2.3.0

(cherry picked from commit bd13be9174)

.env.example

@@ -1,5 +0,0 @@
-# configure your infura api key (not technically required)
-INFURA_API_KEY=
-
-# change the mnemonic that your hd wallet is seeded with
-MNEMONIC=

.eslintrc

@@ -1,22 +1,23 @@
 {
   "extends" : [
     "standard",
-    "plugin:promise/recommended"
+    "plugin:promise/recommended",
   ],
   "plugins": [
-    "promise"
+    "mocha-no-only",
+    "promise",
   ],
   "env": {
     "browser" : true,
     "node"    : true,
     "mocha"   : true,
-    "jest"    : true
+    "jest"    : true,
   },
   "globals" : {
     "artifacts": false,
     "contract": false,
     "assert": false,
-    "web3": false
+    "web3": false,
   },
   "rules": {
 
@@ -49,6 +50,8 @@
     "semi": ["error", "always"],
     "space-before-function-paren": ["error", "always"],
 
+    "mocha-no-only/mocha-no-only": ["error"],
+
     "promise/always-return": "off",
     "promise/avoid-new": "off",
   }

.github/ISSUE_TEMPLATE.md

@@ -1,34 +0,0 @@
-## 🎉 Description
-
-<!-- Briefly describe the issue you are experiencing (or the feature you want to see added to OpenZeppelin). Tell us what you were trying to do and what happened instead. **Remember, this is _not_ a place to ask for help debugging code; for that, we welcome you in the [OpenZeppelin Slack Channel](https://slack.openzeppelin.org/).** -->
-
-- [ ] 🐛 This is a bug report.
-- [ ] 📈 This is a feature request.
-
-<!-- Please check one of the above by placing an x in the box. -->
-
-## 💻 Environment
-
-Next, we need to know what your environment looks like.
-
-- Which version of OpenZeppelin are you using?
-- What network are you deploying to? Ganache? Ropsten?
-- How are you deploying your OpenZeppelin-backed contracts? truffle? Remix? Let us know!
-
-## 📝 Details
-
-Describe the problem you have been experiencing in more detail. Include as much information as you think is relevant. Keep in mind that transactions can fail for many reasons; context is key here.
-
-## 🔢 Code To Reproduce Issue [ Good To Have ]
-
-Please remember that with sample code it's easier to reproduce the bug and it's much faster to fix it.
-
-```
-insert short code snippets here
-```
-
-<!-- If your code is larger, consider linking us to a repo illustrating your issue. -->
-
-## 👍 Other Information
-
-<!-- List any other information that is relevant to your issue. Error logs, related issues, suggestions on how to fix, Stack Overflow links, forum links, etc. -->

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,21 @@
+---
+name: Bug report
+about: Report a bug in OpenZeppelin
+
+---
+
+<!-- Briefly describe the issue you're experiencing. Tell us what you were trying to do and what happened instead. -->
+
+<!-- Remember, this is not a place to ask for help debugging code. For that, we welcome you in the Zeppelin Forum: https://forum.zeppelin.solutions/. -->
+
+**💻 Environment**
+
+<!-- Tell us what version of OpenZeppelin you're using, and how you're using it: Truffle, Remix, etc. -->
+
+**📝 Details**
+
+<!-- Describe the problem you have been experiencing in more detail. Include as much information as you think is relevant. Keep in mind that transactions can fail for many reasons; context is key here. -->
+
+**🔢 Code to reproduce bug**
+
+<!-- We will be able to better help if you provide a minimal example that triggers the bug. -->

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,14 @@
+---
+name: Feature request
+about: Suggest an idea for OpenZeppelin
+
+---
+
+**🧐 Motivation**
+<!-- Is your feature request related to a specific problem? Is it just a crazy idea? Tell us about it! -->
+
+**📝 Details**
+<!-- Please describe your feature request in detail. -->
+
+<!-- Make sure that you have reviewed the OpenZeppelin Contributor Guidelines. -->
+<!-- https://github.com/OpenZeppelin/openzeppelin-solidity/blob/master/CONTRIBUTING.md -->

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,17 +1,22 @@
 <!-- 0. 🎉 Thank you for submitting a PR! -->
 
-<!-- 1. **Does this close any open issues?** If so, list them here. If not, remove the `Fixes #` line. -->
+<!-- 1. Does this close any open issues? Please list them below. -->
+
+<!-- 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 #
 
-# 🚀 Description
-
-<!-- 2. Describe the changes introduced in this pull request -->
+<!-- 2. Describe the changes introduced in this pull request. -->
 <!--    Include any context necessary for understanding the PR's purpose. -->
 
-<!-- 3. Before submitting, please review the following checklist: -->
-
-- [ ] 📘 I've reviewed the [OpenZeppelin Contributor Guidelines](../blob/master/CONTRIBUTING.md)
-- [ ] ✅ I've added tests where applicable to test my new functionality.
-- [ ] 📖 I've made sure that my contracts are well-documented.
-- [ ] 🎨 I've run the JS/Solidity linters and fixed any issues (`npm run lint:fix`).
+<!-- 3. Before submitting, please make sure that you have:
+  - reviewed the OpenZeppelin Contributor Guidelines
+    (https://github.com/OpenZeppelin/openzeppelin-solidity/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.
+-->

.github/stale.yml

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

.gitignore

@@ -32,8 +32,15 @@ npm-debug.log
 # truffle build directory
 build/
 
-# lol macs
-.DS_Store/
+# macOS
+.DS_Store
 
 # truffle
 .node-xmlhttprequest-*
+
+# IntelliJ IDE
+.idea
+
+# docsite artifacts
+docsite-build
+docs/api

.node-version

@@ -1 +0,0 @@
-v8.9.1

.solhint.json

@@ -0,0 +1,12 @@
+{
+  "extends": "default",
+  "rules": {
+    "indent": ["error", 4],
+    "func-order": false,
+    "bracket-align": false,
+    "compiler-fixed": false,
+    "no-simple-event-func-name": false,
+    "separate-by-one-line-in-contract": false,
+    "two-lines-top-level-separator": false
+  }
+}

.soliumignore

@@ -1 +0,0 @@
-node_modules

.soliumrc.json

@@ -1,21 +0,0 @@
-{
-  "extends": "solium:all",
-  "plugins": ["security"],
-  "rules": {
-    "blank-lines": "off",
-    "error-reason": "off",
-    "indentation": ["error", 2],
-    "lbrace": "off",
-    "linebreak-style": ["error", "unix"],
-    "max-len": ["error", 79],
-    "no-constant": ["error"],
-    "no-empty-blocks": "off",
-    "quotes": ["error", "double"],
-    "uppercase": "off",
-    "visibility-first": "error",
-
-    "security/enforce-explicit-visibility": ["error"],
-    "security/no-block-members": ["warning"],
-    "security/no-inline-assembly": ["warning"]
-  }
-}

.travis.yml

@@ -15,37 +15,25 @@ jobs:
   # --elopio - 20180531
   fast_finish: true
   allow_failures:
-    - env: SOLIDITY_COVERAGE=true
     - env: SOLC_NIGHTLY=true
   include:
-    # Run the unit test suite three times in parallel.
-    # The first one gets results faster and is the only one required to pass.
-    # The second one generates the coverage report.
-    # The third one is to keep us informed about possible issues with the
-    # upcoming solidity release.
     - stage: tests
-      name: "unit tests"
+      name: "Linter"
+      script: npm run lint
+
+    - stage: tests
+      name: "Unit tests"
       script: npm run test
+
     - stage: tests
-      name: "unit tests with coverage"
+      name: "Unit tests with coverage report"
       script: npm run test
       env: SOLIDITY_COVERAGE=true
+
     - stage: tests
-      name: "unit tests with solc nightly"
+      name: "Unit tests using solc nightly"
       script: npm run test
       env: SOLC_NIGHTLY=true
-    # solidity and javascript style tests.
-    - stage: tests
-      name: "static tests"
-      script: npm run lint
-    - stage: update docs
-      if: tag =~ ^v[0-9]+\.[0-9]+\.[0-9]+$
-      addons:
-        apt:
-          packages:
-            - curl
-      script:
-        - ./scripts/ci/trigger_docs_update "${TRAVIS_TAG}"
 
 notifications:
   slack:

CHANGELOG.md

@@ -0,0 +1,74 @@
+# Changelog
+
+## 2.3.0 (2019-05-27)
+
+### New features:
+ * `ERC1820`: added support for interacting with the [ERC1820](https://eips.ethereum.org/EIPS/eip-1820) registry contract (`IERC1820Registry`), as well as base contracts that can be registered as implementers there. ([#1677](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1677))
+ * `ERC777`: support for the [ERC777 token](https://eips.ethereum.org/EIPS/eip-777), which has multiple improvements over `ERC20` (but is backwards compatible with it) such as built-in burning, a more  straightforward permission system, and optional sender and receiver hooks on transfer (mandatory for contracts!). ([#1684](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1684))
+ * All contracts now have revert reason strings, which give insight into error conditions, and help debug failing transactions. ([#1704](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1704))
+
+### Improvements:
+ * Reverted the Solidity version bump done in v2.2.0, setting the minimum compiler version to v0.5.0, to prevent unexpected build breakage. Users are encouraged however to stay on top of new compiler releases, which usually include bugfixes. ([#1729](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1729))
+
+### Bugfixes:
+ * `PostDeliveryCrowdsale`: some validations where skipped when paired with other crowdsale flavors, such as `AllowanceCrowdsale`, or `MintableCrowdsale` and `ERC20Capped`, which could cause buyers to not be able to claim their purchased tokens. ([#1721](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1721))
+ * `ERC20._transfer`: the `from` argument was allowed to be the zero address, so it was possible to internally trigger a transfer of 0 tokens from the zero address. This address is not a valid destinatary of transfers, nor can it give or receive allowance, so this behavior was inconsistent. It now reverts. ([#1752](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1752))
+
+## 2.2.0 (2019-03-14)
+
+### New features:
+ * `ERC20Snapshot`: create snapshots on demand of the token balances and total supply, to later retrieve and e.g. calculate dividends at a past time. ([#1617](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1617))
+ * `SafeERC20`: `ERC20` contracts with no return value (i.e. that revert on failure) are now supported. ([#1655](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1655))
+ * `ERC20`: added internal `_approve(address owner, address spender, uint256 value)`, allowing derived contracts to set the allowance of arbitrary accounts. ([#1609](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1609))
+ * `ERC20Metadata`: added internal `_setTokenURI(string memory tokenURI)`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+ * `TimedCrowdsale`: added internal `_extendTime(uint256 newClosingTime)` as well as `TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime)` event allowing to extend the crowdsale, as long as it hasn't already closed.
+
+### Improvements:
+ * 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))
+ * Fixed variable shadowing issues. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
+
+### Bugfixes:
+ * (minor) `SafeERC20`: `safeApprove` wasn't properly checking for a zero allowance when attempting to set a non-zero allowance. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
+
+### Breaking changes in drafts:
+ * `TokenMetadata` has been renamed to `ERC20Metadata`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+ * The library `Counter` has been renamed to `Counters` and its API has been improved. See an example in `ERC721`, lines [17](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L17) and [204](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L204). ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+
+## 2.1.3 (2019-02-26)
+ * Backported `SafeERC20.safeApprove` bugfix. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
+
+## 2.1.2 (2019-01-17)
+ * Removed most of the test suite from the npm package, except `PublicRole.behavior.js`, which may be useful to users testing their own `Roles`.
+
+## 2.1.1 (2019-01-04)
+ * Version bump to avoid conflict in the npm registry.
+
+## 2.1.0 (2019-01-04)
+
+### New features:
+ * Now targeting the 0.5.x line of Solidity compilers. For 0.4.24 support, use version 2.0 of OpenZeppelin.
+ * `WhitelistCrowdsale`: a crowdsale where only whitelisted accounts (`WhitelistedRole`) can purchase tokens. Adding or removing accounts from the whitelist is done by whitelist admins (`WhitelistAdminRole`). Similar to the pre-2.0 `WhitelistedCrowdsale`. ([#1525](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1525), [#1589](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1589))
+ * `RefundablePostDeliveryCrowdsale`: replacement for `RefundableCrowdsale` (deprecated, see below) where tokens are only granted once the crowdsale ends (if it meets its goal). ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))
+ * `PausableCrowdsale`: allows for pausers (`PauserRole`) to pause token purchases. Other crowdsale operations (e.g. withdrawals and refunds, if applicable) are not affected. ([#832](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/832))
+ * `ERC20`: `transferFrom` and `_burnFrom ` now emit `Approval` events, to represent the token's state comprehensively through events. ([#1524](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1524))
+ * `ERC721`: added `_burn(uint256 tokenId)`, replacing the similar deprecated function (see below). ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
+ * `ERC721`: added `_tokensOfOwner(address owner)`, allowing to internally retrieve the array of an account's owned tokens. ([#1522](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1522))
+ * Crowdsales: all constructors are now `public`, meaning it is not necessary to extend these contracts in order to deploy them. The exception is `FinalizableCrowdsale`, since it is meaningless unless extended. ([#1564](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1564))
+ * `SignedSafeMath`: added overflow-safe operations for signed integers (`int256`). ([#1559](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1559), [#1588](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1588))
+
+### Improvements:
+ * The compiler version required by `Array` was behind the rest of the libray so it was updated to `v0.4.24`. ([#1553](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1553))
+ * Now conforming to a 4-space indentation code style. ([1508](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1508))
+ * `ERC20`: more gas efficient due to removed redundant `require`s. ([#1409](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1409))
+ * `ERC721`: fixed a bug that prevented internal data structures from being properly cleaned, missing potential gas refunds. ([#1539](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1539) and [#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
+ * `ERC721`: general gas savings on `transferFrom`, `_mint` and `_burn`, due to redudant `require`s and `SSTORE`s. ([#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
+
+### Bugfixes:
+
+### Breaking changes:
+
+### Deprecations:
+ * `ERC721._burn(address owner, uint256 tokenId)`: due to the `owner` parameter being unnecessary. ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
+ * `RefundableCrowdsale`: due to trading abuse potential on crowdsales that miss their goal. ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))

DOCUMENTATION.md

@@ -0,0 +1,19 @@
+We're building an improved documentation website. It's still in development and
+contributions will be really appreciated.
+
+All of the content for the site is in this repository. The guides are in the
+[docs](/docs) directory, and the API Reference is extracted from comments in
+the source code. If you want to help improve the content, this is the
+repository you should be contributing to.
+
+[`solidity-docgen`](https://github.com/OpenZeppelin/solidity-docgen/tree/next) is the
+program that extracts the API Reference from source code.
+
+The [`openzeppelin-docsite`](https://github.com/OpenZeppelin/openzeppelin-docsite/tree/next)
+repository hosts the configuration for Docusaurus, the static site generator
+that we use.
+
+To run the docsite locally you should run `npm run docsite start` on this
+repository. This will live reload as the guides are edited, but not with
+changes to the source code comments, for that you need to restart the server.
+This should be improved eventually (contributions welcome!).

