solidity's `transfer`, removing the fixed gas stipend. ([#1962](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1962))
+ * Added replacement for functions that don't forward all gas (which have been deprecated): ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))
+   * `PullPayment.withdrawPaymentsWithGas(address payable payee)`
+   * `Escrow.withdrawWithGas(address payable payee)`
+ * `SafeMath`: added support for custom error messages to `sub`, `div` and `mod` functions. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+
+### Improvements
+ * `Address.isContract`: switched from `extcodesize` to `extcodehash` for less gas usage. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
+ * `ERC20` and `ERC777` updated to throw custom errors on subtraction overflows. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+
+### Deprecations
+ * Deprecated functions that don't forward all gas: ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))
+   * `PullPayment.withdrawPayments(address payable payee)`
+   * `Escrow.withdraw(address payable payee)`
+
+### Breaking changes
+ * `Address` now requires a minimum Solidity compiler version of 0.5.5. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
+ * `SignatureBouncer` has been removed from drafts, both to avoid confusions with the GSN and `GSNRecipientSignature` (previously called `GSNBouncerSignature`) and because the API was not very clear. ([#1879](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1879))
+
+### How to upgrade from 2.4.0-beta
+
+The final 2.4.0 release includes a refactor of the GSN contracts that will be a breaking change for 2.4.0-beta users.
+
+ * The default empty implementations of `_preRelayedCall` and `_postRelayedCall` were removed and must now be explicitly implemented always in custom recipients. If your custom recipient didn't include an implementation, you can provide an empty one.
+ * `GSNRecipient`, `GSNBouncerBase`, and `GSNContext` were all merged into `GSNRecipient`.
+ * `GSNBouncerSignature` and `GSNBouncerERC20Fee` were renamed to `GSNRecipientSignature` and `GSNRecipientERC20Fee`.
+ * It is no longer necessary to inherit from `GSNRecipient` when using `GSNRecipientSignature` and `GSNRecipientERC20Fee`.
+
+For example, a contract using `GSNBouncerSignature` would have to be changed in the following way.
+
+```diff
+-contract MyDapp is GSNRecipient, GSNBouncerSignature {
++contract MyDapp is GSNRecipientSignature {
+```
+
+Refer to the table below to adjust your inheritance list.
+
+| 2.4.0-beta                         | 2.4.0                        |
+| ---------------------------------- | ---------------------------- |
+| `GSNRecipient, GSNBouncerSignature`| `GSNRecipientSignature`      |
+| `GSNRecipient, GSNBouncerERC20Fee` | `GSNRecipientERC20Fee`       |
+| `GSNBouncerBase`                   | `GSNRecipient`               |
 
 ## 2.3.0 (2019-05-27)
 
-### New features:
+### New features
  * `ERC1820`: added support for interacting with the [ERC1820](https://eips.ethereum.org/EIPS/eip-1820) registry contract (`IERC1820Registry`), as well as base contracts that can be registered as implementers there. ([#1677](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1677))
  * `ERC777`: support for the [ERC777 token](https://eips.ethereum.org/EIPS/eip-777), which has multiple improvements over `ERC20` (but is backwards compatible with it) such as built-in burning, a more  straightforward permission system, and optional sender and receiver hooks on transfer (mandatory for contracts!). ([#1684](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1684))
  * All contracts now have revert reason strings, which give insight into error conditions, and help debug failing transactions. ([#1704](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1704))
 
-### Improvements:
+### Improvements
  * Reverted the Solidity version bump done in v2.2.0, setting the minimum compiler version to v0.5.0, to prevent unexpected build breakage. Users are encouraged however to stay on top of new compiler releases, which usually include bugfixes. ([#1729](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1729))
 
-### Bugfixes:
+### Bugfixes
  * `PostDeliveryCrowdsale`: some validations where skipped when paired with other crowdsale flavors, such as `AllowanceCrowdsale`, or `MintableCrowdsale` and `ERC20Capped`, which could cause buyers to not be able to claim their purchased tokens. ([#1721](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1721))
  * `ERC20._transfer`: the `from` argument was allowed to be the zero address, so it was possible to internally trigger a transfer of 0 tokens from the zero address. This address is not a valid destinatary of transfers, nor can it give or receive allowance, so this behavior was inconsistent. It now reverts. ([#1752](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1752))
 
 ## 2.2.0 (2019-03-14)
 
-### New features:
+### New features
  * `ERC20Snapshot`: create snapshots on demand of the token balances and total supply, to later retrieve and e.g. calculate dividends at a past time. ([#1617](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1617))
  * `SafeERC20`: `ERC20` contracts with no return value (i.e. that revert on failure) are now supported. ([#1655](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1655))
  * `ERC20`: added internal `_approve(address owner, address spender, uint256 value)`, allowing derived contracts to set the allowance of arbitrary accounts. ([#1609](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1609))
  * `ERC20Metadata`: added internal `_setTokenURI(string memory tokenURI)`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
  * `TimedCrowdsale`: added internal `_extendTime(uint256 newClosingTime)` as well as `TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime)` event allowing to extend the crowdsale, as long as it hasn't already closed.
 
-### Improvements:
+### Improvements
  * Upgraded the minimum compiler version to v0.5.2: this removes many Solidity warnings that were false positives. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
  * `ECDSA`: `recover` no longer accepts malleable signatures (those using upper-range values for `s`, or 0/1 for `v`). ([#1622](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1622))
- * `ERC721`'s transfers are now more gas efficient due to removal of unnecessary `SafeMath` calls. ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+ * ``ERC721``'s transfers are now more gas efficient due to removal of unnecessary `SafeMath` calls. ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
  * Fixed variable shadowing issues. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
 
-### Bugfixes:
+### Bugfixes
  * (minor) `SafeERC20`: `safeApprove` wasn't properly checking for a zero allowance when attempting to set a non-zero allowance. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
 
-### Breaking changes in drafts:
+### Breaking changes in drafts
  * `TokenMetadata` has been renamed to `ERC20Metadata`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
  * The library `Counter` has been renamed to `Counters` and its API has been improved. See an example in `ERC721`, lines [17](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L17) and [204](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L204). ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
 
@@ -59,7 +277,7 @@
 
 ## 2.1.0 (2019-01-04)
 
-### New features:
+### New features
  * Now targeting the 0.5.x line of Solidity compilers. For 0.4.24 support, use version 2.0 of OpenZeppelin.
  * `WhitelistCrowdsale`: a crowdsale where only whitelisted accounts (`WhitelistedRole`) can purchase tokens. Adding or removing accounts from the whitelist is done by whitelist admins (`WhitelistAdminRole`). Similar to the pre-2.0 `WhitelistedCrowdsale`. ([#1525](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1525), [#1589](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1589))
  * `RefundablePostDeliveryCrowdsale`: replacement for `RefundableCrowdsale` (deprecated, see below) where tokens are only granted once the crowdsale ends (if it meets its goal). ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))
@@ -70,17 +288,17 @@
  * Crowdsales: all constructors are now `public`, meaning it is not necessary to extend these contracts in order to deploy them. The exception is `FinalizableCrowdsale`, since it is meaningless unless extended. ([#1564](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1564))
  * `SignedSafeMath`: added overflow-safe operations for signed integers (`int256`). ([#1559](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1559), [#1588](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1588))
 
-### Improvements:
+### Improvements
  * The compiler version required by `Array` was behind the rest of the libray so it was updated to `v0.4.24`. ([#1553](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1553))
  * Now conforming to a 4-space indentation code style. ([1508](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1508))
  * `ERC20`: more gas efficient due to removed redundant `require`s. ([#1409](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1409))
  * `ERC721`: fixed a bug that prevented internal data structures from being properly cleaned, missing potential gas refunds. ([#1539](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1539) and [#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
  * `ERC721`: general gas savings on `transferFrom`, `_mint` and `_burn`, due to redudant `require`s and `SSTORE`s. ([#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
 
-### Bugfixes:
+### Bugfixes
 
-### Breaking changes:
+### Breaking changes
 
-### Deprecations:
+### Deprecations
  * `ERC721._burn(address owner, uint256 tokenId)`: due to the `owner` parameter being unnecessary. ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
  * `RefundableCrowdsale`: due to trading abuse potential on crowdsales that miss their goal. ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))

CODE_STYLE.md

@@ -1,69 +0,0 @@
-# Code Style
-
-We value clean code and consistency, and those are prerequisites for us to
-include new code in the repository. Before proposing a change, please read this
-document and take some time to familiarize yourself with the style of the
-existing codebase.
-
-## Solidity code
-
-In order to be consistent with all the other Solidity projects, we follow the
-[official recommendations documented in the Solidity style guide](http://solidity.readthedocs.io/en/latest/style-guide.html).
-
-Any exception or additions specific to our project are documented below.
-
-### Naming
-
-* Try to avoid acronyms and abbreviations.
-
-* All state variables should be private.
-
-* Private state variables should have an underscore prefix.
-
-    ```
-    contract TestContract {
-      uint256 private _privateVar;
-      uint256 internal _internalVar;
-    }
-    ```
-
-* Parameters must not be prefixed with an underscore.
-
-    ```
-    function test(uint256 testParameter1, uint256 testParameter2) {
-    ...
-    }
-    ```
-
-* Internal and private functions should have an underscore prefix.
-
-    ```
-    function _testInternal() internal {
-      ...
-    }
-    ```
-
-    ```
-    function _testPrivate() private {
-      ...
-    }
-    ```
-
-* Events should be emitted immediately after the state change that they
-  represent, and consequently they should be named in past tense.
-
-    ```
-    function _burn(address _who, uint256 _value) internal {
-      super._burn(_who, _value);
-      emit TokensBurned(_who, _value);
-    }
-    ```
-
-  Some standards (e.g. ERC20) use present tense, and in those cases the
-  standard specification prevails.
-  
-* Interface names should have a capital I prefix.
-
-    ```
-    interface IERC777 {
-    ```

CONTRIBUTING.md

@@ -44,13 +44,6 @@ npm test
 npm run lint
 ```
 
-or you can simply run CircleCI locally
-```bash
-circleci local execute --job build
-circleci local execute --job test
-```
-*Note*: requires installing CircleCI and docker locally on your machine.
-
 5) Go to [github.com/OpenZeppelin/openzeppelin-contracts](https://github.com/OpenZeppelin/openzeppelin-contracts) in your web browser and issue a new pull request.
 
 *IMPORTANT* Read the PR template very carefully and make sure to follow all the instructions. These instructions

DOCUMENTATION.md

@@ -1,5 +1,4 @@
-We're building an improved documentation website. It's still in development and
-contributions will be really appreciated.
+Documentation is hosted at https://docs.openzeppelin.com/contracts.
 
 All of the content for the site is in this repository. The guides are in the
 [docs](/docs) directory, and the API Reference is extracted from comments in
@@ -9,11 +8,9 @@ repository you should be contributing to.
 [`solidity-docgen`](https://github.com/OpenZeppelin/solidity-docgen) is the
 program that extracts the API Reference from source code.
 
-The [`openzeppelin-docsite`](https://github.com/OpenZeppelin/openzeppelin-docsite)
-repository hosts the configuration for Docusaurus, the static site generator
-that we use.
+The [`docs.openzeppelin.com`](https://github.com/OpenZeppelin/docs.openzeppelin.com)
+repository hosts the configuration for the entire site, which includes
+documentation for all of the OpenZeppelin projects.
 
-To run the docsite locally you should run `npm run docsite start` on this
-repository. This will live reload as the guides are edited, but not with
-changes to the source code comments, for that you need to restart the server.
-This should be improved eventually (contributions welcome!).
+To run the docs locally you should run `npm run docs:watch` on this
+repository.

GUIDELINES.md

@@ -28,37 +28,78 @@ Consistency on the way classes are used is paramount to an easier understanding
 #### D6 - Regular Audits
 Following good programming practices is a way to reduce the risk of vulnerabilities, but professional code audits are still needed. We will perform regular code audits on major releases, and hire security professionals to provide independent review.
 
-## Style Guidelines
+# Style Guidelines
 
-The design guidelines have quite a high abstraction level. These style guidelines are more concrete and easier to apply, and also more opinionated.
+The design guidelines have quite a high abstraction level. These style guidelines are more concrete and easier to apply, and also more opinionated. We value clean code and consistency, and those are prerequisites for us to include new code in the repository. Before proposing a change, please read these guidelines and take some time to familiarize yourself with the style of the existing codebase.
 
-### General
+## Solidity code
 
-#### G0 - Default to Solidity's official style guide.
+In order to be consistent with all the other Solidity projects, we follow the
+[official recommendations documented in the Solidity style guide](http://solidity.readthedocs.io/en/latest/style-guide.html).
 
-Follow the official Solidity style guide: https://solidity.readthedocs.io/en/latest/style-guide.html
+Any exception or additions specific to our project are documented below.
 
-#### G1 - No Magic Constants
+* Try to avoid acronyms and abbreviations.
 
-Avoid constants in the code as much as possible. Magic strings are also magic constants.
+* All state variables should be private.
 
-#### G2 - Code that Fails Early
+* Private state variables should have an underscore prefix.
 
-We ask our code to fail as soon as possible when an unexpected input was provided or unexpected state was found.
+    ```
+    contract TestContract {
+      uint256 private _privateVar;
+      uint256 internal _internalVar;
+    }
+    ```
 
-#### G3 - Internal Amounts Must be Signed Integers and Represent the Smallest Units.
+* Parameters must not be prefixed with an underscore.
 
-Avoid representation errors by always dealing with weis when handling ether. GUIs can convert to more human-friendly representations. Use Signed Integers (int) to prevent underflow problems.
+    ```
+    function test(uint256 testParameter1, uint256 testParameter2) {
+    ...
+    }
+    ```
+
+* Internal and private functions should have an underscore prefix.
+
+    ```
+    function _testInternal() internal {
+      ...
+    }
+    ```
+
+    ```
+    function _testPrivate() private {
+      ...
+    }
+    ```
+
+* Events should be emitted immediately after the state change that they
+  represent, and consequently they should be named in past tense.
+
+    ```
+    function _burn(address who, uint256 value) internal {
+      super._burn(who, value);
+      emit TokensBurned(who, value);
+    }
+    ```
+
+  Some standards (e.g. ERC20) use present tense, and in those cases the
+  standard specification prevails.
+  
+* Interface names should have a capital I prefix.
+
+    ```
+    interface IERC777 {
+    ```
 
 
-### Testing
+## Tests
 
-#### T1 - Tests Must be Written Elegantly
+* Tests Must be Written Elegantly
 
-Style guidelines are not relaxed for tests. Tests are a good way to show how to use the library, and maintaining them is extremely necessary.
+    Tests are a good way to show how to use the library, and maintaining them is extremely necessary. Don't write long tests, write helper functions to make them be as short and concise as possible (they should take just a few lines each), and use good variable names.
 
-Don't write long tests, write helper functions to make them be as short and concise as possible (they should take just a few lines each), and use good variable names.
+* Tests Must not be Random
 
-#### T2 - Tests Must not be Random
-
-Inputs for tests should not be generated randomly. Accounts used to create test contracts are an exception, those can be random. Also, the type and structure of outputs should be checked.
+    Inputs for tests should not be generated randomly. Accounts used to create test contracts are an exception, those can be random. Also, the type and structure of outputs should be checked.

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

@@ -1,42 +1,66 @@
-# <img src="logo.png" alt="OpenZeppelin" height="40px">
+# <img src="logo.svg" 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)
 
-**OpenZeppelin Contracts is a library for secure smart contract development.** It provides implementations of standards like ERC20 and ERC721 which you can deploy as-is or extend to suit your needs, as well as Solidity components to build custom contracts and more complex decentralized systems.
+**A library for secure smart contract development.** Build on a solid foundation of community-vetted code.
 
-## Install
+ * Implementations of standards like [ERC20](https://docs.openzeppelin.com/contracts/erc20) and [ERC721](https://docs.openzeppelin.com/contracts/erc721).
+ * 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](https://github.com/OpenZeppelin/openzeppelin-contracts/tree/master/audit) by leading security firms (_last full audit on v2.0.0_).
 
-```
-npm install @openzeppelin/contracts
+## Overview
+
+### Installation
+
+```console
+$ npm install @openzeppelin/contracts
 ```
 
-OpenZeppelin Contracts features a stable API, which means your contracts won't break unexpectedly when upgrading to a newer minor version. You can read ṫhe details in our [API Stability] document.
+OpenZeppelin Contracts features a [stable API](https://docs.openzeppelin.com/contracts/releases-stability#api-stability), which means your contracts won't break unexpectedly when upgrading to a newer minor version.
 
-## Usage
+### Usage
 
-To write your custom contracts, import ours and extend them through inheritance.
+Once installed, you can use the contracts in the library by importing them:
 
 ```solidity
-pragma solidity ^0.5.0;
+pragma solidity ^0.8.0;
 
-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") {
+    }
 }
 ```
 
-> You need an ethereum development framework for the above import statements to work! Check out these guides for [Truffle], [Embark] or [Buidler].
+_If you're new to smart contract development, head to [Developing Smart Contracts](https://docs.openzeppelin.com/learn/developing-smart-contracts) to learn about creating a new project and compiling your contracts._
 
-On our site you will find a few [guides] to learn about the different parts of OpenZeppelin, as well as [documentation for the API][API docs]. Keep in mind that the API docs are work in progress, and don’t hesitate to ask questions in [our forum][forum].
+To keep your system secure, you should **always** use the installed code as-is, and neither copy-paste it from online sources, nor modify it yourself. The library is designed so that only the contracts and functions you use are deployed, so you don't need to worry about it needlessly increasing gas costs.
+
+## Learn More
+
+The guides in the [docs site](https://docs.openzeppelin.com/contracts) will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
+
+* [Access Control](https://docs.openzeppelin.com/contracts/access-control): decide who can perform each of the actions on your system.
+* [Tokens](https://docs.openzeppelin.com/contracts/tokens): create tradeable assets or collectives, and distribute them via [Crowdsales](https://docs.openzeppelin.com/contracts/crowdsales).
+* [Gas Station Network](https://docs.openzeppelin.com/contracts/gsn): let your users interact with your contracts without having to pay for gas themselves.
+* [Utilities](https://docs.openzeppelin.com/contracts/utilities): generic useful tools, including non-overflowing math, signature verification, and trustless paying systems.
+
+The [full API](https://docs.openzeppelin.com/contracts/api/token/ERC20) is also thoroughly documented, and serves as a great reference when developing your smart contract application. You can also ask for help or follow Contracts's development in the [community forum](https://forum.openzeppelin.com).
+
+Finally, you may want to take a look at the [guides on our blog](https://blog.openzeppelin.com/guides), which cover several common use cases and good practices.. The following articles provide great background reading, though please note, some of the referenced tools have changed as the tooling in the ecosystem continues to rapidly evolve.
+
+* [The Hitchhiker’s Guide to Smart Contracts in Ethereum](https://blog.openzeppelin.com/the-hitchhikers-guide-to-smart-contracts-in-ethereum-848f08001f05) will help you get an overview of the various tools available for smart contract development, and help you set up your environment.
+* [A Gentle Introduction to Ethereum Programming, Part 1](https://blog.openzeppelin.com/a-gentle-introduction-to-ethereum-programming-part-1-783cc7796094) provides very useful information on an introductory level, including many basic concepts from the Ethereum platform.
+* For a more in-depth dive, you may read the guide [Designing the Architecture for Your Ethereum Application](https://blog.openzeppelin.com/designing-the-architecture-for-your-ethereum-application-9cec086f8317), which discusses how to better structure your application and its relationship to the real world.
 
 ## Security
 
-This project is maintained by [OpenZeppelin], and developed following our high standards for code quality and security. OpenZeppelin is meant to provide tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problems you might experience.
+This project is maintained by [OpenZeppelin](https://openzeppelin.com), and developed following our high standards for code quality and security. OpenZeppelin is meant to provide tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problems you might experience.
 
 The core development principles and strategies that OpenZeppelin is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.
 
@@ -46,19 +70,8 @@ Please report any security issues you find to security@openzeppelin.org.
 
 ## Contribute
 
-OpenZeppelin exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the [contribution guide]!
+OpenZeppelin exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the [contribution guide](CONTRIBUTING.md)!
 
