Merge branch 'master' into next-v5.0

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: ernestognw <ernestognw@gmail.com>

.changeset/angry-ties-switch.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`TimelockController`: Changed the role architecture to use `DEFAULT_ADMIN_ROLE` as the admin for all roles, instead of the bespoke `TIMELOCK_ADMIN_ROLE` that was used previously. This aligns with the general recommendation for `AccessControl` and makes the addition of new roles easier. Accordingly, the `admin` parameter and timelock will now be granted `DEFAULT_ADMIN_ROLE` instead of `TIMELOCK_ADMIN_ROLE`. ([#3799](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3799))

.changeset/beige-ducks-flow.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Remove deprecated GovernorProposalThreshold module.

.changeset/bright-tomatoes-sing.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`ERC20`, `ERC1155`: Deleted `_beforeTokenTransfer` and `_afterTokenTransfer` hooks, added a new internal `_update` function for customizations, and refactored all extensions using those hooks to use `_update` instead. ([#3838](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3838), [#3876](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3876))

.changeset/chilled-spiders-attack.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`ERC1155Supply`: add a `totalSupply()` function that returns the total amount of token circulating, this change will restrict the total tokens minted across all ids to 2\*\*256-1 .

.changeset/clever-pumas-beg.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`Ownable`: Add an `initialOwner` parameter to the constructor, making the ownership initialization explicit.

.changeset/config.json

@@ -0,0 +1,12 @@
+{
+  "$schema": "https://unpkg.com/@changesets/config@2.3.0/schema.json",
+  "changelog": [
+    "@changesets/changelog-github",
+    {
+      "repo": "OpenZeppelin/openzeppelin-contracts"
+    }
+  ],
+  "commit": false,
+  "access": "public",
+  "baseBranch": "master"
+}

.changeset/dirty-mangos-sort.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Removed presets in favor of [OpenZeppelin Contracts Wizard](https://wizard.openzeppelin.com/).

.changeset/fluffy-gifts-build.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Remove ERC1820Implementer.

.changeset/fresh-birds-kiss.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`Checkpoints`: library moved from `utils` to `utils/structs`

.changeset/friendly-suits-camp.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Remove Checkpoints.History.

.changeset/hungry-impalas-perform.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`ERC165Storage`: Removed this contract in favor of inheritance based approach. ([#3880](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3880))

.changeset/mean-walls-watch.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`Nonces`: Added a new contract to keep track of user nonces. Used for signatures in `ERC20Permit`, `ERC20Votes`, and `ERC721Votes`. ([#3816](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3816))

.changeset/rotten-insects-wash.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`ProxyAdmin`: Removed `getProxyAdmin` and `getProxyImplementation` getters. ([#3820](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3820))

.changeset/selfish-queens-rest.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Remove PullPayment and Escrow contracts (Escrow, ConditionalEscrow, RefundEscrow).

.changeset/short-eels-enjoy.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Bump minimum compiler version required to 0.8.19

.changeset/silly-bees-beam.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`ERC20Votes`: Changed internal vote accounting to reusable `Votes` module previously used by `ERC721Votes`. Removed implicit `ERC20Permit` inheritance. [#3816](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3816)

.changeset/slimy-penguins-attack.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`TransparentUpgradeableProxy`: Removed `admin` and `implementation` getters, which were only callable by the proxy owner and thus not very useful. ([#3820](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3820))

.changeset/smooth-books-wink.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`ERC1155`: Remove check for address zero in `balanceOf`.

.changeset/spicy-ducks-cough.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Remove the Timers library.

.changeset/spotty-hotels-type.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`ERC721Consecutive`: Add a `_firstConsecutiveId` internal function that can be overridden to change the id of the first token minted through `_mintConsecutive`.

.changeset/swift-berries-sort.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Remove ERC777 implementation.

.changeset/tame-geckos-search.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Remove SafeMath and SignedSafeMath libraries.

.changeset/three-weeks-double.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+Remove CrossChain contracts, including AccessControlCrossChain and all the vendored bridge interfaces.

.changeset/unlucky-snakes-drive.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`Address`: Removed `isContract` because of its ambiguous nature and potential for misuse.

.changeset/wild-windows-trade.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`SafeERC20`: Refactor `safeDecreaseAllowance` and `safeIncreaseAllowance` to support USDT-like tokens.

.circleci/config.yml

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

.codecov.yml

@@ -1,3 +1,12 @@
 comment: off
+github_checks:
+  annotations: false
 coverage:
-  range: "100...100"
+  status:
+    patch:
+      default:
+        target: 95%
+        only_pulls: true
+    project:
+      default:
+        threshold: 1%

.editorconfig

@@ -17,5 +17,5 @@ indent_size = 4
 [*.js]
 indent_size = 2
 
-[*.adoc]
+[*.{adoc,md}]
 max_line_length = 0

.eslintrc

@@ -1,62 +1,20 @@
 {
+  "root": true,
   "extends" : [
-    "standard",
-    "plugin:promise/recommended",
-  ],
-  "plugins": [
-    "mocha-no-only",
-    "promise",
+    "eslint:recommended",
+    "prettier",
   ],
   "env": {
-    "browser" : true,
-    "node"    : true,
-    "mocha"   : true,
-    "jest"    : true,
+    "es2022": true,
+    "browser": true,
+    "node": true,
+    "mocha": true,
   },
   "globals" : {
-    "artifacts": false,
-    "contract": false,
-    "assert": false,
-    "web3": false,
-  },
-  "rules": {
-
-    // Strict mode
-    "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}],
-    "dot-notation": ["error", {"allowKeywords": true, "allowPattern": ""}],
-    "eol-last": ["error", "always"],
-    "eqeqeq": ["error", "smart"],
-    "generator-star-spacing": ["error", "before"],
-    "indent": ["error", 2],
-    "linebreak-style": ["error", "unix"],
-    "max-len": ["error", 120, 2],
-    "no-debugger": "off",
-    "no-dupe-args": "error",
-    "no-dupe-keys": "error",
-    "no-mixed-spaces-and-tabs": ["error", "smart-tabs"],
-    "no-redeclare": ["error", {"builtinGlobals": true}],
-    "no-trailing-spaces": ["error", { "skipBlankLines": false }],
-    "no-undef": "error",
-    "no-use-before-define": "off",
-    "no-var": "error",
-    "object-curly-spacing": ["error", "always"],
-    "prefer-const": "error",
-    "quotes": ["error", "single"],
-    "semi": ["error", "always"],
-    "space-before-function-paren": ["error", "always"],
-
-    "mocha-no-only/mocha-no-only": ["error"],
-
-    "promise/always-return": "off",
-    "promise/avoid-new": "off",
-  },
-  "parserOptions": {
-    "ecmaVersion": 2018
+    "artifacts": "readonly",
+    "contract": "readonly",
+    "web3": "readonly",
+    "extendEnvironment": "readonly",
+    "expect": "readonly",
   }
 }

.gitattributes

@@ -1 +0,0 @@
-*.sol linguist-language=Solidity

.github/ISSUE_TEMPLATE/config.yml

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

.github/ISSUE_TEMPLATE/feature_request.md

@@ -10,5 +10,5 @@ about: Suggest an idea for OpenZeppelin Contracts
 **📝 Details**
 <!-- Please describe your feature request in detail. -->
 
-<!-- Make sure that you have reviewed the OpenZeppelin Contributor Guidelines. -->
+<!-- Make sure that you have reviewed the OpenZeppelin Contracts Contributor Guidelines. -->
 <!-- https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/CONTRIBUTING.md -->

.github/PULL_REQUEST_TEMPLATE.md

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

.github/actions/gas-compare/action.yml

@@ -0,0 +1,49 @@
+name: Compare gas costs
+inputs:
+  token:
+    description: github token
+    required: true
+  report:
+    description: report to read from
+    required: false
+    default: gasReporterOutput.json
+  out_report:
+    description: report to read
+    required: false
+    default: ${{ github.ref_name }}.gasreport.json
+  ref_report:
+    description: report to read from
+    required: false
+    default: ${{ github.base_ref }}.gasreport.json
+
+runs:
+  using: composite
+  steps:
+    - name: Download reference report
+      if: github.event_name == 'pull_request'
+      run: |
+        RUN_ID=`gh run list --repo ${{ github.repository }} --branch ${{ github.base_ref }} --workflow ${{ github.workflow }} --limit 100 --json 'conclusion,databaseId,event' --jq 'map(select(.conclusion=="success" and .event!="pull_request"))[0].databaseId'`
+        gh run download ${RUN_ID} --repo ${{ github.repository }} -n gasreport
+      env:
+        GITHUB_TOKEN: ${{ inputs.token }}
+      shell: bash
+      continue-on-error: true
+      id: reference
+    - name: Compare reports
+      if: steps.reference.outcome == 'success' && github.event_name == 'pull_request'
+      run: |
+        node scripts/checks/compareGasReports.js ${{ inputs.report }} ${{ inputs.ref_report }} >> $GITHUB_STEP_SUMMARY
+      env:
+        STYLE: markdown
+      shell: bash
+    - name: Rename report for upload
+      if: github.event_name != 'pull_request'
+      run: |
+        mv ${{ inputs.report }} ${{ inputs.out_report }}
+      shell: bash
+    - name: Save report
+      if: github.event_name != 'pull_request'
+      uses: actions/upload-artifact@v3
+      with:
+        name: gasreport
+        path: ${{ inputs.out_report }}

.github/actions/setup/action.yml

@@ -0,0 +1,19 @@
+name: Setup
+
+runs:
+  using: composite
+  steps:
+    - uses: actions/setup-node@v3
+      with:
+        node-version: 14.x
+    - uses: actions/cache@v3
+      id: cache
+      with:
+        path: '**/node_modules'
+        key: npm-v3-${{ hashFiles('**/package-lock.json') }}
+    - name: Install dependencies
+      run: npm ci
+      shell: bash
+      if: steps.cache.outputs.cache-hit != 'true'
+      env:
+        SKIP_COMPILE: true

.github/actions/storage-layout/action.yml

@@ -0,0 +1,55 @@
+name: Compare storage layouts
+inputs:
+  token:
+    description: github token
+    required: true
+  buildinfo:
+    description: compilation artifacts
+    required: false
+    default: artifacts/build-info/*.json
+  layout:
+    description: extracted storage layout
+    required: false
+    default: HEAD.layout.json
+  out_layout:
+    description: storage layout to upload
+    required: false
+    default: ${{ github.ref_name }}.layout.json
+  ref_layout:
+    description: storage layout for the reference branch
+    required: false
+    default: ${{ github.base_ref }}.layout.json
+
+runs:
+  using: composite
+  steps:
+    - name: Extract layout
+      run: |
+        node scripts/checks/extract-layout.js ${{ inputs.buildinfo }} > ${{ inputs.layout }}
+      shell: bash
+    - name: Download reference
+      if: github.event_name == 'pull_request'
+      run: |
+        RUN_ID=`gh run list --repo ${{ github.repository }} --branch ${{ github.base_ref }} --workflow ${{ github.workflow }} --limit 100 --json 'conclusion,databaseId,event' --jq 'map(select(.conclusion=="success" and .event!="pull_request"))[0].databaseId'`
+        gh run download ${RUN_ID} --repo ${{ github.repository }} -n layout
+      env:
+        GITHUB_TOKEN: ${{ inputs.token }}
+      shell: bash
+      continue-on-error: true
+      id: reference
+    - name: Compare layouts
+      if: steps.reference.outcome == 'success' && github.event_name == 'pull_request'
+      run: |
+        node scripts/checks/compare-layout.js --head ${{ inputs.layout }} --ref ${{ inputs.ref_layout }}
+      shell: bash
+    - name: Rename artifacts for upload
+      if: github.event_name != 'pull_request'
+      run: |
+        mv ${{ inputs.layout }} ${{ inputs.out_layout }}
+      shell: bash
+    - name: Save artifacts
+      if: github.event_name != 'pull_request'
+      uses: actions/upload-artifact@v3
+      with:
+        name: layout
+        path: ${{ inputs.out_layout }}

.github/stale.yml

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

.github/workflows/actionlint.yml

@@ -0,0 +1,18 @@
+name: lint workflows
+
+on:
+  pull_request:
+    paths:
+      - '.github/**/*.ya?ml'
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Add problem matchers
+        run: |
+          # https://github.com/rhysd/actionlint/blob/3a2f2c7/docs/usage.md#problem-matchers
+          curl -LO https://raw.githubusercontent.com/rhysd/actionlint/main/.github/actionlint-matcher.json
+          echo "::add-matcher::actionlint-matcher.json"
+      - uses: docker://rhysd/actionlint:latest

.github/workflows/changeset.yml

@@ -0,0 +1,28 @@
+name: changeset
+
+on:
+  pull_request:
+    branches:
+      - master
+    types:
+      - opened
+      - synchronize
+      - labeled
+      - unlabeled
+
+concurrency:
+  group: changeset-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    if: ${{ !contains(github.event.pull_request.labels.*.name, 'ignore-changeset') }}
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0 # Include history so Changesets finds merge-base
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - name: Check changeset
+        run: npx changeset status --since=origin/${{ github.base_ref }}

.github/workflows/checks.yml

@@ -0,0 +1,115 @@
+name: checks
+
+on:
+  push:
+    branches:
+      - master
+      - next-v*
+      - release-v*
+  pull_request: {}
+  workflow_dispatch: {}
+
+concurrency:
+  group: checks-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - run: npm run lint
+
+  tests:
+    runs-on: ubuntu-latest
+    env:
+      FORCE_COLOR: 1
+      NODE_OPTIONS: --max_old_space_size=4096
+      GAS: true
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - name: Run tests and generate gas report
+        run: npm run test
+      - name: Check linearisation of the inheritance graph
+        run: npm run test:inheritance
+      - name: Check proceduraly generated contracts are up-to-date
+        run: npm run test:generation
+      - name: Compare gas costs
+        uses: ./.github/actions/gas-compare
+        with:
+          token: ${{ github.token }}
+
+  tests-upgradeable:
+    runs-on: ubuntu-latest
+    env:
+      FORCE_COLOR: 1
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0 # Include history so patch conflicts are resolved automatically
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - name: Transpile to upgradeable
+        run: bash scripts/upgradeable/transpile.sh
+      - name: Run tests
+        run: npm run test
+        env:
+          NODE_OPTIONS: --max_old_space_size=4096
+      - name: Check linearisation of the inheritance graph
+        run: npm run test:inheritance
+      - name: Check storage layout
+        uses: ./.github/actions/storage-layout
+        with:
+          token: ${{ github.token }}
+
+  tests-foundry:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          submodules: recursive
+      - name: Install Foundry
+        uses: foundry-rs/foundry-toolchain@v1
+        with:
+          version: nightly
+      - name: Run tests
+        run: forge test -vv
+
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - run: npm run coverage
+        env:
+          NODE_OPTIONS: --max_old_space_size=4096
+      - uses: codecov/codecov-action@v3
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+
+  slither:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - run: rm foundry.toml
+      - uses: crytic/slither-action@v0.3.0
+        with:
+          node-version: 18.15
+
+  codespell:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Run CodeSpell
+        uses: codespell-project/actions-codespell@v2.0
+        with:
+          check_hidden: true
+          check_filenames: true
+          skip: package-lock.json,*.pdf

.github/workflows/docs.yml

@@ -0,0 +1,19 @@
+name: Build Docs
+
+on:
+  push:
+    branches: [release-v*]
+
+permissions:
+  contents: write
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - run: bash scripts/git-user-config.sh
+      - run: node scripts/update-docs-branch.js
+      - run: git push --all origin 

.github/workflows/formal-verification.yml

@@ -0,0 +1,68 @@
+name: formal verification
+
+on:
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - labeled
+  workflow_dispatch: {}
+
+env:
+  PIP_VERSION: '3.10'
+  JAVA_VERSION: '11'
+  SOLC_VERSION: '0.8.19'
+
+concurrency: ${{ github.workflow }}-${{ github.ref }}
+
+jobs:
+  apply-diff:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Apply patches
+        run: make -C certora apply
+
+  verify:
+    runs-on: ubuntu-latest
+    if: github.event_name != 'pull_request' || contains(github.event.pull_request.labels.*.name, 'formal-verification')
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - name: identify specs that need to be run
+        id: arguments
+        run: |
+          if [[ ${{ github.event_name }} = 'pull_request' ]];
+          then
+            RESULT=$(git diff ${{ github.event.pull_request.head.sha }}..${{ github.event.pull_request.base.sha }} --name-only certora/specs/*.spec | while IFS= read -r file; do [[ -f $file ]] && basename "${file%.spec}"; done | tr "\n" " ")
+          else
+            RESULT='--all'
+          fi
+          echo "result=$RESULT" >> "$GITHUB_OUTPUT"
+      - name: Install python
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ env.PIP_VERSION }}
+          cache: 'pip'
+      - name: Install python packages
+        run: pip install -r requirements.txt
+      - name: Install java
+        uses: actions/setup-java@v3
+        with:
+          distribution: temurin
+          java-version: ${{ env.JAVA_VERSION }}
+      - name: Install solc
+        run: |
+          wget https://github.com/ethereum/solidity/releases/download/v${{ env.SOLC_VERSION }}/solc-static-linux
+          sudo mv solc-static-linux /usr/local/bin/solc
+          chmod +x /usr/local/bin/solc
+      - name: Verify specification
+        run: |
+          make -C certora apply
+          node certora/run.js ${{ steps.arguments.outputs.result }} >> "$GITHUB_STEP_SUMMARY"
+        env:
+          CERTORAKEY: ${{ secrets.CERTORAKEY }}

.github/workflows/release-cycle.yml

@@ -0,0 +1,214 @@
+#  D: Manual Dispatch
+#  M: Merge release PR
+#  C: Commit
+#  ┌───────────┐     ┌─────────────┐     ┌────────────────┐
+#  │Development├──D──►RC-Unreleased│  ┌──►Final-Unreleased│
+#  └───────────┘     └─┬─────────▲─┘  │  └─┬────────────▲─┘
+#                      │         │    │    │            │
+#                      M         C    D    M            C
+#                      │         │    │    │            │
+#                     ┌▼─────────┴┐   │   ┌▼────────────┴┐
+#                     │RC-Released├───┘   │Final-Released│
+#                     └───────────┘       └──────────────┘
+name: Release Cycle
+
+on:
+  push:
+    branches:
+      - release-v*
+  workflow_dispatch: {}
+
+concurrency: ${{ github.workflow }}-${{ github.ref }}
+
+jobs:
+  state:
+    name: Check state
+    permissions:
+      pull-requests: read
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - id: state
+        name: Get state
+        uses: actions/github-script@v6
+        env:
+          TRIGGERING_ACTOR: ${{ github.triggering_actor }}
+        with:
+          result-encoding: string
+          script: await require('./scripts/release/workflow/state.js')({ github, context, core })
+    outputs:
+      # Job Flags
+      start: ${{ steps.state.outputs.start }}
+      changesets: ${{ steps.state.outputs.changesets }}
+      promote: ${{ steps.state.outputs.promote }}
+      publish: ${{ steps.state.outputs.publish }}
+      merge: ${{ steps.state.outputs.merge }}
+
+      # Global variables
+      is_prerelease: ${{ steps.state.outputs.is_prerelease }}
+
+  start:
+    needs: state
+    name: Start new release candidate
+    permissions:
+      contents: write
+      actions: write
+    if: needs.state.outputs.start == 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - run: bash scripts/git-user-config.sh
+      - id: start
+        name: Create branch with release candidate
+        run: bash scripts/release/workflow/start.sh
+      - name: Re-run workflow
+        uses: actions/github-script@v6
+        env:
+          REF: ${{ steps.start.outputs.branch }}
+        with:
+          script: await require('./scripts/release/workflow/rerun.js')({ github, context })
+
+  promote:
+    needs: state
+    name: Promote to final release
+    permissions:
+      contents: write
+      actions: write
+    if: needs.state.outputs.promote == 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - run: bash scripts/git-user-config.sh
+      - name: Exit prerelease state
+        if: needs.state.outputs.is_prerelease == 'true'
+        run: bash scripts/release/workflow/exit-prerelease.sh
+      - name: Re-run workflow
+        uses: actions/github-script@v6
+        with:
+          script: await require('./scripts/release/workflow/rerun.js')({ github, context })
+
+  changesets:
+    needs: state
+    name: Update PR to release
+    permissions:
+      contents: write
+      pull-requests: write
+    if: needs.state.outputs.changesets == 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0 # To get all tags
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - name: Set release title
+        uses: actions/github-script@v6
+        with:
+          result-encoding: string
+          script: await require('./scripts/release/workflow/set-changesets-pr-title.js')({ core })
+      - name: Create PR
+        uses: changesets/action@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PRERELEASE: ${{ needs.state.outputs.is_prerelease }}
+        with:
+          version: npm run version
+          title: ${{ env.TITLE }}
+          commit: ${{ env.TITLE }}
+          body: | # Wait for support on this https://github.com/changesets/action/pull/250
+            This is an automated PR for releasing ${{ github.repository }}
+            Check [CHANGELOG.md](${{ github.repository }}/CHANGELOG.md)
+
+  publish:
+    needs: state
+    name: Publish to npm
+    environment: npm
+    permissions:
+      contents: write
+    if: needs.state.outputs.publish == 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - id: pack
+        name: Pack
+        run: bash scripts/release/workflow/pack.sh
+        env:
+          PRERELEASE: ${{ needs.state.outputs.is_prerelease }}
+      - name: Upload tarball artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: ${{ github.ref_name }}
+          path: ${{ steps.pack.outputs.tarball }}
+      - name: Tag
+        run: npx changeset tag
+      - name: Publish
+        run: bash scripts/release/workflow/publish.sh
+        env:
+          NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
+          TARBALL: ${{ steps.pack.outputs.tarball }}
+          TAG: ${{ steps.pack.outputs.tag }}
+      - name: Push tags
+        run: git push --tags
+      - name: Create Github Release
+        uses: actions/github-script@v6
+        env:
+          PRERELEASE: ${{ needs.state.outputs.is_prerelease }}
+        with:
+          script: await require('./scripts/release/workflow/github-release.js')({ github, context })
+    outputs:
+      tarball_name: ${{ steps.pack.outputs.tarball_name }}
+
+  integrity_check:
+    needs: publish
+    name: Tarball Integrity Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Download tarball artifact
+        id: artifact
+        # Replace with actions/upload-artifact@v3 when
+        # https://github.com/actions/download-artifact/pull/194 gets released
+        uses: actions/download-artifact@e9ef242655d12993efdcda9058dee2db83a2cb9b
+        with:
+          name: ${{ github.ref_name }}
+      - name: Check integrity
+        run: bash scripts/release/workflow/integrity-check.sh
+        env:
+          TARBALL: ${{ steps.artifact.outputs.download-path }}/${{ needs.publish.outputs.tarball_name }}
+
+  merge:
+    needs: state
+    name: Create PR back to master
+    permissions:
+      contents: write
+      pull-requests: write
+    if: needs.state.outputs.merge == 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0 # All branches
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - run: bash scripts/git-user-config.sh
+      - name: Create branch to merge
+        run: bash scripts/release/workflow/prepare-release-merge.sh
+      - name: Create PR back to master
+        uses: actions/github-script@v6
+        with:
+          script: |
+            await github.rest.pulls.create({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              head: 'merge/${{ github.ref_name }}',
+              base: 'master',
+              title: '${{ format('Merge {0} branch', github.ref_name) }}'
+            });

.github/workflows/upgradeable.yml

@@ -0,0 +1,30 @@
+name: transpile upgradeable
+
+on:
+  push:
+    branches:
+      - master
+      - release-v*
+
+jobs:
+  transpile:
+    environment: push-upgradeable
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          repository: OpenZeppelin/openzeppelin-contracts-upgradeable
+          fetch-depth: 0
+          token: ${{ secrets.GH_TOKEN_UPGRADEABLE }}
+      - name: Fetch current non-upgradeable branch
+        run: |
+          git fetch "https://github.com/${{ github.repository }}.git" "$REF"
+          git checkout FETCH_HEAD
+        env:
+          REF: ${{ github.ref }}
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - run: bash scripts/git-user-config.sh
+      - name: Transpile to upgradeable
+        run: bash scripts/upgradeable/transpile-onto.sh ${{ github.ref_name }} origin/${{ github.ref_name }}
+      - run: git push origin ${{ github.ref_name }}

.gitignore

@@ -50,3 +50,22 @@ contracts/README.md
 
 # temporary artifact from solidity-coverage
 allFiredEvents
+.coverage_artifacts
+.coverage_cache
+.coverage_contracts
+
+# hardat-exposed
+contracts-exposed
+
+# Hardhat
+/cache
+/artifacts
+
+# Foundry
+/out
+
+# Certora
+.certora*
+.last_confs
+certora_*
+.zip-output-url.txt

.gitmodules

@@ -0,0 +1,7 @@
+[submodule "lib/forge-std"]
+	branch = v1
+	path = lib/forge-std
+	url = https://github.com/foundry-rs/forge-std
+[submodule "lib/erc4626-tests"]
+	path = lib/erc4626-tests
+	url = https://github.com/a16z/erc4626-tests.git

.mocharc.js

@@ -1,3 +1,4 @@
 module.exports = {
+  require: 'hardhat/register',
   timeout: 4000,
 };

.prettierrc

@@ -0,0 +1,14 @@
+{
+  "printWidth": 120,
+  "singleQuote": true,
+  "trailingComma": "all",
+  "arrowParens": "avoid",
+  "overrides": [
+    {
+      "files": "*.sol",
+      "options": {
+        "singleQuote": false
+      }
+    }
+  ]
+}

.solcover.js

@@ -1,8 +1,13 @@
 module.exports = {
-    norpc: true,
-    testCommand: 'npm test',
-    compileCommand: 'npm run compile',
-    skipFiles: [
-        'mocks',
-    ]
-}
+  norpc: true,
+  testCommand: 'npm test',
+  compileCommand: 'npm run compile',
+  skipFiles: ['mocks'],
+  providerOptions: {
+    default_balance_ether: '10000000000000000000000000',
+  },
+  mocha: {
+    fgrep: '[skip-on-coverage]',
+    invert: true,
+  },
+};

.solhint.json

@@ -1,11 +1,14 @@
 {
-  "extends": "solhint:recommended",
   "rules": {
-    "func-order": "off",
-    "mark-callable-contracts": "off",
-    "no-empty-blocks": "off",
-    "compiler-version": ["error", "^0.6.0"],
+    "no-unused-vars": "error",
+    "const-name-snakecase": "error",
+    "contract-name-camelcase": "error",
+    "event-name-camelcase": "error",
+    "func-name-mixedcase": "error",
+    "func-param-name-mixedcase": "error",
+    "modifier-name-mixedcase": "error",
     "private-vars-leading-underscore": "error",
-    "reason-string": "off"
+    "var-name-mixedcase": "error",
+    "imports-on-top": "error"
   }
 }

