4.0.0-beta.1

(cherry picked from commit 1705067e65)

.circleci/config.yml

@@ -1,84 +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:10
-
-  - &cache_key_node_modules
-    key: v1-node_modules-{{ checksum "package-lock.json" }}
-
-jobs:
-  dependencies:
-    <<: *defaults
-    steps:
-      - checkout
-      - restore_cache:
-          <<: *cache_key_node_modules
-      - run:
-          name: Install npm dependencies and prepare
-          command: |
-            if [ ! -d node_modules ]; then
-              npm ci
-            else
-              npm run prepare
-            fi
-      - persist_to_workspace:
-          root: .
-          paths:
-            - node_modules
-            - build
-      - save_cache:
-          paths:
-            - node_modules
-          <<: *cache_key_node_modules
-
-  lint:
-    <<: *defaults
-    steps:
-      - checkout
-      - attach_workspace:
-          at: .
-      - run:
-          name: Linter
-          command: npm run lint
-  test:
-    <<: *defaults
-    steps:
-      - checkout
-      - attach_workspace:
-          at: .
-      - run:
-          name: Unit tests
-          command: npm run test
-
-  coverage:
-    <<: *defaults
-    steps:
-      - checkout
-      - attach_workspace:
-          at: .
-      - 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%

.dependabot/config.yml

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

.editorconfig

@@ -8,10 +8,14 @@ charset = utf-8
 end_of_line = lf
 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": {
 

.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

@@ -1,67 +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
-  - meta
-
-# 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

@@ -50,3 +50,10 @@ 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

@@ -4,5 +4,12 @@ module.exports = {
     compileCommand: 'npm run compile',
     skipFiles: [
         '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

@@ -1,5 +1,155 @@
 # Changelog
 
+## 4.0.0
+
+ * 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 upcomming 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 behaviour 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 reorganisation of the contract folder to improve clarity and discoverability. ([#2503](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2503))
+ * `ERC20Capped`: optimize gas usage of by enforcing te 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))
+ * `ERC721TokenUri`: Add a new extension ERC721TokenUri that implements the tokenURI behavior as it was available in 3.4.0. ([#2555](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2555))
+
+### 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.
+
+## 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
@@ -96,7 +246,7 @@ Refer to the table below to adjust your inheritance list.
 ### 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

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

@@ -10,7 +10,7 @@ program that extracts the API Reference from source code.
 
 The [`docs.openzeppelin.com`](https://github.com/OpenZeppelin/docs.openzeppelin.com)
 repository hosts the configuration for the entire site, which includes
-documetation for all of the OpenZeppelin projects.
+documentation for all of the OpenZeppelin projects.
 
-To run the docs locally you should run `npm run docs start` on this
+To run the docs locally you should run `npm run docs:watch` on this
 repository.

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

@@ -1,7 +1,7 @@
-# <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)
 
 **A library for secure smart contract development.** Build on a solid foundation of community-vetted code.
@@ -10,7 +10,7 @@
  * Flexible [role-based permissioning](https://docs.openzeppelin.com/contracts/access-control) scheme.
  * Reusable [Solidity components](https://docs.openzeppelin.com/contracts/utilities) to build custom contracts and complex decentralized systems.
  * First-class integration with the [Gas Station Network](https://docs.openzeppelin.com/contracts/gsn) for systems with no gas fees!
- * Audited by leading security firms.
+ * [Audited](https://github.com/OpenZeppelin/openzeppelin-contracts/tree/master/audit) by leading security firms (_last full audit on v2.0.0_).
 
 ## Overview
 
@@ -27,24 +27,23 @@ OpenZeppelin Contracts features a [stable API](https://docs.openzeppelin.com/con
 Once installed, you can use the contracts in the library by importing them:
 
 ```solidity
-pragma solidity ^0.5.0;
+pragma solidity ^0.8.0;
 
-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") {
     }
 }
 ```
 
-_If you're new to smart contract development, head to [Developing Smart Contracts](https://docs.openzeppelin.com/contracts/learn::developing-smart-contracts) to learn about creating a new project and compiling your contracts._
+_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._
 
-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.
+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 sidebar will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
+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).

