• Replace Address.FailedInnerCall with Errors.FailedCall

• Replace Address.AddressInsufficientBalance with Errors.InsufficientBalance

• Replace Clones.Create2InsufficientBalance with Errors.InsufficientBalance

• Replace Clones.ERC1167FailedCreateClone with Errors.FailedDeployment

• Replace Clones.Create2FailedDeployment with Errors.FailedDeployment

• SafeERC20: Replace Address.AddressEmptyCode with SafeERC20FailedOperation if there is no code at the token's address.

• SafeERC20: Replace generic Error(string) with SafeERC20FailedOperation if the returned data can't be decoded as bool.

• SafeERC20: Replace generic SafeERC20FailedOperation with the revert message from the contract call if it fails.

solidity
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v5.1.0) (token/ERC20/extensions/draft-ERC20TemporaryApproval.sol)

pragma solidity ^0.8.24;

import {IERC20, ERC20} from "../ERC20.sol";
import {IERC7674} from "../../../interfaces/draft-IERC7674.sol";
import {Math} from "../../../utils/math/Math.sol";
import {SlotDerivation} from "../../../utils/SlotDerivation.sol";
import {TransientSlot} from "../../../utils/TransientSlot.sol";

/**
 * @dev Extension of {ERC20} that adds support for temporary allowances following ERC-7674.
 *
 * WARNING: This is a draft contract. The corresponding ERC is still subject to changes.
 *
 * _Available since v5.1._
 */
abstract contract ERC20TemporaryApproval is ERC20, IERC7674 {
    using SlotDerivation for bytes32;
    using TransientSlot for bytes32;
    using TransientSlot for TransientSlot.Uint256Slot;

    // keccak256(abi.encode(uint256(keccak256("openzeppelin.storage.ERC20_TEMPORARY_APPROVAL_STORAGE")) - 1)) & ~bytes32(uint256(0xff))
    bytes32 private constant ERC20_TEMPORARY_APPROVAL_STORAGE =
        0xea2d0e77a01400d0111492b1321103eed560d8fe44b9a7c2410407714583c400;

    /**
     * @dev {allowance} override that includes the temporary allowance when looking up the current allowance. If
     * adding up the persistent and the temporary allowances result in an overflow, type(uint256).max is returned.
     */
    function allowance(address owner, address spender) public view virtual override(IERC20, ERC20) returns (uint256) {
        (bool success, uint256 amount) = Math.tryAdd(
            super.allowance(owner, spender),
            _temporaryAllowance(owner, spender)
        );
        return success ? amount : type(uint256).max;
    }

    /**
     * @dev Internal getter for the current temporary allowance that `spender` has over `owner` tokens.
     */
    function _temporaryAllowance(address owner, address spender) internal view virtual returns (uint256) {
        return _temporaryAllowanceSlot(owner, spender).tload();
    }

    /**
     * @dev Alternative to {approve} that sets a `value` amount of tokens as the temporary allowance of `spender` over
     * the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Requirements:
     * - `spender` cannot be the zero address.
     *
     * Does NOT emit an {Approval} event.
     */
    function temporaryApprove(address spender, uint256 value) public virtual returns (bool) {
        _temporaryApprove(_msgSender(), spender, value);
        return true;
    }

    /**
     * @dev Sets `value` as the temporary allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `temporaryApprove`, and can be used to e.g. set automatic allowances
     * for certain subsystems, etc.
     *
     * Requirements:
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     *
     * Does NOT emit an {Approval} event.
     */
    function _temporaryApprove(address owner, address spender, uint256 value) internal virtual {
        if (owner == address(0)) {
            revert ERC20InvalidApprover(address(0));
        }
        if (spender == address(0)) {
            revert ERC20InvalidSpender(address(0));
        }
        _temporaryAllowanceSlot(owner, spender).tstore(value);
    }

    /**
     * @dev {_spendAllowance} override that consumes the temporary allowance (if any) before eventually falling back
     * to consuming the persistent allowance.
     * NOTE: This function skips calling `super._spendAllowance` if the temporary allowance
     * is enough to cover the spending.
     */
    function _spendAllowance(address owner, address spender, uint256 value) internal virtual override {
        // load transient allowance
        uint256 currentTemporaryAllowance = _temporaryAllowance(owner, spender);