CHANGELOG.md

@@ -1,9 +1,509 @@
 # Changelog
 
+### Removals
+
+The following contracts were removed:
+
+- `ERC20Snapshot`
+- `ERC20VotesComp`
+- `GovernorVotesComp`
+- `PaymentSplitter`
+- `TokenTimelock` (removed in favor of `VestingWallet`)
+
+### How to upgrade from 4.x
+
+#### ERC20, ERC721, and ERC1155
+
+These breaking changes will require modifications to ERC20, ERC721, and ERC1155 contracts, since the `_afterTokenTransfer` and `_beforeTokenTransfer` functions were removed. Any customization made through those hooks should now be done overriding the new `_update` function instead.
+
+Minting and burning are implemented by `_update` and customizations should be done by overriding this function as well. `_mint` and `_burn` are no longer virtual (meaning they are not overridable) to guard against possible inconsistencies.
+
+For example, a contract using `ERC20`'s `_beforeTokenTransfer` hook would have to be changed in the following way.
+
+```diff
+- function _beforeTokenTransfer(
++ function _update(
+      address from,
+      address to,
+      uint256 amount
+  ) internal virtual override {
+-     super._beforeTokenTransfer(from, to, amount);
+      require(!condition(), "ERC20: wrong condition");
++     super._update(from, to, amount);
+  }
+```
+
+#### ERC165Storage
+
+Users that were registering EIP-165 interfaces with `_registerInterface` from `ERC165Storage` should instead do so so by overriding the `supportsInterface` function as seen below:
+
+```solidity
+function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
+    return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
+}
+```
+
+## 4.9.0 (2023-05-23)
+
+- `ReentrancyGuard`: Add a `_reentrancyGuardEntered` function to expose the guard status. ([#3714](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3714))
+- `ERC721Wrapper`: add a new extension of the `ERC721` token which wraps an underlying token. Deposit and withdraw guarantee that the ownership of each token is backed by a corresponding underlying token with the same identifier. ([#3863](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3863))
+- `EnumerableMap`: add a `keys()` function that returns an array containing all the keys. ([#3920](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3920))
+- `Governor`: add a public `cancel(uint256)` function. ([#3983](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3983))
+- `Governor`: Enable timestamp operation for blockchains without a stable block time. This is achieved by connecting a Governor's internal clock to match a voting token's EIP-6372 interface. ([#3934](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3934))
+- `Strings`: add `equal` method. ([#3774](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3774))
+- `IERC5313`: Add an interface for EIP-5313 that is now final. ([#4013](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4013))
+- `IERC4906`: Add an interface for ERC-4906 that is now Final. ([#4012](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4012))
+- `StorageSlot`: Add support for `string` and `bytes`. ([#4008](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4008))
+- `Votes`, `ERC20Votes`, `ERC721Votes`: support timestamp checkpointing using EIP-6372. ([#3934](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3934))
+- `ERC4626`: Add mitigation to the inflation attack through virtual shares and assets. ([#3979](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3979))
+- `Strings`: add `toString` method for signed integers. ([#3773](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3773))
+- `ERC20Wrapper`: Make the `underlying` variable private and add a public accessor. ([#4029](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4029))
+- `EIP712`: add EIP-5267 support for better domain discovery. ([#3969](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3969))
+- `AccessControlDefaultAdminRules`: Add an extension of `AccessControl` with additional security rules for the `DEFAULT_ADMIN_ROLE`. ([#4009](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4009))
+- `SignatureChecker`: Add `isValidERC1271SignatureNow` for checking a signature directly against a smart contract using ERC-1271. ([#3932](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3932))
+- `SafeERC20`: Add a `forceApprove` function to improve compatibility with tokens behaving like USDT. ([#4067](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4067))
+- `ERC1967Upgrade`: removed contract-wide `oz-upgrades-unsafe-allow delegatecall` annotation, replaced by granular annotation in `UUPSUpgradeable`. ([#3971](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3971))
+- `ERC20Wrapper`: self wrapping and deposit by the wrapper itself are now explicitly forbidden. ([#4100](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4100))
+- `ECDSA`: optimize bytes32 computation by using assembly instead of `abi.encodePacked`. ([#3853](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3853))
+- `ERC721URIStorage`: Emit ERC-4906 `MetadataUpdate` in `_setTokenURI`. ([#4012](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4012))
+- `ShortStrings`: Added a library for handling short strings in a gas efficient way, with fallback to storage for longer strings. ([#4023](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4023))
+- `SignatureChecker`: Allow return data length greater than 32 from EIP-1271 signers. ([#4038](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4038))
+- `UUPSUpgradeable`: added granular `oz-upgrades-unsafe-allow-reachable` annotation to improve upgrade safety checks on latest version of the Upgrades Plugins (starting with `@openzeppelin/upgrades-core@1.21.0`). ([#3971](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3971))
+- `Initializable`: optimize `_disableInitializers` by using `!=` instead of `<`. ([#3787](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3787))
+- `Ownable2Step`: make `acceptOwnership` public virtual to enable usecases that require overriding it. ([#3960](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3960))
+- `UUPSUpgradeable.sol`: Change visibility to the functions `upgradeTo ` and `upgradeToAndCall ` from `external` to `public`. ([#3959](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3959))
+- `TimelockController`: Add the `CallSalt` event to emit on operation schedule. ([#4001](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4001))
+- Reformatted codebase with latest version of Prettier Solidity. ([#3898](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3898))
+- `Math`: optimize `log256` rounding check. ([#3745](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3745))
+- `ERC20Votes`: optimize by using unchecked arithmetic. ([#3748](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3748))
+- `Multicall`: annotate `multicall` function as upgrade safe to not raise a flag for its delegatecall. ([#3961](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3961))
+- `ERC20Pausable`, `ERC721Pausable`, `ERC1155Pausable`: Add note regarding missing public pausing functionality ([#4007](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4007))
+- `ECDSA`: Add a function `toDataWithIntendedValidatorHash` that encodes data with version 0x00 following EIP-191. ([#4063](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4063))
+- `MerkleProof`: optimize by using unchecked arithmetic. ([#3745](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3745))
+
+### Breaking changes
+
+- `EIP712`: Addition of ERC5267 support requires support for user defined value types, which was released in Solidity version 0.8.8. This requires a pragma change from `^0.8.0` to `^0.8.8`.
+- `EIP712`: Optimization of the cache for the upgradeable version affects the way `name` and `version` are set. This is no longer done through an initializer, and is instead part of the implementation's constructor. As a consequence, all proxies using the same implementation will necessarily share the same `name` and `version`. Additionally, an implementation upgrade risks changing the EIP712 domain unless the same `name` and `version` are used when deploying the new implementation contract.
+
+### Deprecations
+
+- `ERC20Permit`: Added the file `IERC20Permit.sol` and `ERC20Permit.sol` and deprecated `draft-IERC20Permit.sol` and `draft-ERC20Permit.sol` since [EIP-2612](https://eips.ethereum.org/EIPS/eip-2612) is no longer a Draft. Developers are encouraged to update their imports. ([#3793](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3793))
+- `Timers`: The `Timers` library is now deprecated and will be removed in the next major release. ([#4062](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4062))
+- `ERC777`: The `ERC777` token standard is no longer supported by OpenZeppelin. Our implementation is now deprecated and will be removed in the next major release. The corresponding standard interfaces remain available. ([#4066](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4066))
+- `ERC1820Implementer`: The `ERC1820` pseudo-introspection mechanism is no longer supported by OpenZeppelin. Our implementation is now deprecated and will be removed in the next major release. The corresponding standard interfaces remain available. ([#4066](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4066))
+
+## 4.8.3 (2023-04-13)
+
+- `GovernorCompatibilityBravo`: Fix encoding of proposal data when signatures are missing.
+- `TransparentUpgradeableProxy`: Fix transparency in case of selector clash with non-decodable calldata or payable mutability. ([#4154](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/4154))
+
+## 4.8.2 (2023-03-02)
+
+- `ERC721Consecutive`: Fixed a bug when `_mintConsecutive` is used for batches of size 1 that could lead to balance overflow. Refer to the breaking changes section in the changelog for a note on the behavior of `ERC721._beforeTokenTransfer`.
+
+### Breaking changes
+
+- `ERC721`: The internal function `_beforeTokenTransfer` no longer updates balances, which it previously did when `batchSize` was greater than 1. This change has no consequence unless a custom ERC721 extension is explicitly invoking `_beforeTokenTransfer`. Balance updates in extensions must now be done explicitly using `__unsafe_increaseBalance`, with a name that indicates that there is an invariant that has to be manually verified.
+
+## 4.8.1 (2023-01-12)
+
+- `ERC4626`: Use staticcall instead of call when fetching underlying ERC-20 decimals. ([#3943](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3943))
+
+## 4.8.0 (2022-11-08)
+
+- `TimelockController`: Added a new `admin` constructor parameter that is assigned the admin role instead of the deployer account. ([#3722](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3722))
+- `Initializable`: add internal functions `_getInitializedVersion` and `_isInitializing` ([#3598](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3598))
+- `ERC165Checker`: add `supportsERC165InterfaceUnchecked` for consulting individual interfaces without the full ERC165 protocol. ([#3339](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3339))
+- `Address`: optimize `functionCall` by calling `functionCallWithValue` directly. ([#3468](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3468))
+- `Address`: optimize `functionCall` functions by checking contract size only if there is no returned data. ([#3469](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3469))
+- `Governor`: make the `relay` function payable, and add support for EOA payments. ([#3730](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3730))
+- `GovernorCompatibilityBravo`: remove unused `using` statements. ([#3506](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3506))
+- `ERC20`: optimize `_transfer`, `_mint` and `_burn` by using `unchecked` arithmetic when possible. ([#3513](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3513))
+- `ERC20Votes`, `ERC721Votes`: optimize `getPastVotes` for looking up recent checkpoints. ([#3673](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3673))
+- `ERC20FlashMint`: add an internal `_flashFee` function for overriding. ([#3551](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3551))
+- `ERC4626`: use the same `decimals()` as the underlying asset by default (if available). ([#3639](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3639))
+- `ERC4626`: add internal `_initialConvertToShares` and `_initialConvertToAssets` functions to customize empty vaults behavior. ([#3639](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3639))
+- `ERC721`: optimize transfers by making approval clearing implicit instead of emitting an event. ([#3481](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3481))
+- `ERC721`: optimize burn by making approval clearing implicit instead of emitting an event. ([#3538](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3538))
+- `ERC721`: Fix balance accounting when a custom `_beforeTokenTransfer` hook results in a transfer of the token under consideration. ([#3611](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3611))
+- `ERC721`: use unchecked arithmetic for balance updates. ([#3524](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3524))
+- `ERC721Consecutive`: Implementation of EIP-2309 that allows batch minting of ERC721 tokens during construction. ([#3311](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3311))
+- `ReentrancyGuard`: Reduce code size impact of the modifier by using internal functions. ([#3515](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3515))
+- `SafeCast`: optimize downcasting of signed integers. ([#3565](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3565))
+- `ECDSA`: Remove redundant check on the `v` value. ([#3591](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3591))
+- `VestingWallet`: add `releasable` getters. ([#3580](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3580))
+- `VestingWallet`: remove unused library `Math.sol`. ([#3605](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3605))
+- `VestingWallet`: make constructor payable. ([#3665](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3665))
+- `Create2`: optimize address computation by using assembly instead of `abi.encodePacked`. ([#3600](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3600))
+- `Clones`: optimized the assembly to use only the scratch space during deployments, and optimized `predictDeterministicAddress` to use fewer operations. ([#3640](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3640))
+- `Checkpoints`: Use procedural generation to support multiple key/value lengths. ([#3589](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3589))
+- `Checkpoints`: Add new lookup mechanisms. ([#3589](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3589))
+- `Arrays`: Add `unsafeAccess` functions that allow reading and writing to an element in a storage array bypassing Solidity's "out-of-bounds" check. ([#3589](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3589))
+- `Strings`: optimize `toString`. ([#3573](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3573))
+- `Ownable2Step`: extension of `Ownable` that makes the ownership transfers a two step process. ([#3620](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3620))
+- `Math` and `SignedMath`: optimize function `max` by using `>` instead of `>=`. ([#3679](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3679))
+- `Math`: Add `log2`, `log10` and `log256`. ([#3670](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3670))
+- Arbitrum: Update the vendored arbitrum contracts to match the nitro upgrade. ([#3692](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3692))
+
+### Breaking changes
+
+- `ERC721`: In order to add support for batch minting via `ERC721Consecutive` it was necessary to make a minor breaking change in the internal interface of `ERC721`. Namely, the hooks `_beforeTokenTransfer` and `_afterTokenTransfer` have one additional argument that may need to be added to overrides:
+
+```diff
+ function _beforeTokenTransfer(
+     address from,
+     address to,
+     uint256 tokenId,
++    uint256 batchSize
+ ) internal virtual override
+```
+
+- `ERC4626`: Conversion from shares to assets (and vice-versa) in an empty vault used to consider the possible mismatch between the underlying asset's and the vault's decimals. This initial conversion rate is now set to 1-to-1 irrespective of decimals, which are meant for usability purposes only. The vault now uses the assets decimals by default, so off-chain the numbers should appear the same. Developers overriding the vault decimals to a value that does not match the underlying asset may want to override the `_initialConvertToShares` and `_initialConvertToAssets` to replicate the previous behavior.
+
+- `TimelockController`: During deployment, the TimelockController used to grant the `TIMELOCK_ADMIN_ROLE` to the deployer and to the timelock itself. The deployer was then expected to renounce this role once configuration of the timelock is over. Failing to renounce that role allows the deployer to change the timelock permissions (but not to bypass the delay for any time-locked actions). The role is no longer given to the deployer by default. A new parameter `admin` can be set to a non-zero address to grant the admin role during construction (to the deployer or any other address). Just like previously, this admin role should be renounced after configuration. If this param is given `address(0)`, the role is not allocated and doesn't need to be revoked. In any case, the timelock itself continues to have this role.
+
+### Deprecations
+
+- `EIP712`: Added the file `EIP712.sol` and deprecated `draft-EIP712.sol` since the EIP is no longer a Draft. Developers are encouraged to update their imports. ([#3621](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3621))
+
+```diff
+-import "@openzeppelin/contracts/utils/cryptography/draft-EIP712.sol";
++import "@openzeppelin/contracts/utils/cryptography/EIP712.sol";
+```
+
+- `ERC721Votes`: Added the file `ERC721Votes.sol` and deprecated `draft-ERC721Votes.sol` since it no longer depends on a Draft EIP (EIP-712). Developers are encouraged to update their imports. ([#3699](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3699))
+
+```diff
+-import "@openzeppelin/contracts/token/ERC721/extensions/draft-ERC721Votes.sol";
++import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Votes.sol";
+```
+
+### ERC-721 Compatibility Note
+
+ERC-721 integrators that interpret contract state from events should make sure that they implement the clearing of approval that is implicit in every transfer according to the EIP. Previous versions of OpenZeppelin Contracts emitted an explicit `Approval` event even though it was not required by the specification, and this is no longer the case.
+
+With the new `ERC721Consecutive` extension, the internal workings of `ERC721` are slightly changed. Custom extensions to ERC721 should be reviewed to ensure they remain correct. The internal functions that should be considered are `_ownerOf` (new), `_beforeTokenTransfer`, and `_afterTokenTransfer`.
+
+### ERC-4626 Upgrade Note
+
+Existing `ERC4626` contracts that are upgraded to 4.8 must initialize a new variable that holds the vault token decimals. The recommended way to do this is to use a [reinitializer]:
+
+[reinitializer]: https://docs.openzeppelin.com/contracts/4.x/api/proxy#Initializable-reinitializer-uint8-
+
+```solidity
+function migrateToV48() public reinitializer(2) {
+  __ERC4626_init(IERC20Upgradeable(asset()));
+}
+```
+
+## 4.7.3 (2022-08-10)
+
+### Breaking changes
+
+- `ECDSA`: `recover(bytes32,bytes)` and `tryRecover(bytes32,bytes)` no longer accept compact signatures to prevent malleability. Compact signature support remains available using `recover(bytes32,bytes32,bytes32)` and `tryRecover(bytes32,bytes32,bytes32)`.
+
+## 4.7.2 (2022-07-25)
+
+- `LibArbitrumL2`, `CrossChainEnabledArbitrumL2`: Fixed detection of cross-chain calls for EOAs. Previously, calls from EOAs would be classified as cross-chain calls. ([#3578](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3578))
+- `GovernorVotesQuorumFraction`: Fixed quorum updates so they do not affect past proposals that failed due to lack of quorum. ([#3561](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3561))
+- `ERC165Checker`: Added protection against large returndata. ([#3587](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3587))
+
+## 4.7.1 (2022-07-18)
+
+- `SignatureChecker`: Fix an issue that causes `isValidSignatureNow` to revert when the target contract returns ill-encoded data. ([#3552](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3552))
+- `ERC165Checker`: Fix an issue that causes `supportsInterface` to revert when the target contract returns ill-encoded data. ([#3552](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3552))
+
+## 4.7.0 (2022-06-29)
+
+- `TimelockController`: Migrate `_call` to `_execute` and allow inheritance and overriding similar to `Governor`. ([#3317](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3317))
+- `CrossChainEnabledPolygonChild`: replace the `require` statement with the custom error `NotCrossChainCall`. ([#3380](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3380))
+- `ERC20FlashMint`: Add customizable flash fee receiver. ([#3327](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3327))
+- `ERC4626`: add an extension of `ERC20` that implements the ERC4626 Tokenized Vault Standard. ([#3171](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3171))
+- `SafeERC20`: add `safePermit` as mitigation against phantom permit functions. ([#3280](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3280))
+- `Math`: add a `mulDiv` function that can round the result either up or down. ([#3171](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3171))
+- `Math`: Add a `sqrt` function to compute square roots of integers, rounding either up or down. ([#3242](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3242))
+- `Strings`: add a new overloaded function `toHexString` that converts an `address` with fixed length of 20 bytes to its not checksummed ASCII `string` hexadecimal representation. ([#3403](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3403))
+- `EnumerableMap`: add new `UintToUintMap` map type. ([#3338](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3338))
+- `EnumerableMap`: add new `Bytes32ToUintMap` map type. ([#3416](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3416))
+- `SafeCast`: add support for many more types, using procedural code generation. ([#3245](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3245))
+- `MerkleProof`: add `multiProofVerify` to prove multiple values are part of a Merkle tree. ([#3276](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3276))
+- `MerkleProof`: add calldata versions of the functions to avoid copying input arrays to memory and save gas. ([#3200](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3200))
+- `ERC721`, `ERC1155`: simplified revert reasons. ([#3254](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3254), ([#3438](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3438)))
+- `ERC721`: removed redundant require statement. ([#3434](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3434))
+- `PaymentSplitter`: add `releasable` getters. ([#3350](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3350))
+- `Initializable`: refactored implementation of modifiers for easier understanding. ([#3450](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3450))
+- `Proxies`: remove runtime check of ERC1967 storage slots. ([#3455](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3455))
+
+### Breaking changes
+
+- `Initializable`: functions decorated with the modifier `reinitializer(1)` may no longer invoke each other.
+
+## 4.6.0 (2022-04-26)
+
+- `crosschain`: Add a new set of contracts for cross-chain applications. `CrossChainEnabled` is a base contract with instantiations for several chains and bridges, and `AccessControlCrossChain` is an extension of access control that allows cross-chain operation. ([#3183](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3183))
+- `AccessControl`: add a virtual `_checkRole(bytes32)` function that can be overridden to alter the `onlyRole` modifier behavior. ([#3137](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3137))
+- `EnumerableMap`: add new `AddressToUintMap` map type. ([#3150](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3150))
+- `EnumerableMap`: add new `Bytes32ToBytes32Map` map type. ([#3192](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3192))
+- `ERC20FlashMint`: support infinite allowance when paying back a flash loan. ([#3226](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3226))
+- `ERC20Wrapper`: the `decimals()` function now tries to fetch the value from the underlying token instance. If that calls revert, then the default value is used. ([#3259](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3259))
+- `draft-ERC20Permit`: replace `immutable` with `constant` for `_PERMIT_TYPEHASH` since the `keccak256` of string literals is treated specially and the hash is evaluated at compile time. ([#3196](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3196))
+- `ERC1155`: Add a `_afterTokenTransfer` hook for improved extensibility. ([#3166](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3166))
+- `ERC1155URIStorage`: add a new extension that implements a `_setURI` behavior similar to ERC721's `_setTokenURI`. ([#3210](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3210))
+- `DoubleEndedQueue`: a new data structure that supports efficient push and pop to both front and back, useful for FIFO and LIFO queues. ([#3153](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3153))
+- `Governor`: improved security of `onlyGovernance` modifier when using an external executor contract (e.g. a timelock) that can operate without necessarily going through the governance protocol. ([#3147](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3147))
+- `Governor`: Add a way to parameterize votes. This can be used to implement voting systems such as fractionalized voting, ERC721 based voting, or any number of other systems. The `params` argument added to `_countVote` method, and included in the newly added `_getVotes` method, can be used by counting and voting modules respectively for such purposes. ([#3043](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3043))
+- `Governor`: rewording of revert reason for consistency. ([#3275](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3275))
+- `Governor`: fix an inconsistency in data locations that could lead to invalid bytecode being produced. ([#3295](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3295))
+- `Governor`: Implement `IERC721Receiver` and `IERC1155Receiver` to improve token custody by governors. ([#3230](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3230))
+- `TimelockController`: Implement `IERC721Receiver` and `IERC1155Receiver` to improve token custody by timelocks. ([#3230](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3230))
+- `TimelockController`: Add a separate canceller role for the ability to cancel. ([#3165](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3165))
+- `Initializable`: add a reinitializer modifier that enables the initialization of new modules, added to already initialized contracts through upgradeability. ([#3232](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3232))
+- `Initializable`: add an Initialized event that tracks initialized version numbers. ([#3294](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3294))
+- `ERC2981`: make `royaltyInfo` public to allow super call in overrides. ([#3305](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3305))
+
+### Upgradeability notice
+
+- `TimelockController`: **(Action needed)** The upgrade from <4.6 to >=4.6 introduces a new `CANCELLER_ROLE` that requires set up to be assignable. After the upgrade, only addresses with this role will have the ability to cancel. Proposers will no longer be able to cancel. Assigning cancellers can be done by an admin (including the timelock itself) once the role admin is set up. To do this, we recommend upgrading to the `TimelockControllerWith46MigrationUpgradeable` contract and then calling the `migrateTo46` function.
+
+### Breaking changes
+
+- `Governor`: Adds internal virtual `_getVotes` method that must be implemented; this is a breaking change for existing concrete extensions to `Governor`. To fix this on an existing voting module extension, rename `getVotes` to `_getVotes` and add a `bytes memory` argument. ([#3043](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3043))
+- `Governor`: Adds `params` parameter to internal virtual `_countVote` method; this is a breaking change for existing concrete extensions to `Governor`. To fix this on an existing counting module extension, add a `bytes memory` argument to `_countVote`. ([#3043](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3043))
+- `Governor`: Does not emit `VoteCast` event when params data is non-empty; instead emits `VoteCastWithParams` event. To fix this on an integration that consumes the `VoteCast` event, also fetch/monitor `VoteCastWithParams` events. ([#3043](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3043))
+- `Votes`: The internal virtual function `_getVotingUnits` was made `view` (which was accidentally missing). Any overrides should now be updated so they are `view` as well.
+
+## 4.5.0 (2022-02-09)
+
+- `ERC2981`: add implementation of the royalty standard, and the respective extensions for `ERC721` and `ERC1155`. ([#3012](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3012))
+- `GovernorTimelockControl`: improve the `state()` function to have it reflect cases where a proposal has been canceled directly on the timelock. ([#2977](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2977))
+- Preset contracts are now deprecated in favor of [Contracts Wizard](https://wizard.openzeppelin.com). ([#2986](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2986))
+- `Governor`: add a relay function to help recover assets sent to a governor that is not its own executor (e.g. when using a timelock). ([#2926](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2926))
+- `GovernorPreventLateQuorum`: add new module to ensure a minimum voting duration is available after the quorum is reached. ([#2973](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2973))
+- `ERC721`: improved revert reason when transferring from wrong owner. ([#2975](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2975))
+- `Votes`: Added a base contract for vote tracking with delegation. ([#2944](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2944))
+- `ERC721Votes`: Added an extension of ERC721 enabled with vote tracking and delegation. ([#2944](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2944))
+- `ERC2771Context`: use immutable storage to store the forwarder address, no longer an issue since Solidity >=0.8.8 allows reading immutable variables in the constructor. ([#2917](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2917))
+- `Base64`: add a library to parse bytes into base64 strings using `encode(bytes memory)` function, and provide examples to show how to use to build URL-safe `tokenURIs`. ([#2884](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2884))
+- `ERC20`: reduce allowance before triggering transfer. ([#3056](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3056))
+- `ERC20`: do not update allowance on `transferFrom` when allowance is `type(uint256).max`. ([#3085](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3085))
+- `ERC20`: add a `_spendAllowance` internal function. ([#3170](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3170))
+- `ERC20Burnable`: do not update allowance on `burnFrom` when allowance is `type(uint256).max`. ([#3170](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3170))
+- `ERC777`: do not update allowance on `transferFrom` when allowance is `type(uint256).max`. ([#3085](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3085))
+- `ERC777`: add a `_spendAllowance` internal function. ([#3170](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3170))
+- `SignedMath`: a new signed version of the Math library with `max`, `min`, and `average`. ([#2686](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2686))
+- `SignedMath`: add an `abs(int256)` method that returns the unsigned absolute value of a signed value. ([#2984](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2984))
+- `ERC1967Upgrade`: Refactor the secure upgrade to use `ERC1822` instead of the previous rollback mechanism. This reduces code complexity and attack surface with similar security guarantees. ([#3021](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3021))
+- `UUPSUpgradeable`: Add `ERC1822` compliance to support the updated secure upgrade mechanism. ([#3021](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3021))
+- Some more functions have been made virtual to customize them via overrides. In many cases this will not imply that other functions in the contract will automatically adapt to the overridden definitions. People who wish to override should consult the source code to understand the impact and if they need to override any additional functions to achieve the desired behavior.
+
+### Breaking changes
+
+- `ERC1967Upgrade`: The function `_upgradeToAndCallSecure` was renamed to `_upgradeToAndCallUUPS`, along with the change in security mechanism described above.
+- `Address`: The Solidity pragma is increased from `^0.8.0` to `^0.8.1`. This is required by the `account.code.length` syntax that replaces inline assembly. This may require users to bump their compiler version from `0.8.0` to `0.8.1` or later. Note that other parts of the code already include stricter requirements.
+
+## 4.4.2 (2022-01-11)
+
+### Bugfixes
+
+- `GovernorCompatibilityBravo`: Fix error in the encoding of calldata for proposals submitted through the compatibility interface with explicit signatures. ([#3100](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3100))
+
+## 4.4.1 (2021-12-14)
+
+- `Initializable`: change the existing `initializer` modifier and add a new `onlyInitializing` modifier to prevent reentrancy risk. ([#3006](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3006))
+
+### Breaking change
+
+It is no longer possible to call an `initializer`-protected function from within another `initializer` function outside the context of a constructor. Projects using OpenZeppelin upgradeable proxies should continue to work as is, since in the common case the initializer is invoked in the constructor directly. If this is not the case for you, the suggested change is to use the new `onlyInitializing` modifier in the following way:
+
+```diff
+ contract A {
+-    function initialize() public   initializer { ... }
++    function initialize() internal onlyInitializing { ... }
+ }
+ contract B is A {
+     function initialize() public initializer {
+         A.initialize();
+     }
+ }
+```
+
+## 4.4.0 (2021-11-25)
+
+- `Ownable`: add an internal `_transferOwnership(address)`. ([#2568](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2568))
+- `AccessControl`: add internal `_grantRole(bytes32,address)` and `_revokeRole(bytes32,address)`. ([#2568](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2568))
+- `AccessControl`: mark `_setupRole(bytes32,address)` as deprecated in favor of `_grantRole(bytes32,address)`. ([#2568](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2568))
+- `AccessControlEnumerable`: hook into `_grantRole(bytes32,address)` and `_revokeRole(bytes32,address)`. ([#2946](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2946))
+- `EIP712`: cache `address(this)` to immutable storage to avoid potential issues if a vanilla contract is used in a delegatecall context. ([#2852](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2852))
+- Add internal `_setApprovalForAll` to `ERC721` and `ERC1155`. ([#2834](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2834))
+- `Governor`: shift vote start and end by one block to better match Compound's GovernorBravo and prevent voting at the Governor level if the voting snapshot is not ready. ([#2892](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2892))
+- `GovernorCompatibilityBravo`: consider quorum an inclusive rather than exclusive minimum to match Compound's GovernorBravo. ([#2974](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2974))
+- `GovernorSettings`: a new governor module that manages voting settings updatable through governance actions. ([#2904](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2904))
+- `PaymentSplitter`: now supports ERC20 assets in addition to Ether. ([#2858](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2858))
+- `ECDSA`: add a variant of `toEthSignedMessageHash` for arbitrary length message hashing. ([#2865](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2865))
+- `MerkleProof`: add a `processProof` function that returns the rebuilt root hash given a leaf and a proof. ([#2841](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2841))
+- `VestingWallet`: new contract that handles the vesting of Ether and ERC20 tokens following a customizable vesting schedule. ([#2748](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2748))
+- `Governor`: enable receiving Ether when a Timelock contract is not used. ([#2849](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2849))
+- `GovernorTimelockCompound`: fix ability to use Ether stored in the Timelock contract. ([#2849](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2849))
+
+## 4.3.3 (2021-11-08)
+
+- `ERC1155Supply`: Handle `totalSupply` changes by hooking into `_beforeTokenTransfer` to ensure consistency of balances and supply during `IERC1155Receiver.onERC1155Received` calls.
+
+## 4.3.2 (2021-09-14)
+
+- `UUPSUpgradeable`: Add modifiers to prevent `upgradeTo` and `upgradeToAndCall` being executed on any contract that is not the active ERC1967 proxy. This prevents these functions being called on implementation contracts or minimal ERC1167 clones, in particular.
+
+## 4.3.1 (2021-08-26)
+
+- `TimelockController`: Add additional isOperationReady check.
+
+## 4.3.0 (2021-08-17)
+
+- `ERC2771Context`: use private variable from storage to store the forwarder address. Fixes issues where `_msgSender()` was not callable from constructors. ([#2754](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2754))
+- `EnumerableSet`: add `values()` functions that returns an array containing all values in a single call. ([#2768](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2768))
+- `Governor`: added a modular system of `Governor` contracts based on `GovernorAlpha` and `GovernorBravo`. ([#2672](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2672))
+- Add an `interfaces` folder containing solidity interfaces to final ERCs. ([#2517](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2517))
+- `ECDSA`: add `tryRecover` functions that will not throw if the signature is invalid, and will return an error flag instead. ([#2661](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2661))
+- `SignatureChecker`: Reduce gas usage of the `isValidSignatureNow` function for the "signature by EOA" case. ([#2661](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2661))
+
+## 4.2.0 (2021-06-30)
+
+- `ERC20Votes`: add a new extension of the `ERC20` token with support for voting snapshots and delegation. ([#2632](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2632))
+- `ERC20VotesComp`: Variant of `ERC20Votes` that is compatible with Compound's `Comp` token interface but restricts supply to `uint96`. ([#2706](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2706))
+- `ERC20Wrapper`: add a new extension of the `ERC20` token which wraps an underlying token. Deposit and withdraw guarantee that the total supply is backed by a corresponding amount of underlying token. ([#2633](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2633))
+- Enumerables: Improve gas cost of removal in `EnumerableSet` and `EnumerableMap`.
+- Enumerables: Improve gas cost of lookup in `EnumerableSet` and `EnumerableMap`.
+- `Counter`: add a reset method. ([#2678](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2678))
+- Tokens: Wrap definitely safe subtractions in `unchecked` blocks.
+- `Math`: Add a `ceilDiv` method for performing ceiling division.
+- `ERC1155Supply`: add a new `ERC1155` extension that keeps track of the totalSupply of each tokenId. ([#2593](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2593))
+- `BitMaps`: add a new `BitMaps` library that provides a storage efficient datastructure for `uint256` to `bool` mapping with contiguous keys. ([#2710](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2710))
+
+### Breaking Changes
+
+- `ERC20FlashMint` is no longer a Draft ERC. ([#2673](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2673)))
+
+**How to update:** Change your import paths by removing the `draft-` prefix from `@openzeppelin/contracts/token/ERC20/extensions/draft-ERC20FlashMint.sol`.
+
+> See [Releases and Stability: Drafts](https://docs.openzeppelin.com/contracts/4.x/releases-stability#drafts).
+
+## 4.1.0 (2021-04-29)
+
+- `IERC20Metadata`: add a new extended interface that includes the optional `name()`, `symbol()` and `decimals()` functions. ([#2561](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2561))
+- `ERC777`: make reception acquirement optional in `_mint`. ([#2552](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2552))
+- `ERC20Permit`: add a `_useNonce` to enable further usage of ERC712 signatures. ([#2565](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2565))
+- `ERC20FlashMint`: add an implementation of the ERC3156 extension for flash-minting ERC20 tokens. ([#2543](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2543))
+- `SignatureChecker`: add a signature verification library that supports both EOA and ERC1271 compliant contracts as signers. ([#2532](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2532))
+- `Multicall`: add abstract contract with `multicall(bytes[] calldata data)` function to bundle multiple calls together ([#2608](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2608))
+- `ECDSA`: add support for ERC2098 short-signatures. ([#2582](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2582))
+- `AccessControl`: add an `onlyRole` modifier to restrict specific function to callers bearing a specific role. ([#2609](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2609))
+- `StorageSlot`: add a library for reading and writing primitive types to specific storage slots. ([#2542](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2542))
+- UUPS Proxies: add `UUPSUpgradeable` to implement the UUPS proxy pattern together with `EIP1967Proxy`. ([#2542](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2542))
+
+### Breaking changes
+
+This release includes two small breaking changes in `TimelockController`.
+
+1. The `onlyRole` modifier in this contract was designed to let anyone through if the role was granted to `address(0)`,
+   allowing the possibility to to make a role "open", which can be used for `EXECUTOR_ROLE`. This modifier is now
+   replaced by `AccessControl.onlyRole`, which does not have this ability. The previous behavior was moved to the
+   modifier `TimelockController.onlyRoleOrOpenRole`.
+2. It was possible to make `PROPOSER_ROLE` an open role (as described in the previous item) if it was granted to
+   `address(0)`. This would affect the `schedule`, `scheduleBatch`, and `cancel` operations in `TimelockController`.
+   This ability was removed as it does not make sense to open up the `PROPOSER_ROLE` in the same way that it does for
+   `EXECUTOR_ROLE`.
+
+## 4.0.0 (2021-03-23)
+
+- Now targeting the 0.8.x line of Solidity compilers. For 0.6.x (resp 0.7.x) support, use version 3.4.0 (resp 3.4.0-solc-0.7) of OpenZeppelin.
+- `Context`: making `_msgData` return `bytes calldata` instead of `bytes memory` ([#2492](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2492))
+- `ERC20`: removed the `_setDecimals` function and the storage slot associated to decimals. ([#2502](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2502))
+- `Strings`: addition of a `toHexString` function. ([#2504](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2504))
+- `EnumerableMap`: change implementation to optimize for `key → value` lookups instead of enumeration. ([#2518](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2518))
+- `GSN`: deprecate GSNv1 support in favor of upcoming support for GSNv2. ([#2521](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2521))
+- `ERC165`: remove uses of storage in the base ERC165 implementation. ERC165 based contracts now use storage-less virtual functions. Old behavior remains available in the `ERC165Storage` extension. ([#2505](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2505))
+- `Initializable`: make initializer check stricter during construction. ([#2531](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2531))
+- `ERC721`: remove enumerability of tokens from the base implementation. This feature is now provided separately through the `ERC721Enumerable` extension. ([#2511](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2511))
+- `AccessControl`: removed enumerability by default for a more lightweight contract. It is now opt-in through `AccessControlEnumerable`. ([#2512](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2512))
+- Meta Transactions: add `ERC2771Context` and a `MinimalForwarder` for meta-transactions. ([#2508](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2508))
+- Overall reorganization of the contract folder to improve clarity and discoverability. ([#2503](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2503))
+- `ERC20Capped`: optimize gas usage by enforcing the check directly in `_mint`. ([#2524](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2524))
+- Rename `UpgradeableProxy` to `ERC1967Proxy`. ([#2547](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2547))
+- `ERC777`: optimize the gas costs of the constructor. ([#2551](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2551))
+- `ERC721URIStorage`: add a new extension that implements the `_setTokenURI` behavior as it was available in 3.4.0. ([#2555](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2555))
+- `AccessControl`: added ERC165 interface detection. ([#2562](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2562))
+- `ERC1155`: make `uri` public so overloading function can call it using super. ([#2576](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2576))
+
+### Bug fixes for beta releases
+
+- `AccessControlEnumerable`: Fixed `renounceRole` not updating enumerable set of addresses for a role. ([#2572](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2572))
+
+### How to upgrade from 3.x
+
+Since this version has moved a few contracts to different directories, users upgrading from a previous version will need to adjust their import statements. To make this easier, the package includes a script that will migrate import statements automatically. After upgrading to the latest version of the package, run:
+
+```
+npx openzeppelin-contracts-migrate-imports
+```
+
+Make sure you're using git or another version control system to be able to recover from any potential error in our script.
+
+### How to upgrade from 4.0-beta.x
+
+Some further changes have been done between the different beta iterations. Transitions made during this period are configured in the `migrate-imports` script. Consequently, you can upgrade from any previous 4.0-beta.x version using the same script as described in the _How to upgrade from 3.x_ section.
+
+## 3.4.2 (2021-07-24)
+
+- `TimelockController`: Add additional isOperationReady check.
+
+## 3.4.1 (2021-03-03)
+
+- `ERC721`: made `_approve` an internal function (was private).
+
+## 3.4.0 (2021-02-02)
+
+- `BeaconProxy`: added new kind of proxy that allows simultaneous atomic upgrades. ([#2411](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2411))
+- `EIP712`: added helpers to verify EIP712 typed data signatures on chain. ([#2418](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2418))
+- `ERC20Permit`: added an implementation of the ERC20 permit extension for gasless token approvals. ([#2237](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2237))
+- Presets: added token presets with preminted fixed supply `ERC20PresetFixedSupply` and `ERC777PresetFixedSupply`. ([#2399](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2399))
+- `Address`: added `functionDelegateCall`, similar to the existing `functionCall`. ([#2333](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2333))
+- `Clones`: added a library for deploying EIP 1167 minimal proxies. ([#2449](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2449))
+- `Context`: moved from `contracts/GSN` to `contracts/utils`. ([#2453](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2453))
+- `PaymentSplitter`: replace usage of `.transfer()` with `Address.sendValue` for improved compatibility with smart wallets. ([#2455](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2455))
+- `UpgradeableProxy`: bubble revert reasons from initialization calls. ([#2454](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2454))
+- `SafeMath`: fix a memory allocation issue by adding new `SafeMath.tryOp(uint,uint)→(bool,uint)` functions. `SafeMath.op(uint,uint,string)→uint` are now deprecated. ([#2462](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2462))
+- `EnumerableMap`: fix a memory allocation issue by adding new `EnumerableMap.tryGet(uint)→(bool,address)` functions. `EnumerableMap.get(uint)→string` is now deprecated. ([#2462](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2462))
+- `ERC165Checker`: added batch `getSupportedInterfaces`. ([#2469](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2469))
+- `RefundEscrow`: `beneficiaryWithdraw` will forward all available gas to the beneficiary. ([#2480](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2480))
+- Many view and pure functions have been made virtual to customize them via overrides. In many cases this will not imply that other functions in the contract will automatically adapt to the overridden definitions. People who wish to override should consult the source code to understand the impact and if they need to override any additional functions to achieve the desired behavior.
+
+### Security Fixes
+
+- `ERC777`: fix potential reentrancy issues for custom extensions to `ERC777`. ([#2483](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2483))
+
+If you're using our implementation of ERC777 from version 3.3.0 or earlier, and you define a custom `_beforeTokenTransfer` function that writes to a storage variable, you may be vulnerable to a reentrancy attack. If you're affected and would like assistance please write to security@openzeppelin.com. [Read more in the pull request.](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2483)
+
+## 3.3.0 (2020-11-26)
+
+- Now supports both Solidity 0.6 and 0.7. Compiling with solc 0.7 will result in warnings. Install the `solc-0.7` tag to compile without warnings.
+- `Address`: added `functionStaticCall`, similar to the existing `functionCall`. ([#2333](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2333))
+- `TimelockController`: added a contract to augment access control schemes with a delay. ([#2354](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2354))
+- `EnumerableSet`: added `Bytes32Set`, for sets of `bytes32`. ([#2395](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2395))
+
+## 3.2.2-solc-0.7 (2020-10-28)
+
+- Resolve warnings introduced by Solidity 0.7.4. ([#2396](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2396))
+
+## 3.2.1-solc-0.7 (2020-09-15)
+
+- `ERC777`: Remove a warning about function state visibility in Solidity 0.7. ([#2327](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2327))
+
 ## 3.2.0 (2020-09-10)
 