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/GSNRecipient.sol

@@ -1,228 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "./IRelayRecipient.sol";
-import "./IRelayHub.sol";
-import "./Context.sol";
-
-/**
- * @dev Base GSN recipient contract: includes the {IRelayRecipient} interface
- * and enables GSN support on all contracts in the inheritance tree.
- *
- * TIP: This contract is abstract. The functions {IRelayRecipient-acceptRelayedCall},
- *  {_preRelayedCall}, and {_postRelayedCall} are not implemented and must be
- * provided by derived contracts. See the
- * xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategies] for more
- * information on how to use the pre-built {GSNRecipientSignature} and
- * {GSNRecipientERC20Fee}, or how to write your own.
- */
-contract GSNRecipient is IRelayRecipient, Context {
-    // Default RelayHub address, deployed on mainnet and all testnets at the same address
-    address private _relayHub = 0xD216153c06E857cD7f72665E0aF1d7D82172F494;
-
-    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;
-
-    /**
-     * @dev Emitted when a contract changes its {IRelayHub} contract to a new one.
-     */
-    event RelayHubChanged(address indexed oldRelayHub, address indexed newRelayHub);
-
-    /**
-     * @dev Returns the address of the {IRelayHub} contract for this recipient.
-     */
-    function getHubAddr() public view returns (address) {
-        return _relayHub;
-    }
-
-    /**
-     * @dev Switches to a new {IRelayHub} instance. This method is added for future-proofing: there's no reason to not
-     * use the default instance.
-     *
-     * IMPORTANT: After upgrading, the {GSNRecipient} will no longer be able to receive relayed calls from the old
-     * {IRelayHub} instance. Additionally, all funds should be previously withdrawn via {_withdrawDeposits}.
-     */
-    function _upgradeRelayHub(address newRelayHub) internal {
-        address currentRelayHub = _relayHub;
-        require(newRelayHub != address(0), "GSNRecipient: new RelayHub is the zero address");
-        require(newRelayHub != currentRelayHub, "GSNRecipient: new RelayHub is the current one");
-
-        emit RelayHubChanged(currentRelayHub, newRelayHub);
-
-        _relayHub = newRelayHub;
-    }
-
-    /**
-     * @dev Returns the version string of the {IRelayHub} for which this recipient implementation was built. If
-     * {_upgradeRelayHub} is used, the new {IRelayHub} instance should be compatible with this version.
-     */
-    // 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";
-    }
-
-    /**
-     * @dev Withdraws the recipient's deposits in `RelayHub`.
-     *
-     * Derived contracts should expose this in an external interface with proper access control.
-     */
-    function _withdrawDeposits(uint256 amount, address payable payee) internal {
-        IRelayHub(_relayHub).withdraw(amount, payee);
-    }
-
-    // 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.
-
-    /**
-     * @dev Replacement for msg.sender. Returns the actual sender of a transaction: msg.sender for regular transactions,
-     * and the end-user for GSN relayed calls (where msg.sender is actually `RelayHub`).
-     *
-     * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.sender`, and use {_msgSender} instead.
-     */
-    function _msgSender() internal view returns (address payable) {
-        if (msg.sender != _relayHub) {
-            return msg.sender;
-        } else {
-            return _getRelayedCallSender();
-        }
-    }
-
-    /**
-     * @dev Replacement for msg.data. Returns the actual calldata of a transaction: msg.data for regular transactions,
-     * and a reduced version for GSN relayed calls (where msg.data contains additional information).
-     *
-     * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.data`, and use {_msgData} instead.
-     */
-    function _msgData() internal view returns (bytes memory) {
-        if (msg.sender != _relayHub) {
-            return msg.data;
-        } else {
-            return _getRelayedCallData();
-        }
-    }
-
-    // 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(), "GSNRecipient: caller is not RelayHub");
-        return _preRelayedCall(context);
-    }
-
-    /**
-     * @dev See `IRelayRecipient.preRelayedCall`.
-     *
-     * Called by `GSNRecipient.preRelayedCall`, which asserts the caller is the `RelayHub` contract. Derived contracts
-     * must implement this function with any relayed-call preprocessing they may wish to do.
-     *
-     */
-    function _preRelayedCall(bytes memory context) internal returns (bytes32);
-
-    /**
-     * @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(), "GSNRecipient: caller is not RelayHub");
-        _postRelayedCall(context, success, actualCharge, preRetVal);
-    }
-
-    /**
-     * @dev See `IRelayRecipient.postRelayedCall`.
-     *
-     * Called by `GSNRecipient.postRelayedCall`, which asserts the caller is the `RelayHub` contract. Derived contracts
-     * must implement this function with any relayed-call postprocessing they may wish to do.
-     *
-     */
-    function _postRelayedCall(bytes memory context, bool success, uint256 actualCharge, bytes32 preRetVal) internal;
-
-    /**
-     * @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 `GSNRecipient._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, "");
-    }
-
-    /*
-     * @dev Calculates how much RelayHub 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;
-    }
-
-    function _getRelayedCallSender() private pure returns (address payable 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/GSNRecipientERC20Fee.sol

