Release v4.9.0 (rc) (#4228)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

.babelrc

@@ -1,3 +0,0 @@
-{
-  "presets": ["es2015", "stage-2", "stage-3"]
-}

.changeset/beige-buses-drop.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`Initializable`: optimize `_disableInitializers` by using `!=` instead of `<`.
+
+pr: #3787

.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/curvy-shrimps-enjoy.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`ReentrancyGuard`: Add a `_reentrancyGuardEntered` function to expose the guard status.
+
+pr: #3714

.changeset/curvy-suns-sort.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`Ownable2Step`: make `acceptOwnership` public virtual to enable usecases that require overriding it.
+
+pr: #3960

.changeset/early-oranges-raise.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`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.

.changeset/famous-rules-burn.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`EnumerableMap`: add a `keys()` function that returns an array containing all the keys.
+
+pr: #3920

.changeset/five-ducks-develop.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`UUPSUpgradeable.sol`: Change visibility to the functions `upgradeTo ` and `upgradeToAndCall ` from `external` to `public`.

.changeset/five-poets-mix.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`TimelockController`: Add the `CallSalt` event to emit on operation schedule.

.changeset/flat-deers-end.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`Governor`: add a public `cancel(uint256)` function.

.changeset/four-bats-sniff.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`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.

.changeset/funny-rockets-compete.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': patch
+---
+
+Reformatted codebase with latest version of Prettier Solidity.
+
+pr: #3898

.changeset/gold-chicken-clean.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`Strings`: add `equal` method.
+
+pr: #3774

.changeset/happy-socks-travel.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`IERC5313`: Add an interface for EIP-5313 that is now final.

.changeset/healthy-squids-stare.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`Math`: optimize `log256` rounding check.
+
+pr: #3745

.changeset/lemon-dogs-kiss.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`ERC20Votes`: optimize by using unchecked arithmetic.
+
+pr: #3748

.changeset/little-kiwis-ring.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`Multicall`: annotate `multicall` function as upgrade safe to not raise a flag for its delegatecall.
+
+pr: #3961

.changeset/lovely-dragons-appear.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`IERC4906`: Add an interface for ERC-4906 that is now Final.

.changeset/modern-games-exist.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`StorageSlot`: Add support for `string` and `bytes`.

.changeset/new-ways-own.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`ERC20Pausable`, `ERC721Pausable`, `ERC1155Pausable`: Add note regarding missing public pausing functionality

.changeset/ninety-hornets-kick.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`Votes`, `ERC20Votes`, `ERC721Votes`: support timestamp checkpointing using EIP-6372.

.changeset/perfect-insects-listen.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`ERC4626`: Add mitigation to the inflation attack through virtual shares and assets.

.changeset/pre.json

@@ -0,0 +1,44 @@
+{
+  "mode": "pre",
+  "tag": "rc",
+  "initialVersions": {
+    "openzeppelin-solidity": "4.8.2"
+  },
+  "changesets": [
+    "beige-buses-drop",
+    "curvy-shrimps-enjoy",
+    "curvy-suns-sort",
+    "early-oranges-raise",
+    "famous-rules-burn",
+    "five-ducks-develop",
+    "five-poets-mix",
+    "flat-deers-end",
+    "four-bats-sniff",
+    "funny-rockets-compete",
+    "gold-chicken-clean",
+    "happy-socks-travel",
+    "healthy-squids-stare",
+    "lemon-dogs-kiss",
+    "little-kiwis-ring",
+    "lovely-dragons-appear",
+    "modern-games-exist",
+    "new-ways-own",
+    "ninety-hornets-kick",
+    "perfect-insects-listen",
+    "pretty-hornets-play",
+    "proud-comics-deliver",
+    "short-roses-judge",
+    "silent-dancers-type",
+    "slimy-knives-hug",
+    "small-cars-appear",
+    "small-terms-sleep",
+    "strong-bulldogs-buy",
+    "tame-ladybugs-sit",
+    "tender-needles-dance",
+    "thin-dragons-report",
+    "thirty-swans-exercise",
+    "violet-frogs-hide",
+    "warm-masks-obey",
+    "yellow-swans-cover"
+  ]
+}

.changeset/pretty-hornets-play.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`Strings`: add `toString` method for signed integers.
+
+pr: #3773

.changeset/proud-comics-deliver.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`ERC20Wrapper`: Make the `underlying` variable private and add a public accessor.

.changeset/short-roses-judge.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`EIP712`: add EIP-5267 support for better domain discovery.

.changeset/silent-dancers-type.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`AccessControlDefaultAdminRules`: Add an extension of `AccessControl` with additional security rules for the `DEFAULT_ADMIN_ROLE`.

.changeset/slimy-knives-hug.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`SignatureChecker`: Add `isValidERC1271SignatureNow` for checking a signature directly against a smart contract using ERC-1271.

.changeset/small-cars-appear.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`ECDSA`: Add a function `toDataWithIntendedValidatorHash` that encodes data with version 0x00 following EIP-191.

.changeset/small-terms-sleep.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`SafeERC20`: Add a `forceApprove` function to improve compatibility with tokens behaving like USDT.

.changeset/strong-bulldogs-buy.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`ERC1967Upgrade`: removed contract-wide `oz-upgrades-unsafe-allow delegatecall` annotation, replaced by granular annotation in `UUPSUpgradeable`.

.changeset/tame-ladybugs-sit.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`MerkleProof`: optimize by using unchecked arithmetic.
+
+pr: #3745

.changeset/tender-needles-dance.md

@@ -0,0 +1,7 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`ERC20Wrapper`: self wrapping and deposit by the wrapper itself are now explicitelly forbiden.
+
+commit: 3214f6c25

.changeset/thin-dragons-report.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`ECDSA`: optimize bytes32 computation by using assembly instead of `abi.encodePacked`.

.changeset/thirty-swans-exercise.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`ERC721URIStorage`: Emit ERC-4906 `MetadataUpdate` in `_setTokenURI`.

.changeset/violet-frogs-hide.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`ShortStrings`: Added a library for handling short strings in a gas efficient way, with fallback to storage for longer strings.

.changeset/warm-masks-obey.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`SignatureChecker`: Allow return data length greater than 32 from EIP-1271 signers.

.changeset/yellow-swans-cover.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`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`).

