From 50db94a4492b3af99a2ac5047f8a572a7732cd0c Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Thu, 24 Nov 2022 15:12:13 -0400
Subject: [PATCH 01/42] remove beforeTokenTranser and afterTokenTransfer hooks

---
 contracts/mocks/ERC20VotesMock.sol            |   4 +-
 contracts/token/ERC20/ERC20.sol               | 123 ++++--------------
 .../token/ERC20/extensions/ERC20Capped.sol    |   6 +-
 .../token/ERC20/extensions/ERC20Pausable.sol  |   5 +-
 .../token/ERC20/extensions/ERC20Snapshot.sol  |  10 +-
 .../token/ERC20/extensions/ERC20Votes.sol     |  30 ++---
 .../ERC20/presets/ERC20PresetMinterPauser.sol |   4 +-
 .../ERC20/extensions/ERC20FlashMint.test.js   |   6 +-
 8 files changed, 52 insertions(+), 136 deletions(-)

diff --git a/contracts/mocks/ERC20VotesMock.sol b/contracts/mocks/ERC20VotesMock.sol
index 0975e8b9f7e..6719f64b102 100644
--- a/contracts/mocks/ERC20VotesMock.sol
+++ b/contracts/mocks/ERC20VotesMock.sol
@@ -8,11 +8,11 @@ contract ERC20VotesMock is ERC20Votes {
     constructor(string memory name, string memory symbol) ERC20(name, symbol) ERC20Permit(name) {}
 
     function mint(address account, uint256 amount) public {
-        _mint(account, amount);
+        _transfer(address(0), account, amount);
     }
 
     function burn(address account, uint256 amount) public {
-        _burn(account, amount);
+        _transfer(account, address(0), amount);
     }
 
     function getChainId() external view returns (uint256) {
diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 492e261018d..94b4011a0d1 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -215,89 +215,60 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      * This internal function is equivalent to {transfer}, and can be used to
      * e.g. implement automatic token fees, slashing mechanisms, etc.
      *
-     * Emits a {Transfer} event.
+     * Will mint (or burn) if `from` (or `to`) is address(0).
      *
-     * Requirements:
+     * Emits a {Transfer} event.
      *
-     * - `from` cannot be the zero address.
-     * - `to` cannot be the zero address.
-     * - `from` must have a balance of at least `amount`.
      */
     function _transfer(
         address from,
         address to,
         uint256 amount
     ) internal virtual {
-        require(from != address(0), "ERC20: transfer from the zero address");
-        require(to != address(0), "ERC20: transfer to the zero address");
-
-        _beforeTokenTransfer(from, to, amount);
+        require(from != address(0) || to != address(0), "ERC721: mint to the zero address");
 
         uint256 fromBalance = _balances[from];
-        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
         unchecked {
-            _balances[from] = fromBalance - amount;
-            // Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
-            // decrementing then incrementing.
-            _balances[to] += amount;
+            if (from == address(0)) {
+                _balances[to] += amount;
+                _totalSupply += amount;
+            } else if (to == address(0)) {
+                require(fromBalance >= amount, "ERC20: burn amount exceeds balance");
+                _balances[from] -= amount;
+                _totalSupply -= amount;
+            } else {
+                require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
+                _balances[from] -= amount;
+                _balances[to] += amount;
+            }
         }
-
+        
         emit Transfer(from, to, amount);
-
-        _afterTokenTransfer(from, to, amount);
     }
 
-    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
-     * the total supply.
+    /** @dev Creates `amount` tokens and assigns them to `account`, by transfering it from address(0).
+     * Relies on the `_transfer` mechanism
      *
      * Emits a {Transfer} event with `from` set to the zero address.
      *
-     * Requirements:
+     * Note: this function is not virtual, {_transfer} should be overriden instead.
      *
-     * - `account` cannot be the zero address.
      */
-    function _mint(address account, uint256 amount) internal virtual {
-        require(account != address(0), "ERC20: mint to the zero address");
-
-        _beforeTokenTransfer(address(0), account, amount);
-
-        _totalSupply += amount;
-        unchecked {
-            // Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
-            _balances[account] += amount;
-        }
-        emit Transfer(address(0), account, amount);
-
-        _afterTokenTransfer(address(0), account, amount);
+    function _mint(address account, uint256 amount) internal {
+        _transfer(address(0), account, amount);
     }
 
     /**
-     * @dev Destroys `amount` tokens from `account`, reducing the
-     * total supply.
+     * @dev Destroys `amount` tokens from `account`, by transfering it to address(0).
+     * Relies on the `_transfer` mechanism.
      *
-     * Emits a {Transfer} event with `to` set to the zero address.
+     * Note: this function is not virtual, {_transfer} should be overriden instead
      *
-     * Requirements:
+     * Emits a {Transfer} event with `to` set to the zero address.
      *
-     * - `account` cannot be the zero address.
-     * - `account` must have at least `amount` tokens.
      */
-    function _burn(address account, uint256 amount) internal virtual {
-        require(account != address(0), "ERC20: burn from the zero address");
-
-        _beforeTokenTransfer(account, address(0), amount);
-
-        uint256 accountBalance = _balances[account];
-        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
-        unchecked {
-            _balances[account] = accountBalance - amount;
-            // Overflow not possible: amount <= accountBalance <= totalSupply.
-            _totalSupply -= amount;
-        }
-
-        emit Transfer(account, address(0), amount);
-
-        _afterTokenTransfer(account, address(0), amount);
+    function _burn(address account, uint256 amount) internal {
+        _transfer(account, address(0), amount);
     }
 
     /**
@@ -346,44 +317,4 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
             }
         }
     }
-
-    /**
-     * @dev Hook that is called before any transfer of tokens. This includes
-     * minting and burning.
-     *
-     * Calling conditions:
-     *
-     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
-     * will be transferred to `to`.
-     * - when `from` is zero, `amount` tokens will be minted for `to`.
-     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
-     * - `from` and `to` are never both zero.
-     *
-     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
-     */
-    function _beforeTokenTransfer(
-        address from,
-        address to,
-        uint256 amount
-    ) internal virtual {}
-
-    /**
-     * @dev Hook that is called after any transfer of tokens. This includes
-     * minting and burning.
-     *
-     * Calling conditions:
-     *
-     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
-     * has been transferred to `to`.
-     * - when `from` is zero, `amount` tokens have been minted for `to`.
-     * - when `to` is zero, `amount` of ``from``'s tokens have been burned.
-     * - `from` and `to` are never both zero.
-     *
-     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
-     */
-    function _afterTokenTransfer(
-        address from,
-        address to,
-        uint256 amount
-    ) internal virtual {}
 }
diff --git a/contracts/token/ERC20/extensions/ERC20Capped.sol b/contracts/token/ERC20/extensions/ERC20Capped.sol
index 16f830d18a5..24d52166301 100644
--- a/contracts/token/ERC20/extensions/ERC20Capped.sol
+++ b/contracts/token/ERC20/extensions/ERC20Capped.sol
@@ -28,10 +28,10 @@ abstract contract ERC20Capped is ERC20 {
     }
 