@@ -1,151 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "./GSNRecipient.sol";
-import "../math/SafeMath.sol";
-import "../ownership/Secondary.sol";
-import "../token/ERC20/SafeERC20.sol";
-import "../token/ERC20/ERC20.sol";
-import "../token/ERC20/ERC20Detailed.sol";
-
-/**
- * @dev A xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategy] that charges transaction fees in a special purpose ERC20
- * token, which we refer to as the gas payment token. The amount charged is exactly the amount of Ether charged to the
- * recipient. This means that the token is essentially pegged to the value of Ether.
- *
- * The distribution strategy of the gas payment token to users is not defined by this contract. It's a mintable token
- * whose only minter is the recipient, so the strategy must be implemented in a derived contract, making use of the
- * internal {_mint} function.
- */
-contract GSNRecipientERC20Fee is GSNRecipient {
-    using SafeERC20 for __unstable__ERC20PrimaryAdmin;
-    using SafeMath for uint256;
-
-    enum GSNRecipientERC20FeeErrorCodes {
-        INSUFFICIENT_BALANCE
-    }
-
-    __unstable__ERC20PrimaryAdmin private _token;
-
-    /**
-     * @dev The arguments to the constructor are the details that the gas payment token will have: `name` and `symbol`. `decimals` is hard-coded to 18.
-     */
-    constructor(string memory name, string memory symbol) public {
-        _token = new __unstable__ERC20PrimaryAdmin(name, symbol, 18);
-    }
-
-    /**
-     * @dev Returns the gas payment token.
-     */
-    function token() public view returns (IERC20) {
-        return IERC20(_token);
-    }
-
-    /**
-     * @dev Internal function that mints the gas payment token. Derived contracts should expose this function in their public API, with proper access control mechanisms.
-     */
-    function _mint(address account, uint256 amount) internal {
-        _token.mint(account, amount);
-    }
-
-    /**
-     * @dev Ensures that only users with enough gas payment token balance can have transactions relayed through the GSN.
-     */
-    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(GSNRecipientERC20FeeErrorCodes.INSUFFICIENT_BALANCE));
-        }
-
-        return _approveRelayedCall(abi.encode(from, maxPossibleCharge, transactionFee, gasPrice));
-    }
-
-    /**
-     * @dev Implements the precharge to the user. The maximum possible charge (depending on gas limit, gas price, and
-     * fee) will be deducted from the user balance of gas payment token. Note that this is an overestimation of the
-     * actual charge, necessary because we cannot predict how much gas the execution will actually need. The remainder
-     * is returned to the user in {_postRelayedCall}.
-     */
-    function _preRelayedCall(bytes memory context) internal returns (bytes32) {
-        (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);
-    }
-
-    /**
-     * @dev Returns to the user the extra amount that was previously charged, once the actual execution cost is known.
-     */
-    function _postRelayedCall(bytes memory context, bool, uint256 actualCharge, bytes32) internal {
-        (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/GSNRecipientSignature.sol