.codecov.yml

@@ -0,0 +1,12 @@
+comment: off
+github_checks:
+  annotations: false
+coverage:
+  status:
+    patch:
+      default:
+        target: 95%
+        only_pulls: true
+    project:
+      default:
+        threshold: 1%

.editorconfig

@@ -0,0 +1,21 @@
+# EditorConfig is awesome: https://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_style = space
+insert_final_newline = true
+trim_trailing_whitespace = false
+max_line_length = 120
+
+[*.sol]
+indent_size = 4
+
+[*.js]
+indent_size = 2
+
+[*.{adoc,md}]
+max_line_length = 0

.eslintrc

@@ -0,0 +1,20 @@
+{
+  "root": true,
+  "extends" : [
+    "eslint:recommended",
+    "prettier",
+  ],
+  "env": {
+    "es2022": true,
+    "browser": true,
+    "node": true,
+    "mocha": true,
+  },
+  "globals" : {
+    "artifacts": "readonly",
+    "contract": "readonly",
+    "web3": "readonly",
+    "extendEnvironment": "readonly",
+    "expect": "readonly",
+  }
+}

.github/ISSUE_TEMPLATE/bug_report.md

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

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,4 @@
+contact_links:
+  - name: Questions & Support Requests
+    url: https://forum.openzeppelin.com/c/support/contracts/18
+    about: Ask in the OpenZeppelin Forum

.github/ISSUE_TEMPLATE/feature_request.md

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

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,20 @@
+<!-- Thank you for your interest in contributing to OpenZeppelin! -->
+
+<!-- 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. -->
+
+Fixes #???? <!-- Fill in with issue number -->
+
+<!-- Describe the changes introduced in this pull request. -->
+<!-- Include any context necessary for understanding the PR's purpose. -->
+
+
+#### 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/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 +1,113 @@
+name: checks
+
+on:
+  push:
+    branches:
+      - master
+      - 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@v1.0
+        with:
+          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

@@ -1,5 +1,71 @@
 *.swp
 *.swo
-node_modules/
+
+# Logs
+logs
+*.log
+
+# Runtime data
+pids
+*.pid
+*.seed
+allFiredEvents
+scTopics
+
+# Coverage directory used by tools like istanbul
+coverage
+coverage.json
+coverageEnv
+
+# node-waf configuration
+.lock-wscript
+
+# Dependency directory
+node_modules
+
+# Debug log from npm
+npm-debug.log
+
+# local env variables
+.env
+
+# truffle build directory
 build/
-.DS_Store/
+
+# macOS
+.DS_Store
+
+# truffle
+.node-xmlhttprequest-*
+
+# IntelliJ IDE
+.idea
+
+# docs artifacts
+docs/modules/api
+
+# only used to package @openzeppelin/contracts
+contracts/build/
+contracts/README.md
+
+# temporary artifact from solidity-coverage
+allFiredEvents
+.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

@@ -0,0 +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

@@ -0,0 +1,13 @@
+module.exports = {
+  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

@@ -0,0 +1,14 @@
+{
+  "rules": {
+    "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",
+    "var-name-mixedcase": "error",
+    "imports-on-top": "error"
+  }
+}

.travis.yml

@@ -1,12 +0,0 @@
-dist: trusty
-sudo: false
-group: beta
-language: node_js
-node_js:
-  - "6"
-before_install:
-  - npm i -g ethereumjs-testrpc
-  - npm i -g truffle
-script:
-  - testrpc&
-  - npm test