        // Check and update (if needed) the temporary allowance + set remaining value
        if (currentTemporaryAllowance > 0) {
            // All value is covered by the infinite allowance. nothing left to spend, we can return early
            if (currentTemporaryAllowance == type(uint256).max) {
                return;
            }
            // check how much of the value is covered by the transient allowance
            uint256 spendTemporaryAllowance = Math.min(currentTemporaryAllowance, value);
            unchecked {
                // decrease transient allowance accordingly
                _temporaryApprove(owner, spender, currentTemporaryAllowance - spendTemporaryAllowance);
                // update value necessary
                value -= spendTemporaryAllowance;
            }
        }
        // reduce any remaining value from the persistent allowance
        if (value > 0) {
            super._spendAllowance(owner, spender, value);
        }
    }

    function _temporaryAllowanceSlot(address owner, address spender) private pure returns (TransientSlot.Uint256Slot) {
        return ERC20_TEMPORARY_APPROVAL_STORAGE.deriveMapping(owner).deriveMapping(spender).asUint256();
    }
}

solidity
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v5.1.0) (utils/cryptography/MerkleProof.sol)
// This file was procedurally generated from scripts/generate/templates/MerkleProof.js.

pragma solidity ^0.8.20;

import {Hashes} from "./Hashes.sol";

/**
 * @dev These functions deal with verification of Merkle Tree proofs.
 *
 * The tree and the proofs can be generated using our
 * https://github.com/OpenZeppelin/merkle-tree[JavaScript library].
 * You will find a quickstart guide in the readme.
 *
 * WARNING: You should avoid using leaf values that are 64 bytes long prior to
 * hashing, or use a hash function other than keccak256 for hashing leaves.
 * This is because the concatenation of a sorted pair of internal nodes in
 * the Merkle tree could be reinterpreted as a leaf value.
 * OpenZeppelin's JavaScript library generates Merkle trees that are safe
 * against this attack out of the box.
 *
 * IMPORTANT: Consider memory side-effects when using custom hashing functions
 * that access memory in an unsafe way.
 *
 * NOTE: This library supports proof verification for merkle trees built using
 * custom _commutative_ hashing functions (i.e. `H(a, b) == H(b, a)`). Proving
 * leaf inclusion in trees built using non-commutative hashing functions requires
 * additional logic that is not supported by this library.
 */
library MerkleProof {
    /**
     *@dev The multiproof provided is not valid.
     */
    error MerkleProofInvalidMultiproof();

    /**
     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
     * defined by `root`. For this, a `proof` must be provided, containing
     * sibling hashes on the branch from the leaf to the root of the tree. Each
     * pair of leaves and each pair of pre-images are assumed to be sorted.
     *
     * This version handles proofs in memory with the default hashing function.
     */
    function verify(bytes32[] memory proof, bytes32 root, bytes32 leaf) internal pure returns (bool) {
        return processProof(proof, leaf) == root;
    }

    /**
     * @dev Returns the rebuilt hash obtained by traversing a Merkle tree up
     * from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
     * hash matches the root of the tree. When processing the proof, the pairs
     * of leaves & pre-images are assumed to be sorted.
     *
     * This version handles proofs in memory with the default hashing function.
     */
    function processProof(bytes32[] memory proof, bytes32 leaf) internal pure returns (bytes32) {
        bytes32 computedHash = leaf;
        for (uint256 i = 0; i < proof.length; i++) {
            computedHash = Hashes.commutativeKeccak256(computedHash, proof[i]);
        }
        return computedHash;
    }

    /**
     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
     * defined by `root`. For this, a `proof` must be provided, containing
     * sibling hashes on the branch from the leaf to the root of the tree. Each
     * pair of leaves and each pair of pre-images are assumed to be sorted.
     *
     * This version handles proofs in memory with a custom hashing function.
     */
    function verify(
        bytes32[] memory proof,
        bytes32 root,
        bytes32 leaf,
        function(bytes32, bytes32) view returns (bytes32) hasher
    ) internal view returns (bool) {
        return processProof(proof, leaf, hasher) == root;
    }

    /**
     * @dev Returns the rebuilt hash obtained by traversing a Merkle tree up
     * from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
     * hash matches the root of the tree. When processing the proof, the pairs
     * of leaves & pre-images are assumed to be sorted.
     *
     * This version handles proofs in memory with a custom hashing function.
     */
    function processProof(
        bytes32[] memory proof,
        bytes32 leaf,
        function(bytes32, bytes32) view returns (bytes32) hasher
    ) internal view returns (bytes32) {
        bytes32 computedHash = leaf;
        for (uint256 i = 0; i < proof.length; i++) {
            computedHash = hasher(computedHash, proof[i]);
        }
        return computedHash;
    }