 ## License
 
 OpenZeppelin is released under the [MIT License](LICENSE).
-
-
-[API docs]: https://docs.openzeppelin.com/contracts/api/token/erc20
-[guides]: https://docs.openzeppelin.com/contracts
-[API Stability]: https://docs.openzeppelin.com/contracts/api-stability
-[forum]: https://forum.openzeppelin.com
-[OpenZeppelin]: https://openzeppelin.com
-[contribution guide]: CONTRIBUTING.md
-[Truffle]: https://truffleframework.com/docs/truffle/quickstart
-[Embark]: https://embark.status.im/docs/quick_start.html
-[Buidler]: https://buidler.dev/guides/#getting-started

RELEASING.md

@@ -1,83 +1,20 @@
 # Releasing
 
-This document describes our release process, and contains the steps to be followed by an OpenZeppelin maintainer at the several stages of a release.
+> Visit the documentation for [details about release schedule].
 
-We release a new version of OpenZeppelin monthly. Release cycles are tracked in the [issue milestones](https://github.com/OpenZeppelin/openzeppelin-contracts/milestones).
+Start on an up-to-date `master` branch.
 
-Each release has at least one release candidate published first, intended for community review and any critical fixes that may come out of it. At the moment we leave 1 week between the first release candidate and the final release.
+Create the release branch with `npm run release start minor`.
 
-Before starting make sure to verify the following items.
-* Your local `master` branch is in sync with your `upstream` remote (it may have another name depending on your setup).
-* Your repo is clean, particularly with no untracked files in the contracts and tests directories. Verify with `git clean -n`.
+Publish a release candidate with `npm run release rc`.
 
+Publish the final release with `npm run release final`.
 
-## Creating the release branch
+Follow the general [OpenZeppelin release checklist].
 
-We'll refer to a release `vX.Y.Z`.
+[details about release schedule]: https://docs.openzeppelin.com/contracts/releases-stability
+[OpenZeppelin release checklist]: https://github.com/OpenZeppelin/code-style/blob/master/RELEASE_CHECKLIST.md
 
-```
-git checkout master
-git checkout -b release-vX.Y.Z
-```
-
-## Creating a release candidate
-
-Once in the release branch, change the version string in `package.json`, `package-lock.json` and `ethpm.json` to `X.Y.Z-rc.R`. (This will be `X.Y.Z-rc.1` for the first release candidate.) Commit these changes and tag the commit as `vX.Y.Z-rc.R`.
-
-```
-git add package.json package-lock.json ethpm.json
-git commit -m "Release candidate vX.Y.Z-rc.R"
-git tag -a vX.Y.Z-rc.R
-git push upstream release-vX.Y.Z
-git push upstream vX.Y.Z-rc.R
-```
-
-Draft the release notes in our [GitHub releases](https://github.com/OpenZeppelin/openzeppelin-contracts/releases). Make sure to mark it as a pre-release! Try to be consistent with our previous release notes in the title and format of the text. Release candidates don't need a detailed changelog, but make sure to include a link to GitHub's compare page.
-
-Once the CI run for the new tag is green, publish on npm under the `next` tag. You should see the contracts compile automatically.
-
-```
-npm publish --tag next
-```
-
-Publish the release notes on GitHub and the forum, and ask our community manager to announce the release candidate on at least Twitter.
-
-## Creating the final release
-
-Make sure to have the latest changes from `upstream` in your local release branch.
-
-```
-git checkout release-vX.Y.Z
-git pull upstream
-```
-
-Before starting the release process, make one final commit to CHANGELOG.md, including the date of the release.
-
-Change the version string in `package.json`, `package-lock.json` and `ethpm.json` removing the "-rc.R" suffix. Commit these changes and tag the commit as `vX.Y.Z`.
-
-```
-git add package.json package-lock.json ethpm.json
-git commit -m "Release vX.Y.Z"
-git tag -a vX.Y.Z
-git push upstream release-vX.Y.Z
-git push upstream vX.Y.Z
-```
-
-Draft the release notes in GitHub releases. Try to be consistent with our previous release notes in the title and format of the text. Make sure to include a detailed changelog.
-
-Once the CI run for the new tag is green, publish on npm. You should see the contracts compile automatically.
-
-```
-npm publish
-```
-
-Publish the release notes on GitHub and ask our community manager to announce the release!
-
-Delete the `next` tag in the npm package as there is no longer a release candidate.
-
-```
-npm dist-tag rm --otp $2FA_CODE @openzeppelin/contracts next
-```
 
 ## Merging the release branch
 

contracts/GSN/Context.sol

@@ -1,27 +0,0 @@
-pragma solidity ^0.5.0;
-
-/*
- * @dev Provides information about the current execution context, including the
- * sender of the transaction and its data. While these are generally available
- * via msg.sender and msg.data, they not should not be accessed in such a direct
- * manner, since when dealing with GSN meta-transactions the account sending and
- * paying for execution may not be the actual sender (as far as an application
- * is concerned).
- *
- * 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, with should be used via inheritance.
-    constructor () internal { }
-    // solhint-disable-previous-line no-empty-blocks
-
-    function _msgSender() internal view returns (address) {
-        return msg.sender;
-    }
-
-    function _msgData() internal view returns (bytes memory) {
-        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
-        return msg.data;
-    }
-}

contracts/GSN/GSNContext.sol

@@ -1,102 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "./Context.sol";
-
-/*
- * @dev Enables GSN support on `Context` contracts by recognizing calls from
- * RelayHub and extracting the actual sender and call data from the received
- * calldata.
- *
- * > This contract does not perform all required tasks to implement a GSN
- * recipient contract: end users should use `GSNRecipient` instead.
- */
-contract GSNContext is Context {
-    // We use a random storage slot to allow proxy contracts to enable GSN support in an upgrade without changing their
-    // storage layout. This value is calculated as: keccak256('gsn.relayhub.address'), minus 1.
-    bytes32 private constant RELAY_HUB_ADDRESS_STORAGE_SLOT = 0x06b7792c761dcc05af1761f0315ce8b01ac39c16cc934eb0b2f7a8e71414f262;
-
-    event RelayHubChanged(address indexed oldRelayHub, address indexed newRelayHub);
-
-    constructor() internal {
-        _upgradeRelayHub(0xD216153c06E857cD7f72665E0aF1d7D82172F494);
-    }
-
-    function _getRelayHub() internal view returns (address relayHub) {
-        bytes32 slot = RELAY_HUB_ADDRESS_STORAGE_SLOT;
-        // solhint-disable-next-line no-inline-assembly
-        assembly {
-            relayHub := sload(slot)
-        }
-    }
-
-    function _upgradeRelayHub(address newRelayHub) internal {
-        address currentRelayHub = _getRelayHub();
-        require(newRelayHub != address(0), "GSNContext: new RelayHub is the zero address");
-        require(newRelayHub != currentRelayHub, "GSNContext: new RelayHub is the current one");
-
-        emit RelayHubChanged(currentRelayHub, newRelayHub);
-
-        bytes32 slot = RELAY_HUB_ADDRESS_STORAGE_SLOT;
-        // solhint-disable-next-line no-inline-assembly
-        assembly {
-            sstore(slot, newRelayHub)
-        }
-    }
-
-    // Overrides for Context's functions: when called from RelayHub, sender and
-    // data require some pre-processing: the actual sender is stored at the end
-    // of the call data, which in turns means it needs to be removed from it
-    // when handling said data.
-
-    function _msgSender() internal view returns (address) {
-        if (msg.sender != _getRelayHub()) {
-            return msg.sender;
-        } else {
-            return _getRelayedCallSender();
-        }
-    }
-
-    function _msgData() internal view returns (bytes memory) {
-        if (msg.sender != _getRelayHub()) {
-            return msg.data;
-        } else {
-            return _getRelayedCallData();
-        }
-    }
-
-    function _getRelayedCallSender() private pure returns (address result) {
-        // We need to read 20 bytes (an address) located at array index msg.data.length - 20. In memory, the array
-        // is prefixed with a 32-byte length value, so we first add 32 to get the memory read index. However, doing
-        // so would leave the address in the upper 20 bytes of the 32-byte word, which is inconvenient and would
-        // require bit shifting. We therefore subtract 12 from the read index so the address lands on the lower 20
-        // bytes. This can always be done due to the 32-byte prefix.
-
-        // The final memory read index is msg.data.length - 20 + 32 - 12 = msg.data.length. Using inline assembly is the
-        // easiest/most-efficient way to perform this operation.
-
-        // These fields are not accessible from assembly
-        bytes memory array = msg.data;
-        uint256 index = msg.data.length;
-
-        // solhint-disable-next-line no-inline-assembly
-        assembly {
-            // Load the 32 bytes word from memory with the address on the lower 20 bytes, and mask those.
-            result := and(mload(add(array, index)), 0xffffffffffffffffffffffffffffffffffffffff)
-        }
-        return result;
-    }
-
-    function _getRelayedCallData() private pure returns (bytes memory) {
-        // RelayHub appends the sender address at the end of the calldata, so in order to retrieve the actual msg.data,
-        // we must strip the last 20 bytes (length of an address type) from it.
-
-        uint256 actualDataLength = msg.data.length - 20;
-        bytes memory actualData = new bytes(actualDataLength);
-
-        for (uint256 i = 0; i < actualDataLength; ++i) {
-            actualData[i] = msg.data[i];
-        }
-
-        return actualData;
-    }
-}

contracts/GSN/GSNRecipient.sol

@@ -1,28 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "./IRelayRecipient.sol";
-import "./GSNContext.sol";
-import "./bouncers/GSNBouncerBase.sol";
-import "./IRelayHub.sol";
-
-/*
- * @dev Base GSN recipient contract, adding the recipient interface and enabling
- * GSN support. Not all interface methods are implemented, derived contracts
- * must do so themselves.
- */
-contract GSNRecipient is IRelayRecipient, GSNContext, GSNBouncerBase {
-    function getHubAddr() public view returns (address) {
-        return _getRelayHub();
-    }
-
-    // This function is view for future-proofing, it may require reading from
-    // storage in the future.
-    function relayHubVersion() public view returns (string memory) {
-        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
-        return "1.0.0";
-    }
-
-    function _withdrawDeposits(uint256 amount, address payable payee) internal {
-        IRelayHub(_getRelayHub()).withdraw(amount, payee);
-    }
-}

contracts/GSN/IRelayHub.sol

@@ -1,188 +0,0 @@
-pragma solidity ^0.5.0;
-
-contract IRelayHub {
-    // Relay management
-
-    // Add stake to a relay and sets its unstakeDelay.
-    // If the relay does not exist, it is created, and the caller
-    // of this function becomes its owner. If the relay already exists, only the owner can call this function. A relay
-    // cannot be its own owner.
-    // All Ether in this function call will be added to the relay's stake.
-    // Its unstake delay will be assigned to unstakeDelay, but the new value must be greater or equal to the current one.
-    // Emits a Staked event.
-    function stake(address relayaddr, uint256 unstakeDelay) external payable;
-
-    // Emited when a relay's stake or unstakeDelay are increased
-    event Staked(address indexed relay, uint256 stake, uint256 unstakeDelay);
-
-    // Registers the caller as a relay.
-    // The relay must be staked for, and not be a contract (i.e. this function must be called directly from an EOA).
-    // Emits a RelayAdded event.
-    // This function can be called multiple times, emitting new RelayAdded events. Note that the received transactionFee
-    // is not enforced by relayCall.
-    function registerRelay(uint256 transactionFee, string memory url) public;
-
-    // Emitted when a relay is registered or re-registerd. Looking at these events (and filtering out RelayRemoved
-    // events) lets a client discover the list of available relays.
-    event RelayAdded(address indexed relay, address indexed owner, uint256 transactionFee, uint256 stake, uint256 unstakeDelay, string url);
-
-    // Removes (deregisters) a relay. Unregistered (but staked for) relays can also be removed. Can only be called by
-    // the owner of the relay. After the relay's unstakeDelay has elapsed, unstake will be callable.
-    // Emits a RelayRemoved event.
-    function removeRelayByOwner(address relay) public;
-
-    // Emitted when a relay is removed (deregistered). unstakeTime is the time when unstake will be callable.
-    event RelayRemoved(address indexed relay, uint256 unstakeTime);
-
-    // Deletes the relay from the system, and gives back its stake to the owner. Can only be called by the relay owner,
-    // after unstakeDelay has elapsed since removeRelayByOwner was called.
-    // Emits an Unstaked event.
-    function unstake(address relay) public;
-
-    // Emitted when a relay is unstaked for, including the returned stake.
-    event Unstaked(address indexed relay, uint256 stake);
-
-    // States a relay can be in
-    enum RelayState {
-        Unknown, // The relay is unknown to the system: it has never been staked for
-        Staked, // The relay has been staked for, but it is not yet active
-        Registered, // The relay has registered itself, and is active (can relay calls)
-        Removed    // The relay has been removed by its owner and can no longer relay calls. It must wait for its unstakeDelay to elapse before it can unstake
-    }
-
-    // Returns a relay's status. Note that relays can be deleted when unstaked or penalized.
-    function getRelay(address relay) external view returns (uint256 totalStake, uint256 unstakeDelay, uint256 unstakeTime, address payable owner, RelayState state);
-
-    // Balance management
-
-    // Deposits ether for a contract, so that it can receive (and pay for) relayed transactions. Unused balance can only
-    // be withdrawn by the contract itself, by callingn withdraw.
-    // Emits a Deposited event.
-    function depositFor(address target) public payable;
-
-    // Emitted when depositFor is called, including the amount and account that was funded.
-    event Deposited(address indexed recipient, address indexed from, uint256 amount);
-
-    // Returns an account's deposits. These can be either a contnract's funds, or a relay owner's revenue.
-    function balanceOf(address target) external view returns (uint256);
-
-    // Withdraws from an account's balance, sending it back to it. Relay owners call this to retrieve their revenue, and
-    // contracts can also use it to reduce their funding.
-    // Emits a Withdrawn event.
-    function withdraw(uint256 amount, address payable dest) public;
-
-    // Emitted when an account withdraws funds from RelayHub.
-    event Withdrawn(address indexed account, address indexed dest, uint256 amount);
-
-    // Relaying
-
-    // Check if the RelayHub will accept a relayed operation. Multiple things must be true for this to happen:
-    //  - all arguments must be signed for by the sender (from)
-    //  - the sender's nonce must be the current one
-    //  - the recipient must accept this transaction (via acceptRelayedCall)
-    // Returns a PreconditionCheck value (OK when the transaction can be relayed), or a recipient-specific error code if
-    // it returns one in acceptRelayedCall.
-    function canRelay(
-        address relay,
-        address from,
-        address to,
-        bytes memory encodedFunction,
-        uint256 transactionFee,
-        uint256 gasPrice,
-        uint256 gasLimit,
-        uint256 nonce,
-        bytes memory signature,
-        bytes memory approvalData
-    ) public view returns (uint256 status, bytes memory recipientContext);
-
-    // Preconditions for relaying, checked by canRelay and returned as the corresponding numeric values.
-    enum PreconditionCheck {
-        OK,                         // All checks passed, the call can be relayed
-        WrongSignature,             // The transaction to relay is not signed by requested sender
-        WrongNonce,                 // The provided nonce has already been used by the sender
-        AcceptRelayedCallReverted,  // The recipient rejected this call via acceptRelayedCall
-        InvalidRecipientStatusCode  // The recipient returned an invalid (reserved) status code
-    }
-
-    // Relays a transaction. For this to suceed, multiple conditions must be met:
-    //  - canRelay must return PreconditionCheck.OK
-    //  - the sender must be a registered relay
-    //  - the transaction's gas price must be larger or equal to the one that was requested by the sender
-    //  - the transaction must have enough gas to not run out of gas if all internal transactions (calls to the
-    // recipient) use all gas available to them
-    //  - the recipient must have enough balance to pay the relay for the worst-case scenario (i.e. when all gas is
-    // spent)
-    //
-    // If all conditions are met, the call will be relayed and the recipient charged. preRelayedCall, the encoded
-    // function and postRelayedCall will be called in order.
-    //
-    // Arguments:
-    //  - from: the client originating the request
-    //  - recipient: the target IRelayRecipient contract
-    //  - encodedFunction: the function call to relay, including data
-    //  - transactionFee: fee (%) the relay takes over actual gas cost
-    //  - gasPrice: gas price the client is willing to pay
-    //  - 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 Hub, but
-    //    it still can be used for e.g. a signature.
-    //
-    // Emits a TransactionRelayed event.
-    function relayCall(
-        address from,
-        address to,
-        bytes memory encodedFunction,
-        uint256 transactionFee,
-        uint256 gasPrice,
-        uint256 gasLimit,
-        uint256 nonce,
-        bytes memory signature,
-        bytes memory approvalData
-    ) public;
-
-    // Emitted when an attempt to relay a call failed. This can happen due to incorrect relayCall arguments, or the
-    // recipient not accepting the relayed call. The actual relayed call was not executed, and the recipient not charged.
-    // The reason field contains an error code: values 1-10 correspond to PreconditionCheck entries, and values over 10
-    // are custom recipient error codes returned from acceptRelayedCall.
-    event CanRelayFailed(address indexed relay, address indexed from, address indexed to, bytes4 selector, uint256 reason);
-
-    // Emitted when a transaction is relayed. Note that the actual encoded function might be reverted: this will be
-    // indicated in the status field.
-    // Useful when monitoring a relay's operation and relayed calls to a contract.
-    // Charge is the ether value deducted from the recipient's balance, paid to the relay's owner.
-    event TransactionRelayed(address indexed relay, address indexed from, address indexed to, bytes4 selector, RelayCallStatus status, uint256 charge);
-
-    // Reason error codes for the TransactionRelayed event
-    enum RelayCallStatus {
-        OK,                      // The transaction was successfully relayed and execution successful - never included in the event
-        RelayedCallFailed,       // The transaction was relayed, but the relayed call failed
-        PreRelayedFailed,        // The transaction was not relayed due to preRelatedCall reverting
-        PostRelayedFailed,       // The transaction was relayed and reverted due to postRelatedCall reverting
-        RecipientBalanceChanged  // The transaction was relayed and reverted due to the recipient's balance changing
-    }
-
-    // Returns how much gas should be forwarded to a call to relayCall, in order to relay a transaction that will spend
-    // up to relayedCallStipend gas.
-    function requiredGas(uint256 relayedCallStipend) public view returns (uint256);
-
-    // Returns the maximum recipient charge, given the amount of gas forwarded, gas price and relay fee.
-    function maxPossibleCharge(uint256 relayedCallStipend, uint256 gasPrice, uint256 transactionFee) public view returns (uint256);
-
-    // Relay penalization. Any account can penalize relays, removing them from the system immediately, and rewarding the
-    // reporter with half of the relay's stake. The other half is burned so that, even if the relay penalizes itself, it
-    // still loses half of its stake.
-
-    // Penalize a relay that signed two transactions using the same nonce (making only the first one valid) and
-    // different data (gas price, gas limit, etc. may be different). The (unsigned) transaction data and signature for
-    // both transactions must be provided.
-    function penalizeRepeatedNonce(bytes memory unsignedTx1, bytes memory signature1, bytes memory unsignedTx2, bytes memory signature2) public;
-
-    // Penalize a relay that sent a transaction that didn't target RelayHub's registerRelay or relayCall.
-    function penalizeIllegalTransaction(bytes memory unsignedTx, bytes memory signature) public;
-
-    event Penalized(address indexed relay, address sender, uint256 amount);
-
-    function getNonce(address from) external view returns (uint256);
-}
-

contracts/GSN/IRelayRecipient.sol

@@ -1,30 +0,0 @@
-pragma solidity ^0.5.0;
-
-/*
- * @dev Interface for a contract that will be called via the GSN from RelayHub.
- */
-contract IRelayRecipient {
-    /**
-     * @dev Returns the address of the RelayHub instance this recipient interacts with.
-     */
-    function getHubAddr() public view returns (address);
-
-    function acceptRelayedCall(
-        address relay,
-        address from,
-        bytes calldata encodedFunction,
-        uint256 transactionFee,
-        uint256 gasPrice,
-        uint256 gasLimit,
-        uint256 nonce,
-        bytes calldata approvalData,
-        uint256 maxPossibleCharge
-    )
-        external
-        view
-        returns (uint256, bytes memory);
-
-    function preRelayedCall(bytes calldata context) external returns (bytes32);
-
-    function postRelayedCall(bytes calldata context, bool success, uint actualCharge, bytes32 preRetVal) external;
-}

contracts/GSN/README.adoc

@@ -1,10 +0,0 @@
-= GSN
-
-== Recipient
-
-{{GSNRecipient}}
-
-== Bouncers
-
-{{GSNBouncerERC20Fee}}
-{{GSNBouncerSignature}}

