3.0.0

* remove ethpm.json

* update releasing document

* fix release documentation to be more realistic

.circleci/config.yml

@@ -0,0 +1,84 @@
+version: 2
+# 2.1 does not yet support local run
+# unless with workaround. For simplicity just use it.
+# https://github.com/CircleCI-Public/circleci-cli/issues/79
+
+aliases:
+  - &defaults
+    docker:
+      - image: circleci/node:10
+
+  - &cache_key_node_modules
+    key: v1-node_modules-{{ checksum "package-lock.json" }}
+
+jobs:
+  dependencies:
+    <<: *defaults
+    steps:
+      - checkout
+      - restore_cache:
+          <<: *cache_key_node_modules
+      - run:
+          name: Install npm dependencies and prepare
+          command: |
+            if [ ! -d node_modules ]; then
+              npm ci
+            else
+              npm run prepare
+            fi
+      - persist_to_workspace:
+          root: .
+          paths:
+            - node_modules
+            - build
+      - save_cache:
+          paths:
+            - node_modules
+          <<: *cache_key_node_modules
+
+  lint:
+    <<: *defaults
+    steps:
+      - checkout
+      - attach_workspace:
+          at: .
+      - run:
+          name: Linter
+          command: npm run lint
+  test:
+    <<: *defaults
+    steps:
+      - checkout
+      - attach_workspace:
+          at: .
+      - run:
+          name: Unit tests
+          command: npm run test
+
+  coverage:
+    <<: *defaults
+    steps:
+      - checkout
+      - attach_workspace:
+          at: .
+      - run:
+          name: Unit tests with coverage report
+          command: npm run coverage
+
+      # TODO(xinbenlv, #1839): run SOLC_NIGHTLY to be run but allow it to fail.
+
+workflows:
+  version: 2
+  everything:
+    jobs:
+      - dependencies
+      - lint:
+          requires:
+            - dependencies
+      - test:
+          requires:
+            - dependencies
+      - coverage:
+          requires:
+            - dependencies
+

.codecov.yml

@@ -0,0 +1,3 @@
+comment: off
+coverage:
+  range: "100...100"

.dependabot/config.yml

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

.editorconfig

@@ -6,7 +6,13 @@ root = true
 [*]
 charset = utf-8
 end_of_line = lf
-indent_size = 2
 indent_style = space
 insert_final_newline = true
 trim_trailing_whitespace = true
+max_line_length = 120
+
+[*.sol]
+indent_size = 4
+
+[*.js]
+indent_size = 2

.eslintrc

@@ -25,6 +25,7 @@
     "strict": ["error", "global"],
 
     // Code style
+    "array-bracket-spacing": ["off"],
     "camelcase": ["error", {"properties": "always"}],
     "comma-dangle": ["error", "always-multiline"],
     "comma-spacing": ["error", {"before": false, "after": true}],
@@ -54,5 +55,8 @@
 
     "promise/always-return": "off",
     "promise/avoid-new": "off",
+  },
+  "parserOptions": {
+    "ecmaVersion": 2018
   }
 }

.github/ISSUE_TEMPLATE/bug_report.md

@@ -1,16 +1,16 @@
 ---
 name: Bug report
-about: Report a bug in OpenZeppelin
+about: Report a bug in OpenZeppelin Contracts
 
 ---
 
 <!-- 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 OpenZeppelin Slack channel: https://slack.openzeppelin.org/. -->
+<!-- Remember, this is not a place to ask for help debugging code. For that, we welcome you in the OpenZeppelin Community Forum: https://forum.openzeppelin.com/. -->
 
 **💻 Environment**
 
-<!-- Tell us what version of OpenZeppelin you're using, and how you're using it: Truffle, Remix, etc. -->
+<!-- Tell us what version of OpenZeppelin Contracts you're using, and how you're using it: Truffle, Remix, etc. -->
 
 **📝 Details**
 

.github/ISSUE_TEMPLATE/config.yml

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

.github/ISSUE_TEMPLATE/feature_request.md

@@ -1,6 +1,6 @@
 ---
 name: Feature request
-about: Suggest an idea for OpenZeppelin
+about: Suggest an idea for OpenZeppelin Contracts
 
 ---
 
@@ -11,4 +11,4 @@ about: Suggest an idea for OpenZeppelin
 <!-- 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 -->
+<!-- https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/CONTRIBUTING.md -->

.github/PULL_REQUEST_TEMPLATE.md

@@ -13,7 +13,7 @@ Fixes #
 
 <!-- 3. Before submitting, please make sure that you have:
   - reviewed the OpenZeppelin Contributor Guidelines
-    (https://github.com/OpenZeppelin/openzeppelin-solidity/blob/master/CONTRIBUTING.md),
+    (https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/CONTRIBUTING.md),
   - added tests where applicable to test new functionality,
   - made sure that your contracts are well-documented,
   - run the Solidity linter (`npm run lint:sol`) and fixed any issues,

.github/stale.yml

@@ -0,0 +1,67 @@
+# Configuration for probot-stale - https://github.com/probot/stale
+
+# Number of days of inactivity before an Issue or Pull Request becomes stale
+daysUntilStale: 15
+
+# Number of days of inactivity before an Issue or Pull Request with the stale label is closed.
+# Set to false to disable. If disabled, issues still need to be closed manually, but will remain marked as stale.
+daysUntilClose: 15
+
+# Issues or Pull Requests with these labels will never be considered stale. Set to `[]` to disable
+exemptLabels:
+  - on hold
+  - meta
+
+# Set to true to ignore issues in a project (defaults to false)
+exemptProjects: false
+
+# Set to true to ignore issues in a milestone (defaults to false)
+exemptMilestones: false
+
+# Set to true to ignore issues with an assignee (defaults to false)
+exemptAssignees: false
+
+# Label to use when marking as stale
+staleLabel: stale
+
+# Comment to post when marking as stale. Set to `false` to disable
+markComment: >
+  Hi all!
+
+  This Pull Request has not had any recent activity, is it still relevant? If so, what is blocking it?
+  Is there anything we can do to help move it forward?
+
+  Thanks!
+
+
+# Comment to post when removing the stale label.
+# unmarkComment: >
+#   Your comment here.
+
+# Comment to post when closing a stale Issue or Pull Request.
+closeComment: >
+  Hi folks!
+
+  This Pull Request is being closed as there was no response to the previous prompt.
+  However, please leave a comment whenever you're ready to resume, so it can be reopened.
+
+  Thanks again!
+
+
+# Limit the number of actions per hour, from 1-30. Default is 30
+limitPerRun: 30
+
+# Limit to only `issues` or `pulls`
+only: pulls
+
+# Optionally, specify configuration settings that are specific to just 'issues' or 'pulls':
+# pulls:
+#   daysUntilStale: 30
+#   markComment: >
+#     This pull request has been automatically marked as stale because it has not had
+#     recent activity. It will be closed if no further activity occurs. Thank you
+#     for your contributions.
+
+# issues:
+#   exemptLabels:
+#     - confirmed

.gitignore

@@ -40,3 +40,13 @@ build/
 
 # IntelliJ IDE
 .idea
+
+# docs artifacts
+docs/modules/api
+
+# only used to package @openzeppelin/contracts
+contracts/build/
+contracts/README.md
+
+# temporary artifact from solidity-coverage
+allFiredEvents

.solcover.js

@@ -1,9 +1,8 @@
 module.exports = {
     norpc: true,
-    testCommand: 'node --max-old-space-size=4096 ../node_modules/.bin/truffle test --network coverage',
-    compileCommand: 'node --max-old-space-size=4096 ../node_modules/.bin/truffle compile --network coverage',
+    testCommand: 'npm test',
+    compileCommand: 'npm run compile',
     skipFiles: [
-        'lifecycle/Migrations.sol',
-        'mocks'
+        'mocks',
     ]
 }

.solhint.json

@@ -1,11 +1,10 @@
 {
-  "extends": "default",
+  "extends": "solhint:recommended",
   "rules": {
-    "indent": ["error", 4],
-
-    "bracket-align": false,
-    "compiler-fixed": false,
-    "no-simple-event-func-name": false,
-    "two-lines-top-level-separator": false
+    "func-order": "off",
+    "mark-callable-contracts": "off",
+    "no-empty-blocks": "off",
+    "compiler-version": ["error", "^0.6.0"],
+    "private-vars-leading-underscore": "error"
   }
 }

.travis.yml

@@ -1,53 +0,0 @@
-dist: trusty
-sudo: false
-group: beta
-language: node_js
-node_js:
-  - "8"
-
-cache:
-  directories:
-    - node_modules
-
-jobs:
-  # XXX fast_finish doesn't work with stages yet. See
-  # https://github.com/travis-ci/travis-ci/issues/8425
-  # --elopio - 20180531
-  fast_finish: true
-  allow_failures:
-    - env: SOLC_NIGHTLY=true
-  include:
-    - stage: tests
-      name: "Linter"
-      script: npm run lint
-
-    - stage: tests
-      name: "Unit tests"
-      script: npm run test
-
-    - stage: tests
-      name: "Unit tests with coverage report"
-      script: npm run test
-      env: SOLIDITY_COVERAGE=true
-
-    - stage: tests
-      name: "Unit tests using solc nightly"
-      script: npm run test
-      env: SOLC_NIGHTLY=true
-
-    - 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:
-    rooms:
-      - secure: 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
-    on_success: change
-    on_failure: always
-    on_pull_requests: false

CHANGELOG.md

@@ -1,26 +1,142 @@
 # Changelog
 
-## 2.2.0 (unreleased)
+## 3.0.0 (2020-04-20)
 
-### New features:
+### New features
+ * `AccessControl`: new contract for managing permissions in a system, replacement for `Ownable` and `Roles`. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
+ * `SafeCast`: new functions to convert to and from signed and unsigned values: `toUint256` and `toInt256`. ([#2123](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2123))
+ * `EnumerableMap`: a new data structure for key-value pairs (like `mapping`) that can be iterated over. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+
+### Breaking changes
+ * `ERC721`: `burn(owner, tokenId)` was removed, use `burn(tokenId)` instead. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+ * `ERC721`: `_checkOnERC721Received` was removed. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+ * `ERC721`: `_transferFrom` and `_safeTransferFrom` were renamed to `_transfer` and `_safeTransfer`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+ * `Ownable`: removed `_transferOwnership`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+ * `PullPayment`, `Escrow`: `withdrawWithGas` was removed. The old `withdraw` function now forwards all gas. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+ * `Roles` was removed, use `AccessControl` as a replacement. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
+ * `ECDSA`: when receiving an invalid signature, `recover` now reverts instead of returning the zero address. ([#2114](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2114))
+ * `Create2`: added an `amount` argument to `deploy` for contracts with `payable` constructors. ([#2117](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2117))
+ * `Pausable`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `Strings`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `Counters`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `SignedSafeMath`: moved to the `math` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `ERC20Snapshot`: moved to the `token/ERC20` directory. `snapshot` was changed into an `internal` function. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `Ownable`: moved to the `access` directory. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `Ownable`: removed `isOwner`. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `Secondary`: removed from the library, use `Ownable` instead. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `Escrow`, `ConditionalEscrow`, `RefundEscrow`: these now use `Ownable` instead of `Secondary`, their external API changed accordingly. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `ERC20`: removed `_burnFrom`. ([#2119](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2119))
+ * `Address`: removed `toPayable`, use `payable(address)` instead. ([#2133](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2133))
+ * `ERC777`: `_send`, `_mint` and `_burn` now use the caller as the operator. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+ * `ERC777`: removed `_callsTokensToSend` and `_callTokensReceived`. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+ * `EnumerableSet`: renamed `get` to `at`. ([#2151](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2151))
+ * `ERC165Checker`: functions no longer have a leading underscore. ([#2150](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2150))
+ * `ERC721Metadata`, `ERC721Enumerable`: these contracts were removed, and their functionality merged into `ERC721`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+ * `ERC721`: added a constructor for `name` and `symbol`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+ * `ERC20Detailed`: this contract was removed and its functionality merged into `ERC20`. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
+ * `ERC20`: added a constructor for `name` and `symbol`. `decimals` now defaults to 18. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
+ * `Strings`: renamed `fromUint256` to `toString` ([#2188](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2188))
+
+## 2.5.0 (2020-02-04)
+
+### New features
+ * `SafeCast.toUintXX`: new library for integer downcasting, which allows for safe operation on smaller types (e.g. `uint32`) when combined with `SafeMath`. ([#1926](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1926))
+ * `ERC721Metadata`: added `baseURI`, which can be used for dramatic gas savings when all token URIs share a prefix (e.g. `http://api.myapp.com/tokens/<id>`). ([#1970](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1970))
+ * `EnumerableSet`: new library for storing enumerable sets of values. Only `AddressSet` is supported in this release. ([#2061](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/2061))
+ * `Create2`: simple library to make usage of the `CREATE2` opcode easier. ([#1744](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1744))
+
+### Improvements
+ * `ERC777`: `_burn` is now internal, providing more flexibility and making it easier to create tokens that deflate. ([#1908](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1908))
+ * `ReentrancyGuard`: greatly improved gas efficiency by using the net gas metering mechanism introduced in the Istanbul hardfork. ([#1992](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1992), [#1996](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1996))
+ * `ERC777`: improve extensibility by making `_send` and related functions `internal`. ([#2027](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2027))
+ * `ERC721`: improved revert reason when transferring tokens to a non-recipient contract. ([#2018](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2018))
+
+### Breaking changes
+ * `ERC165Checker` now requires a minimum Solidity compiler version of 0.5.10. ([#1829](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1829))
+
+## 2.4.0 (2019-10-29)
+
+### New features
+ * `Address.toPayable`: added a helper to convert between address types without having to resort to low-level casting. ([#1773](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1773))
+ * Facilities to make metatransaction-enabled contracts through the Gas Station Network. ([#1844](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1844))
+ * `Address.sendValue`: added a replacement to Solidity's `transfer`, removing the fixed gas stipend. ([#1962](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1962))
+ * Added replacement for functions that don't forward all gas (which have been deprecated): ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))
+   * `PullPayment.withdrawPaymentsWithGas(address payable payee)`
+   * `Escrow.withdrawWithGas(address payable payee)`
+ * `SafeMath`: added support for custom error messages to `sub`, `div` and `mod` functions. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+
+### Improvements
+ * `Address.isContract`: switched from `extcodesize` to `extcodehash` for less gas usage. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
+ * `ERC20` and `ERC777` updated to throw custom errors on subtraction overflows. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+
+### Deprecations
+ * Deprecated functions that don't forward all gas: ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))
+   * `PullPayment.withdrawPayments(address payable payee)`
+   * `Escrow.withdraw(address payable payee)`
+
+### Breaking changes
+ * `Address` now requires a minimum Solidity compiler version of 0.5.5. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
+ * `SignatureBouncer` has been removed from drafts, both to avoid confusions with the GSN and `GSNRecipientSignature` (previously called `GSNBouncerSignature`) and because the API was not very clear. ([#1879](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1879))
+
+### How to upgrade from 2.4.0-beta
+
+The final 2.4.0 release includes a refactor of the GSN contracts that will be a breaking change for 2.4.0-beta users.
+
+ * The default empty implementations of `_preRelayedCall` and `_postRelayedCall` were removed and must now be explicitly implemented always in custom recipients. If your custom recipient didn't include an implementation, you can provide an empty one.
+ * `GSNRecipient`, `GSNBouncerBase`, and `GSNContext` were all merged into `GSNRecipient`.
+ * `GSNBouncerSignature` and `GSNBouncerERC20Fee` were renamed to `GSNRecipientSignature` and `GSNRecipientERC20Fee`.
+ * It is no longer necessary to inherit from `GSNRecipient` when using `GSNRecipientSignature` and `GSNRecipientERC20Fee`.
+
+For example, a contract using `GSNBouncerSignature` would have to be changed in the following way.
+
+```diff
+-contract MyDapp is GSNRecipient, GSNBouncerSignature {
++contract MyDapp is GSNRecipientSignature {
+```
+
+Refer to the table below to adjust your inheritance list.
+
+| 2.4.0-beta                         | 2.4.0                        |
+| ---------------------------------- | ---------------------------- |
+| `GSNRecipient, GSNBouncerSignature`| `GSNRecipientSignature`      |
+| `GSNRecipient, GSNBouncerERC20Fee` | `GSNRecipientERC20Fee`       |
+| `GSNBouncerBase`                   | `GSNRecipient`               |
+
+## 2.3.0 (2019-05-27)
+
+### New features
+ * `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/))
+ * `SafeERC20`: `ERC20` contracts with no return value (i.e. that revert on failure) are now supported. ([#1655](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1655))
  * `ERC20`: added internal `_approve(address owner, address spender, uint256 value)`, allowing derived contracts to set the allowance of arbitrary accounts. ([#1609](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1609))
  * `ERC20Metadata`: added internal `_setTokenURI(string memory tokenURI)`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
  * `TimedCrowdsale`: added internal `_extendTime(uint256 newClosingTime)` as well as `TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime)` event allowing to extend the crowdsale, as long as it hasn't already closed.
 
-### Improvements:
+### Improvements
  * Upgraded the minimum compiler version to v0.5.2: this removes many Solidity warnings that were false positives. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
  * `ECDSA`: `recover` no longer accepts malleable signatures (those using upper-range values for `s`, or 0/1 for `v`). ([#1622](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1622))
- * `ERC721`'s transfers are now more gas efficient due to removal of unnecessary `SafeMath` calls. ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
- * `Counter`'s API has been improved, and is now used by `ERC721` (though it is still in `drafts`). ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+ * ``ERC721``'s transfers are now more gas efficient due to removal of unnecessary `SafeMath` calls. ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
  * Fixed variable shadowing issues. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
 
-### Bugfixes:
+### Bugfixes
  * (minor) `SafeERC20`: `safeApprove` wasn't properly checking for a zero allowance when attempting to set a non-zero allowance. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
 
-### Breaking changes:
- * `TokenMetadata` (in drafts) has been renamed to `ERC20Metadata`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+### 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))
@@ -33,7 +149,7 @@
 
 ## 2.1.0 (2019-01-04)
 
-### New features:
+### New features
  * Now targeting the 0.5.x line of Solidity compilers. For 0.4.24 support, use version 2.0 of OpenZeppelin.
  * `WhitelistCrowdsale`: a crowdsale where only whitelisted accounts (`WhitelistedRole`) can purchase tokens. Adding or removing accounts from the whitelist is done by whitelist admins (`WhitelistAdminRole`). Similar to the pre-2.0 `WhitelistedCrowdsale`. ([#1525](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1525), [#1589](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1589))
  * `RefundablePostDeliveryCrowdsale`: replacement for `RefundableCrowdsale` (deprecated, see below) where tokens are only granted once the crowdsale ends (if it meets its goal). ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))
@@ -44,17 +160,17 @@
  * Crowdsales: all constructors are now `public`, meaning it is not necessary to extend these contracts in order to deploy them. The exception is `FinalizableCrowdsale`, since it is meaningless unless extended. ([#1564](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1564))
  * `SignedSafeMath`: added overflow-safe operations for signed integers (`int256`). ([#1559](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1559), [#1588](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1588))
 
-### Improvements:
+### Improvements
  * The compiler version required by `Array` was behind the rest of the libray so it was updated to `v0.4.24`. ([#1553](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1553))
  * Now conforming to a 4-space indentation code style. ([1508](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1508))
  * `ERC20`: more gas efficient due to removed redundant `require`s. ([#1409](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1409))
  * `ERC721`: fixed a bug that prevented internal data structures from being properly cleaned, missing potential gas refunds. ([#1539](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1539) and [#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
  * `ERC721`: general gas savings on `transferFrom`, `_mint` and `_burn`, due to redudant `require`s and `SSTORE`s. ([#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
 
-### Bugfixes:
+### Bugfixes
 
-### Breaking changes:
+### Breaking changes
 
-### Deprecations:
+### Deprecations
  * `ERC721._burn(address owner, uint256 tokenId)`: due to the `owner` parameter being unnecessary. ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
  * `RefundableCrowdsale`: due to trading abuse potential on crowdsales that miss their goal. ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))

CODE_STYLE.md

@@ -61,3 +61,9 @@ Any exception or additions specific to our project are documented below.
 