    /**
     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
     * defined by `root`. For this, a `proof` must be provided, containing
     * sibling hashes on the branch from the leaf to the root of the tree. Each
     * pair of leaves and each pair of pre-images are assumed to be sorted.
     *
     * This version handles proofs in calldata with the default hashing function.
     */
    function verifyCalldata(bytes32[] calldata proof, bytes32 root, bytes32 leaf) internal pure returns (bool) {
        return processProofCalldata(proof, leaf) == root;
    }

    /**
     * @dev Returns the rebuilt hash obtained by traversing a Merkle tree up
     * from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
     * hash matches the root of the tree. When processing the proof, the pairs
     * of leaves & pre-images are assumed to be sorted.
     *
     * This version handles proofs in calldata with the default hashing function.
     */
    function processProofCalldata(bytes32[] calldata proof, bytes32 leaf) internal pure returns (bytes32) {
        bytes32 computedHash = leaf;
        for (uint256 i = 0; i < proof.length; i++) {
            computedHash = Hashes.commutativeKeccak256(computedHash, proof[i]);
        }
        return computedHash;
    }

    /**
     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
     * defined by `root`. For this, a `proof` must be provided, containing
     * sibling hashes on the branch from the leaf to the root of the tree. Each
     * pair of leaves and each pair of pre-images are assumed to be sorted.
     *
     * This version handles proofs in calldata with a custom hashing function.
     */
    function verifyCalldata(
        bytes32[] calldata proof,
        bytes32 root,
        bytes32 leaf,
        function(bytes32, bytes32) view returns (bytes32) hasher
    ) internal view returns (bool) {
        return processProofCalldata(proof, leaf, hasher) == root;
    }

    /**
     * @dev Returns the rebuilt hash obtained by traversing a Merkle tree up
     * from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
     * hash matches the root of the tree. When processing the proof, the pairs
     * of leaves & pre-images are assumed to be sorted.
     *
     * This version handles proofs in calldata with a custom hashing function.
     */
    function processProofCalldata(
        bytes32[] calldata proof,
        bytes32 leaf,
        function(bytes32, bytes32) view returns (bytes32) hasher
    ) internal view returns (bytes32) {
        bytes32 computedHash = leaf;
        for (uint256 i = 0; i < proof.length; i++) {
            computedHash = hasher(computedHash, proof[i]);
        }
        return computedHash;
    }

    /**
     * @dev Returns true if the `leaves` can be simultaneously proven to be a part of a Merkle tree defined by
     * `root`, according to `proof` and `proofFlags` as described in {processMultiProof}.
     *
     * This version handles multiproofs in memory with the default hashing function.
     *
     * CAUTION: Not all Merkle trees admit multiproofs. See {processMultiProof} for details.
     *
     * NOTE: Consider the case where `root == proof[0] && leaves.length == 0` as it will return `true`.
     * The `leaves` must be validated independently. See {processMultiProof}.
     */
    function multiProofVerify(
        bytes32[] memory proof,
        bool[] memory proofFlags,
        bytes32 root,
        bytes32[] memory leaves
    ) internal pure returns (bool) {
        return processMultiProof(proof, proofFlags, leaves) == root;
    }

    /**
     * @dev Returns the root of a tree reconstructed from `leaves` and sibling nodes in `proof`. The reconstruction
     * proceeds by incrementally reconstructing all inner nodes by combining a leaf/inner node with either another
     * leaf/inner node or a proof sibling node, depending on whether each `proofFlags` item is true or false
     * respectively.
     *
     * This version handles multiproofs in memory with the default hashing function.
     *
     * CAUTION: Not all Merkle trees admit multiproofs. To use multiproofs, it is sufficient to ensure that: 1) the tree
     * is complete (but not necessarily perfect), 2) the leaves to be proven are in the opposite order they are in the
     * tree (i.e., as seen from right to left starting at the deepest layer and continuing at the next layer).
     *
     * NOTE: The _empty set_ (i.e. the case where `proof.length == 1 && leaves.length == 0`) is considered a no-op,
     * and therefore a valid multiproof (i.e. it returns `proof[0]`). Consider disallowing this case if you're not
     * validating the leaves elsewhere.
     */
    function processMultiProof(
        bytes32[] memory proof,
        bool[] memory proofFlags,
        bytes32[] memory leaves
    ) internal pure returns (bytes32 merkleRoot) {
        // This function rebuilds the root hash by traversing the tree up from the leaves. The root is rebuilt by
        // consuming and producing values on a queue. The queue starts with the `leaves` array, then goes onto the
        // `hashes` array. At the end of the process, the last hash in the `hashes` array should contain the root of
        // the Merkle tree.
        uint256 leavesLen = leaves.length;
        uint256 proofFlagsLen = proofFlags.length;