 ### New features
- * Proxies: added the proxy contracts from OpenZeppelin SDK. ([#2335](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2335))
+
+- Proxies: added the proxy contracts from OpenZeppelin SDK. ([#2335](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2335))
 
 #### Proxy changes with respect to OpenZeppelin SDK
 
@@ -15,10 +515,12 @@ Aside from upgrading them from Solidity 0.5 to 0.6, we've changed a few minor th
 - `UpgradeabilityProxy._setImplementation` and `AdminUpgradeabilityProxy._setAdmin` were made private.
 
 ### Improvements
- * `Address.isContract`: switched from `extcodehash` to `extcodesize` for less gas usage. ([#2311](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2311))
+
+- `Address.isContract`: switched from `extcodehash` to `extcodesize` for less gas usage. ([#2311](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2311))
 
 ### Breaking changes
- * `ERC20Snapshot`: switched to using `_beforeTokenTransfer` hook instead of overriding ERC20 operations. ([#2312](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2312))
+
+- `ERC20Snapshot`: switched to using `_beforeTokenTransfer` hook instead of overriding ERC20 operations. ([#2312](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2312))
 
 This small change in the way we implemented `ERC20Snapshot` may affect users who are combining this contract with
 other ERC20 flavors, since it no longer overrides `_transfer`, `_mint`, and `_burn`. This can result in having to remove Solidity `override(...)` specifiers in derived contracts for these functions, and to instead have to add it for `_beforeTokenTransfer`. See [Using Hooks](https://docs.openzeppelin.com/contracts/3.x/extending-contracts#using-hooks) in the documentation.
@@ -26,119 +528,134 @@ other ERC20 flavors, since it no longer overrides `_transfer`, `_mint`, and `_bu
 ## 3.1.0 (2020-06-23)
 
 ### New features
- * `SafeCast`: added functions to downcast signed integers (e.g. `toInt32`), improving usability of `SignedSafeMath`. ([#2243](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2243))
- * `functionCall`: new helpers that replicate Solidity's function call semantics, reducing the need to rely on `call`. ([#2264](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2264))
- * `ERC1155`: added support for a base implementation, non-standard extensions and a preset contract. ([#2014](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2014), [#2230](https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2230))
+
+- `SafeCast`: added functions to downcast signed integers (e.g. `toInt32`), improving usability of `SignedSafeMath`. ([#2243](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2243))
+- `functionCall`: new helpers that replicate Solidity's function call semantics, reducing the need to rely on `call`. ([#2264](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2264))
+- `ERC1155`: added support for a base implementation, non-standard extensions and a preset contract. ([#2014](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2014), [#2230](https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2230))
 
 ### Improvements
- * `ReentrancyGuard`: reduced overhead of using the `nonReentrant` modifier. ([#2171](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2171))
- * `AccessControl`: added a `RoleAdminChanged` event to `_setAdminRole`. ([#2214](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2214))
- * Made all `public` functions in the token preset contracts `virtual`. ([#2257](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2257))
+
+- `ReentrancyGuard`: reduced overhead of using the `nonReentrant` modifier. ([#2171](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2171))
+- `AccessControl`: added a `RoleAdminChanged` event to `_setAdminRole`. ([#2214](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2214))
+- Made all `public` functions in the token preset contracts `virtual`. ([#2257](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2257))
 
 ### Deprecations
- * `SafeERC20`: deprecated `safeApprove`. ([#2268](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2268))
+
+- `SafeERC20`: deprecated `safeApprove`. ([#2268](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2268))
 
 ## 3.0.2 (2020-06-08)
 
 ### Improvements
- * Added SPX license identifier to all contracts. ([#2235](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2235))
+
+- Added SPX license identifier to all contracts. ([#2235](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2235))
 
 ## 3.0.1 (2020-04-27)
 
 ### Bugfixes
- * `ERC777`: fixed the `_approve` internal function not validating some of their arguments for non-zero addresses. ([#2213](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2213))
+
+- `ERC777`: fixed the `_approve` internal function not validating some of their arguments for non-zero addresses. ([#2213](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2213))
 
 ## 3.0.0 (2020-04-20)
 
 ### New features
- * `AccessControl`: new contract for managing permissions in a system, replacement for `Ownable` and `Roles`. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
- * `SafeCast`: new functions to convert to and from signed and unsigned values: `toUint256` and `toInt256`. ([#2123](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2123))
- * `EnumerableMap`: a new data structure for key-value pairs (like `mapping`) that can be iterated over. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+
+- `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))
+
+- `ERC721`: `burn(owner, tokenId)` was removed, use `burn(tokenId)` instead. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+- `ERC721`: `_checkOnERC721Received` was removed. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+- `ERC721`: `_transferFrom` and `_safeTransferFrom` were renamed to `_transfer` and `_safeTransfer`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+- `Ownable`: removed `_transferOwnership`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+- `PullPayment`, `Escrow`: `withdrawWithGas` was removed. The old `withdraw` function now forwards all gas. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+- `Roles` was removed, use `AccessControl` as a replacement. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
+- `ECDSA`: when receiving an invalid signature, `recover` now reverts instead of returning the zero address. ([#2114](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2114))
+- `Create2`: added an `amount` argument to `deploy` for contracts with `payable` constructors. ([#2117](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2117))
+- `Pausable`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `Strings`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `Counters`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `SignedSafeMath`: moved to the `math` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `ERC20Snapshot`: moved to the `token/ERC20` directory. `snapshot` was changed into an `internal` function. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `Ownable`: moved to the `access` directory. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+- `Ownable`: removed `isOwner`. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+- `Secondary`: removed from the library, use `Ownable` instead. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+- `Escrow`, `ConditionalEscrow`, `RefundEscrow`: these now use `Ownable` instead of `Secondary`, their external API changed accordingly. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+- `ERC20`: removed `_burnFrom`. ([#2119](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2119))
+- `Address`: removed `toPayable`, use `payable(address)` instead. ([#2133](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2133))
+- `ERC777`: `_send`, `_mint` and `_burn` now use the caller as the operator. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+- `ERC777`: removed `_callsTokensToSend` and `_callTokensReceived`. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+- `EnumerableSet`: renamed `get` to `at`. ([#2151](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2151))
+- `ERC165Checker`: functions no longer have a leading underscore. ([#2150](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2150))
+- `ERC721Metadata`, `ERC721Enumerable`: these contracts were removed, and their functionality merged into `ERC721`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+- `ERC721`: added a constructor for `name` and `symbol`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+- `ERC20Detailed`: this contract was removed and its functionality merged into `ERC20`. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
+- `ERC20`: added a constructor for `name` and `symbol`. `decimals` now defaults to 18. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
+- `Strings`: renamed `fromUint256` to `toString` ([#2188](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2188))
 
 ## 2.5.1 (2020-04-24)
 
 ### Bugfixes
- * `ERC777`: fixed the `_send` and `_approve` internal functions not validating some of their arguments for non-zero addresses. ([#2212](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2212))
+
+- `ERC777`: fixed the `_send` and `_approve` internal functions not validating some of their arguments for non-zero addresses. ([#2212](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2212))
 
 ## 2.5.0 (2020-02-04)
 
 ### New features
- * `SafeCast.toUintXX`: new library for integer downcasting, which allows for safe operation on smaller types (e.g. `uint32`) when combined with `SafeMath`. ([#1926](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1926))
- * `ERC721Metadata`: added `baseURI`, which can be used for dramatic gas savings when all token URIs share a prefix (e.g. `http://api.myapp.com/tokens/<id>`). ([#1970](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1970))
- * `EnumerableSet`: new library for storing enumerable sets of values. Only `AddressSet` is supported in this release. ([#2061](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/2061))
- * `Create2`: simple library to make usage of the `CREATE2` opcode easier. ([#1744](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1744))
+
+- `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))
+
+- `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))
+
+- `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))
+
+- `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))
+
+- `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)`
+
+- 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))
+
+- `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`.
+- 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.
 
@@ -149,81 +666,94 @@ For example, a contract using `GSNBouncerSignature` would have to be changed in
 
 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`               |
+| 2.4.0-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))
+
+- `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))
+
+- 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))
+
+- `PostDeliveryCrowdsale`: some validations where skipped when paired with other crowdsale flavors, such as `AllowanceCrowdsale`, or `MintableCrowdsale` and `ERC20Capped`, which could cause buyers to not be able to claim their purchased tokens. ([#1721](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1721))
+- `ERC20._transfer`: the `from` argument was allowed to be the zero address, so it was possible to internally trigger a transfer of 0 tokens from the zero address. This address is not a valid destinatary of transfers, nor can it give or receive allowance, so this behavior was inconsistent. It now reverts. ([#1752](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1752))
 
 ## 2.2.0 (2019-03-14)
 
 ### New features
- * `ERC20Snapshot`: create snapshots on demand of the token balances and total supply, to later retrieve and e.g. calculate dividends at a past time. ([#1617](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1617))
- * `SafeERC20`: `ERC20` contracts with no return value (i.e. that revert on failure) are now supported. ([#1655](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1655))
- * `ERC20`: added internal `_approve(address owner, address spender, uint256 value)`, allowing derived contracts to set the allowance of arbitrary accounts. ([#1609](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1609))
- * `ERC20Metadata`: added internal `_setTokenURI(string memory tokenURI)`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
- * `TimedCrowdsale`: added internal `_extendTime(uint256 newClosingTime)` as well as `TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime)` event allowing to extend the crowdsale, as long as it hasn't already closed.
+
+- `ERC20Snapshot`: create snapshots on demand of the token balances and total supply, to later retrieve and e.g. calculate dividends at a past time. ([#1617](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1617))
+- `SafeERC20`: `ERC20` contracts with no return value (i.e. that revert on failure) are now supported. ([#1655](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1655))
+- `ERC20`: added internal `_approve(address owner, address spender, uint256 value)`, allowing derived contracts to set the allowance of arbitrary accounts. ([#1609](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1609))
+- `ERC20Metadata`: added internal `_setTokenURI(string memory tokenURI)`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+- `TimedCrowdsale`: added internal `_extendTime(uint256 newClosingTime)` as well as `TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime)` event allowing to extend the crowdsale, as long as it hasn't already closed.
 
 ### Improvements
- * Upgraded the minimum compiler version to v0.5.2: this removes many Solidity warnings that were false positives. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
- * `ECDSA`: `recover` no longer accepts malleable signatures (those using upper-range values for `s`, or 0/1 for `v`). ([#1622](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1622))
- * ``ERC721``'s transfers are now more gas efficient due to removal of unnecessary `SafeMath` calls. ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
- * Fixed variable shadowing issues. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
+
+- Upgraded the minimum compiler version to v0.5.2: this removes many Solidity warnings that were false positives. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
+- `ECDSA`: `recover` no longer accepts malleable signatures (those using upper-range values for `s`, or 0/1 for `v`). ([#1622](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1622))
+- `ERC721`'s transfers are now more gas efficient due to removal of unnecessary `SafeMath` calls. ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+- Fixed variable shadowing issues. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
 
 ### Bugfixes
- * (minor) `SafeERC20`: `safeApprove` wasn't properly checking for a zero allowance when attempting to set a non-zero allowance. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
+
+- (minor) `SafeERC20`: `safeApprove` wasn't properly checking for a zero allowance when attempting to set a non-zero allowance. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
 
 ### Breaking changes in drafts
- * `TokenMetadata` has been renamed to `ERC20Metadata`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
- * The library `Counter` has been renamed to `Counters` and its API has been improved. See an example in `ERC721`, lines [17](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L17) and [204](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L204). ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+
+- `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))
+
+- Backported `SafeERC20.safeApprove` bugfix. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
 
 ## 2.1.2 (2019-01-17)
- * Removed most of the test suite from the npm package, except `PublicRole.behavior.js`, which may be useful to users testing their own `Roles`.
+
+- Removed most of the test suite from the npm package, except `PublicRole.behavior.js`, which may be useful to users testing their own `Roles`.
 
 ## 2.1.1 (2019-01-04)
- * Version bump to avoid conflict in the npm registry.
+
+- Version bump to avoid conflict in the npm registry.
 
 ## 2.1.0 (2019-01-04)
 
 ### New features
- * Now targeting the 0.5.x line of Solidity compilers. For 0.4.24 support, use version 2.0 of OpenZeppelin.
- * `WhitelistCrowdsale`: a crowdsale where only whitelisted accounts (`WhitelistedRole`) can purchase tokens. Adding or removing accounts from the whitelist is done by whitelist admins (`WhitelistAdminRole`). Similar to the pre-2.0 `WhitelistedCrowdsale`. ([#1525](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1525), [#1589](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1589))
- * `RefundablePostDeliveryCrowdsale`: replacement for `RefundableCrowdsale` (deprecated, see below) where tokens are only granted once the crowdsale ends (if it meets its goal). ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))
- * `PausableCrowdsale`: allows for pausers (`PauserRole`) to pause token purchases. Other crowdsale operations (e.g. withdrawals and refunds, if applicable) are not affected. ([#832](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/832))
- * `ERC20`: `transferFrom` and `_burnFrom ` now emit `Approval` events, to represent the token's state comprehensively through events. ([#1524](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1524))
- * `ERC721`: added `_burn(uint256 tokenId)`, replacing the similar deprecated function (see below). ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
- * `ERC721`: added `_tokensOfOwner(address owner)`, allowing to internally retrieve the array of an account's owned tokens. ([#1522](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1522))
- * Crowdsales: all constructors are now `public`, meaning it is not necessary to extend these contracts in order to deploy them. The exception is `FinalizableCrowdsale`, since it is meaningless unless extended. ([#1564](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1564))
- * `SignedSafeMath`: added overflow-safe operations for signed integers (`int256`). ([#1559](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1559), [#1588](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1588))
+
+- Now targeting the 0.5.x line of Solidity compilers. For 0.4.24 support, use version 2.0 of OpenZeppelin.
+- `WhitelistCrowdsale`: a crowdsale where only whitelisted accounts (`WhitelistedRole`) can purchase tokens. Adding or removing accounts from the whitelist is done by whitelist admins (`WhitelistAdminRole`). Similar to the pre-2.0 `WhitelistedCrowdsale`. ([#1525](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1525), [#1589](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1589))
+- `RefundablePostDeliveryCrowdsale`: replacement for `RefundableCrowdsale` (deprecated, see below) where tokens are only granted once the crowdsale ends (if it meets its goal). ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))
+- `PausableCrowdsale`: allows for pausers (`PauserRole`) to pause token purchases. Other crowdsale operations (e.g. withdrawals and refunds, if applicable) are not affected. ([#832](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/832))
+- `ERC20`: `transferFrom` and `_burnFrom ` now emit `Approval` events, to represent the token's state comprehensively through events. ([#1524](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1524))
+- `ERC721`: added `_burn(uint256 tokenId)`, replacing the similar deprecated function (see below). ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
+- `ERC721`: added `_tokensOfOwner(address owner)`, allowing to internally retrieve the array of an account's owned tokens. ([#1522](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1522))
+- Crowdsales: all constructors are now `public`, meaning it is not necessary to extend these contracts in order to deploy them. The exception is `FinalizableCrowdsale`, since it is meaningless unless extended. ([#1564](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1564))
+- `SignedSafeMath`: added overflow-safe operations for signed integers (`int256`). ([#1559](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1559), [#1588](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1588))
 
 ### Improvements
- * The compiler version required by `Array` was behind the rest of the libray so it was updated to `v0.4.24`. ([#1553](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1553))
- * Now conforming to a 4-space indentation code style. ([1508](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1508))
- * `ERC20`: more gas efficient due to removed redundant `require`s. ([#1409](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1409))
- * `ERC721`: fixed a bug that prevented internal data structures from being properly cleaned, missing potential gas refunds. ([#1539](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1539) and [#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
- * `ERC721`: general gas savings on `transferFrom`, `_mint` and `_burn`, due to redudant `require`s and `SSTORE`s. ([#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
+
+- The compiler version required by `Array` was behind the rest of the library 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 redundant `require`s and `SSTORE`s. ([#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
 
 ### Bugfixes
 
 ### Breaking changes
 
 ### Deprecations
- * `ERC721._burn(address owner, uint256 tokenId)`: due to the `owner` parameter being unnecessary. ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
- * `RefundableCrowdsale`: due to trading abuse potential on crowdsales that miss their goal. ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))
+
+- `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_OF_CONDUCT.md

@@ -55,7 +55,7 @@ further defined and clarified by project maintainers.
 ## Enforcement
 
 Instances of abusive, harassing, or otherwise unacceptable behavior may be
-reported by contacting the project team at maintainers@openzeppelin.org. All
+reported by contacting the project team at contact@openzeppelin.com. All
 complaints will be reviewed and investigated and will result in a response that
 is deemed necessary and appropriate to the circumstances. The project team is
 obligated to maintain confidentiality with regard to the reporter of an incident.