@@ -1,72 +0,0 @@
-pragma solidity ^0.5.0;
-
-import "./GSNRecipient.sol";
-import "../cryptography/ECDSA.sol";
-
-/**
- * @dev A xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategy] that allows relayed transactions through when they are
- * accompanied by the signature of a trusted signer. The intent is for this signature to be generated by a server that
- * performs validations off-chain. Note that nothing is charged to the user in this scheme. Thus, the server should make
- * sure to account for this in their economic and threat model.
- */
-contract GSNRecipientSignature is GSNRecipient {
-    using ECDSA for bytes32;
-
-    address private _trustedSigner;
-
-    enum GSNRecipientSignatureErrorCodes {
-        INVALID_SIGNER
-    }
-
-    /**
-     * @dev Sets the trusted signer that is going to be producing signatures to approve relayed calls.
-     */
-    constructor(address trustedSigner) public {
-        require(trustedSigner != address(0), "GSNRecipientSignature: trusted signer is the zero address");
-        _trustedSigner = trustedSigner;
-    }
-
-    /**
-     * @dev Ensures that only transactions with a trusted signature can be relayed through the GSN.
-     */
-    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(GSNRecipientSignatureErrorCodes.INVALID_SIGNER));
-        }
-    }
-
-    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
-    }
-}

contracts/GSN/IRelayHub.sol

@@ -1,267 +0,0 @@
-pragma solidity ^0.5.0;
-
-/**
- * @dev Interface for `RelayHub`, the core contract of the GSN. Users should not need to interact with this contract
- * directly.
- *
- * See the https://github.com/OpenZeppelin/openzeppelin-gsn-helpers[OpenZeppelin GSN helpers] for more information on
- * how to deploy an instance of `RelayHub` on your local test network.
- */
-interface IRelayHub {
-    // Relay management
-
-    /**
-     * @dev Adds 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;
-
-    /**
-     * @dev Emitted when a relay's stake or unstakeDelay are increased
-     */
-    event Staked(address indexed relay, uint256 stake, uint256 unstakeDelay);
-
-    /**
-     * @dev 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).
-     *
-     * This function can be called multiple times, emitting new {RelayAdded} events. Note that the received
-     * `transactionFee` is not enforced by {relayCall}.
-     *
-     * Emits a {RelayAdded} event.
-     */
-    function registerRelay(uint256 transactionFee, string calldata url) external;
-
-    /**
-     * @dev 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);
-
-    /**
-     * @dev 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) external;
-
-    /**
-     * @dev 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) external;
-
-    /**
-     * @dev 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
-    }
-
-    /**
-     * @dev Returns a relay's status. Note that relays can be deleted when unstaked or penalized, causing this function
-     * to return an empty entry.
-     */
-    function getRelay(address relay) external view returns (uint256 totalStake, uint256 unstakeDelay, uint256 unstakeTime, address payable owner, RelayState state);
-
-    // Balance management
-
-    /**
-     * @dev 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 calling {withdraw}.
-     *
-     * Emits a {Deposited} event.
-     */
-    function depositFor(address target) external payable;
-
-    /**
-     * @dev Emitted when {depositFor} is called, including the amount and account that was funded.
-     */
-    event Deposited(address indexed recipient, address indexed from, uint256 amount);
-
-    /**
-     * @dev Returns an account's deposits. These can be either a contracts'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 use it to reduce their funding.
-     *
-     * Emits a {Withdrawn} event.
-     */
-    function withdraw(uint256 amount, address payable dest) external;
-
-    /**
-     * @dev Emitted when an account withdraws funds from `RelayHub`.
-     */
-    event Withdrawn(address indexed account, address indexed dest, uint256 amount);
-
-    // Relaying
-
-    /**
-     * @dev Checks 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 calldata encodedFunction,
-        uint256 transactionFee,
-        uint256 gasPrice,
-        uint256 gasLimit,
-        uint256 nonce,
-        bytes calldata signature,
-        bytes calldata approvalData
-    ) external 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
-    }
-
-    /**
-     * @dev Relays a transaction.
-     *
-     * For this to succeed, 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 that order.
-     *
-     * Parameters:
-     *  - `from`: the client originating the request
-     *  - `to`: 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
-     * `RelayHub`, but it still can be used for e.g. a signature.
-     *
-     * Emits a {TransactionRelayed} event.
-     */
-    function relayCall(
-        address from,
-        address to,
-        bytes calldata encodedFunction,
-        uint256 transactionFee,
-        uint256 gasPrice,
-        uint256 gasLimit,
-        uint256 nonce,
-        bytes calldata signature,
-        bytes calldata approvalData
-    ) external;
-
-    /**
-     * @dev 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` parameter 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);
-
-    /**
-     * @dev Emitted when a transaction is relayed. 
-     * Useful when monitoring a relay's operation and relayed calls to a contract
-     *
-     * Note that the actual encoded function might be reverted: this is indicated in the `status` parameter.
-     *
-     * `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
-    }
-
-    /**
-     * @dev 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) external view returns (uint256);
-
-    /**
-     * @dev Returns the maximum recipient charge, given the amount of gas forwarded, gas price and relay fee.
-     */
-    function maxPossibleCharge(uint256 relayedCallStipend, uint256 gasPrice, uint256 transactionFee) external 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.
-
-    /**
-     * @dev 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 calldata unsignedTx1, bytes calldata signature1, bytes calldata unsignedTx2, bytes calldata signature2) external;
-
-    /**
-     * @dev Penalize a relay that sent a transaction that didn't target `RelayHub`'s {registerRelay} or {relayCall}.
-     */
-    function penalizeIllegalTransaction(bytes calldata unsignedTx, bytes calldata signature) external;
-
-    /**
-     * @dev Emitted when a relay is penalized.
-     */
-    event Penalized(address indexed relay, address sender, uint256 amount);
-
-    /**
-     * @dev Returns an account's nonce in `RelayHub`.
-     */
-    function getNonce(address from) external view returns (uint256);
-}
-