   Some standards (e.g. ERC20) use present tense, and in those cases the
   standard specification prevails.
+  
+* Interface names should have a capital I prefix.
+
+    ```
+    interface IERC777 {
+    ```

CONTRIBUTING.md

@@ -1,30 +1,27 @@
-Contributing to OpenZeppelin
+Contributing to OpenZeppelin Contracts
 =======
 
-We really appreciate and value contributions to OpenZeppelin. Please take 5' to review the items listed below to make sure that your contributions are merged as soon as possible. 
+We really appreciate and value contributions to OpenZeppelin Contracts. Please take 5' to review the items listed below to make sure that your contributions are merged as soon as possible.
 
 ## Contribution guidelines
 
-Smart contracts manage value and are highly vulnerable to errors and attacks. We have very strict guidelines, please make sure to review them: ["Contribution guidelines wiki entry"](https://github.com/OpenZeppelin/openzeppelin-solidity/wiki/Contribution-guidelines).
+Smart contracts manage value and are highly vulnerable to errors and attacks. We have very strict [guidelines], please make sure to review them!
 
 ## Creating Pull Requests (PRs)
 
 As a contributor, you are expected to fork this repository, work on your own fork and then submit pull requests. The pull requests will be reviewed and eventually merged into the main repo. See ["Fork-a-Repo"](https://help.github.com/articles/fork-a-repo/) for how this works.
 
-*IMPORTANT* 
-* Please see ["Git flow wiki entry"](https://github.com/OpenZeppelin/openzeppelin-solidity/wiki/Git-flow) for understanding how to use branches in this repository.
-
 ## A typical workflow
 
 1) Make sure your fork is up to date with the main repository:
 
 ```
-cd openzeppelin-solidity
-git remote add upstream https://github.com/OpenZeppelin/openzeppelin-solidity.git
+cd openzeppelin-contracts
+git remote add upstream https://github.com/OpenZeppelin/openzeppelin-contracts.git
 git fetch upstream
 git pull --rebase upstream master
 ```
-NOTE: The directory `openzeppelin-solidity` represents your fork's local copy.
+NOTE: The directory `openzeppelin-contracts` represents your fork's local copy.
 
 2) Branch out from `master` into `fix/some-bug-#123`:
 (Postfixing #123 will associate your PR with the issue #123 and make everyone's life easier =D)
@@ -32,7 +29,7 @@ NOTE: The directory `openzeppelin-solidity` represents your fork's local copy.
 git checkout -b fix/some-bug-#123
 ```
 
-3) Make your changes, add your files, commit and push to your fork.
+3) Make your changes, add your files, commit, and push to your fork.
 
 ```
 git add SomeFile.js
@@ -40,19 +37,35 @@ git commit "Fix some bug #123"
 git push origin fix/some-bug-#123
 ```
 
-4) Go to [github.com/OpenZeppelin/openzeppelin-solidity](https://github.com/OpenZeppelin/zeppelin-solidity) in your web browser and issue a new pull request.
+4) Run tests, linter, etc. This can be done by running local continuous integration and make sure it passes.
 
-*IMPORTANT* Read the PR template very carefully and make sure to follow all the instructions. These instructions 
-refer to some very important conditions that your PR must meet in order to be accepted, such as making sure that all tests pass, JS linting tests pass, solidity linting tests pass, etc.
+```bash
+npm test
+npm run lint
+```
 
-5) Maintainers will review your code and possibly ask for changes before your code is pulled in to the main repository. We'll check that all tests pass, review the coding style, and check for general code correctness. If everything is OK, we'll merge your pull request and your code will be part of OpenZeppelin.
+or you can simply run CircleCI locally
+```bash
+circleci local execute --job build
+circleci local execute --job test
+```
+*Note*: requires installing CircleCI and docker locally on your machine.
+
+5) Go to [github.com/OpenZeppelin/openzeppelin-contracts](https://github.com/OpenZeppelin/openzeppelin-contracts) in your web browser and issue a new pull request.
+
+*IMPORTANT* Read the PR template very carefully and make sure to follow all the instructions. These instructions
+refer to some very important conditions that your PR must meet in order to be accepted, such as making sure that all tests pass, JS linting tests pass, Solidity linting tests pass, etc.
+
+6) Maintainers will review your code and possibly ask for changes before your code is pulled in to the main repository. We'll check that all tests pass, review the coding style, and check for general code correctness. If everything is OK, we'll merge your pull request and your code will be part of OpenZeppelin.
 
 *IMPORTANT* Please pay attention to the maintainer's feedback, since its a necessary step to keep up with the standards OpenZeppelin attains to.
 
 ## All set!
 
-If you have any questions feel free to post them to github.com/OpenZeppelin/openzeppelin-solidity/issues.
+If you have any questions, feel free to post them to github.com/OpenZeppelin/openzeppelin-contracts/issues.
 
-Finally, if you're looking to collaborate and want to find easy tasks to start, look at the issues we marked as ["Good first issue"](https://github.com/OpenZeppelin/openzeppelin-solidity/labels/good%20first%20issue).
+Finally, if you're looking to collaborate and want to find easy tasks to start, look at the issues we marked as ["Good first issue"](https://github.com/OpenZeppelin/openzeppelin-contracts/labels/good%20first%20issue).
 
 Thanks for your time and code!
+
+[guidelines]: GUIDELINES.md

DOCUMENTATION.md

@@ -0,0 +1,16 @@
+Documentation is hosted at https://docs.openzeppelin.com/contracts.
+
+All of the content for the site is in this repository. The guides are in the
+[docs](/docs) directory, and the API Reference is extracted from comments in
+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) is the
+program that extracts the API Reference from source code.
+
+The [`docs.openzeppelin.com`](https://github.com/OpenZeppelin/docs.openzeppelin.com)
+repository hosts the configuration for the entire site, which includes
+documetation for all of the OpenZeppelin projects.
+
+To run the docs locally you should run `npm run docs start` on this
+repository.

GUIDELINES.md

@@ -0,0 +1,64 @@
+Design Guidelines
+=======
+
+These are some global design goals in OpenZeppelin.
+
+#### D0 - Security in Depth
+We strive to provide secure, tested, audited code. To achieve this, we need to match intention with function. Thus, documentation, code clarity, community review and security discussions are fundamental.
+
+#### D1 - Simple and Modular
+Simpler code means easier audits, and better understanding of what each component does. We look for small files, small contracts, and small functions. If you can separate a contract into two independent functionalities you should probably do it.
+
+#### D2 - Naming Matters
+
+We take our time with picking names. Code is going to be written once, and read hundreds of times. Renaming for clarity is encouraged.
+
+#### D3 - Tests
+
+Write tests for all your code. We encourage Test Driven Development so we know when our code is right. Even though not all code in the repository is tested at the moment, we aim to test every line of code in the future.
+
+#### D4 - Check preconditions and post-conditions
+
+A very important way to prevent vulnerabilities is to catch a contract’s inconsistent state as early as possible. This is why we want functions to check pre- and post-conditions for executing its logic. When writing code, ask yourself what you are expecting to be true before and after the function runs, and express it in code.
+
+#### D5 - Code Consistency
+
+Consistency on the way classes are used is paramount to an easier understanding of the library. The codebase should be as unified as possible. Read existing code and get inspired before you write your own. Follow the style guidelines. Don’t hesitate to ask for help on how to best write a specific piece of code.
+
+#### D6 - Regular Audits
+Following good programming practices is a way to reduce the risk of vulnerabilities, but professional code audits are still needed. We will perform regular code audits on major releases, and hire security professionals to provide independent review.
+
+## Style Guidelines
+
+The design guidelines have quite a high abstraction level. These style guidelines are more concrete and easier to apply, and also more opinionated.
+
+### General
+
+#### G0 - Default to Solidity's official style guide.
+
+Follow the official Solidity style guide: https://solidity.readthedocs.io/en/latest/style-guide.html
+
+#### G1 - No Magic Constants
+
+Avoid constants in the code as much as possible. Magic strings are also magic constants.
+
+#### G2 - Code that Fails Early
+
+We ask our code to fail as soon as possible when an unexpected input was provided or unexpected state was found.
+
+#### G3 - Internal Amounts Must be Signed Integers and Represent the Smallest Units.
+
+Avoid representation errors by always dealing with weis when handling ether. GUIs can convert to more human-friendly representations. Use Signed Integers (int) to prevent underflow problems.
+
+
+### Testing
+
+#### T1 - Tests Must be Written Elegantly
+
+Style guidelines are not relaxed for tests. Tests are a good way to show how to use the library, and maintaining them is extremely necessary.
+
+Don't write long tests, write helper functions to make them be as short and concise as possible (they should take just a few lines each), and use good variable names.
+
+#### T2 - Tests Must not be Random
+
+Inputs for tests should not be generated randomly. Accounts used to create test contracts are an exception, those can be random. Also, the type and structure of outputs should be checked.

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

@@ -1,40 +1,67 @@
-# <img src="logo.png" alt="OpenZeppelin" width="400px">
+# <img src="logo.png" alt="OpenZeppelin" height="40px">
 
-[![NPM Package](https://img.shields.io/npm/v/openzeppelin-solidity.svg?style=flat-square)](https://www.npmjs.org/package/openzeppelin-solidity)
-[![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)
+[![NPM Package](https://img.shields.io/npm/v/@openzeppelin/contracts.svg)](https://www.npmjs.org/package/@openzeppelin/contracts)
+[![Build Status](https://circleci.com/gh/OpenZeppelin/openzeppelin-contracts.svg?style=shield)](https://circleci.com/gh/OpenZeppelin/openzeppelin-contracts)
+[![Coverage Status](https://codecov.io/gh/OpenZeppelin/openzeppelin-contracts/graph/badge.svg)](https://codecov.io/gh/OpenZeppelin/openzeppelin-contracts)
 
-**OpenZeppelin is a library for secure smart contract development.** It provides implementations of standards like ERC20 and ERC721 which you can deploy as-is or extend to suit your needs, as well as Solidity components to build custom contracts and more complex decentralized systems.
+**A library for secure smart contract development.** Build on a solid foundation of community-vetted code.
 
-## Install
+ * Implementations of standards like [ERC20](https://docs.openzeppelin.com/contracts/erc20) and [ERC721](https://docs.openzeppelin.com/contracts/erc721).
+ * Flexible [role-based permissioning](https://docs.openzeppelin.com/contracts/access-control) scheme.
+ * Reusable [Solidity components](https://docs.openzeppelin.com/contracts/utilities) to build custom contracts and complex decentralized systems.
+ * First-class integration with the [Gas Station Network](https://docs.openzeppelin.com/contracts/gsn) for systems with no gas fees!
+ * Audited by leading security firms.
 
-```
-npm install openzeppelin-solidity
+## Overview
+
+### Installation
+
+```console
+$ npm install @openzeppelin/contracts
 ```
 
-## Usage
+OpenZeppelin Contracts features a [stable API](https://docs.openzeppelin.com/contracts/releases-stability#api-stability), which means your contracts won't break unexpectedly when upgrading to a newer minor version.
 
-To write your custom contracts, import ours and extend them through inheritance.
+### Usage
+
+Once installed, you can use the contracts in the library by importing them:
 
 ```solidity
 pragma solidity ^0.5.0;
 
-import 'openzeppelin-solidity/contracts/token/ERC721/ERC721Full.sol';
-import 'openzeppelin-solidity/contracts/token/ERC721/ERC721Mintable.sol';
+import "@openzeppelin/contracts/token/ERC721/ERC721Full.sol";
+import "@openzeppelin/contracts/token/ERC721/ERC721Mintable.sol";
 
 contract MyNFT is ERC721Full, ERC721Mintable {
-  constructor() ERC721Full("MyNFT", "MNFT") public {
-  }
+    constructor() ERC721Full("MyNFT", "MNFT") public {
+    }
 }
 ```
 
-> You need an ethereum development framework for the above import statements to work! Check out these guides for [Truffle] or [Embark].
+_If you're new to smart contract development, head to [Developing Smart Contracts](https://docs.openzeppelin.com/learn/developing-smart-contracts) to learn about creating a new project and compiling your contracts._
 
-On our site you will find a few [guides] to learn about the different parts of OpenZeppelin, as well as [documentation for the API][API docs]. Keep in mind that the API docs are work in progress, and don’t hesitate to ask questions in [our Slack][Slack].
+To keep your system secure, you should **always** use the installed code as-is, and neither copy-paste it from online sources, nor modify it yourself. The library is designed so that only the contracts and functions you use are deployed, so you don't need to worry about it needlessly increasing gas costs.
+
+## Learn More
+
+The guides in the sidebar will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
+
+* [Access Control](https://docs.openzeppelin.com/contracts/access-control): decide who can perform each of the actions on your system.
+* [Tokens](https://docs.openzeppelin.com/contracts/tokens): create tradeable assets or collectives, and distribute them via [Crowdsales](https://docs.openzeppelin.com/contracts/crowdsales).
+* [Gas Station Network](https://docs.openzeppelin.com/contracts/gsn): let your users interact with your contracts without having to pay for gas themselves.
+* [Utilities](https://docs.openzeppelin.com/contracts/utilities): generic useful tools, including non-overflowing math, signature verification, and trustless paying systems.
+
+The [full API](https://docs.openzeppelin.com/contracts/api/token/ERC20) is also thoroughly documented, and serves as a great reference when developing your smart contract application. You can also ask for help or follow Contracts's development in the [community forum](https://forum.openzeppelin.com).
+
+Finally, you may want to take a look at the [guides on our blog](https://blog.openzeppelin.com/guides), which cover several common use cases and good practices.. The following articles provide great background reading, though please note, some of the referenced tools have changed as the tooling in the ecosystem continues to rapidly evolve.
+
+* [The Hitchhiker’s Guide to Smart Contracts in Ethereum](https://blog.openzeppelin.com/the-hitchhikers-guide-to-smart-contracts-in-ethereum-848f08001f05) will help you get an overview of the various tools available for smart contract development, and help you set up your environment.
+* [A Gentle Introduction to Ethereum Programming, Part 1](https://blog.openzeppelin.com/a-gentle-introduction-to-ethereum-programming-part-1-783cc7796094) provides very useful information on an introductory level, including many basic concepts from the Ethereum platform.
+* For a more in-depth dive, you may read the guide [Designing the Architecture for Your Ethereum Application](https://blog.openzeppelin.com/designing-the-architecture-for-your-ethereum-application-9cec086f8317), which discusses how to better structure your application and its relationship to the real world.
 
 ## Security
 
-OpenZeppelin the project is maintained by [Zeppelin] the company, and developed following our high standards for code quality and security. OpenZeppelin is meant to provide tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problems you might experience.
+This project is maintained by [OpenZeppelin](https://openzeppelin.com), and developed following our high standards for code quality and security. OpenZeppelin is meant to provide tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problems you might experience.
 
 The core development principles and strategies that OpenZeppelin is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.
 
@@ -44,17 +71,8 @@ Please report any security issues you find to security@openzeppelin.org.
 
 ## Contribute
 
-OpenZeppelin exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the [contribution guide]!
+OpenZeppelin exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the [contribution guide](CONTRIBUTING.md)!
 
 ## License
 
 OpenZeppelin is released under the [MIT License](LICENSE).
-
-
-[API docs]: https://openzeppelin.org/api/docs/token_ERC721_ERC721BasicToken.html
-[guides]: https://openzeppelin.org/api/docs/get-started.html
-[Slack]: https://slack.openzeppelin.org
-[Zeppelin]: https://zeppelin.solutions
-[contribution guide]: CONTRIBUTING.md
-[Truffle]: https://truffleframework.com/docs/truffle/quickstart
-[Embark]: https://embark.status.im/docs/quick_start.html

RELEASING.md

@@ -1,83 +1,20 @@
 # Releasing
 
-This document describes our release process, and contains the steps to be followed by an OpenZeppelin maintainer at the several stages of a release.
+> Visit the documentation for [details about release schedule].
 
-We release a new version of OpenZeppelin monthly. Release cycles are tracked in the [issue milestones](https://github.com/OpenZeppelin/openzeppelin-solidity/milestones).
+Start on an up-to-date `master` branch.
 
-Each release has at least one release candidate published first, intended for community review and any critical fixes that may come out of it. At the moment we leave 1 week between the first release candidate and the final release.
+Create the release branch with `npm run release start minor`.
 
-Before starting make sure to verify the following items.
-* Your local `master` branch is in sync with your `upstream` remote (it may have another name depending on your setup).
-* Your repo is clean, particularly with no untracked files in the contracts and tests directories. Verify with `git clean -n`.
+Publish a release candidate with `npm run release rc`.
 
+Publish the final release with `npm run release final`.
 
-## Creating the release branch
+Follow the general [OpenZeppelin release checklist].
 