        // Check proof validity.
        if (leavesLen + proof.length != proofFlagsLen + 1) {
            revert MerkleProofInvalidMultiproof();
        }

        // The xxxPos values are "pointers" to the next value to consume in each array. All accesses are done using
        // `xxx[xxxPos++]`, which return the current value and increment the pointer, thus mimicking a queue's "pop".
        bytes32[] memory hashes = new bytes32[](proofFlagsLen);
        uint256 leafPos = 0;
        uint256 hashPos = 0;
        uint256 proofPos = 0;
        // At each step, we compute the next hash using two values:
        // - a value from the "main queue". If not all leaves have been consumed, we get the next leaf, otherwise we
        //   get the next hash.
        // - depending on the flag, either another value from the "main queue" (merging branches) or an element from the
        //   `proof` array.
        for (uint256 i = 0; i < proofFlagsLen; i++) {
            bytes32 a = leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++];
            bytes32 b = proofFlags[i]
                ? (leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++])
                : proof[proofPos++];
            hashes[i] = Hashes.commutativeKeccak256(a, b);
        }

        if (proofFlagsLen > 0) {
            if (proofPos != proof.length) {
                revert MerkleProofInvalidMultiproof();
            }
            unchecked {
                return hashes[proofFlagsLen - 1];
            }
        } else if (leavesLen > 0) {
            return leaves[0];
        } else {
            return proof[0];
        }
    }

    /**
     * @dev Returns true if the `leaves` can be simultaneously proven to be a part of a Merkle tree defined by
     * `root`, according to `proof` and `proofFlags` as described in {processMultiProof}.
     *
     * This version handles multiproofs in memory with a custom hashing function.
     *
     * CAUTION: Not all Merkle trees admit multiproofs. See {processMultiProof} for details.
     *
     * NOTE: Consider the case where `root == proof[0] && leaves.length == 0` as it will return `true`.
     * The `leaves` must be validated independently. See {processMultiProof}.
     */
    function multiProofVerify(
        bytes32[] memory proof,
        bool[] memory proofFlags,
        bytes32 root,
        bytes32[] memory leaves,
        function(bytes32, bytes32) view returns (bytes32) hasher
    ) internal view returns (bool) {
        return processMultiProof(proof, proofFlags, leaves, hasher) == root;
    }

    /**
     * @dev Returns the root of a tree reconstructed from `leaves` and sibling nodes in `proof`. The reconstruction
     * proceeds by incrementally reconstructing all inner nodes by combining a leaf/inner node with either another
     * leaf/inner node or a proof sibling node, depending on whether each `proofFlags` item is true or false
     * respectively.
     *
     * This version handles multiproofs in memory with a custom hashing function.
     *
     * CAUTION: Not all Merkle trees admit multiproofs. To use multiproofs, it is sufficient to ensure that: 1) the tree
     * is complete (but not necessarily perfect), 2) the leaves to be proven are in the opposite order they are in the
     * tree (i.e., as seen from right to left starting at the deepest layer and continuing at the next layer).
     *
     * NOTE: The _empty set_ (i.e. the case where `proof.length == 1 && leaves.length == 0`) is considered a no-op,
     * and therefore a valid multiproof (i.e. it returns `proof[0]`). Consider disallowing this case if you're not
     * validating the leaves elsewhere.
     */
    function processMultiProof(
        bytes32[] memory proof,
        bool[] memory proofFlags,
        bytes32[] memory leaves,
        function(bytes32, bytes32) view returns (bytes32) hasher
    ) internal view returns (bytes32 merkleRoot) {
        // This function rebuilds the root hash by traversing the tree up from the leaves. The root is rebuilt by
        // consuming and producing values on a queue. The queue starts with the `leaves` array, then goes onto the
        // `hashes` array. At the end of the process, the last hash in the `hashes` array should contain the root of
        // the Merkle tree.
        uint256 leavesLen = leaves.length;
        uint256 proofFlagsLen = proofFlags.length;

        // Check proof validity.
        if (leavesLen + proof.length != proofFlagsLen + 1) {
            revert MerkleProofInvalidMultiproof();
        }

