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v5.0.0
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Additions Summary

The following contracts and libraries were added:

  • AccessManager: A consolidated system for managing access control in complex systems.
    • AccessManaged: A module for connecting a contract to an authority in charge of its access control.
    • GovernorTimelockAccess: An adapter for time-locking governance proposals using an AccessManager.
    • AuthorityUtils: A library of utilities for interacting with authority contracts.
  • GovernorStorage: A Governor module that stores proposal details in storage.
  • ERC2771Forwarder: An ERC2771 forwarder for meta transactions.
  • ERC1967Utils: A library with ERC1967 events, errors and getters.
  • Nonces: An abstraction for managing account nonces.
  • MessageHashUtils: A library for producing digests for ECDSA operations.
  • Time: A library with helpers for manipulating time-related objects.

Removals Summary

The following contracts, libraries, and functions were removed:

  • Address.isContract (because of its ambiguous nature and potential for misuse)
  • Checkpoints.History
  • Counters
  • ERC20Snapshot
  • ERC20VotesComp
  • ERC165Storage (in favor of inheritance based approach)
  • ERC777
  • ERC1820Implementer
  • GovernorVotesComp
  • GovernorProposalThreshold (deprecated since 4.4)
  • PaymentSplitter
  • PullPayment
  • SafeMath
  • SignedSafeMath
  • Timers
  • TokenTimelock (in favor of VestingWallet)
  • All escrow contracts (Escrow, ConditionalEscrow and RefundEscrow)
  • All cross-chain contracts, including AccessControlCrossChain and all the vendored bridge interfaces
  • All presets in favor of OpenZeppelin Contracts Wizard

These removals were implemented in the following PRs: #3637, #3880, #3945, #4258, #4276, #4289

Changes by category

General

  • Replaced revert strings and require statements with custom errors. (#4261)
  • Bumped minimum compiler version required to 0.8.20 (#4288)
  • Use of abi.encodeCall in place of abi.encodeWithSelector and abi.encodeWithSignature for improved type-checking of parameters (#4293)
  • Replaced some uses of abi.encodePacked with clearer alternatives (e.g. bytes.concat, string.concat). (#4504) (#4296)
  • Overrides are now used internally for a number of functions that were previously hardcoded to their default implementation in certain locations: ERC1155Supply.totalSupply, ERC721.ownerOf, ERC721.balanceOf and ERC721.totalSupply in ERC721Enumerable, ERC20.totalSupply in ERC20FlashMint, and ERC1967._getImplementation in ERC1967Proxy. (#4299)
  • Removed the override specifier from functions that only override a single interface function. (#4315)
  • Switched to using explicit Solidity import statements. Some previously available symbols may now have to be separately imported. (#4399)
  • Governor, Initializable, and UUPSUpgradeable: Use internal functions in modifiers to optimize bytecode size. (#4472)
  • Upgradeable contracts now use namespaced storage (EIP-7201). (#4534)
  • Upgradeable contracts no longer transpile interfaces and libraries. (#4628)

Access

  • Ownable: Added an initialOwner parameter to the constructor, making the ownership initialization explicit. (#4267)
  • Ownable: Prevent using address(0) as the initial owner. (#4531)
  • AccessControl: Added a boolean return value to the internal _grantRole and _revokeRole functions indicating whether the role was granted or revoked. (#4241)
  • access: Moved AccessControl extensions to a dedicated directory. (#4359)
  • AccessManager: Added a new contract for managing access control of complex systems in a consolidated location. (#4121)
  • AccessManager, AccessManaged, GovernorTimelockAccess: Ensure that calldata shorter than 4 bytes is not padded to 4 bytes. (#4624)
  • AccessManager: Use named return parameters in functions that return multiple values. (#4624)
  • AccessManager: Make schedule and execute more conservative when delay is 0. (#4644)

Finance

  • VestingWallet: Fixed revert during 1 second time window when duration is 0. (#4502)
  • VestingWallet: Use Ownable instead of an immutable beneficiary. (#4508)