-We'll refer to a release `vX.Y.Z`.
+[details about release schedule]: https://docs.openzeppelin.com/contracts/releases-stability
+[OpenZeppelin release checklist]: https://github.com/OpenZeppelin/code-style/blob/master/RELEASE_CHECKLIST.md
 
-```
-git checkout master
-git checkout -b release-vX.Y.Z
-```
-
-## Creating a release candidate
-
-Once in the release branch, change the version string in `package.json`, `package-lock.json` and `ethpm.json` to `X.Y.Z-rc.R`. (This will be `X.Y.Z-rc.1` for the first release candidate.) Commit these changes and tag the commit as `vX.Y.Z-rc.R`.
-
-```
-git add package.json package-lock.json ethpm.json
-git commit -m "Release candidate vX.Y.Z-rc.R"
-git tag -a vX.Y.Z-rc.R
-git push upstream release-vX.Y.Z
-git push upstream vX.Y.Z-rc.R
-```
-
-Draft the release notes in our [GitHub releases](https://github.com/OpenZeppelin/openzeppelin-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. 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.
-
-## Creating the final release
-
-Make sure to have the latest changes from `upstream` in your local release branch.
-
-```
-git checkout release-vX.Y.Z
-git pull upstream
-```
-
-Before starting the release process, make one final commit to CHANGELOG.md, including the date of the release.
-
-Change the version string in `package.json`, `package-lock.json` and `ethpm.json` removing the "-rc.R" suffix. Commit these changes and tag the commit as `vX.Y.Z`.
-
-```
-git add package.json package-lock.json ethpm.json
-git commit -m "Release vX.Y.Z"
-git tag -a vX.Y.Z
-git push upstream release-vX.Y.Z
-git push upstream vX.Y.Z
-```
-
-Draft the release notes in GitHub releases. Try to be consistent with our previous release notes in the title and format of the text. Make sure to include a detailed changelog.
-
-Once the CI run for the new tag is green, publish on npm. You should see the contracts compile automatically.
-
-```
-npm publish
-```
-
-Publish the release notes on GitHub and ask our community manager to announce the release!
-
-Delete the `next` tag in the npm package as there is no longer a release candidate.
-
-```
-npm dist-tag rm --otp $2FA_CODE openzeppelin-solidity next
-```
 
 ## Merging the release branch
 

contracts/.npmignore

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

contracts/ARCHITECTURE.md

@@ -1,27 +0,0 @@
-## Architecture
-
-The following provides visibility into how OpenZeppelin's contracts are organized:
-
-- **access** - Smart contracts that enable functionality that can be used for selective restrictions and basic authorization control functions.
-- **crowdsale** - A collection of smart contracts used to manage token crowdsales that allow investors to purchase tokens with ETH. Includes a base contract which implements fundamental crowdsale functionality in its simplest form. The base contract can be extended in order to satisfy your crowdsale’s specific requirements.
-	- **distribution** - Includes extensions of the base crowdsale contract which can be used to customize the completion of a crowdsale.
-	- **emission** - Includes extensions of the base crowdsale contract which can be used to mint and manage how tokens are issued to purchasers.
-	- **price** - Includes extensions of the crowdsale contract that can be used to manage changes in token prices.
-	- **validation**  - Includes extensions of the crowdsale contract that can be used to enforce restraints and limit access to token purchases.
-- **examples** - A collection of simple smart contracts that demonstrate how to add new features to base contracts through multiple inheritance.
-- **introspection**  - An interface that can be used to make a contract comply with the ERC-165 standard as well as a contract that implements ERC-165 using a lookup table.
-- **lifecycle** - A collection of base contracts used to manage the existence and behavior of your contracts and their funds.
-- **math** - Libraries with safety checks on operations that throw on errors.
-- **mocks** - A collection of abstract contracts that are primarily used for unit testing. They also serve as good usage examples and demonstrate how to combine contracts with inheritance when developing your own custom applications.
-- **ownership** - A collection of smart contracts that can be used to manage contract and token ownership
-- **payment** - A collection of smart contracts that can be used to manage payments through escrow arrangements, withdrawals, and claims. Includes support for both single payees and multiple payees.
-- **proposals** - A collection of smart contracts that reflect community Ethereum Improvement Proposals (EIPs). These contracts are under development and standardization. They are not recommended for production, but they are useful for experimentation with pending EIP standards. Go [here](https://github.com/OpenZeppelin/openzeppelin-solidity/wiki/ERC-Process) for more information.
-
-- **token** - A collection of approved ERC standard tokens -- their interfaces and implementations.
-	- **ERC20** - A standard interface for fungible tokens:
-		- *Interfaces* - Includes the ERC-20 token standard basic interface. I.e., what the contract’s ABI can represent.
-		- *Implementations* - Includes ERC-20 token implementations that include all required and some optional ERC-20 functionality.
-	- **ERC721** - A standard interface for non-fungible tokens
-		- *Interfaces* - Includes the ERC-721 token standard basic interface. I.e., what the contract’s ABI can represent.
-		- *Implementations* - Includes ERC-721 token implementations that include all required and some optional ERC-721 functionality.
-

contracts/GSN/Context.sol

@@ -0,0 +1,26 @@
+pragma solidity ^0.6.0;
+
+/*
+ * @dev Provides information about the current execution context, including the
+ * sender of the transaction and its data. While these are generally available
+ * via msg.sender and msg.data, they should not be accessed in such a direct
+ * manner, since when dealing with GSN meta-transactions the account sending and
+ * paying for execution may not be the actual sender (as far as an application
+ * is concerned).
+ *
+ * This contract is only required for intermediate, library-like contracts.
+ */
+contract Context {
+    // Empty internal constructor, to prevent people from mistakenly deploying
+    // an instance of this contract, which should be used via inheritance.
+    constructor () internal { }
+
+    function _msgSender() internal view virtual returns (address payable) {
+        return msg.sender;
+    }
+
+    function _msgData() internal view virtual returns (bytes memory) {
+        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
+        return msg.data;
+    }
+}

contracts/GSN/GSNRecipient.sol

@@ -0,0 +1,228 @@
+pragma solidity ^0.6.0;
+
+import "./IRelayRecipient.sol";
+import "./IRelayHub.sol";
+import "./Context.sol";
+
+/**
+ * @dev Base GSN recipient contract: includes the {IRelayRecipient} interface
+ * and enables GSN support on all contracts in the inheritance tree.
+ *
+ * TIP: This contract is abstract. The functions {IRelayRecipient-acceptRelayedCall},
+ *  {_preRelayedCall}, and {_postRelayedCall} are not implemented and must be
+ * provided by derived contracts. See the
+ * xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategies] for more
+ * information on how to use the pre-built {GSNRecipientSignature} and
+ * {GSNRecipientERC20Fee}, or how to write your own.
+ */
+abstract contract GSNRecipient is IRelayRecipient, Context {
+    // Default RelayHub address, deployed on mainnet and all testnets at the same address
+    address private _relayHub = 0xD216153c06E857cD7f72665E0aF1d7D82172F494;
+
+    uint256 constant private _RELAYED_CALL_ACCEPTED = 0;
+    uint256 constant private _RELAYED_CALL_REJECTED = 11;
+
+    // How much gas is forwarded to postRelayedCall
+    uint256 constant internal _POST_RELAYED_CALL_MAX_GAS = 100000;
+
+    /**
+     * @dev Emitted when a contract changes its {IRelayHub} contract to a new one.
+     */
+    event RelayHubChanged(address indexed oldRelayHub, address indexed newRelayHub);
+
+    /**
+     * @dev Returns the address of the {IRelayHub} contract for this recipient.
+     */
+    function getHubAddr() public view override returns (address) {
+        return _relayHub;
+    }
+
+    /**
+     * @dev Switches to a new {IRelayHub} instance. This method is added for future-proofing: there's no reason to not
+     * use the default instance.
+     *
+     * IMPORTANT: After upgrading, the {GSNRecipient} will no longer be able to receive relayed calls from the old
+     * {IRelayHub} instance. Additionally, all funds should be previously withdrawn via {_withdrawDeposits}.
+     */
+    function _upgradeRelayHub(address newRelayHub) internal virtual {
+        address currentRelayHub = _relayHub;
+        require(newRelayHub != address(0), "GSNRecipient: new RelayHub is the zero address");
+        require(newRelayHub != currentRelayHub, "GSNRecipient: new RelayHub is the current one");
+
+        emit RelayHubChanged(currentRelayHub, newRelayHub);
+
+        _relayHub = newRelayHub;
+    }
+
+    /**
+     * @dev Returns the version string of the {IRelayHub} for which this recipient implementation was built. If
+     * {_upgradeRelayHub} is used, the new {IRelayHub} instance should be compatible with this version.
+     */
+    // This function is view for future-proofing, it may require reading from
+    // storage in the future.
+    function relayHubVersion() public view returns (string memory) {
+        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
+        return "1.0.0";
+    }
+
+    /**
+     * @dev Withdraws the recipient's deposits in `RelayHub`.
+     *
+     * Derived contracts should expose this in an external interface with proper access control.
+     */
+    function _withdrawDeposits(uint256 amount, address payable payee) internal virtual {
+        IRelayHub(_relayHub).withdraw(amount, payee);
+    }
+
+    // Overrides for Context's functions: when called from RelayHub, sender and
+    // data require some pre-processing: the actual sender is stored at the end
+    // of the call data, which in turns means it needs to be removed from it
+    // when handling said data.
+
+    /**
+     * @dev Replacement for msg.sender. Returns the actual sender of a transaction: msg.sender for regular transactions,
+     * and the end-user for GSN relayed calls (where msg.sender is actually `RelayHub`).
+     *
+     * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.sender`, and use {_msgSender} instead.
+     */
+    function _msgSender() internal view virtual override returns (address payable) {
+        if (msg.sender != _relayHub) {
+            return msg.sender;
+        } else {
+            return _getRelayedCallSender();
+        }
+    }
+
+    /**
+     * @dev Replacement for msg.data. Returns the actual calldata of a transaction: msg.data for regular transactions,
+     * and a reduced version for GSN relayed calls (where msg.data contains additional information).
+     *
+     * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.data`, and use {_msgData} instead.
+     */
+    function _msgData() internal view virtual override returns (bytes memory) {
+        if (msg.sender != _relayHub) {
+            return msg.data;
+        } else {
+            return _getRelayedCallData();
+        }
+    }
+
+    // Base implementations for pre and post relayedCall: only RelayHub can invoke them, and data is forwarded to the
+    // internal hook.
+
+    /**
+     * @dev See `IRelayRecipient.preRelayedCall`.
+     *
+     * This function should not be overriden directly, use `_preRelayedCall` instead.
+     *
+     * * Requirements:
+     *
+     * - the caller must be the `RelayHub` contract.
+     */
+    function preRelayedCall(bytes memory context) public virtual override returns (bytes32) {
+        require(msg.sender == getHubAddr(), "GSNRecipient: caller is not RelayHub");
+        return _preRelayedCall(context);
+    }
+
+    /**
+     * @dev See `IRelayRecipient.preRelayedCall`.
+     *
+     * Called by `GSNRecipient.preRelayedCall`, which asserts the caller is the `RelayHub` contract. Derived contracts
+     * must implement this function with any relayed-call preprocessing they may wish to do.
+     *
+     */
+    function _preRelayedCall(bytes memory context) internal virtual returns (bytes32);
+
+    /**
+     * @dev See `IRelayRecipient.postRelayedCall`.
+     *
+     * This function should not be overriden directly, use `_postRelayedCall` instead.
+     *
+     * * Requirements:
+     *
+     * - the caller must be the `RelayHub` contract.
+     */
+    function postRelayedCall(bytes memory context, bool success, uint256 actualCharge, bytes32 preRetVal) public virtual override {
+        require(msg.sender == getHubAddr(), "GSNRecipient: caller is not RelayHub");
+        _postRelayedCall(context, success, actualCharge, preRetVal);
+    }
+
+    /**
+     * @dev See `IRelayRecipient.postRelayedCall`.
+     *
+     * Called by `GSNRecipient.postRelayedCall`, which asserts the caller is the `RelayHub` contract. Derived contracts
+     * must implement this function with any relayed-call postprocessing they may wish to do.
+     *
+     */
+    function _postRelayedCall(bytes memory context, bool success, uint256 actualCharge, bytes32 preRetVal) internal virtual;
+
+    /**
+     * @dev Return this in acceptRelayedCall to proceed with the execution of a relayed call. Note that this contract
+     * will be charged a fee by RelayHub
+     */
+    function _approveRelayedCall() internal pure returns (uint256, bytes memory) {
+        return _approveRelayedCall("");
+    }
+
+    /**
+     * @dev See `GSNRecipient._approveRelayedCall`.
+     *
+     * This overload forwards `context` to _preRelayedCall and _postRelayedCall.
+     */
+    function _approveRelayedCall(bytes memory context) internal pure returns (uint256, bytes memory) {
+        return (_RELAYED_CALL_ACCEPTED, context);
+    }
+
+    /**
+     * @dev Return this in acceptRelayedCall to impede execution of a relayed call. No fees will be charged.
+     */
+    function _rejectRelayedCall(uint256 errorCode) internal pure returns (uint256, bytes memory) {
+        return (_RELAYED_CALL_REJECTED + errorCode, "");
+    }
+
+    /*
+     * @dev Calculates how much RelayHub will charge a recipient for using `gas` at a `gasPrice`, given a relayer's
+     * `serviceFee`.
+     */
+    function _computeCharge(uint256 gas, uint256 gasPrice, uint256 serviceFee) internal pure returns (uint256) {
+        // The fee is expressed as a percentage. E.g. a value of 40 stands for a 40% fee, so the recipient will be
+        // charged for 1.4 times the spent amount.
+        return (gas * gasPrice * (100 + serviceFee)) / 100;
+    }
+
+    function _getRelayedCallSender() private pure returns (address payable result) {
+        // We need to read 20 bytes (an address) located at array index msg.data.length - 20. In memory, the array
+        // is prefixed with a 32-byte length value, so we first add 32 to get the memory read index. However, doing
+        // so would leave the address in the upper 20 bytes of the 32-byte word, which is inconvenient and would
+        // require bit shifting. We therefore subtract 12 from the read index so the address lands on the lower 20
+        // bytes. This can always be done due to the 32-byte prefix.
+
+        // The final memory read index is msg.data.length - 20 + 32 - 12 = msg.data.length. Using inline assembly is the
+        // easiest/most-efficient way to perform this operation.
+
+        // These fields are not accessible from assembly
+        bytes memory array = msg.data;
+        uint256 index = msg.data.length;
+
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            // Load the 32 bytes word from memory with the address on the lower 20 bytes, and mask those.
+            result := and(mload(add(array, index)), 0xffffffffffffffffffffffffffffffffffffffff)
+        }
+        return result;
+    }
+
+    function _getRelayedCallData() private pure returns (bytes memory) {
+        // RelayHub appends the sender address at the end of the calldata, so in order to retrieve the actual msg.data,
+        // we must strip the last 20 bytes (length of an address type) from it.
+
+        uint256 actualDataLength = msg.data.length - 20;
+        bytes memory actualData = new bytes(actualDataLength);
+
+        for (uint256 i = 0; i < actualDataLength; ++i) {
+            actualData[i] = msg.data[i];
+        }
+
+        return actualData;
+    }
+}

contracts/GSN/GSNRecipientERC20Fee.sol

@@ -0,0 +1,150 @@
+pragma solidity ^0.6.0;
+
+import "./GSNRecipient.sol";
+import "../math/SafeMath.sol";
+import "../access/Ownable.sol";
+import "../token/ERC20/SafeERC20.sol";
+import "../token/ERC20/ERC20.sol";
+
+/**
+ * @dev A xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategy] that charges transaction fees in a special purpose ERC20
+ * token, which we refer to as the gas payment token. The amount charged is exactly the amount of Ether charged to the
+ * recipient. This means that the token is essentially pegged to the value of Ether.
+ *
+ * The distribution strategy of the gas payment token to users is not defined by this contract. It's a mintable token
+ * whose only minter is the recipient, so the strategy must be implemented in a derived contract, making use of the
+ * internal {_mint} function.
+ */
+contract GSNRecipientERC20Fee is GSNRecipient {
+    using SafeERC20 for __unstable__ERC20Owned;
+    using SafeMath for uint256;
+
+    enum GSNRecipientERC20FeeErrorCodes {
+        INSUFFICIENT_BALANCE
+    }
+
+    __unstable__ERC20Owned private _token;
+
+    /**
+     * @dev The arguments to the constructor are the details that the gas payment token will have: `name` and `symbol`. `decimals` is hard-coded to 18.
+     */
+    constructor(string memory name, string memory symbol) public {
+        _token = new __unstable__ERC20Owned(name, symbol);
+    }
+
+    /**
+     * @dev Returns the gas payment token.
+     */
+    function token() public view returns (IERC20) {
+        return IERC20(_token);
+    }
+
+    /**
+     * @dev Internal function that mints the gas payment token. Derived contracts should expose this function in their public API, with proper access control mechanisms.
+     */
+    function _mint(address account, uint256 amount) internal virtual {
+        _token.mint(account, amount);
+    }
+
+    /**
+     * @dev Ensures that only users with enough gas payment token balance can have transactions relayed through the GSN.
+     */
+    function acceptRelayedCall(
+        address,
+        address from,
+        bytes memory,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256,
+        uint256,
+        bytes memory,
+        uint256 maxPossibleCharge
+    )
+        public
+        view
+        virtual
+        override
+        returns (uint256, bytes memory)
+    {
+        if (_token.balanceOf(from) < maxPossibleCharge) {
+            return _rejectRelayedCall(uint256(GSNRecipientERC20FeeErrorCodes.INSUFFICIENT_BALANCE));
+        }
+
+        return _approveRelayedCall(abi.encode(from, maxPossibleCharge, transactionFee, gasPrice));
+    }
+
+    /**
+     * @dev Implements the precharge to the user. The maximum possible charge (depending on gas limit, gas price, and
+     * fee) will be deducted from the user balance of gas payment token. Note that this is an overestimation of the
+     * actual charge, necessary because we cannot predict how much gas the execution will actually need. The remainder
+     * is returned to the user in {_postRelayedCall}.
+     */
+    function _preRelayedCall(bytes memory context) internal virtual override returns (bytes32) {
+        (address from, uint256 maxPossibleCharge) = abi.decode(context, (address, uint256));
+
+        // The maximum token charge is pre-charged from the user
+        _token.safeTransferFrom(from, address(this), maxPossibleCharge);
+    }
+
+    /**
+     * @dev Returns to the user the extra amount that was previously charged, once the actual execution cost is known.
+     */
+    function _postRelayedCall(bytes memory context, bool, uint256 actualCharge, bytes32) internal virtual override {
+        (address from, uint256 maxPossibleCharge, uint256 transactionFee, uint256 gasPrice) =
+            abi.decode(context, (address, uint256, uint256, uint256));
+
+        // actualCharge is an _estimated_ charge, which assumes postRelayedCall will use all available gas.
+        // This implementation's gas cost can be roughly estimated as 10k gas, for the two SSTORE operations in an
+        // ERC20 transfer.
+        uint256 overestimation = _computeCharge(_POST_RELAYED_CALL_MAX_GAS.sub(10000), gasPrice, transactionFee);
+        actualCharge = actualCharge.sub(overestimation);
+
+        // After the relayed call has been executed and the actual charge estimated, the excess pre-charge is returned
+        _token.safeTransfer(from, maxPossibleCharge.sub(actualCharge));
+    }
+}
+
+/**
+ * @title __unstable__ERC20Owned
+ * @dev An ERC20 token owned by another contract, which has minting permissions and can use transferFrom to receive
+ * anyone's tokens. This contract is an internal helper for GSNRecipientERC20Fee, and should not be used
+ * outside of this context.
+ */
+// solhint-disable-next-line contract-name-camelcase
+contract __unstable__ERC20Owned is ERC20, Ownable {
+    uint256 private constant _UINT256_MAX = 2**256 - 1;
+
+    constructor(string memory name, string memory symbol) public ERC20(name, symbol) { }
+
+    // The owner (GSNRecipientERC20Fee) can mint tokens
+    function mint(address account, uint256 amount) public onlyOwner {
+        _mint(account, amount);
+    }
+
+    // The owner has 'infinite' allowance for all token holders
+    function allowance(address tokenOwner, address spender) public view override returns (uint256) {
+        if (spender == owner()) {
+            return _UINT256_MAX;
+        } else {
+            return super.allowance(tokenOwner, spender);
+        }
+    }
+
+    // Allowance for the owner cannot be changed (it is always 'infinite')
+    function _approve(address tokenOwner, address spender, uint256 value) internal override {
+        if (spender == owner()) {
+            return;
+        } else {
+            super._approve(tokenOwner, spender, value);
+        }
+    }
+
+    function transferFrom(address sender, address recipient, uint256 amount) public override returns (bool) {
+        if (recipient == owner()) {
+            _transfer(sender, recipient, amount);
+            return true;
+        } else {
+            return super.transferFrom(sender, recipient, amount);
+        }
+    }
+}