contracts/GSN/IRelayRecipient.sol

@@ -1,74 +0,0 @@
-pragma solidity ^0.5.0;
-
-/**
- * @dev Base interface for a contract that will be called via the GSN from {IRelayHub}.
- *
- * TIP: You don't need to write an implementation yourself! Inherit from {GSNRecipient} instead.
- */
-interface IRelayRecipient {
-    /**
-     * @dev Returns the address of the {IRelayHub} instance this recipient interacts with.
-     */
-    function getHubAddr() external view returns (address);
-
-    /**
-     * @dev Called by {IRelayHub} to validate if this recipient accepts being charged for a relayed call. Note that the
-     * recipient will be charged regardless of the execution result of the relayed call (i.e. if it reverts or not).
-     *
-     * The relay request was originated by `from` and will be served by `relay`. `encodedFunction` is the relayed call
-     * calldata, so its first four bytes are the function selector. The relayed call will be forwarded `gasLimit` gas,
-     * and the transaction executed with a gas price of at least `gasPrice`. `relay`'s fee is `transactionFee`, and the
-     * recipient will be charged at most `maxPossibleCharge` (in wei). `nonce` is the sender's (`from`) nonce for
-     * replay attack protection in {IRelayHub}, and `approvalData` is a optional parameter that can be used to hold a signature
-     * over all or some of the previous values.
-     *
-     * Returns a tuple, where the first value is used to indicate approval (0) or rejection (custom non-zero error code,
-     * values 1 to 10 are reserved) and the second one is data to be passed to the other {IRelayRecipient} functions.
-     *
-     * {acceptRelayedCall} is called with 50k gas: if it runs out during execution, the request will be considered
-     * rejected. A regular revert will also trigger a rejection.
-     */
-    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);
-
-    /**
-     * @dev Called by {IRelayHub} on approved relay call requests, before the relayed call is executed. This allows to e.g.
-     * pre-charge the sender of the transaction.
-     *
-     * `context` is the second value returned in the tuple by {acceptRelayedCall}.
-     *
-     * Returns a value to be passed to {postRelayedCall}.
-     *
-     * {preRelayedCall} is called with 100k gas: if it runs out during exection or otherwise reverts, the relayed call
-     * will not be executed, but the recipient will still be charged for the transaction's cost.
-     */
-    function preRelayedCall(bytes calldata context) external returns (bytes32);
-
-    /**
-     * @dev Called by {IRelayHub} on approved relay call requests, after the relayed call is executed. This allows to e.g.
-     * charge the user for the relayed call costs, return any overcharges from {preRelayedCall}, or perform
-     * contract-specific bookkeeping.
-     *
-     * `context` is the second value returned in the tuple by {acceptRelayedCall}. `success` is the execution status of
-     * the relayed call. `actualCharge` is an estimate of how much the recipient will be charged for the transaction,
-     * not including any gas used by {postRelayedCall} itself. `preRetVal` is {preRelayedCall}'s return value.
-     *
-     *
-     * {postRelayedCall} is called with 100k gas: if it runs out during execution or otherwise reverts, the relayed call
-     * and the call to {preRelayedCall} will be reverted retroactively, but the recipient will still be charged for the
-     * transaction's cost.
-     */
-    function postRelayedCall(bytes calldata context, bool success, uint256 actualCharge, bytes32 preRetVal) external;
-}