Governance

  • Governor: Optimized use of storage for proposal data (#4268)
  • Governor: Added validation in ERC1155 and ERC721 receiver hooks to ensure Governor is the executor. (#4314)
  • Governor: Refactored internals to implement common queuing logic in the core module of the Governor. Added queue and _queueOperations functions that act at different levels. Modules that implement queuing via timelocks are expected to override _queueOperations to implement the timelock-specific logic. Added _executeOperations as the equivalent for execution. (#4360)
  • Governor: Added voter and nonce parameters in signed ballots, to avoid forging signatures for random addresses, prevent signature replay, and allow invalidating signatures. Add voter as a new parameter in the castVoteBySig and castVoteWithReasonAndParamsBySig functions. (#4378)
  • Governor: Added support for casting votes with ERC-1271 signatures by using a bytes memory signature instead of r, s and v arguments in the castVoteBySig and castVoteWithReasonAndParamsBySig functions. (#4418)
  • Governor: Added a mechanism to restrict the address of the proposer using a suffix in the description.
  • GovernorStorage: Added a new governor extension that stores the proposal details in storage, with an interface that operates on proposalId, as well as proposal enumerability. This replaces the old GovernorCompatibilityBravo module. (#4360)
  • GovernorTimelockAccess: Added a module to connect a governor with an instance of AccessManager, allowing the governor to make calls that are delay-restricted by the manager using the normal queue workflow. (#4523)
  • GovernorTimelockControl: Clean up timelock id on execution for gas refund. (#4118)
  • GovernorTimelockControl: Added the Governor instance address as part of the TimelockController operation salt to avoid operation id collisions between governors using the same TimelockController. (#4432)
  • TimelockController: Changed the role architecture to use DEFAULT_ADMIN_ROLE as the admin for all roles, instead of the bespoke TIMELOCK_ADMIN_ROLE that was used previously. This aligns with the general recommendation for AccessControl and makes the addition of new roles easier. Accordingly, the admin parameter and timelock will now be granted DEFAULT_ADMIN_ROLE instead of TIMELOCK_ADMIN_ROLE. (#3799)
  • TimelockController: Added a state getter that returns an OperationState enum. (#4358)
  • Votes: Use Trace208 for checkpoints. This enables EIP-6372 clock support for keys but reduces the max supported voting power to uint208. (#4539)

Metatx

  • ERC2771Forwarder: Added deadline for expiring transactions, batching, and more secure handling of msg.value. (#4346)
  • ERC2771Context: Return the forwarder address whenever the msg.data of a call originating from a trusted forwarder is not long enough to contain the request signer address (i.e. msg.data.length is less than 20 bytes), as specified by ERC-2771. (#4481)
  • ERC2771Context: Prevent revert in _msgData() when a call originating from a trusted forwarder is not long enough to contain the request signer address (i.e. msg.data.length is less than 20 bytes). Return the full calldata in that case. (#4484)

Proxy

  • ProxyAdmin: Removed getProxyAdmin and getProxyImplementation getters. (#3820)
  • TransparentUpgradeableProxy: Removed admin and implementation getters, which were only callable by the proxy owner and thus not very useful. (#3820)
  • ERC1967Utils: Refactored the ERC1967Upgrade abstract contract as a library. (#4325)
  • TransparentUpgradeableProxy: Admin is now stored in an immutable variable (set during construction) to avoid unnecessary storage reads on every proxy call. This removed the ability to ever change the admin. Transfer of the upgrade capability is exclusively handled through the ownership of the ProxyAdmin. (#4354)
  • Moved the logic to validate ERC-1822 during an upgrade from ERC1967Utils to UUPSUpgradeable. (#4356)
  • UUPSUpgradeable, TransparentUpgradeableProxy and ProxyAdmin: Removed upgradeTo and upgrade functions, and made upgradeToAndCall and upgradeAndCall ignore the data argument if it is empty. It is no longer possible to invoke the receive function (or send value with empty data) along with an upgrade. (#4382)
  • BeaconProxy: Reject value in initialization unless a payable function is explicitly invoked. (#4382)
  • Proxy: Removed redundant receive function. (#4434)
  • BeaconProxy: Use an immutable variable to store the address of the beacon. It is no longer possible for a BeaconProxy to upgrade by changing to another beacon. (#4435)
  • Initializable: Use the namespaced storage pattern to avoid putting critical variables in slot 0. Allow reinitializer versions greater than 256. (#4460)
  • Initializable: Use intermediate variables to improve readability. (#4576)