contracts/GSN/GSNRecipientSignature.sol

@@ -0,0 +1,70 @@
+pragma solidity ^0.6.0;
+
+import "./GSNRecipient.sol";
+import "../cryptography/ECDSA.sol";
+
+/**
+ * @dev A xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategy] that allows relayed transactions through when they are
+ * accompanied by the signature of a trusted signer. The intent is for this signature to be generated by a server that
+ * performs validations off-chain. Note that nothing is charged to the user in this scheme. Thus, the server should make
+ * sure to account for this in their economic and threat model.
+ */
+contract GSNRecipientSignature is GSNRecipient {
+    using ECDSA for bytes32;
+
+    address private _trustedSigner;
+
+    enum GSNRecipientSignatureErrorCodes {
+        INVALID_SIGNER
+    }
+
+    /**
+     * @dev Sets the trusted signer that is going to be producing signatures to approve relayed calls.
+     */
+    constructor(address trustedSigner) public {
+        require(trustedSigner != address(0), "GSNRecipientSignature: trusted signer is the zero address");
+        _trustedSigner = trustedSigner;
+    }
+
+    /**
+     * @dev Ensures that only transactions with a trusted signature can be relayed through the GSN.
+     */
+    function acceptRelayedCall(
+        address relay,
+        address from,
+        bytes memory encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes memory approvalData,
+        uint256
+    )
+        public
+        view
+        virtual
+        override
+        returns (uint256, bytes memory)
+    {
+        bytes memory blob = abi.encodePacked(
+            relay,
+            from,
+            encodedFunction,
+            transactionFee,
+            gasPrice,
+            gasLimit,
+            nonce, // Prevents replays on RelayHub
+            getHubAddr(), // Prevents replays in multiple RelayHubs
+            address(this) // Prevents replays in multiple recipients
+        );
+        if (keccak256(blob).toEthSignedMessageHash().recover(approvalData) == _trustedSigner) {
+            return _approveRelayedCall();
+        } else {
+            return _rejectRelayedCall(uint256(GSNRecipientSignatureErrorCodes.INVALID_SIGNER));
+        }
+    }
+
+    function _preRelayedCall(bytes memory) internal virtual override returns (bytes32) { }
+
+    function _postRelayedCall(bytes memory, bool, uint256, bytes32) internal virtual override { }
+}

contracts/GSN/IRelayHub.sol

@@ -0,0 +1,267 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Interface for `RelayHub`, the core contract of the GSN. Users should not need to interact with this contract
+ * directly.
+ *
+ * See the https://github.com/OpenZeppelin/openzeppelin-gsn-helpers[OpenZeppelin GSN helpers] for more information on
+ * how to deploy an instance of `RelayHub` on your local test network.
+ */
+interface IRelayHub {
+    // Relay management
+
+    /**
+     * @dev Adds stake to a relay and sets its `unstakeDelay`. If the relay does not exist, it is created, and the caller
+     * of this function becomes its owner. If the relay already exists, only the owner can call this function. A relay
+     * cannot be its own owner.
+     *
+     * All Ether in this function call will be added to the relay's stake.
+     * Its unstake delay will be assigned to `unstakeDelay`, but the new value must be greater or equal to the current one.
+     *
+     * Emits a {Staked} event.
+     */
+    function stake(address relayaddr, uint256 unstakeDelay) external payable;
+
+    /**
+     * @dev Emitted when a relay's stake or unstakeDelay are increased
+     */
+    event Staked(address indexed relay, uint256 stake, uint256 unstakeDelay);
+
+    /**
+     * @dev Registers the caller as a relay.
+     * The relay must be staked for, and not be a contract (i.e. this function must be called directly from an EOA).
+     *
+     * This function can be called multiple times, emitting new {RelayAdded} events. Note that the received
+     * `transactionFee` is not enforced by {relayCall}.
+     *
+     * Emits a {RelayAdded} event.
+     */
+    function registerRelay(uint256 transactionFee, string calldata url) external;
+
+    /**
+     * @dev Emitted when a relay is registered or re-registerd. Looking at these events (and filtering out
+     * {RelayRemoved} events) lets a client discover the list of available relays.
+     */
+    event RelayAdded(address indexed relay, address indexed owner, uint256 transactionFee, uint256 stake, uint256 unstakeDelay, string url);
+
+    /**
+     * @dev Removes (deregisters) a relay. Unregistered (but staked for) relays can also be removed.
+     *
+     * Can only be called by the owner of the relay. After the relay's `unstakeDelay` has elapsed, {unstake} will be
+     * callable.
+     *
+     * Emits a {RelayRemoved} event.
+     */
+    function removeRelayByOwner(address relay) external;
+
+    /**
+     * @dev Emitted when a relay is removed (deregistered). `unstakeTime` is the time when unstake will be callable.
+     */
+    event RelayRemoved(address indexed relay, uint256 unstakeTime);
+
+    /** Deletes the relay from the system, and gives back its stake to the owner.
+     *
+     * Can only be called by the relay owner, after `unstakeDelay` has elapsed since {removeRelayByOwner} was called.
+     *
+     * Emits an {Unstaked} event.
+     */
+    function unstake(address relay) external;
+
+    /**
+     * @dev Emitted when a relay is unstaked for, including the returned stake.
+     */
+    event Unstaked(address indexed relay, uint256 stake);
+
+    // States a relay can be in
+    enum RelayState {
+        Unknown, // The relay is unknown to the system: it has never been staked for
+        Staked, // The relay has been staked for, but it is not yet active
+        Registered, // The relay has registered itself, and is active (can relay calls)
+        Removed    // The relay has been removed by its owner and can no longer relay calls. It must wait for its unstakeDelay to elapse before it can unstake
+    }
+
+    /**
+     * @dev Returns a relay's status. Note that relays can be deleted when unstaked or penalized, causing this function
+     * to return an empty entry.
+     */
+    function getRelay(address relay) external view returns (uint256 totalStake, uint256 unstakeDelay, uint256 unstakeTime, address payable owner, RelayState state);
+
+    // Balance management
+
+    /**
+     * @dev Deposits Ether for a contract, so that it can receive (and pay for) relayed transactions.
+     *
+     * Unused balance can only be withdrawn by the contract itself, by calling {withdraw}.
+     *
+     * Emits a {Deposited} event.
+     */
+    function depositFor(address target) external payable;
+
+    /**
+     * @dev Emitted when {depositFor} is called, including the amount and account that was funded.
+     */
+    event Deposited(address indexed recipient, address indexed from, uint256 amount);
+
+    /**
+     * @dev Returns an account's deposits. These can be either a contracts's funds, or a relay owner's revenue.
+     */
+    function balanceOf(address target) external view returns (uint256);
+
+    /**
+     * Withdraws from an account's balance, sending it back to it. Relay owners call this to retrieve their revenue, and
+     * contracts can use it to reduce their funding.
+     *
+     * Emits a {Withdrawn} event.
+     */
+    function withdraw(uint256 amount, address payable dest) external;
+
+    /**
+     * @dev Emitted when an account withdraws funds from `RelayHub`.
+     */
+    event Withdrawn(address indexed account, address indexed dest, uint256 amount);
+
+    // Relaying
+
+    /**
+     * @dev Checks if the `RelayHub` will accept a relayed operation.
+     * Multiple things must be true for this to happen:
+     *  - all arguments must be signed for by the sender (`from`)
+     *  - the sender's nonce must be the current one
+     *  - the recipient must accept this transaction (via {acceptRelayedCall})
+     *
+     * Returns a `PreconditionCheck` value (`OK` when the transaction can be relayed), or a recipient-specific error
+     * code if it returns one in {acceptRelayedCall}.
+     */
+    function canRelay(
+        address relay,
+        address from,
+        address to,
+        bytes calldata encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes calldata signature,
+        bytes calldata approvalData
+    ) external view returns (uint256 status, bytes memory recipientContext);
+
+    // Preconditions for relaying, checked by canRelay and returned as the corresponding numeric values.
+    enum PreconditionCheck {
+        OK,                         // All checks passed, the call can be relayed
+        WrongSignature,             // The transaction to relay is not signed by requested sender
+        WrongNonce,                 // The provided nonce has already been used by the sender
+        AcceptRelayedCallReverted,  // The recipient rejected this call via acceptRelayedCall
+        InvalidRecipientStatusCode  // The recipient returned an invalid (reserved) status code
+    }
+
+    /**
+     * @dev Relays a transaction.
+     *
+     * For this to succeed, multiple conditions must be met:
+     *  - {canRelay} must `return PreconditionCheck.OK`
+     *  - the sender must be a registered relay
+     *  - the transaction's gas price must be larger or equal to the one that was requested by the sender
+     *  - the transaction must have enough gas to not run out of gas if all internal transactions (calls to the
+     * recipient) use all gas available to them
+     *  - the recipient must have enough balance to pay the relay for the worst-case scenario (i.e. when all gas is
+     * spent)
+     *
+     * If all conditions are met, the call will be relayed and the recipient charged. {preRelayedCall}, the encoded
+     * function and {postRelayedCall} will be called in that order.
+     *
+     * Parameters:
+     *  - `from`: the client originating the request
+     *  - `to`: the target {IRelayRecipient} contract
+     *  - `encodedFunction`: the function call to relay, including data
+     *  - `transactionFee`: fee (%) the relay takes over actual gas cost
+     *  - `gasPrice`: gas price the client is willing to pay
+     *  - `gasLimit`: gas to forward when calling the encoded function
+     *  - `nonce`: client's nonce
+     *  - `signature`: client's signature over all previous params, plus the relay and RelayHub addresses
+     *  - `approvalData`: dapp-specific data forwared to {acceptRelayedCall}. This value is *not* verified by the
+     * `RelayHub`, but it still can be used for e.g. a signature.
+     *
+     * Emits a {TransactionRelayed} event.
+     */
+    function relayCall(
+        address from,
+        address to,
+        bytes calldata encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes calldata signature,
+        bytes calldata approvalData
+    ) external;
+
+    /**
+     * @dev Emitted when an attempt to relay a call failed.
+     *
+     * This can happen due to incorrect {relayCall} arguments, or the recipient not accepting the relayed call. The
+     * actual relayed call was not executed, and the recipient not charged.
+     *
+     * The `reason` parameter contains an error code: values 1-10 correspond to `PreconditionCheck` entries, and values
+     * over 10 are custom recipient error codes returned from {acceptRelayedCall}.
+     */
+    event CanRelayFailed(address indexed relay, address indexed from, address indexed to, bytes4 selector, uint256 reason);
+
+    /**
+     * @dev Emitted when a transaction is relayed.
+     * Useful when monitoring a relay's operation and relayed calls to a contract
+     *
+     * Note that the actual encoded function might be reverted: this is indicated in the `status` parameter.
+     *
+     * `charge` is the Ether value deducted from the recipient's balance, paid to the relay's owner.
+     */
+    event TransactionRelayed(address indexed relay, address indexed from, address indexed to, bytes4 selector, RelayCallStatus status, uint256 charge);
+
+    // Reason error codes for the TransactionRelayed event
+    enum RelayCallStatus {
+        OK,                      // The transaction was successfully relayed and execution successful - never included in the event
+        RelayedCallFailed,       // The transaction was relayed, but the relayed call failed
+        PreRelayedFailed,        // The transaction was not relayed due to preRelatedCall reverting
+        PostRelayedFailed,       // The transaction was relayed and reverted due to postRelatedCall reverting
+        RecipientBalanceChanged  // The transaction was relayed and reverted due to the recipient's balance changing
+    }
+
+    /**
+     * @dev Returns how much gas should be forwarded to a call to {relayCall}, in order to relay a transaction that will
+     * spend up to `relayedCallStipend` gas.
+     */
+    function requiredGas(uint256 relayedCallStipend) external view returns (uint256);
+
+    /**
+     * @dev Returns the maximum recipient charge, given the amount of gas forwarded, gas price and relay fee.
+     */
+    function maxPossibleCharge(uint256 relayedCallStipend, uint256 gasPrice, uint256 transactionFee) external view returns (uint256);
+
+     // Relay penalization.
+     // Any account can penalize relays, removing them from the system immediately, and rewarding the
+    // reporter with half of the relay's stake. The other half is burned so that, even if the relay penalizes itself, it
+    // still loses half of its stake.
+
+    /**
+     * @dev Penalize a relay that signed two transactions using the same nonce (making only the first one valid) and
+     * different data (gas price, gas limit, etc. may be different).
+     *
+     * The (unsigned) transaction data and signature for both transactions must be provided.
+     */
+    function penalizeRepeatedNonce(bytes calldata unsignedTx1, bytes calldata signature1, bytes calldata unsignedTx2, bytes calldata signature2) external;
+
+    /**
+     * @dev Penalize a relay that sent a transaction that didn't target ``RelayHub``'s {registerRelay} or {relayCall}.
+     */
+    function penalizeIllegalTransaction(bytes calldata unsignedTx, bytes calldata signature) external;
+
+    /**
+     * @dev Emitted when a relay is penalized.
+     */
+    event Penalized(address indexed relay, address sender, uint256 amount);
+
+    /**
+     * @dev Returns an account's nonce in `RelayHub`.
+     */
+    function getNonce(address from) external view returns (uint256);
+}
+

contracts/GSN/IRelayRecipient.sol

@@ -0,0 +1,74 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Base interface for a contract that will be called via the GSN from {IRelayHub}.
+ *
+ * TIP: You don't need to write an implementation yourself! Inherit from {GSNRecipient} instead.
+ */
+interface IRelayRecipient {
+    /**
+     * @dev Returns the address of the {IRelayHub} instance this recipient interacts with.
+     */
+    function getHubAddr() external view returns (address);
+
+    /**
+     * @dev Called by {IRelayHub} to validate if this recipient accepts being charged for a relayed call. Note that the
+     * recipient will be charged regardless of the execution result of the relayed call (i.e. if it reverts or not).
+     *
+     * The relay request was originated by `from` and will be served by `relay`. `encodedFunction` is the relayed call
+     * calldata, so its first four bytes are the function selector. The relayed call will be forwarded `gasLimit` gas,
+     * and the transaction executed with a gas price of at least `gasPrice`. ``relay``'s fee is `transactionFee`, and the
+     * recipient will be charged at most `maxPossibleCharge` (in wei). `nonce` is the sender's (`from`) nonce for
+     * replay attack protection in {IRelayHub}, and `approvalData` is a optional parameter that can be used to hold a signature
+     * over all or some of the previous values.
+     *
+     * Returns a tuple, where the first value is used to indicate approval (0) or rejection (custom non-zero error code,
+     * values 1 to 10 are reserved) and the second one is data to be passed to the other {IRelayRecipient} functions.
+     *
+     * {acceptRelayedCall} is called with 50k gas: if it runs out during execution, the request will be considered
+     * rejected. A regular revert will also trigger a rejection.
+     */
+    function acceptRelayedCall(
+        address relay,
+        address from,
+        bytes calldata encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes calldata approvalData,
+        uint256 maxPossibleCharge
+    )
+        external
+        view
+        returns (uint256, bytes memory);
+
+    /**
+     * @dev Called by {IRelayHub} on approved relay call requests, before the relayed call is executed. This allows to e.g.
+     * pre-charge the sender of the transaction.
+     *
+     * `context` is the second value returned in the tuple by {acceptRelayedCall}.
+     *
+     * Returns a value to be passed to {postRelayedCall}.
+     *
+     * {preRelayedCall} is called with 100k gas: if it runs out during exection or otherwise reverts, the relayed call
+     * will not be executed, but the recipient will still be charged for the transaction's cost.
+     */
+    function preRelayedCall(bytes calldata context) external returns (bytes32);
+
+    /**
+     * @dev Called by {IRelayHub} on approved relay call requests, after the relayed call is executed. This allows to e.g.
+     * charge the user for the relayed call costs, return any overcharges from {preRelayedCall}, or perform
+     * contract-specific bookkeeping.
+     *
+     * `context` is the second value returned in the tuple by {acceptRelayedCall}. `success` is the execution status of
+     * the relayed call. `actualCharge` is an estimate of how much the recipient will be charged for the transaction,
+     * not including any gas used by {postRelayedCall} itself. `preRetVal` is {preRelayedCall}'s return value.
+     *
+     *
+     * {postRelayedCall} is called with 100k gas: if it runs out during execution or otherwise reverts, the relayed call
+     * and the call to {preRelayedCall} will be reverted retroactively, but the recipient will still be charged for the
+     * transaction's cost.
+     */
+    function postRelayedCall(bytes calldata context, bool success, uint256 actualCharge, bytes32 preRetVal) external;
+}