contracts/GSN/bouncers/GSNBouncerBase.sol

@@ -1,92 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../IRelayRecipient.sol";
-
-/*
- * @dev Base contract used to implement GSNBouncers.
- *
- * > This contract does not perform all required tasks to implement a GSN
- * recipient contract: end users should use `GSNRecipient` instead.
- */
-contract GSNBouncerBase is IRelayRecipient {
-    uint256 constant private RELAYED_CALL_ACCEPTED = 0;
-    uint256 constant private RELAYED_CALL_REJECTED = 11;
-
-    // How much gas is forwarded to postRelayedCall
-    uint256 constant internal POST_RELAYED_CALL_MAX_GAS = 100000;
-
-    // Base implementations for pre and post relayedCall: only RelayHub can invoke them, and data is forwarded to the
-    // internal hook.
-
-    /**
-     * @dev See `IRelayRecipient.preRelayedCall`.
-     *
-     * This function should not be overriden directly, use `_preRelayedCall` instead.
-     *
-     * * Requirements:
-     *
-     * - the caller must be the `RelayHub` contract.
-     */
-    function preRelayedCall(bytes calldata context) external returns (bytes32) {
-        require(msg.sender == getHubAddr(), "GSNBouncerBase: caller is not RelayHub");
-        return _preRelayedCall(context);
-    }
-
-    /**
-     * @dev See `IRelayRecipient.postRelayedCall`.
-     *
-     * This function should not be overriden directly, use `_postRelayedCall` instead.
-     *
-     * * Requirements:
-     *
-     * - the caller must be the `RelayHub` contract.
-     */
-    function postRelayedCall(bytes calldata context, bool success, uint256 actualCharge, bytes32 preRetVal) external {
-        require(msg.sender == getHubAddr(), "GSNBouncerBase: caller is not RelayHub");
-        _postRelayedCall(context, success, actualCharge, preRetVal);
-    }
-
-    /**
-     * @dev Return this in acceptRelayedCall to proceed with the execution of a relayed call. Note that this contract
-     * will be charged a fee by RelayHub
-     */
-    function _approveRelayedCall() internal pure returns (uint256, bytes memory) {
-        return _approveRelayedCall("");
-    }
-
-    /**
-     * @dev See `GSNBouncerBase._approveRelayedCall`.
-     *
-     * This overload forwards `context` to _preRelayedCall and _postRelayedCall.
-     */
-    function _approveRelayedCall(bytes memory context) internal pure returns (uint256, bytes memory) {
-        return (RELAYED_CALL_ACCEPTED, context);
-    }
-
-    /**
-     * @dev Return this in acceptRelayedCall to impede execution of a relayed call. No fees will be charged.
-     */
-    function _rejectRelayedCall(uint256 errorCode) internal pure returns (uint256, bytes memory) {
-        return (RELAYED_CALL_REJECTED + errorCode, "");
-    }
-
-    // Empty hooks for pre and post relayed call: users only have to define these if they actually use them.
-
-    function _preRelayedCall(bytes memory) internal returns (bytes32) {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    function _postRelayedCall(bytes memory, bool, uint256, bytes32) internal {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    /*
-     * @dev Calculates how much RelaHub will charge a recipient for using `gas` at a `gasPrice`, given a relayer's
-     * `serviceFee`.
-     */
-    function _computeCharge(uint256 gas, uint256 gasPrice, uint256 serviceFee) internal pure returns (uint256) {
-        // The fee is expressed as a percentage. E.g. a value of 40 stands for a 40% fee, so the recipient will be
-        // charged for 1.4 times the spent amount.
-        return (gas * gasPrice * (100 + serviceFee)) / 100;
-    }
-}

contracts/GSN/bouncers/GSNBouncerERC20Fee.sol

@@ -1,121 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "./GSNBouncerBase.sol";
-import "../../math/SafeMath.sol";
-import "../../ownership/Secondary.sol";
-import "../../token/ERC20/SafeERC20.sol";
-import "../../token/ERC20/ERC20.sol";
-import "../../token/ERC20/ERC20Detailed.sol";
-
-contract GSNBouncerERC20Fee is GSNBouncerBase {
-    using SafeERC20 for __unstable__ERC20PrimaryAdmin;
-    using SafeMath for uint256;
-
-    enum GSNBouncerERC20FeeErrorCodes {
-        INSUFFICIENT_BALANCE
-    }
-
-    __unstable__ERC20PrimaryAdmin private _token;
-
-    constructor(string memory name, string memory symbol, uint8 decimals) public {
-        _token = new __unstable__ERC20PrimaryAdmin(name, symbol, decimals);
-    }
-
-    function token() public view returns (IERC20) {
-        return IERC20(_token);
-    }
-
-    function _mint(address account, uint256 amount) internal {
-        _token.mint(account, amount);
-    }
-
-    function acceptRelayedCall(
-        address,
-        address from,
-        bytes calldata,
-        uint256 transactionFee,
-        uint256 gasPrice,
-        uint256,
-        uint256,
-        bytes calldata,
-        uint256 maxPossibleCharge
-    )
-        external
-        view
-        returns (uint256, bytes memory)
-    {
-        if (_token.balanceOf(from) < maxPossibleCharge) {
-            return _rejectRelayedCall(uint256(GSNBouncerERC20FeeErrorCodes.INSUFFICIENT_BALANCE));
-        }
-
-        return _approveRelayedCall(abi.encode(from, maxPossibleCharge, transactionFee, gasPrice));
-    }
-
-    function _preRelayedCall(bytes memory context) internal returns (bytes32) {
-        (address from, uint256 maxPossibleCharge) = abi.decode(context, (address, uint256));
-
-        // The maximum token charge is pre-charged from the user
-        _token.safeTransferFrom(from, address(this), maxPossibleCharge);
-    }
-
-    function _postRelayedCall(bytes memory context, bool, uint256 actualCharge, bytes32) internal {
-        (address from, uint256 maxPossibleCharge, uint256 transactionFee, uint256 gasPrice) =
-            abi.decode(context, (address, uint256, uint256, uint256));
-
-        // actualCharge is an _estimated_ charge, which assumes postRelayedCall will use all available gas.
-        // This implementation's gas cost can be roughly estimated as 10k gas, for the two SSTORE operations in an
-        // ERC20 transfer.
-        uint256 overestimation = _computeCharge(POST_RELAYED_CALL_MAX_GAS.sub(10000), gasPrice, transactionFee);
-        actualCharge = actualCharge.sub(overestimation);
-
-        // After the relayed call has been executed and the actual charge estimated, the excess pre-charge is returned
-        _token.safeTransfer(from, maxPossibleCharge.sub(actualCharge));
-    }
-}
-
-/**
- * @title __unstable__ERC20PrimaryAdmin
- * @dev An ERC20 token owned by another contract, which has minting permissions and can use transferFrom to receive
- * anyone's tokens. This contract is an internal helper for GSNRecipientERC20Fee, and should not be used
- * outside of this context.
- */
-// solhint-disable-next-line contract-name-camelcase
-contract __unstable__ERC20PrimaryAdmin is ERC20, ERC20Detailed, Secondary {
-    uint256 private constant UINT256_MAX = 2**256 - 1;
-
-    constructor(string memory name, string memory symbol, uint8 decimals) public ERC20Detailed(name, symbol, decimals) {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    // The primary account (GSNRecipientERC20Fee) can mint tokens
-    function mint(address account, uint256 amount) public onlyPrimary {
-        _mint(account, amount);
-    }
-
-    // The primary account has 'infinite' allowance for all token holders
-    function allowance(address owner, address spender) public view returns (uint256) {
-        if (spender == primary()) {
-            return UINT256_MAX;
-        } else {
-            return super.allowance(owner, spender);
-        }
-    }
-
-    // Allowance for the primary account cannot be changed (it is always 'infinite')
-    function _approve(address owner, address spender, uint256 value) internal {
-        if (spender == primary()) {
-            return;
-        } else {
-            super._approve(owner, spender, value);
-        }
-    }
-
-    function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
-        if (recipient == primary()) {
-            _transfer(sender, recipient, amount);
-            return true;
-        } else {
-            return super.transferFrom(sender, recipient, amount);
-        }
-    }
-}

contracts/GSN/bouncers/GSNBouncerSignature.sol

@@ -1,51 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "./GSNBouncerBase.sol";
-import "../../cryptography/ECDSA.sol";
-
-contract GSNBouncerSignature is GSNBouncerBase {
-    using ECDSA for bytes32;
-
-    address private _trustedSigner;
-
-    enum GSNBouncerSignatureErrorCodes {
-        INVALID_SIGNER
-    }
-
-    constructor(address trustedSigner) public {
-        _trustedSigner = trustedSigner;
-    }
-
-    function acceptRelayedCall(
-        address relay,
-        address from,
-        bytes calldata encodedFunction,
-        uint256 transactionFee,
-        uint256 gasPrice,
-        uint256 gasLimit,
-        uint256 nonce,
-        bytes calldata approvalData,
-        uint256
-    )
-        external
-        view
-        returns (uint256, bytes memory)
-    {
-        bytes memory blob = abi.encodePacked(
-            relay,
-            from,
-            encodedFunction,
-            transactionFee,
-            gasPrice,
-            gasLimit,
-            nonce, // Prevents replays on RelayHub
-            getHubAddr(), // Prevents replays in multiple RelayHubs
-            address(this) // Prevents replays in multiple recipients
-        );
-        if (keccak256(blob).toEthSignedMessageHash().recover(approvalData) == _trustedSigner) {
-            return _approveRelayedCall();
-        } else {
-            return _rejectRelayedCall(uint256(GSNBouncerSignatureErrorCodes.INVALID_SIGNER));
-        }
-    }
-}

contracts/access/AccessControl.sol

@@ -0,0 +1,213 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/Context.sol";
+import "../utils/introspection/ERC165.sol";
+
+/**
+ * @dev External interface of AccessControl declared to support ERC165 detection.
+ */
+interface IAccessControl {
+    function hasRole(bytes32 role, address account) external view returns (bool);
+    function getRoleAdmin(bytes32 role) external view returns (bytes32);
+    function grantRole(bytes32 role, address account) external;
+    function revokeRole(bytes32 role, address account) external;
+    function renounceRole(bytes32 role, address account) external;
+}
+
+/**
+ * @dev Contract module that allows children to implement role-based access
+ * control mechanisms. This is a lightweight version that doesn't allow enumerating role
+ * members except through off-chain means by accessing the contract event logs. Some
+ * applications may benefit from on-chain enumerability, for those cases see
+ * {AccessControlEnumerable}.
+ *
+ * Roles are referred to by their `bytes32` identifier. These should be exposed
+ * in the external API and be unique. The best way to achieve this is by
+ * using `public constant` hash digests:
+ *
+ * ```
+ * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
+ * ```
+ *
+ * Roles can be used to represent a set of permissions. To restrict access to a
+ * function call, use {hasRole}:
+ *
+ * ```
+ * function foo() public {
+ *     require(hasRole(MY_ROLE, msg.sender));
+ *     ...
+ * }
+ * ```
+ *
+ * Roles can be granted and revoked dynamically via the {grantRole} and
+ * {revokeRole} functions. Each role has an associated admin role, and only
+ * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
+ *
+ * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
+ * 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, IAccessControl, ERC165 {
+    struct RoleData {
+        mapping (address => bool) members;
+        bytes32 adminRole;
+    }
+
+    mapping (bytes32 => RoleData) private _roles;
+
+    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`.
+     *
+     * `sender` is the account that originated the contract call, an admin role
+     * bearer except when using {_setupRole}.
+     */
+    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);
+
+    /**
+     * @dev Emitted when `account` is revoked `role`.
+     *
+     * `sender` is the account that originated the contract call:
+     *   - if using `revokeRole`, it is the admin role bearer
+     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
+     */
+    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);
+
+    /**
+     * @dev See {IERC165-supportsInterface}.
+     */
+    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
+        return interfaceId == type(IAccessControl).interfaceId
+            || super.supportsInterface(interfaceId);
+    }
+
+    /**
+     * @dev Returns `true` if `account` has been granted `role`.
+     */
+    function hasRole(bytes32 role, address account) public view override returns (bool) {
+        return _roles[role].members[account];
+    }
+
+    /**
+     * @dev Returns the admin role that controls `role`. See {grantRole} and
+     * {revokeRole}.
+     *
+     * To change a role's admin, use {_setRoleAdmin}.
+     */
+    function getRoleAdmin(bytes32 role) public view override returns (bytes32) {
+        return _roles[role].adminRole;
+    }
+
+    /**
+     * @dev Grants `role` to `account`.
+     *
+     * If `account` had not been already granted `role`, emits a {RoleGranted}
+     * event.
+     *
+     * Requirements:
+     *
+     * - the caller must have ``role``'s admin role.
+     */
+    function grantRole(bytes32 role, address account) public virtual override {
+        require(hasRole(getRoleAdmin(role), _msgSender()), "AccessControl: sender must be an admin to grant");
+
+        _grantRole(role, account);
+    }
+
+    /**
+     * @dev Revokes `role` from `account`.
+     *
+     * If `account` had been granted `role`, emits a {RoleRevoked} event.
+     *
+     * Requirements:
+     *
+     * - the caller must have ``role``'s admin role.
+     */
+    function revokeRole(bytes32 role, address account) public virtual override {
+        require(hasRole(getRoleAdmin(role), _msgSender()), "AccessControl: sender must be an admin to revoke");
+
+        _revokeRole(role, account);
+    }
+
+    /**
+     * @dev Revokes `role` from the calling account.
+     *
+     * Roles are often managed via {grantRole} and {revokeRole}: this function's
+     * purpose is to provide a mechanism for accounts to lose their privileges
+     * if they are compromised (such as when a trusted device is misplaced).
+     *
+     * If the calling account had been granted `role`, emits a {RoleRevoked}
+     * event.
+     *
+     * Requirements:
+     *
+     * - the caller must be `account`.
+     */
+    function renounceRole(bytes32 role, address account) public virtual override {
+        require(account == _msgSender(), "AccessControl: can only renounce roles for self");
+
+        _revokeRole(role, account);
+    }
+
+    /**
+     * @dev Grants `role` to `account`.
+     *
+     * If `account` had not been already granted `role`, emits a {RoleGranted}
+     * event. Note that unlike {grantRole}, this function doesn't perform any
+     * checks on the calling account.
+     *
+     * [WARNING]
+     * ====
+     * This function should only be called from the constructor when setting
+     * up the initial roles for the system.
+     *
+     * Using this function in any other way is effectively circumventing the admin
+     * system imposed by {AccessControl}.
+     * ====
+     */
+    function _setupRole(bytes32 role, address account) internal virtual {
+        _grantRole(role, account);
+    }
+
+    /**
+     * @dev Sets `adminRole` as ``role``'s admin role.
+     *
+     * Emits a {RoleAdminChanged} event.
+     */
+    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
+        emit RoleAdminChanged(role, getRoleAdmin(role), adminRole);
+        _roles[role].adminRole = adminRole;
+    }
+
+    function _grantRole(bytes32 role, address account) private {
+        if (!hasRole(role, account)) {
+            _roles[role].members[account] = true;
+            emit RoleGranted(role, account, _msgSender());
+        }
+    }
+
+    function _revokeRole(bytes32 role, address account) private {
+        if (hasRole(role, account)) {
+            _roles[role].members[account] = false;
+            emit RoleRevoked(role, account, _msgSender());
+        }
+    }
+}

contracts/access/AccessControlEnumerable.sol

@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "./AccessControl.sol";
+import "../utils/structs/EnumerableSet.sol";
+
+/**
+ * @dev External interface of AccessControlEnumerable declared to support ERC165 detection.
+ */
+interface IAccessControlEnumerable {
+    function getRoleMember(bytes32 role, uint256 index) external view returns (address);
+    function getRoleMemberCount(bytes32 role) external view returns (uint256);
+}
+
+/**
+ * @dev Extension of {AccessControl} that allows enumerating the members of each role.
+ */
+abstract contract AccessControlEnumerable is IAccessControlEnumerable, AccessControl {
+    using EnumerableSet for EnumerableSet.AddressSet;
+
+    mapping (bytes32 => EnumerableSet.AddressSet) private _roleMembers;
+
+    /**
+     * @dev See {IERC165-supportsInterface}.
+     */
+    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
+        return interfaceId == type(IAccessControlEnumerable).interfaceId
+            || super.supportsInterface(interfaceId);
+    }
+
+    /**
+     * @dev Returns one of the accounts that have `role`. `index` must be a
+     * value between 0 and {getRoleMemberCount}, non-inclusive.
+     *
+     * Role bearers are not sorted in any particular way, and their ordering may
+     * change at any point.
+     *
+     * WARNING: When using {getRoleMember} and {getRoleMemberCount}, make sure
+     * you perform all queries on the same block. See the following
+     * https://forum.openzeppelin.com/t/iterating-over-elements-on-enumerableset-in-openzeppelin-contracts/2296[forum post]
+     * for more information.
+     */
+    function getRoleMember(bytes32 role, uint256 index) public view override returns (address) {
+        return _roleMembers[role].at(index);
+    }
+
+    /**
+     * @dev Returns the number of accounts that have `role`. Can be used
+     * together with {getRoleMember} to enumerate all bearers of a role.
+     */
+    function getRoleMemberCount(bytes32 role) public view override returns (uint256) {
+        return _roleMembers[role].length();
+    }
+
+    /**
+     * @dev Overload {grantRole} to track enumerable memberships
+     */
+    function grantRole(bytes32 role, address account) public virtual override {
+        super.grantRole(role, account);
+        _roleMembers[role].add(account);
+    }
+
+    /**
+     * @dev Overload {revokeRole} to track enumerable memberships
+     */
+    function revokeRole(bytes32 role, address account) public virtual override {
+        super.revokeRole(role, account);
+        _roleMembers[role].remove(account);
+    }
+
+    /**
+     * @dev Overload {renounceRole} to track enumerable memberships
+     */
+    function renounceRole(bytes32 role, address account) public virtual override {
+        super.renounceRole(role, account);
+        _roleMembers[role].remove(account);
+    }
+
+    /**
+     * @dev Overload {_setupRole} to track enumerable memberships
+     */
+    function _setupRole(bytes32 role, address account) internal virtual override {
+        super._setupRole(role, account);
+        _roleMembers[role].add(account);
+    }
+}

contracts/access/Ownable.sol

@@ -1,16 +1,21 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-import "../GSN/Context.sol";
+pragma solidity ^0.8.0;
+
+import "../utils/Context.sol";
 /**
  * @dev Contract module which provides a basic access control mechanism, where
  * there is an account (an owner) that can be granted exclusive access to
  * specific functions.
  *
+ * By default, the owner account will be the one that deploys the contract. This
+ * can later be changed with {transferOwnership}.
+ *
  * This module is used through inheritance. It will make available the modifier
  * `onlyOwner`, which can be applied to your functions to restrict their use to
  * the owner.
  */
-contract Ownable is Context {
+abstract contract Ownable is Context {
     address private _owner;
 
     event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
@@ -18,15 +23,16 @@ contract Ownable is Context {
     /**
      * @dev Initializes the contract setting the deployer as the initial owner.
      */
-    constructor () internal {
-        _owner = _msgSender();
-        emit OwnershipTransferred(address(0), _owner);
+    constructor () {
+        address msgSender = _msgSender();
+        _owner = msgSender;
+        emit OwnershipTransferred(address(0), msgSender);
     }
 
     /**
      * @dev Returns the address of the current owner.
      */
-    function owner() public view returns (address) {
+    function owner() public view virtual returns (address) {
         return _owner;
     }
 
@@ -34,17 +40,10 @@ contract Ownable is Context {
      * @dev Throws if called by any account other than the owner.
      */
     modifier onlyOwner() {
-        require(isOwner(), "Ownable: caller is not the owner");
+        require(owner() == _msgSender(), "Ownable: caller is not the owner");
         _;
     }
 
-    /**
-     * @dev Returns true if the caller is the current owner.
-     */
-    function isOwner() public view returns (bool) {
-        return _msgSender() == _owner;
-    }
-
     /**
      * @dev Leaves the contract without owner. It will not be possible to call
      * `onlyOwner` functions anymore. Can only be called by the current owner.
@@ -52,7 +51,7 @@ contract Ownable is Context {
      * NOTE: Renouncing ownership will leave the contract without an owner,
      * thereby removing any functionality that is only available to the owner.
      */
-    function renounceOwnership() public onlyOwner {
+    function renounceOwnership() public virtual onlyOwner {
         emit OwnershipTransferred(_owner, address(0));
         _owner = address(0);
     }
@@ -61,14 +60,7 @@ contract Ownable is Context {
      * @dev Transfers ownership of the contract to a new account (`newOwner`).
      * Can only be called by the current owner.
      */
-    function transferOwnership(address newOwner) public onlyOwner {
-        _transferOwnership(newOwner);
-    }
-
-    /**
-     * @dev Transfers ownership of the contract to a new account (`newOwner`).
-     */
-    function _transferOwnership(address newOwner) internal {
+    function transferOwnership(address newOwner) public virtual onlyOwner {
         require(newOwner != address(0), "Ownable: new owner is the zero address");
         emit OwnershipTransferred(_owner, newOwner);
         _owner = newOwner;

contracts/access/README.adoc

@@ -1,21 +1,17 @@
 = Access
 
-NOTE: This page is incomplete. We're working to improve it for the next release. Stay tuned!
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/access
 
-== Library
+This directory provides ways to restrict who can access the functions of a contract or when they can do it.
 