CHANGELOG.md

@@ -0,0 +1,717 @@
+# Changelog
+
+
+## 4.9.0-rc.0 (2023-05-09)
+
+- `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 explicitelly forbiden. ([#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))
+
+#### Proxy changes with respect to OpenZeppelin SDK
+
+Aside from upgrading them from Solidity 0.5 to 0.6, we've changed a few minor things from the proxy contracts as they were found in OpenZeppelin SDK.
+
+- `UpgradeabilityProxy` was renamed to `UpgradeableProxy`.
+- `AdminUpgradeabilityProxy` was renamed to `TransparentUpgradeableProxy`.
+- `Proxy._willFallback` was renamed to `Proxy._beforeFallback`.
+- `UpgradeabilityProxy._setImplementation` and `AdminUpgradeabilityProxy._setAdmin` were made private.
+
+### Improvements
+
+- `Address.isContract`: switched from `extcodehash` to `extcodesize` for less gas usage. ([#2311](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2311))
+
+### Breaking changes
+
+- `ERC20Snapshot`: switched to using `_beforeTokenTransfer` hook instead of overriding ERC20 operations. ([#2312](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2312))
+
+This small change in the way we implemented `ERC20Snapshot` may affect users who are combining this contract with
+other ERC20 flavors, since it no longer overrides `_transfer`, `_mint`, and `_burn`. This can result in having to remove Solidity `override(...)` specifiers in derived contracts for these functions, and to instead have to add it for `_beforeTokenTransfer`. See [Using Hooks](https://docs.openzeppelin.com/contracts/3.x/extending-contracts#using-hooks) in the documentation.
+
+## 3.1.0 (2020-06-23)
+
+### New features
+
+- `SafeCast`: added functions to downcast signed integers (e.g. `toInt32`), improving usability of `SignedSafeMath`. ([#2243](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2243))
+- `functionCall`: new helpers that replicate Solidity's function call semantics, reducing the need to rely on `call`. ([#2264](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2264))
+- `ERC1155`: added support for a base implementation, non-standard extensions and a preset contract. ([#2014](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2014), [#2230](https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2230))
+
+### Improvements
+
+- `ReentrancyGuard`: reduced overhead of using the `nonReentrant` modifier. ([#2171](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2171))
+- `AccessControl`: added a `RoleAdminChanged` event to `_setAdminRole`. ([#2214](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2214))
+- Made all `public` functions in the token preset contracts `virtual`. ([#2257](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2257))
+
+### Deprecations
+
+- `SafeERC20`: deprecated `safeApprove`. ([#2268](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2268))
+
+## 3.0.2 (2020-06-08)
+
+### Improvements
+
+- Added SPX license identifier to all contracts. ([#2235](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2235))
+
+## 3.0.1 (2020-04-27)
+
+### Bugfixes
+
+- `ERC777`: fixed the `_approve` internal function not validating some of their arguments for non-zero addresses. ([#2213](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2213))
+
+## 3.0.0 (2020-04-20)
+
+### New features
+
+- `AccessControl`: new contract for managing permissions in a system, replacement for `Ownable` and `Roles`. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
+- `SafeCast`: new functions to convert to and from signed and unsigned values: `toUint256` and `toInt256`. ([#2123](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2123))
+- `EnumerableMap`: a new data structure for key-value pairs (like `mapping`) that can be iterated over. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+
+### Breaking changes
+
+- `ERC721`: `burn(owner, tokenId)` was removed, use `burn(tokenId)` instead. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+- `ERC721`: `_checkOnERC721Received` was removed. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+- `ERC721`: `_transferFrom` and `_safeTransferFrom` were renamed to `_transfer` and `_safeTransfer`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+- `Ownable`: removed `_transferOwnership`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+- `PullPayment`, `Escrow`: `withdrawWithGas` was removed. The old `withdraw` function now forwards all gas. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+- `Roles` was removed, use `AccessControl` as a replacement. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
+- `ECDSA`: when receiving an invalid signature, `recover` now reverts instead of returning the zero address. ([#2114](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2114))
+- `Create2`: added an `amount` argument to `deploy` for contracts with `payable` constructors. ([#2117](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2117))
+- `Pausable`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `Strings`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `Counters`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `SignedSafeMath`: moved to the `math` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `ERC20Snapshot`: moved to the `token/ERC20` directory. `snapshot` was changed into an `internal` function. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+- `Ownable`: moved to the `access` directory. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+- `Ownable`: removed `isOwner`. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+- `Secondary`: removed from the library, use `Ownable` instead. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+- `Escrow`, `ConditionalEscrow`, `RefundEscrow`: these now use `Ownable` instead of `Secondary`, their external API changed accordingly. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+- `ERC20`: removed `_burnFrom`. ([#2119](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2119))
+- `Address`: removed `toPayable`, use `payable(address)` instead. ([#2133](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2133))
+- `ERC777`: `_send`, `_mint` and `_burn` now use the caller as the operator. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+- `ERC777`: removed `_callsTokensToSend` and `_callTokensReceived`. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+- `EnumerableSet`: renamed `get` to `at`. ([#2151](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2151))
+- `ERC165Checker`: functions no longer have a leading underscore. ([#2150](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2150))
+- `ERC721Metadata`, `ERC721Enumerable`: these contracts were removed, and their functionality merged into `ERC721`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+- `ERC721`: added a constructor for `name` and `symbol`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+- `ERC20Detailed`: this contract was removed and its functionality merged into `ERC20`. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
+- `ERC20`: added a constructor for `name` and `symbol`. `decimals` now defaults to 18. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
+- `Strings`: renamed `fromUint256` to `toString` ([#2188](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2188))
+
+## 2.5.1 (2020-04-24)
+
+### Bugfixes
+
+- `ERC777`: fixed the `_send` and `_approve` internal functions not validating some of their arguments for non-zero addresses. ([#2212](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2212))
+
+## 2.5.0 (2020-02-04)
+
+### New features
+
+- `SafeCast.toUintXX`: new library for integer downcasting, which allows for safe operation on smaller types (e.g. `uint32`) when combined with `SafeMath`. ([#1926](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1926))
+- `ERC721Metadata`: added `baseURI`, which can be used for dramatic gas savings when all token URIs share a prefix (e.g. `http://api.myapp.com/tokens/<id>`). ([#1970](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1970))
+- `EnumerableSet`: new library for storing enumerable sets of values. Only `AddressSet` is supported in this release. ([#2061](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/2061))
+- `Create2`: simple library to make usage of the `CREATE2` opcode easier. ([#1744](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1744))
+
+### Improvements
+
+- `ERC777`: `_burn` is now internal, providing more flexibility and making it easier to create tokens that deflate. ([#1908](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1908))
+- `ReentrancyGuard`: greatly improved gas efficiency by using the net gas metering mechanism introduced in the Istanbul hardfork. ([#1992](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1992), [#1996](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1996))
+- `ERC777`: improve extensibility by making `_send` and related functions `internal`. ([#2027](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2027))
+- `ERC721`: improved revert reason when transferring tokens to a non-recipient contract. ([#2018](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2018))
+
+### Breaking changes
+
+- `ERC165Checker` now requires a minimum Solidity compiler version of 0.5.10. ([#1829](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1829))
+
+## 2.4.0 (2019-10-29)
+
+### New features
+
+- `Address.toPayable`: added a helper to convert between address types without having to resort to low-level casting. ([#1773](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1773))
+- Facilities to make metatransaction-enabled contracts through the Gas Station Network. ([#1844](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1844))