LICENSE

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2016 Smart Contract Solutions, Inc.
+Copyright (c) 2016-2019 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

@@ -1,8 +1,8 @@
 # <img src="logo.png" alt="OpenZeppelin" width="400px">
 
 [![NPM Package](https://img.shields.io/npm/v/openzeppelin-solidity.svg?style=flat-square)](https://www.npmjs.org/package/openzeppelin-solidity)
-[![Build Status](https://img.shields.io/travis/OpenZeppelin/openzeppelin-solidity.svg?branch=master&style=flat-square)](https://travis-ci.org/OpenZeppelin/openzeppelin-solidity)
-[![Coverage Status](https://img.shields.io/coveralls/github/OpenZeppelin/openzeppelin-solidity/master.svg?style=flat-square)](https://coveralls.io/github/OpenZeppelin/openzeppelin-solidity?branch=master)
+[![Build Status](https://travis-ci.com/OpenZeppelin/openzeppelin-solidity.svg?branch=master)](https://travis-ci.com/OpenZeppelin/openzeppelin-solidity)
+[![Coverage Status](https://coveralls.io/repos/github/OpenZeppelin/openzeppelin-solidity/badge.svg?branch=master)](https://coveralls.io/github/OpenZeppelin/openzeppelin-solidity?branch=master)
 
 **OpenZeppelin is a library for secure smart contract development.** It provides implementations of standards like ERC20 and ERC721 which you can deploy as-is or extend to suit your needs, as well as Solidity components to build custom contracts and more complex decentralized systems.
 
@@ -12,12 +12,14 @@
 npm install openzeppelin-solidity
 ```
 
+OpenZeppelin features a stable API, which means your contracts won't break unexpectedly when upgrading to a newer minor version. You can read ṫhe details in our [API Stability](https://forum.zeppelin.solutions/t/api-stability/138) document.
+
 ## Usage
 
 To write your custom contracts, import ours and extend them through inheritance.
 
 ```solidity
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import 'openzeppelin-solidity/contracts/token/ERC721/ERC721Full.sol';
 import 'openzeppelin-solidity/contracts/token/ERC721/ERC721Mintable.sol';
@@ -28,9 +30,9 @@ contract MyNFT is ERC721Full, ERC721Mintable {
 }
 ```
 
-> You need an ethereum development framework for the above import statements to work! Check out these guides for [Truffle] or [Embark].
+> You need an ethereum development framework for the above import statements to work! Check out these guides for [Truffle], [Embark] or [Buidler].
 
-On our site you will find a few [guides] to learn about the diferent parts of OpenZeppelin, as well as [documentation for the API][API docs]. Keep in mind that the API docs are work in progress, and don’t hesitate to ask questions in [our Slack][Slack].
+On our site you will find a few [guides] to learn about the different parts of OpenZeppelin, as well as [documentation for the API][API docs]. Keep in mind that the API docs are work in progress, and don’t hesitate to ask questions in [our forum][forum].
 
 ## Security
 
@@ -38,6 +40,8 @@ OpenZeppelin the project is maintained by [Zeppelin] the company, and developed
 
 The core development principles and strategies that OpenZeppelin is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.
 
+The latest audit was done on October 2018 on version 2.0.0.
+
 Please report any security issues you find to security@openzeppelin.org.
 
 ## Contribute
@@ -51,8 +55,9 @@ OpenZeppelin is released under the [MIT License](LICENSE).
 
 [API docs]: https://openzeppelin.org/api/docs/token_ERC721_ERC721BasicToken.html
 [guides]: https://openzeppelin.org/api/docs/get-started.html
-[Slack]: https://slack.openzeppelin.org
+[forum]: https://forum.zeppelin.solutions
 [Zeppelin]: https://zeppelin.solutions
 [contribution guide]: CONTRIBUTING.md
 [Truffle]: https://truffleframework.com/docs/truffle/quickstart
 [Embark]: https://embark.status.im/docs/quick_start.html
+[Buidler]: https://buidler.dev/guides/#getting-started

RELEASING.md

@@ -34,13 +34,13 @@ git push upstream vX.Y.Z-rc.R
 
 Draft the release notes in our [GitHub releases](https://github.com/OpenZeppelin/openzeppelin-solidity/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.
+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 ask our community manager to announce the release candidate on at least Slack and Twitter.
+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
 
@@ -51,18 +51,21 @@ 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.
+Once the CI run for the new tag is green, publish on npm. You should see the contracts compile automatically.
 
 ```
 npm publish

contracts/.npmignore

@@ -1,2 +0,0 @@
-mocks
-examples

contracts/access/README.md

@@ -0,0 +1,9 @@
+---
+sections:
+  - title: Library
+    contracts:
+      - Roles
+  - subdirectory: roles
+---
+
+> This page is incomplete. We're working to improve it for the next release. Stay tuned!

contracts/access/Roles.sol

@@ -1,44 +1,36 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 /**
  * @title Roles
  * @dev Library for managing addresses assigned to a Role.
  */
 library Roles {
-  struct Role {
-    mapping (address => bool) bearer;
-  }
+    struct Role {
+        mapping (address => bool) bearer;
+    }
 
-  /**
-   * @dev give an account access to this role
-   */
-  function add(Role storage role, address account) internal {
-    require(account != address(0));
-    require(!has(role, account));
+    /**
+     * @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;
+    }
 
-    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 remove an account's access to this role
-   */
-  function remove(Role storage role, address account) internal {
-    require(account != address(0));
-    require(has(role, account));
-
-    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));
-    return role.bearer[account];
-  }
+    /**
+     * @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

@@ -1,43 +1,43 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../Roles.sol";
 
 contract CapperRole {
-  using Roles for Roles.Role;
+    using Roles for Roles.Role;
 
-  event CapperAdded(address indexed account);
-  event CapperRemoved(address indexed account);
+    event CapperAdded(address indexed account);
+    event CapperRemoved(address indexed account);
 
-  Roles.Role private cappers;
+    Roles.Role private _cappers;
 
-  constructor() internal {
-    _addCapper(msg.sender);
-  }
+    constructor () internal {
+        _addCapper(msg.sender);
+    }
 
-  modifier onlyCapper() {
-    require(isCapper(msg.sender));
-    _;
-  }
+    modifier onlyCapper() {
+        require(isCapper(msg.sender), "CapperRole: caller does not have the Capper role");
+        _;
+    }
 
-  function isCapper(address account) public view returns (bool) {
-    return cappers.has(account);
-  }
+    function isCapper(address account) public view returns (bool) {
+        return _cappers.has(account);
+    }
 
-  function addCapper(address account) public onlyCapper {
-    _addCapper(account);
-  }
+    function addCapper(address account) public onlyCapper {
+        _addCapper(account);
+    }
 
-  function renounceCapper() public {
-    _removeCapper(msg.sender);
-  }
+    function renounceCapper() public {
+        _removeCapper(msg.sender);
+    }
 
-  function _addCapper(address account) internal {
-    cappers.add(account);
-    emit CapperAdded(account);
-  }
+    function _addCapper(address account) internal {
+        _cappers.add(account);
+        emit CapperAdded(account);
+    }
 
-  function _removeCapper(address account) internal {
-    cappers.remove(account);
-    emit CapperRemoved(account);
-  }
+    function _removeCapper(address account) internal {
+        _cappers.remove(account);
+        emit CapperRemoved(account);
+    }
 }

contracts/access/roles/MinterRole.sol

@@ -1,43 +1,43 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../Roles.sol";
 
 contract MinterRole {
-  using Roles for Roles.Role;
+    using Roles for Roles.Role;
 
-  event MinterAdded(address indexed account);
-  event MinterRemoved(address indexed account);
+    event MinterAdded(address indexed account);
+    event MinterRemoved(address indexed account);
 
-  Roles.Role private minters;
+    Roles.Role private _minters;
 
-  constructor() internal {
-    _addMinter(msg.sender);
-  }
+    constructor () internal {
+        _addMinter(msg.sender);
+    }
 
-  modifier onlyMinter() {
-    require(isMinter(msg.sender));
-    _;
-  }
+    modifier onlyMinter() {
+        require(isMinter(msg.sender), "MinterRole: caller does not have the Minter role");
+        _;
+    }
 
-  function isMinter(address account) public view returns (bool) {
-    return minters.has(account);
-  }
+    function isMinter(address account) public view returns (bool) {
+        return _minters.has(account);
+    }
 
-  function addMinter(address account) public onlyMinter {
-    _addMinter(account);
-  }
+    function addMinter(address account) public onlyMinter {
+        _addMinter(account);
+    }
 
-  function renounceMinter() public {
-    _removeMinter(msg.sender);
-  }
+    function renounceMinter() public {
+        _removeMinter(msg.sender);
+    }
 
-  function _addMinter(address account) internal {
-    minters.add(account);
-    emit MinterAdded(account);
-  }
+    function _addMinter(address account) internal {
+        _minters.add(account);
+        emit MinterAdded(account);
+    }
 
-  function _removeMinter(address account) internal {
-    minters.remove(account);
-    emit MinterRemoved(account);
-  }
+    function _removeMinter(address account) internal {
+        _minters.remove(account);
+        emit MinterRemoved(account);
+    }
 }

contracts/access/roles/PauserRole.sol

@@ -1,43 +1,43 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../Roles.sol";
 
 contract PauserRole {
-  using Roles for Roles.Role;
+    using Roles for Roles.Role;
 
-  event PauserAdded(address indexed account);
-  event PauserRemoved(address indexed account);
+    event PauserAdded(address indexed account);
+    event PauserRemoved(address indexed account);
 
-  Roles.Role private pausers;
+    Roles.Role private _pausers;
 
-  constructor() internal {
-    _addPauser(msg.sender);
-  }
+    constructor () internal {
+        _addPauser(msg.sender);
+    }
 
-  modifier onlyPauser() {
-    require(isPauser(msg.sender));
-    _;
-  }
+    modifier onlyPauser() {
+        require(isPauser(msg.sender), "PauserRole: caller does not have the Pauser role");
+        _;
+    }
 
-  function isPauser(address account) public view returns (bool) {
-    return pausers.has(account);
-  }
+    function isPauser(address account) public view returns (bool) {
+        return _pausers.has(account);
+    }
 
-  function addPauser(address account) public onlyPauser {
-    _addPauser(account);
-  }
+    function addPauser(address account) public onlyPauser {
+        _addPauser(account);
+    }
 
-  function renouncePauser() public {
-    _removePauser(msg.sender);
-  }
+    function renouncePauser() public {
+        _removePauser(msg.sender);
+    }
 
-  function _addPauser(address account) internal {
-    pausers.add(account);
-    emit PauserAdded(account);
-  }
+    function _addPauser(address account) internal {
+        _pausers.add(account);
+        emit PauserAdded(account);
+    }
 
-  function _removePauser(address account) internal {
-    pausers.remove(account);
-    emit PauserRemoved(account);
-  }
+    function _removePauser(address account) internal {
+        _pausers.remove(account);
+        emit PauserRemoved(account);
+    }
 }

contracts/access/roles/SignerRole.sol

@@ -1,43 +1,43 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../Roles.sol";
 
 contract SignerRole {
-  using Roles for Roles.Role;
+    using Roles for Roles.Role;
 
-  event SignerAdded(address indexed account);
-  event SignerRemoved(address indexed account);
+    event SignerAdded(address indexed account);
+    event SignerRemoved(address indexed account);
 
-  Roles.Role private signers;
+    Roles.Role private _signers;
 
-  constructor() internal {
-    _addSigner(msg.sender);
-  }
+    constructor () internal {
+        _addSigner(msg.sender);
+    }
 
-  modifier onlySigner() {
-    require(isSigner(msg.sender));
-    _;
-  }
+    modifier onlySigner() {
+        require(isSigner(msg.sender), "SignerRole: caller does not have the Signer role");
+        _;
+    }
 
-  function isSigner(address account) public view returns (bool) {
-    return signers.has(account);
-  }
+    function isSigner(address account) public view returns (bool) {
+        return _signers.has(account);
+    }
 
-  function addSigner(address account) public onlySigner {
-    _addSigner(account);
-  }
+    function addSigner(address account) public onlySigner {
+        _addSigner(account);
+    }
 
-  function renounceSigner() public {
-    _removeSigner(msg.sender);
-  }
+    function renounceSigner() public {
+        _removeSigner(msg.sender);
+    }
 
-  function _addSigner(address account) internal {
-    signers.add(account);
-    emit SignerAdded(account);
-  }
+    function _addSigner(address account) internal {
+        _signers.add(account);
+        emit SignerAdded(account);
+    }
 
-  function _removeSigner(address account) internal {
-    signers.remove(account);
-    emit SignerRemoved(account);
-  }
+    function _removeSigner(address account) internal {
+        _signers.remove(account);
+        emit SignerRemoved(account);
+    }
 }

contracts/access/roles/WhitelistAdminRole.sol

@@ -0,0 +1,47 @@
+pragma solidity ^0.5.0;
+
+import "../Roles.sol";
+
+/**
+ * @title WhitelistAdminRole
+ * @dev WhitelistAdmins are responsible for assigning and removing Whitelisted accounts.
+ */
+contract WhitelistAdminRole {
+    using Roles for Roles.Role;
+
+    event WhitelistAdminAdded(address indexed account);
+    event WhitelistAdminRemoved(address indexed account);
+
+    Roles.Role private _whitelistAdmins;
+
+    constructor () internal {
+        _addWhitelistAdmin(msg.sender);
+    }
+
+    modifier onlyWhitelistAdmin() {
+        require(isWhitelistAdmin(msg.sender), "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(msg.sender);
+    }
+
+    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

@@ -0,0 +1,50 @@
+pragma solidity ^0.5.0;
+
+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 WhitelistAdminRole {
+    using Roles for Roles.Role;
+
+    event WhitelistedAdded(address indexed account);
+    event WhitelistedRemoved(address indexed account);
+
+    Roles.Role private _whitelisteds;
+
+    modifier onlyWhitelisted() {
+        require(isWhitelisted(msg.sender), "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(msg.sender);
+    }
+
+    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

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/IERC20.sol";
 import "../math/SafeMath.sol";
@@ -11,231 +11,188 @@ import "../utils/ReentrancyGuard.sol";
  * 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 conform
- * the base architecture for crowdsales. They are *not* intended to be modified / overridden.
+ * 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 ReentrancyGuard {
-  using SafeMath for uint256;
-  using SafeERC20 for IERC20;
+    using SafeMath for uint256;
+    using SafeERC20 for IERC20;
 
-  // The token being sold
-  IERC20 private _token;
+    // The token being sold
+    IERC20 private _token;
 
-  // Address where funds are collected
-  address private _wallet;
+    // 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;
+    // 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;
+    // 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
-  );
+    /**
+     * 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 wallet, IERC20 token) internal {
-    require(rate > 0);
-    require(wallet != address(0));
-    require(token != address(0));
+    /**
+     * @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;
-  }
+        _rate = rate;
+        _wallet = wallet;
+        _token = token;
+    }
 
-  // -----------------------------------------
-  // Crowdsale external interface
-  // -----------------------------------------
+    /**
+     * @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(msg.sender);
+    }
 