     /**
-     * @dev See {ERC20-_mint}.
+     * @dev See {ERC20-_transfer}.
      */
-    function _mint(address account, uint256 amount) internal virtual override {
+    function _transfer(address, address account, uint256 amount) internal virtual override {
         require(ERC20.totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
-        super._mint(account, amount);
+        super._transfer(address(0), account, amount);
     }
 }
diff --git a/contracts/token/ERC20/extensions/ERC20Pausable.sol b/contracts/token/ERC20/extensions/ERC20Pausable.sol
index e448e96a640..e314cba5b1c 100644
--- a/contracts/token/ERC20/extensions/ERC20Pausable.sol
+++ b/contracts/token/ERC20/extensions/ERC20Pausable.sol
@@ -21,13 +21,12 @@ abstract contract ERC20Pausable is ERC20, Pausable {
      *
      * - the contract must not be paused.
      */
-    function _beforeTokenTransfer(
+    function _transfer(
         address from,
         address to,
         uint256 amount
     ) internal virtual override {
-        super._beforeTokenTransfer(from, to, amount);
-
         require(!paused(), "ERC20Pausable: token transfer while paused");
+        super._transfer(from, to, amount);
     }
 }
diff --git a/contracts/token/ERC20/extensions/ERC20Snapshot.sol b/contracts/token/ERC20/extensions/ERC20Snapshot.sol
index 0b46fc660bf..6db172f3c9d 100644
--- a/contracts/token/ERC20/extensions/ERC20Snapshot.sol
+++ b/contracts/token/ERC20/extensions/ERC20Snapshot.sol
@@ -118,18 +118,15 @@ abstract contract ERC20Snapshot is ERC20 {
         return snapshotted ? value : totalSupply();
     }
 
-    // Update balance and/or total supply snapshots before the values are modified. This is implemented
-    // in the _beforeTokenTransfer hook, which is executed for _mint, _burn, and _transfer operations.
-    function _beforeTokenTransfer(
+    // Update balance and/or total supply snapshots before the values are modified. This is executed
+    // for _mint, _burn, and _transfer operations.
+    function _transfer(
         address from,
         address to,
         uint256 amount
     ) internal virtual override {
-        super._beforeTokenTransfer(from, to, amount);
-
         if (from == address(0)) {
             // mint
-            _updateAccountSnapshot(to);
             _updateTotalSupplySnapshot();
         } else if (to == address(0)) {
             // burn
@@ -140,6 +137,7 @@ abstract contract ERC20Snapshot is ERC20 {
             _updateAccountSnapshot(from);
             _updateAccountSnapshot(to);
         }
+        super._transfer(from, to, amount);
     }
 
     function _valueAt(uint256 snapshotId, Snapshots storage snapshots) private view returns (bool, uint256) {
diff --git a/contracts/token/ERC20/extensions/ERC20Votes.sol b/contracts/token/ERC20/extensions/ERC20Votes.sol
index bf319c26f84..8e66c86ecbd 100644
--- a/contracts/token/ERC20/extensions/ERC20Votes.sol
+++ b/contracts/token/ERC20/extensions/ERC20Votes.sol
@@ -173,36 +173,24 @@ abstract contract ERC20Votes is IVotes, ERC20Permit {
         return type(uint224).max;
     }
 
-    /**
-     * @dev Snapshots the totalSupply after it has been increased.
-     */
-    function _mint(address account, uint256 amount) internal virtual override {
-        super._mint(account, amount);
-        require(totalSupply() <= _maxSupply(), "ERC20Votes: total supply risks overflowing votes");
-
-        _writeCheckpoint(_totalSupplyCheckpoints, _add, amount);
-    }
-
-    /**
-     * @dev Snapshots the totalSupply after it has been decreased.
-     */
-    function _burn(address account, uint256 amount) internal virtual override {
-        super._burn(account, amount);
-
-        _writeCheckpoint(_totalSupplyCheckpoints, _subtract, amount);
-    }
-
     /**
      * @dev Move voting power when tokens are transferred.
      *
      * Emits a {IVotes-DelegateVotesChanged} event.
      */
-    function _afterTokenTransfer(
+    function _transfer(
         address from,
         address to,
         uint256 amount
     ) internal virtual override {
-        super._afterTokenTransfer(from, to, amount);
+        super._transfer(from, to, amount);
+        if(from == address(0)){
+            require(totalSupply() <= _maxSupply(), "ERC20Votes: total supply risks overflowing votes");
+            _writeCheckpoint(_totalSupplyCheckpoints, _add, amount);
+        }
+        if(to == address(0)){
+            _writeCheckpoint(_totalSupplyCheckpoints, _subtract, amount);
+        }
 
         _moveVotingPower(delegates(from), delegates(to), amount);
     }
diff --git a/contracts/token/ERC20/presets/ERC20PresetMinterPauser.sol b/contracts/token/ERC20/presets/ERC20PresetMinterPauser.sol
index e711a894f0c..8ab23590e90 100644
--- a/contracts/token/ERC20/presets/ERC20PresetMinterPauser.sol
+++ b/contracts/token/ERC20/presets/ERC20PresetMinterPauser.sol
@@ -84,11 +84,11 @@ contract ERC20PresetMinterPauser is Context, AccessControlEnumerable, ERC20Burna
         _unpause();
     }
 
-    function _beforeTokenTransfer(
+    function _transfer(
         address from,
         address to,
         uint256 amount
     ) internal virtual override(ERC20, ERC20Pausable) {
-        super._beforeTokenTransfer(from, to, amount);
+        super._transfer(from, to, amount);
     }
 }
diff --git a/test/token/ERC20/extensions/ERC20FlashMint.test.js b/test/token/ERC20/extensions/ERC20FlashMint.test.js
index d08464decfb..a375c214c09 100644
--- a/test/token/ERC20/extensions/ERC20FlashMint.test.js
+++ b/test/token/ERC20/extensions/ERC20FlashMint.test.js
@@ -1,8 +1,8 @@
 /* eslint-disable */
 