+- `Address.sendValue`: added a replacement to Solidity's `transfer`, removing the fixed gas stipend. ([#1962](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1962))
+- Added replacement for functions that don't forward all gas (which have been deprecated): ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))
+  - `PullPayment.withdrawPaymentsWithGas(address payable payee)`
+  - `Escrow.withdrawWithGas(address payable payee)`
+- `SafeMath`: added support for custom error messages to `sub`, `div` and `mod` functions. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+
+### Improvements
+
+- `Address.isContract`: switched from `extcodesize` to `extcodehash` for less gas usage. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
+- `ERC20` and `ERC777` updated to throw custom errors on subtraction overflows. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+
+### Deprecations
+
+- Deprecated functions that don't forward all gas: ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))
+  - `PullPayment.withdrawPayments(address payable payee)`
+  - `Escrow.withdraw(address payable payee)`
+
+### Breaking changes
+
+- `Address` now requires a minimum Solidity compiler version of 0.5.5. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
+- `SignatureBouncer` has been removed from drafts, both to avoid confusions with the GSN and `GSNRecipientSignature` (previously called `GSNBouncerSignature`) and because the API was not very clear. ([#1879](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1879))
+
+### How to upgrade from 2.4.0-beta
+
+The final 2.4.0 release includes a refactor of the GSN contracts that will be a breaking change for 2.4.0-beta users.
+
+- The default empty implementations of `_preRelayedCall` and `_postRelayedCall` were removed and must now be explicitly implemented always in custom recipients. If your custom recipient didn't include an implementation, you can provide an empty one.
+- `GSNRecipient`, `GSNBouncerBase`, and `GSNContext` were all merged into `GSNRecipient`.
+- `GSNBouncerSignature` and `GSNBouncerERC20Fee` were renamed to `GSNRecipientSignature` and `GSNRecipientERC20Fee`.
+- It is no longer necessary to inherit from `GSNRecipient` when using `GSNRecipientSignature` and `GSNRecipientERC20Fee`.
+
+For example, a contract using `GSNBouncerSignature` would have to be changed in the following way.
+
+```diff
+-contract MyDapp is GSNRecipient, GSNBouncerSignature {
++contract MyDapp is GSNRecipientSignature {
+```
+
+Refer to the table below to adjust your inheritance list.
+
+| 2.4.0-beta                          | 2.4.0                   |
+| ----------------------------------- | ----------------------- |
+| `GSNRecipient, GSNBouncerSignature` | `GSNRecipientSignature` |
+| `GSNRecipient, GSNBouncerERC20Fee`  | `GSNRecipientERC20Fee`  |
+| `GSNBouncerBase`                    | `GSNRecipient`          |
+
+## 2.3.0 (2019-05-27)
+
+### New features
+
+- `ERC1820`: added support for interacting with the [ERC1820](https://eips.ethereum.org/EIPS/eip-1820) registry contract (`IERC1820Registry`), as well as base contracts that can be registered as implementers there. ([#1677](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1677))
+- `ERC777`: support for the [ERC777 token](https://eips.ethereum.org/EIPS/eip-777), which has multiple improvements over `ERC20` (but is backwards compatible with it) such as built-in burning, a more straightforward permission system, and optional sender and receiver hooks on transfer (mandatory for contracts!). ([#1684](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1684))
+- All contracts now have revert reason strings, which give insight into error conditions, and help debug failing transactions. ([#1704](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1704))
+
+### Improvements
+
+- Reverted the Solidity version bump done in v2.2.0, setting the minimum compiler version to v0.5.0, to prevent unexpected build breakage. Users are encouraged however to stay on top of new compiler releases, which usually include bugfixes. ([#1729](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1729))
+
+### Bugfixes
+
+- `PostDeliveryCrowdsale`: some validations where skipped when paired with other crowdsale flavors, such as `AllowanceCrowdsale`, or `MintableCrowdsale` and `ERC20Capped`, which could cause buyers to not be able to claim their purchased tokens. ([#1721](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1721))
+- `ERC20._transfer`: the `from` argument was allowed to be the zero address, so it was possible to internally trigger a transfer of 0 tokens from the zero address. This address is not a valid destinatary of transfers, nor can it give or receive allowance, so this behavior was inconsistent. It now reverts. ([#1752](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1752))
+
+## 2.2.0 (2019-03-14)
+
+### New features
+
+- `ERC20Snapshot`: create snapshots on demand of the token balances and total supply, to later retrieve and e.g. calculate dividends at a past time. ([#1617](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1617))
+- `SafeERC20`: `ERC20` contracts with no return value (i.e. that revert on failure) are now supported. ([#1655](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1655))
+- `ERC20`: added internal `_approve(address owner, address spender, uint256 value)`, allowing derived contracts to set the allowance of arbitrary accounts. ([#1609](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1609))
+- `ERC20Metadata`: added internal `_setTokenURI(string memory tokenURI)`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+- `TimedCrowdsale`: added internal `_extendTime(uint256 newClosingTime)` as well as `TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime)` event allowing to extend the crowdsale, as long as it hasn't already closed.
+
+### Improvements
+
+- Upgraded the minimum compiler version to v0.5.2: this removes many Solidity warnings that were false positives. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
+- `ECDSA`: `recover` no longer accepts malleable signatures (those using upper-range values for `s`, or 0/1 for `v`). ([#1622](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1622))
+- `ERC721`'s transfers are now more gas efficient due to removal of unnecessary `SafeMath` calls. ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+- Fixed variable shadowing issues. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
+
+### Bugfixes
+
+- (minor) `SafeERC20`: `safeApprove` wasn't properly checking for a zero allowance when attempting to set a non-zero allowance. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
+
+### Breaking changes in drafts
+
+- `TokenMetadata` has been renamed to `ERC20Metadata`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+- The library `Counter` has been renamed to `Counters` and its API has been improved. See an example in `ERC721`, lines [17](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L17) and [204](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L204). ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+
+## 2.1.3 (2019-02-26)
+
+- Backported `SafeERC20.safeApprove` bugfix. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
+
+## 2.1.2 (2019-01-17)
+
+- Removed most of the test suite from the npm package, except `PublicRole.behavior.js`, which may be useful to users testing their own `Roles`.
+
+## 2.1.1 (2019-01-04)
+
+- Version bump to avoid conflict in the npm registry.
+
+## 2.1.0 (2019-01-04)
+
+### New features
+
+- Now targeting the 0.5.x line of Solidity compilers. For 0.4.24 support, use version 2.0 of OpenZeppelin.
+- `WhitelistCrowdsale`: a crowdsale where only whitelisted accounts (`WhitelistedRole`) can purchase tokens. Adding or removing accounts from the whitelist is done by whitelist admins (`WhitelistAdminRole`). Similar to the pre-2.0 `WhitelistedCrowdsale`. ([#1525](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1525), [#1589](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1589))
+- `RefundablePostDeliveryCrowdsale`: replacement for `RefundableCrowdsale` (deprecated, see below) where tokens are only granted once the crowdsale ends (if it meets its goal). ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))
+- `PausableCrowdsale`: allows for pausers (`PauserRole`) to pause token purchases. Other crowdsale operations (e.g. withdrawals and refunds, if applicable) are not affected. ([#832](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/832))
+- `ERC20`: `transferFrom` and `_burnFrom ` now emit `Approval` events, to represent the token's state comprehensively through events. ([#1524](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1524))
+- `ERC721`: added `_burn(uint256 tokenId)`, replacing the similar deprecated function (see below). ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
+- `ERC721`: added `_tokensOfOwner(address owner)`, allowing to internally retrieve the array of an account's owned tokens. ([#1522](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1522))
+- Crowdsales: all constructors are now `public`, meaning it is not necessary to extend these contracts in order to deploy them. The exception is `FinalizableCrowdsale`, since it is meaningless unless extended. ([#1564](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1564))
+- `SignedSafeMath`: added overflow-safe operations for signed integers (`int256`). ([#1559](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1559), [#1588](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1588))
+
+### Improvements
+
+- The compiler version required by `Array` was behind the rest of the 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))