-  /**
-   * @dev fallback function ***DO NOT OVERRIDE***
-   * Note that other contracts will transfer fund 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(msg.sender);
-  }
+    /**
+     * @return the token being sold.
+     */
+    function token() public view returns (IERC20) {
+        return _token;
+    }
 
-  /**
-   * @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 address where funds are collected.
-   */
-  function wallet() public view returns(address) {
-    return _wallet;
-  }
+    /**
+     * @return the number of token units a buyer gets per wei.
+     */
+    function rate() public view returns (uint256) {
+        return _rate;
+    }
 
-  /**
-   * @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;
+    }
 
-  /**
-   * @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);
 
-  /**
-   * @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 {
+        // calculate token amount to be created
+        uint256 tokens = _getTokenAmount(weiAmount);
 
-    uint256 weiAmount = msg.value;
-    _preValidatePurchase(beneficiary, weiAmount);
+        // update state
+        _weiRaised = _weiRaised.add(weiAmount);
 
-    // calculate token amount to be created
-    uint256 tokens = _getTokenAmount(weiAmount);
+        _processPurchase(beneficiary, tokens);
+        emit TokensPurchased(msg.sender, beneficiary, weiAmount, tokens);
 
-    // update state
-    _weiRaised = _weiRaised.add(weiAmount);
+        _updatePurchasingState(beneficiary, weiAmount);
 
-    _processPurchase(beneficiary, tokens);
-    emit TokensPurchased(
-      msg.sender,
-      beneficiary,
-      weiAmount,
-      tokens
-    );
+        _forwardFunds();
+        _postValidatePurchase(beneficiary, weiAmount);
+    }
 
-    _updatePurchasingState(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");
+    }
 
-    _forwardFunds();
-    _postValidatePurchase(beneficiary, weiAmount);
-  }
+    /**
+     * @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
+    }
 
-  // -----------------------------------------
-  // Internal interface (extensible)
-  // -----------------------------------------
+    /**
+     * @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 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));
-    require(weiAmount != 0);
-  }
+    /**
+     * @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 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
-  {
-    // optional override
-  }
+    /**
+     * @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 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 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 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
-  {
-    // optional override
-  }
-
-  /**
-   * @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);
-  }
+    /**
+     * @dev Determines how ETH is stored/forwarded on purchases.
+     */
+    function _forwardFunds() internal {
+        _wallet.transfer(msg.value);
+    }
 }

contracts/crowdsale/README.md

@@ -0,0 +1,13 @@
+---
+title: Crowdsales
+sections:
+  - title: Core
+    contracts:
+      - Crowdsale
+  - subdirectory: emission
+  - subdirectory: price
+  - subdirectory: validation
+  - subdirectory: distribution
+---
+
+> This page is incomplete. We're working to improve it for the next release. Stay tuned!

contracts/crowdsale/distribution/FinalizableCrowdsale.sol

@@ -1,50 +1,51 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../../math/SafeMath.sol";
 import "../validation/TimedCrowdsale.sol";
 
 /**
  * @title FinalizableCrowdsale
- * @dev Extension of Crowdsale with a one-off finalization action, where one
+ * @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;
+    using SafeMath for uint256;
 
-  bool private _finalized;
+    bool private _finalized;
 
-  event CrowdsaleFinalized();
+    event CrowdsaleFinalized();
 
-  constructor() internal {
-    _finalized = false;
-  }
+    constructor () internal {
+        _finalized = false;
+    }
 
-  /**
-   * @return true if the crowdsale is finalized, false otherwise.
-   */
-  function finalized() public view returns (bool) {
-    return _finalized;
-  }
+    /**
+     * @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);
-    require(hasClosed());
+    /**
+     * @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;
+        _finalized = true;
 
-    _finalization();
-    emit CrowdsaleFinalized();
-  }
+        _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 {
-  }
+    /**
+     * @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

@@ -1,50 +1,65 @@
-pragma solidity ^0.4.24;
+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;
+    using SafeMath for uint256;
 
-  mapping(address => uint256) private _balances;
+    mapping(address => uint256) private _balances;
+    __unstable__TokenVault private _vault;
 
-  constructor() internal {}
+    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());
-    uint256 amount = _balances[beneficiary];
-    require(amount > 0);
-    _balances[beneficiary] = 0;
-    _deliverTokens(beneficiary, amount);
-  }
+    /**
+     * @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");
 
-  /**
-   * @return the balance of an account.
-   */
-  function balanceOf(address account) public view returns(uint256) {
-    return _balances[account];
-  }
+        _balances[beneficiary] = 0;
+        _vault.transfer(token(), beneficiary, amount);
+    }
 
-  /**
-   * @dev Overrides parent by storing balances instead of issuing tokens right away.
-   * @param beneficiary Token purchaser
-   * @param tokenAmount Amount of tokens purchased
-   */
-  function _processPurchase(
-    address beneficiary,
-    uint256 tokenAmount
-  )
-    internal
-  {
-    _balances[beneficiary] = _balances[beneficiary].add(tokenAmount);
-  }
+    /**
+     * @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

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../../math/SafeMath.sol";
 import "./FinalizableCrowdsale.sol";
@@ -6,86 +6,77 @@ import "../../payment/escrow/RefundEscrow.sol";
 
 /**
  * @title RefundableCrowdsale
- * @dev Extension of Crowdsale contract that adds a funding goal, and
- * the possibility of users getting a refund if goal is not met.
- * WARNING: 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. There are many possible ways to avoid this, like making the
- * the crowdsale inherit from PostDeliveryCrowdsale, or imposing 
- * restrictions on token trading until the crowdsale is finalized.
- * This is being discussed in 
- * https://github.com/OpenZeppelin/openzeppelin-solidity/issues/877
- * This contract will be updated when we agree on a general solution
- * for this problem.
+ * @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 FinalizableCrowdsale {
-  using SafeMath for uint256;
+    using SafeMath for uint256;
 
-  // minimum amount of funds to be raised in weis
-  uint256 private _goal;
+    // 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;
+    // refund escrow used to hold funds while crowdsale is running
+    RefundEscrow private _escrow;
 
-  /**
-   * @dev Constructor, creates RefundEscrow.
-   * @param goal Funding goal
-   */
-  constructor(uint256 goal) internal {
-    require(goal > 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 beneficiary Whose refund will be claimed.
-   */
-  function claimRefund(address beneficiary) public {
-    require(finalized());
-    require(!goalReached());
-
-    _escrow.withdraw(beneficiary);
-  }
-
-  /**
-   * @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();
+    /**
+     * @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;
     }
 
-    super._finalization();
-  }
+    /**
+     * @return minimum amount of funds to be raised in wei.
+     */
+    function goal() public view returns (uint256) {
+        return _goal;
+    }
 
-  /**
-   * @dev Overrides Crowdsale fund forwarding, sending funds to escrow.
-   */
-  function _forwardFunds() internal {
-    _escrow.deposit.value(msg.value)(msg.sender);
-  }
+    /**
+     * @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)(msg.sender);
+    }
 }

contracts/crowdsale/distribution/RefundablePostDeliveryCrowdsale.sol

@@ -0,0 +1,20 @@
+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

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../Crowdsale.sol";
 import "../../token/ERC20/IERC20.sol";
@@ -11,49 +11,41 @@ import "../../math/Math.sol";
  * @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;
+    using SafeMath for uint256;
+    using SafeERC20 for IERC20;
 
-  address private _tokenWallet;
+    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) internal {
-    require(tokenWallet != address(0));
-    _tokenWallet = 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;
-  }
+    /**
+     * @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, this)
-    );
-  }
+    /**
+     * @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);
-  }
+    /**
+     * @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

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../Crowdsale.sol";
 import "../../token/ERC20/ERC20Mintable.sol";
@@ -9,21 +9,16 @@ import "../../token/ERC20/ERC20Mintable.sol";
  * Token ownership should be transferred to MintedCrowdsale for minting.
  */
 contract MintedCrowdsale is Crowdsale {
-  constructor() internal {}
-
-  /**
-   * @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));
-  }
+    /**
+     * @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

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../validation/TimedCrowdsale.sol";
 import "../../math/SafeMath.sol";
@@ -10,72 +10,70 @@ import "../../math/SafeMath.sol";
  * 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;
+    using SafeMath for uint256;
 
-  uint256 private _initialRate;
-  uint256 private _finalRate;
+    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) internal {
-    require(finalRate > 0);
-    require(initialRate > finalRate);
-    _initialRate = initialRate;
-    _finalRate = finalRate;
-  }
-
-  /**
-   * The base rate function is overridden to revert, since this crowdsale doens't use it, and
-   * all calls to it are a mistake.
-   */
-  function rate() public view returns(uint256) {
-    revert();
-  }
-
-  /**
-   * @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;
+    /**
+     * @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;
     }
 
-    // solium-disable-next-line security/no-block-members
-    uint256 elapsedTime = block.timestamp.sub(openingTime());
-    uint256 timeRange = closingTime().sub(openingTime());
-    uint256 rateRange = _initialRate.sub(_finalRate);
-    return _initialRate.sub(elapsedTime.mul(rateRange).div(timeRange));
-  }
+    /**
+     * 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");
+    }
 
-  /**
-   * @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);
-  }
+    /**
+     * @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

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../../math/SafeMath.sol";
 import "../Crowdsale.sol";
@@ -8,48 +8,41 @@ import "../Crowdsale.sol";
  * @dev Crowdsale with a limit for total contributions.
  */
 contract CappedCrowdsale is Crowdsale {
-  using SafeMath for uint256;
+    using SafeMath for uint256;
 
-  uint256 private _cap;
+    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) internal {
-    require(cap > 0);
-    _cap = 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;
-  }
+    /**
+     * @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);
-  }
+    /**
+     * @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

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../../math/SafeMath.sol";
 import "../Crowdsale.sol";
@@ -9,73 +9,56 @@ import "../../access/roles/CapperRole.sol";
  * @dev Crowdsale with per-beneficiary caps.
  */
 contract IndividuallyCappedCrowdsale is Crowdsale, CapperRole {
-  using SafeMath for uint256;
+    using SafeMath for uint256;
 
-  mapping(address => uint256) private _contributions;
-  mapping(address => uint256) private _caps;
+    mapping(address => uint256) private _contributions;
+    mapping(address => uint256) private _caps;
 
-  constructor() internal {}
+    /**
+     * @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 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 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 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);
-    require(
-      _contributions[beneficiary].add(weiAmount) <= _caps[beneficiary]);
-  }
-
-  /**
-   * @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);
-  }
+    /**
+     * @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

@@ -0,0 +1,21 @@
+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

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../../math/SafeMath.sol";
 import "../Crowdsale.sol";
@@ -8,78 +8,91 @@ import "../Crowdsale.sol";
  * @dev Crowdsale accepting contributions only within a time frame.
  */
 contract TimedCrowdsale is Crowdsale {
-  using SafeMath for uint256;
+    using SafeMath for uint256;
 
-  uint256 private _openingTime;
-  uint256 private _closingTime;
+    uint256 private _openingTime;
+    uint256 private _closingTime;
 
-  /**
-   * @dev Reverts if not in crowdsale time range.
-   */
-  modifier onlyWhileOpen {
-    require(isOpen());
-    _;
-  }
+    /**
+     * Event for crowdsale extending
+     * @param newClosingTime new closing time
+     * @param prevClosingTime old closing time
+     */
+    event TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime);
 
-  /**
-   * @dev Constructor, takes crowdsale opening and closing times.
-   * @param openingTime Crowdsale opening time
-   * @param closingTime Crowdsale closing time
-   */
-  constructor(uint256 openingTime, uint256 closingTime) internal {
-    // solium-disable-next-line security/no-block-members
-    require(openingTime >= block.timestamp);
-    require(closingTime > openingTime);
+    /**
+     * @dev Reverts if not in crowdsale time range.
+     */
+    modifier onlyWhileOpen {
+        require(isOpen(), "TimedCrowdsale: not open");
+        _;
+    }
 
-    _openingTime = openingTime;
-    _closingTime = closingTime;
-  }
+    /**
+     * @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");
 
-  /**
-   * @return the crowdsale opening time.
-   */
-  function openingTime() public view returns(uint256) {
-    return _openingTime;
-  }
+        _openingTime = openingTime;
+        _closingTime = closingTime;
+    }
 
-  /**
-   * @return the crowdsale closing time.
-   */
-  function closingTime() public view returns(uint256) {
-    return _closingTime;
-  }
+    /**
+     * @return the crowdsale opening time.
+     */
+    function openingTime() public view returns (uint256) {
+        return _openingTime;
+    }
 
-  /**
-   * @return true if the crowdsale is open, false otherwise.
-   */
-  function isOpen() public view returns (bool) {
-    // solium-disable-next-line security/no-block-members
-    return block.timestamp >= _openingTime && block.timestamp <= _closingTime;
-  }
+    /**
+     * @return the crowdsale closing time.
+     */
+    function closingTime() public view returns (uint256) {
+        return _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) {
-    // solium-disable-next-line security/no-block-members
-    return block.timestamp > _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 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 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

@@ -0,0 +1,21 @@
+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/ECDSA.sol

@@ -1,71 +1,82 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 /**
- * @title Elliptic curve signature operations
- * @dev Based on https://gist.github.com/axic/5b33912c6f61ae6fd96d6c4a47afde6d
- * TODO Remove this library once solidity supports passing a signature to ecrecover.
- * See https://github.com/ethereum/solidity/issues/864
+ * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.
+ *
+ * These functions can be used to verify that a message was signed by the holder
+ * of the private keys of a given address.
  */
-
 library ECDSA {
+    /**
+     * @dev Returns the address that signed a hashed message (`hash`) with
+     * `signature`. This address can then be used for verification purposes.
+     *
+     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:
+     * this function rejects them by requiring the `s` value to be in the lower
+     * half order, and the `v` value to be either 27 or 28.
+     *
+     * (.note) This call _does not revert_ if the signature is invalid, or
+     * if the signer is otherwise unable to be retrieved. In those scenarios,
+     * the zero address is returned.
+     *
+     * (.warning) `hash` _must_ be the result of a hash operation for the
+     * verification to be secure: it is possible to craft signatures that
+     * recover to arbitrary addresses for non-hashed data. A safe way to ensure
+     * this is by receiving a hash of the original message (which may otherwise)
+     * be too long), and then calling `toEthSignedMessageHash` on it.
+     */
+    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
+        // Check the signature length
+        if (signature.length != 65) {
+            return (address(0));
+        }
 
-  /**
-   * @dev Recover signer address from a message by using their signature
-   * @param hash bytes32 message, the hash is the signed message. What is recovered is the signer address.
-   * @param signature bytes signature, the signature is generated using web3.eth.sign()
-   */
-  function recover(bytes32 hash, bytes signature)
-    internal
-    pure
-    returns (address)
-  {
-    bytes32 r;
-    bytes32 s;
-    uint8 v;
+        // Divide the signature in r, s and v variables
+        bytes32 r;
+        bytes32 s;
+        uint8 v;
 
