Refactor Nonces from contract to library to mitigate nonces collision…

… between Votes and ERC20Permit

contracts/governance/utils/IVotes.sol

@@ -37,6 +37,11 @@ interface IVotes {
      */
     function getPastTotalSupply(uint256 blockNumber) external view returns (uint256);
 
+    /**
+     * @dev Returns the delegation nonce for `owner`.
+     */
+    function delegationNonces(address owner) external view returns (uint256);
+
     /**
      * @dev Returns the delegate that `account` has chosen.
      */

contracts/governance/utils/Votes.sol

@@ -29,15 +29,17 @@ import "../../utils/math/SafeCast.sol";
  *
  * _Available since v4.5._
  */
-abstract contract Votes is IVotes, Context, EIP712, Nonces {
+abstract contract Votes is IVotes, Context, EIP712 {
     using Checkpoints for Checkpoints.History;
+    using Nonces for Nonces.Data;
 
     bytes32 private constant _DELEGATION_TYPEHASH =
         keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");
 
     mapping(address => address) private _delegation;
     mapping(address => Checkpoints.History) private _delegateCheckpoints;
     Checkpoints.History private _totalCheckpoints;
+    Nonces.Data private _nonces;
 
     /**
      * @dev Returns the current amount of votes that `account` has.
@@ -80,6 +82,13 @@ abstract contract Votes is IVotes, Context, EIP712, Nonces {
         return _totalCheckpoints.latest();
     }
 
+    /**
+     * @dev Returns the delegation nonce for `owner`.
+     */
+    function delegationNonces(address owner) public view virtual override returns (uint256) {
+        return _nonces.nonces(owner);
+    }
+
     /**
      * @dev Returns the delegate that `account` has chosen.
      */
@@ -113,7 +122,7 @@ abstract contract Votes is IVotes, Context, EIP712, Nonces {
             r,
             s
         );
-        require(nonce == _useNonce(signer), "Votes: invalid nonce");
+        require(nonce == _nonces.useNonce(signer), "Votes: invalid nonce");
         _delegate(signer, delegatee);
     }
 

contracts/mocks/NoncesImpl.sol

@@ -4,8 +4,16 @@ pragma solidity ^0.8.0;
 
 import "../utils/Nonces.sol";
 
-contract NoncesImpl is Nonces {
+contract NoncesImpl {
+    using Nonces for Nonces.Data;
+
+    Nonces.Data private _nonces;
+
+    function nonces(address owner) public view returns (uint256) {
+        return _nonces.nonces(owner);
+    }
+
     function useNonce(address owner) public {
-        super._useNonce(owner);
+        _nonces.useNonce(owner);
     }
 }

contracts/token/ERC20/extensions/ERC20Permit.sol

@@ -19,7 +19,9 @@ import "../../../utils/Nonces.sol";
  *
  * _Available since v3.4._
  */
-abstract contract ERC20Permit is ERC20, IERC20Permit, EIP712, Nonces {
+abstract contract ERC20Permit is ERC20, IERC20Permit, EIP712 {
+    using Nonces for Nonces.Data;
+
     // solhint-disable-next-line var-name-mixedcase
     bytes32 private constant _PERMIT_TYPEHASH =
         keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
@@ -31,6 +33,7 @@ abstract contract ERC20Permit is ERC20, IERC20Permit, EIP712, Nonces {
      */
     // solhint-disable-next-line var-name-mixedcase
     bytes32 private _PERMIT_TYPEHASH_DEPRECATED_SLOT;
+    Nonces.Data private _nonces;
 
     /**
      * @dev Initializes the {EIP712} domain separator using the `name` parameter, and setting `version` to `"1"`.
@@ -53,7 +56,7 @@ abstract contract ERC20Permit is ERC20, IERC20Permit, EIP712, Nonces {
     ) public virtual override {
         require(block.timestamp <= deadline, "ERC20Permit: expired deadline");
 
-        bytes32 structHash = keccak256(abi.encode(_PERMIT_TYPEHASH, owner, spender, value, _useNonce(owner), deadline));
+        bytes32 structHash = keccak256(abi.encode(_PERMIT_TYPEHASH, owner, spender, value, _nonces.useNonce(owner), deadline));
 
         bytes32 hash = _hashTypedDataV4(structHash);
 
@@ -66,8 +69,8 @@ abstract contract ERC20Permit is ERC20, IERC20Permit, EIP712, Nonces {
     /**
      * @dev See {IERC20Permit-nonces}.
      */
-    function nonces(address owner) public view virtual override(IERC20Permit, Nonces) returns (uint256) {
-        return super.nonces(owner);
+    function nonces(address owner) public view virtual override returns (uint256) {
+        return _nonces.nonces(owner);
     }
 
     /**

contracts/utils/Nonces.sol

@@ -6,25 +6,27 @@ import "./Counters.sol";
 /**
  * @dev Provides tracking nonces for addresses. Nonces will only increment.
  */
-abstract contract Nonces {
+library Nonces {
     using Counters for Counters.Counter;
 
-    mapping(address => Counters.Counter) private _nonces;
+    struct Data {
+        mapping(address => Counters.Counter) _nonces;
+    }
 
     /**
      * @dev Returns an address nonce.
      */
-    function nonces(address owner) public view virtual returns (uint256) {
-        return _nonces[owner].current();
+    function nonces(Data storage self, address owner) internal view returns (uint256) {
+        return self._nonces[owner].current();
     }
 
     /**
      * @dev Consumes a nonce.
      *
      * Returns the current value and increments nonce.
      */
-    function _useNonce(address owner) internal virtual returns (uint256 current) {
-        Counters.Counter storage nonce = _nonces[owner];
+    function useNonce(Data storage self, address owner) internal returns (uint256 current) {
+        Counters.Counter storage nonce = self._nonces[owner];
         current = nonce.current();
         nonce.increment();
     }

test/governance/utils/Votes.behavior.js

@@ -20,7 +20,7 @@ const version = '1';
 function shouldBehaveLikeVotes () {
   describe('run votes workflow', function () {
     it('initial nonce is 0', async function () {
-      expect(await this.votes.nonces(this.account1)).to.be.bignumber.equal('0');
+      expect(await this.votes.delegationNonces(this.account1)).to.be.bignumber.equal('0');
     });
 
     it('domain separator', async function () {

test/token/ERC20/extensions/ERC20Votes.test.js

@@ -38,7 +38,7 @@ contract('ERC20Votes', function (accounts) {
   });
 
   it('initial nonce is 0', async function () {
-    expect(await this.token.nonces(holder)).to.be.bignumber.equal('0');
+    expect(await this.token.delegationNonces(holder)).to.be.bignumber.equal('0');
   });
 
   it('domain separator', async function () {

test/token/ERC20/extensions/ERC20VotesComp.test.js

@@ -38,7 +38,7 @@ contract('ERC20VotesComp', function (accounts) {
   });
 
   it('initial nonce is 0', async function () {
-    expect(await this.token.nonces(holder)).to.be.bignumber.equal('0');
+    expect(await this.token.delegationNonces(holder)).to.be.bignumber.equal('0');
   });
 
   it('domain separator', async function () {