CODE_OF_CONDUCT.md

@@ -0,0 +1,73 @@
+# Contributor Covenant Code of Conduct
+
+## Our Pledge
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of age, body
+size, disability, ethnicity, sex characteristics, gender identity and expression,
+level of experience, education, socio-economic status, nationality, personal
+appearance, race, religion, or sexual identity and orientation.
+
+## Our Standards
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+* Using welcoming and inclusive language
+* Being respectful of differing viewpoints and experiences
+* Gracefully accepting constructive criticism
+* Focusing on what is best for the community
+* Showing empathy towards other community members
+
+Examples of unacceptable behavior by participants include:
+
+* The use of sexualized language or imagery and unwelcome sexual attention or
+  advances
+* Trolling, insulting/derogatory comments, and personal or political attacks
+* Public or private harassment
+* Publishing others' private information, such as a physical or electronic
+  address, without explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+  professional setting
+
+## Our Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit, or
+reject comments, commits, code, wiki edits, issues, and other contributions
+that are not aligned to this Code of Conduct, or to ban temporarily or
+permanently any contributor for other behaviors that they deem inappropriate,
+threatening, offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project e-mail
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+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 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.
+Further details of specific enforcement policies may be posted separately.
+
+Project maintainers who do not follow or enforce the Code of Conduct in good
+faith may face temporary or permanent repercussions as determined by other
+members of the project's leadership.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4,
+available at https://www.contributor-covenant.org/version/1/4/code-of-conduct.html
+
+[homepage]: https://www.contributor-covenant.org

CONTRIBUTING.md

@@ -1,105 +1,36 @@
-Contributing to Zeppelin
-=======
+# Contributing Guidelines
 
-## Design Guidelines
+There are many ways to contribute to OpenZeppelin Contracts.
 
-These are some global design goals in Zeppelin.
+## Troubleshooting
 
-### 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.
+You can help other users in the community to solve their smart contract issues in the [OpenZeppelin Forum].
 
-### 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.
+[OpenZeppelin Forum]: https://forum.openzeppelin.com/
 
-### D2 - Naming Matters
+## Opening an issue
 
-We take our time with picking names. Code is going to be written once, and read hundreds of times. Renaming for clarity is encouraged.
+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.
 
-### D3 - Tests
+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].
 
-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.
+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.
 
-### D4 - Check preconditions and post-conditions
+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.
 