CONTRIBUTING.md

@@ -1,71 +1,36 @@
-Contributing to OpenZeppelin Contracts
-=======
+# Contributing Guidelines
 
-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.
+There are many ways to contribute to OpenZeppelin Contracts.
 
-## Contribution guidelines
+## Troubleshooting
 
-Smart contracts manage value and are highly vulnerable to errors and attacks. We have very strict [guidelines], please make sure to review them!
+You can help other users in the community to solve their smart contract issues in the [OpenZeppelin Forum].
 
-## Creating Pull Requests (PRs)
+[OpenZeppelin Forum]: https://forum.openzeppelin.com/
 
-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.
+## Opening an issue
 
-## A typical workflow
+You can [open an issue] to suggest a feature or report a minor bug. For serious bugs please do not open an issue, instead refer to our [security policy] for appropriate steps.
 
-1) Make sure your fork is up to date with the main repository:
+If you believe your issue may be due to user error and not a problem in the library, consider instead posting a question on the [OpenZeppelin Forum].
 
-```
-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-contracts` represents your fork's local copy.
+Before opening an issue, be sure to search through the existing open and closed issues, and consider posting a comment in one of those instead.
 
-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)
-```
-git checkout -b fix/some-bug-#123
-```
+When requesting a new feature, include as many details as you can, especially around the use cases that motivate it. Features are prioritized according to the impact they may have on the ecosystem, so we appreciate information showing that the impact could be high.
 
-3) Make your changes, add your files, commit, and push to your fork.
+[security policy]: https://github.com/OpenZeppelin/openzeppelin-contracts/security
+[open an issue]: https://github.com/OpenZeppelin/openzeppelin-contracts/issues/new/choose
 
-```
-git add SomeFile.js
-git commit "Fix some bug #123"
-git push origin fix/some-bug-#123
-```
+## Submitting a pull request
 
-4) Run tests, linter, etc. This can be done by running local continuous integration and make sure it passes.
+If you would like to contribute code or documentation you may do so by forking the repository and submitting a pull request.
 
-```bash
-npm test
-npm run lint
-```
+Any non-trivial code contribution must be first discussed with the maintainers in an issue (see [Opening an issue](#opening-an-issue)). Only very minor changes are accepted without prior discussion.
 
-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.
+Make sure to read and follow the [engineering guidelines](./GUIDELINES.md). Run linter and tests to make sure your pull request is good before submitting it.
 
-5) Go to [github.com/OpenZeppelin/openzeppelin-contracts](https://github.com/OpenZeppelin/openzeppelin-contracts) in your web browser and issue a new pull request.
+Changelog entries should be added to each pull request by using [Changesets](https://github.com/changesets/changesets/).
 
-*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.
+When opening the pull request you will be presented with a template and a series of instructions. Read through it carefully and follow all the steps. Expect a review and feedback from the maintainers afterwards.
 
-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-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-contracts/labels/good%20first%20issue).
-
-Thanks for your time and code!
-
-[guidelines]: GUIDELINES.md
+If you're looking for a good place to start, look for issues labelled ["good first issue"](https://github.com/OpenZeppelin/openzeppelin-contracts/labels/good%20first%20issue)!

GUIDELINES.md

@@ -1,105 +1,117 @@
-Design Guidelines
-=======
+# Engineering Guidelines
 
-These are some global design goals in OpenZeppelin.
+## Testing
 
-#### 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.
+Code must be thoroughly tested with quality unit tests.
 
-#### 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.
+We defer to the [Moloch Testing Guide](https://github.com/MolochVentures/moloch/tree/master/test#readme) for specific recommendations, though not all of it is relevant here. Note the introduction:
 
-#### D2 - Naming Matters
+> Tests should be written, not only to verify correctness of the target code, but to be comprehensively reviewed by other programmers. Therefore, for mission critical Solidity code, the quality of the tests are just as important (if not more so) than the code itself, and should be written with the highest standards of clarity and elegance.
 
-We take our time with picking names. Code is going to be written once, and read hundreds of times. Renaming for clarity is encouraged.
+Every addition or change to the code must come with relevant and comprehensive tests.
 
-#### D3 - Tests
+Refactors should avoid simultaneous changes to 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.
+Flaky tests are not acceptable.
 
-#### D4 - Check preconditions and post-conditions
+The test suite should run automatically for every change in the repository, and in pull requests tests must pass before merging.
 
-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.
+The test suite coverage must be kept as close to 100% as possible, enforced in pull requests.
 
-#### D5 - Code Consistency
+In some cases unit tests may be insufficient and complementary techniques should be used:
 
-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.
+1. Property-based tests (aka. fuzzing) for math-heavy code.
+2. Formal verification for state machines.
 
-#### 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.
+## Code style
 
-# Style Guidelines
+Solidity code should be written in a consistent format enforced by a linter, following the official [Solidity Style Guide](https://docs.soliditylang.org/en/latest/style-guide.html). See below for further [Solidity Conventions](#solidity-conventions).
 
-The design guidelines have quite a high abstraction level. These style guidelines are more concrete and easier to apply, and also more opinionated. We value clean code and consistency, and those are prerequisites for us to include new code in the repository. Before proposing a change, please read these guidelines and take some time to familiarize yourself with the style of the existing codebase.
+The code should be simple and straightforward, prioritizing readability and understandability. Consistency and predictability should be maintained across the codebase. In particular, this applies to naming, which should be systematic, clear, and concise.
 
-## Solidity code
+Sometimes these guidelines may be broken if doing so brings significant efficiency gains, but explanatory comments should be added.
 
-In order to be consistent with all the other Solidity projects, we follow the
-[official recommendations documented in the Solidity style guide](http://solidity.readthedocs.io/en/latest/style-guide.html).
+Modularity should be pursued, but not at the cost of the above priorities.
 
-Any exception or additions specific to our project are documented below.
+## Documentation
 
-* Try to avoid acronyms and abbreviations.
+For contributors, project guidelines and processes must be documented publicly.
+
+For users, features must be abundantly documented. Documentation should include answers to common questions, solutions to common problems, and recommendations for critical decisions that the user may face.
+
+All changes to the core codebase (excluding tests, auxiliary scripts, etc.) must be documented in a changelog, except for purely cosmetic or documentation changes.
+
+## Peer review
+
+All changes must be submitted through pull requests and go through peer code review.
+
+The review must be approached by the reviewer in a similar way as if it was an audit of the code in question (but importantly it is not a substitute for and should not be considered an audit).
+
+Reviewers should enforce code and project guidelines.
+
+External contributions must be reviewed separately by multiple maintainers.
+
+## Automation
+
+Automation should be used as much as possible to reduce the possibility of human error and forgetfulness.
+
+Automations that make use of sensitive credentials must use secure secret management, and must be strengthened against attacks such as [those on GitHub Actions worklows](https://github.com/nikitastupin/pwnhub).
+
+Some other examples of automation are:
+
+- Looking for common security vulnerabilities or errors in our code (eg. reentrancy analysis).
+- Keeping dependencies up to date and monitoring for vulnerable dependencies.
+
+## Pull requests
+
+Pull requests are squash-merged to keep the `master` branch history clean. The title of the pull request becomes the commit message, so it should be written in a consistent format:
+
+1) Begin with a capital letter.
+2) Do not end with a period.
+3) Write in the imperative: "Add feature X" and not "Adds feature X" or "Added feature X".
+
+This repository does not follow conventional commits, so do not prefix the title with "fix:" or "feat:".
+
+Work in progress pull requests should be submitted as Drafts and should not be prefixed with "WIP:".
+
+Branch names don't matter, and commit messages within a pull request mostly don't matter either, although they can help the review process.
+
+# Solidity Conventions
+
+In addition to the official Solidity Style Guide we have a number of other conventions that must be followed.
 
 * All state variables should be private.
 
-* Private state variables should have an underscore prefix.
+  Changes to state should be accompanied by events, and in some cases it is not correct to arbitrarily set state. Encapsulating variables as private and only allowing modification via setters enables us to ensure that events and other rules are followed reliably and prevents this kind of user error.
 
-    ```
-    contract TestContract {
+* Internal or private state variables or functions should have an underscore prefix.
+
+  ```solidity
+  contract TestContract {
       uint256 private _privateVar;
       uint256 internal _internalVar;
-    }
-    ```
-
-* Parameters must not be prefixed with an underscore.
-
-    ```
-    function test(uint256 testParameter1, uint256 testParameter2) {
-    ...
-    }
-    ```
-
-* Internal and private functions should have an underscore prefix.
-
-    ```
-    function _testInternal() internal {
-      ...
-    }
-    ```
-
-    ```
-    function _testPrivate() private {
-      ...
-    }
-    ```
+      function _testInternal() internal { ... }
+      function _testPrivate() private { ... }
+  }
+  ```
 
 * Events should be emitted immediately after the state change that they
-  represent, and consequently they should be named in past tense.
+  represent, and should be named in the past tense.
 
-    ```
-    function _burn(address who, uint256 value) internal {
+  ```solidity
+  function _burn(address who, uint256 value) internal {
       super._burn(who, value);
       emit TokensBurned(who, value);
-    }
-    ```
+  }
+  ```
 
   Some standards (e.g. ERC20) use present tense, and in those cases the
-  standard specification prevails.
+  standard specification is used.
   
 * Interface names should have a capital I prefix.
 
-    ```
-    interface IERC777 {
-    ```
+  ```solidity
+  interface IERC777 {
+  ```
 
-
-## Tests
-
-* Tests Must be Written Elegantly
-
-    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.
-
-* 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.
+* Unchecked arithmetic blocks should contain comments explaining why overflow is guaranteed not to happen. If the reason is immediately apparent from the line above the unchecked block, the comment may be omitted.

LICENSE

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2016-2020 zOS Global Limited
+Copyright (c) 2016-2023 zOS Global Limited and contributors
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the

README.md

@@ -1,59 +1,66 @@
+> **Warning**
+> Version 5.0 is under active development. The code in this branch is not recommended for use.
+
 # <img src="logo.svg" alt="OpenZeppelin" height="40px">
 
-[![Docs](https://img.shields.io/badge/docs-%F0%9F%93%84-blue)](https://docs.openzeppelin.com/contracts)
 [![NPM Package](https://img.shields.io/npm/v/@openzeppelin/contracts.svg)](https://www.npmjs.org/package/@openzeppelin/contracts)
-[![Build Status](https://circleci.com/gh/OpenZeppelin/openzeppelin-contracts.svg?style=shield)](https://circleci.com/gh/OpenZeppelin/openzeppelin-contracts)
 [![Coverage Status](https://codecov.io/gh/OpenZeppelin/openzeppelin-contracts/graph/badge.svg)](https://codecov.io/gh/OpenZeppelin/openzeppelin-contracts)
+[![GitPOAPs](https://public-api.gitpoap.io/v1/repo/OpenZeppelin/openzeppelin-contracts/badge)](https://www.gitpoap.io/gh/OpenZeppelin/openzeppelin-contracts)
+[![Docs](https://img.shields.io/badge/docs-%F0%9F%93%84-yellow)](https://docs.openzeppelin.com/contracts)
+[![Forum](https://img.shields.io/badge/forum-%F0%9F%92%AC-yellow)](https://docs.openzeppelin.com/contracts)
 
 **A library for secure smart contract development.** Build on a solid foundation of community-vetted code.
 
  * 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 (_last full audit on v2.0.0_).
+
+:mage: **Not sure how to get started?** Check out [Contracts Wizard](https://wizard.openzeppelin.com/) — an interactive smart contract generator.
+
+:building_construction: **Want to scale your decentralized application?** Check out [OpenZeppelin Defender](https://openzeppelin.com/defender) — a secure platform for automating and monitoring your operations.
 
 ## Overview
 
 ### Installation
 
-```console
+```
 $ npm install @openzeppelin/contracts
 ```
 
-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.
+OpenZeppelin Contracts features a [stable API](https://docs.openzeppelin.com/contracts/releases-stability#api-stability), which means that your contracts won't break unexpectedly when upgrading to a newer minor version.
+
+An alternative to npm is to use the GitHub repository (`openzeppelin/openzeppelin-contracts`) to retrieve the contracts. When doing this, make sure to specify the tag for a release such as `v4.5.0`, instead of using the `master` branch.
 
 ### Usage
 
 Once installed, you can use the contracts in the library by importing them:
 
 ```solidity
-pragma solidity ^0.6.0;
+pragma solidity ^0.8.19;
 
 import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
 
 contract MyCollectible is ERC721 {
-    constructor() ERC721("MyCollectible", "MCO") public {
+    constructor() ERC721("MyCollectible", "MCO") {
     }
 }
 ```
 
 _If you're new to smart contract development, head to [Developing Smart Contracts](https://docs.openzeppelin.com/learn/developing-smart-contracts) to learn about creating a new project and compiling your contracts._
 
-To keep your system secure, you should **always** use the installed code as-is, and neither copy-paste it from online sources, nor modify it yourself. 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.
+To keep your system secure, you should **always** use the installed code as-is, and neither copy-paste it from online sources nor modify it yourself. The library is designed so that only the contracts and functions you use are deployed, so you don't need to worry about it needlessly increasing gas costs.
 
 ## Learn More
 
-The guides in the [docs site](https://docs.openzeppelin.com/contracts) will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
+The guides in the [documentation site](https://docs.openzeppelin.com/contracts) will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
 
 * [Access Control](https://docs.openzeppelin.com/contracts/access-control): decide who can perform each of the actions on your system.
 * [Tokens](https://docs.openzeppelin.com/contracts/tokens): create tradeable assets or collectives, and distribute them via [Crowdsales](https://docs.openzeppelin.com/contracts/crowdsales).
-* [Gas Station Network](https://docs.openzeppelin.com/contracts/gsn): let your users interact with your contracts without having to pay for gas themselves.
-* [Utilities](https://docs.openzeppelin.com/contracts/utilities): generic useful tools, including non-overflowing math, signature verification, and trustless paying systems.
+* [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.
+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 that 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.
@@ -61,18 +68,26 @@ Finally, you may want to take a look at the [guides on our blog](https://blog.op
 
 ## Security
 
-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.
+This project is maintained by [OpenZeppelin](https://openzeppelin.com) with the goal of providing a secure and reliable library of smart contract components for the ecosystem. We address security through risk management in various areas such as engineering and open source best practices, scoping and API design, multi-layered review processes, and incident response preparedness.
 
-The core development principles and strategies that OpenZeppelin is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.
+The security policy is detailed in [`SECURITY.md`](./SECURITY.md), and specifies how you can report security vulnerabilities, which versions will receive security patches, and how to stay informed about them. We run a [bug bounty program on Immunefi](https://immunefi.com/bounty/openzeppelin) to reward the responsible disclosure of vulnerabilities.
 
-The latest audit was done on October 2018 on version 2.0.0.
+The engineering guidelines we follow to promote project quality can be found in [`GUIDELINES.md`](./GUIDELINES.md).
 
-Please report any security issues you find to security@openzeppelin.org.
+Past audits can be found in [`audits/`](./audits).
+
+Smart contracts are a nascent technology and carry a high level of technical risk and uncertainty. Although OpenZeppelin is well known for its security audits, using OpenZeppelin Contracts is not a substitute for a security audit.
+
+OpenZeppelin Contracts is made available under the MIT License, which disclaims all warranties in relation to the project and which limits the liability of those that contribute and maintain the project, including OpenZeppelin. As set out further in the Terms, you acknowledge that you are solely responsible for any use of OpenZeppelin Contracts and you assume all risks associated with any such use.
 
 ## 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](CONTRIBUTING.md)!
+OpenZeppelin Contracts 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).
+OpenZeppelin Contracts is released under the [MIT License](LICENSE).
+
+## Legal
+
+Your use of this Project is governed by the terms found at www.openzeppelin.com/tos (the "Terms").

RELEASING.md

@@ -1,36 +1,47 @@
 # Releasing
 
-> Visit the documentation for [details about release schedule].
+> Visit the documentation for [details about release schedule](https://docs.openzeppelin.com/contracts/releases-stability).
 
-Start on an up-to-date `master` branch.
+OpenZeppelin Contracts uses a fully automated release process that takes care of compiling, packaging, and publishing the library, all of which is carried out in a clean CI environment (GitHub Actions), implemented in the ([`release-cycle`](.github/workflows/release-cycle.yml)) workflow. This helps to reduce the potential for human error and inconsistencies, and ensures that the release process is ongoing and reliable.
 
-Create the release branch with `npm run release start minor`.
+## Changesets
 
-Publish a release candidate with `npm run release rc`.
+[Changesets](https://github.com/changesets/changesets/) is used as part of our release process for `CHANGELOG.md` management. Each change that is relevant for the codebase is expected to include a changeset.
 
-Publish the final release with `npm run release final`.
+## Branching model
 
-Follow the general [OpenZeppelin release checklist].
+The release cycle happens on release branches called `release-vX.Y`. Each of these branches starts as a release candidate (rc) and is eventually promoted to final.
 
-[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
+A release branch can be updated with cherry-picked patches from `master`, or may sometimes be committed to directly in the case of old releases. These commits will lead to a new release candidate or a patch increment depending on the state of the release branch.
 
+```mermaid
+  %%{init: {'gitGraph': {'mainBranchName': 'master'}} }%%
+  gitGraph
+    commit id: "Feature A"
+    commit id: "Feature B"
+    branch release-vX.Y
+    commit id: "Start release"
+    commit id: "Release vX.Y.0-rc.0"
 
-## Merging the release branch
+    checkout master
+    commit id: "Feature C"
+    commit id: "Fix A"
 
-After the final release, the release branch should be merged back into `master`. This merge must not be squashed because it would lose the tagged release commit. Since the GitHub repo is set up to only allow squashed merges, the merge should be done locally and pushed.
+    checkout release-vX.Y
+    cherry-pick id: "Fix A" tag: ""
+    commit id: "Release vX.Y.0-rc.1"
+    commit id: "Release vX.Y.0"
 
-Make sure to have the latest changes from `upstream` in your local release branch.
+    checkout master
+    merge release-vX.Y
+    commit id: "Feature D"
+    commit id: "Patch B"
 
+    checkout release-vX.Y
+    cherry-pick id: "Patch B" tag: ""
+    commit id: "Release vX.Y.1"
+    
+    checkout master
+    merge release-vX.Y
+    commit id: "Feature E"
 ```
-git checkout release-vX.Y.Z
-git pull upstream
-```
-
-```
-git checkout master
-git merge --no-ff release-vX.Y.Z
-git push upstream master
-```
-
-The release branch can then be deleted on GitHub.

SECURITY.md

@@ -0,0 +1,42 @@
+# Security Policy
+
+Security vulnerabilities should be disclosed to the project maintainers through [Immunefi], or alternatively by email to security@openzeppelin.com.
+
+[Immunefi]: https://immunefi.com/bounty/openzeppelin
+
+## Bug Bounty
+
+Responsible disclosure of security vulnerabilities is rewarded through a bug bounty program on [Immunefi].
+
+There is a bonus reward for issues introduced in release candidates that are reported before making it into a stable release.
+
+## Security Patches
+
+Security vulnerabilities will be patched as soon as responsibly possible, and published as an advisory on this repository (see [advisories]) and on the affected npm packages.
+
+[advisories]: https://github.com/OpenZeppelin/openzeppelin-contracts/security/advisories
+
+Projects that build on OpenZeppelin Contracts are encouraged to clearly state, in their source code and websites, how to be contacted about security issues in the event that a direct notification is considered necessary. We recommend including it in the NatSpec for the contract as `/// @custom:security-contact security@example.com`.
+
+Additionally, we recommend installing the library through npm and setting up vulnerability alerts such as [Dependabot].
+
+[Dependabot]: https://docs.github.com/en/code-security/supply-chain-security/understanding-your-software-supply-chain/about-supply-chain-security#what-is-dependabot
+
+### Supported Versions
+
+Security patches will be released for the latest minor of a given major release. For example, if an issue is found in versions >=4.6.0 and the latest is 4.8.0, the patch will be released only in version 4.8.1.
+
+Only critical severity bug fixes will be backported to past major releases.
+
+| Version | Critical security fixes | Other security fixes |
+| ------- | ----------------------- | -------------------- |
+| 4.x     | :white_check_mark:      | :white_check_mark:   |
+| 3.4     | :white_check_mark:      | :x:                  |
+| 2.5     | :white_check_mark:      | :x:                  |
+| < 2.0   | :x:                     | :x:                  |
+
+Note as well that the Solidity language itself only guarantees security updates for the latest release.
+
+## Legal
+
+Smart contracts are a nascent techology and carry a high level of technical risk and uncertainty.  OpenZeppelin Contracts is made available under the MIT License, which disclaims all warranties in relation to the project and which limits the liability of those that contribute and maintain the project, including OpenZeppelin. Your use of the project is also governed by the terms found at www.openzeppelin.com/tos (the "Terms"). As set out in the Terms, you are solely responsible for any use of OpenZeppelin Contracts and you assume all risks associated with any such use. This Security Policy in no way evidences or represents an on-going duty by any contributor, including OpenZeppelin, to correct any flaws or alert you to all or any of the potential risks of utilizing the project.

audits/2017-03.md

@@ -1,5 +1,7 @@
 # OpenZeppelin Audit
 
+NOTE ON 2021-07-19: This report makes reference to Zeppelin, OpenZeppelin, OpenZeppelin Contracts, the OpenZeppelin team, and OpenZeppelin library. Many of these things have since been renamed and know that this audit applies to what is currently called the OpenZeppelin Contracts which are maintained by the OpenZeppelin Contracts Community.
+
 March, 2017
 Authored by Dennis Peterson and Peter Vessenes
 
@@ -131,7 +133,7 @@ I presume that the goal of this contract is to allow and annotate a migration to
 
 We like these pauses! Note that these allow significant griefing potential by owners, and that this might not be obvious to participants in smart contracts using the OpenZeppelin framework. We would recommend that additional sample logic be added to for instance the TokenContract showing safer use of the pause and resume functions. In particular, we would recommend a timelock after which anyone could unpause the contract.
 
-The modifers use the pattern `if(bool){_;}`. This is fine for functions that return false upon failure, but could be problematic for functions expected to throw upon failure. See our comments above on standardizing on `throw` or `return(false)`.
+The modifiers use the pattern `if(bool){_;}`. This is fine for functions that return false upon failure, but could be problematic for functions expected to throw upon failure. See our comments above on standardizing on `throw` or `return(false)`.
 