contracts/GSN/README.adoc

@@ -0,0 +1,28 @@
+= Gas Station Network (GSN)
+
+This set of contracts provide all the tools required to make a contract callable via the https://gsn.openzeppelin.com[Gas Station Network].
+
+TIP: If you're new to the GSN, head over to our xref:learn::sending-gasless-transactions.adoc[overview of the system] and basic guide to xref:ROOT:gsn.adoc[creating a GSN-capable contract].
+
+The core contract a recipient must inherit from is {GSNRecipient}: it includes all necessary interfaces, as well as some helper methods to make interacting with the GSN easier.
+
+Utilities to make writing xref:ROOT:gsn-strategies.adoc[GSN strategies] easy are available in {GSNRecipient}, or you can simply use one of our pre-made strategies:
+
+* {GSNRecipientERC20Fee} charges the end user for gas costs in an application-specific xref:ROOT:tokens.adoc#ERC20[ERC20 token]
+* {GSNRecipientSignature} accepts all relayed calls that have been signed by a trusted third party (e.g. a private key in a backend)
+
+You can also take a look at the two contract interfaces that make up the GSN protocol: {IRelayRecipient} and {IRelayHub}, but you won't need to use those directly.
+
+== Recipient
+
+{{GSNRecipient}}
+
+== Strategies
+
+{{GSNRecipientSignature}}
+{{GSNRecipientERC20Fee}}
+
+== Protocol
+
+{{IRelayRecipient}}
+{{IRelayHub}}

contracts/access/AccessControl.sol

@@ -0,0 +1,198 @@
+pragma solidity ^0.6.0;
+
+import "../utils/EnumerableSet.sol";
+import "../utils/Address.sol";
+import "../GSN/Context.sol";
+
+/**
+ * @dev Contract module that allows children to implement role-based access
+ * control mechanisms.
+ *
+ * Roles are referred to by their `bytes32` identifier. These should be exposed
+ * in the external API and be unique. The best way to achieve this is by
+ * using `public constant` hash digests:
+ *
+ * ```
+ * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
+ * ```
+ *
+ * Roles can be used to represent a set of permissions. To restrict access to a
+ * function call, use {hasRole}:
+ *
+ * ```
+ * function foo() public {
+ *     require(hasRole(MY_ROLE, _msgSender()));
+ *     ...
+ * }
+ * ```
+ *
+ * Roles can be granted and revoked dynamically via the {grantRole} and
+ * {revokeRole} functions. Each role has an associated admin role, and only
+ * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
+ *
+ * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
+ * that only accounts with this role will be able to grant or revoke other
+ * roles. More complex role relationships can be created by using
+ * {_setRoleAdmin}.
+ */
+abstract contract AccessControl is Context {
+    using EnumerableSet for EnumerableSet.AddressSet;
+    using Address for address;
+
+    struct RoleData {
+        EnumerableSet.AddressSet members;
+        bytes32 adminRole;
+    }
+
+    mapping (bytes32 => RoleData) private _roles;
+
+    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;
+
+    /**
+     * @dev Emitted when `account` is granted `role`.
+     *
+     * `sender` is the account that originated the contract call, an admin role
+     * bearer except when using {_setupRole}.
+     */
+    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);
+
+    /**
+     * @dev Emitted when `account` is revoked `role`.
+     *
+     * `sender` is the account that originated the contract call:
+     *   - if using `revokeRole`, it is the admin role bearer
+     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
+     */
+    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);
+
+    /**
+     * @dev Returns `true` if `account` has been granted `role`.
+     */
+    function hasRole(bytes32 role, address account) public view returns (bool) {
+        return _roles[role].members.contains(account);
+    }
+
+    /**
+     * @dev Returns the number of accounts that have `role`. Can be used
+     * together with {getRoleMember} to enumerate all bearers of a role.
+     */
+    function getRoleMemberCount(bytes32 role) public view returns (uint256) {
+        return _roles[role].members.length();
+    }
+
+    /**
+     * @dev Returns one of the accounts that have `role`. `index` must be a
+     * value between 0 and {getRoleMemberCount}, non-inclusive.
+     *
+     * Role bearers are not sorted in any particular way, and their ordering may
+     * change at any point.
+     *
+     * WARNING: When using {getRoleMember} and {getRoleMemberCount}, make sure
+     * you perform all queries on the same block. See the following
+     * https://forum.openzeppelin.com/t/iterating-over-elements-on-enumerableset-in-openzeppelin-contracts/2296[forum post]
+     * for more information.
+     */
+    function getRoleMember(bytes32 role, uint256 index) public view returns (address) {
+        return _roles[role].members.at(index);
+    }
+
+    /**
+     * @dev Returns the admin role that controls `role`. See {grantRole} and
+     * {revokeRole}.
+     *
+     * To change a role's admin, use {_setRoleAdmin}.
+     */
+    function getRoleAdmin(bytes32 role) public view returns (bytes32) {
+        return _roles[role].adminRole;
+    }
+
+    /**
+     * @dev Grants `role` to `account`.
+     *
+     * If `account` had not been already granted `role`, emits a {RoleGranted}
+     * event.
+     *
+     * Requirements:
+     *
+     * - the caller must have ``role``'s admin role.
+     */
+    function grantRole(bytes32 role, address account) public virtual {
+        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to grant");
+
+        _grantRole(role, account);
+    }
+
+    /**
+     * @dev Revokes `role` from `account`.
+     *
+     * If `account` had been granted `role`, emits a {RoleRevoked} event.
+     *
+     * Requirements:
+     *
+     * - the caller must have ``role``'s admin role.
+     */
+    function revokeRole(bytes32 role, address account) public virtual {
+        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to revoke");
+
+        _revokeRole(role, account);
+    }
+
+    /**
+     * @dev Revokes `role` from the calling account.
+     *
+     * Roles are often managed via {grantRole} and {revokeRole}: this function's
+     * purpose is to provide a mechanism for accounts to lose their privileges
+     * if they are compromised (such as when a trusted device is misplaced).
+     *
+     * If the calling account had been granted `role`, emits a {RoleRevoked}
+     * event.
+     *
+     * Requirements:
+     *
+     * - the caller must be `account`.
+     */
+    function renounceRole(bytes32 role, address account) public virtual {
+        require(account == _msgSender(), "AccessControl: can only renounce roles for self");
+
+        _revokeRole(role, account);
+    }
+
+    /**
+     * @dev Grants `role` to `account`.
+     *
+     * If `account` had not been already granted `role`, emits a {RoleGranted}
+     * event. Note that unlike {grantRole}, this function doesn't perform any
+     * checks on the calling account.
+     *
+     * [WARNING]
+     * ====
+     * This function should only be called from the constructor when setting
+     * up the initial roles for the system.
+     *
+     * Using this function in any other way is effectively circumventing the admin
+     * system imposed by {AccessControl}.
+     * ====
+     */
+    function _setupRole(bytes32 role, address account) internal virtual {
+        _grantRole(role, account);
+    }
+
+    /**
+     * @dev Sets `adminRole` as ``role``'s admin role.
+     */
+    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
+        _roles[role].adminRole = adminRole;
+    }
+
+    function _grantRole(bytes32 role, address account) private {
+        if (_roles[role].members.add(account)) {
+            emit RoleGranted(role, account, _msgSender());
+        }
+    }
+
+    function _revokeRole(bytes32 role, address account) private {
+        if (_roles[role].members.remove(account)) {
+            emit RoleRevoked(role, account, _msgSender());
+        }
+    }
+}

contracts/access/Ownable.sol

@@ -0,0 +1,66 @@
+pragma solidity ^0.6.0;
+
+import "../GSN/Context.sol";
+/**
+ * @dev Contract module which provides a basic access control mechanism, where
+ * there is an account (an owner) that can be granted exclusive access to
+ * specific functions.
+ *
+ * By default, the owner account will be the one that deploys the contract. This
+ * can later be changed with {transferOwnership}.
+ *
+ * This module is used through inheritance. It will make available the modifier
+ * `onlyOwner`, which can be applied to your functions to restrict their use to
+ * the owner.
+ */
+contract Ownable is Context {
+    address private _owner;
+
+    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
+
+    /**
+     * @dev Initializes the contract setting the deployer as the initial owner.
+     */
+    constructor () internal {
+        address msgSender = _msgSender();
+        _owner = msgSender;
+        emit OwnershipTransferred(address(0), msgSender);
+    }
+
+    /**
+     * @dev Returns the address of the current owner.
+     */
+    function owner() public view returns (address) {
+        return _owner;
+    }
+
+    /**
+     * @dev Throws if called by any account other than the owner.
+     */
+    modifier onlyOwner() {
+        require(_owner == _msgSender(), "Ownable: caller is not the owner");
+        _;
+    }
+
+    /**
+     * @dev Leaves the contract without owner. It will not be possible to call
+     * `onlyOwner` functions anymore. Can only be called by the current owner.
+     *
+     * NOTE: Renouncing ownership will leave the contract without an owner,
+     * thereby removing any functionality that is only available to the owner.
+     */
+    function renounceOwnership() public virtual onlyOwner {
+        emit OwnershipTransferred(_owner, address(0));
+        _owner = address(0);
+    }
+
+    /**
+     * @dev Transfers ownership of the contract to a new account (`newOwner`).
+     * Can only be called by the current owner.
+     */
+    function transferOwnership(address newOwner) public virtual onlyOwner {
+        require(newOwner != address(0), "Ownable: new owner is the zero address");
+        emit OwnershipTransferred(_owner, newOwner);
+        _owner = newOwner;
+    }
+}

contracts/access/README.adoc

@@ -0,0 +1,9 @@
+= Access
+
+Contract modules for authorization and access control mechanisms.
+
+== Contracts
+
+{{Ownable}}
+
+{{AccessControl}}

contracts/access/Roles.sol

@@ -1,40 +0,0 @@
-pragma solidity ^0.5.2;
-
-/**
- * @title Roles
- * @dev Library for managing addresses assigned to a Role.
- */
-library Roles {
-    struct Role {
-        mapping (address => bool) bearer;
-    }
-
-    /**
-     * @dev give an account access to this role
-     */
-    function add(Role storage role, address account) internal {
-        require(account != address(0));
-        require(!has(role, account));
-
-        role.bearer[account] = true;
-    }
-
-    /**
-     * @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];
-    }
-}

contracts/access/roles/CapperRole.sol

@@ -1,43 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../Roles.sol";
-
-contract CapperRole {
-    using Roles for Roles.Role;
-
-    event CapperAdded(address indexed account);
-    event CapperRemoved(address indexed account);
-
-    Roles.Role private _cappers;
-
-    constructor () internal {
-        _addCapper(msg.sender);
-    }
-
-    modifier onlyCapper() {
-        require(isCapper(msg.sender));
-        _;
-    }
-
-    function isCapper(address account) public view returns (bool) {
-        return _cappers.has(account);
-    }
-
-    function addCapper(address account) public onlyCapper {
-        _addCapper(account);
-    }
-
-    function renounceCapper() public {
-        _removeCapper(msg.sender);
-    }
-
-    function _addCapper(address account) internal {
-        _cappers.add(account);
-        emit CapperAdded(account);
-    }
-
-    function _removeCapper(address account) internal {
-        _cappers.remove(account);
-        emit CapperRemoved(account);
-    }
-}

contracts/access/roles/MinterRole.sol

@@ -1,43 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../Roles.sol";
-
-contract MinterRole {
-    using Roles for Roles.Role;
-
-    event MinterAdded(address indexed account);
-    event MinterRemoved(address indexed account);
-
-    Roles.Role private _minters;
-
-    constructor () internal {
-        _addMinter(msg.sender);
-    }
-
-    modifier onlyMinter() {
-        require(isMinter(msg.sender));
-        _;
-    }
-
-    function isMinter(address account) public view returns (bool) {
-        return _minters.has(account);
-    }
-
-    function addMinter(address account) public onlyMinter {
-        _addMinter(account);
-    }
-
-    function renounceMinter() public {
-        _removeMinter(msg.sender);
-    }
-
-    function _addMinter(address account) internal {
-        _minters.add(account);
-        emit MinterAdded(account);
-    }
-
-    function _removeMinter(address account) internal {
-        _minters.remove(account);
-        emit MinterRemoved(account);
-    }
-}

contracts/access/roles/PauserRole.sol

@@ -1,43 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../Roles.sol";
-
-contract PauserRole {
-    using Roles for Roles.Role;
-
-    event PauserAdded(address indexed account);
-    event PauserRemoved(address indexed account);
-
-    Roles.Role private _pausers;
-
-    constructor () internal {
-        _addPauser(msg.sender);
-    }
-
-    modifier onlyPauser() {
-        require(isPauser(msg.sender));
-        _;
-    }
-
-    function isPauser(address account) public view returns (bool) {
-        return _pausers.has(account);
-    }
-
-    function addPauser(address account) public onlyPauser {
-        _addPauser(account);
-    }
-
-    function renouncePauser() public {
-        _removePauser(msg.sender);
-    }
-
-    function _addPauser(address account) internal {
-        _pausers.add(account);
-        emit PauserAdded(account);
-    }
-
-    function _removePauser(address account) internal {
-        _pausers.remove(account);
-        emit PauserRemoved(account);
-    }
-}

contracts/access/roles/SignerRole.sol

@@ -1,43 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../Roles.sol";
-
-contract SignerRole {
-    using Roles for Roles.Role;
-
-    event SignerAdded(address indexed account);
-    event SignerRemoved(address indexed account);
-
-    Roles.Role private _signers;
-
-    constructor () internal {
-        _addSigner(msg.sender);
-    }
-
-    modifier onlySigner() {
-        require(isSigner(msg.sender));
-        _;
-    }
-
-    function isSigner(address account) public view returns (bool) {
-        return _signers.has(account);
-    }
-
-    function addSigner(address account) public onlySigner {
-        _addSigner(account);
-    }
-
-    function renounceSigner() public {
-        _removeSigner(msg.sender);
-    }
-
-    function _addSigner(address account) internal {
-        _signers.add(account);
-        emit SignerAdded(account);
-    }
-
-    function _removeSigner(address account) internal {
-        _signers.remove(account);
-        emit SignerRemoved(account);
-    }
-}

contracts/access/roles/WhitelistAdminRole.sol

@@ -1,47 +0,0 @@
-pragma solidity ^0.5.2;
-
-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));
-        _;
-    }
-
-    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

@@ -1,50 +0,0 @@
-pragma solidity ^0.5.2;
-
-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));
-        _;
-    }
-
-    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

@@ -1,198 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../token/ERC20/IERC20.sol";
-import "../math/SafeMath.sol";
-import "../token/ERC20/SafeERC20.sol";
-import "../utils/ReentrancyGuard.sol";
-
-/**
- * @title Crowdsale
- * @dev Crowdsale is a base contract for managing a token crowdsale,
- * allowing investors to purchase tokens with ether. This contract implements
- * such functionality in its most fundamental form and can be extended to provide additional
- * functionality and/or custom behavior.
- * The external interface represents the basic interface for purchasing tokens, and conforms
- * the base architecture for crowdsales. It is *not* intended to be modified / overridden.
- * The internal interface conforms the extensible and modifiable surface of crowdsales. Override
- * the methods to add functionality. Consider using 'super' where appropriate to concatenate
- * behavior.
- */
-contract Crowdsale is ReentrancyGuard {
-    using SafeMath for uint256;
-    using SafeERC20 for IERC20;
-
-    // The token being sold
-    IERC20 private _token;
-
-    // Address where funds are collected
-    address payable private _wallet;
-
-    // How many token units a buyer gets per wei.
-    // The rate is the conversion between wei and the smallest and indivisible token unit.
-    // So, if you are using a rate of 1 with a ERC20Detailed token with 3 decimals called TOK
-    // 1 wei will give you 1 unit, or 0.001 TOK.
-    uint256 private _rate;
-
-    // Amount of wei raised
-    uint256 private _weiRaised;
-
-    /**
-     * Event for token purchase logging
-     * @param purchaser who paid for the tokens
-     * @param beneficiary who got the tokens
-     * @param value weis paid for purchase
-     * @param amount amount of tokens purchased
-     */
-    event TokensPurchased(address indexed purchaser, address indexed beneficiary, uint256 value, uint256 amount);
-
-    /**
-     * @param rate Number of token units a buyer gets per wei
-     * @dev The rate is the conversion between wei and the smallest and indivisible
-     * token unit. So, if you are using a rate of 1 with a ERC20Detailed token
-     * with 3 decimals called TOK, 1 wei will give you 1 unit, or 0.001 TOK.
-     * @param wallet Address where collected funds will be forwarded to
-     * @param token Address of the token being sold
-     */
-    constructor (uint256 rate, address payable wallet, IERC20 token) public {
-        require(rate > 0);
-        require(wallet != address(0));
-        require(address(token) != address(0));
-
-        _rate = rate;
-        _wallet = wallet;
-        _token = token;
-    }
-
-    /**
-     * @dev fallback function ***DO NOT OVERRIDE***
-     * Note that other contracts will transfer funds with a base gas stipend
-     * of 2300, which is not enough to call buyTokens. Consider calling
-     * buyTokens directly when purchasing tokens from a contract.
-     */
-    function () external payable {
-        buyTokens(msg.sender);
-    }
-
-    /**
-     * @return the token being sold.
-     */
-    function token() public view returns (IERC20) {
-        return _token;
-    }
-
-    /**
-     * @return the address where funds are collected.
-     */
-    function wallet() public view returns (address payable) {
-        return _wallet;
-    }
-
-    /**
-     * @return the number of token units a buyer gets per wei.
-     */
-    function rate() public view returns (uint256) {
-        return _rate;
-    }
-
-    /**
-     * @return the amount of wei raised.
-     */
-    function weiRaised() public view returns (uint256) {
-        return _weiRaised;
-    }
-
-    /**
-     * @dev low level token purchase ***DO NOT OVERRIDE***
-     * This function has a non-reentrancy guard, so it shouldn't be called by
-     * another `nonReentrant` function.
-     * @param beneficiary Recipient of the token purchase
-     */
-    function buyTokens(address beneficiary) public nonReentrant payable {
-        uint256 weiAmount = msg.value;
-        _preValidatePurchase(beneficiary, weiAmount);
-
-        // calculate token amount to be created
-        uint256 tokens = _getTokenAmount(weiAmount);
-
-        // update state
-        _weiRaised = _weiRaised.add(weiAmount);
-
-        _processPurchase(beneficiary, tokens);
-        emit TokensPurchased(msg.sender, beneficiary, weiAmount, tokens);
-
-        _updatePurchasingState(beneficiary, weiAmount);
-
-        _forwardFunds();
-        _postValidatePurchase(beneficiary, weiAmount);
-    }
-
-    /**
-     * @dev Validation of an incoming purchase. Use require statements to revert state when conditions are not met.
-     * Use `super` in contracts that inherit from Crowdsale to extend their validations.
-     * Example from CappedCrowdsale.sol's _preValidatePurchase method:
-     *     super._preValidatePurchase(beneficiary, weiAmount);
-     *     require(weiRaised().add(weiAmount) <= cap);
-     * @param beneficiary Address performing the token purchase
-     * @param weiAmount Value in wei involved in the purchase
-     */
-    function _preValidatePurchase(address beneficiary, uint256 weiAmount) internal view {
-        require(beneficiary != address(0));
-        require(weiAmount != 0);
-    }
-
-    /**
-     * @dev Validation of an executed purchase. Observe state and use revert statements to undo rollback when valid
-     * conditions are not met.
-     * @param beneficiary Address performing the token purchase
-     * @param weiAmount Value in wei involved in the purchase
-     */
-    function _postValidatePurchase(address beneficiary, uint256 weiAmount) internal view {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    /**
-     * @dev Source of tokens. Override this method to modify the way in which the crowdsale ultimately gets and sends
-     * its tokens.
-     * @param beneficiary Address performing the token purchase
-     * @param tokenAmount Number of tokens to be emitted
-     */
-    function _deliverTokens(address beneficiary, uint256 tokenAmount) internal {
-        _token.safeTransfer(beneficiary, tokenAmount);
-    }
-
-    /**
-     * @dev Executed when a purchase has been validated and is ready to be executed. Doesn't necessarily emit/send
-     * tokens.
-     * @param beneficiary Address receiving the tokens
-     * @param tokenAmount Number of tokens to be purchased
-     */
-    function _processPurchase(address beneficiary, uint256 tokenAmount) internal {
-        _deliverTokens(beneficiary, tokenAmount);
-    }
-
-    /**
-     * @dev Override for extensions that require an internal state to check for validity (current user contributions,
-     * etc.)
-     * @param beneficiary Address receiving the tokens
-     * @param weiAmount Value in wei involved in the purchase
-     */
-    function _updatePurchasingState(address beneficiary, uint256 weiAmount) internal {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    /**
-     * @dev Override to extend the way in which ether is converted to tokens.
-     * @param weiAmount Value in wei to be converted into tokens
-     * @return Number of tokens that can be purchased with the specified _weiAmount
-     */
-    function _getTokenAmount(uint256 weiAmount) internal view returns (uint256) {
-        return weiAmount.mul(_rate);
-    }
-
-    /**
-     * @dev Determines how ETH is stored/forwarded on purchases.
-     */
-    function _forwardFunds() internal {
-        _wallet.transfer(msg.value);
-    }
-}