-{{Roles}}
+- {AccessControl} provides a general role based access control mechanism. Multiple hierarchical roles can be created and assigned each to multiple accounts.
+- {Ownable} is a simpler mechanism with a single owner "role" that can be assigned to a single account. This simpler mechanism can be useful for quick tests but projects with production concerns are likely to outgrow it.
 
-== Roles
+== Authorization
 
-{{CapperRole}}
+{{Ownable}}
 
-{{MinterRole}}
+{{AccessControl}}
 
-{{PauserRole}}
-
-{{SignerRole}}
-
-{{WhitelistAdminRole}}
-
-{{WhitelistedRole}}
+{{AccessControlEnumerable}}

contracts/access/Roles.sol

@@ -1,36 +0,0 @@
-pragma solidity ^0.5.0;
-
-/**
- * @title Roles
- * @dev Library for managing addresses assigned to a Role.
- */
-library Roles {
-    struct Role {
-        mapping (address => bool) bearer;
-    }
-
-    /**
-     * @dev Give an account access to this role.
-     */
-    function add(Role storage role, address account) internal {
-        require(!has(role, account), "Roles: account already has role");
-        role.bearer[account] = true;
-    }
-
-    /**
-     * @dev Remove an account's access to this role.
-     */
-    function remove(Role storage role, address account) internal {
-        require(has(role, account), "Roles: account does not have role");
-        role.bearer[account] = false;
-    }
-
-    /**
-     * @dev Check if an account has this role.
-     * @return bool
-     */
-    function has(Role storage role, address account) internal view returns (bool) {
-        require(account != address(0), "Roles: account is the zero address");
-        return role.bearer[account];
-    }
-}

contracts/access/roles/CapperRole.sol

@@ -1,44 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../GSN/Context.sol";
-import "../Roles.sol";
-
-contract CapperRole is Context {
-    using Roles for Roles.Role;
-
-    event CapperAdded(address indexed account);
-    event CapperRemoved(address indexed account);
-
-    Roles.Role private _cappers;
-
-    constructor () internal {
-        _addCapper(_msgSender());
-    }
-
-    modifier onlyCapper() {
-        require(isCapper(_msgSender()), "CapperRole: caller does not have the Capper role");
-        _;
-    }
-
-    function isCapper(address account) public view returns (bool) {
-        return _cappers.has(account);
-    }
-
-    function addCapper(address account) public onlyCapper {
-        _addCapper(account);
-    }
-
-    function renounceCapper() public {
-        _removeCapper(_msgSender());
-    }
-
-    function _addCapper(address account) internal {
-        _cappers.add(account);
-        emit CapperAdded(account);
-    }
-
-    function _removeCapper(address account) internal {
-        _cappers.remove(account);
-        emit CapperRemoved(account);
-    }
-}

contracts/access/roles/MinterRole.sol

@@ -1,44 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../GSN/Context.sol";
-import "../Roles.sol";
-
-contract MinterRole is Context {
-    using Roles for Roles.Role;
-
-    event MinterAdded(address indexed account);
-    event MinterRemoved(address indexed account);
-
-    Roles.Role private _minters;
-
-    constructor () internal {
-        _addMinter(_msgSender());
-    }
-
-    modifier onlyMinter() {
-        require(isMinter(_msgSender()), "MinterRole: caller does not have the Minter role");
-        _;
-    }
-
-    function isMinter(address account) public view returns (bool) {
-        return _minters.has(account);
-    }
-
-    function addMinter(address account) public onlyMinter {
-        _addMinter(account);
-    }
-
-    function renounceMinter() public {
-        _removeMinter(_msgSender());
-    }
-
-    function _addMinter(address account) internal {
-        _minters.add(account);
-        emit MinterAdded(account);
-    }
-
-    function _removeMinter(address account) internal {
-        _minters.remove(account);
-        emit MinterRemoved(account);
-    }
-}

contracts/access/roles/PauserRole.sol

@@ -1,44 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../GSN/Context.sol";
-import "../Roles.sol";
-
-contract PauserRole is Context {
-    using Roles for Roles.Role;
-
-    event PauserAdded(address indexed account);
-    event PauserRemoved(address indexed account);
-
-    Roles.Role private _pausers;
-
-    constructor () internal {
-        _addPauser(_msgSender());
-    }
-
-    modifier onlyPauser() {
-        require(isPauser(_msgSender()), "PauserRole: caller does not have the Pauser role");
-        _;
-    }
-
-    function isPauser(address account) public view returns (bool) {
-        return _pausers.has(account);
-    }
-
-    function addPauser(address account) public onlyPauser {
-        _addPauser(account);
-    }
-
-    function renouncePauser() public {
-        _removePauser(_msgSender());
-    }
-
-    function _addPauser(address account) internal {
-        _pausers.add(account);
-        emit PauserAdded(account);
-    }
-
-    function _removePauser(address account) internal {
-        _pausers.remove(account);
-        emit PauserRemoved(account);
-    }
-}

contracts/access/roles/SignerRole.sol

@@ -1,44 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../GSN/Context.sol";
-import "../Roles.sol";
-
-contract SignerRole is Context {
-    using Roles for Roles.Role;
-
-    event SignerAdded(address indexed account);
-    event SignerRemoved(address indexed account);
-
-    Roles.Role private _signers;
-
-    constructor () internal {
-        _addSigner(_msgSender());
-    }
-
-    modifier onlySigner() {
-        require(isSigner(_msgSender()), "SignerRole: caller does not have the Signer role");
-        _;
-    }
-
-    function isSigner(address account) public view returns (bool) {
-        return _signers.has(account);
-    }
-
-    function addSigner(address account) public onlySigner {
-        _addSigner(account);
-    }
-
-    function renounceSigner() public {
-        _removeSigner(_msgSender());
-    }
-
-    function _addSigner(address account) internal {
-        _signers.add(account);
-        emit SignerAdded(account);
-    }
-
-    function _removeSigner(address account) internal {
-        _signers.remove(account);
-        emit SignerRemoved(account);
-    }
-}

contracts/access/roles/WhitelistAdminRole.sol

@@ -1,48 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../GSN/Context.sol";
-import "../Roles.sol";
-
-/**
- * @title WhitelistAdminRole
- * @dev WhitelistAdmins are responsible for assigning and removing Whitelisted accounts.
- */
-contract WhitelistAdminRole is Context {
-    using Roles for Roles.Role;
-
-    event WhitelistAdminAdded(address indexed account);
-    event WhitelistAdminRemoved(address indexed account);
-
-    Roles.Role private _whitelistAdmins;
-
-    constructor () internal {
-        _addWhitelistAdmin(_msgSender());
-    }
-
-    modifier onlyWhitelistAdmin() {
-        require(isWhitelistAdmin(_msgSender()), "WhitelistAdminRole: caller does not have the WhitelistAdmin role");
-        _;
-    }
-
-    function isWhitelistAdmin(address account) public view returns (bool) {
-        return _whitelistAdmins.has(account);
-    }
-
-    function addWhitelistAdmin(address account) public onlyWhitelistAdmin {
-        _addWhitelistAdmin(account);
-    }
-
-    function renounceWhitelistAdmin() public {
-        _removeWhitelistAdmin(_msgSender());
-    }
-
-    function _addWhitelistAdmin(address account) internal {
-        _whitelistAdmins.add(account);
-        emit WhitelistAdminAdded(account);
-    }
-
-    function _removeWhitelistAdmin(address account) internal {
-        _whitelistAdmins.remove(account);
-        emit WhitelistAdminRemoved(account);
-    }
-}

contracts/access/roles/WhitelistedRole.sol

@@ -1,51 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../GSN/Context.sol";
-import "../Roles.sol";
-import "./WhitelistAdminRole.sol";
-
-/**
- * @title WhitelistedRole
- * @dev Whitelisted accounts have been approved by a WhitelistAdmin to perform certain actions (e.g. participate in a
- * crowdsale). This role is special in that the only accounts that can add it are WhitelistAdmins (who can also remove
- * it), and not Whitelisteds themselves.
- */
-contract WhitelistedRole is Context, WhitelistAdminRole {
-    using Roles for Roles.Role;
-
-    event WhitelistedAdded(address indexed account);
-    event WhitelistedRemoved(address indexed account);
-
-    Roles.Role private _whitelisteds;
-
-    modifier onlyWhitelisted() {
-        require(isWhitelisted(_msgSender()), "WhitelistedRole: caller does not have the Whitelisted role");
-        _;
-    }
-
-    function isWhitelisted(address account) public view returns (bool) {
-        return _whitelisteds.has(account);
-    }
-
-    function addWhitelisted(address account) public onlyWhitelistAdmin {
-        _addWhitelisted(account);
-    }
-
-    function removeWhitelisted(address account) public onlyWhitelistAdmin {
-        _removeWhitelisted(account);
-    }
-
-    function renounceWhitelisted() public {
-        _removeWhitelisted(_msgSender());
-    }
-
-    function _addWhitelisted(address account) internal {
-        _whitelisteds.add(account);
-        emit WhitelistedAdded(account);
-    }
-
-    function _removeWhitelisted(address account) internal {
-        _whitelisteds.remove(account);
-        emit WhitelistedRemoved(account);
-    }
-}

contracts/crowdsale/Crowdsale.sol

@@ -1,200 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../GSN/Context.sol";
-import "../token/ERC20/IERC20.sol";
-import "../math/SafeMath.sol";
-import "../token/ERC20/SafeERC20.sol";
-import "../utils/ReentrancyGuard.sol";
-
-/**
- * @title Crowdsale
- * @dev Crowdsale is a base contract for managing a token crowdsale,
- * allowing investors to purchase tokens with ether. This contract implements
- * such functionality in its most fundamental form and can be extended to provide additional
- * functionality and/or custom behavior.
- * The external interface represents the basic interface for purchasing tokens, and conforms
- * the base architecture for crowdsales. It is *not* intended to be modified / overridden.
- * The internal interface conforms the extensible and modifiable surface of crowdsales. Override
- * the methods to add functionality. Consider using 'super' where appropriate to concatenate
- * behavior.
- */
-contract Crowdsale is Context, ReentrancyGuard {
-    using SafeMath for uint256;
-    using SafeERC20 for IERC20;
-
-    // The token being sold
-    IERC20 private _token;
-
-    // Address where funds are collected
-    address payable private _wallet;
-
-    // How many token units a buyer gets per wei.
-    // The rate is the conversion between wei and the smallest and indivisible token unit.
-    // So, if you are using a rate of 1 with a ERC20Detailed token with 3 decimals called TOK
-    // 1 wei will give you 1 unit, or 0.001 TOK.
-    uint256 private _rate;
-
-    // Amount of wei raised
-    uint256 private _weiRaised;
-
-    /**
-     * Event for token purchase logging
-     * @param purchaser who paid for the tokens
-     * @param beneficiary who got the tokens
-     * @param value weis paid for purchase
-     * @param amount amount of tokens purchased
-     */
-    event TokensPurchased(address indexed purchaser, address indexed beneficiary, uint256 value, uint256 amount);
-
-    /**
-     * @param rate Number of token units a buyer gets per wei
-     * @dev The rate is the conversion between wei and the smallest and indivisible
-     * token unit. So, if you are using a rate of 1 with a ERC20Detailed token
-     * with 3 decimals called TOK, 1 wei will give you 1 unit, or 0.001 TOK.
-     * @param wallet Address where collected funds will be forwarded to
-     * @param token Address of the token being sold
-     */
-    constructor (uint256 rate, address payable wallet, IERC20 token) public {
-        require(rate > 0, "Crowdsale: rate is 0");
-        require(wallet != address(0), "Crowdsale: wallet is the zero address");
-        require(address(token) != address(0), "Crowdsale: token is the zero address");
-
-        _rate = rate;
-        _wallet = wallet;
-        _token = token;
-    }
-
-    /**
-     * @dev fallback function ***DO NOT OVERRIDE***
-     * Note that other contracts will transfer funds with a base gas stipend
-     * of 2300, which is not enough to call buyTokens. Consider calling
-     * buyTokens directly when purchasing tokens from a contract.
-     */
-    function () external payable {
-        buyTokens(_msgSender());
-    }
-
-    /**
-     * @return the token being sold.
-     */
-    function token() public view returns (IERC20) {
-        return _token;
-    }
-
-    /**
-     * @return the address where funds are collected.
-     */
-    function wallet() public view returns (address payable) {
-        return _wallet;
-    }
-
-    /**
-     * @return the number of token units a buyer gets per wei.
-     */
-    function rate() public view returns (uint256) {
-        return _rate;
-    }
-
-    /**
-     * @return the amount of wei raised.
-     */
-    function weiRaised() public view returns (uint256) {
-        return _weiRaised;
-    }
-
-    /**
-     * @dev low level token purchase ***DO NOT OVERRIDE***
-     * This function has a non-reentrancy guard, so it shouldn't be called by
-     * another `nonReentrant` function.
-     * @param beneficiary Recipient of the token purchase
-     */
-    function buyTokens(address beneficiary) public nonReentrant payable {
-        uint256 weiAmount = msg.value;
-        _preValidatePurchase(beneficiary, weiAmount);
-
-        // calculate token amount to be created
-        uint256 tokens = _getTokenAmount(weiAmount);
-
-        // update state
-        _weiRaised = _weiRaised.add(weiAmount);
-
-        _processPurchase(beneficiary, tokens);
-        emit TokensPurchased(_msgSender(), beneficiary, weiAmount, tokens);
-
-        _updatePurchasingState(beneficiary, weiAmount);
-
-        _forwardFunds();
-        _postValidatePurchase(beneficiary, weiAmount);
-    }
-
-    /**
-     * @dev Validation of an incoming purchase. Use require statements to revert state when conditions are not met.
-     * Use `super` in contracts that inherit from Crowdsale to extend their validations.
-     * Example from CappedCrowdsale.sol's _preValidatePurchase method:
-     *     super._preValidatePurchase(beneficiary, weiAmount);
-     *     require(weiRaised().add(weiAmount) <= cap);
-     * @param beneficiary Address performing the token purchase
-     * @param weiAmount Value in wei involved in the purchase
-     */
-    function _preValidatePurchase(address beneficiary, uint256 weiAmount) internal view {
-        require(beneficiary != address(0), "Crowdsale: beneficiary is the zero address");
-        require(weiAmount != 0, "Crowdsale: weiAmount is 0");
-        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
-    }
-
-    /**
-     * @dev Validation of an executed purchase. Observe state and use revert statements to undo rollback when valid
-     * conditions are not met.
-     * @param beneficiary Address performing the token purchase
-     * @param weiAmount Value in wei involved in the purchase
-     */
-    function _postValidatePurchase(address beneficiary, uint256 weiAmount) internal view {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    /**
-     * @dev Source of tokens. Override this method to modify the way in which the crowdsale ultimately gets and sends
-     * its tokens.
-     * @param beneficiary Address performing the token purchase
-     * @param tokenAmount Number of tokens to be emitted
-     */
-    function _deliverTokens(address beneficiary, uint256 tokenAmount) internal {
-        _token.safeTransfer(beneficiary, tokenAmount);
-    }
-
-    /**
-     * @dev Executed when a purchase has been validated and is ready to be executed. Doesn't necessarily emit/send
-     * tokens.
-     * @param beneficiary Address receiving the tokens
-     * @param tokenAmount Number of tokens to be purchased
-     */
-    function _processPurchase(address beneficiary, uint256 tokenAmount) internal {
-        _deliverTokens(beneficiary, tokenAmount);
-    }
-
-    /**
-     * @dev Override for extensions that require an internal state to check for validity (current user contributions,
-     * etc.)
-     * @param beneficiary Address receiving the tokens
-     * @param weiAmount Value in wei involved in the purchase
-     */
-    function _updatePurchasingState(address beneficiary, uint256 weiAmount) internal {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    /**
-     * @dev Override to extend the way in which ether is converted to tokens.
-     * @param weiAmount Value in wei to be converted into tokens
-     * @return Number of tokens that can be purchased with the specified _weiAmount
-     */
-    function _getTokenAmount(uint256 weiAmount) internal view returns (uint256) {
-        return weiAmount.mul(_rate);
-    }
-
-    /**
-     * @dev Determines how ETH is stored/forwarded on purchases.
-     */
-    function _forwardFunds() internal {
-        _wallet.transfer(msg.value);
-    }
-}

contracts/crowdsale/README.adoc

@@ -1,35 +0,0 @@
-= Crowdsales
-
-NOTE: This page is incomplete. We're working to improve it for the next release. Stay tuned!
-
-== Core
-
-{{Crowdsale}}
-
-== Emission
-
-{{AllowanceCrowdsale}}
-
-{{MintedCrowdsale}}
-
-== Validation
-
-{{CappedCrowdsale}}
-
-{{IndividuallyCappedCrowdsale}}
-
-{{PausableCrowdsale}}
-
-{{TimedCrowdsale}}
-
-{{WhitelistCrowdsale}}
-
-== Distribution
-
-{{FinalizableCrowdsale}}
-
-{{PostDeliveryCrowdsale}}
-
-{{RefundableCrowdsale}}
-
-{{RefundablePostDeliveryCrowdsale}}

contracts/crowdsale/distribution/FinalizableCrowdsale.sol

@@ -1,51 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../math/SafeMath.sol";
-import "../validation/TimedCrowdsale.sol";
-
-/**
- * @title FinalizableCrowdsale
- * @dev Extension of TimedCrowdsale with a one-off finalization action, where one
- * can do extra work after finishing.
- */
-contract FinalizableCrowdsale is TimedCrowdsale {
-    using SafeMath for uint256;
-
-    bool private _finalized;
-
-    event CrowdsaleFinalized();
-
-    constructor () internal {
-        _finalized = false;
-    }
-
-    /**
-     * @return true if the crowdsale is finalized, false otherwise.
-     */
-    function finalized() public view returns (bool) {
-        return _finalized;
-    }
-
-    /**
-     * @dev Must be called after crowdsale ends, to do some extra finalization
-     * work. Calls the contract's finalization function.
-     */
-    function finalize() public {
-        require(!_finalized, "FinalizableCrowdsale: already finalized");
-        require(hasClosed(), "FinalizableCrowdsale: not closed");
-
-        _finalized = true;
-
-        _finalization();
-        emit CrowdsaleFinalized();
-    }
-
-    /**
-     * @dev Can be overridden to add finalization logic. The overriding function
-     * should call super._finalization() to ensure the chain of finalization is
-     * executed entirely.
-     */
-    function _finalization() internal {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}