-    // Check the signature length
-    if (signature.length != 65) {
-      return (address(0));
+        // ecrecover takes the signature parameters, and the only way to get them
+        // currently is to use assembly.
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            r := mload(add(signature, 0x20))
+            s := mload(add(signature, 0x40))
+            v := byte(0, mload(add(signature, 0x60)))
+        }
+
+        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
+        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
+        // the valid range for s in (281): 0 < s < secp256k1n ÷ 2 + 1, and for v in (282): v ∈ {27, 28}. Most
+        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
+        //
+        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
+        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
+        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
+        // these malleable signatures as well.
+        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) {
+            return address(0);
+        }
+
+        if (v != 27 && v != 28) {
+            return address(0);
+        }
+
+        // If the signature is valid (and not malleable), return the signer address
+        return ecrecover(hash, v, r, s);
     }
 
-    // Divide the signature in r, s and v variables
-    // ecrecover takes the signature parameters, and the only way to get them
-    // currently is to use assembly.
-    // solium-disable-next-line security/no-inline-assembly
-    assembly {
-      r := mload(add(signature, 0x20))
-      s := mload(add(signature, 0x40))
-      v := byte(0, mload(add(signature, 0x60)))
+    /**
+     * @dev Returns an Ethereum Signed Message, created from a `hash`. This
+     * replicates the behavior of the
+     * [`eth_sign`](https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign)
+     * JSON-RPC method.
+     *
+     * See `recover`.
+     */
+    function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
+        // 32 is the length in bytes of hash,
+        // enforced by the type signature above
+        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
     }
-
-    // Version of signature should be 27 or 28, but 0 and 1 are also possible versions
-    if (v < 27) {
-      v += 27;
-    }
-
-    // If the version is correct return the signer address
-    if (v != 27 && v != 28) {
-      return (address(0));
-    } else {
-      // solium-disable-next-line arg-overflow
-      return ecrecover(hash, v, r, s);
-    }
-  }
-
-  /**
-   * toEthSignedMessageHash
-   * @dev prefix a bytes32 value with "\x19Ethereum Signed Message:"
-   * and hash the result
-   */
-  function toEthSignedMessageHash(bytes32 hash)
-    internal
-    pure
-    returns (bytes32)
-  {
-    // 32 is the length in bytes of hash,
-    // enforced by the type signature above
-    return keccak256(
-      abi.encodePacked("\x19Ethereum Signed Message:\n32", hash)
-    );
-  }
 }

contracts/cryptography/MerkleProof.sol

@@ -1,42 +1,31 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 /**
- * @title MerkleProof
- * @dev Merkle proof verification based on
- * https://github.com/ameensol/merkle-tree-solidity/blob/master/src/MerkleProof.sol
+ * @dev These functions deal with verification of Merkle trees (hash trees),
  */
 library MerkleProof {
-  /**
-   * @dev Verifies a Merkle proof proving the existence of a leaf in a Merkle tree. Assumes that each pair of leaves
-   * and each pair of pre-images are sorted.
-   * @param proof Merkle proof containing sibling hashes on the branch from the leaf to the root of the Merkle tree
-   * @param root Merkle root
-   * @param leaf Leaf of Merkle tree
-   */
-  function verify(
-    bytes32[] proof,
-    bytes32 root,
-    bytes32 leaf
-  )
-    internal
-    pure
-    returns (bool)
-  {
-    bytes32 computedHash = leaf;
+    /**
+     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
+     * defined by `root`. For this, a `proof` must be provided, containing
+     * sibling hashes on the branch from the leaf to the root of the tree. Each
+     * pair of leaves and each pair of pre-images are assumed to be sorted.
+     */
+    function verify(bytes32[] memory proof, bytes32 root, bytes32 leaf) internal pure returns (bool) {
+        bytes32 computedHash = leaf;
 
-    for (uint256 i = 0; i < proof.length; i++) {
-      bytes32 proofElement = proof[i];
+        for (uint256 i = 0; i < proof.length; i++) {
+            bytes32 proofElement = proof[i];
 
-      if (computedHash < proofElement) {
-        // Hash(current computed hash + current element of the proof)
-        computedHash = keccak256(abi.encodePacked(computedHash, proofElement));
-      } else {
-        // Hash(current element of the proof + current computed hash)
-        computedHash = keccak256(abi.encodePacked(proofElement, computedHash));
-      }
+            if (computedHash < proofElement) {
+                // Hash(current computed hash + current element of the proof)
+                computedHash = keccak256(abi.encodePacked(computedHash, proofElement));
+            } else {
+                // Hash(current element of the proof + current computed hash)
+                computedHash = keccak256(abi.encodePacked(proofElement, computedHash));
+            }
+        }
+
+        // Check if the computed hash (root) is equal to the provided root
+        return computedHash == root;
     }
-
-    // Check if the computed hash (root) is equal to the provided root
-    return computedHash == root;
-  }
 }

contracts/cryptography/README.md

@@ -0,0 +1,9 @@
+---
+sections:
+  - title: Libraries
+    contracts:
+      - ECDSA
+      - MerkleProof
+---
+
+This collection of libraries provides simple and safe ways to use different cryptographic primitives.

contracts/drafts/Counter.sol

@@ -1,28 +0,0 @@
-pragma solidity ^0.4.24;
-
-/**
- * @title Counter
- * @author Matt Condon (@shrugs)
- * @dev Provides an incrementing uint256 id acquired by the `Counter#next` getter.
- * Use this for issuing ERC721 ids or keeping track of request ids, anything you want, really.
- *
- * Include with `using Counter for Counter.Counter;`
- * @notice Does not allow an Id of 0, which is popularly used to signify a null state in solidity.
- * Does not protect from overflows, but if you have 2^256 ids, you have other problems.
- * (But actually, it's generally impossible to increment a counter this many times, energy wise
- * so it's not something you have to worry about.)
- */
-library Counter {
-
-  struct Counter {
-    uint256 current; // default: 0
-  }
-
-  function next(Counter storage index)
-    internal
-    returns (uint256)
-  {
-    index.current += 1;
-    return index.current;
-  }
-}

contracts/drafts/Counters.sol

@@ -0,0 +1,37 @@
+pragma solidity ^0.5.0;
+
+import "../math/SafeMath.sol";
+
+/**
+ * @title Counters
+ * @author Matt Condon (@shrugs)
+ * @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
+ * of elements in a mapping, issuing ERC721 ids, or counting request ids.
+ *
+ * Include with `using Counters for Counters.Counter;`
+ * Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the SafeMath
+ * overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never
+ * directly accessed.
+ */
+library Counters {
+    using SafeMath for uint256;
+
+    struct Counter {
+        // This variable should never be directly accessed by users of the library: interactions must be restricted to
+        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
+        // this feature: see https://github.com/ethereum/solidity/issues/4637
+        uint256 _value; // default: 0
+    }
+
+    function current(Counter storage counter) internal view returns (uint256) {
+        return counter._value;
+    }
+
+    function increment(Counter storage counter) internal {
+        counter._value += 1;
+    }
+
+    function decrement(Counter storage counter) internal {
+        counter._value = counter._value.sub(1);
+    }
+}

contracts/drafts/ERC1046/ERC20Metadata.sol

@@ -0,0 +1,24 @@
+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/ERC1046/TokenMetadata.sol

@@ -1,27 +0,0 @@
-pragma solidity ^0.4.24;
-
-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
- * @dev TODO - update https://github.com/OpenZeppelin/openzeppelin-solidity/blob/master/contracts/token/ERC721/IERC721.sol#L17 when 1046 is finalized
- */
-contract ERC20TokenMetadata is IERC20 {
-  function tokenURI() external view returns (string);
-}
-
-contract ERC20WithMetadata is ERC20TokenMetadata {
-  string private _tokenURI;
-
-  constructor(string tokenURI)
-    public
-  {
-    _tokenURI = tokenURI;
-  }
-
-  function tokenURI() external view returns (string) {
-    return _tokenURI;
-  }
-}