 ## Ownership
 

audits/README.md

@@ -0,0 +1,16 @@
+# Audits
+
+| Date         | Version | Commit    | Auditor      | Scope                | Links                                                       |
+| ------------ | ------- | --------- | ------------ | -------------------- | ----------------------------------------------------------- |
+| May 2023     | v4.9.0  | `91df66c` | OpenZeppelin | v4.9 Changes         | [🔗](./2023-05-v4.9.pdf)                                    |
+| October 2022 | v4.8.0  | `14f98db` | OpenZeppelin | ERC4626, Checkpoints | [🔗](./2022-10-ERC4626.pdf) [🔗](./2022-10-Checkpoints.pdf) |
+| October 2018 | v2.0.0  | `dac5bcc` | LevelK       | Everything           | [🔗](./2018-10.pdf)                                         |
+| March 2017   | v1.0.4  | `9c5975a` | New Alchemy  | Everything           | [🔗](./2017-03.md)                                          |
+
+# Formal Verification
+
+| Date         | Version | Commit    | Tool    | Scope                                                                                                                            | Links                                |
+| ------------ | ------- | --------- | ------- | -------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------ |
+| May 2022     | v4.7.0  | `109778c` | Certora | Initializable, GovernorPreventLateQuorum, ERC1155Burnable, ERC1155Pausable, ERC1155Supply, ERC1155Holder, ERC1155Receiver        | [🔗](../certora/reports/2022-05.pdf) |
+| March 2022   | v4.4.0  | `4088540` | Certora | ERC20Votes, ERC20FlashMint, ERC20Wrapper, TimelockController, ERC721Votes, Votes, AccessControl, ERC1155                         | [🔗](../certora/reports/2022-03.pdf) |
+| October 2021 | v4.4.0  | `4088540` | Certora | Governor, GovernorCountingSimple, GovernorProposalThreshold, GovernorTimelockControl, GovernorVotes, GovernorVotesQuorumFraction | [🔗](../certora/reports/2021-10.pdf) |

certora/.gitignore

@@ -0,0 +1 @@
+patched

certora/Makefile

@@ -0,0 +1,54 @@
+default: help
+
+SRC   := ../contracts
+DST   := patched
+DIFF  := diff
+SRCS  := $(shell find $(SRC) -type f)
+DSTS  := $(shell find $(DST) -type f)
+DIFFS := $(shell find $(DIFF) -type f)
+
+###############################################################################
+# Apply all patches in the $DIFF folder to the $DST folder
+apply: $(DST) $(patsubst $(DIFF)/%.patch,$(DST)/%,$(subst _,/,$(DIFFS)))
+
+# Reset the $DST folder
+$(DST): FORCE
+	@rm -rf $@
+	@cp -r $(SRC) $@
+
+# Update a solidity file in the $DST directory using the corresponding patch
+$(DST)/%.sol: FORCE
+	@echo Applying patch to $@
+	@patch -p0 -d $(DST) < $(patsubst $(DST)_%,$(DIFF)/%.patch,$(subst /,_,$@))
+
+###############################################################################
+# Record all difference between $SRC and $DST in patches
+record: $(DIFF) $(patsubst %,$(DIFF)/%.patch,$(subst /,_,$(subst $(SRC)/,,$(SRCS)) $(subst $(DST)/,,$(DSTS))))
+
+# Create the $DIFF folder
+$(DIFF): FORCE
+	@rm -rf $@
+	@mkdir $@
+
+# Create the patch file by comparing the source and the destination
+$(DIFF)/%.patch: FORCE
+	@echo Generating patch $@
+	@diff -ruN \
+		$(patsubst $(DIFF)/%.patch,$(SRC)/%,$(subst _,/,$@)) \
+		$(patsubst $(DIFF)/%.patch,$(DST)/%,$(subst _,/,$@)) \
+		| sed 's+$(SRC)/++g' \
+		| sed 's+$(DST)/++g' \
+		> $@
+	@[ -s $@ ] || rm $@
+
+###############################################################################
+help:
+	@echo "usage:"
+	@echo "  make apply:  create $(DST) directory by applying the patches to $(SRC)"
+	@echo "  make record: record the patches capturing the differences between $(SRC) and $(DST)"
+	@echo "  make clean:  remove all generated files (those ignored by git)"
+
+clean:
+	git clean -fdX
+
+FORCE: ;

certora/README.md

@@ -0,0 +1,60 @@
+# Running the certora verification tool
+
+These instructions detail the process for running Certora Verification Tool on OpenZeppelin Contracts.
+
+Documentation for CVT and the specification language are available [here](https://certora.atlassian.net/wiki/spaces/CPD/overview).
+
+## Prerequisites
+
+Follow the [Certora installation guide](https://docs.certora.com/en/latest/docs/user-guide/getting-started/install.html) in order to get the Certora Prover Package and the `solc` executable folder in your path.
+
+> **Note**
+> An API Key is required for local testing. Although the prover will run on a Github Actions' CI environment on selected Pull Requests.
+
+## Running the verification
+
+The Certora Verification Tool proves specs for contracts, which are defined by the `./specs.json` file along with their pre-configured options.
+
+The verification script `./run.js` is used to submit verification jobs to the Certora Verification service.
+
+You can run it from the root of the repository with the following command:
+
+```bash
+node certora/run.js [[CONTRACT_NAME:]SPEC_NAME] [OPTIONS...]
+```
+
+Where:
+
+- `CONTRACT_NAME` matches the `contract` key in the `./spec.json` file and may be empty. It will run all matching contracts if not provided.
+- `SPEC_NAME` refers to a `spec` key from the `./specs.json` file. It will run every spec if not provided.
+- `OPTIONS` extend the [Certora Prover CLI options](https://docs.certora.com/en/latest/docs/prover/cli/options.html#certora-prover-cli-options) and will respect the preconfigured options in the `specs.json` file.
+
+> **Note**
+> A single spec may be configured to run for multiple contracts, whereas a single contract may run multiple specs.
+
+Example usage:
+
+```bash
+node certora/run.js AccessControl # Run the AccessControl spec against every contract implementing it
+```
+
+## Adapting to changes in the contracts
+
+Some of our rules require the code to be simplified in various ways. Our primary tool for performing these simplifications is to run verification on a contract that extends the original contracts and overrides some of the methods. These "harness" contracts can be found in the `certora/harness` directory.
+
+This pattern does require some modifications to the original code: some methods need to be made virtual or public, for example. These changes are handled by applying a patch
+to the code before verification by running:
+
+```bash
+make -C certora apply
+```
+
+Before running the `certora/run.js` script, it's required to apply the corresponding patches to the `contracts` directory, placing the output in the `certora/patched` directory. Then, the contracts are verified by running the verification for the `certora/patched` directory.
+
+If the original contracts change, it is possible to create a conflict with the patch. In this case, the verify scripts will report an error message and output rejected changes in the `patched` directory. After merging the changes, run `make record` in the `certora` directory; this will regenerate the patch file, which can then be checked into git.
+
+For more information about the `make` scripts available, run:
+
+```bash
+make -C certora help
+```

certora/diff/token_ERC721_ERC721.sol.patch

@@ -0,0 +1,14 @@
+--- token/ERC721/ERC721.sol	2023-03-07 10:48:47.736822221 +0100
++++ token/ERC721/ERC721.sol	2023-03-09 19:49:39.669338673 +0100
+@@ -199,6 +199,11 @@
+         return _owners[tokenId];
+     }
+ 
++    // FV
++    function _getApproved(uint256 tokenId) internal view returns (address) {
++        return _tokenApprovals[tokenId];
++    }
++
+     /**
+      * @dev Returns whether `tokenId` exists.
+      *

certora/harnesses/AccessControlDefaultAdminRulesHarness.sol

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/access/AccessControlDefaultAdminRules.sol";
+
+contract AccessControlDefaultAdminRulesHarness is AccessControlDefaultAdminRules {
+    uint48 private _delayIncreaseWait;
+
+    constructor(
+        uint48 initialDelay,
+        address initialDefaultAdmin,
+        uint48 delayIncreaseWait
+    ) AccessControlDefaultAdminRules(initialDelay, initialDefaultAdmin) {
+        _delayIncreaseWait = delayIncreaseWait;
+    }
+
+    // FV
+    function pendingDefaultAdmin_() external view returns (address) {
+        (address newAdmin, ) = pendingDefaultAdmin();
+        return newAdmin;
+    }
+
+    function pendingDefaultAdminSchedule_() external view returns (uint48) {
+        (, uint48 schedule) = pendingDefaultAdmin();
+        return schedule;
+    }
+
+    function pendingDelay_() external view returns (uint48) {
+        (uint48 newDelay, ) = pendingDefaultAdminDelay();
+        return newDelay;
+    }
+
+    function pendingDelaySchedule_() external view returns (uint48) {
+        (, uint48 schedule) = pendingDefaultAdminDelay();
+        return schedule;
+    }
+
+    function delayChangeWait_(uint48 newDelay) external view returns (uint48) {
+        return _delayChangeWait(newDelay);
+    }
+
+    // Overrides
+    function defaultAdminDelayIncreaseWait() public view override returns (uint48) {
+        return _delayIncreaseWait;
+    }
+}

certora/harnesses/AccessControlHarness.sol

@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/access/AccessControl.sol";
+
+contract AccessControlHarness is AccessControl {}

certora/harnesses/DoubleEndedQueueHarness.sol

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/utils/structs/DoubleEndedQueue.sol";
+
+contract DoubleEndedQueueHarness {
+    using DoubleEndedQueue for DoubleEndedQueue.Bytes32Deque;
+
+    DoubleEndedQueue.Bytes32Deque private _deque;
+
+    function pushFront(bytes32 value) external {
+        _deque.pushFront(value);
+    }
+
+    function pushBack(bytes32 value) external {
+        _deque.pushBack(value);
+    }
+
+    function popFront() external returns (bytes32 value) {
+        return _deque.popFront();
+    }
+
+    function popBack() external returns (bytes32 value) {
+        return _deque.popBack();
+    }
+
+    function clear() external {
+        _deque.clear();
+    }
+
+    function begin() external view returns (int128) {
+        return _deque._begin;
+    }
+
+    function end() external view returns (int128) {
+        return _deque._end;
+    }
+
+    function length() external view returns (uint256) {
+        return _deque.length();
+    }
+
+    function empty() external view returns (bool) {
+        return _deque.empty();
+    }
+
+    function front() external view returns (bytes32 value) {
+        return _deque.front();
+    }
+
+    function back() external view returns (bytes32 value) {
+        return _deque.back();
+    }
+
+    function at_(uint256 index) external view returns (bytes32 value) {
+        return _deque.at(index);
+    }
+}

certora/harnesses/ERC20FlashMintHarness.sol

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/token/ERC20/ERC20.sol";
+import "../patched/token/ERC20/extensions/ERC20Permit.sol";
+import "../patched/token/ERC20/extensions/ERC20FlashMint.sol";
+
+contract ERC20FlashMintHarness is ERC20, ERC20Permit, ERC20FlashMint {
+    uint256 someFee;
+    address someFeeReceiver;
+
+    constructor(string memory name, string memory symbol) ERC20(name, symbol) ERC20Permit(name) {}
+
+    function mint(address account, uint256 amount) external {
+        _mint(account, amount);
+    }
+
+    function burn(address account, uint256 amount) external {
+        _burn(account, amount);
+    }
+
+    // public accessor
+    function flashFeeReceiver() public view returns (address) {
+        return someFeeReceiver;
+    }
+
+    // internal hook
+    function _flashFee(address, uint256) internal view override returns (uint256) {
+        return someFee;
+    }
+
+    function _flashFeeReceiver() internal view override returns (address) {
+        return someFeeReceiver;
+    }
+}

certora/harnesses/ERC20PermitHarness.sol

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/token/ERC20/extensions/ERC20Permit.sol";
+
+contract ERC20PermitHarness is ERC20Permit {
+    constructor(string memory name, string memory symbol) ERC20(name, symbol) ERC20Permit(name) {}
+
+    function mint(address account, uint256 amount) external {
+        _mint(account, amount);
+    }
+
+    function burn(address account, uint256 amount) external {
+        _burn(account, amount);
+    }
+}

certora/harnesses/ERC20WrapperHarness.sol

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/token/ERC20/extensions/ERC20Wrapper.sol";
+
+contract ERC20WrapperHarness is ERC20Wrapper {
+    constructor(IERC20 _underlying, string memory _name, string memory _symbol) ERC20(_name, _symbol) ERC20Wrapper(_underlying) {}
+
+    function underlyingTotalSupply() public view returns (uint256) {
+        return underlying().totalSupply();
+    }
+
+    function underlyingBalanceOf(address account) public view returns (uint256) {
+        return underlying().balanceOf(account);
+    }
+
+    function underlyingAllowanceToThis(address account) public view returns (uint256) {
+        return underlying().allowance(account, address(this));
+    }
+
+    function recover(address account) public returns (uint256) {
+        return _recover(account);
+    }
+}

certora/harnesses/ERC3156FlashBorrowerHarness.sol

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: MIT
+
+import "../patched/interfaces/IERC3156FlashBorrower.sol";
+
+pragma solidity ^0.8.19;
+
+contract ERC3156FlashBorrowerHarness is IERC3156FlashBorrower {
+    bytes32 somethingToReturn;
+
+    function onFlashLoan(address, address, uint256, uint256, bytes calldata) external view override returns (bytes32) {
+        return somethingToReturn;
+    }
+}

certora/harnesses/ERC721Harness.sol

@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/token/ERC721/ERC721.sol";
+
+contract ERC721Harness is ERC721 {
+    constructor(string memory name, string memory symbol) ERC721(name, symbol) {}
+
+    function mint(address account, uint256 tokenId) external {
+        _mint(account, tokenId);
+    }
+
+    function safeMint(address to, uint256 tokenId) external {
+        _safeMint(to, tokenId);
+    }
+
+    function safeMint(address to, uint256 tokenId, bytes memory data) external {
+        _safeMint(to, tokenId, data);
+    }
+
+    function burn(uint256 tokenId) external {
+        _burn(tokenId);
+    }
+
+    function tokenExists(uint256 tokenId) external view returns (bool) {
+        return _exists(tokenId);
+    }
+
+    function unsafeOwnerOf(uint256 tokenId) external view returns (address) {
+        return _ownerOf(tokenId);
+    }
+
+    function unsafeGetApproved(uint256 tokenId) external view returns (address) {
+        return _getApproved(tokenId);
+    }
+}

certora/harnesses/ERC721ReceiverHarness.sol

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/interfaces/IERC721Receiver.sol";
+
+contract ERC721ReceiverHarness is IERC721Receiver {
+    function onERC721Received(address, address, uint256, bytes calldata) external pure returns (bytes4) {
+        return this.onERC721Received.selector;
+    }
+}

certora/harnesses/EnumerableMapHarness.sol

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/utils/structs/EnumerableMap.sol";
+
+contract EnumerableMapHarness {
+    using EnumerableMap for EnumerableMap.Bytes32ToBytes32Map;
+
+    EnumerableMap.Bytes32ToBytes32Map private _map;
+
+    function set(bytes32 key, bytes32 value) public returns (bool) {
+        return _map.set(key, value);
+    }
+
+    function remove(bytes32 key) public returns (bool) {
+        return _map.remove(key);
+    }
+
+    function contains(bytes32 key) public view returns (bool) {
+        return _map.contains(key);
+    }
+
+    function length() public view returns (uint256) {
+        return _map.length();
+    }
+
+    function key_at(uint256 index) public view returns (bytes32) {
+        (bytes32 key,) = _map.at(index);
+        return key;
+    }
+
+    function value_at(uint256 index) public view returns (bytes32) {
+        (,bytes32 value) = _map.at(index);
+        return value;
+    }
+
+    function tryGet_contains(bytes32 key) public view returns (bool) {
+        (bool contained,) = _map.tryGet(key);
+        return contained;
+    }
+
+    function tryGet_value(bytes32 key) public view returns (bytes32) {
+        (,bytes32 value) = _map.tryGet(key);
+        return value;
+    }
+
+    function get(bytes32 key) public view returns (bytes32) {
+        return _map.get(key);
+    }
+
+    function _indexOf(bytes32 key) public view returns (uint256) {
+        return _map._keys._inner._indexes[key];
+    }
+}

certora/harnesses/EnumerableSetHarness.sol

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/utils/structs/EnumerableSet.sol";
+
+contract EnumerableSetHarness {
+    using EnumerableSet for EnumerableSet.Bytes32Set;
+
+    EnumerableSet.Bytes32Set private _set;
+
+    function add(bytes32 value) public returns (bool) {
+        return _set.add(value);
+    }
+
+    function remove(bytes32 value) public returns (bool) {
+        return _set.remove(value);
+    }
+
+    function contains(bytes32 value) public view returns (bool) {
+        return _set.contains(value);
+    }
+
+    function length() public view returns (uint256) {
+        return _set.length();
+    }
+
+    function at_(uint256 index) public view returns (bytes32) {
+        return _set.at(index);
+    }
+
+    function _indexOf(bytes32 value) public view returns (uint256) {
+        return _set._inner._indexes[value];
+    }
+}

certora/harnesses/InitializableHarness.sol

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.19;
+
+import "../patched/proxy/utils/Initializable.sol";
+
+contract InitializableHarness is Initializable {
+    function initialize()          public initializer      {}
+    function reinitialize(uint8 n) public reinitializer(n) {}
+    function disable()             public { _disableInitializers(); }
+
+    function nested_init_init()                     public initializer      { initialize();    }
+    function nested_init_reinit(uint8 m)            public initializer      { reinitialize(m); }
+    function nested_reinit_init(uint8 n)            public reinitializer(n) { initialize();    }
+    function nested_reinit_reinit(uint8 n, uint8 m) public reinitializer(n) { reinitialize(m); }
+
+    function version() public view returns (uint8) {
+        return _getInitializedVersion();
+    }
+
+    function initializing() public view returns (bool) {
+        return _isInitializing();
+    }
+}

certora/harnesses/Ownable2StepHarness.sol

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/access/Ownable2Step.sol";
+
+contract Ownable2StepHarness is Ownable2Step {
+  function restricted() external onlyOwner {}
+}

certora/harnesses/OwnableHarness.sol

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/access/Ownable.sol";
+
+contract OwnableHarness is Ownable {
+  function restricted() external onlyOwner {}
+}

certora/harnesses/PausableHarness.sol

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "../patched/security/Pausable.sol";
+
+contract PausableHarness is Pausable {
+    function pause() external {
+        _pause();
+    }
+
+    function unpause() external {
+        _unpause();
+    }
+
+    function onlyWhenPaused() external whenPaused {}
+
+    function onlyWhenNotPaused() external whenNotPaused {}
+}

certora/harnesses/TimelockControllerHarness.sol

@@ -0,0 +1,12 @@
+pragma solidity ^0.8.19;
+
+import "../patched/governance/TimelockController.sol";
+
+contract TimelockControllerHarness is TimelockController {
+    constructor(
+        uint256 minDelay,
+        address[] memory proposers,
+        address[] memory executors,
+        address admin
+    ) TimelockController(minDelay, proposers, executors, admin) {}
+}

certora/run.js

@@ -0,0 +1,146 @@
+#!/usr/bin/env node
+
+// USAGE:
+//    node certora/run.js [[CONTRACT_NAME:]SPEC_NAME]* [--all] [--options OPTIONS...] [--specs PATH]
+// EXAMPLES:
+//    node certora/run.js --all
+//    node certora/run.js AccessControl
+//    node certora/run.js AccessControlHarness:AccessControl
+
+const proc = require('child_process');
+const { PassThrough } = require('stream');
+const events = require('events');
+
+const argv = require('yargs')
+  .env('')
+  .options({
+    all: {
+      alias: 'a',
+      type: 'boolean',
+    },
+    spec: {
+      alias: 's',
+      type: 'string',
+      default: __dirname + '/specs.json',
+    },
+    parallel: {
+      alias: 'p',
+      type: 'number',
+      default: 4,
+    },
+    options: {
+      alias: 'o',
+      type: 'array',
+      default: [],
+    },
+  }).argv;
+
+function match(entry, request) {
+  const [reqSpec, reqContract] = request.split(':').reverse();
+  return entry.spec == reqSpec && (!reqContract || entry.contract == reqContract);
+}
+
+const specs = require(argv.spec).filter(s => argv.all || argv._.some(r => match(s, r)));
+const limit = require('p-limit')(argv.parallel);
+
+if (argv._.length == 0 && !argv.all) {
+  console.error(`Warning: No specs requested. Did you forgot to toggle '--all'?`);
+}
+
+for (const r of argv._) {
+  if (!specs.some(s => match(s, r))) {
+    console.error(`Error: Requested spec '${r}' not found in ${argv.spec}`);
+    process.exitCode = 1;
+  }
+}
+
+if (process.exitCode) {
+  process.exit(process.exitCode);
+}
+
+for (const { spec, contract, files, options = [] } of specs) {
+  limit(runCertora, spec, contract, files, [...options.flatMap(opt => opt.split(' ')), ...argv.options]);
+}
+
+// Run certora, aggregate the output and print it at the end
+async function runCertora(spec, contract, files, options = []) {
+  const args = [...files, '--verify', `${contract}:certora/specs/${spec}.spec`, ...options];
+  const child = proc.spawn('certoraRun', args);
+
+  const stream = new PassThrough();
+  const output = collect(stream);
+
+  child.stdout.pipe(stream, { end: false });
+  child.stderr.pipe(stream, { end: false });
+
+  // as soon as we have a job id, print the output link
+  stream.on('data', function logStatusUrl(data) {
+    const { '-DjobId': jobId, '-DuserId': userId } = Object.fromEntries(
+      data
+        .toString('utf8')
+        .match(/-D\S+=\S+/g)
+        ?.map(s => s.split('=')) || [],
+    );
+
+    if (jobId && userId) {
+      console.error(`[${spec}] https://prover.certora.com/output/${userId}/${jobId}/`);
+      stream.off('data', logStatusUrl);
+    }
+  });
+
+  // wait for process end
+  const [code, signal] = await events.once(child, 'exit');
+
+  // error
+  if (code || signal) {
+    console.error(`[${spec}] Exited with code ${code || signal}`);
+    process.exitCode = 1;
+  }
+
+  // get all output
+  stream.end();
+
+  // write results in markdown format
+  writeEntry(spec, contract, code || signal, (await output).match(/https:\/\/prover.certora.com\/output\/\S*/)?.[0]);
+
+  // write all details
+  console.error(`+ certoraRun ${args.join(' ')}\n` + (await output));
+}
+
+// Collects stream data into a string
+async function collect(stream) {
+  const buffers = [];
+  for await (const data of stream) {
+    const buf = Buffer.isBuffer(data) ? data : Buffer.from(data);
+    buffers.push(buf);
+  }
+  return Buffer.concat(buffers).toString('utf8');
+}
+
+// Formatting
+let hasHeader = false;
+
+function formatRow(...array) {
+  return ['', ...array, ''].join(' | ');
+}
+
+function writeHeader() {
+  console.log(formatRow('spec', 'contract', 'result', 'status', 'output'));
+  console.log(formatRow('-', '-', '-', '-', '-'));
+}
+
+function writeEntry(spec, contract, success, url) {
+  if (!hasHeader) {
+    hasHeader = true;
+    writeHeader();
+  }
+  console.log(
+    formatRow(
+      spec,
+      contract,
+      success ? ':x:' : ':heavy_check_mark:',
+      url ? `[link](${url?.replace('/output/', '/jobStatus/')})` : 'error',
+      url ? `[link](${url})` : 'error',
+    ),
+  );
+}

certora/specs.json

@@ -0,0 +1,86 @@
+[
+  {
+    "spec": "Pausable",
+    "contract": "PausableHarness",
+    "files": ["certora/harnesses/PausableHarness.sol"]
+  },
+  {
+    "spec": "AccessControl",
+    "contract": "AccessControlHarness",
+    "files": ["certora/harnesses/AccessControlHarness.sol"]
+  },
+  {
+    "spec": "AccessControlDefaultAdminRules",
+    "contract": "AccessControlDefaultAdminRulesHarness",
+    "files": ["certora/harnesses/AccessControlDefaultAdminRulesHarness.sol"]
+  },
+  {
+    "spec": "DoubleEndedQueue",
+    "contract": "DoubleEndedQueueHarness",
+    "files": ["certora/harnesses/DoubleEndedQueueHarness.sol"]
+  },
+  {
+    "spec": "Ownable",
+    "contract": "OwnableHarness",
+    "files": ["certora/harnesses/OwnableHarness.sol"]
+  },
+  {
+    "spec": "Ownable2Step",
+    "contract": "Ownable2StepHarness",
+    "files": ["certora/harnesses/Ownable2StepHarness.sol"]
+  },
+  {
+    "spec": "ERC20",
+    "contract": "ERC20PermitHarness",
+    "files": ["certora/harnesses/ERC20PermitHarness.sol"],
+    "options": ["--optimistic_loop"]
+  },
+  {
+    "spec": "ERC20FlashMint",
+    "contract": "ERC20FlashMintHarness",
+    "files": [
+      "certora/harnesses/ERC20FlashMintHarness.sol",
+      "certora/harnesses/ERC3156FlashBorrowerHarness.sol"
+    ],
+    "options": ["--optimistic_loop"]
+  },
+  {
+    "spec": "ERC20Wrapper",
+    "contract": "ERC20WrapperHarness",
+    "files": [
+      "certora/harnesses/ERC20PermitHarness.sol",
+      "certora/harnesses/ERC20WrapperHarness.sol"
+    ],
+    "options": [
+      "--link ERC20WrapperHarness:_underlying=ERC20PermitHarness",
+      "--optimistic_loop"
+    ]
+  },
+  {
+    "spec": "ERC721",
+    "contract": "ERC721Harness",
+    "files": ["certora/harnesses/ERC721Harness.sol", "certora/harnesses/ERC721ReceiverHarness.sol"],
+    "options": ["--optimistic_loop"]
+  },
+  {
+    "spec": "Initializable",
+    "contract": "InitializableHarness",
+    "files": ["certora/harnesses/InitializableHarness.sol"]
+  },
+  {
+    "spec": "EnumerableSet",
+    "contract": "EnumerableSetHarness",
+    "files": ["certora/harnesses/EnumerableSetHarness.sol"]
+  },
+  {
+    "spec": "EnumerableMap",
+    "contract": "EnumerableMapHarness",
+    "files": ["certora/harnesses/EnumerableMapHarness.sol"]
+  },
+  {
+    "spec": "TimelockController",
+    "contract": "TimelockControllerHarness",
+    "files": ["certora/harnesses/TimelockControllerHarness.sol"],
+    "options": ["--optimistic_hashing", "--optimistic_loop"]
+  }
+]

certora/specs/AccessControl.spec

@@ -0,0 +1,126 @@
+import "helpers/helpers.spec"
+import "methods/IAccessControl.spec"
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Definitions                                                                                                         │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+definition DEFAULT_ADMIN_ROLE() returns bytes32 = 0x0000000000000000000000000000000000000000000000000000000000000000;
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Identify entrypoints: only grantRole, revokeRole and renounceRole can alter permissions                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule onlyGrantCanGrant(env e, method f, bytes32 role, address account) {
+    calldataarg args;
+
+    bool hasRoleBefore = hasRole(role, account);
+    f(e, args);
+    bool hasRoleAfter = hasRole(role, account);
+
+    assert (
+        !hasRoleBefore &&
+        hasRoleAfter
+    ) => (
+        f.selector == grantRole(bytes32, address).selector
+    );
+
+    assert (
+        hasRoleBefore &&
+        !hasRoleAfter
+    ) => (
+        f.selector == revokeRole(bytes32, address).selector ||
+        f.selector == renounceRole(bytes32, address).selector
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: grantRole only affects the specified user/role combo                                          │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule grantRoleEffect(env e, bytes32 role) {
+    require nonpayable(e);
+
+    bytes32 otherRole;
+    address account;
+    address otherAccount;
+
+    bool isCallerAdmin = hasRole(getRoleAdmin(role), e.msg.sender);
+    bool hasOtherRoleBefore = hasRole(otherRole, otherAccount);
+
+    grantRole@withrevert(e, role, account);
+    bool success = !lastReverted;
+
+    bool hasOtherRoleAfter = hasRole(otherRole, otherAccount);
+
+    // liveness
+    assert success <=> isCallerAdmin;
+
+    // effect
+    assert success => hasRole(role, account);
+
+    // no side effect
+    assert hasOtherRoleBefore != hasOtherRoleAfter => (role == otherRole && account == otherAccount);
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: revokeRole only affects the specified user/role combo                                         │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule revokeRoleEffect(env e, bytes32 role) {
+    require nonpayable(e);
+
+    bytes32 otherRole;
+    address account;
+    address otherAccount;
+
+    bool isCallerAdmin = hasRole(getRoleAdmin(role), e.msg.sender);
+    bool hasOtherRoleBefore = hasRole(otherRole, otherAccount);
+
+    revokeRole@withrevert(e, role, account);
+    bool success = !lastReverted;
+
+    bool hasOtherRoleAfter = hasRole(otherRole, otherAccount);
+
+    // liveness
+    assert success <=> isCallerAdmin;
+
+    // effect
+    assert success => !hasRole(role, account);
+
+    // no side effect
+    assert hasOtherRoleBefore != hasOtherRoleAfter => (role == otherRole && account == otherAccount);
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: renounceRole only affects the specified user/role combo                                       │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule renounceRoleEffect(env e, bytes32 role) {
+    require nonpayable(e);
+
+    bytes32 otherRole;
+    address account;
+    address otherAccount;
+
+    bool hasOtherRoleBefore = hasRole(otherRole, otherAccount);
+
+    renounceRole@withrevert(e, role, account);
+    bool success = !lastReverted;
+
+    bool hasOtherRoleAfter = hasRole(otherRole, otherAccount);
+
+    // liveness
+    assert success <=> account == e.msg.sender;
+
+    // effect
+    assert success => !hasRole(role, account);
+
+    // no side effect
+    assert hasOtherRoleBefore != hasOtherRoleAfter => (role == otherRole && account == otherAccount);
+}