contracts/crowdsale/distribution/PostDeliveryCrowdsale.sol

@@ -1,65 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../validation/TimedCrowdsale.sol";
-import "../../math/SafeMath.sol";
-import "../../ownership/Secondary.sol";
-import "../../token/ERC20/IERC20.sol";
-
-/**
- * @title PostDeliveryCrowdsale
- * @dev Crowdsale that locks tokens from withdrawal until it ends.
- */
-contract PostDeliveryCrowdsale is TimedCrowdsale {
-    using SafeMath for uint256;
-
-    mapping(address => uint256) private _balances;
-    __unstable__TokenVault private _vault;
-
-    constructor() public {
-        _vault = new __unstable__TokenVault();
-    }
-
-    /**
-     * @dev Withdraw tokens only after crowdsale ends.
-     * @param beneficiary Whose tokens will be withdrawn.
-     */
-    function withdrawTokens(address beneficiary) public {
-        require(hasClosed(), "PostDeliveryCrowdsale: not closed");
-        uint256 amount = _balances[beneficiary];
-        require(amount > 0, "PostDeliveryCrowdsale: beneficiary is not due any tokens");
-
-        _balances[beneficiary] = 0;
-        _vault.transfer(token(), beneficiary, amount);
-    }
-
-    /**
-     * @return the balance of an account.
-     */
-    function balanceOf(address account) public view returns (uint256) {
-        return _balances[account];
-    }
-
-    /**
-     * @dev Overrides parent by storing due balances, and delivering tokens to the vault instead of the end user. This
-     * ensures that the tokens will be available by the time they are withdrawn (which may not be the case if
-     * `_deliverTokens` was called later).
-     * @param beneficiary Token purchaser
-     * @param tokenAmount Amount of tokens purchased
-     */
-    function _processPurchase(address beneficiary, uint256 tokenAmount) internal {
-        _balances[beneficiary] = _balances[beneficiary].add(tokenAmount);
-        _deliverTokens(address(_vault), tokenAmount);
-    }
-}
-
-/**
- * @title __unstable__TokenVault
- * @dev Similar to an Escrow for tokens, this contract allows its primary account to spend its tokens as it sees fit.
- * This contract is an internal helper for PostDeliveryCrowdsale, and should not be used outside of this context.
- */
-// solhint-disable-next-line contract-name-camelcase
-contract __unstable__TokenVault is Secondary {
-    function transfer(IERC20 token, address to, uint256 amount) public onlyPrimary {
-        token.transfer(to, amount);
-    }
-}

contracts/crowdsale/distribution/RefundableCrowdsale.sol

@@ -1,83 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../GSN/Context.sol";
-import "../../math/SafeMath.sol";
-import "./FinalizableCrowdsale.sol";
-import "../../payment/escrow/RefundEscrow.sol";
-
-/**
- * @title RefundableCrowdsale
- * @dev Extension of `FinalizableCrowdsale` contract that adds a funding goal, and the possibility of users
- * getting a refund if goal is not met.
- *
- * Deprecated, use `RefundablePostDeliveryCrowdsale` instead. Note that if you allow tokens to be traded before the goal
- * is met, then an attack is possible in which the attacker purchases tokens from the crowdsale and when they sees that
- * the goal is unlikely to be met, they sell their tokens (possibly at a discount). The attacker will be refunded when
- * the crowdsale is finalized, and the users that purchased from them will be left with worthless tokens.
- */
-contract RefundableCrowdsale is Context, FinalizableCrowdsale {
-    using SafeMath for uint256;
-
-    // minimum amount of funds to be raised in weis
-    uint256 private _goal;
-
-    // refund escrow used to hold funds while crowdsale is running
-    RefundEscrow private _escrow;
-
-    /**
-     * @dev Constructor, creates RefundEscrow.
-     * @param goal Funding goal
-     */
-    constructor (uint256 goal) public {
-        require(goal > 0, "RefundableCrowdsale: goal is 0");
-        _escrow = new RefundEscrow(wallet());
-        _goal = goal;
-    }
-
-    /**
-     * @return minimum amount of funds to be raised in wei.
-     */
-    function goal() public view returns (uint256) {
-        return _goal;
-    }
-
-    /**
-     * @dev Investors can claim refunds here if crowdsale is unsuccessful.
-     * @param refundee Whose refund will be claimed.
-     */
-    function claimRefund(address payable refundee) public {
-        require(finalized(), "RefundableCrowdsale: not finalized");
-        require(!goalReached(), "RefundableCrowdsale: goal reached");
-
-        _escrow.withdraw(refundee);
-    }
-
-    /**
-     * @dev Checks whether funding goal was reached.
-     * @return Whether funding goal was reached
-     */
-    function goalReached() public view returns (bool) {
-        return weiRaised() >= _goal;
-    }
-
-    /**
-     * @dev Escrow finalization task, called when finalize() is called.
-     */
-    function _finalization() internal {
-        if (goalReached()) {
-            _escrow.close();
-            _escrow.beneficiaryWithdraw();
-        } else {
-            _escrow.enableRefunds();
-        }
-
-        super._finalization();
-    }
-
-    /**
-     * @dev Overrides Crowdsale fund forwarding, sending funds to escrow.
-     */
-    function _forwardFunds() internal {
-        _escrow.deposit.value(msg.value)(_msgSender());
-    }
-}

contracts/crowdsale/distribution/RefundablePostDeliveryCrowdsale.sol

@@ -1,20 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "./RefundableCrowdsale.sol";
-import "./PostDeliveryCrowdsale.sol";
-
-
-/**
- * @title RefundablePostDeliveryCrowdsale
- * @dev Extension of RefundableCrowdsale contract that only delivers the tokens
- * once the crowdsale has closed and the goal met, preventing refunds to be issued
- * to token holders.
- */
-contract RefundablePostDeliveryCrowdsale is RefundableCrowdsale, PostDeliveryCrowdsale {
-    function withdrawTokens(address beneficiary) public {
-        require(finalized(), "RefundablePostDeliveryCrowdsale: not finalized");
-        require(goalReached(), "RefundablePostDeliveryCrowdsale: goal not reached");
-
-        super.withdrawTokens(beneficiary);
-    }
-}

contracts/crowdsale/emission/AllowanceCrowdsale.sol

@@ -1,51 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../Crowdsale.sol";
-import "../../token/ERC20/IERC20.sol";
-import "../../token/ERC20/SafeERC20.sol";
-import "../../math/SafeMath.sol";
-import "../../math/Math.sol";
-
-/**
- * @title AllowanceCrowdsale
- * @dev Extension of Crowdsale where tokens are held by a wallet, which approves an allowance to the crowdsale.
- */
-contract AllowanceCrowdsale is Crowdsale {
-    using SafeMath for uint256;
-    using SafeERC20 for IERC20;
-
-    address private _tokenWallet;
-
-    /**
-     * @dev Constructor, takes token wallet address.
-     * @param tokenWallet Address holding the tokens, which has approved allowance to the crowdsale.
-     */
-    constructor (address tokenWallet) public {
-        require(tokenWallet != address(0), "AllowanceCrowdsale: token wallet is the zero address");
-        _tokenWallet = tokenWallet;
-    }
-
-    /**
-     * @return the address of the wallet that will hold the tokens.
-     */
-    function tokenWallet() public view returns (address) {
-        return _tokenWallet;
-    }
-
-    /**
-     * @dev Checks the amount of tokens left in the allowance.
-     * @return Amount of tokens left in the allowance
-     */
-    function remainingTokens() public view returns (uint256) {
-        return Math.min(token().balanceOf(_tokenWallet), token().allowance(_tokenWallet, address(this)));
-    }
-
-    /**
-     * @dev Overrides parent behavior by transferring tokens from wallet.
-     * @param beneficiary Token purchaser
-     * @param tokenAmount Amount of tokens purchased
-     */
-    function _deliverTokens(address beneficiary, uint256 tokenAmount) internal {
-        token().safeTransferFrom(_tokenWallet, beneficiary, tokenAmount);
-    }
-}

contracts/crowdsale/emission/MintedCrowdsale.sol

@@ -1,24 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../Crowdsale.sol";
-import "../../token/ERC20/ERC20Mintable.sol";
-
-/**
- * @title MintedCrowdsale
- * @dev Extension of Crowdsale contract whose tokens are minted in each purchase.
- * Token ownership should be transferred to MintedCrowdsale for minting.
- */
-contract MintedCrowdsale is Crowdsale {
-    /**
-     * @dev Overrides delivery by minting tokens upon purchase.
-     * @param beneficiary Token purchaser
-     * @param tokenAmount Number of tokens to be minted
-     */
-    function _deliverTokens(address beneficiary, uint256 tokenAmount) internal {
-        // Potentially dangerous assumption about the type of the token.
-        require(
-            ERC20Mintable(address(token())).mint(beneficiary, tokenAmount),
-                "MintedCrowdsale: minting failed"
-        );
-    }
-}

contracts/crowdsale/price/IncreasingPriceCrowdsale.sol

@@ -1,79 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../validation/TimedCrowdsale.sol";
-import "../../math/SafeMath.sol";
-
-/**
- * @title IncreasingPriceCrowdsale
- * @dev Extension of Crowdsale contract that increases the price of tokens linearly in time.
- * Note that what should be provided to the constructor is the initial and final _rates_, that is,
- * the amount of tokens per wei contributed. Thus, the initial rate must be greater than the final rate.
- */
-contract IncreasingPriceCrowdsale is TimedCrowdsale {
-    using SafeMath for uint256;
-
-    uint256 private _initialRate;
-    uint256 private _finalRate;
-
-    /**
-     * @dev Constructor, takes initial and final rates of tokens received per wei contributed.
-     * @param initialRate Number of tokens a buyer gets per wei at the start of the crowdsale
-     * @param finalRate Number of tokens a buyer gets per wei at the end of the crowdsale
-     */
-    constructor (uint256 initialRate, uint256 finalRate) public {
-        require(finalRate > 0, "IncreasingPriceCrowdsale: final rate is 0");
-        // solhint-disable-next-line max-line-length
-        require(initialRate > finalRate, "IncreasingPriceCrowdsale: initial rate is not greater than final rate");
-        _initialRate = initialRate;
-        _finalRate = finalRate;
-    }
-
-    /**
-     * The base rate function is overridden to revert, since this crowdsale doesn't use it, and
-     * all calls to it are a mistake.
-     */
-    function rate() public view returns (uint256) {
-        revert("IncreasingPriceCrowdsale: rate() called");
-    }
-
-    /**
-     * @return the initial rate of the crowdsale.
-     */
-    function initialRate() public view returns (uint256) {
-        return _initialRate;
-    }
-
-    /**
-     * @return the final rate of the crowdsale.
-     */
-    function finalRate() public view returns (uint256) {
-        return _finalRate;
-    }
-
-    /**
-     * @dev Returns the rate of tokens per wei at the present time.
-     * Note that, as price _increases_ with time, the rate _decreases_.
-     * @return The number of tokens a buyer gets per wei at a given time
-     */
-    function getCurrentRate() public view returns (uint256) {
-        if (!isOpen()) {
-            return 0;
-        }
-
-        // solhint-disable-next-line not-rely-on-time
-        uint256 elapsedTime = block.timestamp.sub(openingTime());
-        uint256 timeRange = closingTime().sub(openingTime());
-        uint256 rateRange = _initialRate.sub(_finalRate);
-        return _initialRate.sub(elapsedTime.mul(rateRange).div(timeRange));
-    }
-
-    /**
-     * @dev Overrides parent method taking into account variable rate.
-     * @param weiAmount The value in wei to be converted into tokens
-     * @return The number of tokens _weiAmount wei will buy at present time
-     */
-    function _getTokenAmount(uint256 weiAmount) internal view returns (uint256) {
-        uint256 currentRate = getCurrentRate();
-        return currentRate.mul(weiAmount);
-    }
-}

contracts/crowdsale/validation/CappedCrowdsale.sol

@@ -1,48 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../math/SafeMath.sol";
-import "../Crowdsale.sol";
-
-/**
- * @title CappedCrowdsale
- * @dev Crowdsale with a limit for total contributions.
- */
-contract CappedCrowdsale is Crowdsale {
-    using SafeMath for uint256;
-
-    uint256 private _cap;
-
-    /**
-     * @dev Constructor, takes maximum amount of wei accepted in the crowdsale.
-     * @param cap Max amount of wei to be contributed
-     */
-    constructor (uint256 cap) public {
-        require(cap > 0, "CappedCrowdsale: cap is 0");
-        _cap = cap;
-    }
-
-    /**
-     * @return the cap of the crowdsale.
-     */
-    function cap() public view returns (uint256) {
-        return _cap;
-    }
-
-    /**
-     * @dev Checks whether the cap has been reached.
-     * @return Whether the cap was reached
-     */
-    function capReached() public view returns (bool) {
-        return weiRaised() >= _cap;
-    }
-
-    /**
-     * @dev Extend parent behavior requiring purchase to respect the funding cap.
-     * @param beneficiary Token purchaser
-     * @param weiAmount Amount of wei contributed
-     */
-    function _preValidatePurchase(address beneficiary, uint256 weiAmount) internal view {
-        super._preValidatePurchase(beneficiary, weiAmount);
-        require(weiRaised().add(weiAmount) <= _cap, "CappedCrowdsale: cap exceeded");
-    }
-}

contracts/crowdsale/validation/IndividuallyCappedCrowdsale.sol

@@ -1,64 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../math/SafeMath.sol";
-import "../Crowdsale.sol";
-import "../../access/roles/CapperRole.sol";
-
-/**
- * @title IndividuallyCappedCrowdsale
- * @dev Crowdsale with per-beneficiary caps.
- */
-contract IndividuallyCappedCrowdsale is Crowdsale, CapperRole {
-    using SafeMath for uint256;
-
-    mapping(address => uint256) private _contributions;
-    mapping(address => uint256) private _caps;
-
-    /**
-     * @dev Sets a specific beneficiary's maximum contribution.
-     * @param beneficiary Address to be capped
-     * @param cap Wei limit for individual contribution
-     */
-    function setCap(address beneficiary, uint256 cap) external onlyCapper {
-        _caps[beneficiary] = cap;
-    }
-
-    /**
-     * @dev Returns the cap of a specific beneficiary.
-     * @param beneficiary Address whose cap is to be checked
-     * @return Current cap for individual beneficiary
-     */
-    function getCap(address beneficiary) public view returns (uint256) {
-        return _caps[beneficiary];
-    }
-
-    /**
-     * @dev Returns the amount contributed so far by a specific beneficiary.
-     * @param beneficiary Address of contributor
-     * @return Beneficiary contribution so far
-     */
-    function getContribution(address beneficiary) public view returns (uint256) {
-        return _contributions[beneficiary];
-    }
-
-    /**
-     * @dev Extend parent behavior requiring purchase to respect the beneficiary's funding cap.
-     * @param beneficiary Token purchaser
-     * @param weiAmount Amount of wei contributed
-     */
-    function _preValidatePurchase(address beneficiary, uint256 weiAmount) internal view {
-        super._preValidatePurchase(beneficiary, weiAmount);
-        // solhint-disable-next-line max-line-length
-        require(_contributions[beneficiary].add(weiAmount) <= _caps[beneficiary], "IndividuallyCappedCrowdsale: beneficiary's cap exceeded");
-    }
-
-    /**
-     * @dev Extend parent behavior to update beneficiary contributions.
-     * @param beneficiary Token purchaser
-     * @param weiAmount Amount of wei contributed
-     */
-    function _updatePurchasingState(address beneficiary, uint256 weiAmount) internal {
-        super._updatePurchasingState(beneficiary, weiAmount);
-        _contributions[beneficiary] = _contributions[beneficiary].add(weiAmount);
-    }
-}

contracts/crowdsale/validation/PausableCrowdsale.sol

@@ -1,21 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../Crowdsale.sol";
-import "../../lifecycle/Pausable.sol";
-
-/**
- * @title PausableCrowdsale
- * @dev Extension of Crowdsale contract where purchases can be paused and unpaused by the pauser role.
- */
-contract PausableCrowdsale is Crowdsale, Pausable {
-    /**
-     * @dev Validation of an incoming purchase. Use require statements to revert state when conditions are not met.
-     * Use super to concatenate validations.
-     * Adds the validation that the crowdsale must not be paused.
-     * @param _beneficiary Address performing the token purchase
-     * @param _weiAmount Value in wei involved in the purchase
-     */
-    function _preValidatePurchase(address _beneficiary, uint256 _weiAmount) internal view whenNotPaused {
-        return super._preValidatePurchase(_beneficiary, _weiAmount);
-    }
-}

contracts/crowdsale/validation/TimedCrowdsale.sol

@@ -1,98 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../math/SafeMath.sol";
-import "../Crowdsale.sol";
-
-/**
- * @title TimedCrowdsale
- * @dev Crowdsale accepting contributions only within a time frame.
- */
-contract TimedCrowdsale is Crowdsale {
-    using SafeMath for uint256;
-
-    uint256 private _openingTime;
-    uint256 private _closingTime;
-
-    /**
-     * Event for crowdsale extending
-     * @param newClosingTime new closing time
-     * @param prevClosingTime old closing time
-     */
-    event TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime);
-
-    /**
-     * @dev Reverts if not in crowdsale time range.
-     */
-    modifier onlyWhileOpen {
-        require(isOpen(), "TimedCrowdsale: not open");
-        _;
-    }
-
-    /**
-     * @dev Constructor, takes crowdsale opening and closing times.
-     * @param openingTime Crowdsale opening time
-     * @param closingTime Crowdsale closing time
-     */
-    constructor (uint256 openingTime, uint256 closingTime) public {
-        // solhint-disable-next-line not-rely-on-time
-        require(openingTime >= block.timestamp, "TimedCrowdsale: opening time is before current time");
-        // solhint-disable-next-line max-line-length
-        require(closingTime > openingTime, "TimedCrowdsale: opening time is not before closing time");
-
-        _openingTime = openingTime;
-        _closingTime = closingTime;
-    }
-
-    /**
-     * @return the crowdsale opening time.
-     */
-    function openingTime() public view returns (uint256) {
-        return _openingTime;
-    }
-
-    /**
-     * @return the crowdsale closing time.
-     */
-    function closingTime() public view returns (uint256) {
-        return _closingTime;
-    }
-
-    /**
-     * @return true if the crowdsale is open, false otherwise.
-     */
-    function isOpen() public view returns (bool) {
-        // solhint-disable-next-line not-rely-on-time
-        return block.timestamp >= _openingTime && block.timestamp <= _closingTime;
-    }
-
-    /**
-     * @dev Checks whether the period in which the crowdsale is open has already elapsed.
-     * @return Whether crowdsale period has elapsed
-     */
-    function hasClosed() public view returns (bool) {
-        // solhint-disable-next-line not-rely-on-time
-        return block.timestamp > _closingTime;
-    }
-
-    /**
-     * @dev Extend parent behavior requiring to be within contributing period.
-     * @param beneficiary Token purchaser
-     * @param weiAmount Amount of wei contributed
-     */
-    function _preValidatePurchase(address beneficiary, uint256 weiAmount) internal onlyWhileOpen view {
-        super._preValidatePurchase(beneficiary, weiAmount);
-    }
-
-    /**
-     * @dev Extend crowdsale.
-     * @param newClosingTime Crowdsale closing time
-     */
-    function _extendTime(uint256 newClosingTime) internal {
-        require(!hasClosed(), "TimedCrowdsale: already closed");
-        // solhint-disable-next-line max-line-length
-        require(newClosingTime > _closingTime, "TimedCrowdsale: new closing time is before current closing time");
-
-        emit TimedCrowdsaleExtended(_closingTime, newClosingTime);
-        _closingTime = newClosingTime;
-    }
-}

contracts/crowdsale/validation/WhitelistCrowdsale.sol

@@ -1,21 +0,0 @@
-pragma solidity ^0.5.0;
-import "../Crowdsale.sol";
-import "../../access/roles/WhitelistedRole.sol";
-
-
-/**
- * @title WhitelistCrowdsale
- * @dev Crowdsale in which only whitelisted users can contribute.
- */
-contract WhitelistCrowdsale is WhitelistedRole, Crowdsale {
-    /**
-     * @dev Extend parent behavior requiring beneficiary to be whitelisted. Note that no
-     * restriction is imposed on the account sending the transaction.
-     * @param _beneficiary Token beneficiary
-     * @param _weiAmount Amount of wei contributed
-     */
-    function _preValidatePurchase(address _beneficiary, uint256 _weiAmount) internal view {
-        require(isWhitelisted(_beneficiary), "WhitelistCrowdsale: beneficiary doesn't have the Whitelisted role");
-        super._preValidatePurchase(_beneficiary, _weiAmount);
-    }
-}

contracts/cryptography/README.adoc

@@ -1,9 +0,0 @@
-= Cryptography
-
-This collection of libraries provides simple and safe ways to use different cryptographic primitives.
-
-== Libraries
-
-{{ECDSA}}
-
-{{MerkleProof}}

contracts/drafts/ERC1046/ERC20Metadata.sol

@@ -1,24 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../../token/ERC20/IERC20.sol";
-
-/**
- * @title ERC-1047 Token Metadata
- * @dev See https://eips.ethereum.org/EIPS/eip-1046
- * @dev {tokenURI} must respond with a URI that implements https://eips.ethereum.org/EIPS/eip-1047
- */
-contract ERC20Metadata {
-    string private _tokenURI;
-
-    constructor (string memory tokenURI_) public {
-        _setTokenURI(tokenURI_);
-    }
-
-    function tokenURI() external view returns (string memory) {
-        return _tokenURI;
-    }
-
-    function _setTokenURI(string memory tokenURI_) internal {
-        _tokenURI = tokenURI_;
-    }
-}