contracts/drafts/ERC20Migrator.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/IERC20.sol";
 import "../token/ERC20/ERC20Mintable.sol";
@@ -17,7 +17,7 @@ import "../math/Math.sol";
  * OpenZeppelin's ERC20Mintable, but the only functions that are needed are
  * `isMinter(address)` and `mint(address, amount)`. The migrator will check
  * that it is a minter for the token.
- * The balance from the legacy token will be transfered to the migrator, as it
+ * 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
@@ -32,69 +32,71 @@ import "../math/Math.sol";
  * ```
  */
 contract ERC20Migrator {
-  using SafeERC20 for IERC20;
+    using SafeERC20 for IERC20;
 
-  /// Address of the old token contract
-  IERC20 private _legacyToken;
+    /// Address of the old token contract
+    IERC20 private _legacyToken;
 
-  /// Address of the new token contract
-  ERC20Mintable private _newToken;
+    /// Address of the new token contract
+    ERC20Mintable private _newToken;
 
-  /**
-   * @param legacyToken address of the old token contract
-   */
-  constructor(IERC20 legacyToken) public {
-    require(legacyToken != address(0));
-    _legacyToken = legacyToken;
-  }
+    /**
+     * @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 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 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(_newToken == address(0));
-    require(newToken != address(0));
-    require(newToken.isMinter(this));
+    /**
+     * @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;
-  }
+        _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 {
-    _legacyToken.safeTransferFrom(account, this, amount);
-    _newToken.mint(account, amount);
-  }
+    /**
+     * @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, this);
-    uint256 amount = Math.min(balance, allowance);
-    migrate(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

@@ -0,0 +1,140 @@
+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 MiniMeToken to record historical balances:
+ * https://github.com/Giveth/minime/blob/ea04d950eea153a04c51fa510b068b9dded390cb/contracts/MiniMeToken.sol
+ * When a snapshot is made, the balances and totalSupply 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.md

@@ -0,0 +1,16 @@
+---
+sections:
+  - title: ERC 20
+    contracts:
+    - ERC20Migrator
+    - ERC20Snapshot
+    - TokenVesting
+  - title: Miscellenous
+    contracts:
+    - Counters
+    - SignatureBouncer
+    - SignedSafeMath
+  - subdirectory: ERC1046
+---
+
+> This page is incomplete. We're working to improve it for the next release. Stay tuned!

contracts/drafts/SignatureBouncer.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../access/roles/SignerRole.sol";
 import "../cryptography/ECDSA.sol";
@@ -29,118 +29,94 @@ import "../cryptography/ECDSA.sol";
  * @notice A method that uses the `onlyValidSignatureAndData` modifier must make
  * the _signature parameter the "last" parameter. You cannot sign a message that
  * has its own signature in it so the last 128 bytes of msg.data (which
- * represents the length of the _signature data and the _signaature data itself)
+ * represents the length of the _signature data and the _signature data itself)
  * is ignored when validating. Also non fixed sized parameters make constructing
  * the data in the signature much more complex.
  * See https://ethereum.stackexchange.com/a/50616 for more details.
  */
 contract SignatureBouncer is SignerRole {
-  using ECDSA for bytes32;
+    using ECDSA for bytes32;
 
-  // Function selectors are 4 bytes long, as documented in
-  // https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector
-  uint256 private constant _METHOD_ID_SIZE = 4;
-  // Signature size is 65 bytes (tightly packed v + r + s), but gets padded to 96 bytes
-  uint256 private constant _SIGNATURE_SIZE = 96;
+    // Function selectors are 4 bytes long, as documented in
+    // https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector
+    uint256 private constant _METHOD_ID_SIZE = 4;
+    // Signature size is 65 bytes (tightly packed v + r + s), but gets padded to 96 bytes
+    uint256 private constant _SIGNATURE_SIZE = 96;
 
-  constructor() internal {}
-
-  /**
-   * @dev requires that a valid signature of a signer was provided
-   */
-  modifier onlyValidSignature(bytes signature)
-  {
-    require(_isValidSignature(msg.sender, signature));
-    _;
-  }
-
-  /**
-   * @dev requires that a valid signature with a specifed method of a signer was provided
-   */
-  modifier onlyValidSignatureAndMethod(bytes signature)
-  {
-    require(_isValidSignatureAndMethod(msg.sender, signature));
-    _;
-  }
-
-  /**
-   * @dev requires that a valid signature with a specifed method and params of a signer was provided
-   */
-  modifier onlyValidSignatureAndData(bytes signature)
-  {
-    require(_isValidSignatureAndData(msg.sender, signature));
-    _;
-  }
-
-  /**
-   * @dev is the signature of `this + sender` from a signer?
-   * @return bool
-   */
-  function _isValidSignature(address account, bytes signature)
-    internal
-    view
-    returns (bool)
-  {
-    return _isValidDataHash(
-      keccak256(abi.encodePacked(address(this), account)),
-      signature
-    );
-  }
-
-  /**
-   * @dev is the signature of `this + sender + methodId` from a signer?
-   * @return bool
-   */
-  function _isValidSignatureAndMethod(address account, bytes signature)
-    internal
-    view
-    returns (bool)
-  {
-    bytes memory data = new bytes(_METHOD_ID_SIZE);
-    for (uint i = 0; i < data.length; i++) {
-      data[i] = msg.data[i];
+    constructor () internal {
+        // solhint-disable-previous-line no-empty-blocks
     }
-    return _isValidDataHash(
-      keccak256(abi.encodePacked(address(this), account, data)),
-      signature
-    );
-  }
 
-  /**
-    * @dev is the signature of `this + sender + methodId + params(s)` from a signer?
-    * @notice the signature parameter of the method being validated must be the "last" parameter
-    * @return bool
-    */
-  function _isValidSignatureAndData(address account, bytes signature)
-    internal
-    view
-    returns (bool)
-  {
-    require(msg.data.length > _SIGNATURE_SIZE);
-    bytes memory data = new bytes(msg.data.length - _SIGNATURE_SIZE);
-    for (uint i = 0; i < data.length; i++) {
-      data[i] = msg.data[i];
+    /**
+     * @dev Requires that a valid signature of a signer was provided.
+     */
+    modifier onlyValidSignature(bytes memory signature) {
+        require(_isValidSignature(msg.sender, signature), "SignatureBouncer: invalid signature for caller");
+        _;
     }
-    return _isValidDataHash(
-      keccak256(abi.encodePacked(address(this), account, data)),
-      signature
-    );
-  }
 
-  /**
-   * @dev internal function to convert a hash to an eth signed message
-   * and then recover the signature and check it against the signer role
-   * @return bool
-   */
-  function _isValidDataHash(bytes32 hash, bytes signature)
-    internal
-    view
-    returns (bool)
-  {
-    address signer = hash
-      .toEthSignedMessageHash()
-      .recover(signature);
+    /**
+     * @dev Requires that a valid signature with a specified method of a signer was provided.
+     */
+    modifier onlyValidSignatureAndMethod(bytes memory signature) {
+        // solhint-disable-next-line max-line-length
+        require(_isValidSignatureAndMethod(msg.sender, signature), "SignatureBouncer: invalid signature for caller and method");
+        _;
+    }
 
-    return signer != address(0) && isSigner(signer);
-  }
+    /**
+     * @dev Requires that a valid signature with a specified method and params of a signer was provided.
+     */
+    modifier onlyValidSignatureAndData(bytes memory signature) {
+        // solhint-disable-next-line max-line-length
+        require(_isValidSignatureAndData(msg.sender, signature), "SignatureBouncer: invalid signature for caller and data");
+        _;
+    }
+
+    /**
+     * @dev is the signature of `this + account` from a signer?
+     * @return bool
+     */
+    function _isValidSignature(address account, bytes memory signature) internal view returns (bool) {
+        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account)), signature);
+    }
+
+    /**
+     * @dev is the signature of `this + account + methodId` from a signer?
+     * @return bool
+     */
+    function _isValidSignatureAndMethod(address account, bytes memory signature) internal view returns (bool) {
+        bytes memory data = new bytes(_METHOD_ID_SIZE);
+        for (uint i = 0; i < data.length; i++) {
+            data[i] = msg.data[i];
+        }
+        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account, data)), signature);
+    }
+
+    /**
+     * @dev is the signature of `this + account + methodId + params(s)` from a signer?
+     * @notice the signature parameter of the method being validated must be the "last" parameter
+     * @return bool
+     */
+    function _isValidSignatureAndData(address account, bytes memory signature) internal view returns (bool) {
+        require(msg.data.length > _SIGNATURE_SIZE, "SignatureBouncer: data is too short");
+
+        bytes memory data = new bytes(msg.data.length - _SIGNATURE_SIZE);
+        for (uint i = 0; i < data.length; i++) {
+            data[i] = msg.data[i];
+        }
+
+        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account, data)), signature);
+    }
+
+    /**
+     * @dev Internal function to convert a hash to an eth signed message
+     * and then recover the signature and check it against the signer role.
+     * @return bool
+     */
+    function _isValidDataHash(bytes32 hash, bytes memory signature) internal view returns (bool) {
+        address signer = hash.toEthSignedMessageHash().recover(signature);
+
+        return signer != address(0) && isSigner(signer);
+    }
 }

contracts/drafts/SignedSafeMath.sol

@@ -0,0 +1,60 @@
+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-solidity/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/TokenVesting.sol

@@ -1,6 +1,4 @@
-/* solium-disable security/no-block-members */
-
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/SafeERC20.sol";
 import "../ownership/Ownable.sol";
@@ -13,163 +11,164 @@ import "../math/SafeMath.sol";
  * owner.
  */
 contract TokenVesting is Ownable {
-  using SafeMath for uint256;
-  using SafeERC20 for IERC20;
+    // 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
 
-  event TokensReleased(address token, uint256 amount);
-  event TokenVestingRevoked(address token);
+    using SafeMath for uint256;
+    using SafeERC20 for IERC20;
 
-  // beneficiary of tokens after they are released
-  address private _beneficiary;
+    event TokensReleased(address token, uint256 amount);
+    event TokenVestingRevoked(address token);
 
-  uint256 private _cliff;
-  uint256 private _start;
-  uint256 private _duration;
+    // beneficiary of tokens after they are released
+    address private _beneficiary;
 
-  bool private _revocable;
+    // Durations and timestamps are expressed in UNIX time, the same units as block.timestamp.
+    uint256 private _cliff;
+    uint256 private _start;
+    uint256 private _duration;
 
-  mapping (address => uint256) private _released;
-  mapping (address => bool) private _revoked;
+    bool private _revocable;
 
-  /**
-   * @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));
-    require(cliffDuration <= duration);
-    require(duration > 0);
-    require(start.add(duration) > block.timestamp);
+    mapping (address => uint256) private _released;
+    mapping (address => bool) private _revoked;
 
-    _beneficiary = beneficiary;
-    _revocable = revocable;
-    _duration = duration;
-    _cliff = start.add(cliffDuration);
-    _start = start;
-  }
+    /**
+     * @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");
 
-  /**
-   * @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);
-
-    _released[token] = _released[token].add(unreleased);
-
-    token.safeTransfer(_beneficiary, unreleased);
-
-    emit TokensReleased(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);
-    require(!_revoked[token]);
-
-    uint256 balance = token.balanceOf(address(this));
-
-    uint256 unreleased = _releasableAmount(token);
-    uint256 refund = balance.sub(unreleased);
-
-    _revoked[token] = true;
-
-    token.safeTransfer(owner(), refund);
-
-    emit TokenVestingRevoked(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[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(this);
-    uint256 totalBalance = currentBalance.add(_released[token]);
-
-    if (block.timestamp < _cliff) {
-      return 0;
-    } else if (block.timestamp >= _start.add(_duration) || _revoked[token]) {
-      return totalBalance;
-    } else {
-      return totalBalance.mul(block.timestamp.sub(_start)).div(_duration);
+        _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

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../crowdsale/validation/CappedCrowdsale.sol";
 import "../crowdsale/distribution/RefundableCrowdsale.sol";
@@ -12,7 +12,9 @@ import "../token/ERC20/ERC20Detailed.sol";
  * It is meant to be used in a crowdsale contract.
  */
 contract SampleCrowdsaleToken is ERC20Mintable, ERC20Detailed {
-  constructor() public ERC20Detailed("Sample Crowdsale Token", "SCT", 18) {}
+    constructor () public ERC20Detailed("Sample Crowdsale Token", "SCT", 18) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
 }
 
 /**
@@ -28,30 +30,24 @@ contract SampleCrowdsaleToken is ERC20Mintable, ERC20Detailed {
  * After adding multiple features it's good practice to run integration tests
  * to ensure that subcontracts works together as intended.
  */
-// XXX There doesn't seem to be a way to split this line that keeps solium
-// happy. See:
-// https://github.com/duaraghav8/Solium/issues/205
-// --elopio - 2018-05-10
-// solium-disable-next-line max-len
 contract SampleCrowdsale is CappedCrowdsale, RefundableCrowdsale, MintedCrowdsale {
-
-  constructor(
-    uint256 openingTime,
-    uint256 closingTime,
-    uint256 rate,
-    address 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);
-  }
+    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

@@ -1,6 +1,7 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/ERC20.sol";
+import "../token/ERC20/ERC20Detailed.sol";
 
 /**
  * @title SimpleToken
@@ -8,19 +9,14 @@ import "../token/ERC20/ERC20.sol";
  * Note they can later distribute these tokens as they wish using `transfer` and other
  * `ERC20` functions.
  */
-contract SimpleToken is ERC20 {
-
-  string public constant name = "SimpleToken";
-  string public constant symbol = "SIM";
-  uint8 public constant decimals = 18;
-
-  uint256 public constant INITIAL_SUPPLY = 10000 * (10 ** uint256(decimals));
-
-  /**
-   * @dev Constructor that gives msg.sender all of existing tokens.
-   */
-  constructor() public {
-    _mint(msg.sender, INITIAL_SUPPLY);
-  }
+contract SimpleToken is ERC20, ERC20Detailed {
+    uint8 public constant DECIMALS = 18;
+    uint256 public constant INITIAL_SUPPLY = 10000 * (10 ** uint256(DECIMALS));
 
+    /**
+     * @dev Constructor that gives msg.sender all of existing tokens.
+     */
+    constructor () public ERC20Detailed("SimpleToken", "SIM", DECIMALS) {
+        _mint(msg.sender, INITIAL_SUPPLY);
+    }
 }

contracts/introspection/ERC165.sol

@@ -1,53 +1,52 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "./IERC165.sol";
 
 /**
- * @title ERC165
- * @author Matt Condon (@shrugs)
- * @dev Implements ERC165 using a lookup table.
+ * @dev Implementation of the `IERC165` interface.
+ *
+ * Contracts may inherit from this and call `_registerInterface` to declare
+ * their support of an interface.
  */
 contract ERC165 is IERC165 {
+    /*
+     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
+     */
+    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
 
-  bytes4 private constant _InterfaceId_ERC165 = 0x01ffc9a7;
-  /**
-   * 0x01ffc9a7 ===
-   *   bytes4(keccak256('supportsInterface(bytes4)'))
-   */
+    /**
+     * @dev Mapping of interface ids to whether or not it's supported.
+     */
+    mapping(bytes4 => bool) private _supportedInterfaces;
 
-  /**
-   * @dev a mapping of interface id to whether or not it's supported
-   */
-  mapping(bytes4 => bool) private _supportedInterfaces;
+    constructor () internal {
+        // Derived contracts need only register support for their own interfaces,
+        // we register support for ERC165 itself here
+        _registerInterface(_INTERFACE_ID_ERC165);
+    }
 
-  /**
-   * @dev A contract implementing SupportsInterfaceWithLookup
-   * implement ERC165 itself
-   */
-  constructor()
-    internal
-  {
-    _registerInterface(_InterfaceId_ERC165);
-  }
+    /**
+     * @dev See `IERC165.supportsInterface`.
+     *
+     * Time complexity O(1), guaranteed to always use less than 30 000 gas.
+     */
+    function supportsInterface(bytes4 interfaceId) external view returns (bool) {
+        return _supportedInterfaces[interfaceId];
+    }
 
-  /**
-   * @dev implement supportsInterface(bytes4) using a lookup table
-   */
-  function supportsInterface(bytes4 interfaceId)
-    external
-    view
-    returns (bool)
-  {
-    return _supportedInterfaces[interfaceId];
-  }
-
-  /**
-   * @dev internal method for registering an interface
-   */
-  function _registerInterface(bytes4 interfaceId)
-    internal
-  {
-    require(interfaceId != 0xffffffff);
-    _supportedInterfaces[interfaceId] = true;
-  }
+    /**
+     * @dev Registers the contract as an implementer of the interface defined by