        // The xxxPos values are "pointers" to the next value to consume in each array. All accesses are done using
        // `xxx[xxxPos++]`, which return the current value and increment the pointer, thus mimicking a queue's "pop".
        bytes32[] memory hashes = new bytes32[](proofFlagsLen);
        uint256 leafPos = 0;
        uint256 hashPos = 0;
        uint256 proofPos = 0;
        // At each step, we compute the next hash using two values:
        // - a value from the "main queue". If not all leaves have been consumed, we get the next leaf, otherwise we
        //   get the next hash.
        // - depending on the flag, either another value from the "main queue" (merging branches) or an element from the
        //   `proof` array.
        for (uint256 i = 0; i < proofFlagsLen; i++) {
            bytes32 a = leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++];
            bytes32 b = proofFlags[i]
                ? (leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++])
                : proof[proofPos++];
            hashes[i] = hasher(a, b);
        }

        if (proofFlagsLen > 0) {
            if (proofPos != proof.length) {
                revert MerkleProofInvalidMultiproof();
            }
            unchecked {
                return hashes[proofFlagsLen - 1];
            }
        } else if (leavesLen > 0) {
            return leaves[0];
        } else {
            return proof[0];
        }
    }

    /**
     * @dev Returns true if the `leaves` can be simultaneously proven to be a part of a Merkle tree defined by
     * `root`, according to `proof` and `proofFlags` as described in {processMultiProof}.
     *
     * This version handles multiproofs in calldata with the default hashing function.
     *
     * CAUTION: Not all Merkle trees admit multiproofs. See {processMultiProof} for details.
     *
     * NOTE: Consider the case where `root == proof[0] && leaves.length == 0` as it will return `true`.
     * The `leaves` must be validated independently. See {processMultiProofCalldata}.
     */
    function multiProofVerifyCalldata(
        bytes32[] calldata proof,
        bool[] calldata proofFlags,
        bytes32 root,
        bytes32[] memory leaves
    ) internal pure returns (bool) {
        return processMultiProofCalldata(proof, proofFlags, leaves) == root;
    }

    /**
     * @dev Returns the root of a tree reconstructed from `leaves` and sibling nodes in `proof`. The reconstruction
     * proceeds by incrementally reconstructing all inner nodes by combining a leaf/inner node with either another
     * leaf/inner node or a proof sibling node, depending on whether each `proofFlags` item is true or false
     * respectively.
     *
     * This version handles multiproofs in calldata with the default hashing function.
     *
     * CAUTION: Not all Merkle trees admit multiproofs. To use multiproofs, it is sufficient to ensure that: 1) the tree
     * is complete (but not necessarily perfect), 2) the leaves to be proven are in the opposite order they are in the
     * tree (i.e., as seen from right to left starting at the deepest layer and continuing at the next layer).
     *
     * NOTE: The _empty set_ (i.e. the case where `proof.length == 1 && leaves.length == 0`) is considered a no-op,
     * and therefore a valid multiproof (i.e. it returns `proof[0]`). Consider disallowing this case if you're not
     * validating the leaves elsewhere.
     */
    function processMultiProofCalldata(
        bytes32[] calldata proof,
        bool[] calldata proofFlags,
        bytes32[] memory leaves
    ) internal pure returns (bytes32 merkleRoot) {
        // This function rebuilds the root hash by traversing the tree up from the leaves. The root is rebuilt by
        // consuming and producing values on a queue. The queue starts with the `leaves` array, then goes onto the
        // `hashes` array. At the end of the process, the last hash in the `hashes` array should contain the root of
        // the Merkle tree.
        uint256 leavesLen = leaves.length;
        uint256 proofFlagsLen = proofFlags.length;

        // Check proof validity.
        if (leavesLen + proof.length != proofFlagsLen + 1) {
            revert MerkleProofInvalidMultiproof();
        }

        // The xxxPos values are "pointers" to the next value to consume in each array. All accesses are done using
        // `xxx[xxxPos++]`, which return the current value and increment the pointer, thus mimicking a queue's "pop".
        bytes32[] memory hashes = new bytes32[](proofFlagsLen);
        uint256 leafPos = 0;
        uint256 hashPos = 0;
        uint256 proofPos = 0;
        // At each step, we compute the next hash using two values:
        // - a value from the "main queue". If not all leaves have been consumed, we get the next leaf, otherwise we
        //   get the next hash.
        // - depending on the flag, either another value from the "main queue" (merging branches) or an element from the
        //   `proof` array.
        for (uint256 i = 0; i < proofFlagsLen; i++) {
            bytes32 a = leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++];
            bytes32 b = proofFlags[i]
                ? (leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++])
                : proof[proofPos++];
            hashes[i] = Hashes.commutativeKeccak256(a, b);
        }

        if (proofFlagsLen > 0) {
            if (proofPos != proof.length) {
                revert MerkleProofInvalidMultiproof();
            }
            unchecked {
                return hashes[proofFlagsLen - 1];
            }
        } else if (leavesLen > 0) {
            return leaves[0];
        } else {
            return proof[0];
        }
    }