contracts/drafts/ERC20Migrator.sol

@@ -1,103 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../token/ERC20/IERC20.sol";
-import "../token/ERC20/ERC20Mintable.sol";
-import "../token/ERC20/SafeERC20.sol";
-import "../math/Math.sol";
-
-/**
- * @title ERC20Migrator
- * @dev This contract can be used to migrate an ERC20 token from one
- * contract to another, where each token holder has to opt-in to the migration.
- * To opt-in, users must approve for this contract the number of tokens they
- * want to migrate. Once the allowance is set up, anyone can trigger the
- * migration to the new token contract. In this way, token holders "turn in"
- * their old balance and will be minted an equal amount in the new token.
- * The new token contract must be mintable. For the precise interface refer to
- * OpenZeppelin's {ERC20Mintable}, but the only functions that are needed are
- * {MinterRole-isMinter} and {ERC20Mintable-mint}. The migrator will check
- * that it is a minter for the token.
- * The balance from the legacy token will be transferred to the migrator, as it
- * is migrated, and remain there forever.
- * Although this contract can be used in many different scenarios, the main
- * motivation was to provide a way to migrate ERC20 tokens into an upgradeable
- * version of it using ZeppelinOS. To read more about how this can be done
- * using this implementation, please follow the official documentation site of
- * ZeppelinOS: https://docs.zeppelinos.org/docs/erc20_onboarding.html
- *
- * Example of usage:
- * ```
- * const migrator = await ERC20Migrator.new(legacyToken.address);
- * await newToken.addMinter(migrator.address);
- * await migrator.beginMigration(newToken.address);
- * ```
- */
-contract ERC20Migrator {
-    using SafeERC20 for IERC20;
-
-    /// Address of the old token contract
-    IERC20 private _legacyToken;
-
-    /// Address of the new token contract
-    ERC20Mintable private _newToken;
-
-    /**
-     * @param legacyToken address of the old token contract
-     */
-    constructor (IERC20 legacyToken) public {
-        require(address(legacyToken) != address(0), "ERC20Migrator: legacy token is the zero address");
-        _legacyToken = legacyToken;
-    }
-
-    /**
-     * @dev Returns the legacy token that is being migrated.
-     */
-    function legacyToken() public view returns (IERC20) {
-        return _legacyToken;
-    }
-
-    /**
-     * @dev Returns the new token to which we are migrating.
-     */
-    function newToken() public view returns (IERC20) {
-        return _newToken;
-    }
-
-    /**
-     * @dev Begins the migration by setting which is the new token that will be
-     * minted. This contract must be a minter for the new token.
-     * @param newToken_ the token that will be minted
-     */
-    function beginMigration(ERC20Mintable newToken_) public {
-        require(address(_newToken) == address(0), "ERC20Migrator: migration already started");
-        require(address(newToken_) != address(0), "ERC20Migrator: new token is the zero address");
-        //solhint-disable-next-line max-line-length
-        require(newToken_.isMinter(address(this)), "ERC20Migrator: not a minter for new token");
-
-        _newToken = newToken_;
-    }
-
-    /**
-     * @dev Transfers part of an account's balance in the old token to this
-     * contract, and mints the same amount of new tokens for that account.
-     * @param account whose tokens will be migrated
-     * @param amount amount of tokens to be migrated
-     */
-    function migrate(address account, uint256 amount) public {
-        require(address(_newToken) != address(0), "ERC20Migrator: migration not started");
-        _legacyToken.safeTransferFrom(account, address(this), amount);
-        _newToken.mint(account, amount);
-    }
-
-    /**
-     * @dev Transfers all of an account's allowed balance in the old token to
-     * this contract, and mints the same amount of new tokens for that account.
-     * @param account whose tokens will be migrated
-     */
-    function migrateAll(address account) public {
-        uint256 balance = _legacyToken.balanceOf(account);
-        uint256 allowance = _legacyToken.allowance(account, address(this));
-        uint256 amount = Math.min(balance, allowance);
-        migrate(account, amount);
-    }
-}

contracts/drafts/ERC20Snapshot.sol

@@ -1,142 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../math/SafeMath.sol";
-import "../utils/Arrays.sol";
-import "../drafts/Counters.sol";
-import "../token/ERC20/ERC20.sol";
-
-/**
- * @title ERC20 token with snapshots.
- * @dev Inspired by Jordi Baylina's
- * https://github.com/Giveth/minimd/blob/ea04d950eea153a04c51fa510b068b9dded390cb/contracts/MiniMeToken.sol[MiniMeToken]
- * to record historical balances.
- *
- * When a snapshot is made, the balances and total supply at the time of the snapshot are recorded for later
- * access.
- *
- * To make a snapshot, call the {snapshot} function, which will emit the {Snapshot} event and return a snapshot id.
- * To get the total supply from a snapshot, call the function {totalSupplyAt} with the snapshot id.
- * To get the balance of an account from a snapshot, call the {balanceOfAt} function with the snapshot id and the
- * account address.
- * @author Validity Labs AG <info@validitylabs.org>
- */
-contract ERC20Snapshot is ERC20 {
-    using SafeMath for uint256;
-    using Arrays for uint256[];
-    using Counters for Counters.Counter;
-
-    // Snapshotted values have arrays of ids and the value corresponding to that id. These could be an array of a
-    // Snapshot struct, but that would impede usage of functions that work on an array.
-    struct Snapshots {
-        uint256[] ids;
-        uint256[] values;
-    }
-
-    mapping (address => Snapshots) private _accountBalanceSnapshots;
-    Snapshots private _totalSupplySnapshots;
-
-    // Snapshot ids increase monotonically, with the first value being 1. An id of 0 is invalid.
-    Counters.Counter private _currentSnapshotId;
-
-    event Snapshot(uint256 id);
-
-    // Creates a new snapshot id. Balances are only stored in snapshots on demand: unless a snapshot was taken, a
-    // balance change will not be recorded. This means the extra added cost of storing snapshotted balances is only paid
-    // when required, but is also flexible enough that it allows for e.g. daily snapshots.
-    function snapshot() public returns (uint256) {
-        _currentSnapshotId.increment();
-
-        uint256 currentId = _currentSnapshotId.current();
-        emit Snapshot(currentId);
-        return currentId;
-    }
-
-    function balanceOfAt(address account, uint256 snapshotId) public view returns (uint256) {
-        (bool snapshotted, uint256 value) = _valueAt(snapshotId, _accountBalanceSnapshots[account]);
-
-        return snapshotted ? value : balanceOf(account);
-    }
-
-    function totalSupplyAt(uint256 snapshotId) public view returns(uint256) {
-        (bool snapshotted, uint256 value) = _valueAt(snapshotId, _totalSupplySnapshots);
-
-        return snapshotted ? value : totalSupply();
-    }
-
-    // _transfer, _mint and _burn are the only functions where the balances are modified, so it is there that the
-    // snapshots are updated. Note that the update happens _before_ the balance change, with the pre-modified value.
-    // The same is true for the total supply and _mint and _burn.
-    function _transfer(address from, address to, uint256 value) internal {
-        _updateAccountSnapshot(from);
-        _updateAccountSnapshot(to);
-
-        super._transfer(from, to, value);
-    }
-
-    function _mint(address account, uint256 value) internal {
-        _updateAccountSnapshot(account);
-        _updateTotalSupplySnapshot();
-
-        super._mint(account, value);
-    }
-
-    function _burn(address account, uint256 value) internal {
-        _updateAccountSnapshot(account);
-        _updateTotalSupplySnapshot();
-
-        super._burn(account, value);
-    }
-
-    // When a valid snapshot is queried, there are three possibilities:
-    //  a) The queried value was not modified after the snapshot was taken. Therefore, a snapshot entry was never
-    //  created for this id, and all stored snapshot ids are smaller than the requested one. The value that corresponds
-    //  to this id is the current one.
-    //  b) The queried value was modified after the snapshot was taken. Therefore, there will be an entry with the
-    //  requested id, and its value is the one to return.
-    //  c) More snapshots were created after the requested one, and the queried value was later modified. There will be
-    //  no entry for the requested id: the value that corresponds to it is that of the smallest snapshot id that is
-    //  larger than the requested one.
-    //
-    // In summary, we need to find an element in an array, returning the index of the smallest value that is larger if
-    // it is not found, unless said value doesn't exist (e.g. when all values are smaller). Arrays.findUpperBound does
-    // exactly this.
-    function _valueAt(uint256 snapshotId, Snapshots storage snapshots)
-        private view returns (bool, uint256)
-    {
-        require(snapshotId > 0, "ERC20Snapshot: id is 0");
-        // solhint-disable-next-line max-line-length
-        require(snapshotId <= _currentSnapshotId.current(), "ERC20Snapshot: nonexistent id");
-
-        uint256 index = snapshots.ids.findUpperBound(snapshotId);
-
-        if (index == snapshots.ids.length) {
-            return (false, 0);
-        } else {
-            return (true, snapshots.values[index]);
-        }
-    }
-
-    function _updateAccountSnapshot(address account) private {
-        _updateSnapshot(_accountBalanceSnapshots[account], balanceOf(account));
-    }
-
-    function _updateTotalSupplySnapshot() private {
-        _updateSnapshot(_totalSupplySnapshots, totalSupply());
-    }
-
-    function _updateSnapshot(Snapshots storage snapshots, uint256 currentValue) private {
-        uint256 currentId = _currentSnapshotId.current();
-        if (_lastSnapshotId(snapshots.ids) < currentId) {
-            snapshots.ids.push(currentId);
-            snapshots.values.push(currentValue);
-        }
-    }
-
-    function _lastSnapshotId(uint256[] storage ids) private view returns (uint256) {
-        if (ids.length == 0) {
-            return 0;
-        } else {
-            return ids[ids.length - 1];
-        }
-    }
-}

contracts/drafts/README.adoc

@@ -1,23 +0,0 @@
-= Drafts
-
-NOTE: This page is incomplete. We're working to improve it for the next release. Stay tuned!
-
-== ERC 20
-
-{{ERC20Migrator}}
-
-{{ERC20Snapshot}}
-
-{{TokenVesting}}
-
-== Miscellaneous
-
-{{Counters}}
-
-{{SignatureBouncer}}
-
-{{SignedSafeMath}}
-
-== ERC 1046
-
-{{ERC1046}}

contracts/drafts/SignatureBouncer.sol

@@ -1,125 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../GSN/Context.sol";
-import "../access/roles/SignerRole.sol";
-import "../cryptography/ECDSA.sol";
-
-/**
- * @title SignatureBouncer
- * @author PhABC, Shrugs and aflesher
- * @dev SignatureBouncer allows users to submit a signature as a permission to
- * do an action.
- * If the signature is from one of the authorized signer addresses, the
- * signature is valid.
- * Note that SignatureBouncer offers no protection against replay attacks, users
- * must add this themselves!
- *
- * Signer addresses can be individual servers signing grants or different
- * users within a decentralized club that have permission to invite other
- * members. This technique is useful for whitelists and airdrops; instead of
- * putting all valid addresses on-chain, simply sign a grant of the form
- * keccak256(abi.encodePacked(`:contractAddress` + `:granteeAddress`)) using a
- * valid signer address.
- * Then restrict access to your crowdsale/whitelist/airdrop using the
- * `onlyValidSignature` modifier (or implement your own using _isValidSignature).
- * In addition to `onlyValidSignature`, `onlyValidSignatureAndMethod` and
- * `onlyValidSignatureAndData` can be used to restrict access to only a given
- * method or a given method with given parameters respectively.
- * See the tests in SignatureBouncer.test.js for specific usage examples.
- *
- * @notice A method that uses the `onlyValidSignatureAndData` modifier must make
- * the _signature parameter the "last" parameter. You cannot sign a message that
- * has its own signature in it so the last 128 bytes of msg.data (which
- * represents the length of the _signature data and the _signature data itself)
- * is ignored when validating. Also non fixed sized parameters make constructing
- * the data in the signature much more complex.
- * See https://ethereum.stackexchange.com/a/50616 for more details.
- */
-contract SignatureBouncer is Context, SignerRole {
-    using ECDSA for bytes32;
-
-    // Function selectors are 4 bytes long, as documented in
-    // https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector
-    uint256 private constant _METHOD_ID_SIZE = 4;
-    // Signature size is 65 bytes (tightly packed v + r + s), but gets padded to 96 bytes
-    uint256 private constant _SIGNATURE_SIZE = 96;
-
-    constructor () internal {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    /**
-     * @dev Requires that a valid signature of a signer was provided.
-     */
-    modifier onlyValidSignature(bytes memory signature) {
-        require(_isValidSignature(_msgSender(), signature), "SignatureBouncer: invalid signature for caller");
-        _;
-    }
-
-    /**
-     * @dev Requires that a valid signature with a specified method of a signer was provided.
-     */
-    modifier onlyValidSignatureAndMethod(bytes memory signature) {
-        // solhint-disable-next-line max-line-length
-        require(_isValidSignatureAndMethod(_msgSender(), signature), "SignatureBouncer: invalid signature for caller and method");
-        _;
-    }
-
-    /**
-     * @dev Requires that a valid signature with a specified method and params of a signer was provided.
-     */
-    modifier onlyValidSignatureAndData(bytes memory signature) {
-        // solhint-disable-next-line max-line-length
-        require(_isValidSignatureAndData(_msgSender(), signature), "SignatureBouncer: invalid signature for caller and data");
-        _;
-    }
-
-    /**
-     * @dev is the signature of `this + account` from a signer?
-     * @return bool
-     */
-    function _isValidSignature(address account, bytes memory signature) internal view returns (bool) {
-        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account)), signature);
-    }
-
-    /**
-     * @dev is the signature of `this + account + methodId` from a signer?
-     * @return bool
-     */
-    function _isValidSignatureAndMethod(address account, bytes memory signature) internal view returns (bool) {
-        bytes memory msgData = _msgData();
-        bytes memory data = new bytes(_METHOD_ID_SIZE);
-        for (uint256 i = 0; i < data.length; i++) {
-            data[i] = msgData[i];
-        }
-        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account, data)), signature);
-    }
-
-    /**
-     * @dev is the signature of `this + account + methodId + params(s)` from a signer?
-     * @notice the signature parameter of the method being validated must be the "last" parameter
-     * @return bool
-     */
-    function _isValidSignatureAndData(address account, bytes memory signature) internal view returns (bool) {
-        bytes memory msgData = _msgData();
-        require(msgData.length > _SIGNATURE_SIZE, "SignatureBouncer: data is too short");
-
-        bytes memory data = new bytes(msgData.length - _SIGNATURE_SIZE);
-        for (uint256 i = 0; i < data.length; i++) {
-            data[i] = msgData[i];
-        }
-
-        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account, data)), signature);
-    }
-
-    /**
-     * @dev Internal function to convert a hash to an eth signed message
-     * and then recover the signature and check it against the signer role.
-     * @return bool
-     */
-    function _isValidDataHash(bytes32 hash, bytes memory signature) internal view returns (bool) {
-        address signer = hash.toEthSignedMessageHash().recover(signature);
-
-        return signer != address(0) && isSigner(signer);
-    }
-}

contracts/drafts/SignedSafeMath.sol

@@ -1,60 +0,0 @@
-pragma solidity ^0.5.0;
-
-/**
- * @title SignedSafeMath
- * @dev Signed math operations with safety checks that revert on error.
- */
-library SignedSafeMath {
-    int256 constant private INT256_MIN = -2**255;
-
-    /**
-     * @dev Multiplies two signed integers, reverts on overflow.
-     */
-    function mul(int256 a, int256 b) internal pure returns (int256) {
-        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
-        // benefit is lost if 'b' is also tested.
-        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
-        if (a == 0) {
-            return 0;
-        }
-
-        require(!(a == -1 && b == INT256_MIN), "SignedSafeMath: multiplication overflow");
-
-        int256 c = a * b;
-        require(c / a == b, "SignedSafeMath: multiplication overflow");
-
-        return c;
-    }
-
-    /**
-     * @dev Integer division of two signed integers truncating the quotient, reverts on division by zero.
-     */
-    function div(int256 a, int256 b) internal pure returns (int256) {
-        require(b != 0, "SignedSafeMath: division by zero");
-        require(!(b == -1 && a == INT256_MIN), "SignedSafeMath: division overflow");
-
-        int256 c = a / b;
-
-        return c;
-    }
-
-    /**
-     * @dev Subtracts two signed integers, reverts on overflow.
-     */
-    function sub(int256 a, int256 b) internal pure returns (int256) {
-        int256 c = a - b;
-        require((b >= 0 && c <= a) || (b < 0 && c > a), "SignedSafeMath: subtraction overflow");
-
-        return c;
-    }
-
-    /**
-     * @dev Adds two signed integers, reverts on overflow.
-     */
-    function add(int256 a, int256 b) internal pure returns (int256) {
-        int256 c = a + b;
-        require((b >= 0 && c >= a) || (b < 0 && c < a), "SignedSafeMath: addition overflow");
-
-        return c;
-    }
-}

contracts/drafts/Strings.sol

@@ -1,32 +0,0 @@
-pragma solidity ^0.5.0;
-
-/**
- * @title Strings
- * @dev String operations.
- */
-library Strings {
-    /**
-     * @dev Converts a `uint256` to a `string`.
-     * via OraclizeAPI - MIT licence
-     * https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol
-     */
-    function fromUint256(uint256 value) internal pure returns (string memory) {
-        if (value == 0) {
-            return "0";
-        }
-        uint256 temp = value;
-        uint256 digits;
-        while (temp != 0) {
-            digits++;
-            temp /= 10;
-        }
-        bytes memory buffer = new bytes(digits);
-        uint256 index = digits - 1;
-        temp = value;
-        while (temp != 0) {
-            buffer[index--] = byte(uint8(48 + temp % 10));
-            temp /= 10;
-        }
-        return string(buffer);
-    }
-}

contracts/drafts/TokenVesting.sol

@@ -1,174 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../token/ERC20/SafeERC20.sol";
-import "../ownership/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/examples/SampleCrowdsale.sol

@@ -1,53 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../crowdsale/validation/CappedCrowdsale.sol";
-import "../crowdsale/distribution/RefundableCrowdsale.sol";
-import "../crowdsale/emission/MintedCrowdsale.sol";
-import "../token/ERC20/ERC20Mintable.sol";
-import "../token/ERC20/ERC20Detailed.sol";
-
-/**
- * @title SampleCrowdsaleToken
- * @dev Very simple ERC20 Token that can be minted.
- * It is meant to be used in a crowdsale contract.
- */
-contract SampleCrowdsaleToken is ERC20Mintable, ERC20Detailed {
-    constructor () public ERC20Detailed("Sample Crowdsale Token", "SCT", 18) {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}
-
-/**
- * @title SampleCrowdsale
- * @dev This is an example of a fully fledged crowdsale.
- * The way to add new features to a base crowdsale is by multiple inheritance.
- * In this example we are providing following extensions:
- * CappedCrowdsale - sets a max boundary for raised funds
- * RefundableCrowdsale - set a min goal to be reached and returns funds if it's not met
- * MintedCrowdsale - assumes the token can be minted by the crowdsale, which does so
- * when receiving purchases.
- *
- * After adding multiple features it's good practice to run integration tests
- * to ensure that subcontracts works together as intended.
- */
-contract SampleCrowdsale is CappedCrowdsale, RefundableCrowdsale, MintedCrowdsale {
-    constructor (
-        uint256 openingTime,
-        uint256 closingTime,
-        uint256 rate,
-        address payable wallet,
-        uint256 cap,
-        ERC20Mintable token,
-        uint256 goal
-    )
-        public
-        Crowdsale(rate, wallet, token)
-        CappedCrowdsale(cap)
-        TimedCrowdsale(openingTime, closingTime)
-        RefundableCrowdsale(goal)
-    {
-        //As goal needs to be met for a successful crowdsale
-        //the value needs to less or equal than a cap which is limit for accepted funds
-        require(goal <= cap, "SampleCrowdSale: goal is greater than cap");
-    }
-}

contracts/examples/SimpleToken.sol

@@ -1,21 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../GSN/Context.sol";
-import "../token/ERC20/ERC20.sol";
-import "../token/ERC20/ERC20Detailed.sol";
-
-/**
- * @title SimpleToken
- * @dev Very simple ERC20 Token example, where all tokens are pre-assigned to the creator.
- * Note they can later distribute these tokens as they wish using `transfer` and other
- * `ERC20` functions.
- */
-contract SimpleToken is Context, ERC20, ERC20Detailed {
-
-    /**
-     * @dev Constructor that gives _msgSender() all of existing tokens.
-     */
-    constructor () public ERC20Detailed("SimpleToken", "SIM", 18) {
-        _mint(_msgSender(), 10000 * (10 ** uint256(decimals())));
-    }
-}

contracts/finance/PaymentSplitter.sol

@@ -1,7 +1,10 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-import "../GSN/Context.sol";
-import "../math/SafeMath.sol";
+pragma solidity ^0.8.0;
+
+import "../utils/Address.sol";
+import "../utils/Context.sol";
+import "../utils/math/SafeMath.sol";
 