contracts/crowdsale/distribution/FinalizableCrowdsale.sol

@@ -1,51 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../../math/SafeMath.sol";
-import "../validation/TimedCrowdsale.sol";
-
-/**
- * @title FinalizableCrowdsale
- * @dev Extension of TimedCrowdsale with a one-off finalization action, where one
- * can do extra work after finishing.
- */
-contract FinalizableCrowdsale is TimedCrowdsale {
-    using SafeMath for uint256;
-
-    bool private _finalized;
-
-    event CrowdsaleFinalized();
-
-    constructor () internal {
-        _finalized = false;
-    }
-
-    /**
-     * @return true if the crowdsale is finalized, false otherwise.
-     */
-    function finalized() public view returns (bool) {
-        return _finalized;
-    }
-
-    /**
-     * @dev Must be called after crowdsale ends, to do some extra finalization
-     * work. Calls the contract's finalization function.
-     */
-    function finalize() public {
-        require(!_finalized);
-        require(hasClosed());
-
-        _finalized = true;
-
-        _finalization();
-        emit CrowdsaleFinalized();
-    }
-
-    /**
-     * @dev Can be overridden to add finalization logic. The overriding function
-     * should call super._finalization() to ensure the chain of finalization is
-     * executed entirely.
-     */
-    function _finalization() internal {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}

contracts/crowdsale/distribution/PostDeliveryCrowdsale.sol

@@ -1,43 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../validation/TimedCrowdsale.sol";
-import "../../math/SafeMath.sol";
-
-/**
- * @title PostDeliveryCrowdsale
- * @dev Crowdsale that locks tokens from withdrawal until it ends.
- */
-contract PostDeliveryCrowdsale is TimedCrowdsale {
-    using SafeMath for uint256;
-
-    mapping(address => uint256) private _balances;
-
-    /**
-     * @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);
-    }
-
-    /**
-     * @return the balance of an account.
-     */
-    function balanceOf(address account) public view returns (uint256) {
-        return _balances[account];
-    }
-
-    /**
-     * @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);
-    }
-
-}

contracts/crowdsale/distribution/RefundableCrowdsale.sol

@@ -1,82 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../../math/SafeMath.sol";
-import "./FinalizableCrowdsale.sol";
-import "../../payment/escrow/RefundEscrow.sol";
-
-/**
- * @title RefundableCrowdsale
- * @dev Extension of FinalizableCrowdsale contract that adds a funding goal, and the possibility of users
- * getting a refund if goal is not met.
- *
- * Deprecated, use RefundablePostDeliveryCrowdsale instead. Note that if you allow tokens to be traded before the goal
- * is met, then an attack is possible in which the attacker purchases tokens from the crowdsale and when they sees that
- * the goal is unlikely to be met, they sell their tokens (possibly at a discount). The attacker will be refunded when
- * the crowdsale is finalized, and the users that purchased from them will be left with worthless tokens.
- */
-contract RefundableCrowdsale is FinalizableCrowdsale {
-    using SafeMath for uint256;
-
-    // minimum amount of funds to be raised in weis
-    uint256 private _goal;
-
-    // refund escrow used to hold funds while crowdsale is running
-    RefundEscrow private _escrow;
-
-    /**
-     * @dev Constructor, creates RefundEscrow.
-     * @param goal Funding goal
-     */
-    constructor (uint256 goal) public {
-        require(goal > 0);
-        _escrow = new RefundEscrow(wallet());
-        _goal = goal;
-    }
-
-    /**
-     * @return minimum amount of funds to be raised in wei.
-     */
-    function goal() public view returns (uint256) {
-        return _goal;
-    }
-
-    /**
-     * @dev Investors can claim refunds here if crowdsale is unsuccessful
-     * @param refundee Whose refund will be claimed.
-     */
-    function claimRefund(address payable refundee) public {
-        require(finalized());
-        require(!goalReached());
-
-        _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

@@ -1,20 +0,0 @@
-pragma solidity ^0.5.2;
-
-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());
-        require(goalReached());
-
-        super.withdrawTokens(beneficiary);
-    }
-}

contracts/crowdsale/emission/AllowanceCrowdsale.sol

@@ -1,51 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../Crowdsale.sol";
-import "../../token/ERC20/IERC20.sol";
-import "../../token/ERC20/SafeERC20.sol";
-import "../../math/SafeMath.sol";
-import "../../math/Math.sol";
-
-/**
- * @title AllowanceCrowdsale
- * @dev Extension of Crowdsale where tokens are held by a wallet, which approves an allowance to the crowdsale.
- */
-contract AllowanceCrowdsale is Crowdsale {
-    using SafeMath for uint256;
-    using SafeERC20 for IERC20;
-
-    address private _tokenWallet;
-
-    /**
-     * @dev Constructor, takes token wallet address.
-     * @param tokenWallet Address holding the tokens, which has approved allowance to the crowdsale
-     */
-    constructor (address tokenWallet) public {
-        require(tokenWallet != address(0));
-        _tokenWallet = tokenWallet;
-    }
-
-    /**
-     * @return the address of the wallet that will hold the tokens.
-     */
-    function tokenWallet() public view returns (address) {
-        return _tokenWallet;
-    }
-
-    /**
-     * @dev Checks the amount of tokens left in the allowance.
-     * @return Amount of tokens left in the allowance
-     */
-    function remainingTokens() public view returns (uint256) {
-        return Math.min(token().balanceOf(_tokenWallet), token().allowance(_tokenWallet, address(this)));
-    }
-
-    /**
-     * @dev Overrides parent behavior by transferring tokens from wallet.
-     * @param beneficiary Token purchaser
-     * @param tokenAmount Amount of tokens purchased
-     */
-    function _deliverTokens(address beneficiary, uint256 tokenAmount) internal {
-        token().safeTransferFrom(_tokenWallet, beneficiary, tokenAmount);
-    }
-}

contracts/crowdsale/emission/MintedCrowdsale.sol

@@ -1,21 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../Crowdsale.sol";
-import "../../token/ERC20/ERC20Mintable.sol";
-
-/**
- * @title MintedCrowdsale
- * @dev Extension of Crowdsale contract whose tokens are minted in each purchase.
- * Token ownership should be transferred to MintedCrowdsale for minting.
- */
-contract MintedCrowdsale is Crowdsale {
-    /**
-     * @dev Overrides delivery by minting tokens upon purchase.
-     * @param beneficiary Token purchaser
-     * @param tokenAmount Number of tokens to be minted
-     */
-    function _deliverTokens(address beneficiary, uint256 tokenAmount) internal {
-        // Potentially dangerous assumption about the type of the token.
-        require(ERC20Mintable(address(token())).mint(beneficiary, tokenAmount));
-    }
-}

contracts/crowdsale/price/IncreasingPriceCrowdsale.sol

@@ -1,78 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../validation/TimedCrowdsale.sol";
-import "../../math/SafeMath.sol";
-
-/**
- * @title IncreasingPriceCrowdsale
- * @dev Extension of Crowdsale contract that increases the price of tokens linearly in time.
- * Note that what should be provided to the constructor is the initial and final _rates_, that is,
- * the amount of tokens per wei contributed. Thus, the initial rate must be greater than the final rate.
- */
-contract IncreasingPriceCrowdsale is TimedCrowdsale {
-    using SafeMath for uint256;
-
-    uint256 private _initialRate;
-    uint256 private _finalRate;
-
-    /**
-     * @dev Constructor, takes initial and final rates of tokens received per wei contributed.
-     * @param initialRate Number of tokens a buyer gets per wei at the start of the crowdsale
-     * @param finalRate Number of tokens a buyer gets per wei at the end of the crowdsale
-     */
-    constructor (uint256 initialRate, uint256 finalRate) public {
-        require(finalRate > 0);
-        require(initialRate > finalRate);
-        _initialRate = initialRate;
-        _finalRate = finalRate;
-    }
-
-    /**
-     * The base rate function is overridden to revert, since this crowdsale doesn't use it, and
-     * all calls to it are a mistake.
-     */
-    function rate() public view returns (uint256) {
-        revert();
-    }
-
-    /**
-     * @return the initial rate of the crowdsale.
-     */
-    function initialRate() public view returns (uint256) {
-        return _initialRate;
-    }
-
-    /**
-     * @return the final rate of the crowdsale.
-     */
-    function finalRate() public view returns (uint256) {
-        return _finalRate;
-    }
-
-    /**
-     * @dev Returns the rate of tokens per wei at the present time.
-     * Note that, as price _increases_ with time, the rate _decreases_.
-     * @return The number of tokens a buyer gets per wei at a given time
-     */
-    function getCurrentRate() public view returns (uint256) {
-        if (!isOpen()) {
-            return 0;
-        }
-
-        // solhint-disable-next-line not-rely-on-time
-        uint256 elapsedTime = block.timestamp.sub(openingTime());
-        uint256 timeRange = closingTime().sub(openingTime());
-        uint256 rateRange = _initialRate.sub(_finalRate);
-        return _initialRate.sub(elapsedTime.mul(rateRange).div(timeRange));
-    }
-
-    /**
-     * @dev Overrides parent method taking into account variable rate.
-     * @param weiAmount The value in wei to be converted into tokens
-     * @return The number of tokens _weiAmount wei will buy at present time
-     */
-    function _getTokenAmount(uint256 weiAmount) internal view returns (uint256) {
-        uint256 currentRate = getCurrentRate();
-        return currentRate.mul(weiAmount);
-    }
-}

contracts/crowdsale/validation/CappedCrowdsale.sol

@@ -1,48 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../../math/SafeMath.sol";
-import "../Crowdsale.sol";
-
-/**
- * @title CappedCrowdsale
- * @dev Crowdsale with a limit for total contributions.
- */
-contract CappedCrowdsale is Crowdsale {
-    using SafeMath for uint256;
-
-    uint256 private _cap;
-
-    /**
-     * @dev Constructor, takes maximum amount of wei accepted in the crowdsale.
-     * @param cap Max amount of wei to be contributed
-     */
-    constructor (uint256 cap) public {
-        require(cap > 0);
-        _cap = cap;
-    }
-
-    /**
-     * @return the cap of the crowdsale.
-     */
-    function cap() public view returns (uint256) {
-        return _cap;
-    }
-
-    /**
-     * @dev Checks whether the cap has been reached.
-     * @return Whether the cap was reached
-     */
-    function capReached() public view returns (bool) {
-        return weiRaised() >= _cap;
-    }
-
-    /**
-     * @dev Extend parent behavior requiring purchase to respect the funding cap.
-     * @param beneficiary Token purchaser
-     * @param weiAmount Amount of wei contributed
-     */
-    function _preValidatePurchase(address beneficiary, uint256 weiAmount) internal view {
-        super._preValidatePurchase(beneficiary, weiAmount);
-        require(weiRaised().add(weiAmount) <= _cap);
-    }
-}

contracts/crowdsale/validation/IndividuallyCappedCrowdsale.sol

@@ -1,63 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../../math/SafeMath.sol";
-import "../Crowdsale.sol";
-import "../../access/roles/CapperRole.sol";
-
-/**
- * @title IndividuallyCappedCrowdsale
- * @dev Crowdsale with per-beneficiary caps.
- */
-contract IndividuallyCappedCrowdsale is Crowdsale, CapperRole {
-    using SafeMath for uint256;
-
-    mapping(address => uint256) private _contributions;
-    mapping(address => uint256) private _caps;
-
-    /**
-     * @dev Sets a specific beneficiary's maximum contribution.
-     * @param beneficiary Address to be capped
-     * @param cap Wei limit for individual contribution
-     */
-    function setCap(address beneficiary, uint256 cap) external onlyCapper {
-        _caps[beneficiary] = cap;
-    }
-
-    /**
-     * @dev Returns the cap of a specific beneficiary.
-     * @param beneficiary Address whose cap is to be checked
-     * @return Current cap for individual beneficiary
-     */
-    function getCap(address beneficiary) public view returns (uint256) {
-        return _caps[beneficiary];
-    }
-
-    /**
-     * @dev Returns the amount contributed so far by a specific beneficiary.
-     * @param beneficiary Address of contributor
-     * @return Beneficiary contribution so far
-     */
-    function getContribution(address beneficiary) public view returns (uint256) {
-        return _contributions[beneficiary];
-    }
-
-    /**
-     * @dev Extend parent behavior requiring purchase to respect the beneficiary's funding cap.
-     * @param beneficiary Token purchaser
-     * @param weiAmount Amount of wei contributed
-     */
-    function _preValidatePurchase(address beneficiary, uint256 weiAmount) internal view {
-        super._preValidatePurchase(beneficiary, weiAmount);
-        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);
-    }
-}

contracts/crowdsale/validation/PausableCrowdsale.sol

@@ -1,21 +0,0 @@
-pragma solidity ^0.5.2;
-
-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

@@ -1,96 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../../math/SafeMath.sol";
-import "../Crowdsale.sol";
-
-/**
- * @title TimedCrowdsale
- * @dev Crowdsale accepting contributions only within a time frame.
- */
-contract TimedCrowdsale is Crowdsale {
-    using SafeMath for uint256;
-
-    uint256 private _openingTime;
-    uint256 private _closingTime;
-
-    /**
-     * Event for crowdsale extending
-     * @param newClosingTime new closing time
-     * @param prevClosingTime old closing time
-     */
-    event TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime);
-
-    /**
-     * @dev Reverts if not in crowdsale time range.
-     */
-    modifier onlyWhileOpen {
-        require(isOpen());
-        _;
-    }
-
-    /**
-     * @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);
-        require(closingTime > openingTime);
-
-        _openingTime = openingTime;
-        _closingTime = closingTime;
-    }
-
-    /**
-     * @return the crowdsale opening time.
-     */
-    function openingTime() public view returns (uint256) {
-        return _openingTime;
-    }
-
-    /**
-     * @return the crowdsale closing time.
-     */
-    function closingTime() public view returns (uint256) {
-        return _closingTime;
-    }
-
-    /**
-     * @return true if the crowdsale is open, false otherwise.
-     */
-    function isOpen() public view returns (bool) {
-        // solhint-disable-next-line not-rely-on-time
-        return block.timestamp >= _openingTime && block.timestamp <= _closingTime;
-    }
-
-    /**
-     * @dev Checks whether the period in which the crowdsale is open has already elapsed.
-     * @return Whether crowdsale period has elapsed
-     */
-    function hasClosed() public view returns (bool) {
-        // solhint-disable-next-line not-rely-on-time
-        return block.timestamp > _closingTime;
-    }
-
-    /**
-     * @dev Extend parent behavior requiring to be within contributing period
-     * @param beneficiary Token purchaser
-     * @param weiAmount Amount of wei contributed
-     */
-    function _preValidatePurchase(address beneficiary, uint256 weiAmount) internal onlyWhileOpen view {
-        super._preValidatePurchase(beneficiary, weiAmount);
-    }
-
-    /**
-     * @dev Extend crowdsale
-     * @param newClosingTime Crowdsale closing time
-     */
-    function _extendTime(uint256 newClosingTime) internal {
-        require(!hasClosed());
-        require(newClosingTime > _closingTime);
-
-        emit TimedCrowdsaleExtended(_closingTime, newClosingTime);
-        _closingTime = newClosingTime;
-    }
-}

contracts/crowdsale/validation/WhitelistCrowdsale.sol

@@ -1,21 +0,0 @@
-pragma solidity ^0.5.2;
-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));
-        super._preValidatePurchase(_beneficiary, _weiAmount);
-    }
-}

contracts/cryptography/ECDSA.sol

@@ -1,22 +1,30 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 /**
- * @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 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()
+     * @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.
+     *
+     * IMPORTANT: `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));
+            revert("ECDSA: invalid signature length");
         }
 
         // Divide the signature in r, s and v variables
@@ -43,21 +51,27 @@ library ECDSA {
         // 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);
+            revert("ECDSA: invalid signature 's' value");
         }
 
         if (v != 27 && v != 28) {
-            return address(0);
+            revert("ECDSA: invalid signature 'v' value");
         }
 