certora/specs/AccessControlDefaultAdminRules.spec

@@ -0,0 +1,464 @@
+import "helpers/helpers.spec"
+import "methods/IAccessControlDefaultAdminRules.spec"
+import "methods/IAccessControl.spec"
+import "AccessControl.spec"
+
+use rule onlyGrantCanGrant filtered {
+  f -> f.selector != acceptDefaultAdminTransfer().selector
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Helpers                                                                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+definition timeSanity(env e) returns bool =
+  e.block.timestamp > 0 && e.block.timestamp + defaultAdminDelay(e) < max_uint48();
+
+definition delayChangeWaitSanity(env e, uint48 newDelay) returns bool =
+  e.block.timestamp + delayChangeWait_(e, newDelay) < max_uint48();
+
+definition isSet(uint48 schedule) returns bool =
+  schedule != 0;
+
+definition hasPassed(env e, uint48 schedule) returns bool =
+  schedule < e.block.timestamp;
+
+definition increasingDelaySchedule(env e, uint48 newDelay) returns mathint =
+  e.block.timestamp + min(newDelay, defaultAdminDelayIncreaseWait());
+
+definition decreasingDelaySchedule(env e, uint48 newDelay) returns mathint =
+  e.block.timestamp + defaultAdminDelay(e) - newDelay;
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: defaultAdmin holds the DEFAULT_ADMIN_ROLE                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant defaultAdminConsistency(address account)
+  (account == defaultAdmin() && account != 0) <=> hasRole(DEFAULT_ADMIN_ROLE(), account)
+  {
+    preserved with (env e) {
+      require nonzerosender(e);
+    }
+  }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: Only one account holds the DEFAULT_ADMIN_ROLE                                                            │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant singleDefaultAdmin(address account, address another)
+  hasRole(DEFAULT_ADMIN_ROLE(), account) && hasRole(DEFAULT_ADMIN_ROLE(), another) => another == account
+  {
+    preserved {
+      requireInvariant defaultAdminConsistency(account);
+      requireInvariant defaultAdminConsistency(another);
+    }
+  }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: DEFAULT_ADMIN_ROLE's admin is always DEFAULT_ADMIN_ROLE                                                  │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant defaultAdminRoleAdminConsistency()
+  getRoleAdmin(DEFAULT_ADMIN_ROLE()) == DEFAULT_ADMIN_ROLE()
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: owner is the defaultAdmin                                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant ownerConsistency()
+  defaultAdmin() == owner()
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: revokeRole only affects the specified user/role combo                                         │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule revokeRoleEffect(env e, bytes32 role) {
+    require nonpayable(e);
+
+    bytes32 otherRole;
+    address account;
+    address otherAccount;
+
+    bool isCallerAdmin = hasRole(getRoleAdmin(role), e.msg.sender);
+    bool hasOtherRoleBefore = hasRole(otherRole, otherAccount);
+
+    revokeRole@withrevert(e, role, account);
+    bool success = !lastReverted;
+
+    bool hasOtherRoleAfter = hasRole(otherRole, otherAccount);
+
+    // liveness
+    assert success <=> isCallerAdmin && role != DEFAULT_ADMIN_ROLE(),
+      "roles can only be revoked by their owner except for the default admin role";
+
+    // effect
+    assert success => !hasRole(role, account),
+      "role is revoked";
+
+    // no side effect
+    assert hasOtherRoleBefore != hasOtherRoleAfter => (role == otherRole && account == otherAccount),
+      "no other role is affected";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: renounceRole only affects the specified user/role combo                                       │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule renounceRoleEffect(env e, bytes32 role) {
+    require nonpayable(e);
+
+    bytes32 otherRole;
+    address account;
+    address otherAccount;
+
+    bool    hasOtherRoleBefore = hasRole(otherRole, otherAccount);
+    address adminBefore        = defaultAdmin();
+    address pendingAdminBefore = pendingDefaultAdmin_();
+    uint48  scheduleBefore     = pendingDefaultAdminSchedule_();
+
+    renounceRole@withrevert(e, role, account);
+    bool success = !lastReverted;
+
+    bool    hasOtherRoleAfter = hasRole(otherRole, otherAccount);
+    address adminAfter        = defaultAdmin();
+    address pendingAdminAfter = pendingDefaultAdmin_();
+    uint48  scheduleAfter     = pendingDefaultAdminSchedule_();
+
+    // liveness
+    assert success <=> (
+      account == e.msg.sender &&
+      (
+        role    != DEFAULT_ADMIN_ROLE() ||
+        account != adminBefore          ||
+        (
+          pendingAdminBefore == 0 &&
+          isSet(scheduleBefore) &&
+          hasPassed(e, scheduleBefore)
+        )
+      )
+    ),
+      "an account only can renounce by itself with a delay for the default admin role";
+
+    // effect
+    assert success => !hasRole(role, account),
+      "role is renounced";
+
+    assert success => (
+      (
+        role    == DEFAULT_ADMIN_ROLE() &&
+        account == adminBefore
+      ) ? (
+        adminAfter        == 0 &&
+        pendingAdminAfter == 0 &&
+        scheduleAfter     == 0
+      ) : (
+        adminAfter        == adminBefore        &&
+        pendingAdminAfter == pendingAdminBefore &&
+        scheduleAfter     == scheduleBefore
+      )
+    ),
+      "renouncing default admin role cleans state iff called by previous admin";
+
+    // no side effect
+    assert hasOtherRoleBefore != hasOtherRoleAfter => (
+      role == otherRole &&
+      account == otherAccount
+    ),
+      "no other role is affected";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: defaultAdmin is only affected by accepting an admin transfer or renoucing                                     │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule noDefaultAdminChange(env e, method f, calldataarg args) {
+  address adminBefore = defaultAdmin();
+  f(e, args);
+  address adminAfter = defaultAdmin();
+
+  assert adminBefore != adminAfter => (
+    f.selector == acceptDefaultAdminTransfer().selector ||
+    f.selector == renounceRole(bytes32,address).selector
+  ),
+    "default admin is only affected by accepting an admin transfer or renoucing";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: pendingDefaultAdmin is only affected by beginning, completing (accept or renounce), or canceling an admin     │
+│ transfer                                                                                                            │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule noPendingDefaultAdminChange(env e, method f, calldataarg args) {
+  address pendingAdminBefore = pendingDefaultAdmin_();
+  address scheduleBefore = pendingDefaultAdminSchedule_();
+  f(e, args);
+  address pendingAdminAfter = pendingDefaultAdmin_();
+  address scheduleAfter = pendingDefaultAdminSchedule_();
+
+  assert (
+    pendingAdminBefore != pendingAdminAfter ||
+    scheduleBefore != scheduleAfter
+  ) => (
+    f.selector == beginDefaultAdminTransfer(address).selector ||
+    f.selector == acceptDefaultAdminTransfer().selector ||
+    f.selector == cancelDefaultAdminTransfer().selector ||
+    f.selector == renounceRole(bytes32,address).selector
+  ),
+    "pending admin and its schedule is only affected by beginning, completing, or cancelling an admin transfer";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: defaultAdminDelay can't be changed atomically by any function                                                 │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule noDefaultAdminDelayChange(env e, method f, calldataarg args) {
+  uint48 delayBefore = defaultAdminDelay(e);
+  f(e, args);
+  uint48 delayAfter = defaultAdminDelay(e);
+
+  assert delayBefore == delayAfter,
+    "delay can't be changed atomically by any function";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: pendingDefaultAdminDelay is only affected by changeDefaultAdminDelay or rollbackDefaultAdminDelay             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule noPendingDefaultAdminDelayChange(env e, method f, calldataarg args) {
+  uint48 pendingDelayBefore = pendingDelay_(e);
+  f(e, args);
+  uint48 pendingDelayAfter = pendingDelay_(e);
+
+  assert pendingDelayBefore != pendingDelayAfter => (
+    f.selector == changeDefaultAdminDelay(uint48).selector ||
+    f.selector == rollbackDefaultAdminDelay().selector
+  ),
+    "pending delay is only affected by changeDefaultAdminDelay or rollbackDefaultAdminDelay";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: defaultAdminDelayIncreaseWait can't be changed atomically by any function                                     │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule noDefaultAdminDelayIncreaseWaitChange(env e, method f, calldataarg args) {
+  uint48 delayIncreaseWaitBefore = defaultAdminDelayIncreaseWait();
+  f(e, args);
+  uint48 delayIncreaseWaitAfter = defaultAdminDelayIncreaseWait();
+
+  assert delayIncreaseWaitBefore == delayIncreaseWaitAfter,
+    "delay increase wait can't be changed atomically by any function";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: beginDefaultAdminTransfer sets a pending default admin and its schedule                       │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule beginDefaultAdminTransfer(env e, address newAdmin) {
+  require timeSanity(e);
+  require nonpayable(e);
+  require nonzerosender(e);
+  requireInvariant defaultAdminConsistency(e.msg.sender);
+
+  beginDefaultAdminTransfer@withrevert(e, newAdmin);
+  bool success = !lastReverted;
+
+  // liveness
+  assert success <=> e.msg.sender == defaultAdmin(),
+    "only the current default admin can begin a transfer";
+
+  // effect
+  assert success => pendingDefaultAdmin_() == newAdmin,
+    "pending default admin is set";
+  assert success => pendingDefaultAdminSchedule_() == e.block.timestamp + defaultAdminDelay(e),
+    "pending default admin delay is set";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: A default admin can't change in less than the applied schedule                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule pendingDefaultAdminDelayEnforced(env e1, env e2, method f, calldataarg args, address newAdmin) {
+  require e1.block.timestamp <= e2.block.timestamp;
+
+  uint48 delayBefore = defaultAdminDelay(e1);
+  address adminBefore = defaultAdmin();
+
+  // There might be a better way to generalize this without requiring `beginDefaultAdminTransfer`, but currently
+  // it's the only way in which we can attest that only `delayBefore` has passed before a change.
+  beginDefaultAdminTransfer(e1, newAdmin);
+  f(e2, args);
+
+  address adminAfter = defaultAdmin();
+
+  // change can only happen towards the newAdmin, with the delay
+  assert adminAfter != adminBefore => (
+    adminAfter == newAdmin &&
+    e2.block.timestamp >= e1.block.timestamp + delayBefore
+  ),
+    "The admin can only change after the enforced delay and to the previously scheduled new admin";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: acceptDefaultAdminTransfer updates defaultAdmin resetting the pending admin and its schedule  │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule acceptDefaultAdminTransfer(env e) {
+  require nonpayable(e);
+
+  address pendingAdminBefore = pendingDefaultAdmin_();
+  uint48 scheduleBefore = pendingDefaultAdminSchedule_();
+
+  acceptDefaultAdminTransfer@withrevert(e);
+  bool success = !lastReverted;
+
+  // liveness
+  assert success <=> (
+    e.msg.sender == pendingAdminBefore &&
+    isSet(scheduleBefore) &&
+    hasPassed(e, scheduleBefore)
+  ),
+    "only the pending default admin can accept the role after the schedule has been set and passed";
+
+  // effect
+  assert success => defaultAdmin() == pendingAdminBefore,
+    "Default admin is set to the previous pending default admin";
+  assert success => pendingDefaultAdmin_() == 0,
+    "Pending default admin is reset";
+  assert success => pendingDefaultAdminSchedule_() == 0,
+    "Pending default admin delay is reset";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: cancelDefaultAdminTransfer resets pending default admin and its schedule                      │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule cancelDefaultAdminTransfer(env e) {
+  require nonpayable(e);
+  require nonzerosender(e);
+  requireInvariant defaultAdminConsistency(e.msg.sender);
+
+  cancelDefaultAdminTransfer@withrevert(e);
+  bool success = !lastReverted;
+
+  // liveness
+  assert success <=> e.msg.sender == defaultAdmin(),
+    "only the current default admin can cancel a transfer";
+
+  // effect
+  assert success => pendingDefaultAdmin_() == 0,
+    "Pending default admin is reset";
+  assert success => pendingDefaultAdminSchedule_() == 0,
+    "Pending default admin delay is reset";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: changeDefaultAdminDelay sets a pending default admin delay and its schedule                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule changeDefaultAdminDelay(env e, uint48 newDelay) {
+  require timeSanity(e);
+  require nonpayable(e);
+  require nonzerosender(e);
+  require delayChangeWaitSanity(e, newDelay);
+  requireInvariant defaultAdminConsistency(e.msg.sender);
+
+  uint48 delayBefore = defaultAdminDelay(e);
+
+  changeDefaultAdminDelay@withrevert(e, newDelay);
+  bool success = !lastReverted;
+
+  // liveness
+  assert success <=> e.msg.sender == defaultAdmin(),
+    "only the current default admin can begin a delay change";
+
+  // effect
+  assert success => pendingDelay_(e) == newDelay,
+    "pending delay is set";
+
+  assert success => (
+    pendingDelaySchedule_(e) > e.block.timestamp ||
+    delayBefore == newDelay || // Interpreted as decreasing, x - x = 0
+    defaultAdminDelayIncreaseWait() == 0
+  ),
+    "pending delay schedule is set in the future unless accepted edge cases";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: A delay can't change in less than the applied schedule                                                        │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule pendingDelayWaitEnforced(env e1, env e2, method f, calldataarg args, uint48 newDelay) {
+  require e1.block.timestamp <= e2.block.timestamp;
+
+  uint48 delayBefore = defaultAdminDelay(e1);
+
+  changeDefaultAdminDelay(e1, newDelay);
+  f(e2, args);
+
+  uint48 delayAfter = defaultAdminDelay(e2);
+
+  mathint delayWait = newDelay > delayBefore ? increasingDelaySchedule(e1, newDelay) : decreasingDelaySchedule(e1, newDelay);
+
+  assert delayAfter != delayBefore => (
+    delayAfter == newDelay &&
+    e2.block.timestamp >= delayWait
+  ),
+    "A delay can only change after the applied schedule";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: pending delay wait is set depending on increasing or decreasing the delay                                     │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule pendingDelayWait(env e, uint48 newDelay) {
+  uint48 oldDelay = defaultAdminDelay(e);
+  changeDefaultAdminDelay(e, newDelay);
+
+  assert newDelay > oldDelay => pendingDelaySchedule_(e) == increasingDelaySchedule(e, newDelay),
+    "Delay wait is the minimum between the new delay and a threshold when the delay is increased";
+  assert newDelay <= oldDelay => pendingDelaySchedule_(e) == decreasingDelaySchedule(e, newDelay),
+    "Delay wait is the difference between the current and the new delay when the delay is decreased";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: rollbackDefaultAdminDelay resets the delay and its schedule                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule rollbackDefaultAdminDelay(env e) {
+  require nonpayable(e);
+  require nonzerosender(e);
+  requireInvariant defaultAdminConsistency(e.msg.sender);
+
+  rollbackDefaultAdminDelay@withrevert(e);
+  bool success = !lastReverted;
+
+  // liveness
+  assert success <=> e.msg.sender == defaultAdmin(),
+    "only the current default admin can rollback a delay change";
+
+  // effect
+  assert success => pendingDelay_(e) == 0,
+    "Pending default admin is reset";
+  assert success => pendingDelaySchedule_(e) == 0,
+    "Pending default admin delay is reset";
+}

certora/specs/DoubleEndedQueue.spec

@@ -0,0 +1,366 @@
+import "helpers/helpers.spec"
+
+methods {
+    pushFront(bytes32)                    envfree
+    pushBack(bytes32)                     envfree
+    popFront()          returns (bytes32) envfree
+    popBack()           returns (bytes32) envfree
+    clear()                               envfree
+
+    // exposed for FV
+    begin()             returns (int128)  envfree
+    end()               returns (int128)  envfree
+
+    // view
+    length()            returns (uint256) envfree
+    empty()             returns (bool)    envfree
+    front()             returns (bytes32) envfree
+    back()              returns (bytes32) envfree
+    at_(uint256)        returns (bytes32) envfree // at is a reserved word
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Helpers                                                                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+
+function min_int128() returns mathint {
+    return -(1 << 127);
+}
+
+function max_int128() returns mathint {
+    return (1 << 127) - 1;
+}
+
+// Could be broken in theory, but not in practice
+function boundedQueue() returns bool {
+    return
+        max_int128() > to_mathint(end()) &&
+        min_int128() < to_mathint(begin());
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: end is larger or equal than begin                                                                        │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant boundariesConsistency()
+    end() >= begin()
+    filtered { f -> !f.isView }
+    { preserved { require boundedQueue(); } }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: length is end minus begin                                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant lengthConsistency()
+    length() == to_mathint(end()) - to_mathint(begin())
+    filtered { f -> !f.isView }
+    { preserved { require boundedQueue(); } }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: empty() is length 0 and no element exists                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant emptiness()
+    empty() <=> length() == 0
+    filtered { f -> !f.isView }
+    { preserved { require boundedQueue(); } }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: front points to the first index and back points to the last one                                          │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant queueEndings()
+    at_(length() - 1) == back() && at_(0) == front()
+    filtered { f -> !f.isView }
+    {
+        preserved {
+            requireInvariant boundariesConsistency();
+            require boundedQueue();
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: pushFront adds an element at the beginning of the queue                                       │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule pushFront(bytes32 value) {
+    require boundedQueue();
+
+    uint256 lengthBefore = length();
+
+    pushFront@withrevert(value);
+
+    // liveness
+    assert !lastReverted, "never reverts";
+
+    // effect
+    assert front() == value, "front set to value";
+    assert length() == lengthBefore + 1, "queue extended";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: pushFront preserves the previous values in the queue with a +1 offset                                         │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule pushFrontConsistency(uint256 index) {
+    require boundedQueue();
+
+    bytes32 beforeAt = at_(index);
+
+    bytes32 value;
+    pushFront(value);
+
+    // try to read value
+    bytes32 afterAt = at_@withrevert(index + 1);
+
+    assert !lastReverted, "value still there";
+    assert afterAt == beforeAt, "data is preserved";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: pushBack adds an element at the end of the queue                                              │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule pushBack(bytes32 value) {
+    require boundedQueue();
+
+    uint256 lengthBefore = length();
+
+    pushBack@withrevert(value);
+
+    // liveness
+    assert !lastReverted, "never reverts";
+
+    // effect
+    assert back() == value, "back set to value";
+    assert length() == lengthBefore + 1, "queue increased";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: pushBack preserves the previous values in the queue                                                           │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule pushBackConsistency(uint256 index) {
+    require boundedQueue();
+
+    bytes32 beforeAt = at_(index);
+
+    bytes32 value;
+    pushBack(value);
+
+    // try to read value
+    bytes32 afterAt = at_@withrevert(index);
+
+    assert !lastReverted, "value still there";
+    assert afterAt == beforeAt, "data is preserved";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: popFront removes an element from the beginning of the queue                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule popFront {
+    requireInvariant boundariesConsistency();
+    require boundedQueue();
+
+    uint256 lengthBefore = length();
+    bytes32 frontBefore = front@withrevert();
+
+    bytes32 popped = popFront@withrevert();
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> lengthBefore != 0, "never reverts if not previously empty";
+
+    // effect
+    assert success => frontBefore == popped, "previous front is returned";
+    assert success => length() == lengthBefore - 1, "queue decreased";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: at(x) is preserved and offset to at(x - 1) after calling popFront                                             |
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule popFrontConsistency(uint256 index) {
+    requireInvariant boundariesConsistency();
+    require boundedQueue();
+
+    // Read (any) value that is not the front (this asserts the value exists / the queue is long enough)
+    require index > 1;
+    bytes32 before = at_(index);
+
+    popFront();
+
+    // try to read value
+    bytes32 after = at_@withrevert(index - 1);
+
+    assert !lastReverted, "value still exists in the queue";
+    assert before == after, "values are offset and not modified";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: popBack removes an element from the end of the queue                                          │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule popBack {
+    requireInvariant boundariesConsistency();
+    require boundedQueue();
+
+    uint256 lengthBefore = length();
+    bytes32 backBefore = back@withrevert();
+
+    bytes32 popped = popBack@withrevert();
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> lengthBefore != 0, "never reverts if not previously empty";
+
+    // effect
+    assert success => backBefore == popped, "previous back is returned";
+    assert success => length() == lengthBefore - 1, "queue decreased";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: at(x) is preserved after calling popBack                                                                     |
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule popBackConsistency(uint256 index) {
+    requireInvariant boundariesConsistency();
+    require boundedQueue();
+
+    // Read (any) value that is not the back (this asserts the value exists / the queue is long enough)
+    require index < length() - 1;
+    bytes32 before = at_(index);
+
+    popBack();
+
+    // try to read value
+    bytes32 after = at_@withrevert(index);
+
+    assert !lastReverted, "value still exists in the queue";
+    assert before == after, "values are offset and not modified";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: clear sets length to 0                                                                        │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule clear {
+    clear@withrevert();
+
+    // liveness
+    assert !lastReverted, "never reverts";
+
+    // effect
+    assert length() == 0, "sets length to 0";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: front/back access reverts only if the queue is empty or querying out of bounds                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule onlyEmptyRevert(env e) {
+    require nonpayable(e);
+    requireInvariant boundariesConsistency();
+    require boundedQueue();
+
+    method f;
+    calldataarg args;
+
+    bool emptyBefore = empty();
+
+    f@withrevert(e, args);
+
+    assert lastReverted => (
+        (f.selector == front().selector && emptyBefore) ||
+        (f.selector == back().selector && emptyBefore) ||
+        (f.selector == popFront().selector  && emptyBefore) ||
+        (f.selector == popBack().selector  && emptyBefore) ||
+        f.selector == at_(uint256).selector // revert conditions are verified in onlyOutOfBoundsRevert
+    ), "only revert if empty or out of bounds";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: at(index) only reverts if index is out of bounds                                                                  |
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule onlyOutOfBoundsRevert(uint256 index) {
+    requireInvariant boundariesConsistency();
+    require boundedQueue();
+
+    at_@withrevert(index);
+
+    assert lastReverted <=> index >= length(), "only reverts if index is out of bounds";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: only clear/push/pop operations can change the length of the queue                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule noLengthChange(env e) {
+    requireInvariant boundariesConsistency();
+    require boundedQueue();
+
+    method f;
+    calldataarg args;
+
+    uint256 lengthBefore = length();
+    f(e, args);
+    uint256 lengthAfter = length();
+
+    assert lengthAfter != lengthBefore => (
+        (f.selector == pushFront(bytes32).selector && lengthAfter == lengthBefore + 1) ||
+        (f.selector == pushBack(bytes32).selector && lengthAfter == lengthBefore + 1) ||
+        (f.selector == popBack().selector && lengthAfter == lengthBefore - 1) ||
+        (f.selector == popFront().selector && lengthAfter == lengthBefore - 1) ||
+        (f.selector == clear().selector && lengthAfter == 0)
+    ), "length is only affected by clear/pop/push operations";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: only push/pop can change values bounded in the queue (outside values aren't cleared)                          │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule noDataChange(env e) {
+    requireInvariant boundariesConsistency();
+    require boundedQueue();
+
+    method f;
+    calldataarg args;
+
+    uint256 index;
+    bytes32 atBefore = at_(index);
+    f(e, args);
+    bytes32 atAfter = at_@withrevert(index);
+    bool atAfterSuccess = !lastReverted;
+
+    assert !atAfterSuccess <=> (
+        f.selector == clear().selector ||
+        (f.selector == popBack().selector && index == length()) ||
+        (f.selector == popFront().selector && index == length())
+    ), "indexes of the queue are only removed by clear or pop";
+
+    assert atAfterSuccess && atAfter != atBefore => (
+        f.selector == popFront().selector ||
+        f.selector == pushFront(bytes32).selector
+    ), "values of the queue are only changed by popFront or pushFront";
+}