 /**
  * @title PaymentSplitter
@@ -17,8 +20,6 @@ import "../math/SafeMath.sol";
  * function.
  */
 contract PaymentSplitter is Context {
-    using SafeMath for uint256;
-
     event PayeeAdded(address account, uint256 shares);
     event PaymentReleased(address to, uint256 amount);
     event PaymentReceived(address from, uint256 amount);
@@ -37,13 +38,13 @@ 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 == shares_.length, "PaymentSplitter: payees and shares length mismatch");
         require(payees.length > 0, "PaymentSplitter: no payees");
 
         for (uint256 i = 0; i < payees.length; i++) {
-            _addPayee(payees[i], shares[i]);
+            _addPayee(payees[i], shares_[i]);
         }
     }
 
@@ -56,7 +57,7 @@ contract PaymentSplitter is Context {
      * https://solidity.readthedocs.io/en/latest/contracts.html#fallback-function[fallback
      * functions].
      */
-    function () external payable {
+    receive () external payable virtual {
         emit PaymentReceived(_msgSender(), msg.value);
     }
 
@@ -99,18 +100,18 @@ contract PaymentSplitter is Context {
      * @dev Triggers a transfer to `account` of the amount of Ether they are owed, according to their percentage of the
      * total shares and their previous withdrawals.
      */
-    function release(address payable account) public {
+    function release(address payable account) public virtual {
         require(_shares[account] > 0, "PaymentSplitter: account has no shares");
 
-        uint256 totalReceived = address(this).balance.add(_totalReleased);
-        uint256 payment = totalReceived.mul(_shares[account]).div(_totalShares).sub(_released[account]);
+        uint256 totalReceived = address(this).balance + _totalReleased;
+        uint256 payment = totalReceived * _shares[account] / _totalShares - _released[account];
 
         require(payment != 0, "PaymentSplitter: account is not due payment");
 
-        _released[account] = _released[account].add(payment);
-        _totalReleased = _totalReleased.add(payment);
+        _released[account] = _released[account] + payment;
+        _totalReleased = _totalReleased + payment;
 
-        account.transfer(payment);
+        Address.sendValue(account, payment);
         emit PaymentReleased(account, payment);
     }
 
@@ -126,7 +127,7 @@ contract PaymentSplitter is Context {
 
         _payees.push(account);
         _shares[account] = shares_;
-        _totalShares = _totalShares.add(shares_);
+        _totalShares = _totalShares + shares_;
         emit PayeeAdded(account, shares_);
     }
 }

contracts/finance/README.adoc

@@ -0,0 +1,10 @@
+= Finance
+
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/finance
+
+This directory includes primitives for financial systems. We currently only offer the {PaymentSplitter} contract, but we want to grow this directory so we welcome ideas.
+
+== PaymentSplitter
+
+{{PaymentSplitter}}

contracts/governance/README.adoc

@@ -0,0 +1,91 @@
+= Governance
+
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/governance
+
+This directory includes primitives for on-chain governance. We currently only offer the {TimelockController} contract, that can be used as a component in a governance systems to introduce a delay between a proposal and its execution.
+
+== Timelock
+
+{{TimelockController}}
+
+[[timelock-terminology]]
+==== Terminology
+
+* *Operation:* A transaction (or a set of transactions) that is the subject of the timelock. It has to be scheduled by a proposer and executed by an executor. The timelock enforces a minimum delay between the proposition and the execution (see xref:access-control.adoc#operation_lifecycle[operation lifecycle]). If the operation contains multiple transactions (batch mode), they are executed atomically. Operations are identified by the hash of their content.
+* *Operation status:*
+** *Unset:* An operation that is not part of the timelock mechanism.
+** *Pending:* An operation that has been scheduled, before the timer expires.
+** *Ready:* An operation that has been scheduled, after the timer expires.
+** *Done:* An operation that has been executed.
+* *Predecessor*: An (optional) dependency between operations. An operation can depend on another operation (its predecessor), forcing the execution order of these two operations.
+* *Role*:
+** *Proposer:* An address (smart contract or EOA) that is in charge of scheduling (and cancelling) operations.
+** *Executor:* An address (smart contract or EOA) that is in charge of executing operations.
+
+[[timelock-operation]]
+==== Operation structure
+
+Operation executed by the xref:api:governance.adoc#TimelockController[`TimelockControler`] can contain one or multiple subsequent calls. Depending on whether you need to multiple calls to be executed atomically, you can either use simple or batched operations.
+
+Both operations contain:
+
+* *Target*, the address of the smart contract that the timelock should operate on.
+* *Value*, in wei, that should be sent with the transaction. Most of the time this will be 0. Ether can be deposited before-end or passed along when executing the transaction.
+* *Data*, containing the encoded function selector and parameters of the call. This can be produced using a number of tools. For example, a maintenance operation granting role `ROLE` to `ACCOUNT` can be encode using web3js as follows:
+
+```javascript
+const data = timelock.contract.methods.grantRole(ROLE, ACCOUNT).encodeABI()
+```
+
+* *Predecessor*, that specifies a dependency between operations. This dependency is optional. Use `bytes32(0)` if the operation does not have any dependency.
+* *Salt*, used to disambiguate two otherwise identical operations. This can be any random value.
+
+In the case of batched operations, `target`, `value` and `data` are specified as arrays, which must be of the same length.
+
+[[timelock-operation-lifecycle]]
+==== Operation lifecycle
+
+Timelocked operations are identified by a unique id (their hash) and follow a specific lifecycle:
+
+`Unset` -> `Pending` -> `Pending` + `Ready` -> `Done`
+
+* By calling xref:api:governance.adoc#TimelockController-schedule-address-uint256-bytes-bytes32-bytes32-uint256-[`schedule`] (or xref:api:governance.adoc#TimelockController-scheduleBatch-address---uint256---bytes---bytes32-bytes32-uint256-[`scheduleBatch`]), a proposer moves the operation from the `Unset` to the `Pending` state. This starts a timer that must be longer than the minimum delay. The timer expires at a timestamp accessible through the xref:api:governance.adoc#TimelockController-getTimestamp-bytes32-[`getTimestamp`] method.
+* Once the timer expires, the operation automatically gets the `Ready` state. At this point, it can be executed.
+* By calling xref:api:governance.adoc#TimelockController-TimelockController-execute-address-uint256-bytes-bytes32-bytes32-[`execute`] (or xref:api:governance.adoc#TimelockController-executeBatch-address---uint256---bytes---bytes32-bytes32-[`executeBatch`]), an executor triggers the operation's underlying transactions and moves it to the `Done` state. If the operation has a predecessor, it has to be in the `Done` state for this transition to succeed.
+* xref:api:governance.adoc#TimelockController-TimelockController-cancel-bytes32-[`cancel`] allows proposers to cancel any `Pending` operation. This resets the operation to the `Unset` state. It is thus possible for a proposer to re-schedule an operation that has been cancelled. In this case, the timer restarts when the operation is re-scheduled.
+
+Operations status can be queried using the functions:
+
+* xref:api:governance.adoc#TimelockController-isOperationPending-bytes32-[`isOperationPending(bytes32)`]
+* xref:api:governance.adoc#TimelockController-isOperationReady-bytes32-[`isOperationReady(bytes32)`]
+* xref:api:governance.adoc#TimelockController-isOperationDone-bytes32-[`isOperationDone(bytes32)`]
+
+[[timelock-roles]]
+==== Roles
+
+[[timelock-admin]]
+===== Admin
+
+The admins are in charge of managing proposers and executors. For the timelock to be self-governed, this role should only be given to the timelock itself. Upon deployment, both the timelock and the deployer have this role. After further configuration and testing, the deployer can renounce this role such that all further maintenance operations have to go through the timelock process.
+
+This role is identified by the *TIMELOCK_ADMIN_ROLE* value: `0x5f58e3a2316349923ce3780f8d587db2d72378aed66a8261c916544fa6846ca5`
+
+[[timelock-proposer]]
+===== Proposer
+
+The proposers are in charge of scheduling (and cancelling) operations. This is a critical role, that should be given to governing entities. This could be an EOA, a multisig, or a DAO.
+
+WARNING: *Proposer fight:* Having multiple proposers, while providing redundancy in case one becomes unavailable, can be dangerous. As proposer have their say on all operations, they could cancel operations they disagree with, including operations to remove them for the proposers.
+
+This role is identified by the *PROPOSER_ROLE* value: `0xb09aa5aeb3702cfd50b6b62bc4532604938f21248a27a1d5ca736082b6819cc1`
+
+[[timelock-executor]]
+===== Executor
+
+The executors are in charge of executing the operations scheduled by the proposers once the timelock expires. Logic dictates that multisig or DAO that are proposers should also be executors in order to guarantee operations that have been scheduled will eventually be executed. However, having additional executor can reduce the cost (the executing transaction does not require validation by the multisig or DAO that proposed it), while ensuring whoever is in charge of execution cannot trigger actions that have not been scheduled by the proposers.
+
+This role is identified by the *EXECUTOR_ROLE* value: `0xd8aa0f3194971a2a116679f7c2090f6939c8d4e01a2a8d7e41d55e5351469e63`
+
+
+WARNING: A live contract without at least one proposer and one executor is locked. Make sure these roles are filled by reliable entities before the deployer renounces its administrative rights in favour of the timelock contract itself. See the {AccessControl} documentation to learn more about role management.

contracts/governance/TimelockController.sol

@@ -0,0 +1,296 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../access/AccessControl.sol";
+
+/**
+ * @dev Contract module which acts as a timelocked controller. When set as the
+ * owner of an `Ownable` smart contract, it enforces a timelock on all
+ * `onlyOwner` maintenance operations. This gives time for users of the
+ * controlled contract to exit before a potentially dangerous maintenance
+ * operation is applied.
+ *
+ * By default, this contract is self administered, meaning administration tasks
+ * have to go through the timelock process. The proposer (resp executor) role
+ * is in charge of proposing (resp executing) operations. A common use case is
+ * to position this {TimelockController} as the owner of a smart contract, with
+ * a multisig or a DAO as the sole proposer.
+ *
+ * _Available since v3.3._
+ */
+contract TimelockController is AccessControl {
+    bytes32 public constant TIMELOCK_ADMIN_ROLE = keccak256("TIMELOCK_ADMIN_ROLE");
+    bytes32 public constant PROPOSER_ROLE = keccak256("PROPOSER_ROLE");
+    bytes32 public constant EXECUTOR_ROLE = keccak256("EXECUTOR_ROLE");
+    uint256 internal constant _DONE_TIMESTAMP = uint256(1);
+
+    mapping(bytes32 => uint256) private _timestamps;
+    uint256 private _minDelay;
+
+    /**
+     * @dev Emitted when a call is scheduled as part of operation `id`.
+     */
+    event CallScheduled(bytes32 indexed id, uint256 indexed index, address target, uint256 value, bytes data, bytes32 predecessor, uint256 delay);
+
+    /**
+     * @dev Emitted when a call is performed as part of operation `id`.
+     */
+    event CallExecuted(bytes32 indexed id, uint256 indexed index, address target, uint256 value, bytes data);
+
+    /**
+     * @dev Emitted when operation `id` is cancelled.
+     */
+    event Cancelled(bytes32 indexed id);
+
+    /**
+     * @dev Emitted when the minimum delay for future operations is modified.
+     */
+    event MinDelayChange(uint256 oldDuration, uint256 newDuration);
+
+    /**
+     * @dev Initializes the contract with a given `minDelay`.
+     */
+    constructor(uint256 minDelay, address[] memory proposers, address[] memory executors) {
+        _setRoleAdmin(TIMELOCK_ADMIN_ROLE, TIMELOCK_ADMIN_ROLE);
+        _setRoleAdmin(PROPOSER_ROLE, TIMELOCK_ADMIN_ROLE);
+        _setRoleAdmin(EXECUTOR_ROLE, TIMELOCK_ADMIN_ROLE);
+
+        // deployer + self administration
+        _setupRole(TIMELOCK_ADMIN_ROLE, _msgSender());
+        _setupRole(TIMELOCK_ADMIN_ROLE, address(this));
+
+        // register proposers
+        for (uint256 i = 0; i < proposers.length; ++i) {
+            _setupRole(PROPOSER_ROLE, proposers[i]);
+        }
+
+        // register executors
+        for (uint256 i = 0; i < executors.length; ++i) {
+            _setupRole(EXECUTOR_ROLE, executors[i]);
+        }
+
+        _minDelay = minDelay;
+        emit MinDelayChange(0, minDelay);
+    }
+
+    /**
+     * @dev Modifier to make a function callable only by a certain role. In
+     * addition to checking the sender's role, `address(0)` 's role is also
+     * considered. Granting a role to `address(0)` is equivalent to enabling
+     * this role for everyone.
+     */
+    modifier onlyRole(bytes32 role) {
+        require(hasRole(role, _msgSender()) || hasRole(role, address(0)), "TimelockController: sender requires permission");
+        _;
+    }
+
+    /**
+     * @dev Contract might receive/hold ETH as part of the maintenance process.
+     */
+    receive() external payable {}
+
+    /**
+     * @dev Returns whether an id correspond to a registered operation. This
+     * includes both Pending, Ready and Done operations.
+     */
+    function isOperation(bytes32 id) public view virtual returns (bool pending) {
+        return getTimestamp(id) > 0;
+    }
+
+    /**
+     * @dev Returns whether an operation is pending or not.
+     */
+    function isOperationPending(bytes32 id) public view virtual returns (bool pending) {
+        return getTimestamp(id) > _DONE_TIMESTAMP;
+    }
+
+    /**
+     * @dev Returns whether an operation is ready or not.
+     */
+    function isOperationReady(bytes32 id) public view virtual returns (bool ready) {
+        uint256 timestamp = getTimestamp(id);
+        // solhint-disable-next-line not-rely-on-time
+        return timestamp > _DONE_TIMESTAMP && timestamp <= block.timestamp;
+    }
+
+    /**
+     * @dev Returns whether an operation is done or not.
+     */
+    function isOperationDone(bytes32 id) public view virtual returns (bool done) {
+        return getTimestamp(id) == _DONE_TIMESTAMP;
+    }
+
+    /**
+     * @dev Returns the timestamp at with an operation becomes ready (0 for
+     * unset operations, 1 for done operations).
+     */
+    function getTimestamp(bytes32 id) public view virtual returns (uint256 timestamp) {
+        return _timestamps[id];
+    }
+
+    /**
+     * @dev Returns the minimum delay for an operation to become valid.
+     *
+     * This value can be changed by executing an operation that calls `updateDelay`.
+     */
+    function getMinDelay() public view virtual returns (uint256 duration) {
+        return _minDelay;
+    }
+
+    /**
+     * @dev Returns the identifier of an operation containing a single
+     * transaction.
+     */
+    function hashOperation(address target, uint256 value, bytes calldata data, bytes32 predecessor, bytes32 salt) public pure virtual returns (bytes32 hash) {
+        return keccak256(abi.encode(target, value, data, predecessor, salt));
+    }
+
+    /**
+     * @dev Returns the identifier of an operation containing a batch of
+     * transactions.
+     */
+    function hashOperationBatch(address[] calldata targets, uint256[] calldata values, bytes[] calldata datas, bytes32 predecessor, bytes32 salt) public pure virtual returns (bytes32 hash) {
+        return keccak256(abi.encode(targets, values, datas, predecessor, salt));
+    }
+
+    /**
+     * @dev Schedule an operation containing a single transaction.
+     *
+     * Emits a {CallScheduled} event.
+     *
+     * Requirements:
+     *
+     * - the caller must have the 'proposer' role.
+     */
+    function schedule(address target, uint256 value, bytes calldata data, bytes32 predecessor, bytes32 salt, uint256 delay) public virtual onlyRole(PROPOSER_ROLE) {
+        bytes32 id = hashOperation(target, value, data, predecessor, salt);
+        _schedule(id, delay);
+        emit CallScheduled(id, 0, target, value, data, predecessor, delay);
+    }
+
+    /**
+     * @dev Schedule an operation containing a batch of transactions.
+     *
+     * Emits one {CallScheduled} event per transaction in the batch.
+     *
+     * Requirements:
+     *
+     * - the caller must have the 'proposer' role.
+     */
+    function scheduleBatch(address[] calldata targets, uint256[] calldata values, bytes[] calldata datas, bytes32 predecessor, bytes32 salt, uint256 delay) public virtual onlyRole(PROPOSER_ROLE) {
+        require(targets.length == values.length, "TimelockController: length mismatch");
+        require(targets.length == datas.length, "TimelockController: length mismatch");
+
+        bytes32 id = hashOperationBatch(targets, values, datas, predecessor, salt);
+        _schedule(id, delay);
+        for (uint256 i = 0; i < targets.length; ++i) {
+            emit CallScheduled(id, i, targets[i], values[i], datas[i], predecessor, delay);
+        }
+    }
+
+    /**
+     * @dev Schedule an operation that is to becomes valid after a given delay.
+     */
+    function _schedule(bytes32 id, uint256 delay) private {
+        require(!isOperation(id), "TimelockController: operation already scheduled");
+        require(delay >= getMinDelay(), "TimelockController: insufficient delay");
+        // solhint-disable-next-line not-rely-on-time
+        _timestamps[id] = block.timestamp + delay;
+    }
+
+    /**
+     * @dev Cancel an operation.
+     *
+     * Requirements:
+     *
+     * - the caller must have the 'proposer' role.
+     */
+    function cancel(bytes32 id) public virtual onlyRole(PROPOSER_ROLE) {
+        require(isOperationPending(id), "TimelockController: operation cannot be cancelled");
+        delete _timestamps[id];
+
+        emit Cancelled(id);
+    }
+
+    /**
+     * @dev Execute an (ready) operation containing a single transaction.
+     *
+     * Emits a {CallExecuted} event.
+     *
+     * Requirements:
+     *
+     * - the caller must have the 'executor' role.
+     */
+    function execute(address target, uint256 value, bytes calldata data, bytes32 predecessor, bytes32 salt) public payable virtual onlyRole(EXECUTOR_ROLE) {
+        bytes32 id = hashOperation(target, value, data, predecessor, salt);
+        _beforeCall(predecessor);
+        _call(id, 0, target, value, data);
+        _afterCall(id);
+    }
+
+    /**
+     * @dev Execute an (ready) operation containing a batch of transactions.
+     *
+     * Emits one {CallExecuted} event per transaction in the batch.
+     *
+     * Requirements:
+     *
+     * - the caller must have the 'executor' role.
+     */
+    function executeBatch(address[] calldata targets, uint256[] calldata values, bytes[] calldata datas, bytes32 predecessor, bytes32 salt) public payable virtual onlyRole(EXECUTOR_ROLE) {
+        require(targets.length == values.length, "TimelockController: length mismatch");
+        require(targets.length == datas.length, "TimelockController: length mismatch");
+
+        bytes32 id = hashOperationBatch(targets, values, datas, predecessor, salt);
+        _beforeCall(predecessor);
+        for (uint256 i = 0; i < targets.length; ++i) {
+            _call(id, i, targets[i], values[i], datas[i]);
+        }
+        _afterCall(id);
+    }
+
+    /**
+     * @dev Checks before execution of an operation's calls.
+     */
+    function _beforeCall(bytes32 predecessor) private view {
+        require(predecessor == bytes32(0) || isOperationDone(predecessor), "TimelockController: missing dependency");
+    }
+
+    /**
+     * @dev Checks after execution of an operation's calls.
+     */
+    function _afterCall(bytes32 id) private {
+        require(isOperationReady(id), "TimelockController: operation is not ready");
+        _timestamps[id] = _DONE_TIMESTAMP;
+    }
+
+    /**
+     * @dev Execute an operation's call.
+     *
+     * Emits a {CallExecuted} event.
+     */
+    function _call(bytes32 id, uint256 index, address target, uint256 value, bytes calldata data) private {
+        // solhint-disable-next-line avoid-low-level-calls
+        (bool success,) = target.call{value: value}(data);
+        require(success, "TimelockController: underlying transaction reverted");
+
+        emit CallExecuted(id, index, target, value, data);
+    }
+
+    /**
+     * @dev Changes the minimum timelock duration for future operations.
+     *
+     * Emits a {MinDelayChange} event.
+     *
+     * Requirements:
+     *
+     * - the caller must be the timelock itself. This can only be achieved by scheduling and later executing
+     * an operation where the timelock is the target and the data is the ABI-encoded call to this function.
+     */
+    function updateDelay(uint256 newDelay) external virtual {
+        require(msg.sender == address(this), "TimelockController: caller must be timelock");
+        emit MinDelayChange(_minDelay, newDelay);
+        _minDelay = newDelay;
+    }
+}