-const { BN, constants, expectEvent, expectRevert, time } = require('@openzeppelin/test-helpers');
+const { BN, constants, expectEvent, expectRevert } = require('@openzeppelin/test-helpers');
 const { expect } = require('chai');
-const { MAX_UINT256, ZERO_ADDRESS, ZERO_BYTES32 } = constants;
+const { MAX_UINT256, ZERO_ADDRESS } = constants;
 
 const ERC20FlashMintMock = artifacts.require('ERC20FlashMintMock');
 const ERC3156FlashBorrowerMock = artifacts.require('ERC3156FlashBorrowerMock');
@@ -77,7 +77,7 @@ contract('ERC20FlashMint', function (accounts) {
       );
     });
 
-    it('unavailable funds', async function () {
+    it.only('unavailable funds', async function () {
       const receiver = await ERC3156FlashBorrowerMock.new(true, true);
       const data = this.token.contract.methods.transfer(other, 10).encodeABI();
       await expectRevert(

From 2e68978965e3dec65da64ecd6f980846de5637f0 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Fri, 25 Nov 2022 08:44:51 -0400
Subject: [PATCH 02/42] Update contracts using the hooks

---
 contracts/token/ERC20/ERC20.sol               |  8 +++++--
 .../token/ERC20/extensions/ERC20Capped.sol    |  6 ++++-
 .../token/ERC20/extensions/ERC20Votes.sol     |  4 ++--
 test/token/ERC20/ERC20.behavior.js            | 23 -------------------
 test/token/ERC20/ERC20.test.js                | 12 ++--------
 .../ERC20/extensions/ERC20FlashMint.test.js   |  2 +-
 6 files changed, 16 insertions(+), 39 deletions(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 94b4011a0d1..69ceb3831c8 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -6,6 +6,7 @@ pragma solidity ^0.8.0;
 import "./IERC20.sol";
 import "./extensions/IERC20Metadata.sol";
 import "../../utils/Context.sol";
+import "hardhat/console.sol";
 
 /**
  * @dev Implementation of the {IERC20} interface.
@@ -225,24 +226,27 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         address to,
         uint256 amount
     ) internal virtual {
-        require(from != address(0) || to != address(0), "ERC721: mint to the zero address");
+        require(from != address(0) || to != address(0), "ERC20: invalid transfer operation");
 
         uint256 fromBalance = _balances[from];
         unchecked {
             if (from == address(0)) {
+                console.log("ERC mint", amount);
                 _balances[to] += amount;
                 _totalSupply += amount;
             } else if (to == address(0)) {
+                console.log("erc burn", amount);
                 require(fromBalance >= amount, "ERC20: burn amount exceeds balance");
                 _balances[from] -= amount;
                 _totalSupply -= amount;
             } else {
+                console.log("erc transfer", amount);
                 require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
                 _balances[from] -= amount;
                 _balances[to] += amount;
             }
         }
-        
+
         emit Transfer(from, to, amount);
     }
 
diff --git a/contracts/token/ERC20/extensions/ERC20Capped.sol b/contracts/token/ERC20/extensions/ERC20Capped.sol
index 24d52166301..559123b15cb 100644
--- a/contracts/token/ERC20/extensions/ERC20Capped.sol
+++ b/contracts/token/ERC20/extensions/ERC20Capped.sol
@@ -30,7 +30,11 @@ abstract contract ERC20Capped is ERC20 {
     /**
      * @dev See {ERC20-_transfer}.
      */
-    function _transfer(address, address account, uint256 amount) internal virtual override {
+    function _transfer(
+        address,
+        address account,
+        uint256 amount
+    ) internal virtual override {
         require(ERC20.totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
         super._transfer(address(0), account, amount);
     }
diff --git a/contracts/token/ERC20/extensions/ERC20Votes.sol b/contracts/token/ERC20/extensions/ERC20Votes.sol
index 8e66c86ecbd..fa791b16c10 100644
--- a/contracts/token/ERC20/extensions/ERC20Votes.sol
+++ b/contracts/token/ERC20/extensions/ERC20Votes.sol
@@ -184,11 +184,11 @@ abstract contract ERC20Votes is IVotes, ERC20Permit {
         uint256 amount
     ) internal virtual override {
         super._transfer(from, to, amount);
-        if(from == address(0)){
+        if (from == address(0)) {
             require(totalSupply() <= _maxSupply(), "ERC20Votes: total supply risks overflowing votes");
             _writeCheckpoint(_totalSupplyCheckpoints, _add, amount);
         }
-        if(to == address(0)){
+        if (to == address(0)) {
             _writeCheckpoint(_totalSupplyCheckpoints, _subtract, amount);
         }
 
diff --git a/test/token/ERC20/ERC20.behavior.js b/test/token/ERC20/ERC20.behavior.js
index 8bc54762ac8..96c30aeda92 100644
--- a/test/token/ERC20/ERC20.behavior.js
+++ b/test/token/ERC20/ERC20.behavior.js
@@ -148,21 +148,6 @@ function shouldBehaveLikeERC20 (errorPrefix, initialSupply, initialHolder, recip
           });
         });
       });
-
-      describe('when the recipient is the zero address', function () {
-        const amount = initialSupply;
-        const to = ZERO_ADDRESS;
-
-        beforeEach(async function () {
-          await this.token.approve(spender, amount, { from: tokenOwner });
-        });
-
-        it('reverts', async function () {
-          await expectRevert(this.token.transferFrom(
-            tokenOwner, to, amount, { from: spender }), `${errorPrefix}: transfer to the zero address`,
-          );
-        });
-      });
     });
 
     describe('when the token owner is the zero address', function () {
@@ -240,14 +225,6 @@ function shouldBehaveLikeERC20Transfer (errorPrefix, from, to, balance, transfer
       });
     });
   });
-
-  describe('when the recipient is the zero address', function () {
-    it('reverts', async function () {
-      await expectRevert(transfer.call(this, from, ZERO_ADDRESS, balance),
-        `${errorPrefix}: transfer to the zero address`,
-      );
-    });
-  });
 }
 
 function shouldBehaveLikeERC20Approve (errorPrefix, owner, spender, supply, approve) {
diff --git a/test/token/ERC20/ERC20.test.js b/test/token/ERC20/ERC20.test.js
index 992edf93b17..54417933844 100644
--- a/test/token/ERC20/ERC20.test.js
+++ b/test/token/ERC20/ERC20.test.js
@@ -203,7 +203,7 @@ contract('ERC20', function (accounts) {
     const amount = new BN(50);
     it('rejects a null account', async function () {
       await expectRevert(
-        this.token.mint(ZERO_ADDRESS, amount), 'ERC20: mint to the zero address',
+        this.token.mint(ZERO_ADDRESS, amount), 'ERC20: invalid transfer operation',
       );
     });
 