Token

  • ERC20, ERC721, ERC1155: Deleted _beforeTokenTransfer and _afterTokenTransfer hooks, added a new internal _update function for customizations, and refactored all extensions using those hooks to use _update instead. (#3838, #3876, #4377)
  • ERC20: Removed Approval event previously emitted in transferFrom to indicate that part of the allowance was consumed. With this change, allowances are no longer reconstructible from events. See the code for guidelines on how to re-enable this event if needed. (#4370)
  • ERC20: Removed the non-standard increaseAllowance and decreaseAllowance functions. (#4585)
  • ERC20Votes: Changed internal vote accounting to reusable Votes module previously used by ERC721Votes. Removed implicit ERC20Permit inheritance. Note that the DOMAIN_SEPARATOR getter was previously guaranteed to be available for ERC20Votes contracts, but is no longer available unless ERC20Permit is explicitly used; ERC-5267 support is included in ERC20Votes with EIP712 and is recommended as an alternative. (#3816)
  • SafeERC20: Refactored safeDecreaseAllowance and safeIncreaseAllowance to support USDT-like tokens. (#4260)
  • SafeERC20: Removed safePermit in favor of documentation-only permit recommendations. Based on recommendations from @trust1995 (#4582)
  • ERC721: _approve no longer allows approving the owner of the tokenId. (#4377) _setApprovalForAll no longer allows setting address(0) as an operator. (#4377)
  • ERC721: Renamed _requireMinted to _requireOwned and added a return value with the current owner. Implemented ownerOf in terms of _requireOwned. (#4566)
  • ERC721Consecutive: Added a _firstConsecutiveId internal function that can be overridden to change the id of the first token minted through _mintConsecutive. (#4097)
  • ERC721URIStorage: Allow setting the token URI prior to minting. (#4559)
  • ERC721URIStorage, ERC721Royalty: Stop resetting token-specific URI and royalties when burning. (#4561)
  • ERC1155: Optimized array allocation. (#4196)
  • ERC1155: Removed check for address zero in balanceOf. (#4263)
  • ERC1155: Optimized array accesses by skipping bounds checking when unnecessary. (#4300)
  • ERC1155: Bubble errors triggered in the onERC1155Received and onERC1155BatchReceived hooks. (#4314)
  • ERC1155Supply: Added a totalSupply() function that returns the total amount of token circulating, this change will restrict the total tokens minted across all ids to 2**256-1 . (#3962)
  • ERC1155Receiver: Removed in favor of ERC1155Holder. (#4450)

Utils

  • Address: Removed the ability to customize error messages. A common custom error is always used if the underlying revert reason cannot be bubbled up. (#4502)
  • Arrays: Added unsafeMemoryAccess helpers to read from a memory array without checking the length. (#4300)
  • Arrays: Optimized findUpperBound by removing redundant SLOAD. (#4442)
  • Checkpoints: Library moved from utils to utils/structs (#4275)
  • DoubleEndedQueue: Refactored internal structure to use uint128 instead of int128. This has no effect on the library interface. (#4150)
  • ECDSA: Use unchecked arithmetic for the tryRecover function that receives the r and vs short-signature fields separately. (#4301)
  • EIP712: Added internal getters for the name and version strings (#4303)
  • Math: Makes ceilDiv to revert on 0 division even if the numerator is 0 (#4348)
  • Math: Optimized stack operations in mulDiv. (#4494)
  • Math: Renamed members of Rounding enum, and added a new rounding mode for "away from zero". (#4455)
  • MerkleProof: Use custom error to report invalid multiproof instead of reverting with overflow panic. (#4564)
  • MessageHashUtils: Added a new library for creating message digest to be used along with signing or recovery such as ECDSA or ERC-1271. These functions are moved from the ECDSA library. (#4430)
  • Nonces: Added a new contract to keep track of user nonces. Used for signatures in ERC20Permit, ERC20Votes, and ERC721Votes. (#3816)
  • ReentrancyGuard, Pausable: Moved to utils directory. (#4551)
  • Strings: Renamed toString(int256) to toStringSigned(int256). (#4330)
  • Optimized Strings.equal (#4262)

How to migrate from 4.x

ERC20, ERC721, and ERC1155

These breaking changes will require modifications to ERC20, ERC721, and ERC1155 contracts, since the _afterTokenTransfer and _beforeTokenTransfer functions were removed. Thus, any customization made through those hooks should now be done overriding the new _update function instead.

Minting and burning are implemented by _update and customizations should be done by overriding this function as well. _transfer, _mint and _burn are no longer virtual (meaning they are not overridable) to guard against possible inconsistencies.

For example, a contract using ERC20's _beforeTokenTransfer hook would have to be changed in the following way.

-function _beforeTokenTransfer(
+function _update(
   address from,
   address to,
   uint256 amount
 ) internal virtual override {
-  super._beforeTokenTransfer(from, to, amount);
   require(!condition(), "ERC20: wrong condition");
+  super._update(from, to, amount);
 }

More about ERC721

In the case of ERC721, the _update function does not include a from parameter, as the sender is implicitly the previous owner of the tokenId. The address of this previous owner is returned by the _update function, so it can be used for a posteriori checks. In addition to to and tokenId, a third parameter (auth) is present in this function. This parameter enabled an optional check that the caller/spender is approved to do the transfer. This check cannot be performed after the transfer (because the transfer resets the approval), and doing it before _update would require a duplicate call to _ownerOf.