+     * `interfaceId`. Support of the actual ERC165 interface is automatic and
+     * registering its interface id is not required.
+     *
+     * See `IERC165.supportsInterface`.
+     *
+     * Requirements:
+     *
+     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
+     */
+    function _registerInterface(bytes4 interfaceId) internal {
+        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
+        _supportedInterfaces[interfaceId] = true;
+    }
 }

contracts/introspection/ERC165Checker.sol

@@ -1,146 +1,121 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 /**
- * @title ERC165Checker
- * @dev Use `using ERC165Checker for address`; to include this library
- * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-165.md
+ * @dev Library used to query support of an interface declared via `IERC165`.
+ *
+ * Note that these functions return the actual result of the query: they do not
+ * `revert` if an interface is not supported. It is up to the caller to decide
+ * what to do in these cases.
  */
 library ERC165Checker {
-  // As per the EIP-165 spec, no interface should ever match 0xffffffff
-  bytes4 private constant _InterfaceId_Invalid = 0xffffffff;
+    // As per the EIP-165 spec, no interface should ever match 0xffffffff
+    bytes4 private constant _INTERFACE_ID_INVALID = 0xffffffff;
 
-  bytes4 private constant _InterfaceId_ERC165 = 0x01ffc9a7;
-  /**
-   * 0x01ffc9a7 ===
-   *   bytes4(keccak256('supportsInterface(bytes4)'))
-   */
+    /*
+     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
+     */
+    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
 
-  /**
-   * @notice Query if a contract supports ERC165
-   * @param account The address of the contract to query for support of ERC165
-   * @return true if the contract at account implements ERC165
-   */
-  function _supportsERC165(address account)
-    internal
-    view
-    returns (bool)
-  {
-    // Any contract that implements ERC165 must explicitly indicate support of
-    // InterfaceId_ERC165 and explicitly indicate non-support of InterfaceId_Invalid
-    return _supportsERC165Interface(account, _InterfaceId_ERC165) &&
-      !_supportsERC165Interface(account, _InterfaceId_Invalid);
-  }
-
-  /**
-   * @notice Query if a contract implements an interface, also checks support of ERC165
-   * @param account The address of the contract to query for support of an interface
-   * @param interfaceId The interface identifier, as specified in ERC-165
-   * @return true if the contract at account indicates support of the interface with
-   * identifier interfaceId, false otherwise
-   * @dev Interface identification is specified in ERC-165.
-   */
-  function _supportsInterface(address account, bytes4 interfaceId)
-    internal
-    view
-    returns (bool)
-  {
-    // query support of both ERC165 as per the spec and support of _interfaceId
-    return _supportsERC165(account) &&
-      _supportsERC165Interface(account, interfaceId);
-  }
-
-  /**
-   * @notice Query if a contract implements interfaces, also checks support of ERC165
-   * @param account The address of the contract to query for support of an interface
-   * @param interfaceIds A list of interface identifiers, as specified in ERC-165
-   * @return true if the contract at account indicates support all interfaces in the
-   * interfaceIds list, false otherwise
-   * @dev Interface identification is specified in ERC-165.
-   */
-  function _supportsAllInterfaces(address account, bytes4[] interfaceIds)
-    internal
-    view
-    returns (bool)
-  {
-    // query support of ERC165 itself
-    if (!_supportsERC165(account)) {
-      return false;
+    /**
+     * @dev Returns true if `account` supports the `IERC165` interface,
+     */
+    function _supportsERC165(address account) internal view returns (bool) {
+        // Any contract that implements ERC165 must explicitly indicate support of
+        // InterfaceId_ERC165 and explicitly indicate non-support of InterfaceId_Invalid
+        return _supportsERC165Interface(account, _INTERFACE_ID_ERC165) &&
+            !_supportsERC165Interface(account, _INTERFACE_ID_INVALID);
     }
 
-    // query support of each interface in _interfaceIds
-    for (uint256 i = 0; i < interfaceIds.length; i++) {
-      if (!_supportsERC165Interface(account, interfaceIds[i])) {
-        return false;
-      }
+    /**
+     * @dev Returns true if `account` supports the interface defined by
+     * `interfaceId`. Support for `IERC165` itself is queried automatically.
+     *
+     * See `IERC165.supportsInterface`.
+     */
+    function _supportsInterface(address account, bytes4 interfaceId) internal view returns (bool) {
+        // query support of both ERC165 as per the spec and support of _interfaceId
+        return _supportsERC165(account) &&
+            _supportsERC165Interface(account, interfaceId);
     }
 
-    // all interfaces supported
-    return true;
-  }
+    /**
+     * @dev Returns true if `account` supports all the interfaces defined in
+     * `interfaceIds`. Support for `IERC165` itself is queried automatically.
+     *
+     * Batch-querying can lead to gas savings by skipping repeated checks for
+     * `IERC165` support.
+     *
+     * See `IERC165.supportsInterface`.
+     */
+    function _supportsAllInterfaces(address account, bytes4[] memory interfaceIds) internal view returns (bool) {
+        // query support of ERC165 itself
+        if (!_supportsERC165(account)) {
+            return false;
+        }
 
-  /**
-   * @notice Query if a contract implements an interface, does not check ERC165 support
-   * @param account The address of the contract to query for support of an interface
-   * @param interfaceId The interface identifier, as specified in ERC-165
-   * @return true if the contract at account indicates support of the interface with
-   * identifier interfaceId, false otherwise
-   * @dev Assumes that account contains a contract that supports ERC165, otherwise
-   * the behavior of this method is undefined. This precondition can be checked
-   * with the `supportsERC165` method in this library.
-   * Interface identification is specified in ERC-165.
-   */
-  function _supportsERC165Interface(address account, bytes4 interfaceId)
-    private
-    view
-    returns (bool)
-  {
-    // success determines whether the staticcall succeeded and result determines
-    // whether the contract at account indicates support of _interfaceId
-    (bool success, bool result) = _callERC165SupportsInterface(
-      account, interfaceId);
+        // query support of each interface in _interfaceIds
+        for (uint256 i = 0; i < interfaceIds.length; i++) {
+            if (!_supportsERC165Interface(account, interfaceIds[i])) {
+                return false;
+            }
+        }
 
-    return (success && result);
-  }
-
-  /**
-   * @notice Calls the function with selector 0x01ffc9a7 (ERC165) and suppresses throw
-   * @param account The address of the contract to query for support of an interface
-   * @param interfaceId The interface identifier, as specified in ERC-165
-   * @return success true if the STATICCALL succeeded, false otherwise
-   * @return result true if the STATICCALL succeeded and the contract at account
-   * indicates support of the interface with identifier interfaceId, false otherwise
-   */
-  function _callERC165SupportsInterface(
-    address account,
-    bytes4 interfaceId
-  )
-    private
-    view
-    returns (bool success, bool result)
-  {
-    bytes memory encodedParams = abi.encodeWithSelector(
-      _InterfaceId_ERC165,
-      interfaceId
-    );
-
-    // solium-disable-next-line security/no-inline-assembly
-    assembly {
-      let encodedParams_data := add(0x20, encodedParams)
-      let encodedParams_size := mload(encodedParams)
-
-      let output := mload(0x40)  // Find empty storage location using "free memory pointer"
-      mstore(output, 0x0)
-
-      success := staticcall(
-        30000,                 // 30k gas
-        account,              // To addr
-        encodedParams_data,
-        encodedParams_size,
-        output,
-        0x20                   // Outputs are 32 bytes long
-      )
-
-      result := mload(output)  // Load the result
+        // all interfaces supported
+        return true;
+    }
+
+    /**
+     * @notice Query if a contract implements an interface, does not check ERC165 support
+     * @param account The address of the contract to query for support of an interface
+     * @param interfaceId The interface identifier, as specified in ERC-165
+     * @return true if the contract at account indicates support of the interface with
+     * identifier interfaceId, false otherwise
+     * @dev Assumes that account contains a contract that supports ERC165, otherwise
+     * the behavior of this method is undefined. This precondition can be checked
+     * with the `supportsERC165` method in this library.
+     * Interface identification is specified in ERC-165.
+     */
+    function _supportsERC165Interface(address account, bytes4 interfaceId) private view returns (bool) {
+        // success determines whether the staticcall succeeded and result determines
+        // whether the contract at account indicates support of _interfaceId
+        (bool success, bool result) = _callERC165SupportsInterface(account, interfaceId);
+
+        return (success && result);
+    }
+
+    /**
+     * @notice Calls the function with selector 0x01ffc9a7 (ERC165) and suppresses throw
+     * @param account The address of the contract to query for support of an interface
+     * @param interfaceId The interface identifier, as specified in ERC-165
+     * @return success true if the STATICCALL succeeded, false otherwise
+     * @return result true if the STATICCALL succeeded and the contract at account
+     * indicates support of the interface with identifier interfaceId, false otherwise
+     */
+    function _callERC165SupportsInterface(address account, bytes4 interfaceId)
+        private
+        view
+        returns (bool success, bool result)
+    {
+        bytes memory encodedParams = abi.encodeWithSelector(_INTERFACE_ID_ERC165, interfaceId);
+
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            let encodedParams_data := add(0x20, encodedParams)
+            let encodedParams_size := mload(encodedParams)
+
+            let output := mload(0x40)    // Find empty storage location using "free memory pointer"
+            mstore(output, 0x0)
+
+            success := staticcall(
+                30000,                   // 30k gas
+                account,                 // To addr
+                encodedParams_data,
+                encodedParams_size,
+                output,
+                0x20                     // Outputs are 32 bytes long
+            )
+
+            result := mload(output)      // Load the result
+        }
     }
-  }
 }

contracts/introspection/ERC1820Implementer.sol

@@ -0,0 +1,35 @@
+pragma solidity ^0.5.0;
+
+import "./IERC1820Implementer.sol";
+
+/**
+ * @dev Implementation of the `IERC1820Implementer` interface.
+ *
+ * Contracts may inherit from this and call `_registerInterfaceForAddress` to
+ * declare their willingness to be implementers.
+ * `IERC1820Registry.setInterfaceImplementer` should then be called for the
+ * registration to be complete.
+ */
+contract ERC1820Implementer is IERC1820Implementer {
+    bytes32 constant private ERC1820_ACCEPT_MAGIC = keccak256(abi.encodePacked("ERC1820_ACCEPT_MAGIC"));
+
+    mapping(bytes32 => mapping(address => bool)) private _supportedInterfaces;
+
+    /**
+     * See `IERC1820Implementer.canImplementInterfaceForAddress`.
+     */
+    function canImplementInterfaceForAddress(bytes32 interfaceHash, address account) external view returns (bytes32) {
+        return _supportedInterfaces[interfaceHash][account] ? ERC1820_ACCEPT_MAGIC : bytes32(0x00);
+    }
+
+    /**
+     * @dev Declares the contract as willing to be an implementer of
+     * `interfaceHash` for `account`.
+     *
+     * See `IERC1820Registry.setInterfaceImplementer` and
+     * `IERC1820Registry.interfaceHash`.
+     */
+    function _registerInterfaceForAddress(bytes32 interfaceHash, address account) internal {
+        _supportedInterfaces[interfaceHash][account] = true;
+    }
+}

contracts/introspection/IERC165.sol

@@ -1,19 +1,22 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 /**
- * @title IERC165
- * @dev https://github.com/ethereum/EIPs/blob/master/EIPS/eip-165.md
+ * @dev Interface of the ERC165 standard, as defined in the
+ * [EIP](https://eips.ethereum.org/EIPS/eip-165).
+ *
+ * Implementers can declare support of contract interfaces, which can then be
+ * queried by others (`ERC165Checker`).
+ *
+ * For an implementation, see `ERC165`.
  */
 interface IERC165 {
-
-  /**
-   * @notice Query if a contract implements an interface
-   * @param interfaceId The interface identifier, as specified in ERC-165
-   * @dev Interface identification is specified in ERC-165. This function
-   * uses less than 30,000 gas.
-   */
-  function supportsInterface(bytes4 interfaceId)
-    external
-    view
-    returns (bool);
+    /**
+     * @dev Returns true if this contract implements the interface defined by
+     * `interfaceId`. See the corresponding
+     * [EIP section](https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified)
+     * to learn more about how these ids are created.
+     *
+     * This function call must use less than 30 000 gas.
+     */
+    function supportsInterface(bytes4 interfaceId) external view returns (bool);
 }

contracts/introspection/IERC1820Implementer.sol

@@ -0,0 +1,17 @@
+pragma solidity ^0.5.0;
+
+/**
+ * @dev Interface for an ERC1820 implementer, as defined in the
+ * [EIP](https://eips.ethereum.org/EIPS/eip-1820#interface-implementation-erc1820implementerinterface).
+ * Used by contracts that will be registered as implementers in the
+ * `IERC1820Registry`.
+ */
+interface IERC1820Implementer {
+    /**
+     * @dev Returns a special value (`ERC1820_ACCEPT_MAGIC`) if this contract
+     * implements `interfaceHash` for `account`.
+     *
+     * See `IERC1820Registry.setInterfaceImplementer`.
+     */
+    function canImplementInterfaceForAddress(bytes32 interfaceHash, address account) external view returns (bytes32);
+}

contracts/introspection/IERC1820Registry.sol

@@ -0,0 +1,109 @@
+pragma solidity ^0.5.0;
+
+/**
+ * @dev Interface of the global ERC1820 Registry, as defined in the
+ * [EIP](https://eips.ethereum.org/EIPS/eip-1820). Accounts may register
+ * implementers for interfaces in this registry, as well as query support.
+ *
+ * Implementers may be shared by multiple accounts, and can also implement more
+ * than a single interface for each account. Contracts can implement interfaces
+ * for themselves, but externally-owned accounts (EOA) must delegate this to a
+ * contract.
+ *
+ * `IERC165` interfaces can also be queried via the registry.
+ *
+ * For an in-depth explanation and source code analysis, see the EIP text.
+ */
+interface IERC1820Registry {
+    /**
+     * @dev Sets `newManager` as the manager for `account`. A manager of an
+     * account is able to set interface implementers for it.
+     *
+     * By default, each account is its own manager. Passing a value of `0x0` in
+     * `newManager` will reset the manager to this initial state.
+     *
+     * Emits a `ManagerChanged` event.
+     *
+     * Requirements:
+     *
+     * - the caller must be the current manager for `account`.
+     */
+    function setManager(address account, address newManager) external;
+
+    /**
+     * @dev Returns the manager for `account`.
+     *
+     * See `setManager`.
+     */
+    function getManager(address account) external view returns (address);
+
+    /**
+     * @dev Sets the `implementer` contract as `account`'s implementer for
+     * `interfaceHash`.
+     *
+     * `account` being the zero address is an alias for the caller's address.
+     * The zero address can also be used in `implementer` to remove an old one.
+     *
+     * See `interfaceHash` to learn how these are created.
+     *
+     * Emits an `InterfaceImplementerSet` event.
+     *
+     * Requirements:
+     *
+     * - the caller must be the current manager for `account`.
+     * - `interfaceHash` must not be an `IERC165` interface id (i.e. it must not
+     * end in 28 zeroes).
+     * - `implementer` must implement `IERC1820Implementer` and return true when
+     * queried for support, unless `implementer` is the caller. See
+     * `IERC1820Implementer.canImplementInterfaceForAddress`.
+     */
+    function setInterfaceImplementer(address account, bytes32 interfaceHash, address implementer) external;
+
+    /**
+     * @dev Returns the implementer of `interfaceHash` for `account`. If no such
+     * implementer is registered, returns the zero address.
+     *
+     * If `interfaceHash` is an `IERC165` interface id (i.e. it ends with 28
+     * zeroes), `account` will be queried for support of it.
+     *
+     * `account` being the zero address is an alias for the caller's address.
+     */
+    function getInterfaceImplementer(address account, bytes32 interfaceHash) external view returns (address);
+
+    /**
+     * @dev Returns the interface hash for an `interfaceName`, as defined in the
+     * corresponding
+     * [section of the EIP](https://eips.ethereum.org/EIPS/eip-1820#interface-name).
+     */
+    function interfaceHash(string calldata interfaceName) external pure returns (bytes32);
+
+    /**
+     *  @notice Updates the cache with whether the contract implements an ERC165 interface or not.