         // If the signature is valid (and not malleable), return the signer address
-        return ecrecover(hash, v, r, s);
+        address signer = ecrecover(hash, v, r, s);
+        require(signer != address(0), "ECDSA: invalid signature");
+
+        return signer;
     }
 
     /**
-     * toEthSignedMessageHash
-     * @dev prefix a bytes32 value with "\x19Ethereum Signed Message:"
-     * and hash the result
+     * @dev Returns an Ethereum Signed Message, created from a `hash`. This
+     * replicates the behavior of the
+     * https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign[`eth_sign`]
+     * JSON-RPC method.
+     *
+     * See {recover}.
      */
     function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
         // 32 is the length in bytes of hash,

contracts/cryptography/MerkleProof.sol

@@ -1,17 +1,14 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 /**
- * @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
+     * @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;
@@ -19,7 +16,7 @@ library MerkleProof {
         for (uint256 i = 0; i < proof.length; i++) {
             bytes32 proofElement = proof[i];
 
-            if (computedHash < proofElement) {
+            if (computedHash <= proofElement) {
                 // Hash(current computed hash + current element of the proof)
                 computedHash = keccak256(abi.encodePacked(computedHash, proofElement));
             } else {

contracts/cryptography/README.adoc

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

contracts/drafts/ERC1046/ERC20Metadata.sol

@@ -1,24 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../../token/ERC20/IERC20.sol";
-
-/**
- * @title ERC-1047 Token Metadata
- * @dev See https://eips.ethereum.org/EIPS/eip-1046
- * @dev tokenURI must respond with a URI that implements https://eips.ethereum.org/EIPS/eip-1047
- */
-contract ERC20Metadata {
-    string private _tokenURI;
-
-    constructor (string memory tokenURI_) public {
-        _setTokenURI(tokenURI_);
-    }
-
-    function tokenURI() external view returns (string memory) {
-        return _tokenURI;
-    }
-
-    function _setTokenURI(string memory tokenURI_) internal {
-        _tokenURI = tokenURI_;
-    }
-}

contracts/drafts/ERC20Migrator.sol

@@ -1,101 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../token/ERC20/IERC20.sol";
-import "../token/ERC20/ERC20Mintable.sol";
-import "../token/ERC20/SafeERC20.sol";
-import "../math/Math.sol";
-
-/**
- * @title ERC20Migrator
- * @dev This contract can be used to migrate an ERC20 token from one
- * contract to another, where each token holder has to opt-in to the migration.
- * To opt-in, users must approve for this contract the number of tokens they
- * want to migrate. Once the allowance is set up, anyone can trigger the
- * migration to the new token contract. In this way, token holders "turn in"
- * their old balance and will be minted an equal amount in the new token.
- * The new token contract must be mintable. For the precise interface refer to
- * OpenZeppelin's ERC20Mintable, but the only functions that are needed are
- * `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 transferred to the migrator, as it
- * is migrated, and remain there forever.
- * Although this contract can be used in many different scenarios, the main
- * motivation was to provide a way to migrate ERC20 tokens into an upgradeable
- * version of it using ZeppelinOS. To read more about how this can be done
- * using this implementation, please follow the official documentation site of
- * ZeppelinOS: https://docs.zeppelinos.org/docs/erc20_onboarding.html
- * Example of usage:
- * ```
- * const migrator = await ERC20Migrator.new(legacyToken.address);
- * await newToken.addMinter(migrator.address);
- * await migrator.beginMigration(newToken.address);
- * ```
- */
-contract ERC20Migrator {
-    using SafeERC20 for IERC20;
-
-    /// Address of the old token contract
-    IERC20 private _legacyToken;
-
-    /// Address of the new token contract
-    ERC20Mintable private _newToken;
-
-    /**
-     * @param legacyToken address of the old token contract
-     */
-    constructor (IERC20 legacyToken) public {
-        require(address(legacyToken) != address(0));
-        _legacyToken = legacyToken;
-    }
-
-    /**
-     * @dev Returns the legacy token that is being migrated.
-     */
-    function legacyToken() public view returns (IERC20) {
-        return _legacyToken;
-    }
-
-    /**
-     * @dev Returns the new token to which we are migrating.
-     */
-    function newToken() public view returns (IERC20) {
-        return _newToken;
-    }
-
-    /**
-     * @dev Begins the migration by setting which is the new token that will be
-     * minted. This contract must be a minter for the new token.
-     * @param newToken_ the token that will be minted
-     */
-    function beginMigration(ERC20Mintable newToken_) public {
-        require(address(_newToken) == address(0));
-        require(address(newToken_) != address(0));
-        require(newToken_.isMinter(address(this)));
-
-        _newToken = newToken_;
-    }
-
-    /**
-     * @dev Transfers part of an account's balance in the old token to this
-     * contract, and mints the same amount of new tokens for that account.
-     * @param account whose tokens will be migrated
-     * @param amount amount of tokens to be migrated
-     */
-    function migrate(address account, uint256 amount) public {
-        require(address(_newToken) != address(0));
-        _legacyToken.safeTransferFrom(account, address(this), amount);
-        _newToken.mint(account, amount);
-    }
-
-    /**
-     * @dev Transfers all of an account's allowed balance in the old token to
-     * this contract, and mints the same amount of new tokens for that account.
-     * @param account whose tokens will be migrated
-     */
-    function migrateAll(address account) public {
-        uint256 balance = _legacyToken.balanceOf(account);
-        uint256 allowance = _legacyToken.allowance(account, address(this));
-        uint256 amount = Math.min(balance, allowance);
-        migrate(account, amount);
-    }
-}

contracts/drafts/ERC20Snapshot.sol

@@ -1,139 +0,0 @@
-pragma solidity ^0.5.2;
-
-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 _totalSupplySnaphots;
-
-    // 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, _totalSupplySnaphots);
-
-        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);
-        require(snapshotId <= _currentSnapshotId.current());
-
-        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(_totalSupplySnaphots, 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/SignatureBouncer.sol

@@ -1,120 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../access/roles/SignerRole.sol";
-import "../cryptography/ECDSA.sol";
-
-/**
- * @title SignatureBouncer
- * @author PhABC, Shrugs and aflesher
- * @dev SignatureBouncer allows users to submit a signature as a permission to
- * do an action.
- * If the signature is from one of the authorized signer addresses, the
- * signature is valid.
- * Note that SignatureBouncer offers no protection against replay attacks, users
- * must add this themselves!
- *
- * Signer addresses can be individual servers signing grants or different
- * users within a decentralized club that have permission to invite other
- * members. This technique is useful for whitelists and airdrops; instead of
- * putting all valid addresses on-chain, simply sign a grant of the form
- * keccak256(abi.encodePacked(`:contractAddress` + `:granteeAddress`)) using a
- * valid signer address.
- * Then restrict access to your crowdsale/whitelist/airdrop using the
- * `onlyValidSignature` modifier (or implement your own using _isValidSignature).
- * In addition to `onlyValidSignature`, `onlyValidSignatureAndMethod` and
- * `onlyValidSignatureAndData` can be used to restrict access to only a given
- * method or a given method with given parameters respectively.
- * See the tests in SignatureBouncer.test.js for specific usage examples.
- *
- * @notice A method that uses the `onlyValidSignatureAndData` modifier must make
- * the _signature parameter the "last" parameter. You cannot sign a message that
- * has its own signature in it so the last 128 bytes of msg.data (which
- * represents the length of the _signature data and the _signature data itself)
- * is ignored when validating. Also non fixed sized parameters make constructing
- * the data in the signature much more complex.
- * See https://ethereum.stackexchange.com/a/50616 for more details.
- */
-contract SignatureBouncer is SignerRole {
-    using ECDSA for bytes32;
-
-    // Function selectors are 4 bytes long, as documented in
-    // https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector
-    uint256 private constant _METHOD_ID_SIZE = 4;
-    // Signature size is 65 bytes (tightly packed v + r + s), but gets padded to 96 bytes
-    uint256 private constant _SIGNATURE_SIZE = 96;
-
-    constructor () internal {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    /**
-     * @dev requires that a valid signature of a signer was provided
-     */
-    modifier onlyValidSignature(bytes memory signature) {
-        require(_isValidSignature(msg.sender, signature));
-        _;
-    }
-
-    /**
-     * @dev requires that a valid signature with a specified method of a signer was provided
-     */
-    modifier onlyValidSignatureAndMethod(bytes memory signature) {
-        require(_isValidSignatureAndMethod(msg.sender, signature));
-        _;
-    }
-
-    /**
-     * @dev requires that a valid signature with a specified method and params of a signer was provided
-     */
-    modifier onlyValidSignatureAndData(bytes memory signature) {
-        require(_isValidSignatureAndData(msg.sender, signature));
-        _;
-    }
-
-    /**
-     * @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);
-
-        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/TokenVesting.sol

@@ -1,7 +1,7 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 import "../token/ERC20/SafeERC20.sol";
-import "../ownership/Ownable.sol";
+import "../access/Ownable.sol";
 import "../math/SafeMath.sol";
 
 /**
@@ -47,10 +47,12 @@ contract TokenVesting is Ownable {
      * @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);
+        require(beneficiary != address(0), "TokenVesting: beneficiary is the zero address");
+        // solhint-disable-next-line max-line-length
+        require(cliffDuration <= duration, "TokenVesting: cliff is longer than duration");
+        require(duration > 0, "TokenVesting: duration is 0");
+        // solhint-disable-next-line max-line-length
+        require(start.add(duration) > block.timestamp, "TokenVesting: final time is before current time");
 
         _beneficiary = beneficiary;
         _revocable = revocable;
@@ -115,7 +117,7 @@ contract TokenVesting is Ownable {
     function release(IERC20 token) public {
         uint256 unreleased = _releasableAmount(token);
 
-        require(unreleased > 0);
+        require(unreleased > 0, "TokenVesting: no tokens are due");
 
         _released[address(token)] = _released[address(token)].add(unreleased);
 
@@ -130,8 +132,8 @@ contract TokenVesting is Ownable {
      * @param token ERC20 token which is being vested
      */
     function revoke(IERC20 token) public onlyOwner {
-        require(_revocable);
-        require(!_revoked[address(token)]);
+        require(_revocable, "TokenVesting: cannot revoke");
+        require(!_revoked[address(token)], "TokenVesting: token already revoked");
 
         uint256 balance = token.balanceOf(address(this));
 

contracts/examples/SampleCrowdsale.sol

@@ -1,53 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../crowdsale/validation/CappedCrowdsale.sol";
-import "../crowdsale/distribution/RefundableCrowdsale.sol";
-import "../crowdsale/emission/MintedCrowdsale.sol";
-import "../token/ERC20/ERC20Mintable.sol";
-import "../token/ERC20/ERC20Detailed.sol";
-
-/**
- * @title SampleCrowdsaleToken
- * @dev Very simple ERC20 Token that can be minted.
- * It is meant to be used in a crowdsale contract.
- */
-contract SampleCrowdsaleToken is ERC20Mintable, ERC20Detailed {
-    constructor () public ERC20Detailed("Sample Crowdsale Token", "SCT", 18) {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}
-
-/**
- * @title SampleCrowdsale
- * @dev This is an example of a fully fledged crowdsale.
- * The way to add new features to a base crowdsale is by multiple inheritance.
- * In this example we are providing following extensions:
- * CappedCrowdsale - sets a max boundary for raised funds
- * RefundableCrowdsale - set a min goal to be reached and returns funds if it's not met
- * MintedCrowdsale - assumes the token can be minted by the crowdsale, which does so
- * when receiving purchases.
- *
- * After adding multiple features it's good practice to run integration tests
- * to ensure that subcontracts works together as intended.
- */
-contract SampleCrowdsale is CappedCrowdsale, RefundableCrowdsale, MintedCrowdsale {
-    constructor (
-        uint256 openingTime,
-        uint256 closingTime,
-        uint256 rate,
-        address payable wallet,
-        uint256 cap,
-        ERC20Mintable token,
-        uint256 goal
-    )
-        public
-        Crowdsale(rate, wallet, token)
-        CappedCrowdsale(cap)
-        TimedCrowdsale(openingTime, closingTime)
-        RefundableCrowdsale(goal)
-    {
-        //As goal needs to be met for a successful crowdsale
-        //the value needs to less or equal than a cap which is limit for accepted funds
-        require(goal <= cap);
-    }
-}

contracts/examples/SimpleToken.sol

@@ -1,22 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../token/ERC20/ERC20.sol";
-import "../token/ERC20/ERC20Detailed.sol";
-
-/**
- * @title SimpleToken
- * @dev Very simple ERC20 Token example, where all tokens are pre-assigned to the creator.
- * Note they can later distribute these tokens as they wish using `transfer` and other
- * `ERC20` functions.
- */
-contract SimpleToken is 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

@@ -1,44 +1,52 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 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 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
     /*
-     * 0x01ffc9a7 ===
-     *     bytes4(keccak256('supportsInterface(bytes4)'))
+     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
      */
+    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
 
     /**
-     * @dev a mapping of interface id to whether or not it's supported
+     * @dev Mapping of interface ids to whether or not it's supported.
      */
     mapping(bytes4 => bool) private _supportedInterfaces;
 
-    /**
-     * @dev A contract implementing SupportsInterfaceWithLookup
-     * implement ERC165 itself
-     */
     constructor () internal {
+        // Derived contracts need only register support for their own interfaces,
+        // we register support for ERC165 itself here
         _registerInterface(_INTERFACE_ID_ERC165);
     }
 
     /**
-     * @dev implement supportsInterface(bytes4) using a lookup table
+     * @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) {
+    function supportsInterface(bytes4 interfaceId) public view override returns (bool) {
         return _supportedInterfaces[interfaceId];
     }
 
     /**
-     * @dev internal method for registering an interface
+     * @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);
+    function _registerInterface(bytes4 interfaceId) internal virtual {
+        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
         _supportedInterfaces[interfaceId] = true;
     }
 }

contracts/introspection/ERC165Checker.sol

@@ -1,26 +1,25 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.2;
 
 /**
- * @title ERC165Checker
- * @dev Use `using ERC165Checker for address`; to include this library
- * https://eips.ethereum.org/EIPS/eip-165
+ * @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 _INTERFACE_ID_INVALID = 0xffffffff;
 
-    bytes4 private constant _INTERFACE_ID_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
+     * @dev Returns true if `account` supports the {IERC165} interface,
      */
-    function _supportsERC165(address account) internal view returns (bool) {
+    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) &&
@@ -28,30 +27,29 @@ library ERC165Checker {
     }
 
     /**
-     * @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.
+     * @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) {
+    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) &&
+        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.
+     * @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) {
+    function supportsAllInterfaces(address account, bytes4[] memory interfaceIds) internal view returns (bool) {
         // query support of ERC165 itself
-        if (!_supportsERC165(account)) {
+        if (!supportsERC165(account)) {
             return false;
         }
 
@@ -74,7 +72,7 @@ library ERC165Checker {
      * 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.
+     * with {supportsERC165}.
      * Interface identification is specified in ERC-165.
      */
     function _supportsERC165Interface(address account, bytes4 interfaceId) private view returns (bool) {
@@ -96,28 +94,11 @@ library ERC165Checker {
     function _callERC165SupportsInterface(address account, bytes4 interfaceId)
         private
         view
-        returns (bool success, bool result)
+        returns (bool, bool)
     {
         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
-        }
+        (bool success, bytes memory result) = account.staticcall{ gas: 30000 }(encodedParams);
+        if (result.length < 32) return (false, false);
+        return (success, abi.decode(result, (bool)));
     }
 }

contracts/introspection/ERC1820Implementer.sol

@@ -0,0 +1,35 @@
+pragma solidity ^0.6.0;
+
+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) public view override 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 virtual {
+        _supportedInterfaces[interfaceHash][account] = true;
+    }
+}

contracts/introspection/IERC165.sol

@@ -1,15 +1,22 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 /**
- * @title IERC165
- * @dev https://eips.ethereum.org/EIPS/eip-165
+ * @dev Interface of the ERC165 standard, as defined in the
+ * https://eips.ethereum.org/EIPS/eip-165[EIP].
+ *
+ * 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.
+     * @dev Returns true if this contract implements the interface defined by
+     * `interfaceId`. See the corresponding
+     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
+     * 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 ^0.6.0;
+
+/**
+ * @dev Interface for an ERC1820 implementer, as defined in the
+ * https://eips.ethereum.org/EIPS/eip-1820#interface-implementation-erc1820implementerinterface[EIP].
+ * 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 ^0.6.0;
+
+/**
+ * @dev Interface of the global ERC1820 Registry, as defined in the
+ * https://eips.ethereum.org/EIPS/eip-1820[EIP]. 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
+     * https://eips.ethereum.org/EIPS/eip-1820#interface-name[section of the EIP].
+     */
+    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` 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` 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.adoc

@@ -0,0 +1,28 @@
+= Introspection
+
+This set of interfaces and contracts deal with https://en.wikipedia.org/wiki/Type_introspection[type introspection] of contracts, that is, examining which functions can be called on them. This is usually referred to as a contract's _interface_.
+
+Ethereum contracts have no native concept of an interface, so applications must usually simply trust they are not making an incorrect call. For trusted setups this is a non-issue, but often unknown and untrusted third-party addresses need to be interacted with. There may even not be any direct calls to them! (e.g. `ERC20` tokens may be sent to a contract that lacks a way to transfer them out of it, locking them forever). In these cases, a contract _declaring_ its interface can be very helpful in preventing errors.
+
+There are two main ways to approach this.
+
+* Locally, where a contract implements `IERC165` and declares an interface, and a second one queries it directly via `ERC165Checker`.
+* Globally, where a global and unique registry (`IERC1820Registry`) is used to register implementers of a certain interface (`IERC1820Implementer`). It is then the registry that is queried, which allows for more complex setups, like contracts implementing interfaces for externally-owned accounts.
+
+Note that, in all cases, accounts simply _declare_ their interfaces, but they are not required to actually implement them. This mechanism can therefore be used to both prevent errors and allow for complex interactions (see `ERC777`), but it must not be relied on for security.
+
+== Local
+
+{{IERC165}}
+
+{{ERC165}}
+
+{{ERC165Checker}}
+
+== Global
+
+{{IERC1820Registry}}
+
+{{IERC1820Implementer}}
+
+{{ERC1820Implementer}}

contracts/lifecycle/Pausable.sol

@@ -1,57 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../access/roles/PauserRole.sol";
-
-/**
- * @title Pausable
- * @dev Base contract which allows children to implement an emergency stop mechanism.
- */
-contract Pausable is PauserRole {
-    event Paused(address account);
-    event Unpaused(address account);
-
-    bool private _paused;
-
-    constructor () internal {
-        _paused = false;
-    }
-
-    /**
-     * @return true if the contract is paused, false otherwise.
-     */
-    function paused() public view returns (bool) {
-        return _paused;
-    }
-
-    /**
-     * @dev Modifier to make a function callable only when the contract is not paused.
-     */
-    modifier whenNotPaused() {
-        require(!_paused);
-        _;
-    }
-
-    /**
-     * @dev Modifier to make a function callable only when the contract is paused.
-     */
-    modifier whenPaused() {
-        require(_paused);
-        _;
-    }
-
-    /**
-     * @dev called by the owner to pause, triggers stopped state
-     */
-    function pause() public onlyPauser whenNotPaused {
-        _paused = true;
-        emit Paused(msg.sender);
-    }
-
-    /**
-     * @dev called by the owner to unpause, returns to normal state
-     */
-    function unpause() public onlyPauser whenPaused {
-        _paused = false;
-        emit Unpaused(msg.sender);
-    }
-}

contracts/math/Math.sol

@@ -1,8 +1,7 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 /**
- * @title Math
- * @dev Assorted math operations
+ * @dev Standard math utilities missing in the Solidity language.
  */
 library Math {
     /**
@@ -20,9 +19,8 @@ library Math {
     }
 