@@ -236,7 +236,7 @@ contract('ERC20', function (accounts) {
   describe('_burn', function () {
     it('rejects a null account', async function () {
       await expectRevert(this.token.burn(ZERO_ADDRESS, new BN(1)),
-        'ERC20: burn from the zero address');
+        'ERC20: invalid transfer operation');
     });
 
     describe('for a non zero account', function () {
@@ -283,14 +283,6 @@ contract('ERC20', function (accounts) {
     shouldBehaveLikeERC20Transfer('ERC20', initialHolder, recipient, initialSupply, function (from, to, amount) {
       return this.token.transferInternal(from, to, amount);
     });
-
-    describe('when the sender is the zero address', function () {
-      it('reverts', async function () {
-        await expectRevert(this.token.transferInternal(ZERO_ADDRESS, recipient, initialSupply),
-          'ERC20: transfer from the zero address',
-        );
-      });
-    });
   });
 
   describe('_approve', function () {
diff --git a/test/token/ERC20/extensions/ERC20FlashMint.test.js b/test/token/ERC20/extensions/ERC20FlashMint.test.js
index a375c214c09..4354dd90c2b 100644
--- a/test/token/ERC20/extensions/ERC20FlashMint.test.js
+++ b/test/token/ERC20/extensions/ERC20FlashMint.test.js
@@ -77,7 +77,7 @@ contract('ERC20FlashMint', function (accounts) {
       );
     });
 
-    it.only('unavailable funds', async function () {
+    it('unavailable funds', async function () {
       const receiver = await ERC3156FlashBorrowerMock.new(true, true);
       const data = this.token.contract.methods.transfer(other, 10).encodeABI();
       await expectRevert(

From bdd94d131240abe66c141bdf8abb2d9c46aa0c0a Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Fri, 25 Nov 2022 08:45:25 -0400
Subject: [PATCH 03/42] ERC20Snapshot changes

---
 contracts/mocks/ERC20SnapshotMock.sol              | 2 ++
 contracts/token/ERC20/extensions/ERC20Snapshot.sol | 4 ++++
 test/token/ERC20/extensions/ERC20Snapshot.test.js  | 5 ++++-
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/contracts/mocks/ERC20SnapshotMock.sol b/contracts/mocks/ERC20SnapshotMock.sol
index cb3048322bf..cc150788c07 100644
--- a/contracts/mocks/ERC20SnapshotMock.sol
+++ b/contracts/mocks/ERC20SnapshotMock.sol
@@ -3,6 +3,7 @@
 pragma solidity ^0.8.0;
 
 import "../token/ERC20/extensions/ERC20Snapshot.sol";
+import "hardhat/console.sol";
 
 contract ERC20SnapshotMock is ERC20Snapshot {
     constructor(
@@ -11,6 +12,7 @@ contract ERC20SnapshotMock is ERC20Snapshot {
         address initialAccount,
         uint256 initialBalance
     ) ERC20(name, symbol) {
+        console.log("we'll mint");
         _mint(initialAccount, initialBalance);
     }
 
diff --git a/contracts/token/ERC20/extensions/ERC20Snapshot.sol b/contracts/token/ERC20/extensions/ERC20Snapshot.sol
index 6db172f3c9d..9782a20210b 100644
--- a/contracts/token/ERC20/extensions/ERC20Snapshot.sol
+++ b/contracts/token/ERC20/extensions/ERC20Snapshot.sol
@@ -6,6 +6,7 @@ pragma solidity ^0.8.0;
 import "../ERC20.sol";
 import "../../../utils/Arrays.sol";
 import "../../../utils/Counters.sol";
+import "hardhat/console.sol";
 
 /**
  * @dev This contract extends an ERC20 token with a snapshot mechanism. When a snapshot is created, the balances and
@@ -127,13 +128,16 @@ abstract contract ERC20Snapshot is ERC20 {
     ) internal virtual override {
         if (from == address(0)) {
             // mint
+            console.log("mint", amount);
             _updateTotalSupplySnapshot();
         } else if (to == address(0)) {
             // burn
+            console.log("burn", amount);
             _updateAccountSnapshot(from);
             _updateTotalSupplySnapshot();
         } else {
             // transfer
+            console.log("transfer", amount);
             _updateAccountSnapshot(from);
             _updateAccountSnapshot(to);
         }
diff --git a/test/token/ERC20/extensions/ERC20Snapshot.test.js b/test/token/ERC20/extensions/ERC20Snapshot.test.js
index 64d922706d7..241ffc71b69 100644
--- a/test/token/ERC20/extensions/ERC20Snapshot.test.js
+++ b/test/token/ERC20/extensions/ERC20Snapshot.test.js
@@ -129,10 +129,13 @@ contract('ERC20Snapshot', function (accounts) {
         });
       });
 
-      context('with balance changes after the snapshot', function () {
+      context.only('with balance changes after the snapshot', function () {
         beforeEach(async function () {
+          console.log('transfer 10');
           await this.token.transfer(recipient, new BN('10'), { from: initialHolder });
+          console.log('mint 50');
           await this.token.mint(other, new BN('50'));
+          console.log('burn 20');
           await this.token.burn(initialHolder, new BN('20'));
         });
 

From e03c773376a90f5a0a965e9b9a4ad1f6de0b54ca Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 28 Nov 2022 10:37:25 -0400
Subject: [PATCH 04/42] Update ERC20Snapshot mock

---
 contracts/mocks/ERC20SnapshotMock.sol              | 6 ++----
 contracts/token/ERC20/ERC20.sol                    | 4 ----
 contracts/token/ERC20/extensions/ERC20Snapshot.sol | 5 +----
 test/token/ERC20/extensions/ERC20Snapshot.test.js  | 5 +----
 4 files changed, 4 insertions(+), 16 deletions(-)

diff --git a/contracts/mocks/ERC20SnapshotMock.sol b/contracts/mocks/ERC20SnapshotMock.sol
index cc150788c07..c319af872ad 100644
--- a/contracts/mocks/ERC20SnapshotMock.sol
+++ b/contracts/mocks/ERC20SnapshotMock.sol
@@ -3,7 +3,6 @@
 pragma solidity ^0.8.0;
 
 import "../token/ERC20/extensions/ERC20Snapshot.sol";
-import "hardhat/console.sol";
 
 contract ERC20SnapshotMock is ERC20Snapshot {
     constructor(
@@ -12,7 +11,6 @@ contract ERC20SnapshotMock is ERC20Snapshot {
         address initialAccount,
         uint256 initialBalance
     ) ERC20(name, symbol) {
-        console.log("we'll mint");
         _mint(initialAccount, initialBalance);
     }
 