+     *  @param account Address of the contract for which to update the cache.
+     *  @param interfaceId ERC165 interface for which to update the cache.
+     */
+    function updateERC165Cache(address account, bytes4 interfaceId) external;
+
+    /**
+     *  @notice Checks whether a contract implements an ERC165 interface or not.
+     *  If the result is not cached a direct lookup on the contract address is performed.
+     *  If the result is not cached or the cached value is out-of-date, the cache MUST be updated manually by calling
+     *  'updateERC165Cache' with the contract address.
+     *  @param account Address of the contract to check.
+     *  @param interfaceId ERC165 interface to check.
+     *  @return True if `account.address()` implements `interfaceId`, false otherwise.
+     */
+    function implementsERC165Interface(address account, bytes4 interfaceId) external view returns (bool);
+
+    /**
+     *  @notice Checks whether a contract implements an ERC165 interface or not without using nor updating the cache.
+     *  @param account Address of the contract to check.
+     *  @param interfaceId ERC165 interface to check.
+     *  @return True if `account.address()` implements `interfaceId`, false otherwise.
+     */
+    function implementsERC165InterfaceNoCache(address account, bytes4 interfaceId) external view returns (bool);
+
+    event InterfaceImplementerSet(address indexed account, bytes32 indexed interfaceHash, address indexed implementer);
+
+    event ManagerChanged(address indexed account, address indexed newManager);
+}

contracts/introspection/README.md

@@ -0,0 +1,23 @@
+---
+sections:
+  - title: Local
+    contracts:
+      - IERC165
+      - ERC165
+      - ERC165Checker
+  - title: Global
+    contracts:
+      - IERC1820Registry
+      - IERC1820Implementer
+      - ERC1820Implementer
+---
+
+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.

contracts/lifecycle/Pausable.sol

@@ -1,57 +1,73 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../access/roles/PauserRole.sol";
 
 /**
- * @title Pausable
- * @dev Base contract which allows children to implement an emergency stop mechanism.
+ * @dev Contract module which allows children to implement an emergency stop
+ * mechanism that can be triggered by an authorized account.
+ *
+ * This module is used through inheritance. It will make available the
+ * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
+ * the functions of your contract. Note that they will not be pausable by
+ * simply including this module, only once the modifiers are put in place.
  */
 contract Pausable is PauserRole {
-  event Paused(address account);
-  event Unpaused(address account);
+    /**
+     * @dev Emitted when the pause is triggered by a pauser (`account`).
+     */
+    event Paused(address account);
 
-  bool private _paused;
+    /**
+     * @dev Emitted when the pause is lifted by a pauser (`account`).
+     */
+    event Unpaused(address account);
 
-  constructor() internal {
-    _paused = false;
-  }
+    bool private _paused;
 
-  /**
-   * @return true if the contract is paused, false otherwise.
-   */
-  function paused() public view returns(bool) {
-    return _paused;
-  }
+    /**
+     * @dev Initializes the contract in unpaused state. Assigns the Pauser role
+     * to the deployer.
+     */
+    constructor () internal {
+        _paused = false;
+    }
 
-  /**
-   * @dev Modifier to make a function callable only when the contract is not paused.
-   */
-  modifier whenNotPaused() {
-    require(!_paused);
-    _;
-  }
+    /**
+     * @dev Returns true if the contract is paused, and false otherwise.
+     */
+    function paused() public view returns (bool) {
+        return _paused;
+    }
 
-  /**
-   * @dev Modifier to make a function callable only when the contract is paused.
-   */
-  modifier whenPaused() {
-    require(_paused);
-    _;
-  }
+    /**
+     * @dev Modifier to make a function callable only when the contract is not paused.
+     */
+    modifier whenNotPaused() {
+        require(!_paused, "Pausable: paused");
+        _;
+    }
 
-  /**
-   * @dev called by the owner to pause, triggers stopped state
-   */
-  function pause() public onlyPauser whenNotPaused {
-    _paused = true;
-    emit Paused(msg.sender);
-  }
+    /**
+     * @dev Modifier to make a function callable only when the contract is paused.
+     */
+    modifier whenPaused() {
+        require(_paused, "Pausable: not paused");
+        _;
+    }
 
-  /**
-   * @dev called by the owner to unpause, returns to normal state
-   */
-  function unpause() public onlyPauser whenPaused {
-    _paused = false;
-    emit Unpaused(msg.sender);
-  }
+    /**
+     * @dev Called by a pauser to pause, triggers stopped state.
+     */
+    function pause() public onlyPauser whenNotPaused {
+        _paused = true;
+        emit Paused(msg.sender);
+    }
+
+    /**
+     * @dev Called by a pauser to unpause, returns to normal state.
+     */
+    function unpause() public onlyPauser whenPaused {
+        _paused = false;
+        emit Unpaused(msg.sender);
+    }
 }

contracts/math/Math.sol

@@ -1,31 +1,29 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 /**
- * @title Math
- * @dev Assorted math operations
+ * @dev Standard math utilities missing in the Solidity language.
  */
 library Math {
-  /**
-  * @dev Returns the largest of two numbers.
-  */
-  function max(uint256 a, uint256 b) internal pure returns (uint256) {
-    return a >= b ? a : b;
-  }
+    /**
+     * @dev Returns the largest of two numbers.
+     */
+    function max(uint256 a, uint256 b) internal pure returns (uint256) {
+        return a >= b ? a : b;
+    }
 
-  /**
-  * @dev Returns the smallest of two numbers.
-  */
-  function min(uint256 a, uint256 b) internal pure returns (uint256) {
-    return a < b ? a : b;
-  }
+    /**
+     * @dev Returns the smallest of two numbers.
+     */
+    function min(uint256 a, uint256 b) internal pure returns (uint256) {
+        return a < b ? a : b;
+    }
 
-  /**
-  * @dev Calculates the average of two numbers. Since these are integers,
-  * averages of an even and odd number cannot be represented, and will be
-  * rounded down.
-  */
-  function average(uint256 a, uint256 b) internal pure returns (uint256) {
-    // (a + b) / 2 can overflow, so we distribute
-    return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
-  }
+    /**
+     * @dev Returns the average of two numbers. The result is rounded towards
+     * zero.
+     */
+    function average(uint256 a, uint256 b) internal pure returns (uint256) {
+        // (a + b) / 2 can overflow, so we distribute
+        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
+    }
 }

contracts/math/README.md

@@ -0,0 +1,10 @@
+---
+title: Math
+sections:
+  - title: Libraries
+    contracts:
+      - SafeMath
+      - Math
+---
+
+These are math-related utilities.

contracts/math/SafeMath.sol

@@ -1,65 +1,107 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 /**
- * @title SafeMath
- * @dev Math operations with safety checks that revert on error
+ * @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");
 
-  /**
-  * @dev Multiplies two numbers, reverts on 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-solidity/pull/522
-    if (a == 0) {
-      return 0;
+        return c;
     }
 
-    uint256 c = a * b;
-    require(c / a == b);
+    /**
+     * @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) {
+        require(b <= a, "SafeMath: subtraction overflow");
+        uint256 c = a - b;
 
-    return c;
-  }
+        return c;
+    }
 
-  /**
-  * @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
-  */
-  function div(uint256 a, uint256 b) internal pure returns (uint256) {
-    require(b > 0); // Solidity only automatically asserts when dividing by 0
-    uint256 c = a / b;
-    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
+    /**
+     * @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-solidity/pull/522
+        if (a == 0) {
+            return 0;
+        }
 
-    return c;
-  }
+        uint256 c = a * b;
+        require(c / a == b, "SafeMath: multiplication overflow");
 
-  /**
-  * @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
-  */
-  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
-    require(b <= a);
-    uint256 c = a - b;
+        return c;
+    }
 
-    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) {
+        // Solidity only automatically asserts when dividing by 0
+        require(b > 0, "SafeMath: division by zero");
+        uint256 c = a / b;
+        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
 
-  /**
-  * @dev Adds two numbers, reverts on overflow.
-  */
-  function add(uint256 a, uint256 b) internal pure returns (uint256) {
-    uint256 c = a + b;
-    require(c >= a);
+        return c;
+    }
 
-    return c;
-  }
-
-  /**
-  * @dev Divides two numbers and returns the remainder (unsigned integer modulo),
-  * reverts when dividing by zero.
-  */
-  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
-    require(b != 0);
-    return a % b;
-  }
+    /**
+     * @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) {
+        require(b != 0, "SafeMath: modulo by zero");
+        return a % b;
+    }
 }

contracts/mocks/AddressImpl.sol

@@ -1,14 +1,9 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../utils/Address.sol";
 
 contract AddressImpl {
-  function isContract(address account)
-    external
-    view
-    returns (bool)
-  {
-    return Address.isContract(account); 
-  }
-  
+    function isContract(address account) external view returns (bool) {
+        return Address.isContract(account);
+    }
 }

contracts/mocks/AllowanceCrowdsaleImpl.sol

@@ -1,20 +1,14 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/emission/AllowanceCrowdsale.sol";
 
 contract AllowanceCrowdsaleImpl is AllowanceCrowdsale {
-
-  constructor (
-    uint256 rate,
-    address wallet,
-    IERC20 token,
-    address tokenWallet
-  )
-    public
-    Crowdsale(rate, wallet, token)
-    AllowanceCrowdsale(tokenWallet)
-  {
-  }
-
+    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

@@ -1,18 +1,17 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../utils/Arrays.sol";
 
 contract ArraysImpl {
+    using Arrays for uint256[];
 
-  using Arrays for uint256[];
+    uint256[] private array;
 
-  uint256[] private array;
+    constructor (uint256[] memory _array) public {
+        array = _array;
+    }
 
-  constructor(uint256[] _array) public {
-    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/CappedCrowdsaleImpl.sol

@@ -1,20 +1,14 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/validation/CappedCrowdsale.sol";
 
 contract CappedCrowdsaleImpl is CappedCrowdsale {
-
-  constructor (
-    uint256 rate,
-    address wallet,
-    IERC20 token,
-    uint256 cap
-  )
-    public
-    Crowdsale(rate, wallet, token)
-    CappedCrowdsale(cap)
-  {
-  }
-
+    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

@@ -1,17 +1,18 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../access/roles/CapperRole.sol";
 
 contract CapperRoleMock is CapperRole {
-  function removeCapper(address account) public {
-    _removeCapper(account);
-  }
+    function removeCapper(address account) public {
+        _removeCapper(account);
+    }
 
-  function onlyCapperMock() public view onlyCapper {
-  }
+    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);
-  }
+    // Causes a compilation error if super._removeCapper is not internal
+    function _removeCapper(address account) internal {
+        super._removeCapper(account);
+    }
 }

contracts/mocks/ConditionalEscrowMock.sol

@@ -1,16 +1,16 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../payment/escrow/ConditionalEscrow.sol";
 
 // mock class using ConditionalEscrow
 contract ConditionalEscrowMock is ConditionalEscrow {
-  mapping(address => bool) private _allowed;
+    mapping(address => bool) private _allowed;
 
-  function setAllowed(address payee, bool allowed) public {
-    _allowed[payee] = allowed;
-  }
+    function setAllowed(address payee, bool allowed) public {
+        _allowed[payee] = allowed;
+    }
 
-  function withdrawalAllowed(address payee) public view returns (bool) {
-    return _allowed[payee];
-  }
+    function withdrawalAllowed(address payee) public view returns (bool) {
+        return _allowed[payee];
+    }
 }

contracts/mocks/CounterImpl.sol

@@ -1,20 +0,0 @@
-pragma solidity ^0.4.24;
-
-import "../drafts/Counter.sol";
-
-contract CounterImpl {
-  using Counter for Counter.Counter;
-
-  uint256 public theId;
-
-  // use whatever key you want to track your counters
-  mapping(string => Counter.Counter) private _counters;
-
-  function doThing(string key)
-    public
-    returns (uint256)
-  {
-    theId = _counters[key].next();
-    return theId;
-  }
-}

contracts/mocks/CountersImpl.sol

@@ -0,0 +1,21 @@
+pragma solidity ^0.5.0;
+
+import "../drafts/Counters.sol";
+
+contract CountersImpl {
+    using Counters for Counters.Counter;
+
+    Counters.Counter private _counter;
+
+    function current() public view returns (uint256) {
+        return _counter.current();
+    }
+
+    function increment() public {
+        _counter.increment();
+    }
+
+    function decrement() public {
+        _counter.decrement();
+    }
+}

contracts/mocks/CrowdsaleMock.sol

@@ -1,9 +1,9 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../crowdsale/Crowdsale.sol";
 
 contract CrowdsaleMock is Crowdsale {
-  constructor(uint256 rate, address wallet, IERC20 token) public
-    Crowdsale(rate, wallet, token) {
-  }
+    constructor (uint256 rate, address payable wallet, IERC20 token) public Crowdsale(rate, wallet, token) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
 }

contracts/mocks/DetailedERC20Mock.sol

@@ -1,15 +0,0 @@
-pragma solidity ^0.4.24;
-
-import "../token/ERC20/ERC20.sol";
-import "../token/ERC20/ERC20Detailed.sol";
-
-contract ERC20DetailedMock is ERC20, ERC20Detailed {
-  constructor(
-    string name,
-    string symbol,
-    uint8 decimals
-  )
-    ERC20Detailed(name, symbol, decimals)
-    public
-  {}
-}

contracts/mocks/ECDSAMock.sol

@@ -1,23 +1,15 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../cryptography/ECDSA.sol";
 
 contract ECDSAMock {
-  using ECDSA for bytes32;
+    using ECDSA for bytes32;
 
-  function recover(bytes32 hash, bytes signature)
-    public
-    pure
-    returns (address)
-  {
-    return hash.recover(signature);
-  }
+    function recover(bytes32 hash, bytes memory signature) public pure returns (address) {
+        return hash.recover(signature);
+    }
 
-  function toEthSignedMessageHash(bytes32 hash)
-    public
-    pure
-    returns (bytes32)
-  {
-    return hash.toEthSignedMessageHash();
-  }
+    function toEthSignedMessageHash(bytes32 hash) public pure returns (bytes32) {
+        return hash.toEthSignedMessageHash();
+    }
 }

contracts/mocks/ERC165/ERC165InterfacesSupported.sol

@@ -1,66 +1,56 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../../introspection/IERC165.sol";
 
 /**
- * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-214.md#specification
- * > Any attempts to make state-changing operations inside an execution instance with STATIC set to true will instead throw an exception.
+ * https://eips.ethereum.org/EIPS/eip-214#specification
+ * From the specification:
+ * > Any attempts to make state-changing operations inside an execution instance with STATIC set to true will instead
+ * throw an exception.
  * > These operations include [...], LOG0, LOG1, LOG2, [...]
  *
  * therefore, because this contract is staticcall'd we need to not emit events (which is how solidity-coverage works)
  * solidity-coverage ignores the /mocks folder, so we duplicate its implementation here to avoid instrumenting it
  */
 contract SupportsInterfaceWithLookupMock is IERC165 {
+    /*
+     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
+     */
+    bytes4 public constant INTERFACE_ID_ERC165 = 0x01ffc9a7;
 
-  bytes4 public constant InterfaceId_ERC165 = 0x01ffc9a7;
-  /**
-   * 0x01ffc9a7 ===
-   *   bytes4(keccak256('supportsInterface(bytes4)'))
-   */
+    /**
+     * @dev A mapping of interface id to whether or not it's supported.
+     */
+    mapping(bytes4 => bool) private _supportedInterfaces;
 
-  /**
-   * @dev a mapping of interface id to whether or not it's supported
-   */
-  mapping(bytes4 => bool) private _supportedInterfaces;
+    /**
+     * @dev A contract implementing SupportsInterfaceWithLookup
+     * implement ERC165 itself.
+     */
+    constructor () public {
+        _registerInterface(INTERFACE_ID_ERC165);
+    }
 
-  /**
-   * @dev A contract implementing SupportsInterfaceWithLookup
-   * implement ERC165 itself
-   */
-  constructor()
-    public
-  {
-    _registerInterface(InterfaceId_ERC165);
-  }
+    /**
+     * @dev Implement supportsInterface(bytes4) using a lookup table.
+     */
+    function supportsInterface(bytes4 interfaceId) external view returns (bool) {
+        return _supportedInterfaces[interfaceId];
+    }
 
-  /**
-   * @dev implement supportsInterface(bytes4) using a lookup table
-   */
-  function supportsInterface(bytes4 interfaceId)
-    external
-    view
-    returns (bool)
-  {
-    return _supportedInterfaces[interfaceId];
-  }
-
-  /**
-   * @dev private method for registering an interface
-   */
-  function _registerInterface(bytes4 interfaceId)
-    internal
-  {
-    require(interfaceId != 0xffffffff);
-    _supportedInterfaces[interfaceId] = true;
-  }
+    /**