contracts/GSN/README.adoc

@@ -1,30 +0,0 @@
-= Gas Station Network (GSN)
-
-_Available since v2.4.0._
-
-This set of contracts provide all the tools required to make a contract callable via the https://gsn.openzeppelin.com[Gas Station Network].
-
-TIP: If you're new to the GSN, head over to our xref:learn::sending-gasless-transactions.adoc[overview of the system] and basic guide to xref:ROOT:gsn.adoc[creating a GSN-capable contract].
-
-The core contract a recipient must inherit from is {GSNRecipient}: it includes all necessary interfaces, as well as some helper methods to make interacting with the GSN easier.
-
-Utilities to make writing xref:ROOT:gsn-strategies.adoc[GSN strategies] easy are available in {GSNRecipient}, or you can simply use one of our pre-made strategies:
-
-* {GSNRecipientERC20Fee} charges the end user for gas costs in an application-specific xref:ROOT:tokens.adoc#ERC20[ERC20 token]
-* {GSNRecipientSignature} accepts all relayed calls that have been signed by a trusted third party (e.g. a private key in a backend)
-
-You can also take a look at the two contract interfaces that make up the GSN protocol: {IRelayRecipient} and {IRelayHub}, but you won't need to use those directly.
-
-== Recipient
-
-{{GSNRecipient}}
-
-== Strategies
-
-{{GSNRecipientSignature}}
-{{GSNRecipientERC20Fee}}
-
-== Protocol
-
-{{IRelayRecipient}}
-{{IRelayHub}}

contracts/access/AccessControl.sol

@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/Context.sol";
+
+/**
+ * @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 {
+    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 Returns `true` if `account` has been granted `role`.
+     */
+    function hasRole(bytes32 role, address account) public view 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 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 {
+        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 {
+        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 {
+        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 +1,63 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "./AccessControl.sol";
+import "../utils/structs/EnumerableSet.sol";
+
+/**
+ * @dev Extension of {AccessControl} that allows enumerating the members of each role.
+ */
+abstract contract AccessControlEnumerable is AccessControl {
+    using EnumerableSet for EnumerableSet.AddressSet;
+
+    mapping (bytes32 => EnumerableSet.AddressSet) private _roleMembers;
+
+    /**
+     * @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 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 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 {_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);
@@ -18,7 +23,7 @@ contract Ownable is Context {
     /**
      * @dev Initializes the contract setting the deployer as the initial owner.
      */
-    constructor () internal {
+    constructor () {
         address msgSender = _msgSender();
         _owner = msgSender;
         emit OwnershipTransferred(address(0), msgSender);
@@ -27,7 +32,7 @@ contract Ownable is Context {
     /**
      * @dev Returns the address of the current owner.
      */
-    function owner() public view returns (address) {
+    function owner() public view virtual returns (address) {
         return _owner;
     }
 
@@ -35,17 +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.
@@ -53,7 +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);
     }
@@ -62,14 +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
-
-Contracts in this category should be considered unstable. They are as thoroughly reviewed as everything else in OpenZeppelin Contracts, but we have doubts about their API so we don't commit to backwards compatibility. This means these contracts can receive breaking changes in a minor version, so you should pay special attention to the changelog when upgrading. For anything that is outside of this category you can read more about xref:ROOT:api-stability.adoc[API Stability].
-
-NOTE: This page is incomplete. We're working to improve it for the next release. Stay tuned!
-
-== ERC 20
-
-{{ERC20Migrator}}
-
-{{ERC20Snapshot}}
-
-{{TokenVesting}}
-
-== Miscellaneous
-
-{{Counters}}
-
-{{SignedSafeMath}}
-
-== ERC 1046
-
-{{ERC1046}}