@@ -21,10 +19,10 @@ contract ERC20SnapshotMock is ERC20Snapshot {
     }
 
     function mint(address account, uint256 amount) public {
-        _mint(account, amount);
+        _transfer(address(0), account, amount);
     }
 
     function burn(address account, uint256 amount) public {
-        _burn(account, amount);
+        _transfer(account, address(0), amount);
     }
 }
diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 69ceb3831c8..13fca961784 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -6,7 +6,6 @@ pragma solidity ^0.8.0;
 import "./IERC20.sol";
 import "./extensions/IERC20Metadata.sol";
 import "../../utils/Context.sol";
-import "hardhat/console.sol";
 
 /**
  * @dev Implementation of the {IERC20} interface.
@@ -231,16 +230,13 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         uint256 fromBalance = _balances[from];
         unchecked {
             if (from == address(0)) {
-                console.log("ERC mint", amount);
                 _balances[to] += amount;
                 _totalSupply += amount;
             } else if (to == address(0)) {
-                console.log("erc burn", amount);
                 require(fromBalance >= amount, "ERC20: burn amount exceeds balance");
                 _balances[from] -= amount;
                 _totalSupply -= amount;
             } else {
-                console.log("erc transfer", amount);
                 require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
                 _balances[from] -= amount;
                 _balances[to] += amount;
diff --git a/contracts/token/ERC20/extensions/ERC20Snapshot.sol b/contracts/token/ERC20/extensions/ERC20Snapshot.sol
index 9782a20210b..fcb65d09f53 100644
--- a/contracts/token/ERC20/extensions/ERC20Snapshot.sol
+++ b/contracts/token/ERC20/extensions/ERC20Snapshot.sol
@@ -6,7 +6,6 @@ pragma solidity ^0.8.0;
 import "../ERC20.sol";
 import "../../../utils/Arrays.sol";
 import "../../../utils/Counters.sol";
-import "hardhat/console.sol";
 
 /**
  * @dev This contract extends an ERC20 token with a snapshot mechanism. When a snapshot is created, the balances and
@@ -128,16 +127,14 @@ abstract contract ERC20Snapshot is ERC20 {
     ) internal virtual override {
         if (from == address(0)) {
             // mint
-            console.log("mint", amount);
+            _updateAccountSnapshot(to);
             _updateTotalSupplySnapshot();
         } else if (to == address(0)) {
             // burn
-            console.log("burn", amount);
             _updateAccountSnapshot(from);
             _updateTotalSupplySnapshot();
         } else {
             // transfer
-            console.log("transfer", amount);
             _updateAccountSnapshot(from);
             _updateAccountSnapshot(to);
         }
diff --git a/test/token/ERC20/extensions/ERC20Snapshot.test.js b/test/token/ERC20/extensions/ERC20Snapshot.test.js
index 241ffc71b69..64d922706d7 100644
--- a/test/token/ERC20/extensions/ERC20Snapshot.test.js
+++ b/test/token/ERC20/extensions/ERC20Snapshot.test.js
@@ -129,13 +129,10 @@ contract('ERC20Snapshot', function (accounts) {
         });
       });
 
-      context.only('with balance changes after the snapshot', function () {
+      context('with balance changes after the snapshot', function () {
         beforeEach(async function () {
-          console.log('transfer 10');
           await this.token.transfer(recipient, new BN('10'), { from: initialHolder });
-          console.log('mint 50');
           await this.token.mint(other, new BN('50'));
-          console.log('burn 20');
           await this.token.burn(initialHolder, new BN('20'));
         });
 

From 616c148fa1ae7483675338495986d3f3ee752729 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 28 Nov 2022 11:00:32 -0400
Subject: [PATCH 05/42] Update changelog

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index dafdf499018..f121e3ab8aa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## Unreleased (Breaking)
 
  * `TimelockController`: Changed the role architecture to use `DEFAULT_ADMIN_ROLE` as the admin for all roles, instead of the bespoke `TIMELOCK_ADMIN_ROLE` that was used previously. This aligns with the general recommendation for `AccessControl` and makes the addition of new roles easier. Accordingly, the `admin` parameter and timelock will now be granted `DEFAULT_ADMIN_ROLE` instead of `TIMELOCK_ADMIN_ROLE`. ([#3799](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3799))
+ * `ERC20`: Deleted `_beforeTokenTransfer` and `_afterTokenTransfer` hooks, and refactor all extensions using those hooks for customization, by using `transfer` instead. ([#3838](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3838))
 
 ## Unreleased
 

From a81f1a5b01569c1729ac0d581e4010d39faeceec Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 28 Nov 2022 12:45:45 -0400
Subject: [PATCH 06/42] update documentation

---
 contracts/token/ERC20/ERC20.sol | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 0be9d897742..07be9cb37e8 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -245,12 +245,12 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         emit Transfer(from, to, amount);
     }
 
-    /** @dev Creates `amount` tokens and assigns them to `account`, by transfering it from address(0).
+    /** @dev Creates `amount` tokens and assigns them to `account`, by transferring it from address(0).
      * Relies on the `_transfer` mechanism
      *
      * Emits a {Transfer} event with `from` set to the zero address.
      *
-     * Note: this function is not virtual, {_transfer} should be overriden instead.
+     * Note: this function is not virtual, {_transfer} should be overridden instead.
      *
      */
     function _mint(address account, uint256 amount) internal {
@@ -258,10 +258,10 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
     }
 
     /**
-     * @dev Destroys `amount` tokens from `account`, by transfering it to address(0).
+     * @dev Destroys `amount` tokens from `account`, by transferring it to address(0).
      * Relies on the `_transfer` mechanism.
      *
-     * Note: this function is not virtual, {_transfer} should be overriden instead
+     * Note: this function is not virtual, {_transfer} should be overridden instead
      *
      * Emits a {Transfer} event with `to` set to the zero address.
      *

From 4f3adcbb35cf83505eb6c160c14a9d9f46a5c1c3 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Tue, 29 Nov 2022 16:07:11 -0400
Subject: [PATCH 07/42] update documentation