    /**
     * @dev Returns true if the `leaves` can be simultaneously proven to be a part of a Merkle tree defined by
     * `root`, according to `proof` and `proofFlags` as described in {processMultiProof}.
     *
     * This version handles multiproofs in calldata with a custom hashing function.
     *
     * CAUTION: Not all Merkle trees admit multiproofs. See {processMultiProof} for details.
     *
     * NOTE: Consider the case where `root == proof[0] && leaves.length == 0` as it will return `true`.
     * The `leaves` must be validated independently. See {processMultiProofCalldata}.
     */
    function multiProofVerifyCalldata(
        bytes32[] calldata proof,
        bool[] calldata proofFlags,
        bytes32 root,
        bytes32[] memory leaves,
        function(bytes32, bytes32) view returns (bytes32) hasher
    ) internal view returns (bool) {
        return processMultiProofCalldata(proof, proofFlags, leaves, hasher) == root;
    }

    /**
     * @dev Returns the root of a tree reconstructed from `leaves` and sibling nodes in `proof`. The reconstruction
     * proceeds by incrementally reconstructing all inner nodes by combining a leaf/inner node with either another
     * leaf/inner node or a proof sibling node, depending on whether each `proofFlags` item is true or false
     * respectively.
     *
     * This version handles multiproofs in calldata with a custom hashing function.
     *
     * CAUTION: Not all Merkle trees admit multiproofs. To use multiproofs, it is sufficient to ensure that: 1) the tree
     * is complete (but not necessarily perfect), 2) the leaves to be proven are in the opposite order they are in the
     * tree (i.e., as seen from right to left starting at the deepest layer and continuing at the next layer).
     *
     * NOTE: The _empty set_ (i.e. the case where `proof.length == 1 && leaves.length == 0`) is considered a no-op,
     * and therefore a valid multiproof (i.e. it returns `proof[0]`). Consider disallowing this case if you're not
     * validating the leaves elsewhere.
     */
    function processMultiProofCalldata(
        bytes32[] calldata proof,
        bool[] calldata proofFlags,
        bytes32[] memory leaves,
        function(bytes32, bytes32) view returns (bytes32) hasher
    ) internal view returns (bytes32 merkleRoot) {
        // This function rebuilds the root hash by traversing the tree up from the leaves. The root is rebuilt by
        // consuming and producing values on a queue. The queue starts with the `leaves` array, then goes onto the
        // `hashes` array. At the end of the process, the last hash in the `hashes` array should contain the root of
        // the Merkle tree.
        uint256 leavesLen = leaves.length;
        uint256 proofFlagsLen = proofFlags.length;

        // Check proof validity.
        if (leavesLen + proof.length != proofFlagsLen + 1) {
            revert MerkleProofInvalidMultiproof();
        }

        // The xxxPos values are "pointers" to the next value to consume in each array. All accesses are done using
        // `xxx[xxxPos++]`, which return the current value and increment the pointer, thus mimicking a queue's "pop".
        bytes32[] memory hashes = new bytes32[](proofFlagsLen);
        uint256 leafPos = 0;
        uint256 hashPos = 0;
        uint256 proofPos = 0;
        // At each step, we compute the next hash using two values:
        // - a value from the "main queue". If not all leaves have been consumed, we get the next leaf, otherwise we
        //   get the next hash.
        // - depending on the flag, either another value from the "main queue" (merging branches) or an element from the
        //   `proof` array.
        for (uint256 i = 0; i < proofFlagsLen; i++) {
            bytes32 a = leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++];
            bytes32 b = proofFlags[i]
                ? (leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++])
                : proof[proofPos++];
            hashes[i] = hasher(a, b);
        }

        if (proofFlagsLen > 0) {
            if (proofPos != proof.length) {
                revert MerkleProofInvalidMultiproof();
            }
            unchecked {
                return hashes[proofFlagsLen - 1];
            }
        } else if (leavesLen > 0) {
            return leaves[0];
        } else {
            return proof[0];
        }
    }
}