certora/specs/ERC20.spec

@@ -0,0 +1,414 @@
+import "helpers/helpers.spec"
+import "methods/IERC20.spec"
+import "methods/IERC2612.spec"
+
+methods {
+    // non standard ERC20 functions
+    increaseAllowance(address,uint256) returns (bool)
+    decreaseAllowance(address,uint256) returns (bool)
+
+    // exposed for FV
+    mint(address,uint256)
+    burn(address,uint256)
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Ghost & hooks: sum of all balances                                                                                  │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+ghost sumOfBalances() returns uint256 {
+  init_state axiom sumOfBalances() == 0;
+}
+
+hook Sstore _balances[KEY address addr] uint256 newValue (uint256 oldValue) STORAGE {
+    havoc sumOfBalances assuming sumOfBalances@new() == sumOfBalances@old() + newValue - oldValue;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: totalSupply is the sum of all balances                                                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant totalSupplyIsSumOfBalances()
+    totalSupply() == sumOfBalances()
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: balance of address(0) is 0                                                                               │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant zeroAddressNoBalance()
+    balanceOf(0) == 0
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: only mint and burn can change total supply                                                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule noChangeTotalSupply(env e) {
+    requireInvariant totalSupplyIsSumOfBalances();
+
+    method f;
+    calldataarg args;
+
+    uint256 totalSupplyBefore = totalSupply();
+    f(e, args);
+    uint256 totalSupplyAfter = totalSupply();
+
+    assert totalSupplyAfter > totalSupplyBefore => f.selector == mint(address,uint256).selector;
+    assert totalSupplyAfter < totalSupplyBefore => f.selector == burn(address,uint256).selector;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: only the token holder or an approved third party can reduce an account's balance                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule onlyAuthorizedCanTransfer(env e) {
+    requireInvariant totalSupplyIsSumOfBalances();
+
+    method f;
+    calldataarg args;
+    address account;
+
+    uint256 allowanceBefore = allowance(account, e.msg.sender);
+    uint256 balanceBefore   = balanceOf(account);
+    f(e, args);
+    uint256 balanceAfter    = balanceOf(account);
+
+    assert (
+        balanceAfter < balanceBefore
+    ) => (
+        f.selector == burn(address,uint256).selector ||
+        e.msg.sender == account ||
+        balanceBefore - balanceAfter <= allowanceBefore
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: only the token holder (or a permit) can increase allowance. The spender can decrease it by using it          │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule onlyHolderOfSpenderCanChangeAllowance(env e) {
+    requireInvariant totalSupplyIsSumOfBalances();
+
+    method f;
+    calldataarg args;
+    address holder;
+    address spender;
+
+    uint256 allowanceBefore = allowance(holder, spender);
+    f(e, args);
+    uint256 allowanceAfter = allowance(holder, spender);
+
+    assert (
+        allowanceAfter > allowanceBefore
+    ) => (
+        (f.selector == approve(address,uint256).selector           && e.msg.sender == holder) ||
+        (f.selector == increaseAllowance(address,uint256).selector && e.msg.sender == holder) ||
+        (f.selector == permit(address,address,uint256,uint256,uint8,bytes32,bytes32).selector)
+    );
+
+    assert (
+        allowanceAfter < allowanceBefore
+    ) => (
+        (f.selector == transferFrom(address,address,uint256).selector && e.msg.sender == spender) ||
+        (f.selector == approve(address,uint256).selector              && e.msg.sender == holder ) ||
+        (f.selector == decreaseAllowance(address,uint256).selector    && e.msg.sender == holder ) ||
+        (f.selector == permit(address,address,uint256,uint256,uint8,bytes32,bytes32).selector)
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: mint behavior and side effects                                                                               │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule mint(env e) {
+    requireInvariant totalSupplyIsSumOfBalances();
+    require nonpayable(e);
+
+    address to;
+    address other;
+    uint256 amount;
+
+    // cache state
+    uint256 toBalanceBefore    = balanceOf(to);
+    uint256 otherBalanceBefore = balanceOf(other);
+    uint256 totalSupplyBefore  = totalSupply();
+
+    // run transaction
+    mint@withrevert(e, to, amount);
+
+    // check outcome
+    if (lastReverted) {
+        assert to == 0 || totalSupplyBefore + amount > max_uint256;
+    } else {
+        // updates balance and totalSupply
+        assert balanceOf(to) == toBalanceBefore   + amount;
+        assert totalSupply() == totalSupplyBefore + amount;
+
+        // no other balance is modified
+        assert balanceOf(other) != otherBalanceBefore => other == to;
+    }
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: burn behavior and side effects                                                                               │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule burn(env e) {
+    requireInvariant totalSupplyIsSumOfBalances();
+    require nonpayable(e);
+
+    address from;
+    address other;
+    uint256 amount;
+
+    // cache state
+    uint256 fromBalanceBefore  = balanceOf(from);
+    uint256 otherBalanceBefore = balanceOf(other);
+    uint256 totalSupplyBefore  = totalSupply();
+
+    // run transaction
+    burn@withrevert(e, from, amount);
+
+    // check outcome
+    if (lastReverted) {
+        assert from == 0 || fromBalanceBefore < amount;
+    } else {
+        // updates balance and totalSupply
+        assert balanceOf(from) == fromBalanceBefore   - amount;
+        assert totalSupply()   == totalSupplyBefore - amount;
+
+        // no other balance is modified
+        assert balanceOf(other) != otherBalanceBefore => other == from;
+    }
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: transfer behavior and side effects                                                                            │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule transfer(env e) {
+    requireInvariant totalSupplyIsSumOfBalances();
+    require nonpayable(e);
+
+    address holder = e.msg.sender;
+    address recipient;
+    address other;
+    uint256 amount;
+
+    // cache state
+    uint256 holderBalanceBefore    = balanceOf(holder);
+    uint256 recipientBalanceBefore = balanceOf(recipient);
+    uint256 otherBalanceBefore     = balanceOf(other);
+
+    // run transaction
+    transfer@withrevert(e, recipient, amount);
+
+    // check outcome
+    if (lastReverted) {
+        assert holder == 0 || recipient == 0 || amount > holderBalanceBefore;
+    } else {
+        // balances of holder and recipient are updated
+        assert balanceOf(holder)    == holderBalanceBefore    - (holder == recipient ? 0 : amount);
+        assert balanceOf(recipient) == recipientBalanceBefore + (holder == recipient ? 0 : amount);
+
+        // no other balance is modified
+        assert balanceOf(other) != otherBalanceBefore => (other == holder || other == recipient);
+    }
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: transferFrom behavior and side effects                                                                        │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule transferFrom(env e) {
+    requireInvariant totalSupplyIsSumOfBalances();
+    require nonpayable(e);
+
+    address spender = e.msg.sender;
+    address holder;
+    address recipient;
+    address other;
+    uint256 amount;
+
+    // cache state
+    uint256 allowanceBefore        = allowance(holder, spender);
+    uint256 holderBalanceBefore    = balanceOf(holder);
+    uint256 recipientBalanceBefore = balanceOf(recipient);
+    uint256 otherBalanceBefore     = balanceOf(other);
+
+    // run transaction
+    transferFrom@withrevert(e, holder, recipient, amount);
+
+    // check outcome
+    if (lastReverted) {
+        assert holder == 0 || recipient == 0 || spender == 0 || amount > holderBalanceBefore || amount > allowanceBefore;
+    } else {
+        // allowance is valid & updated
+        assert allowanceBefore            >= amount;
+        assert allowance(holder, spender) == (allowanceBefore == max_uint256 ? to_uint256(max_uint256) : allowanceBefore - amount);
+
+        // balances of holder and recipient are updated
+        assert balanceOf(holder)    == holderBalanceBefore    - (holder == recipient ? 0 : amount);
+        assert balanceOf(recipient) == recipientBalanceBefore + (holder == recipient ? 0 : amount);
+
+        // no other balance is modified
+        assert balanceOf(other) != otherBalanceBefore => (other == holder || other == recipient);
+    }
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: approve behavior and side effects                                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule approve(env e) {
+    require nonpayable(e);
+
+    address holder = e.msg.sender;
+    address spender;
+    address otherHolder;
+    address otherSpender;
+    uint256 amount;
+
+    // cache state
+    uint256 otherAllowanceBefore = allowance(otherHolder, otherSpender);
+
+    // run transaction
+    approve@withrevert(e, spender, amount);
+
+    // check outcome
+    if (lastReverted) {
+        assert holder == 0 || spender == 0;
+    } else {
+        // allowance is updated
+        assert allowance(holder, spender) == amount;
+
+        // other allowances are untouched
+        assert allowance(otherHolder, otherSpender) != otherAllowanceBefore => (otherHolder == holder && otherSpender == spender);
+    }
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: increaseAllowance behavior and side effects                                                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule increaseAllowance(env e) {
+    require nonpayable(e);
+
+    address holder = e.msg.sender;
+    address spender;
+    address otherHolder;
+    address otherSpender;
+    uint256 amount;
+
+    // cache state
+    uint256 allowanceBefore      = allowance(holder, spender);
+    uint256 otherAllowanceBefore = allowance(otherHolder, otherSpender);
+
+    // run transaction
+    increaseAllowance@withrevert(e, spender, amount);
+
+    // check outcome
+    if (lastReverted) {
+        assert holder == 0 || spender == 0 || allowanceBefore + amount > max_uint256;
+    } else {
+        // allowance is updated
+        assert allowance(holder, spender) == allowanceBefore + amount;
+
+        // other allowances are untouched
+        assert allowance(otherHolder, otherSpender) != otherAllowanceBefore => (otherHolder == holder && otherSpender == spender);
+    }
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: decreaseAllowance behavior and side effects                                                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule decreaseAllowance(env e) {
+    require nonpayable(e);
+
+    address holder = e.msg.sender;
+    address spender;
+    address otherHolder;
+    address otherSpender;
+    uint256 amount;
+
+    // cache state
+    uint256 allowanceBefore      = allowance(holder, spender);
+    uint256 otherAllowanceBefore = allowance(otherHolder, otherSpender);
+
+    // run transaction
+    decreaseAllowance@withrevert(e, spender, amount);
+
+    // check outcome
+    if (lastReverted) {
+        assert holder == 0 || spender == 0 || allowanceBefore < amount;
+    } else {
+        // allowance is updated
+        assert allowance(holder, spender) == allowanceBefore - amount;
+
+        // other allowances are untouched
+        assert allowance(otherHolder, otherSpender) != otherAllowanceBefore => (otherHolder == holder && otherSpender == spender);
+    }
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: permit behavior and side effects                                                                              │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule permit(env e) {
+    require nonpayable(e);
+
+    address holder;
+    address spender;
+    uint256 amount;
+    uint256 deadline;
+    uint8 v;
+    bytes32 r;
+    bytes32 s;
+
+    address account1;
+    address account2;
+    address account3;
+
+    // cache state
+    uint256 nonceBefore          = nonces(holder);
+    uint256 otherNonceBefore     = nonces(account1);
+    uint256 otherAllowanceBefore = allowance(account2, account3);
+
+    // sanity: nonce overflow, which possible in theory, is assumed to be impossible in practice
+    require nonceBefore      < max_uint256;
+    require otherNonceBefore < max_uint256;
+
+    // run transaction
+    permit@withrevert(e, holder, spender, amount, deadline, v, r, s);
+
+    // check outcome
+    if (lastReverted) {
+        // Without formally checking the signature, we can't verify exactly the revert causes
+        assert true;
+    } else {
+        // allowance and nonce are updated
+        assert allowance(holder, spender) == amount;
+        assert nonces(holder) == nonceBefore + 1;
+
+        // deadline was respected
+        assert deadline >= e.block.timestamp;
+
+        // no other allowance or nonce is modified
+        assert nonces(account1)              != otherNonceBefore     => account1 == holder;
+        assert allowance(account2, account3) != otherAllowanceBefore => (account2 == holder && account3 == spender);
+    }
+}

certora/specs/ERC20FlashMint.spec

@@ -0,0 +1,48 @@
+import "helpers/helpers.spec"
+import "methods/IERC20.spec"
+import "methods/IERC3156.spec"
+
+methods {
+    // non standard ERC3156 functions
+    flashFeeReceiver() returns (address) envfree
+
+    // function summaries below
+    _mint(address account, uint256 amount)              => specMint(account, amount)
+    _burn(address account, uint256 amount)              => specBurn(account, amount)
+    _transfer(address from, address to, uint256 amount) => specTransfer(from, to, amount)
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Ghost: track mint and burns in the CVL                                                                              │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+ghost mapping(address => uint256)                     trackedMintAmount;
+ghost mapping(address => uint256)                     trackedBurnAmount;
+ghost mapping(address => mapping(address => uint256)) trackedTransferedAmount;
+
+function specMint(address account, uint256 amount)              returns bool { trackedMintAmount[account] = amount;        return true; }
+function specBurn(address account, uint256 amount)              returns bool { trackedBurnAmount[account] = amount;        return true; }
+function specTransfer(address from, address to, uint256 amount) returns bool { trackedTransferedAmount[from][to] = amount; return true; }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: When doing a flashLoan, "amount" is minted and burnt, additionally, the fee is either burnt                   │
+│ (if the fee recipient is 0) or transferred (if the fee recipient is not 0)                                          │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule checkMintAndBurn(env e) {
+    address receiver;
+    address token;
+    uint256 amount;
+    bytes data;
+
+    uint256 fees = flashFee(token, amount);
+    address recipient = flashFeeReceiver();
+
+    flashLoan(e, receiver, token, amount, data);
+
+    assert trackedMintAmount[receiver] == amount;
+    assert trackedBurnAmount[receiver] == amount + (recipient == 0 ? fees : 0);
+    assert (fees > 0 && recipient != 0) => trackedTransferedAmount[receiver][recipient] == fees;
+}

certora/specs/ERC20Wrapper.spec

@@ -0,0 +1,198 @@
+import "helpers/helpers.spec"
+import "ERC20.spec"
+
+methods {
+    underlying()                       returns(address) envfree
+    underlyingTotalSupply()            returns(uint256) envfree
+    underlyingBalanceOf(address)       returns(uint256) envfree
+    underlyingAllowanceToThis(address) returns(uint256) envfree
+
+    depositFor(address, uint256)       returns(bool)
+    withdrawTo(address, uint256)       returns(bool)
+    recover(address)                   returns(uint256)
+}
+
+use invariant totalSupplyIsSumOfBalances
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Helper: consequence of `totalSupplyIsSumOfBalances` applied to underlying                                           │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+function underlyingBalancesLowerThanUnderlyingSupply(address a) returns bool {
+    return underlyingBalanceOf(a) <= underlyingTotalSupply();
+}
+
+function sumOfUnderlyingBalancesLowerThanUnderlyingSupply(address a, address b) returns bool {
+    return a != b => underlyingBalanceOf(a) + underlyingBalanceOf(b) <= underlyingTotalSupply();
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: wrapped token can't be undercollateralized (solvency of the wrapper)                                     │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant totalSupplyIsSmallerThanUnderlyingBalance()
+    totalSupply() <= underlyingBalanceOf(currentContract) &&
+    underlyingBalanceOf(currentContract) <= underlyingTotalSupply() &&
+    underlyingTotalSupply() <= max_uint256
+    {
+        preserved {
+            requireInvariant totalSupplyIsSumOfBalances;
+            require underlyingBalancesLowerThanUnderlyingSupply(currentContract);
+        }
+        preserved depositFor(address account, uint256 amount) with (env e) {
+            require sumOfUnderlyingBalancesLowerThanUnderlyingSupply(e.msg.sender, currentContract);
+        }
+    }
+
+invariant noSelfWrap()
+    currentContract != underlying()
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: depositFor liveness and effects                                                                               │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule depositFor(env e) {
+    require nonpayable(e);
+
+    address sender = e.msg.sender;
+    address receiver;
+    address other;
+    uint256 amount;
+
+    // sanity
+    requireInvariant noSelfWrap;
+    requireInvariant totalSupplyIsSumOfBalances;
+    requireInvariant totalSupplyIsSmallerThanUnderlyingBalance;
+    require sumOfUnderlyingBalancesLowerThanUnderlyingSupply(currentContract, sender);
+
+    uint256 balanceBefore                   = balanceOf(receiver);
+    uint256 supplyBefore                    = totalSupply();
+    uint256 senderUnderlyingBalanceBefore   = underlyingBalanceOf(sender);
+    uint256 senderUnderlyingAllowanceBefore = underlyingAllowanceToThis(sender);
+    uint256 wrapperUnderlyingBalanceBefore  = underlyingBalanceOf(currentContract);
+    uint256 underlyingSupplyBefore          = underlyingTotalSupply();
+
+    uint256 otherBalanceBefore              = balanceOf(other);
+    uint256 otherUnderlyingBalanceBefore    = underlyingBalanceOf(other);
+
+    depositFor@withrevert(e, receiver, amount);
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> (
+        sender   != currentContract               && // invalid sender
+        sender   != 0                             && // invalid sender
+        receiver != 0                             && // invalid receiver
+        amount   <= senderUnderlyingBalanceBefore && // deposit doesn't exceed balance
+        amount   <= senderUnderlyingAllowanceBefore  // deposit doesn't exceed allowance
+    );
+
+    // effects
+    assert success => (
+        balanceOf(receiver) == balanceBefore + amount &&
+        totalSupply() == supplyBefore + amount &&
+        underlyingBalanceOf(currentContract) == wrapperUnderlyingBalanceBefore + amount &&
+        underlyingBalanceOf(sender) == senderUnderlyingBalanceBefore - amount
+    );
+
+    // no side effect
+    assert underlyingTotalSupply() == underlyingSupplyBefore;
+    assert balanceOf(other)           != otherBalanceBefore           => other == receiver;
+    assert underlyingBalanceOf(other) != otherUnderlyingBalanceBefore => (other == sender || other == currentContract);
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: withdrawTo liveness and effects                                                                               │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule withdrawTo(env e) {
+    require nonpayable(e);
+
+    address sender = e.msg.sender;
+    address receiver;
+    address other;
+    uint256 amount;
+
+    // sanity
+    requireInvariant noSelfWrap;
+    requireInvariant totalSupplyIsSumOfBalances;
+    requireInvariant totalSupplyIsSmallerThanUnderlyingBalance;
+    require sumOfUnderlyingBalancesLowerThanUnderlyingSupply(currentContract, receiver);
+
+    uint256 balanceBefore                   = balanceOf(sender);
+    uint256 supplyBefore                    = totalSupply();
+    uint256 receiverUnderlyingBalanceBefore = underlyingBalanceOf(receiver);
+    uint256 wrapperUnderlyingBalanceBefore  = underlyingBalanceOf(currentContract);
+    uint256 underlyingSupplyBefore          = underlyingTotalSupply();
+
+    uint256 otherBalanceBefore              = balanceOf(other);
+    uint256 otherUnderlyingBalanceBefore    = underlyingBalanceOf(other);
+
+    withdrawTo@withrevert(e, receiver, amount);
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> (
+        sender   != 0          && // invalid sender
+        receiver != 0          && // invalid receiver
+        amount   <= balanceBefore // withdraw doesn't exceed balance
+    );
+
+    // effects
+    assert success => (
+        balanceOf(sender) == balanceBefore - amount &&
+        totalSupply() == supplyBefore - amount &&
+        underlyingBalanceOf(currentContract) == wrapperUnderlyingBalanceBefore - (currentContract != receiver ? amount : 0) &&
+        underlyingBalanceOf(receiver) == receiverUnderlyingBalanceBefore + (currentContract != receiver ? amount : 0)
+    );
+
+    // no side effect
+    assert underlyingTotalSupply() == underlyingSupplyBefore;
+    assert balanceOf(other)           != otherBalanceBefore           => other == sender;
+    assert underlyingBalanceOf(other) != otherUnderlyingBalanceBefore => (other == receiver || other == currentContract);
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: recover liveness and effects                                                                                  │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule recover(env e) {
+    require nonpayable(e);
+
+    address receiver;
+    address other;
+
+    // sanity
+    requireInvariant noSelfWrap;
+    requireInvariant totalSupplyIsSumOfBalances;
+    requireInvariant totalSupplyIsSmallerThanUnderlyingBalance;
+
+    uint256 value                        = underlyingBalanceOf(currentContract) - totalSupply();
+    uint256 supplyBefore                 = totalSupply();
+    uint256 balanceBefore                = balanceOf(receiver);
+
+    uint256 otherBalanceBefore           = balanceOf(other);
+    uint256 otherUnderlyingBalanceBefore = underlyingBalanceOf(other);
+
+    recover@withrevert(e, receiver);
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> receiver != 0;
+
+    // effect
+    assert success => (
+        balanceOf(receiver) == balanceBefore + value &&
+        totalSupply() == supplyBefore + value &&
+        totalSupply() == underlyingBalanceOf(currentContract)
+    );
+
+    // no side effect
+    assert underlyingBalanceOf(other) == otherUnderlyingBalanceBefore;
+    assert balanceOf(other) != otherBalanceBefore => other == receiver;
+}

certora/specs/ERC721.spec

@@ -0,0 +1,589 @@
+import "helpers/helpers.spec"
+import "methods/IERC721.spec"
+
+methods {
+    // exposed for FV
+    mint(address,uint256)
+    safeMint(address,uint256)
+    safeMint(address,uint256,bytes)
+    burn(uint256)
+
+    tokenExists(uint256) returns (bool) envfree
+    unsafeOwnerOf(uint256) returns (address) envfree
+    unsafeGetApproved(uint256) returns (address) envfree
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Helpers                                                                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+
+// Could be broken in theory, but not in practice
+function balanceLimited(address account) returns bool {
+    return balanceOf(account) < max_uint256;
+}
+
+function helperTransferWithRevert(env e, method f, address from, address to, uint256 tokenId) {
+    if (f.selector == transferFrom(address,address,uint256).selector) {
+        transferFrom@withrevert(e, from, to, tokenId);
+    } else if (f.selector == safeTransferFrom(address,address,uint256).selector) {
+        safeTransferFrom@withrevert(e, from, to, tokenId);
+    } else if (f.selector == safeTransferFrom(address,address,uint256,bytes).selector) {
+        bytes params;
+        require params.length < 0xffff;
+        safeTransferFrom@withrevert(e, from, to, tokenId, params);
+    } else {
+        calldataarg args;
+        f@withrevert(e, args);
+    }
+}
+
+function helperMintWithRevert(env e, method f, address to, uint256 tokenId) {
+    if (f.selector == mint(address,uint256).selector) {
+        mint@withrevert(e, to, tokenId);
+    } else if (f.selector == safeMint(address,uint256).selector) {
+        safeMint@withrevert(e, to, tokenId);
+    } else if (f.selector == safeMint(address,uint256,bytes).selector) {
+        bytes params;
+        require params.length < 0xffff;
+        safeMint@withrevert(e, to, tokenId, params);
+    } else {
+        require false;
+    }
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Ghost & hooks: ownership count                                                                                      │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+ghost ownedTotal() returns uint256 {
+  init_state axiom ownedTotal() == 0;
+}
+
+ghost mapping(address => uint256) ownedByUser {
+    init_state axiom forall address a. ownedByUser[a] == 0;
+}
+
+hook Sstore _owners[KEY uint256 tokenId] address newOwner (address oldOwner) STORAGE {
+    ownedByUser[newOwner] = ownedByUser[newOwner] + to_uint256(newOwner != 0 ? 1 : 0);
+    ownedByUser[oldOwner] = ownedByUser[oldOwner] - to_uint256(oldOwner != 0 ? 1 : 0);
+
+    havoc ownedTotal assuming ownedTotal@new() == ownedTotal@old()
+        + to_uint256(newOwner != 0 ? 1 : 0)
+        - to_uint256(oldOwner != 0 ? 1 : 0);
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Ghost & hooks: sum of all balances                                                                                  │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+ghost sumOfBalances() returns uint256 {
+  init_state axiom sumOfBalances() == 0;
+}
+
+hook Sstore _balances[KEY address addr] uint256 newValue (uint256 oldValue) STORAGE {
+    havoc sumOfBalances assuming sumOfBalances@new() == sumOfBalances@old() + newValue - oldValue;
+}
+
+ghost mapping(address => uint256) ghostBalanceOf {
+    init_state axiom forall address a. ghostBalanceOf[a] == 0;
+}
+
+hook Sload uint256 value _balances[KEY address user] STORAGE {
+    require ghostBalanceOf[user] == value;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: ownedTotal is the sum of all balances                                                                    │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant ownedTotalIsSumOfBalances()
+    ownedTotal() == sumOfBalances()
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: balanceOf is the number of tokens owned                                                                  │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant balanceOfConsistency(address user)
+    balanceOf(user) == ownedByUser[user] &&
+    balanceOf(user) == ghostBalanceOf[user]
+    {
+        preserved {
+            require balanceLimited(user);
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: owner of a token must have some balance                                                                  │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant ownerHasBalance(uint256 tokenId)
+    balanceOf(ownerOf(tokenId)) > 0
+    {
+        preserved {
+            requireInvariant balanceOfConsistency(ownerOf(tokenId));
+            require balanceLimited(ownerOf(tokenId));
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: tokens that do not exist are not owned and not approved                                                  │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant notMintedUnset(uint256 tokenId)
+    (!tokenExists(tokenId) <=> unsafeOwnerOf(tokenId) == 0) &&
+    (!tokenExists(tokenId) => unsafeGetApproved(tokenId) == 0)
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: ownerOf and getApproved revert if token does not exist                                                        │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule notMintedRevert(uint256 tokenId) {
+    requireInvariant notMintedUnset(tokenId);
+
+    bool e = tokenExists(tokenId);
+
+    address owner = ownerOf@withrevert(tokenId);
+    assert e <=> !lastReverted;
+    assert e => owner == unsafeOwnerOf(tokenId); // notMintedUnset tells us this is non-zero
+
+    address approved = getApproved@withrevert(tokenId);
+    assert e <=> !lastReverted;
+    assert e => approved == unsafeGetApproved(tokenId);
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: unsafeOwnerOf and unsafeGetApproved don't revert                                                              │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule unsafeDontRevert(uint256 tokenId) {
+    unsafeOwnerOf@withrevert(tokenId);
+    assert !lastReverted;
+
+    unsafeGetApproved@withrevert(tokenId);
+    assert !lastReverted;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: balance of address(0) is 0                                                                                    │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule zeroAddressBalanceRevert() {
+    balanceOf@withrevert(0);
+    assert lastReverted;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: total supply can only change through mint and burn                                                           │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule supplyChange(env e) {
+    uint256 supplyBefore = ownedTotal();
+    method f; calldataarg args; f(e, args);
+    uint256 supplyAfter = ownedTotal();
+
+    assert supplyAfter > supplyBefore => (
+        supplyAfter == supplyBefore + 1 &&
+        (
+            f.selector == mint(address,uint256).selector ||
+            f.selector == safeMint(address,uint256).selector ||
+            f.selector == safeMint(address,uint256,bytes).selector
+        )
+    );
+    assert supplyAfter < supplyBefore => (
+        supplyAfter == supplyBefore - 1 &&
+        f.selector == burn(uint256).selector
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: balanceOf can only change through mint, burn or transfers. balanceOf cannot change by more than 1.           │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule balanceChange(env e, address account) {
+    requireInvariant balanceOfConsistency(account);
+    require balanceLimited(account);
+
+    uint256 balanceBefore = balanceOf(account);
+    method f; calldataarg args; f(e, args);
+    uint256 balanceAfter  = balanceOf(account);
+
+    // balance can change by at most 1
+    assert balanceBefore != balanceAfter => (
+        balanceAfter == balanceBefore - 1 ||
+        balanceAfter == balanceBefore + 1
+    );
+
+    // only selected function can change balances
+    assert balanceBefore != balanceAfter => (
+        f.selector == transferFrom(address,address,uint256).selector ||
+        f.selector == safeTransferFrom(address,address,uint256).selector ||
+        f.selector == safeTransferFrom(address,address,uint256,bytes).selector ||
+        f.selector == mint(address,uint256).selector ||
+        f.selector == safeMint(address,uint256).selector ||
+        f.selector == safeMint(address,uint256,bytes).selector ||
+        f.selector == burn(uint256).selector
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: ownership can only change through mint, burn or transfers.                                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule ownershipChange(env e, uint256 tokenId) {
+    address ownerBefore = unsafeOwnerOf(tokenId);
+    method f; calldataarg args; f(e, args);
+    address ownerAfter  = unsafeOwnerOf(tokenId);
+
+    assert ownerBefore == 0 && ownerAfter != 0 => (
+        f.selector == mint(address,uint256).selector ||
+        f.selector == safeMint(address,uint256).selector ||
+        f.selector == safeMint(address,uint256,bytes).selector
+    );
+
+    assert ownerBefore != 0 && ownerAfter == 0 => (
+        f.selector == burn(uint256).selector
+    );
+
+    assert (ownerBefore != ownerAfter && ownerBefore != 0 && ownerAfter != 0) => (
+        f.selector == transferFrom(address,address,uint256).selector ||
+        f.selector == safeTransferFrom(address,address,uint256).selector ||
+        f.selector == safeTransferFrom(address,address,uint256,bytes).selector
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: token approval can only change through approve or transfers (implicitly).                                    │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule approvalChange(env e, uint256 tokenId) {
+    address approvalBefore = unsafeGetApproved(tokenId);
+    method f; calldataarg args; f(e, args);
+    address approvalAfter  = unsafeGetApproved(tokenId);
+
+    // approve can set any value, other functions reset
+    assert approvalBefore != approvalAfter => (
+        f.selector == approve(address,uint256).selector ||
+        (
+            (
+                f.selector == transferFrom(address,address,uint256).selector ||
+                f.selector == safeTransferFrom(address,address,uint256).selector ||
+                f.selector == safeTransferFrom(address,address,uint256,bytes).selector ||
+                f.selector == burn(uint256).selector
+            ) && approvalAfter == 0
+        )
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rules: approval for all tokens can only change through isApprovedForAll.                                            │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule approvedForAllChange(env e, address owner, address spender) {
+    bool approvedForAllBefore = isApprovedForAll(owner, spender);
+    method f; calldataarg args; f(e, args);
+    bool approvedForAllAfter  = isApprovedForAll(owner, spender);
+
+    assert approvedForAllBefore != approvedForAllAfter => f.selector == setApprovalForAll(address,bool).selector;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: transferFrom behavior and side effects                                                                        │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule transferFrom(env e, address from, address to, uint256 tokenId) {
+    require nonpayable(e);
+
+    address operator = e.msg.sender;
+    uint256 otherTokenId;
+    address otherAccount;
+
+    requireInvariant ownerHasBalance(tokenId);
+    require balanceLimited(to);
+
+    uint256 balanceOfFromBefore  = balanceOf(from);
+    uint256 balanceOfToBefore    = balanceOf(to);
+    uint256 balanceOfOtherBefore = balanceOf(otherAccount);
+    address ownerBefore          = unsafeOwnerOf(tokenId);
+    address otherOwnerBefore     = unsafeOwnerOf(otherTokenId);
+    address approvalBefore       = unsafeGetApproved(tokenId);
+    address otherApprovalBefore  = unsafeGetApproved(otherTokenId);
+
+    transferFrom@withrevert(e, from, to, tokenId);
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> (
+        from == ownerBefore &&
+        from != 0 &&
+        to   != 0 &&
+        (operator == from || operator == approvalBefore || isApprovedForAll(ownerBefore, operator))
+    );
+
+    // effect
+    assert success => (
+        balanceOf(from)            == balanceOfFromBefore - to_uint256(from != to ? 1 : 0) &&
+        balanceOf(to)              == balanceOfToBefore   + to_uint256(from != to ? 1 : 0) &&
+        unsafeOwnerOf(tokenId)     == to &&
+        unsafeGetApproved(tokenId) == 0
+    );
+
+    // no side effect
+    assert balanceOf(otherAccount)         != balanceOfOtherBefore => (otherAccount == from || otherAccount == to);
+    assert unsafeOwnerOf(otherTokenId)     != otherOwnerBefore     => otherTokenId == tokenId;
+    assert unsafeGetApproved(otherTokenId) != otherApprovalBefore  => otherTokenId == tokenId;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: safeTransferFrom behavior and side effects                                                                    │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule safeTransferFrom(env e, method f, address from, address to, uint256 tokenId) filtered { f ->
+    f.selector == safeTransferFrom(address,address,uint256).selector ||
+    f.selector == safeTransferFrom(address,address,uint256,bytes).selector
+} {
+    require nonpayable(e);
+
+    address operator = e.msg.sender;
+    uint256 otherTokenId;
+    address otherAccount;
+
+    requireInvariant ownerHasBalance(tokenId);
+    require balanceLimited(to);
+
+    uint256 balanceOfFromBefore  = balanceOf(from);
+    uint256 balanceOfToBefore    = balanceOf(to);
+    uint256 balanceOfOtherBefore = balanceOf(otherAccount);
+    address ownerBefore          = unsafeOwnerOf(tokenId);
+    address otherOwnerBefore     = unsafeOwnerOf(otherTokenId);
+    address approvalBefore       = unsafeGetApproved(tokenId);
+    address otherApprovalBefore  = unsafeGetApproved(otherTokenId);
+
+    helperTransferWithRevert(e, f, from, to, tokenId);
+    bool success = !lastReverted;
+
+    assert success <=> (
+        from == ownerBefore &&
+        from != 0 &&
+        to   != 0 &&
+        (operator == from || operator == approvalBefore || isApprovedForAll(ownerBefore, operator))
+    );
+
+    // effect
+    assert success => (
+        balanceOf(from)            == balanceOfFromBefore - to_uint256(from != to ? 1: 0) &&
+        balanceOf(to)              == balanceOfToBefore   + to_uint256(from != to ? 1: 0) &&
+        unsafeOwnerOf(tokenId)     == to &&
+        unsafeGetApproved(tokenId) == 0
+    );
+
+    // no side effect
+    assert balanceOf(otherAccount)         != balanceOfOtherBefore => (otherAccount == from || otherAccount == to);
+    assert unsafeOwnerOf(otherTokenId)     != otherOwnerBefore     => otherTokenId == tokenId;
+    assert unsafeGetApproved(otherTokenId) != otherApprovalBefore  => otherTokenId == tokenId;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: mint behavior and side effects                                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule mint(env e, address to, uint256 tokenId) {
+    require nonpayable(e);
+    requireInvariant notMintedUnset(tokenId);
+
+    uint256 otherTokenId;
+    address otherAccount;
+
+    require balanceLimited(to);
+
+    uint256 supplyBefore         = ownedTotal();
+    uint256 balanceOfToBefore    = balanceOf(to);
+    uint256 balanceOfOtherBefore = balanceOf(otherAccount);
+    address ownerBefore          = unsafeOwnerOf(tokenId);
+    address otherOwnerBefore     = unsafeOwnerOf(otherTokenId);
+
+    mint@withrevert(e, to, tokenId);
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> (
+        ownerBefore == 0 &&
+        to != 0
+    );
+
+    // effect
+    assert success => (
+        ownedTotal()           == supplyBefore + 1 &&
+        balanceOf(to)          == balanceOfToBefore + 1 &&
+        unsafeOwnerOf(tokenId) == to
+    );
+
+    // no side effect
+    assert balanceOf(otherAccount)     != balanceOfOtherBefore => otherAccount == to;
+    assert unsafeOwnerOf(otherTokenId) != otherOwnerBefore     => otherTokenId == tokenId;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: safeMint behavior and side effects                                                                            │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule safeMint(env e, method f, address to, uint256 tokenId) filtered { f ->
+    f.selector == safeMint(address,uint256).selector ||
+    f.selector == safeMint(address,uint256,bytes).selector
+} {
+    require nonpayable(e);
+    requireInvariant notMintedUnset(tokenId);
+
+    uint256 otherTokenId;
+    address otherAccount;
+
+    require balanceLimited(to);
+
+    uint256 supplyBefore         = ownedTotal();
+    uint256 balanceOfToBefore    = balanceOf(to);
+    uint256 balanceOfOtherBefore = balanceOf(otherAccount);
+    address ownerBefore          = unsafeOwnerOf(tokenId);
+    address otherOwnerBefore     = unsafeOwnerOf(otherTokenId);
+
+    helperMintWithRevert(e, f, to, tokenId);
+    bool success = !lastReverted;
+
+    assert success <=> (
+        ownerBefore == 0 &&
+        to != 0
+    );
+
+    // effect
+    assert success => (
+        ownedTotal()           == supplyBefore + 1 &&
+        balanceOf(to)          == balanceOfToBefore + 1 &&
+        unsafeOwnerOf(tokenId) == to
+    );
+
+    // no side effect
+    assert balanceOf(otherAccount)     != balanceOfOtherBefore => otherAccount == to;
+    assert unsafeOwnerOf(otherTokenId) != otherOwnerBefore     => otherTokenId == tokenId;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: burn behavior and side effects                                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule burn(env e, uint256 tokenId) {
+    require nonpayable(e);
+
+    address from = unsafeOwnerOf(tokenId);
+    uint256 otherTokenId;
+    address otherAccount;
+
+    requireInvariant ownerHasBalance(tokenId);
+
+    uint256 supplyBefore         = ownedTotal();
+    uint256 balanceOfFromBefore  = balanceOf(from);
+    uint256 balanceOfOtherBefore = balanceOf(otherAccount);
+    address ownerBefore          = unsafeOwnerOf(tokenId);
+    address otherOwnerBefore     = unsafeOwnerOf(otherTokenId);
+    address otherApprovalBefore  = unsafeGetApproved(otherTokenId);
+
+    burn@withrevert(e, tokenId);
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> (
+        ownerBefore != 0
+    );
+
+    // effect
+    assert success => (
+        ownedTotal()               == supplyBefore   - 1 &&
+        balanceOf(from)            == balanceOfFromBefore - 1 &&
+        unsafeOwnerOf(tokenId)     == 0 &&
+        unsafeGetApproved(tokenId) == 0
+    );
+
+    // no side effect
+    assert balanceOf(otherAccount)         != balanceOfOtherBefore => otherAccount == from;
+    assert unsafeOwnerOf(otherTokenId)     != otherOwnerBefore     => otherTokenId == tokenId;
+    assert unsafeGetApproved(otherTokenId) != otherApprovalBefore  => otherTokenId == tokenId;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: approve behavior and side effects                                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule approve(env e, address spender, uint256 tokenId) {
+    require nonpayable(e);
+
+    address caller = e.msg.sender;
+    address owner = unsafeOwnerOf(tokenId);
+    uint256 otherTokenId;
+
+    address otherApprovalBefore  = unsafeGetApproved(otherTokenId);
+
+    approve@withrevert(e, spender, tokenId);
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> (
+        owner != 0 &&
+        owner != spender &&
+        (owner == caller || isApprovedForAll(owner, caller))
+    );
+
+    // effect
+    assert success => unsafeGetApproved(tokenId) == spender;
+
+    // no side effect
+    assert unsafeGetApproved(otherTokenId) != otherApprovalBefore  => otherTokenId == tokenId;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: setApprovalForAll behavior and side effects                                                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule setApprovalForAll(env e, address operator, bool approved) {
+    require nonpayable(e);
+
+    address owner = e.msg.sender;
+    address otherOwner;
+    address otherOperator;
+
+    bool otherIsApprovedForAllBefore = isApprovedForAll(otherOwner, otherOperator);
+
+    setApprovalForAll@withrevert(e, operator, approved);
+    bool success = !lastReverted;
+
+    // liveness
+    assert success <=> owner != operator;
+
+    // effect
+    assert success => isApprovedForAll(owner, operator) == approved;
+
+    // no side effect
+    assert isApprovedForAll(otherOwner, otherOperator) != otherIsApprovedForAllBefore => (
+        otherOwner    == owner &&
+        otherOperator == operator
+    );
+}