---
 .../token/ERC20/extensions/ERC20Pausable.sol  |  2 +-
 .../ERC20/presets/ERC20PresetMinterPauser.sol | 94 -------------------
 2 files changed, 1 insertion(+), 95 deletions(-)
 delete mode 100644 contracts/token/ERC20/presets/ERC20PresetMinterPauser.sol

diff --git a/contracts/token/ERC20/extensions/ERC20Pausable.sol b/contracts/token/ERC20/extensions/ERC20Pausable.sol
index e314cba5b1c..97410fb9320 100644
--- a/contracts/token/ERC20/extensions/ERC20Pausable.sol
+++ b/contracts/token/ERC20/extensions/ERC20Pausable.sol
@@ -15,7 +15,7 @@ import "../../../security/Pausable.sol";
  */
 abstract contract ERC20Pausable is ERC20, Pausable {
     /**
-     * @dev See {ERC20-_beforeTokenTransfer}.
+     * @dev See {ERC20-_transfer}.
      *
      * Requirements:
      *
diff --git a/contracts/token/ERC20/presets/ERC20PresetMinterPauser.sol b/contracts/token/ERC20/presets/ERC20PresetMinterPauser.sol
deleted file mode 100644
index 8ab23590e90..00000000000
--- a/contracts/token/ERC20/presets/ERC20PresetMinterPauser.sol
+++ /dev/null
@@ -1,94 +0,0 @@
-// SPDX-License-Identifier: MIT
-// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC20/presets/ERC20PresetMinterPauser.sol)
-
-pragma solidity ^0.8.0;
-
-import "../ERC20.sol";
-import "../extensions/ERC20Burnable.sol";
-import "../extensions/ERC20Pausable.sol";
-import "../../../access/AccessControlEnumerable.sol";
-import "../../../utils/Context.sol";
-
-/**
- * @dev {ERC20} token, including:
- *
- *  - ability for holders to burn (destroy) their tokens
- *  - a minter role that allows for token minting (creation)
- *  - a pauser role that allows to stop all token transfers
- *
- * This contract uses {AccessControl} to lock permissioned functions using the
- * different roles - head to its documentation for details.
- *
- * The account that deploys the contract will be granted the minter and pauser
- * roles, as well as the default admin role, which will let it grant both minter
- * and pauser roles to other accounts.
- *
- * _Deprecated in favor of https://wizard.openzeppelin.com/[Contracts Wizard]._
- */
-contract ERC20PresetMinterPauser is Context, AccessControlEnumerable, ERC20Burnable, ERC20Pausable {
-    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
-    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");
-
-    /**
-     * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE` and `PAUSER_ROLE` to the
-     * account that deploys the contract.
-     *
-     * See {ERC20-constructor}.
-     */
-    constructor(string memory name, string memory symbol) ERC20(name, symbol) {
-        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
-
-        _setupRole(MINTER_ROLE, _msgSender());
-        _setupRole(PAUSER_ROLE, _msgSender());
-    }
-
-    /**
-     * @dev Creates `amount` new tokens for `to`.
-     *
-     * See {ERC20-_mint}.
-     *
-     * Requirements:
-     *
-     * - the caller must have the `MINTER_ROLE`.
-     */
-    function mint(address to, uint256 amount) public virtual {
-        require(hasRole(MINTER_ROLE, _msgSender()), "ERC20PresetMinterPauser: must have minter role to mint");
-        _mint(to, amount);
-    }
-
-    /**
-     * @dev Pauses all token transfers.
-     *
-     * See {ERC20Pausable} and {Pausable-_pause}.
-     *
-     * Requirements:
-     *
-     * - the caller must have the `PAUSER_ROLE`.
-     */
-    function pause() public virtual {
-        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC20PresetMinterPauser: must have pauser role to pause");
-        _pause();
-    }
-
-    /**
-     * @dev Unpauses all token transfers.
-     *
-     * See {ERC20Pausable} and {Pausable-_unpause}.
-     *
-     * Requirements:
-     *
-     * - the caller must have the `PAUSER_ROLE`.
-     */
-    function unpause() public virtual {
-        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC20PresetMinterPauser: must have pauser role to unpause");
-        _unpause();
-    }
-
-    function _transfer(
-        address from,
-        address to,
-        uint256 amount
-    ) internal virtual override(ERC20, ERC20Pausable) {
-        super._transfer(from, to, amount);
-    }
-}

From 054777ec69c5a56eef1c5ef8875f884e381e7614 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Tue, 29 Nov 2022 16:20:42 -0400
Subject: [PATCH 08/42] Post merge fix

---
 contracts/token/ERC20/extensions/ERC20Votes.sol | 17 ++---------------
 test/token/ERC20/extensions/ERC20Votes.test.js  |  2 +-
 2 files changed, 3 insertions(+), 16 deletions(-)

diff --git a/contracts/token/ERC20/extensions/ERC20Votes.sol b/contracts/token/ERC20/extensions/ERC20Votes.sol
index 989a5cdfa0e..b47f366ada7 100644
--- a/contracts/token/ERC20/extensions/ERC20Votes.sol
+++ b/contracts/token/ERC20/extensions/ERC20Votes.sol
@@ -41,15 +41,10 @@ abstract contract ERC20Votes is ERC20, Votes {
         uint256 amount
     ) internal virtual override {
         super._transfer(from, to, amount);
-        if (from == address(0)) {
+        if(from == address(0)) {
             require(totalSupply() <= _maxSupply(), "ERC20Votes: total supply risks overflowing votes");
-            _writeCheckpoint(_totalSupplyCheckpoints, _add, amount);
         }
-        if (to == address(0)) {
-            _writeCheckpoint(_totalSupplyCheckpoints, _subtract, amount);
-        }
-
-        _moveVotingPower(delegates(from), delegates(to), amount);
+        _transferVotingUnits(from, to, amount);
     }
 
     /**
@@ -72,12 +67,4 @@ abstract contract ERC20Votes is ERC20, Votes {
     function _getVotingUnits(address account) internal view virtual override returns (uint256) {
         return balanceOf(account);
     }
-
-    /**
-     * @dev Snapshots the totalSupply after it has been increased.
-     */
-    function _mint(address account, uint256 amount) internal virtual override {
-        super._mint(account, amount);
-        require(totalSupply() <= _maxSupply(), "ERC20Votes: total supply risks overflowing votes");
-    }
 }
diff --git a/test/token/ERC20/extensions/ERC20Votes.test.js b/test/token/ERC20/extensions/ERC20Votes.test.js
index 0d3ab74aadc..d89a7b9fb54 100644
--- a/test/token/ERC20/extensions/ERC20Votes.test.js
+++ b/test/token/ERC20/extensions/ERC20Votes.test.js
@@ -53,7 +53,7 @@ contract('ERC20Votes', function (accounts) {
     const amount = new BN('2').pow(new BN('224'));
     await expectRevert(
       this.token.mint(holder, amount),
-      "SafeCast: value doesn't fit in 224 bits",
+      "ERC20Votes: total supply risks overflowing votes",
     );
   });
 