-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.
+[security policy]: https://github.com/OpenZeppelin/openzeppelin-contracts/security
+[open an issue]: https://github.com/OpenZeppelin/openzeppelin-contracts/issues/new/choose
 
-### D5 - Code Consistency
+## Submitting a pull request
 
-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.
+If you would like to contribute code or documentation you may do so by forking the repository and submitting a pull request.
 
-### 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.
+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.
 
-## Style Guidelines
+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.
 
-The design guidelines have quite a high abstraction level. These style guidelines are more concrete and easier to apply, and also more opinionated.
+Changelog entries should be added to each pull request by using [Changesets](https://github.com/changesets/changesets/).
 
-### General
+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.
 
-#### G0 - Default to Solidity's official style guide.
-
-Follow the official Solidity style guide: http://solidity.readthedocs.io/en/latest/style-guide.html
-
-#### G1 - No Magic Constants
-
-Avoid constants in the code as much as possible. Magic strings are also magic constants.
-
-#### G2 - Code that Fails Early
-
-We ask our code to fail as soon as possible when an unexpected input was provided or unexpected state was found.
-
-#### G3 - Internal Amounts Must be Signed Integers and Represent the Smallest Units.
-
-Avoid representation errors by always dealing with weis when handling ether. GUIs can convert to more human-friendly representations. Use Signed Integers (int) to prevent underflow problems.
-
-
-### Testing
-
-#### T1 - Tests Must be Written Elegantly
-
-Style guidelines are not relaxed for tests. Tests are a good way to show how to use the library, and maintaining them is extremely necessary.
-
-Don't write long tests, write helper functions to make them be as short and concise as possible (they should take just a few lines each), and use good variable names.
-
-#### T2 - Tests Must not be Random
-
-Inputs for tests should not be generated randomly. Accounts used to create test contracts are an exception, those can be random. Also, the type and structure of outputs should be checked.
-
-
-### Documentation
-
-TODO
-
-## Pull Request Workflow
-
-Our workflow is based on GitHub's pull requests. We use feature branches, prepended with: `test`, `feature`, `fix`, `refactor`, or `remove` according to the change the branch introduces. Some examples for such branches are:
-```sh
-git checkout -b test/some-module
-git checkout -b feature/some-new-stuff
-git checkout -b fix/some-bug
-git checkout -b remove/some-file
-```
-
-We expect pull requests to be rebased to the master branch before merging:
-```sh
-git remote add zep git@github.com:OpenZeppelin/zeppelin-solidity.git
-git pull --rebase zep master
-```
-
-Note that we require rebasing your branch instead of merging it, for commit readability reasons.
-
-After that, you can push the changes to your fork, by doing:
-```sh
-git push origin your_branch_name
-git push origin feature/some-new-stuff
-git push origin fix/some-bug
-```
-
-Finally go to [github.com/OpenZeppelin/zeppelin-solidity](https://github.com/OpenZeppelin/zeppelin-solidity) in your web browser and issue a new pull request.
-
-Main contributors 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 Zeppelin.
-
-If you have any questions feel free to post them to
-[github.com/OpenZeppelin/zeppelin-solidity/issues](https://github.com/OpenZeppelin/zeppelin-solidity/issues).
-
-Thanks for your time and code!
+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

@@ -0,0 +1,117 @@
+# Engineering Guidelines
+
+## Testing
+
+Code must be thoroughly tested with quality unit tests.
+
+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:
+
+> 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.
+
+Every addition or change to the code must come with relevant and comprehensive tests.
+
+Refactors should avoid simultaneous changes to tests.
+
+Flaky tests are not acceptable.
+
+The test suite should run automatically for every change in the repository, and in pull requests tests must pass before merging.
+
+The test suite coverage must be kept as close to 100% as possible, enforced in pull requests.
+
+In some cases unit tests may be insufficient and complementary techniques should be used:
+
+1. Property-based tests (aka. fuzzing) for math-heavy code.
+2. Formal verification for state machines.
+
+## Code style
+
+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 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.
+
+Sometimes these guidelines may be broken if doing so brings significant efficiency gains, but explanatory comments should be added.
+
+Modularity should be pursued, but not at the cost of the above priorities.
+
+## Documentation
+
+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.
+
+  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.
+
+* Internal or private state variables or functions should have an underscore prefix.
+
+  ```solidity
+  contract TestContract {
+      uint256 private _privateVar;
+      uint256 internal _internalVar;
+      function _testInternal() internal { ... }
+      function _testPrivate() private { ... }
+  }
+  ```
+
+* Events should be emitted immediately after the state change that they
+  represent, and should be named in the past tense.
+
+  ```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 is used.
+  
+* Interface names should have a capital I prefix.
+
+  ```solidity
+  interface IERC777 {
+  ```
+
+* 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

@@ -1,22 +1,22 @@
 The MIT License (MIT)
 
-Copyright (c) 2016 Smart Contract Solutions, Inc.
+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
 "Software"), to deal in the Software without restriction, including
-without limitation the rights to use, copy, modify, merge, publish, 
+without limitation the rights to use, copy, modify, merge, publish,
 distribute, sublicense, and/or sell copies of the Software, and to
-permit persons to whom the Software is furnished to do so, subject to 
+permit persons to whom the Software is furnished to do so, subject to
 the following conditions:
 
 The above copyright notice and this permission notice shall be included
 in all copies or substantial portions of the Software.
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS 
-OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 
-MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
-IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY 
-CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
-TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE 
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

@@ -1,89 +1,90 @@
-# Zeppelin Solidity
-[![NPM Package](https://img.shields.io/npm/v/zeppelin-solidity.svg?style=flat-square)](https://www.npmjs.org/package/zeppelin-solidity)
-[![Build Status](https://img.shields.io/travis/OpenZeppelin/zeppelin-solidity.svg?branch=master&style=flat-square)](https://travis-ci.org/OpenZeppelin/zeppelin-solidity)
+# <img src="logo.svg" alt="OpenZeppelin" height="40px">
 
-Zeppelin is a library for writing secure [Smart Contracts](https://en.wikipedia.org/wiki/Smart_contract) on Ethereum.
+[![NPM Package](https://img.shields.io/npm/v/@openzeppelin/contracts.svg)](https://www.npmjs.org/package/@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)
 
-With Zeppelin, you can build distributed applications, protocols and organizations:
-- using common contract security patterns (See [Onward with Ethereum Smart Contract Security](https://medium.com/bitcorps-blog/onward-with-ethereum-smart-contract-security-97a827e47702#.y3kvdetbz))
-- in the [Solidity language](http://solidity.readthedocs.io/en/develop/).
+**A library for secure smart contract development.** Build on a solid foundation of community-vetted code.
 
-> NOTE: New to smart contract development? Check our [introductory guide](https://medium.com/zeppelin-blog/the-hitchhikers-guide-to-smart-contracts-in-ethereum-848f08001f05#.cox40d2ut).
+ * 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.
 
-## Getting Started
+:mage: **Not sure how to get started?** Check out [Contracts Wizard](https://wizard.openzeppelin.com/) — an interactive smart contract generator.
 
-Zeppelin integrates with [Truffle](https://github.com/ConsenSys/truffle), an Ethereum development environment. Please install Truffle and initialize your project with `truffle init`.
-```sh
-npm install -g truffle
-mkdir myproject && cd myproject
-truffle init
+: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
+
+```
+$ npm install @openzeppelin/contracts
 ```
 
-To install the Zeppelin library, run:
-```sh
-npm i zeppelin-solidity
-```
+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.
 