In this logic of removing hidden SLOADs, the _isApprovedOrOwner function was removed in favor of a new _isAuthorized function. Overrides that used to target the _isApprovedOrOwner should now be performed on the _isAuthorized function. Calls to _isApprovedOrOwner that preceded a call to _transfer, _burn or _approve should be removed in favor of using the auth argument in _update and _approve. This is showcased in ERC721Burnable.burn and in ERC721Wrapper.withdrawTo.

The _exists function was removed. Calls to this function can be replaced by _ownerOf(tokenId) != address(0).

More about ERC1155

Batch transfers will now emit TransferSingle if the batch consists of a single token, while in previous versions the TransferBatch event would be used for all transfers initiated through safeBatchTransferFrom. Both behaviors are compliant with the ERC-1155 specification.

ERC165Storage

Users that were registering EIP-165 interfaces with _registerInterface from ERC165Storage should instead do so so by overriding the supportsInterface function as seen below:

function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
  return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
}

SafeMath

Methods in SafeMath superseded by native overflow checks in Solidity 0.8.0 were removed along with operations providing an interface for revert strings. The remaining methods were moved to utils/Math.sol.

- import "@openzeppelin/contracts/utils/math/SafeMath.sol";
+ import "@openzeppelin/contracts/utils/math/Math.sol";

 function tryOperations(uint256 x, uint256 y) external view {
-  (bool overflowsAdd, uint256 resultAdd) = SafeMath.tryAdd(x, y);
+  (bool overflowsAdd, uint256 resultAdd) = Math.tryAdd(x, y);
-  (bool overflowsSub, uint256 resultSub) = SafeMath.trySub(x, y);
+  (bool overflowsSub, uint256 resultSub) = Math.trySub(x, y);
-  (bool overflowsMul, uint256 resultMul) = SafeMath.tryMul(x, y);
+  (bool overflowsMul, uint256 resultMul) = Math.tryMul(x, y);
-  (bool overflowsDiv, uint256 resultDiv) = SafeMath.tryDiv(x, y);
+  (bool overflowsDiv, uint256 resultDiv) = Math.tryDiv(x, y);
   // ...
 }

Adapting Governor modules

Custom Governor modules that override internal functions may require modifications if migrated to v5. In particular, the new internal functions _queueOperations and _executeOperations may need to be used. If assistance with this migration is needed reach out via the OpenZeppelin Support Forum.

ECDSA and MessageHashUtils

The ECDSA library is now focused on signer recovery. Previously it also included utility methods for producing digests to be used with signing or recovery. These utilities have been moved to the MessageHashUtils library and should be imported if needed:

 import {ECDSA} from "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
+import {MessageHashUtils} from "@openzeppelin/contracts/utils/cryptography/MessageHashUtils.sol";

 contract Verifier {
   using ECDSA for bytes32;
+  using MessageHashUtils for bytes32;

   function _verify(bytes32 data, bytes memory signature, address account) internal pure returns (bool) {
     return data
       .toEthSignedMessageHash()
       .recover(signature) == account;
   }
 }

Interfaces and libraries in upgradeable contracts

The upgradeable version of the contracts library used to include a variant suffixed with Upgradeable for every contract. These variants, which are produced automatically, mainly include changes for dealing with storage that don't apply to libraries and interfaces.

The upgradeable library no longer includes upgradeable variants for libraries and interfaces. Projects migrating to 5.0 should replace their library and interface imports with their corresponding non-upgradeable version:

 // Libraries
-import {AddressUpgradeable} from '@openzeppelin/contracts-upgradeable/utils/AddressUpgradeable.sol';
+import {Address} from '@openzeppelin/contracts/utils/Address.sol';

 // Interfaces
-import {IERC20Upgradeable} from '@openzeppelin/contracts-upgradeable/interfaces/IERC20.sol';
+import {IERC20} from '@openzeppelin/contracts/interfaces/IERC20.sol';

Offchain Considerations

Some changes may affect offchain systems if they rely on assumptions that are changed along with these new breaking changes. These cases are:

Relying on revert strings for processing errors

A concrete example is AccessControl, where it was previously advised to catch revert reasons using the following regex:

/^AccessControl: account (0x[0-9a-f]{40}) is missing role (0x[0-9a-f]{64})$/

Instead, contracts now revert with custom errors. Systems that interact with smart contracts outside of the network should consider reliance on revert strings and possibly support the new custom errors.

Relying on storage locations for retrieving data

After 5.0, the storage location of some variables were changed. This is the case for Initializable and all the upgradeable contracts since they now use namespaced storaged locations. Any system relying on storage locations for retrieving data or detecting capabilities should be updated to support these new locations.

Contributors

trust1995
Assets 2