From b3da557582c9d08db662f6d3c57c2898a7086216 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Tue, 29 Nov 2022 16:23:07 -0400
Subject: [PATCH 09/42] Update ERC20Votes

---
 contracts/token/ERC20/extensions/ERC20Votes.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contracts/token/ERC20/extensions/ERC20Votes.sol b/contracts/token/ERC20/extensions/ERC20Votes.sol
index b47f366ada7..0a7bb70385b 100644
--- a/contracts/token/ERC20/extensions/ERC20Votes.sol
+++ b/contracts/token/ERC20/extensions/ERC20Votes.sol
@@ -41,7 +41,7 @@ abstract contract ERC20Votes is ERC20, Votes {
         uint256 amount
     ) internal virtual override {
         super._transfer(from, to, amount);
-        if(from == address(0)) {
+        if (from == address(0)) {
             require(totalSupply() <= _maxSupply(), "ERC20Votes: total supply risks overflowing votes");
         }
         _transferVotingUnits(from, to, amount);

From 27c7090480c2dc26f361def7b4a62960a591f55b Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 30 Nov 2022 14:31:05 -0400
Subject: [PATCH 10/42] add overflow test

---
 contracts/token/ERC20/ERC20.sol | 23 +++++++++++++----------
 test/token/ERC20/ERC20.test.js  |  7 +++++++
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 07be9cb37e8..5e90d63d9d9 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -227,19 +227,22 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         require(from != address(0) || to != address(0), "ERC20: invalid transfer operation");
 
         uint256 fromBalance = _balances[from];
-        unchecked {
-            if (from == address(0)) {
+        if (from == address(0)) {
+            _totalSupply += amount;
+            unchecked {
+                // Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
                 _balances[to] += amount;
-                _totalSupply += amount;
-            } else if (to == address(0)) {
-                require(fromBalance >= amount, "ERC20: burn amount exceeds balance");
-                _balances[from] -= amount;
-                _totalSupply -= amount;
-            } else {
-                require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
+            }
+        } else if (to == address(0)) {
+            require(fromBalance >= amount, "ERC20: burn amount exceeds balance");
+            _totalSupply -= amount;
+            unchecked {
                 _balances[from] -= amount;
-                _balances[to] += amount;
             }
+        } else {
+            require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
+            _balances[from] -= amount;
+            _balances[to] += amount;
         }
 
         emit Transfer(from, to, amount);
diff --git a/test/token/ERC20/ERC20.test.js b/test/token/ERC20/ERC20.test.js
index 54417933844..42b24cc4abb 100644
--- a/test/token/ERC20/ERC20.test.js
+++ b/test/token/ERC20/ERC20.test.js
@@ -207,6 +207,13 @@ contract('ERC20', function (accounts) {
       );
     });
 
+    it('rejects overflow', async function () {
+      const maxUint256 = new BN('2').pow(new BN(256)).subn(1);
+      await expectRevert.unspecified(
+        this.token.mint(recipient, maxUint256),
+      );
+    });
+
     describe('for a non zero account', function () {
       beforeEach('minting', async function () {
         this.receipt = await this.token.mint(recipient, amount);

From b4ab7c7a442047704fcefe6328e558a5987c2d36 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Fri, 2 Dec 2022 11:10:59 -0400
Subject: [PATCH 11/42] Update contracts/token/ERC20/ERC20.sol

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 contracts/token/ERC20/ERC20.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 5e90d63d9d9..4caf1c81214 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -214,7 +214,7 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      * This internal function is equivalent to {transfer}, and can be used to
      * e.g. implement automatic token fees, slashing mechanisms, etc.
      *
-     * Will mint (or burn) if `from` (or `to`) is address(0).
+     * Will mint (or burn) if `from` (or `to`) is the zero address.
      *
      * Emits a {Transfer} event.
      *

From dcbc27514478324316dd82008e7964a9615797f9 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Fri, 2 Dec 2022 11:11:09 -0400
Subject: [PATCH 12/42] Update contracts/token/ERC20/ERC20.sol

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 contracts/token/ERC20/ERC20.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 4caf1c81214..73fe624f397 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -224,7 +224,7 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         address to,
         uint256 amount
     ) internal virtual {
-        require(from != address(0) || to != address(0), "ERC20: invalid transfer operation");
+        require(!(from == address(0) && to == address(0)), "ERC20: invalid transfer operation");
 
         uint256 fromBalance = _balances[from];
         if (from == address(0)) {

From c3350bd34eef8b058fc36c8584f3fa3efa9039c3 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 5 Dec 2022 08:43:59 -0400
Subject: [PATCH 13/42] Update ERC20

---
 contracts/mocks/ERC20SnapshotMock.sol | 4 ++--
 contracts/token/ERC20/ERC20.sol       | 5 +++--
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/contracts/mocks/ERC20SnapshotMock.sol b/contracts/mocks/ERC20SnapshotMock.sol
index c319af872ad..cb3048322bf 100644
--- a/contracts/mocks/ERC20SnapshotMock.sol
+++ b/contracts/mocks/ERC20SnapshotMock.sol
@@ -19,10 +19,10 @@ contract ERC20SnapshotMock is ERC20Snapshot {
     }
 
     function mint(address account, uint256 amount) public {
-        _transfer(address(0), account, amount);
+        _mint(account, amount);
     }
 
     function burn(address account, uint256 amount) public {
-        _transfer(account, address(0), amount);
+        _burn(account, amount);
     }
 }
diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 5e90d63d9d9..c148648076d 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -237,11 +237,12 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
             require(fromBalance >= amount, "ERC20: burn amount exceeds balance");
             _totalSupply -= amount;
             unchecked {
-                _balances[from] -= amount;
+                // Overflow not possible: balance - amount is at most totalSupply - amount, which is checked above.
+                _balances[from] = fromBalance - amount;
             }
         } else {
             require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
-            _balances[from] -= amount;
+            _balances[from] = fromBalance - amount;
             _balances[to] += amount;
         }
 

From a56afc463af5130e1cf9ace96e22d49b8e8e703a Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 5 Dec 2022 08:50:40 -0400
Subject: [PATCH 14/42] update ERC20Capped