-After that, you'll get all the library's contracts in the `contracts/zeppelin` folder. You can use the contracts in the library like so:
+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.
 
-```js
-import "./zeppelin/Ownable.sol";
+### Usage
 
-contract MyContract is Ownable {
-  ...
+Once installed, you can use the contracts in the library by importing them:
+
+```solidity
+pragma solidity ^0.8.0;
+
+import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
+
+contract MyCollectible is ERC721 {
+    constructor() ERC721("MyCollectible", "MCO") {
+    }
 }
 ```
 
-> NOTE: The current distribution channel is npm, which is not ideal. [We're looking into providing a better tool for code distribution](https://github.com/OpenZeppelin/zeppelin-solidity/issues/13), and ideas are welcome.
+_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._
 
-#### Truffle Beta Support
-We also support Truffle Beta npm integration. If you're using Truffle Beta, the contracts in `node_modules` will be enough, so feel free to delete the copies at your `contracts` folder. If you're using Truffle Beta, you can use Zeppelin contracts like so:
+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.
 
-```js
-import "zeppelin-solidity/contracts/Ownable.sol";
+## Learn More
 
-contract MyContract is Ownable {
-  ...
-}
-```
+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:
 
-For more info see [the Truffle Beta package management tutorial](http://truffleframework.com/tutorials/package-management).
+* [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).
+* [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 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.
+* For a more in-depth dive, you may read the guide [Designing the Architecture for Your Ethereum Application](https://blog.openzeppelin.com/designing-the-architecture-for-your-ethereum-application-9cec086f8317), which discusses how to better structure your application and its relationship to the real world.
 
 ## Security
-Zeppelin is meant to provide secure, 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 problem you might experience.
 
-If you find a security issue, please email [security@openzeppelin.org](mailto:security@openzeppelin.org).
+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.
 
-## Developer Resources
+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.
 
-Building a distributed application, protocol or organization with Zeppelin?
+The engineering guidelines we follow to promote project quality can be found in [`GUIDELINES.md`](./GUIDELINES.md).
 
-- Read documentation: http://zeppelin-solidity.readthedocs.io/en/latest/
+Past audits can be found in [`audits/`](./audits).
 
-- Ask for help and follow progress at: https://zeppelin-slackin.herokuapp.com/
+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.
 
-Interested in contributing to Zeppelin?
+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.
 
-- Framework proposal and roadmap: https://medium.com/zeppelin-blog/zeppelin-framework-proposal-and-development-roadmap-fdfa9a3a32ab#.iain47pak
-- Issue tracker: https://github.com/OpenZeppelin/zeppelin-solidity/issues
-- Contribution guidelines: https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/CONTRIBUTING.md
-
-## Collaborating organizations and audits by Zeppelin
-- [Golem](https://golem.network/)
-- [Mediachain](https://golem.network/)
-- [Truffle](http://truffleframework.com/)
-- [Firstblood](http://firstblood.io/)
-- [Rootstock](http://www.rsk.co/)
-- [Consensys](https://consensys.net/)
-- [DigixGlobal](https://www.dgx.io/)
-- [Coinfund](https://coinfund.io/)
-- [DemocracyEarth](http://democracy.earth/)
-- [Signatura](https://signatura.co/)
-- [Ether.camp](http://www.ether.camp/)
-
-among others...
+## Contribute
 
+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
-Code released under the [MIT License](https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/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

@@ -0,0 +1,47 @@
+# Releasing
+
+> Visit the documentation for [details about release schedule](https://docs.openzeppelin.com/contracts/releases-stability).
+
+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.
+
+## Changesets
+
+[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.
+
+## Branching model
+
+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.
+
+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"
+
+    checkout master
+    commit id: "Feature C"
+    commit id: "Fix A"
+
+    checkout release-vX.Y
+    cherry-pick id: "Fix A" tag: ""
+    commit id: "Release vX.Y.0-rc.1"
+    commit id: "Release vX.Y.0"
+
+    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"
+```

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

@@ -0,0 +1,292 @@
+# 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
+
+# Introduction
+
+Zeppelin requested that New Alchemy perform an audit of the contracts in their OpenZeppelin library. The OpenZeppelin contracts are a set of contracts intended to be a safe building block for a variety of uses by parties that may not be as sophisticated as the OpenZeppelin team. It is a design goal that the contracts be deployable safely and "as-is".
+
+The contracts are hosted at:
+
+https://github.com/OpenZeppelin/zeppelin-solidity
+
+All the contracts in the "contracts" folder are in scope.
+
+The git commit hash we evaluated is:
+9c5975a706b076b7000e8179f8101e0c61024c87
+
+# Disclaimer
+
+The audit makes no statements or warrantees about utility of the code, safety of the code, suitability of the business model, regulatory regime for the business model, or any other statements about fitness of the contracts to purpose, or their bugfree status. The audit documentation is for discussion purposes only.
+
+# Executive Summary
+
+Overall the OpenZeppelin codebase is of reasonably high quality -- it is clean, modular and follows best practices throughout.
+
+It is still in flux as a codebase, and needs better documentation per file as to expected behavior and future plans. It probably needs more comprehensive and aggressive tests written by people less nice than the current OpenZeppelin team.
+
+We identified two critical errors and one moderate issue, and would not recommend this commit hash for public use until these bugs are remedied.
+
+The repository includes a set of Truffle unit tests, a requirement and best practice for smart contracts like these; we recommend these be bulked up.
+
+# Discussion
+
+## Big Picture: Is This A Worthwhile Project?
+
+As soon as a developer touches OpenZeppelin contracts, they will modify something, leaving them in an un-audited state. We do not recommend developers deploy any unaudited code to the Blockchain if it will handle money, information or other things of value.
+
+> "In accordance with Unix philosophy, Perl gives you enough rope to hang yourself"
+> --Larry Wall
+
+We think this is an incredibly worthwhile project -- aided by the high code quality. Creating a framework that can be easily extended helps increase the average code quality on the Blockchain by charting a course for developers and encouraging containment of modifications to certain sections.
+
+> "Rust: The language that makes you take the safety off before shooting yourself in the foot"
+> -- (@mbrubeck)
+
+We think much more could be done here, and recommend the OpenZeppelin team keep at this and keep focusing on the design goal of removing rope and adding safety.
+
+## Solidity Version Updates Recommended
+
+Most of the code uses Solidity 0.4.11, but some files under `Ownership` are marked 0.4.0. These should be updated.
+
+Solidity 0.4.10 will add several features which could be useful in these contracts:
+
+- `assert(condition)`, which throws if the condition is false
+
+- `revert()`, which rolls back without consuming all remaining gas.
+
+- `address.transfer(value)`, which is like `send` but automatically propagates exceptions, and supports `.gas()`. See https://github.com/ethereum/solidity/issues/610 for more on this.
+
+## Error Handling: Throw vs Return False
+Solidity standards allow two ways to handle an error -- either calling `throw` or returning `false`. Both have benefits. In particular, a `throw` guarantees a complete wipe of the call stack (up to the preceding external call), whereas `false` allows a function to continue.
+
+In general we prefer `throw` in our code audits, because it is simpler -- it's less for an engineer to keep track of. Returning `false` and using logic to check results can quickly become a poorly-tracked state machine, and this sort of complexity can cause errors.
+
+In the OpenZeppelin contracts, both styles are used in different parts of the codebase. `SimpleToken` transfers throw upon failure, while the full ERC20 token returns `false`. Some modifiers `throw`, others just wrap the function body in a conditional, effectively allowing the function to return false if the condition is not met.
+
+We don't love this, and would usually recommend you stick with one style or the other throughout the codebase.
+
+In at least one case, these different techniques are combined cleverly (see the Multisig comments, line 65). As a set of contracts intended for general use, we recommend you either strive for more consistency or document explicit design criteria that govern which techniques are used where.
+
+Note that it may be impossible to use either one in all situations. For example, SafeMath functions pretty much have to throw upon failure, but ERC20 specifies returning booleans. Therefore we make no particular recommendations, but simply point out inconsistencies to consider.
+
+# Critical Issues
+
+## Stuck Ether in Crowdsale contract
+CrowdsaleToken.sol has no provision for withdrawing the raised ether. We *strongly* recommend a standard `withdraw` function be added. There is no scenario in which someone should deploy this contract as is, whether for testing or live.
+
+## Recursive Call in MultisigWallet
+Line 45 of `MultisigWallet.sol` checks if the amount being sent by `execute` is under a daily limit.
+
+This function can only be called by the "Owner". As a first angle of attack, it's worth asking what will happen if the multisig wallet owners reset the daily limit by approving a call to `resetSpentToday`.
+
+If a chain of calls can be constructed in which the owner confirms the `resetSpentToday` function and then withdraws through `execute` in a recursive call, the contract can be drained. In fact, this could be done without a recursive call, just through repeated `execute` calls alternating with the `confirm` calls.
+
+We are still working through the confirmation protocol in `Shareable.sol`, but we are not convinced that this is impossible, in fact it looks possible. The flexibility any shared owner has in being able to revoke confirmation later is another worrisome angle of approach even if some simple patches are included.
+
+This bug has a number of causes that need to be addressed:
+
+1. `resetSpentToday` and `confirm` together do not limit the days on which the function can be called or (it appears) the number of times it can be called.
+1. Once a call has been confirmed and `execute`d it appears that it can be re-executed. This is not good.
+3. `confirmandCheck` doesn't seem to have logic about whether or not the function in question has been called.
+4. Even if it did, `revoke` would need updates and logic to deal with revocation requests after a function call had been completed.
+
+We do not recommend using the MultisigWallet until these issues are fixed.
+
+# Moderate to Minor Issues
+
+## PullPayment
+PullPayment.sol needs some work. It has no explicit provision for cancelling a payment. This would be desirable in a number of scenarios; consider a payee losing their wallet, or giving a griefing address, or just an address that requires more than the default gas offered by `send`.
+
+`asyncSend` has no overflow checking. This is a bad plan. We recommend overflow and underflow checking at the layer closest to the data manipulation.
+