+     * @dev Private method for registering an interface.
+     */
+    function _registerInterface(bytes4 interfaceId) internal {
+        require(interfaceId != 0xffffffff, "ERC165InterfacesSupported: invalid interface id");
+        _supportedInterfaces[interfaceId] = true;
+    }
 }
 
 contract ERC165InterfacesSupported is SupportsInterfaceWithLookupMock {
-  constructor (bytes4[] interfaceIds)
-    public
-  {
-    for (uint256 i = 0; i < interfaceIds.length; i++) {
-      _registerInterface(interfaceIds[i]);
+    constructor (bytes4[] memory interfaceIds) public {
+        for (uint256 i = 0; i < interfaceIds.length; i++) {
+            _registerInterface(interfaceIds[i]);
+        }
     }
-  }
 }

contracts/mocks/ERC165/ERC165NotSupported.sol

@@ -1,5 +1,5 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 contract ERC165NotSupported {
-
+    // solhint-disable-previous-line no-empty-blocks
 }

contracts/mocks/ERC165CheckerMock.sol

@@ -1,31 +1,19 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../introspection/ERC165Checker.sol";
 
 contract ERC165CheckerMock {
-  using ERC165Checker for address;
+    using ERC165Checker for address;
 
-  function supportsERC165(address account)
-    public
-    view
-    returns (bool)
-  {
-    return account._supportsERC165();
-  }
+    function supportsERC165(address account) public view returns (bool) {
+        return account._supportsERC165();
+    }
 
-  function supportsInterface(address account, bytes4 interfaceId)
-    public
-    view
-    returns (bool)
-  {
-    return account._supportsInterface(interfaceId);
-  }
+    function supportsInterface(address account, bytes4 interfaceId) public view returns (bool) {
+        return account._supportsInterface(interfaceId);
+    }
 
-  function supportsAllInterfaces(address account, bytes4[] interfaceIds)
-    public
-    view
-    returns (bool)
-  {
-    return account._supportsAllInterfaces(interfaceIds);
-  }
+    function supportsAllInterfaces(address account, bytes4[] memory interfaceIds) public view returns (bool) {
+        return account._supportsAllInterfaces(interfaceIds);
+    }
 }

contracts/mocks/ERC165Mock.sol

@@ -1,11 +1,9 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../introspection/ERC165.sol";
 
 contract ERC165Mock is ERC165 {
-  function registerInterface(bytes4 interfaceId)
-    public
-  {
-    _registerInterface(interfaceId);
-  }
+    function registerInterface(bytes4 interfaceId) public {
+        _registerInterface(interfaceId);
+    }
 }

contracts/mocks/ERC1820ImplementerMock.sol

@@ -0,0 +1,9 @@
+pragma solidity ^0.5.0;
+
+import "../introspection/ERC1820Implementer.sol";
+
+contract ERC1820ImplementerMock is ERC1820Implementer {
+    function registerInterfaceForAddress(bytes32 interfaceHash, address account) public {
+        _registerInterfaceForAddress(interfaceHash, account);
+    }
+}

contracts/mocks/ERC20BurnableMock.sol

@@ -1,11 +1,9 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/ERC20Burnable.sol";
 
 contract ERC20BurnableMock is ERC20Burnable {
-
-  constructor(address initialAccount, uint256 initialBalance) public {
-    _mint(initialAccount, initialBalance);
-  }
-
+    constructor (address initialAccount, uint256 initialBalance) public {
+        _mint(initialAccount, initialBalance);
+    }
 }

contracts/mocks/ERC20DetailedMock.sol

@@ -0,0 +1,13 @@
+pragma solidity ^0.5.0;
+
+import "../token/ERC20/ERC20.sol";
+import "../token/ERC20/ERC20Detailed.sol";
+
+contract ERC20DetailedMock is ERC20, ERC20Detailed {
+    constructor (string memory name, string memory symbol, uint8 decimals)
+        public
+        ERC20Detailed(name, symbol, decimals)
+    {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+}

contracts/mocks/ERC20MetadataMock.sol

@@ -0,0 +1,14 @@
+pragma solidity ^0.5.0;
+
+import "../token/ERC20/ERC20.sol";
+import "../drafts/ERC1046/ERC20Metadata.sol";
+
+contract ERC20MetadataMock is ERC20, ERC20Metadata {
+    constructor (string memory tokenURI) public ERC20Metadata(tokenURI) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    function setTokenURI(string memory tokenURI) public {
+        _setTokenURI(tokenURI);
+    }
+}

contracts/mocks/ERC20MintableMock.sol

@@ -1,7 +1,8 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/ERC20Mintable.sol";
 import "./MinterRoleMock.sol";
 
 contract ERC20MintableMock is ERC20Mintable, MinterRoleMock {
+    // solhint-disable-previous-line no-empty-blocks
 }

contracts/mocks/ERC20Mock.sol

@@ -1,24 +1,30 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/ERC20.sol";
 
 // mock class using ERC20
 contract ERC20Mock is ERC20 {
+    constructor (address initialAccount, uint256 initialBalance) public {
+        _mint(initialAccount, initialBalance);
+    }
 
-  constructor(address initialAccount, uint256 initialBalance) public {
-    _mint(initialAccount, initialBalance);
-  }
+    function mint(address account, uint256 amount) public {
+        _mint(account, amount);
+    }
 
-  function mint(address account, uint256 amount) public {
-    _mint(account, amount);
-  }
+    function burn(address account, uint256 amount) public {
+        _burn(account, amount);
+    }
 
-  function burn(address account, uint256 amount) public {
-    _burn(account, amount);
-  }
+    function burnFrom(address account, uint256 amount) public {
+        _burnFrom(account, amount);
+    }
 
-  function burnFrom(address account, uint256 amount) public {
-    _burnFrom(account, amount);
-  }
+    function transferInternal(address from, address to, uint256 value) public {
+        _transfer(from, to, value);
+    }
 
+    function approveInternal(address owner, address spender, uint256 value) public {
+        _approve(owner, spender, value);
+    }
 }

contracts/mocks/ERC20PausableMock.sol

@@ -1,13 +1,11 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/ERC20Pausable.sol";
 import "./PauserRoleMock.sol";
 
 // mock class using ERC20Pausable
 contract ERC20PausableMock is ERC20Pausable, PauserRoleMock {
-
-  constructor(address initialAccount, uint initialBalance) public {
-    _mint(initialAccount, initialBalance);
-  }
-
+    constructor (address initialAccount, uint initialBalance) public {
+        _mint(initialAccount, initialBalance);
+    }
 }

contracts/mocks/ERC20SnapshotMock.sol

@@ -0,0 +1,18 @@
+pragma solidity ^0.5.0;
+
+import "../drafts/ERC20Snapshot.sol";
+
+
+contract ERC20SnapshotMock is ERC20Snapshot {
+    constructor(address initialAccount, uint256 initialBalance) public {
+        _mint(initialAccount, initialBalance);
+    }
+
+    function mint(address account, uint256 amount) public {
+        _mint(account, amount);
+    }
+
+    function burn(address account, uint256 amount) public {
+        _burn(account, amount);
+    }
+}

contracts/mocks/ERC20WithMetadataMock.sol

@@ -1,11 +0,0 @@
-pragma solidity ^0.4.24;
-
-import "../token/ERC20/ERC20.sol";
-import "../drafts/ERC1046/TokenMetadata.sol";
-
-contract ERC20WithMetadataMock is ERC20, ERC20WithMetadata {
-  constructor(string tokenURI) public
-    ERC20WithMetadata(tokenURI)
-  {
-  }
-}

contracts/mocks/ERC721FullMock.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC721/ERC721Full.sol";
 import "../token/ERC721/ERC721Mintable.sol";
@@ -7,26 +7,23 @@ import "../token/ERC721/ERC721Burnable.sol";
 
 /**
  * @title ERC721FullMock
- * This mock just provides a public mint and burn functions for testing purposes,
- * and a public setter for metadata URI
+ * This mock just provides public functions for setting metadata URI, getting all tokens of an owner,
+ * checking token existence, removal of a token from an address
  */
-contract ERC721FullMock
-  is ERC721Full, ERC721Mintable, ERC721MetadataMintable, ERC721Burnable {
+contract ERC721FullMock is ERC721Full, ERC721Mintable, ERC721MetadataMintable, ERC721Burnable {
+    constructor (string memory name, string memory symbol) public ERC721Mintable() ERC721Full(name, symbol) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
 
-  constructor(string name, string symbol) public
-    ERC721Mintable()
-    ERC721Full(name, symbol)
-  {}
+    function exists(uint256 tokenId) public view returns (bool) {
+        return _exists(tokenId);
+    }
 
-  function exists(uint256 tokenId) public view returns (bool) {
-    return _exists(tokenId);
-  }
+    function tokensOfOwner(address owner) public view returns (uint256[] memory) {
+        return _tokensOfOwner(owner);
+    }
 
-  function setTokenURI(uint256 tokenId, string uri) public {
-    _setTokenURI(tokenId, uri);
-  }
-
-  function removeTokenFrom(address from, uint256 tokenId) public {
-    _removeTokenFrom(from, tokenId);
-  }
+    function setTokenURI(uint256 tokenId, string memory uri) public {
+        _setTokenURI(tokenId, uri);
+    }
 }

contracts/mocks/ERC721MintableBurnableImpl.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC721/ERC721Full.sol";
 import "../token/ERC721/ERC721Mintable.sol";
@@ -8,13 +8,8 @@ import "../token/ERC721/ERC721Burnable.sol";
 /**
  * @title ERC721MintableBurnableImpl
  */
-contract ERC721MintableBurnableImpl
-  is ERC721Full, ERC721Mintable, ERC721MetadataMintable, ERC721Burnable {
-
-  constructor()
-    ERC721Mintable()
-    ERC721Full("Test", "TEST")
-    public
-  {
-  }
+contract ERC721MintableBurnableImpl is ERC721Full, ERC721Mintable, ERC721MetadataMintable, ERC721Burnable {
+    constructor () public ERC721Mintable() ERC721Full("Test", "TEST") {
+        // solhint-disable-previous-line no-empty-blocks
+    }
 }

contracts/mocks/ERC721Mock.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC721/ERC721.sol";
 
@@ -7,11 +7,15 @@ import "../token/ERC721/ERC721.sol";
  * This mock just provides a public mint and burn functions for testing purposes
  */
 contract ERC721Mock is ERC721 {
-  function mint(address to, uint256 tokenId) public {
-    _mint(to, tokenId);
-  }
+    function mint(address to, uint256 tokenId) public {
+        _mint(to, tokenId);
+    }
 
-  function burn(uint256 tokenId) public {
-    _burn(ownerOf(tokenId), tokenId);
-  }
+    function burn(address owner, uint256 tokenId) public {
+        _burn(owner, tokenId);
+    }
+
+    function burn(uint256 tokenId) public {
+        _burn(tokenId);
+    }
 }

contracts/mocks/ERC721PausableMock.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC721/ERC721Pausable.sol";
 import "./PauserRoleMock.sol";
@@ -8,15 +8,15 @@ import "./PauserRoleMock.sol";
  * This mock just provides a public mint, burn and exists functions for testing purposes
  */
 contract ERC721PausableMock is ERC721Pausable, PauserRoleMock {
-  function mint(address to, uint256 tokenId) public {
-    super._mint(to, tokenId);
-  }
+    function mint(address to, uint256 tokenId) public {
+        super._mint(to, tokenId);
+    }
 
-  function burn(uint256 tokenId) public {
-    super._burn(ownerOf(tokenId), tokenId);
-  }
+    function burn(uint256 tokenId) public {
+        super._burn(tokenId);
+    }
 
-  function exists(uint256 tokenId) public view returns (bool) {
-    return super._exists(tokenId);
-  }
+    function exists(uint256 tokenId) public view returns (bool) {
+        return super._exists(tokenId);
+    }
 }

contracts/mocks/ERC721ReceiverMock.sol

@@ -1,41 +1,23 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC721/IERC721Receiver.sol";
 
 contract ERC721ReceiverMock is IERC721Receiver {
-  bytes4 private _retval;
-  bool private _reverts;
+    bytes4 private _retval;
+    bool private _reverts;
 
-  event Received(
-    address operator,
-    address from,
-    uint256 tokenId,
-    bytes data,
-    uint256 gas
-  );
+    event Received(address operator, address from, uint256 tokenId, bytes data, uint256 gas);
 
-  constructor(bytes4 retval, bool reverts) public {
-    _retval = retval;
-    _reverts = reverts;
-  }
+    constructor (bytes4 retval, bool reverts) public {
+        _retval = retval;
+        _reverts = reverts;
+    }
 
-  function onERC721Received(
-    address operator,
-    address from,
-    uint256 tokenId,
-    bytes data
-  )
-    public
-    returns(bytes4)
-  {
-    require(!_reverts);
-    emit Received(
-      operator,
-      from,
-      tokenId,
-      data,
-      gasleft() // msg.gas was deprecated in solidityv0.4.21
-    );
-    return _retval;
-  }
+    function onERC721Received(address operator, address from, uint256 tokenId, bytes memory data)
+        public returns (bytes4)
+    {
+        require(!_reverts, "ERC721ReceiverMock: reverting");
+        emit Received(operator, from, tokenId, data, gasleft());
+        return _retval;
+    }
 }

contracts/mocks/ERC777Mock.sol

@@ -0,0 +1,25 @@
+pragma solidity ^0.5.0;
+
+import "../token/ERC777/ERC777.sol";
+
+contract ERC777Mock is ERC777 {
+    constructor(
+        address initialHolder,
+        uint256 initialBalance,
+        string memory name,
+        string memory symbol,
+        address[] memory defaultOperators
+    ) public ERC777(name, symbol, defaultOperators) {
+        _mint(msg.sender, initialHolder, initialBalance, "", "");
+    }
+
+    function mintInternal (
+        address operator,
+        address to,
+        uint256 amount,
+        bytes memory userData,
+        bytes memory operatorData
+    ) public {
+        _mint(operator, to, amount, userData, operatorData);
+    }
+}

contracts/mocks/ERC777SenderRecipientMock.sol

@@ -0,0 +1,147 @@
+pragma solidity ^0.5.0;
+
+import "../token/ERC777/IERC777.sol";
+import "../token/ERC777/IERC777Sender.sol";
+import "../token/ERC777/IERC777Recipient.sol";
+import "../introspection/IERC1820Registry.sol";
+import "../introspection/ERC1820Implementer.sol";
+
+contract ERC777SenderRecipientMock is IERC777Sender, IERC777Recipient, ERC1820Implementer {
+    event TokensToSendCalled(
+        address operator,
+        address from,
+        address to,
+        uint256 amount,
+        bytes data,
+        bytes operatorData,
+        address token,
+        uint256 fromBalance,
+        uint256 toBalance
+    );
+
+    event TokensReceivedCalled(
+        address operator,
+        address from,
+        address to,
+        uint256 amount,
+        bytes data,
+        bytes operatorData,
+        address token,
+        uint256 fromBalance,
+        uint256 toBalance
+    );
+
+    bool private _shouldRevertSend;
+    bool private _shouldRevertReceive;
+
+    IERC1820Registry private _erc1820 = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);
+
+    bytes32 constant private TOKENS_SENDER_INTERFACE_HASH = keccak256("ERC777TokensSender");
+    bytes32 constant private TOKENS_RECIPIENT_INTERFACE_HASH = keccak256("ERC777TokensRecipient");
+
+    function tokensToSend(
+        address operator,
+        address from,
+        address to,
+        uint amount,
+        bytes calldata userData,
+        bytes calldata operatorData
+    ) external {
+        if (_shouldRevertSend) {
+            revert();
+        }
+
+        IERC777 token = IERC777(msg.sender);
+
+        uint256 fromBalance = token.balanceOf(from);
+        // when called due to burn, to will be the zero address, which will have a balance of 0
+        uint256 toBalance = token.balanceOf(to);
+
+        emit TokensToSendCalled(
+            operator,
+            from,
+            to,
+            amount,
+            userData,
+            operatorData,
+            address(token),
+            fromBalance,
+            toBalance
+        );
+    }
+
+    function tokensReceived(
+        address operator,
+        address from,
+        address to,
+        uint amount,
+        bytes calldata userData,
+        bytes calldata operatorData
+    ) external{
+        if (_shouldRevertReceive) {
+            revert();
+        }
+
+        IERC777 token = IERC777(msg.sender);
+
+        uint256 fromBalance = token.balanceOf(from);
+        // when called due to burn, to will be the zero address, which will have a balance of 0
+        uint256 toBalance = token.balanceOf(to);
+
+        emit TokensReceivedCalled(
+            operator,
+            from,
+            to,
+            amount,
+            userData,
+            operatorData,
+            address(token),
+            fromBalance,
+            toBalance
+        );
+    }
+
+    function senderFor(address account) public {
+        _registerInterfaceForAddress(TOKENS_SENDER_INTERFACE_HASH, account);
+
+        address self = address(this);
+        if (account == self) {
+            registerSender(self);
+        }
+    }
+
+    function registerSender(address sender) public {
+        _erc1820.setInterfaceImplementer(address(this), TOKENS_SENDER_INTERFACE_HASH, sender);
+    }
+
+    function recipientFor(address account) public {
+        _registerInterfaceForAddress(TOKENS_RECIPIENT_INTERFACE_HASH, account);
+
+        address self = address(this);
+        if (account == self) {
+            registerRecipient(self);
+        }
+    }
+
+    function registerRecipient(address recipient) public {
+        _erc1820.setInterfaceImplementer(address(this), TOKENS_RECIPIENT_INTERFACE_HASH, recipient);
+    }
+
+    function setShouldRevertSend(bool shouldRevert) public {
+        _shouldRevertSend = shouldRevert;
+    }
+
+    function setShouldRevertReceive(bool shouldRevert) public {
+        _shouldRevertReceive = shouldRevert;
+    }
+
+    function send(IERC777 token, address to, uint256 amount, bytes memory data) public {
+        // This is 777's send function, not the Solidity send function
+        token.send(to, amount, data); // solhint-disable-line check-send-result
+    }
+
+    function burn(IERC777 token, uint256 amount, bytes memory data) public {
+        token.burn(amount, data);
+    }
+}
+