certora/specs/EnumerableMap.spec

@@ -0,0 +1,334 @@
+import "helpers/helpers.spec"
+
+methods {
+    // library
+    set(bytes32,bytes32)     returns (bool)    envfree
+    remove(bytes32)          returns (bool)    envfree
+    contains(bytes32)        returns (bool)    envfree
+    length()                 returns (uint256) envfree
+    key_at(uint256)          returns (bytes32) envfree
+    value_at(uint256)        returns (bytes32) envfree
+    tryGet_contains(bytes32) returns (bool)    envfree
+    tryGet_value(bytes32)    returns (bytes32) envfree
+    get(bytes32)             returns (bytes32) envfree
+
+    // FV
+    _indexOf(bytes32) returns (uint256) envfree
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Helpers                                                                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+function sanity() returns bool {
+    return length() < max_uint256;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: the value mapping is empty for keys that are not in the EnumerableMap.                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant noValueIfNotContained(bytes32 key)
+    !contains(key) => tryGet_value(key) == 0
+    {
+        preserved set(bytes32 otherKey, bytes32 someValue) {
+            require sanity();
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: All indexed keys are contained                                                                           │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant indexedContained(uint256 index)
+    index < length() => contains(key_at(index))
+    {
+        preserved {
+            requireInvariant consistencyIndex(index);
+            requireInvariant consistencyIndex(to_uint256(length() - 1));
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: A value can only be stored at a single location                                                          │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant atUniqueness(uint256 index1, uint256 index2)
+    index1 == index2 <=> key_at(index1) == key_at(index2)
+    {
+        preserved remove(bytes32 key) {
+            requireInvariant atUniqueness(index1, to_uint256(length() - 1));
+            requireInvariant atUniqueness(index2, to_uint256(length() - 1));
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: index <> value relationship is consistent                                                                │
+│                                                                                                                     │
+│ Note that the two consistencyXxx invariants, put together, prove that at_ and _indexOf are inverse of one another.  │
+│ This proves that we have a bijection between indices (the enumerability part) and keys (the entries that are set    │
+│ and removed from the EnumerableMap).                                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant consistencyIndex(uint256 index)
+    index < length() => _indexOf(key_at(index)) == index + 1
+    {
+        preserved remove(bytes32 key) {
+            requireInvariant consistencyIndex(to_uint256(length() - 1));
+        }
+    }
+
+invariant consistencyKey(bytes32 key)
+    contains(key) => (
+        _indexOf(key) > 0 &&
+        _indexOf(key) <= length() &&
+        key_at(to_uint256(_indexOf(key) - 1)) == key
+    )
+    {
+        preserved remove(bytes32 otherKey) {
+            requireInvariant consistencyKey(otherKey);
+            requireInvariant atUniqueness(
+                to_uint256(_indexOf(key) - 1),
+                to_uint256(_indexOf(otherKey) - 1)
+            );
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: state only changes by setting or removing elements                                                            │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule stateChange(env e, bytes32 key) {
+    require sanity();
+    requireInvariant consistencyKey(key);
+
+    uint256 lengthBefore   = length();
+    bool    containsBefore = contains(key);
+    bytes32 valueBefore    = tryGet_value(key);
+
+    method f;
+    calldataarg args;
+    f(e, args);
+
+    uint256 lengthAfter   = length();
+    bool    containsAfter = contains(key);
+    bytes32 valueAfter    = tryGet_value(key);
+
+    assert lengthBefore != lengthAfter => (
+        (f.selector == set(bytes32,bytes32).selector && lengthAfter == lengthBefore + 1) ||
+        (f.selector == remove(bytes32).selector      && lengthAfter == lengthBefore - 1)
+    );
+
+    assert containsBefore != containsAfter => (
+        (f.selector == set(bytes32,bytes32).selector && containsAfter) ||
+        (f.selector == remove(bytes32).selector      && !containsAfter)
+    );
+
+    assert valueBefore != valueAfter => (
+        (f.selector == set(bytes32,bytes32).selector && containsAfter) ||
+        (f.selector == remove(bytes32).selector      && !containsAfter && valueAfter == 0)
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: check liveness of view functions.                                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule liveness_1(bytes32 key) {
+    requireInvariant consistencyKey(key);
+
+    // contains never revert
+    bool contains = contains@withrevert(key);
+    assert !lastReverted;
+
+    // tryGet never reverts (key)
+    tryGet_contains@withrevert(key);
+    assert !lastReverted;
+
+    // tryGet never reverts (value)
+    tryGet_value@withrevert(key);
+    assert !lastReverted;
+
+    // get reverts iff  the key is not in the map
+    get@withrevert(key);
+    assert !lastReverted <=> contains;
+}
+
+rule liveness_2(uint256 index) {
+    requireInvariant consistencyIndex(index);
+
+    // length never revert
+    uint256 length = length@withrevert();
+    assert !lastReverted;
+
+    // key_at reverts iff the index is out of bound
+    key_at@withrevert(index);
+    assert !lastReverted <=> index < length;
+
+    // value_at reverts iff the index is out of bound
+    value_at@withrevert(index);
+    assert !lastReverted <=> index < length;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: get and tryGet return the expected values.                                                                    │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule getAndTryGet(bytes32 key) {
+    requireInvariant noValueIfNotContained(key);
+
+    bool    contained    = contains(key);
+    bool    tryContained = tryGet_contains(key);
+    bytes32 tryValue     = tryGet_value(key);
+    bytes32 value        = get@withrevert(key); // revert is not contained
+
+    assert contained == tryContained;
+    assert contained => tryValue == value;
+    assert !contained => tryValue == 0;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: set key-value in EnumerableMap                                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule set(bytes32 key, bytes32 value, bytes32 otherKey) {
+    require sanity();
+
+    uint256 lengthBefore        = length();
+    bool    containsBefore      = contains(key);
+    bool    containsOtherBefore = contains(otherKey);
+    bytes32 otherValueBefore    = tryGet_value(otherKey);
+
+    bool added = set@withrevert(key, value);
+    bool success = !lastReverted;
+
+    assert success && contains(key) && get(key) == value,
+        "liveness & immediate effect";
+
+    assert added <=> !containsBefore,
+        "return value: added iff not contained";
+
+    assert length() == lengthBefore + to_mathint(added ? 1 : 0),
+        "effect: length increases iff added";
+
+    assert added => (key_at(lengthBefore) == key && value_at(lengthBefore) == value),
+        "effect: add at the end";
+
+    assert containsOtherBefore != contains(otherKey) => (added && key == otherKey),
+        "side effect: other keys are not affected";
+
+    assert otherValueBefore != tryGet_value(otherKey) => key == otherKey,
+        "side effect: values attached to other keys are not affected";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: remove key from EnumerableMap                                                                                 │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule remove(bytes32 key, bytes32 otherKey) {
+    requireInvariant consistencyKey(key);
+    requireInvariant consistencyKey(otherKey);
+
+    uint256 lengthBefore        = length();
+    bool    containsBefore      = contains(key);
+    bool    containsOtherBefore = contains(otherKey);
+    bytes32 otherValueBefore    = tryGet_value(otherKey);
+
+    bool removed = remove@withrevert(key);
+    bool success = !lastReverted;
+
+    assert success && !contains(key),
+        "liveness & immediate effect";
+
+    assert removed <=> containsBefore,
+        "return value: removed iff contained";
+
+    assert length() == lengthBefore - to_mathint(removed ? 1 : 0),
+        "effect: length decreases iff removed";
+
+    assert containsOtherBefore != contains(otherKey) => (removed && key == otherKey),
+        "side effect: other keys are not affected";
+
+    assert otherValueBefore != tryGet_value(otherKey) => key == otherKey,
+        "side effect: values attached to other keys are not affected";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: when adding a new key, the other keys remain in set, at the same index.                                       │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule setEnumerability(bytes32 key, bytes32 value, uint256 index) {
+    require sanity();
+
+    bytes32 atKeyBefore = key_at(index);
+    bytes32 atValueBefore = value_at(index);
+
+    set(key, value);
+
+    bytes32 atKeyAfter = key_at@withrevert(index);
+    assert !lastReverted;
+
+    bytes32 atValueAfter = value_at@withrevert(index);
+    assert !lastReverted;
+
+    assert atKeyAfter == atKeyBefore;
+    assert atValueAfter != atValueBefore => (
+        key == atKeyBefore &&
+        value == atValueAfter
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: when removing a existing key, the other keys remain in set, at the same index (except for the last one).      │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule removeEnumerability(bytes32 key, uint256 index) {
+    uint256 last = length() - 1;
+
+    requireInvariant consistencyKey(key);
+    requireInvariant consistencyIndex(index);
+    requireInvariant consistencyIndex(last);
+
+    bytes32 atKeyBefore     = key_at(index);
+    bytes32 atValueBefore   = value_at(index);
+    bytes32 lastKeyBefore   = key_at(last);
+    bytes32 lastValueBefore = value_at(last);
+
+    remove(key);
+
+    // can't read last value & keys (length decreased)
+    bytes32 atKeyAfter = key_at@withrevert(index);
+    assert lastReverted <=> index == last;
+
+    bytes32 atValueAfter = value_at@withrevert(index);
+    assert lastReverted <=> index == last;
+
+    // One value that is allowed to change is if previous value was removed,
+    // in that case the last value before took its place.
+    assert (
+        index != last &&
+        atKeyBefore != atKeyAfter
+    ) => (
+        atKeyBefore == key &&
+        atKeyAfter == lastKeyBefore
+    );
+
+    assert (
+        index != last &&
+        atValueBefore != atValueAfter
+    ) => (
+        atValueAfter == lastValueBefore
+    );
+}

certora/specs/EnumerableSet.spec

@@ -0,0 +1,247 @@
+import "helpers/helpers.spec"
+
+methods {
+    // library
+    add(bytes32)      returns (bool)    envfree
+    remove(bytes32)   returns (bool)    envfree
+    contains(bytes32) returns (bool)    envfree
+    length()          returns (uint256) envfree
+    at_(uint256)      returns (bytes32) envfree
+
+    // FV
+    _indexOf(bytes32) returns (uint256) envfree
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Helpers                                                                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+function sanity() returns bool {
+    return length() < max_uint256;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: All indexed keys are contained                                                                           │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant indexedContained(uint256 index)
+    index < length() => contains(at_(index))
+    {
+        preserved {
+            requireInvariant consistencyIndex(index);
+            requireInvariant consistencyIndex(to_uint256(length() - 1));
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: A value can only be stored at a single location                                                          │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant atUniqueness(uint256 index1, uint256 index2)
+    index1 == index2 <=> at_(index1) == at_(index2)
+    {
+        preserved remove(bytes32 key) {
+            requireInvariant atUniqueness(index1, to_uint256(length() - 1));
+            requireInvariant atUniqueness(index2, to_uint256(length() - 1));
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: index <> key relationship is consistent                                                                  │
+│                                                                                                                     │
+│ Note that the two consistencyXxx invariants, put together, prove that at_ and _indexOf are inverse of one another.  │
+│ This proves that we have a bijection between indices (the enumerability part) and keys (the entries that are added  │
+│ and removed from the EnumerableSet).                                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant consistencyIndex(uint256 index)
+    index < length() => _indexOf(at_(index)) == index + 1
+    {
+        preserved remove(bytes32 key) {
+            requireInvariant consistencyIndex(to_uint256(length() - 1));
+        }
+    }
+
+invariant consistencyKey(bytes32 key)
+    contains(key) => (
+        _indexOf(key) > 0 &&
+        _indexOf(key) <= length() &&
+        at_(to_uint256(_indexOf(key) - 1)) == key
+    )
+    {
+        preserved remove(bytes32 otherKey) {
+            requireInvariant consistencyKey(otherKey);
+            requireInvariant atUniqueness(
+                to_uint256(_indexOf(key) - 1),
+                to_uint256(_indexOf(otherKey) - 1)
+            );
+        }
+    }
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: state only changes by adding or removing elements                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule stateChange(env e, bytes32 key) {
+    require sanity();
+    requireInvariant consistencyKey(key);
+
+    uint256 lengthBefore   = length();
+    bool    containsBefore = contains(key);
+
+    method f;
+    calldataarg args;
+    f(e, args);
+
+    uint256 lengthAfter   = length();
+    bool    containsAfter = contains(key);
+
+    assert lengthBefore != lengthAfter => (
+        (f.selector == add(bytes32).selector    && lengthAfter == lengthBefore + 1) ||
+        (f.selector == remove(bytes32).selector && lengthAfter == lengthBefore - 1)
+    );
+
+    assert containsBefore != containsAfter => (
+        (f.selector == add(bytes32).selector    && containsAfter) ||
+        (f.selector == remove(bytes32).selector && containsBefore)
+    );
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: check liveness of view functions.                                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule liveness_1(bytes32 key) {
+    requireInvariant consistencyKey(key);
+
+    // contains never revert
+    contains@withrevert(key);
+    assert !lastReverted;
+}
+
+rule liveness_2(uint256 index) {
+    requireInvariant consistencyIndex(index);
+
+    // length never revert
+    uint256 length = length@withrevert();
+    assert !lastReverted;
+
+    // at reverts iff the index is out of bound
+    at_@withrevert(index);
+    assert !lastReverted <=> index < length;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: add key to EnumerableSet if not already contained                                                             │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule add(bytes32 key, bytes32 otherKey) {
+    require sanity();
+
+    uint256 lengthBefore        = length();
+    bool    containsBefore      = contains(key);
+    bool    containsOtherBefore = contains(otherKey);
+
+    bool added = add@withrevert(key);
+    bool success = !lastReverted;
+
+    assert success && contains(key),
+        "liveness & immediate effect";
+
+    assert added <=> !containsBefore,
+        "return value: added iff not contained";
+
+    assert length() == lengthBefore + to_mathint(added ? 1 : 0),
+        "effect: length increases iff added";
+
+    assert added => at_(lengthBefore) == key,
+        "effect: add at the end";
+
+    assert containsOtherBefore != contains(otherKey) => (added && key == otherKey),
+        "side effect: other keys are not affected";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: remove key from EnumerableSet if already contained                                                            │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule remove(bytes32 key, bytes32 otherKey) {
+    requireInvariant consistencyKey(key);
+    requireInvariant consistencyKey(otherKey);
+
+    uint256 lengthBefore        = length();
+    bool    containsBefore      = contains(key);
+    bool    containsOtherBefore = contains(otherKey);
+
+    bool removed = remove@withrevert(key);
+    bool success = !lastReverted;
+
+    assert success && !contains(key),
+        "liveness & immediate effect";
+
+    assert removed <=> containsBefore,
+        "return value: removed iff contained";
+
+    assert length() == lengthBefore - to_mathint(removed ? 1 : 0),
+        "effect: length decreases iff removed";
+
+    assert containsOtherBefore != contains(otherKey) => (removed && key == otherKey),
+        "side effect: other keys are not affected";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: when adding a new key, the other keys remain in set, at the same index.                                       │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule addEnumerability(bytes32 key, uint256 index) {
+    require sanity();
+
+    bytes32 atBefore = at_(index);
+    add(key);
+    bytes32 atAfter = at_@withrevert(index);
+    bool atAfterSuccess = !lastReverted;
+
+    assert atAfterSuccess;
+    assert atBefore == atAfter;
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: when removing a existing key, the other keys remain in set, at the same index (except for the last one).      │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule removeEnumerability(bytes32 key, uint256 index) {
+    uint256 last = length() - 1;
+
+    requireInvariant consistencyKey(key);
+    requireInvariant consistencyIndex(index);
+    requireInvariant consistencyIndex(last);
+
+    bytes32 atBefore = at_(index);
+    bytes32 lastBefore = at_(last);
+
+    remove(key);
+
+    // can't read last value (length decreased)
+    bytes32 atAfter = at_@withrevert(index);
+    assert lastReverted <=> index == last;
+
+    // One value that is allowed to change is if previous value was removed,
+    // in that case the last value before took its place.
+    assert (
+        index != last &&
+        atBefore != atAfter
+    ) => (
+        atBefore == key &&
+        atAfter == lastBefore
+    );
+}

certora/specs/Initializable.spec

@@ -0,0 +1,165 @@
+import "helpers/helpers.spec"
+
+methods {
+    // initialize, reinitialize, disable
+    initialize()        envfree
+    reinitialize(uint8) envfree
+    disable()           envfree
+
+    nested_init_init()            envfree
+    nested_init_reinit(uint8)       envfree
+    nested_reinit_init(uint8)       envfree
+    nested_reinit_reinit(uint8,uint8) envfree
+
+    // view
+    version()      returns uint8 envfree
+    initializing() returns bool  envfree
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Definitions                                                                                                         │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+definition isUninitialized() returns bool = version() == 0;
+definition isInitialized()   returns bool = version() > 0;
+definition isDisabled()      returns bool = version() == 255;
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Invariant: A contract must only ever be in an initializing state while in the middle of a transaction execution.    │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+invariant notInitializing()
+    !initializing()
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: The version cannot decrease & disable state is irrevocable.                                                   │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule increasingVersion(env e) {
+    uint8 versionBefore = version();
+    bool disabledBefore = isDisabled();
+
+    method f; calldataarg args;
+    f(e, args);
+
+    assert versionBefore <= version(), "_initialized must only increase";
+    assert disabledBefore => isDisabled(), "a disabled initializer must stay disabled";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: Cannot initialize a contract that is already initialized.                                                     │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule cannotInitializeTwice() {
+    require isInitialized();
+
+    initialize@withrevert();
+
+    assert lastReverted, "contract must only be initialized once";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: Cannot initialize once disabled.                                                                              │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule cannotInitializeOnceDisabled() {
+    require isDisabled();
+
+    initialize@withrevert();
+
+    assert lastReverted, "contract is disabled";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: Cannot reinitialize once disabled.                                                                            │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule cannotReinitializeOnceDisabled() {
+    require isDisabled();
+
+    uint8 n;
+    reinitialize@withrevert(n);
+
+    assert lastReverted, "contract is disabled";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: Cannot nest initializers (after construction).                                                                │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule cannotNestInitializers_init_init() {
+    nested_init_init@withrevert();
+    assert lastReverted, "nested initializers";
+}
+
+rule cannotNestInitializers_init_reinit(uint8 m) {
+    nested_init_reinit@withrevert(m);
+    assert lastReverted, "nested initializers";
+}
+
+rule cannotNestInitializers_reinit_init(uint8 n) {
+    nested_reinit_init@withrevert(n);
+    assert lastReverted, "nested initializers";
+}
+
+rule cannotNestInitializers_reinit_reinit(uint8 n, uint8 m) {
+    nested_reinit_reinit@withrevert(n, m);
+    assert lastReverted, "nested initializers";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: Initialize correctly sets the version.                                                                        │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule initializeEffects() {
+    requireInvariant notInitializing();
+
+    bool isUninitializedBefore = isUninitialized();
+
+    initialize@withrevert();
+    bool success = !lastReverted;
+
+    assert success <=> isUninitializedBefore, "can only initialize uninitialized contracts";
+    assert success => version() == 1,         "initialize must set version() to 1";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: Reinitialize correctly sets the version.                                                                      │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule reinitializeEffects() {
+    requireInvariant notInitializing();
+
+    uint8 versionBefore = version();
+
+    uint8 n;
+    reinitialize@withrevert(n);
+    bool success = !lastReverted;
+
+    assert success <=> versionBefore < n, "can only reinitialize to a latter versions";
+    assert success => version() == n,     "reinitialize must set version() to n";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: Can disable.                                                                                                  │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule disableEffect() {
+    requireInvariant notInitializing();
+
+    disable@withrevert();
+    bool success = !lastReverted;
+
+    assert success,      "call to _disableInitializers failed";
+    assert isDisabled(), "disable state not set";
+}

certora/specs/Ownable.spec

@@ -0,0 +1,78 @@
+import "helpers/helpers.spec"
+import "methods/IOwnable.spec"
+
+methods {
+    restricted()
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: transferOwnership changes ownership                                                           │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule transferOwnership(env e) {
+    require nonpayable(e);
+
+    address newOwner;
+    address current = owner();
+
+    transferOwnership@withrevert(e, newOwner);
+    bool success = !lastReverted;
+
+    assert success <=> (e.msg.sender == current && newOwner != 0), "unauthorized caller or invalid arg";
+    assert success => owner() == newOwner, "current owner changed";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Function correctness: renounceOwnership removes the owner                                                           │
+
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule renounceOwnership(env e) {
+    require nonpayable(e);
+
+    address current = owner();
+
+    renounceOwnership@withrevert(e);
+    bool success = !lastReverted;
+
+    assert success <=> e.msg.sender == current, "unauthorized caller";
+    assert success => owner() == 0, "owner not cleared";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Access control: only current owner can call restricted functions                                                    │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule onlyCurrentOwnerCanCallOnlyOwner(env e) {
+    require nonpayable(e);
+
+    address current = owner();
+
+    calldataarg args;
+    restricted@withrevert(e, args);
+
+    assert !lastReverted <=> e.msg.sender == current, "access control failed";
+}
+
+/*
+┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
+│ Rule: ownership can only change in specific ways                                                                    │
+└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+*/
+rule onlyOwnerOrPendingOwnerCanChangeOwnership(env e) {
+    address oldCurrent = owner();
+
+    method f; calldataarg args;
+    f(e, args);
+
+    address newCurrent = owner();
+
+    // If owner changes, must be either transferOwnership or renounceOwnership
+    assert oldCurrent != newCurrent => (
+        (e.msg.sender == oldCurrent && newCurrent != 0 && f.selector == transferOwnership(address).selector) ||
+        (e.msg.sender == oldCurrent && newCurrent == 0 && f.selector == renounceOwnership().selector)
+    );
+}