     /**
-     * @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.
+     * @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

contracts/math/README.adoc

@@ -0,0 +1,11 @@
+= Math
+
+These are math-related utilities.
+
+== Libraries
+
+{{SafeMath}}
+
+{{SignedSafeMath}}
+
+{{Math}}

contracts/math/SafeMath.sol

@@ -1,33 +1,116 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 /**
- * @title SafeMath
- * @dev Unsigned 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 Multiplies two unsigned integers, reverts on overflow.
+     * @dev Returns the addition of two unsigned integers, reverting on
+     * overflow.
+     *
+     * Counterpart to Solidity's `+` operator.
+     *
+     * Requirements:
+     * - Addition 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;
-        }
-
-        uint256 c = a * b;
-        require(c / a == b);
+    function add(uint256 a, uint256 b) internal pure returns (uint256) {
+        uint256 c = a + b;
+        require(c >= a, "SafeMath: addition overflow");
 
         return c;
     }
 
     /**
-     * @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
+     * @dev Returns the subtraction of two unsigned integers, reverting on
+     * overflow (when the result is negative).
+     *
+     * Counterpart to Solidity's `-` operator.
+     *
+     * Requirements:
+     * - Subtraction cannot overflow.
+     */
+    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
+        return sub(a, b, "SafeMath: subtraction overflow");
+    }
+
+    /**
+     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
+     * overflow (when the result is negative).
+     *
+     * Counterpart to Solidity's `-` operator.
+     *
+     * Requirements:
+     * - Subtraction cannot overflow.
+     */
+    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
+        require(b <= a, errorMessage);
+        uint256 c = a - b;
+
+        return c;
+    }
+
+    /**
+     * @dev Returns the multiplication of two unsigned integers, reverting on
+     * overflow.
+     *
+     * Counterpart to Solidity's `*` operator.
+     *
+     * Requirements:
+     * - Multiplication cannot overflow.
+     */
+    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
+        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
+        // benefit is lost if 'b' is also tested.
+        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
+        if (a == 0) {
+            return 0;
+        }
+
+        uint256 c = a * b;
+        require(c / a == b, "SafeMath: multiplication overflow");
+
+        return c;
+    }
+
+    /**
+     * @dev Returns the integer division of two unsigned integers. Reverts on
+     * division by zero. The result is rounded towards zero.
+     *
+     * Counterpart to Solidity's `/` operator. Note: this function uses a
+     * `revert` opcode (which leaves remaining gas untouched) while Solidity
+     * uses an invalid opcode to revert (consuming all remaining gas).
+     *
+     * Requirements:
+     * - The divisor cannot be zero.
      */
     function div(uint256 a, uint256 b) internal pure returns (uint256) {
+        return div(a, b, "SafeMath: division by zero");
+    }
+
+    /**
+     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
+     * division by zero. The result is rounded towards zero.
+     *
+     * Counterpart to Solidity's `/` operator. Note: this function uses a
+     * `revert` opcode (which leaves remaining gas untouched) while Solidity
+     * uses an invalid opcode to revert (consuming all remaining gas).
+     *
+     * Requirements:
+     * - The divisor cannot be zero.
+     */
+    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
         // Solidity only automatically asserts when dividing by 0
-        require(b > 0);
+        require(b > 0, errorMessage);
         uint256 c = a / b;
         // assert(a == b * c + a % b); // There is no case in which this doesn't hold
 
@@ -35,31 +118,33 @@ library SafeMath {
     }
 
     /**
-     * @dev Subtracts two unsigned integers, 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;
-    }
-
-    /**
-     * @dev Adds two unsigned integers, reverts on overflow.
-     */
-    function add(uint256 a, uint256 b) internal pure returns (uint256) {
-        uint256 c = a + b;
-        require(c >= a);
-
-        return c;
-    }
-
-    /**
-     * @dev Divides two unsigned integers and returns the remainder (unsigned integer modulo),
-     * reverts when dividing by zero.
+     * @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);
+        return mod(a, b, "SafeMath: modulo by zero");
+    }
+
+    /**
+     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
+     * Reverts with custom message when dividing by zero.
+     *
+     * Counterpart to Solidity's `%` operator. This function uses a `revert`
+     * opcode (which leaves remaining gas untouched) while Solidity uses an
+     * invalid opcode to revert (consuming all remaining gas).
+     *
+     * Requirements:
+     * - The divisor cannot be zero.
+     */
+    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
+        require(b != 0, errorMessage);
         return a % b;
     }
 }

contracts/math/SignedSafeMath.sol

@@ -1,11 +1,11 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 /**
  * @title SignedSafeMath
- * @dev Signed math operations with safety checks that revert on error
+ * @dev Signed math operations with safety checks that revert on error.
  */
 library SignedSafeMath {
-    int256 constant private INT256_MIN = -2**255;
+    int256 constant private _INT256_MIN = -2**255;
 
     /**
      * @dev Multiplies two signed integers, reverts on overflow.
@@ -13,15 +13,15 @@ library SignedSafeMath {
     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
+        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
         if (a == 0) {
             return 0;
         }
 
-        require(!(a == -1 && b == INT256_MIN)); // This is the only case of overflow not detected by the check below
+        require(!(a == -1 && b == _INT256_MIN), "SignedSafeMath: multiplication overflow");
 
         int256 c = a * b;
-        require(c / a == b);
+        require(c / a == b, "SignedSafeMath: multiplication overflow");
 
         return c;
     }
@@ -30,8 +30,8 @@ library SignedSafeMath {
      * @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); // Solidity only automatically asserts when dividing by 0
-        require(!(b == -1 && a == INT256_MIN)); // This is the only case of overflow
+        require(b != 0, "SignedSafeMath: division by zero");
+        require(!(b == -1 && a == _INT256_MIN), "SignedSafeMath: division overflow");
 
         int256 c = a / b;
 
@@ -43,7 +43,7 @@ library SignedSafeMath {
      */
     function sub(int256 a, int256 b) internal pure returns (int256) {
         int256 c = a - b;
-        require((b >= 0 && c <= a) || (b < 0 && c > a));
+        require((b >= 0 && c <= a) || (b < 0 && c > a), "SignedSafeMath: subtraction overflow");
 
         return c;
     }
@@ -53,7 +53,7 @@ library SignedSafeMath {
      */
     function add(int256 a, int256 b) internal pure returns (int256) {
         int256 c = a + b;
-        require((b >= 0 && c >= a) || (b < 0 && c < a));
+        require((b >= 0 && c >= a) || (b < 0 && c < a), "SignedSafeMath: addition overflow");
 
         return c;
     }

contracts/mocks/AccessControlMock.sol

@@ -0,0 +1,13 @@
+pragma solidity ^0.6.0;
+
+import "../access/AccessControl.sol";
+
+contract AccessControlMock is AccessControl {
+    constructor() public {
+        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
+    }
+
+    function setRoleAdmin(bytes32 roleId, bytes32 adminRoleId) public {
+        _setRoleAdmin(roleId, adminRoleId);
+    }
+}

contracts/mocks/Acknowledger.sol

@@ -1,19 +0,0 @@
-pragma solidity ^0.5.2;
-
-contract Acknowledger {
-    event AcknowledgeFoo(uint256 a);
-    event AcknowledgeBarSingle(uint256 a);
-    event AcknowledgeBarDouble(uint256 a, uint256 b);
-
-    function foo(uint256 a) public {
-        emit AcknowledgeFoo(a);
-    }
-
-    function bar(uint256 a) public {
-        emit AcknowledgeBarSingle(a);
-    }
-
-    function bar(uint256 a, uint256 b) public {
-        emit AcknowledgeBarDouble(a, b);
-    }
-}

contracts/mocks/AddressImpl.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 import "../utils/Address.sol";
 
@@ -6,4 +6,11 @@ contract AddressImpl {
     function isContract(address account) external view returns (bool) {
         return Address.isContract(account);
     }
+
+    function sendValue(address payable receiver, uint256 amount) external {
+        Address.sendValue(receiver, amount);
+    }
+
+    // sendValue's tests require the contract to hold Ether
+    receive () external payable { }
 }

contracts/mocks/AllowanceCrowdsaleImpl.sol

@@ -1,14 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../token/ERC20/IERC20.sol";
-import "../crowdsale/emission/AllowanceCrowdsale.sol";
-
-contract AllowanceCrowdsaleImpl is AllowanceCrowdsale {
-    constructor (uint256 rate, address payable wallet, IERC20 token, address tokenWallet)
-        public
-        Crowdsale(rate, wallet, token)
-        AllowanceCrowdsale(tokenWallet)
-    {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}

contracts/mocks/ArraysImpl.sol

@@ -1,17 +1,17 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 import "../utils/Arrays.sol";
 
 contract ArraysImpl {
     using Arrays for uint256[];
 
-    uint256[] private array;
+    uint256[] private _array;
 
-    constructor (uint256[] memory _array) public {
-        array = _array;
+    constructor (uint256[] memory array) 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

@@ -1,14 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../token/ERC20/IERC20.sol";
-import "../crowdsale/validation/CappedCrowdsale.sol";
-
-contract CappedCrowdsaleImpl is CappedCrowdsale {
-    constructor (uint256 rate, address payable wallet, IERC20 token, uint256 cap)
-        public
-        Crowdsale(rate, wallet, token)
-        CappedCrowdsale(cap)
-    {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}

contracts/mocks/CapperRoleMock.sol

@@ -1,18 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../access/roles/CapperRole.sol";
-
-contract CapperRoleMock is CapperRole {
-    function removeCapper(address account) public {
-        _removeCapper(account);
-    }
-
-    function onlyCapperMock() public view onlyCapper {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    // Causes a compilation error if super._removeCapper is not internal
-    function _removeCapper(address account) internal {
-        super._removeCapper(account);
-    }
-}

contracts/mocks/ConditionalEscrowMock.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 import "../payment/escrow/ConditionalEscrow.sol";
 
@@ -10,7 +10,7 @@ contract ConditionalEscrowMock is ConditionalEscrow {
         _allowed[payee] = allowed;
     }
 
-    function withdrawalAllowed(address payee) public view returns (bool) {
+    function withdrawalAllowed(address payee) public view override returns (bool) {
         return _allowed[payee];
     }
 }

contracts/mocks/ContextMock.sol

@@ -0,0 +1,27 @@
+pragma solidity ^0.6.0;
+
+import "../GSN/Context.sol";
+
+contract ContextMock is Context {
+    event Sender(address sender);
+
+    function msgSender() public {
+        emit Sender(_msgSender());
+    }
+
+    event Data(bytes data, uint256 integerValue, string stringValue);
+
+    function msgData(uint256 integerValue, string memory stringValue) public {
+        emit Data(_msgData(), integerValue, stringValue);
+    }
+}
+
+contract ContextMockCaller {
+    function callSender(ContextMock context) public {
+        context.msgSender();
+    }
+
+    function callData(ContextMock context, uint256 integerValue, string memory stringValue) public {
+        context.msgData(integerValue, stringValue);
+    }
+}

contracts/mocks/CountersImpl.sol

@@ -1,6 +1,6 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
-import "../drafts/Counters.sol";
+import "../utils/Counters.sol";
 
 contract CountersImpl {
     using Counters for Counters.Counter;

contracts/mocks/Create2Impl.sol

@@ -0,0 +1,25 @@
+pragma solidity ^0.6.0;
+
+import "../utils/Create2.sol";
+import "../introspection/ERC1820Implementer.sol";
+
+contract Create2Impl {
+    function deploy(uint256 value, bytes32 salt, bytes memory code) public {
+        Create2.deploy(value, salt, code);
+    }
+
+    function deployERC1820Implementer(uint256 value, bytes32 salt) public {
+        // solhint-disable-next-line indent
+        Create2.deploy(value, salt, type(ERC1820Implementer).creationCode);
+    }
+
+    function computeAddress(bytes32 salt, bytes32 codeHash) public view returns (address) {
+        return Create2.computeAddress(salt, codeHash);
+    }
+
+    function computeAddressWithDeployer(bytes32 salt, bytes32 codeHash, address deployer) public pure returns (address) {
+        return Create2.computeAddress(salt, codeHash, deployer);
+    }
+
+    receive() payable external {}
+}

contracts/mocks/CrowdsaleMock.sol

@@ -1,9 +0,0 @@
-pragma solidity ^0.5.2;
-
-import "../crowdsale/Crowdsale.sol";
-
-contract CrowdsaleMock is Crowdsale {
-    constructor (uint256 rate, address payable wallet, IERC20 token) public Crowdsale(rate, wallet, token) {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-}

contracts/mocks/ECDSAMock.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 import "../cryptography/ECDSA.sol";
 

contracts/mocks/ERC165/ERC165InterfacesSupported.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 import "../../introspection/IERC165.sol";
 
@@ -13,37 +13,36 @@ import "../../introspection/IERC165.sol";
  * solidity-coverage ignores the /mocks folder, so we duplicate its implementation here to avoid instrumenting it
  */
 contract SupportsInterfaceWithLookupMock is IERC165 {
-    bytes4 public constant INTERFACE_ID_ERC165 = 0x01ffc9a7;
     /*
-     * 0x01ffc9a7 ===
-     *     bytes4(keccak256('supportsInterface(bytes4)'))
+     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
      */
+    bytes4 public constant INTERFACE_ID_ERC165 = 0x01ffc9a7;
 
     /**
-     * @dev a mapping of interface id to whether or not it's supported
+     * @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
+     * implement ERC165 itself.
      */
     constructor () public {
         _registerInterface(INTERFACE_ID_ERC165);
     }
 
     /**
-     * @dev implement supportsInterface(bytes4) using a lookup table
+     * @dev Implement supportsInterface(bytes4) using a lookup table.
      */
-    function supportsInterface(bytes4 interfaceId) external view returns (bool) {
+    function supportsInterface(bytes4 interfaceId) public view override returns (bool) {
         return _supportedInterfaces[interfaceId];
     }
 
     /**
-     * @dev private method for registering an interface
+     * @dev Private method for registering an interface.
      */
     function _registerInterface(bytes4 interfaceId) internal {
-        require(interfaceId != 0xffffffff);
+        require(interfaceId != 0xffffffff, "ERC165InterfacesSupported: invalid interface id");
         _supportedInterfaces[interfaceId] = true;
     }
 }

contracts/mocks/ERC165/ERC165NotSupported.sol

@@ -1,5 +1,3 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
-contract ERC165NotSupported {
-    // solhint-disable-previous-line no-empty-blocks
-}
+contract ERC165NotSupported { }

contracts/mocks/ERC165CheckerMock.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 import "../introspection/ERC165Checker.sol";
 
@@ -6,14 +6,14 @@ contract ERC165CheckerMock {
     using ERC165Checker for address;
 
     function supportsERC165(address account) public view returns (bool) {
-        return account._supportsERC165();
+        return account.supportsERC165();
     }
 
     function supportsInterface(address account, bytes4 interfaceId) public view returns (bool) {
-        return account._supportsInterface(interfaceId);
+        return account.supportsInterface(interfaceId);
     }
 
     function supportsAllInterfaces(address account, bytes4[] memory interfaceIds) public view returns (bool) {
-        return account._supportsAllInterfaces(interfaceIds);
+        return account.supportsAllInterfaces(interfaceIds);
     }
 }

contracts/mocks/ERC165Mock.sol

@@ -1,4 +1,4 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 import "../introspection/ERC165.sol";
 

contracts/mocks/ERC1820ImplementerMock.sol

@@ -0,0 +1,9 @@
+pragma solidity ^0.6.0;
+
+import "../introspection/ERC1820Implementer.sol";
+
+contract ERC1820ImplementerMock is ERC1820Implementer {
+    function registerInterfaceForAddress(bytes32 interfaceHash, address account) public {
+        _registerInterfaceForAddress(interfaceHash, account);
+    }
+}

contracts/mocks/ERC20BurnableMock.sol

@@ -1,9 +1,14 @@
-pragma solidity ^0.5.2;
+pragma solidity ^0.6.0;
 
 import "../token/ERC20/ERC20Burnable.sol";
 
 contract ERC20BurnableMock is ERC20Burnable {
-    constructor (address initialAccount, uint256 initialBalance) public {
+    constructor (
+        string memory name,
+        string memory symbol,
+        address initialAccount,
+        uint256 initialBalance
+    ) public ERC20(name, symbol) {
         _mint(initialAccount, initialBalance);
     }
 }

contracts/mocks/ERC20CappedMock.sol

@@ -0,0 +1,13 @@
+pragma solidity ^0.6.0;
+
+import "../token/ERC20/ERC20Capped.sol";
+
+contract ERC20CappedMock is ERC20Capped {
+    constructor (string memory name, string memory symbol, uint256 cap)
+        public ERC20(name, symbol) ERC20Capped(cap)
+    { }
+
+    function mint(address to, uint256 tokenId) public {
+        _mint(to, tokenId);
+    }
+}

contracts/mocks/ERC20DecimalsMock.sol

@@ -0,0 +1,9 @@
+pragma solidity ^0.6.0;
+
+import "../token/ERC20/ERC20.sol";
+
+contract ERC20DecimalsMock is ERC20 {
+    constructor (string memory name, string memory symbol, uint8 decimals) public ERC20(name, symbol) {
+        _setupDecimals(decimals);
+    }
+}

contracts/mocks/ERC20DetailedMock.sol

@@ -1,13 +0,0 @@
-pragma solidity ^0.5.2;
-
-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

@@ -1,14 +0,0 @@
-pragma solidity ^0.5.2;
-
-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);
-    }
-}