+`asyncSend` allows more balance to be queued up for sending than the contract holds. This is probably a bad idea, or at the very least should be called something different. If the intent is to allow this, it should have provisions for dealing with race conditions between competing `withdrawPayments` calls.
+
+It would be nice to see how many payments are pending. This would imply a bit of a rewrite; we recommend this contract get some design time, and that developers don't rely on it in its current state.
+
+## Shareable Contract
+
+We do not believe the `Shareable.sol` contract is ready for primetime. It is missing functions, and as written may be vulnerable to a reordering attack -- an attack in which a miner or other party "racing" with a smart contract participant inserts their own information into a list or mapping.
+
+The confirmation and revocation code needs to be looked over with a very careful eye imagining extraordinarily bad behavior by shared owners before this contract can be called safe.
+
+No sanity checks on the initial constructor's `required` argument are worrisome as well.
+
+# Line by Line Comments
+
+## Lifecycle
+
+### Killable
+
+Very simple, allows owner to call selfdestruct, sending funds to owner. No issues. However, note that `selfdestruct` should typically not be used; it is common that a developer may want to access data in a former contract, and they may not understand that `selfdestruct` limits access to the contract. We recommend better documentation about this dynamic, and an alternate function name for `kill` like `completelyDestroy` while `kill` would perhaps merely send funds to the owner.
+
+Also note that a killable function allows the owner to take funds regardless of other logic. This may be desirable or undesirable depending on the circumstances. Perhaps `Killable` should have a different name as well.
+
+### Migrations
+
+I presume that the goal of this contract is to allow and annotate a migration to a new smart contract address. We are not clear here how this would be accomplished by the code; we'd like to review with the OpenZeppelin team.
+
+### Pausable
+
+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 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
+
+### Ownable
+
+Line 19: Modifier throws if doesn't meet condition, in contrast to some other inheritable modifiers (e.g. in Pausable) that use `if(bool){_;}`.
+
+### Claimable
+
+Inherits from Ownable but the existing owner sets a pendingOwner who has to claim ownership.
+
+Line 17: Another modifier that throws.
+
+### DelayedClaimable
+
+Is there any reason to descend from Ownable directly, instead of just Claimable, which descends from Ownable? If not, descending from both just adds confusion.
+
+### Contactable
+
+Allows owner to set a public string of contract information. No issues.
+
+### Shareable
+
+This needs some work. Doesn't check if `_required <= len(_owners)` for instance, that would be a bummer. What if _required were like `MAX - 1`?
+
+I have a general concern about the difference between `owners`, `_owners`, and `owner` in `Ownable.sol`. I recommend "Owners" be renamed. In general we do not recomment single character differences in variable names, although a preceding underscore is not uncommon in Solidity code.
+
+Line 34: "this contract only has six types of events"...actually only two.
+
+Line 61: Why is `ownerIndex` keyed by addresses hashed to `uint`s? Why not use the addresses directly, so `ownerIndex` is less obscure, and so there's stronger typing?
+
+Line 62: Do not love `++i) ... owners[2+ i]`. Makes me do math, which is not what I want to do. I want to not have to do math.
+
+There should probably be a function for adding a new operation, so the developer doesn't have to work directly with the internal data. (This would make the multisig contract even shorter.)
+
+There's a `revoke` function but not a `propose` function that we can see.
+
+Beware reordering. If `propose` allows the user to choose a bytes string for their proposal, bad things(TM) will happen as currently written.
+
+
+### Multisig
+
+Just an interface. Note it allows changing an owner address, but not changing the number of owners. This is somewhat limiting but also simplifies implementation.
+
+## Payment
+
+### PullPayment
+
+Safe from reentrance attack since ether send is at the end, plus it uses `.send()` rather than `.call.value()`.
+
+There's an argument to be made that `.call.value()` is a better option *if* you're sure that it will be done after all state updates, since `.send` will fail if the recipient has an expensive fallback function. However, in the context of a function meant to be embedded in other contracts, it's probably better to use `.send`. One possible compromise is to add a function which allows only the owner to send ether via `.call.value`.
+
+If you don't use `call.value` you should implement a `cancel` function in case some value is pending here.
+
+Line 14:
+Doesn't use safeAdd. Although it appears that payout amounts can only be increased, in fact the payer could lower the payout as much as desired via overflow. Also, the payer could add a large non-overflowing amount, causing the payment to exceed the contract balance and therefore fail when withdraw is attempted.
+
+Recommendation: track the sum of non-withdrawn asyncSends, and don't allow a new one which exceeds the leftover balance. If it's ever desirable to make payments revocable, it should be done explicitly.
+
+## Tokens
+
+### ERC20
+
+Standard ERC20 interface only.
+
+There's a security hole in the standard, reported at Edcon: `approve` does not protect against race conditions and simply replaces the current value. An approved spender could wait for the owner to call `approve` again, then attempt to spend the old limit before the new limit is applied. If successful, this attacker could successfully spend the sum of both limits.
+
+This could be fixed by either (1) including the old limit as a parameter, so the update will fail if some gets spent, or (2) using the value parameter as a delta instead of replacement value.
+
+This is not fixable while adhering to the current full ERC20 standard, though it would be possible to add a "secureApprove" function. The impact isn't extreme since at least you can only be attacked by addresses you approved. Also, users could mitigate this by always setting spending limits to zero and checking for spends, before setting the new limit.
+
+Edcon slides:
+https://drive.google.com/file/d/0ByMtMw2hul0EN3NCaVFHSFdxRzA/view
+
+### ERC20Basic
+
+Simpler interface skipping the Approve function. Note this departs from ERC20 in another way: transfer throws instead of returning false.
+
+### BasicToken
+
+Uses `SafeSub` and `SafeMath`, so transfer `throw`s instead of returning false. This complies with ERC20Basic but not the actual ERC20 standard.
+
+### StandardToken
+
+Implementation of full ERC20 token.
+
+Transfer() and transferFrom() use SafeMath functions, which will cause them to throw instead of returning false. Not a security issue but departs from standard.
+
+### SimpleToken
+
+Sample instantiation of StandardToken. Note that in this sample, decimals is 18 and supply only 10,000, so the supply is a small fraction of a single nominal token.
+
+### CrowdsaleToken
+
+StandardToken which mints tokens at a fixed price when sent ether.
+
+There's no provision for owner withdrawing the ether. As a sample for crowdsales it should be Ownable and allow the owner to withdraw ether, rather than stranding the ether in the contract.
+
+Note: an alternative pattern is a mint() function which is only callable from a separate crowdsale contract, so any sort of rules can be added without modifying the token itself.
+
+### VestedToken
+
+Lines 23, 27:
+Functions `transfer()` and `transferFrom()` have a modifier canTransfer which throws if not enough tokens are available. However, transfer() returns a boolean success. Inconsistent treatment of failure conditions may cause problems for other contracts using the token. (Note that transferableTokens() relies on safeSub(), so will also throw if there's insufficient balance.)
+
+Line 64:
+Delete not actually necessary since the value is overwritten in the next line anyway.
+
+## Root level
+
+### Bounty
+
+Avoids potential race condition by having each researcher deploy a separate contract for attack; if a research manages to break his associated contract, other researchers can't immediately claim the reward, they have to reproduce the attack in their own contracts.
+
+A developer could subvert this intent by implementing `deployContract()` to always return the same address. However, this would break the `researchers` mapping, updating the researcher address associated with the contract. This could be prevented by blocking rewrites in `researchers`.
+
+### DayLimit
+
+The modifier `limitedDaily` calls `underLimit`, which both checks that the spend is below the daily limit, and adds the input value to the daily spend. This is fine if all functions throw upon failure. However, not all OpenZeppelin functions do this; there are functions that returns false, and modifiers that wrap the function body in `if (bool) {_;}`. In these cases, `_value` will be added to `spentToday`, but ether may not actually be sent because other preconditions were not met. (However in the OpenZeppelin multisig this is not a problem.)
+
+Lines 4, 11:
+Comment claims that `DayLimit` is multiowned, and Shareable is imported, but DayLimit does not actually inherit from Shareable. The intent may be for child contracts to inherit from Shareable (as Multisig does); in this case the import should be removed and the comment altered.
+
+Line 46:
+Manual overflow check instead of using safeAdd. Since this is called from a function that throws upon failure anyway, there's no real downside to using safeAdd.
+
+### LimitBalance
+
+No issues.
+
+### MultisigWallet
+
+Lines 28, 76, 80:
+`kill`, `setDailyLimit`, and `resetSpentToday` only happen with multisig approval, and hashes for these actions are logged by Shareable. However, they should probably post their own events for easy reading.
+
+Line 45:
+This call to underLimit will reduce the daily limit, and then either throw or return 0. So in this case there's no danger that the limit will be reduced without the operation going through.
+
+Line 65:
+Shareable's onlyManyOwners will take the user's confirmation, and execute the function body if and only if enough users have confirmed. Whole thing throws if the send fails, which will roll back the confirmation. Confirm returns false if not enough have confirmed yet, true if the whole thing succeeds, and throws only in the exceptional circumstance that the designated transaction unexpectedly fails. Elegant design.
+
+Line 68:
+Throw here is good but note this function can fail either by returning false or by throwing.
+
+Line 92:
+A bit odd to split `clearPending()` between this contract and Shareable. However this does allow contracts inheriting from Shareable to use custom structs for pending transactions.
+
+
+### SafeMath
+
+Another interesting comment from the same Edcon presentation was that the overflow behavior of Solidity is undocumented, so in theory, source code that relies on it could break with a future revision.
+
+However, compiled code should be fine, and in the unlikely event that the compiler is revised in this way, there should be plenty of warning. (But this is an argument for keeping overflow checks isolated in SafeMath.)
+
+Aside from that small caveat, these are fine.
+

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 ^0.8.0;
+
+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 ^0.8.0;
+
+import "../patched/access/AccessControl.sol";
+
+contract AccessControlHarness is AccessControl {}

certora/harnesses/DoubleEndedQueueHarness.sol

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.2;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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 ^0.8.0;
+
+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',
+    ),
+  );
+}