contracts/introspection/README.adoc

@@ -1,28 +0,0 @@
-= Introspection
-
-This set of interfaces and contracts deal with [type introspection](https://en.wikipedia.org/wiki/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.
-
-There are two main ways to approach this.
-
-* Locally, where a contract implements `IERC165` and declares an interface, and a second one queries it directly via `ERC165Checker`.
-* Globally, where a global and unique registry (`IERC1820Registry`) is used to register implementers of a certain interface (`IERC1820Implementer`). It is then the registry that is queried, which allows for more complex setups, like contracts implementing interfaces for externally-owned accounts.
-
-Note that, in all cases, accounts simply _declare_ their interfaces, but they are not required to actually implement them. This mechanism can therefore be used to both prevent errors and allow for complex interactions (see `ERC777`), but it must not be relied on for security.
-
-== Local
-
-{{IERC165}}
-
-{{ERC165}}
-
-{{ERC165Checker}}
-
-== Global
-
-{{IERC1820Registry}}
-
-{{IERC1820Implementer}}
-
-{{ERC1820Implementer}}

contracts/math/README.adoc

@@ -1,9 +0,0 @@
-= Math
-
-These are math-related utilities.
-
-== Libraries
-
-{{SafeMath}}
-
-{{Math}}

contracts/math/SafeMath.sol

@@ -1,150 +0,0 @@
-pragma solidity ^0.5.0;
-
-/**
- * @dev Wrappers over Solidity's arithmetic operations with added overflow
- * checks.
- *
- * Arithmetic operations in Solidity wrap on overflow. This can easily result
- * in bugs, because programmers usually assume that an overflow raises an
- * error, which is the standard behavior in high level programming languages.
- * `SafeMath` restores this intuition by reverting the transaction when an
- * operation overflows.
- *
- * Using this library instead of the unchecked operations eliminates an entire
- * class of bugs, so it's recommended to use it always.
- */
-library SafeMath {
-    /**
-     * @dev Returns the addition of two unsigned integers, reverting on
-     * overflow.
-     *
-     * Counterpart to Solidity's `+` operator.
-     *
-     * Requirements:
-     * - Addition cannot overflow.
-     */
-    function add(uint256 a, uint256 b) internal pure returns (uint256) {
-        uint256 c = a + b;
-        require(c >= a, "SafeMath: addition overflow");
-
-        return c;
-    }
-
-    /**
-     * @dev Returns the subtraction of two unsigned integers, reverting on
-     * overflow (when the result is negative).
-     *
-     * Counterpart to Solidity's `-` operator.
-     *
-     * Requirements:
-     * - Subtraction cannot overflow.
-     */
-    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
-        return sub(a, b, "SafeMath: subtraction overflow");
-    }
-
-    /**
-     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
-     * overflow (when the result is negative).
-     *
-     * Counterpart to Solidity's `-` operator.
-     *
-     * Requirements:
-     * - Subtraction cannot overflow.
-     */
-    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
-        require(b <= a, errorMessage);
-        uint256 c = a - b;
-
-        return c;
-    }
-
-    /**
-     * @dev Returns the multiplication of two unsigned integers, reverting on
-     * overflow.
-     *
-     * Counterpart to Solidity's `*` operator.
-     *
-     * Requirements:
-     * - Multiplication cannot overflow.
-     */
-    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
-        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
-        // benefit is lost if 'b' is also tested.
-        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
-        if (a == 0) {
-            return 0;
-        }
-
-        uint256 c = a * b;
-        require(c / a == b, "SafeMath: multiplication overflow");
-
-        return c;
-    }
-
-    /**
-     * @dev Returns the integer division of two unsigned 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(uint256 a, uint256 b) internal pure returns (uint256) {
-        return div(a, b, "SafeMath: division by zero");
-    }
-
-    /**
-     * @dev Returns the integer division of two unsigned integers. Reverts with custom message 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(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
-
-        return c;
-    }
-
-    /**
-     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
-     * Reverts when dividing by zero.
-     *
-     * Counterpart to Solidity's `%` operator. 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 mod(uint256 a, uint256 b) internal pure returns (uint256) {
-        return mod(a, b, "SafeMath: modulo by zero");
-    }
-
-    /**
-     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
-     * Reverts with custom message when dividing by zero.
-     *
-     * Counterpart to Solidity's `%` operator. 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 mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
-        require(b != 0, errorMessage);
-        return a % b;
-    }
-}

contracts/metatx/ERC2771Context.sol

@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/Context.sol";
+
+/*
+ * @dev Context variant with ERC2771 support.
+ */
+abstract contract ERC2771Context is Context {
+    address immutable _trustedForwarder;
+
+    constructor(address trustedForwarder) {
+        _trustedForwarder = trustedForwarder;
+    }
+
+    function isTrustedForwarder(address forwarder) public view virtual returns(bool) {
+        return forwarder == _trustedForwarder;
+    }
+
+    function _msgSender() internal view virtual override returns (address sender) {
+        if (isTrustedForwarder(msg.sender)) {
+            // The assembly code is more direct than the Solidity version using `abi.decode`.
+            assembly { sender := shr(96, calldataload(sub(calldatasize(), 20))) }
+        } else {
+            return super._msgSender();
+        }
+    }
+
+    function _msgData() internal view virtual override returns (bytes calldata) {
+        if (isTrustedForwarder(msg.sender)) {
+            return msg.data[:msg.data.length-20];
+        } else {
+            return super._msgData();
+        }
+    }
+}

contracts/metatx/MinimalForwarder.sol

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/cryptography/ECDSA.sol";
+import "../utils/cryptography/draft-EIP712.sol";
+
+/*
+ * @dev Simple minimal forwarder to be used together with an ERC2771 compatible contract. See {ERC2771Context}.
+ */
+contract MinimalForwarder is EIP712 {
+    using ECDSA for bytes32;
+
+    struct ForwardRequest {
+        address from;
+        address to;
+        uint256 value;
+        uint256 gas;
+        uint256 nonce;
+        bytes data;
+    }
+
+    bytes32 private constant TYPEHASH = keccak256("ForwardRequest(address from,address to,uint256 value,uint256 gas,uint256 nonce,bytes data)");
+
+    mapping(address => uint256) private _nonces;
+
+    constructor() EIP712("MinimalForwarder", "0.0.1") {}
+
+    function getNonce(address from) public view returns (uint256) {
+        return _nonces[from];
+    }
+
+    function verify(ForwardRequest calldata req, bytes calldata signature) public view returns (bool) {
+        address signer = _hashTypedDataV4(keccak256(abi.encode(
+            TYPEHASH,
+            req.from,
+            req.to,
+            req.value,
+            req.gas,
+            req.nonce,
+            keccak256(req.data)
+        ))).recover(signature);
+        return _nonces[req.from] == req.nonce && signer == req.from;
+    }
+
+    function execute(ForwardRequest calldata req, bytes calldata signature) public payable returns (bool, bytes memory) {
+        require(verify(req, signature), "MinimalForwarder: signature does not match request");
+        _nonces[req.from] = req.nonce + 1;
+
+        // solhint-disable-next-line avoid-low-level-calls
+        (bool success, bytes memory returndata) = req.to.call{gas: req.gas, value: req.value}(abi.encodePacked(req.data, req.from));
+        // Validate that the relayer has sent enough gas for the call.
+        // See https://ronan.eth.link/blog/ethereum-gas-dangers/
+        assert(gasleft() > req.gas / 63);
+
+        return (success, returndata);
+    }
+}

contracts/metatx/README.adoc

@@ -0,0 +1,12 @@
+= Meta Transactions
+
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/metatx
+
+== Core
+
+{{ERC2771Context}}
+
+== Utils
+
+{{MinimalForwarder}}

contracts/mocks/AccessControlEnumerableMock.sol

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../access/AccessControlEnumerable.sol";
+
+contract AccessControlEnumerableMock is AccessControlEnumerable {
+    constructor() {
+        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
+    }
+
+    function setRoleAdmin(bytes32 roleId, bytes32 adminRoleId) public {
+        _setRoleAdmin(roleId, adminRoleId);
+    }
+}

contracts/mocks/AccessControlMock.sol

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../access/AccessControl.sol";
+
+contract AccessControlMock is AccessControl {
+    constructor() {
+        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
+    }
+
+    function setRoleAdmin(bytes32 roleId, bytes32 adminRoleId) public {
+        _setRoleAdmin(roleId, adminRoleId);
+    }
+}

contracts/mocks/AddressImpl.sol

@@ -1,13 +1,42 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
 
 import "../utils/Address.sol";
 
 contract AddressImpl {
+    string public sharedAnswer;
+
+    event CallReturnValue(string data);
+
     function isContract(address account) external view returns (bool) {
         return Address.isContract(account);
     }
 
-    function toPayable(address account) external pure returns (address payable) {
-        return Address.toPayable(account);
+    function sendValue(address payable receiver, uint256 amount) external {
+        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)));
+    }
+
+    function functionStaticCall(address target, bytes calldata data) external {
+        bytes memory returnData = Address.functionStaticCall(target, data);
+        emit CallReturnValue(abi.decode(returnData, (string)));
+    }
+
+    function functionDelegateCall(address target, bytes calldata data) external {
+        bytes memory returnData = Address.functionDelegateCall(target, data);
+        emit CallReturnValue(abi.decode(returnData, (string)));
+    }
+
+    // sendValue's tests require the contract to hold Ether
+    receive () external payable { }
 }

contracts/mocks/AllowanceCrowdsaleImpl.sol

@@ -1,14 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../token/ERC20/IERC20.sol";
-import "../crowdsale/emission/AllowanceCrowdsale.sol";
-
-contract AllowanceCrowdsaleImpl is AllowanceCrowdsale {
-    constructor (uint256 rate, address payable wallet, IERC20 token, address tokenWallet)
-        public
-        Crowdsale(rate, wallet, token)
-        AllowanceCrowdsale(tokenWallet)
-    {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}

contracts/mocks/ArraysImpl.sol

@@ -1,17 +1,19 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
 
 import "../utils/Arrays.sol";
 
 contract ArraysImpl {
     using Arrays for uint256[];
 
-    uint256[] private array;
+    uint256[] private _array;
 
-    constructor (uint256[] memory _array) public {
-        array = _array;
+    constructor (uint256[] memory array) {
+        _array = array;
     }
 
-    function findUpperBound(uint256 _element) external view returns (uint256) {
-        return array.findUpperBound(_element);
+    function findUpperBound(uint256 element) external view returns (uint256) {
+        return _array.findUpperBound(element);
     }
 }

contracts/mocks/BadBeacon.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+contract BadBeaconNoImpl {
+}
+
+contract BadBeaconNotContract {
+    function implementation() external pure returns (address) {
+        return address(0x1);
+    }
+}

contracts/mocks/CallReceiverMock.sol

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+contract CallReceiverMock {
+    string public sharedAnswer;
+
+    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 mockStaticFunction() public pure returns (string memory) {
+        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);
+        }
+    }
+
+    function mockFunctionWritesStorage() public returns (string memory) {
+        sharedAnswer = "42";
+        return "0x1234";
+    }
+}

contracts/mocks/CappedCrowdsaleImpl.sol

@@ -1,14 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../token/ERC20/IERC20.sol";
-import "../crowdsale/validation/CappedCrowdsale.sol";
-
-contract CappedCrowdsaleImpl is CappedCrowdsale {
-    constructor (uint256 rate, address payable wallet, IERC20 token, uint256 cap)
-        public
-        Crowdsale(rate, wallet, token)
-        CappedCrowdsale(cap)
-    {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}

contracts/mocks/CapperRoleMock.sol

@@ -1,18 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../access/roles/CapperRole.sol";
-
-contract CapperRoleMock is CapperRole {
-    function removeCapper(address account) public {
-        _removeCapper(account);
-    }
-
-    function onlyCapperMock() public view onlyCapper {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    // Causes a compilation error if super._removeCapper is not internal
-    function _removeCapper(address account) internal {
-        super._removeCapper(account);
-    }
-}

contracts/mocks/ClashingImplementation.sol

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+
+/**
+ * @dev Implementation contract with an admin() function made to clash with
+ * @dev TransparentUpgradeableProxy's to test correct functioning of the
+ * @dev Transparent Proxy feature.
+ */
+contract ClashingImplementation {
+
+  function admin() external pure returns (address) {
+    return 0x0000000000000000000000000000000011111142;
+  }
+
+  function delegatedFunction() external pure returns (bool) {
+    return true;
+  }
+}

contracts/mocks/ClonesMock.sol

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../proxy/Clones.sol";
+import "../utils/Address.sol";
+
+contract ClonesMock {
+    using Address for address;
+    using Clones for address;
+
+    event NewInstance(address instance);
+
+    function clone(address implementation, bytes calldata initdata) public payable {
+        _initAndEmit(implementation.clone(), initdata);
+    }
+
+    function cloneDeterministic(address implementation, bytes32 salt, bytes calldata initdata) public payable {
+        _initAndEmit(implementation.cloneDeterministic(salt), initdata);
+    }
+
+    function predictDeterministicAddress(address implementation, bytes32 salt) public view returns (address predicted) {
+        return implementation.predictDeterministicAddress(salt);
+    }
+
+    function _initAndEmit(address instance, bytes memory initdata) private {
+        if (initdata.length > 0) {
+            instance.functionCallWithValue(initdata, msg.value);
+        }
+        emit NewInstance(instance);
+    }
+}

contracts/mocks/ConditionalEscrowMock.sol

@@ -1,6 +1,8 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-import "../payment/escrow/ConditionalEscrow.sol";
+pragma solidity ^0.8.0;
+
+import "../utils/escrow/ConditionalEscrow.sol";
 
 // mock class using ConditionalEscrow
 contract ConditionalEscrowMock is ConditionalEscrow {
@@ -10,7 +12,7 @@ contract ConditionalEscrowMock is ConditionalEscrow {
         _allowed[payee] = allowed;
     }
 
-    function withdrawalAllowed(address payee) public view returns (bool) {
+    function withdrawalAllowed(address payee) public view override returns (bool) {
         return _allowed[payee];
     }
 }

contracts/mocks/ContextMock.sol

@@ -1,6 +1,8 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-import "../GSN/Context.sol";
+pragma solidity ^0.8.0;
+
+import "../utils/Context.sol";
 
 contract ContextMock is Context {
     event Sender(address sender);

contracts/mocks/CountersImpl.sol

@@ -1,6 +1,8 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-import "../drafts/Counters.sol";
+pragma solidity ^0.8.0;
+
+import "../utils/Counters.sol";
 
 contract CountersImpl {
     using Counters for Counters.Counter;

contracts/mocks/Create2Impl.sol

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/Create2.sol";
+import "../utils/introspection/ERC1820Implementer.sol";
+
+contract Create2Impl {
+    function deploy(uint256 value, bytes32 salt, bytes memory code) public {
+        Create2.deploy(value, salt, code);
+    }
+
+    function deployERC1820Implementer(uint256 value, bytes32 salt) public {
+        // solhint-disable-next-line indent
+        Create2.deploy(value, salt, type(ERC1820Implementer).creationCode);
+    }
+
+    function computeAddress(bytes32 salt, bytes32 codeHash) public view returns (address) {
+        return Create2.computeAddress(salt, codeHash);
+    }
+
+    function computeAddressWithDeployer(bytes32 salt, bytes32 codeHash, address deployer) public pure returns (address) {
+        return Create2.computeAddress(salt, codeHash, deployer);
+    }
+
+    receive() external payable {}
+}

contracts/mocks/CrowdsaleMock.sol

@@ -1,9 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "../crowdsale/Crowdsale.sol";
-
-contract CrowdsaleMock is Crowdsale {
-    constructor (uint256 rate, address payable wallet, IERC20 token) public Crowdsale(rate, wallet, token) {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}

contracts/mocks/DummyImplementation.sol

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+abstract contract Impl {
+  function version() public pure virtual returns (string memory); 
+}
+
+contract DummyImplementation {
+  uint256 public value;
+  string public text;
+  uint256[] public values;
+
+  function initializeNonPayable() public {
+    value = 10;
+  }
+
+  function initializePayable() public payable {
+    value = 100;
+  }
+
+  function initializeNonPayableWithValue(uint256 _value) public {
+    value = _value;
+  }
+
+  function initializePayableWithValue(uint256 _value) public payable {
+    value = _value;
+  }
+
+  function initialize(uint256 _value, string memory _text, uint256[] memory _values) public {
+    value = _value;
+    text = _text;
+    values = _values;
+  }
+
+  function get() public pure returns (bool) {
+    return true;
+  }
+
+  function version() public pure virtual returns (string memory) {
+    return "V1";
+  }
+
+  function reverts() public pure {
+    require(false, "DummyImplementation reverted");
+  }
+}
+
+contract DummyImplementationV2 is DummyImplementation {
+  function migrate(uint256 newVal) public payable {
+    value = newVal;
+  }
+
+  function version() public pure override returns (string memory) {
+    return "V2";
+  }
+}

contracts/mocks/ECDSAMock.sol

@@ -1,6 +1,8 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-import "../cryptography/ECDSA.sol";
+pragma solidity ^0.8.0;
+
+import "../utils/cryptography/ECDSA.sol";
 
 contract ECDSAMock {
     using ECDSA for bytes32;

contracts/mocks/EIP712External.sol

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/cryptography/draft-EIP712.sol";
+import "../utils/cryptography/ECDSA.sol";
+
+contract EIP712External is EIP712 {
+    constructor(string memory name, string memory version) EIP712(name, version) {}
+
+    function domainSeparator() external view returns (bytes32) {
+        return _domainSeparatorV4();
+    }
+
+    function verify(bytes memory signature, address signer, address mailTo, string memory mailContents) external view {
+        bytes32 digest = _hashTypedDataV4(keccak256(abi.encode(
+            keccak256("Mail(address to,string contents)"),
+            mailTo,
+            keccak256(bytes(mailContents))
+        )));
+        address recoveredSigner = ECDSA.recover(digest, signature);
+        require(recoveredSigner == signer);
+    }
+
+    function getChainId() external view returns (uint256) {
+        return block.chainid;
+    }
+}

contracts/mocks/ERC1155BurnableMock.sol

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../token/ERC1155/extensions/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 ^0.8.0;
+
+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 ^0.8.0;
+
+import "./ERC1155Mock.sol";
+import "../token/ERC1155/extensions/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 ^0.8.0;
+
+import "../token/ERC1155/IERC1155Receiver.sol";
+import "../utils/introspection/ERC165.sol";
+
+contract ERC1155ReceiverMock is IERC1155Receiver, ERC165 {
+    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

@@ -1,6 +1,8 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-import "../../introspection/IERC165.sol";
+pragma solidity ^0.8.0;
+
+import "../../utils/introspection/IERC165.sol";
 
 /**
  * https://eips.ethereum.org/EIPS/eip-214#specification
@@ -27,14 +29,14 @@ contract SupportsInterfaceWithLookupMock is IERC165 {
      * @dev A contract implementing SupportsInterfaceWithLookup
      * implement ERC165 itself.
      */
-    constructor () public {
+    constructor () {
         _registerInterface(INTERFACE_ID_ERC165);
     }
 
     /**
      * @dev Implement supportsInterface(bytes4) using a lookup table.
      */
-    function supportsInterface(bytes4 interfaceId) external view returns (bool) {
+    function supportsInterface(bytes4 interfaceId) public view override returns (bool) {
         return _supportedInterfaces[interfaceId];
     }
 
@@ -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]);
         }