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/governance/README.adoc

@@ -0,0 +1,91 @@
+= Governance
+
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/access
+
+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/lifecycle/README.adoc

@@ -1,5 +0,0 @@
-= Lifecycle
-
-== Pausable
-
-{{Pausable}}

contracts/math/README.adoc

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

contracts/math/SafeMath.sol

@@ -1,156 +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.
-     *
-     * _Available since v2.4.0._
-     */
-    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.
-     *
-     * _Available since v2.4.0._
-     */
-    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.
-     *
-     * _Available since v2.4.0._
-     */
-    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

@@ -1,19 +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 () external payable { } // sendValue's tests require the contract to hold Ether
+    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

@@ -1,23 +1,27 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
 
 import "../utils/Create2.sol";
-import "../token/ERC20/ERC20.sol";
+import "../utils/introspection/ERC1820Implementer.sol";
 
 contract Create2Impl {
-    function deploy(bytes32 salt, bytes memory code) public {
-        Create2.deploy(salt, code);
+    function deploy(uint256 value, bytes32 salt, bytes memory code) public {
+        Create2.deploy(value, salt, code);
     }
 
-    function deployERC20(bytes32 salt) public {
+    function deployERC1820Implementer(uint256 value, bytes32 salt) public {
         // solhint-disable-next-line indent
-        Create2.deploy(salt, type(ERC20).creationCode);
+        Create2.deploy(value, salt, type(ERC1820Implementer).creationCode);
     }
 
-    function computeAddress(bytes32 salt, bytes memory code) public view returns (address) {
-        return Create2.computeAddress(salt, code);
+    function computeAddress(bytes32 salt, bytes32 codeHash) public view returns (address) {
+        return Create2.computeAddress(salt, codeHash);
     }
 
-    function computeAddress(bytes32 salt, bytes memory code, address deployer) public pure returns (address) {
-        return Create2.computeAddress(salt, code, deployer);
+    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]);
         }

contracts/mocks/ERC165/ERC165MissingData.sol

@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+contract ERC165MissingData {
+    function supportsInterface(bytes4 interfaceId) public view {} // missing return
+}

contracts/mocks/ERC165/ERC165NotSupported.sol

@@ -1,5 +1,5 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-contract ERC165NotSupported {
-    // solhint-disable-previous-line no-empty-blocks
-}
+pragma solidity ^0.8.0;
+
+contract ERC165NotSupported { }

contracts/mocks/ERC165CheckerMock.sol

@@ -1,19 +1,25 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-import "../introspection/ERC165Checker.sol";
+pragma solidity ^0.8.0;
+
+import "../utils/introspection/ERC165Checker.sol";
 
 contract ERC165CheckerMock {
     using ERC165Checker for address;
 
     function supportsERC165(address account) public view returns (bool) {
-        return account._supportsERC165();
+        return account.supportsERC165();
     }
 
     function supportsInterface(address account, bytes4 interfaceId) public view returns (bool) {
-        return account._supportsInterface(interfaceId);
+        return account.supportsInterface(interfaceId);
     }
 
     function supportsAllInterfaces(address account, bytes4[] memory interfaceIds) public view returns (bool) {
-        return account._supportsAllInterfaces(interfaceIds);
+        return account.supportsAllInterfaces(interfaceIds);
+    }
+
+    function getSupportedInterfaces(address account, bytes4[] memory interfaceIds) public view returns (bool[] memory) {
+        return account.getSupportedInterfaces(interfaceIds);
     }
 }

contracts/mocks/ERC165Mock.sol

@@ -1,9 +1,8 @@
-pragma solidity ^0.5.0;
+// SPDX-License-Identifier: MIT
 
-import "../introspection/ERC165.sol";
+pragma solidity ^0.8.0;
+
+import "../utils/introspection/ERC165.sol";
 
 contract ERC165Mock is ERC165 {
-    function registerInterface(bytes4 interfaceId) public {
-        _registerInterface(interfaceId);
-    }
 }

contracts/mocks/ERC165StorageMock.sol

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/introspection/ERC165Storage.sol";
+
+contract ERC165StorageMock is ERC165Storage {
+    function registerInterface(bytes4 interfaceId) public {
+        _registerInterface(interfaceId);
+    }
+}