---
 contracts/token/ERC20/extensions/ERC20Capped.sol | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/contracts/token/ERC20/extensions/ERC20Capped.sol b/contracts/token/ERC20/extensions/ERC20Capped.sol
index 559123b15cb..63b7f630819 100644
--- a/contracts/token/ERC20/extensions/ERC20Capped.sol
+++ b/contracts/token/ERC20/extensions/ERC20Capped.sol
@@ -31,11 +31,14 @@ abstract contract ERC20Capped is ERC20 {
      * @dev See {ERC20-_transfer}.
      */
     function _transfer(
-        address,
-        address account,
+        address from,
+        address to,
         uint256 amount
     ) internal virtual override {
-        require(ERC20.totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
-        super._transfer(address(0), account, amount);
+        if(from == address(0)){
+            require(ERC20.totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
+        }
+        
+        super._transfer(from, to, amount);
     }
 }

From 3ec8abfc8862c96c8b99ba38036c097b06084139 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 5 Dec 2022 08:51:06 -0400
Subject: [PATCH 15/42] Add format

---
 contracts/token/ERC20/extensions/ERC20Capped.sol | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/contracts/token/ERC20/extensions/ERC20Capped.sol b/contracts/token/ERC20/extensions/ERC20Capped.sol
index 63b7f630819..8acc7248c2c 100644
--- a/contracts/token/ERC20/extensions/ERC20Capped.sol
+++ b/contracts/token/ERC20/extensions/ERC20Capped.sol
@@ -35,10 +35,10 @@ abstract contract ERC20Capped is ERC20 {
         address to,
         uint256 amount
     ) internal virtual override {
-        if(from == address(0)){
+        if (from == address(0)) {
             require(ERC20.totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
         }
-        
+
         super._transfer(from, to, amount);
     }
 }

From 4213df3d41ee753d07da8b570d68ba3cc24894a1 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 5 Dec 2022 10:09:10 -0400
Subject: [PATCH 16/42] update revert reason

---
 test/token/ERC20/ERC20.test.js | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/test/token/ERC20/ERC20.test.js b/test/token/ERC20/ERC20.test.js
index 42b24cc4abb..dcb1363987d 100644
--- a/test/token/ERC20/ERC20.test.js
+++ b/test/token/ERC20/ERC20.test.js
@@ -203,14 +203,14 @@ contract('ERC20', function (accounts) {
     const amount = new BN(50);
     it('rejects a null account', async function () {
       await expectRevert(
-        this.token.mint(ZERO_ADDRESS, amount), 'ERC20: invalid transfer operation',
+        this.token.mint(ZERO_ADDRESS, amount), 'ERC20: invalid transfer operation'
       );
     });
 
     it('rejects overflow', async function () {
       const maxUint256 = new BN('2').pow(new BN(256)).subn(1);
-      await expectRevert.unspecified(
-        this.token.mint(recipient, maxUint256),
+      await expectRevert(
+        this.token.mint(recipient, maxUint256),'reverted with panic code 0x11 (Arithmetic operation underflowed or overflowed outside of an unchecked block)'
       );
     });
 

From 0fc5d3a0e8bd687faba7a7453ec26b9d6375f126 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 5 Dec 2022 11:39:50 -0400
Subject: [PATCH 17/42] run lint

---
 test/token/ERC20/ERC20.test.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/test/token/ERC20/ERC20.test.js b/test/token/ERC20/ERC20.test.js
index dcb1363987d..e8fa042dd1e 100644
--- a/test/token/ERC20/ERC20.test.js
+++ b/test/token/ERC20/ERC20.test.js
@@ -203,14 +203,15 @@ contract('ERC20', function (accounts) {
     const amount = new BN(50);
     it('rejects a null account', async function () {
       await expectRevert(
-        this.token.mint(ZERO_ADDRESS, amount), 'ERC20: invalid transfer operation'
+        this.token.mint(ZERO_ADDRESS, amount), 'ERC20: invalid transfer operation',
       );
     });
 
     it('rejects overflow', async function () {
       const maxUint256 = new BN('2').pow(new BN(256)).subn(1);
       await expectRevert(
-        this.token.mint(recipient, maxUint256),'reverted with panic code 0x11 (Arithmetic operation underflowed or overflowed outside of an unchecked block)'
+        this.token.mint(recipient, maxUint256),
+        'reverted with panic code 0x11 (Arithmetic operation underflowed or overflowed outside of an unchecked block)',
       );
     });
 

From 975ed992aa93bedfd60c9564b998f1341f28e4cb Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 5 Dec 2022 13:40:25 -0400
Subject: [PATCH 18/42] add checks for external transfer calls

---
 contracts/token/ERC20/ERC20.sol    |  3 +++
 test/token/ERC20/ERC20.behavior.js | 19 +++++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 60a57d7db56..8586d9984d2 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -110,6 +110,7 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      * - the caller must have a balance of at least `amount`.
      */
     function transfer(address to, uint256 amount) public virtual override returns (bool) {
+        require(to != address(0), "ERC20: transfer to the zero address");
         address owner = _msgSender();
         _transfer(owner, to, amount);
         return true;
@@ -159,6 +160,8 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         address to,
         uint256 amount
     ) public virtual override returns (bool) {
+        require(from != address(0), "ERC20: transfer from the zero address");
+        require(to != address(0), "ERC20: transfer to the zero address");
         address spender = _msgSender();
         _spendAllowance(from, spender, amount);
         _transfer(from, to, amount);
diff --git a/test/token/ERC20/ERC20.behavior.js b/test/token/ERC20/ERC20.behavior.js
index 96c30aeda92..a1884a72ddf 100644
--- a/test/token/ERC20/ERC20.behavior.js
+++ b/test/token/ERC20/ERC20.behavior.js
@@ -148,6 +148,21 @@ function shouldBehaveLikeERC20 (errorPrefix, initialSupply, initialHolder, recip
           });
         });
       });
+
+      describe('when the recipient is the zero address', function () {
+        const amount = initialSupply;
+        const to = ZERO_ADDRESS;
+  
+        beforeEach(async function () {
+          await this.token.approve(spender, amount, { from: tokenOwner });
+        });
+  
+        it('reverts', async function () {
+          await expectRevert(this.token.transferFrom(
+            tokenOwner, to, amount, { from: spender }), `${errorPrefix}: transfer to the zero address`,
+          );
+        });
+      });
     });
 
     describe('when the token owner is the zero address', function () {
@@ -223,8 +238,8 @@ function shouldBehaveLikeERC20Transfer (errorPrefix, from, to, balance, transfer
           { from, to, value: amount },
         );
       });
-    });
-  });
+    }); 
+  }); 
 }
 
 function shouldBehaveLikeERC20Approve (errorPrefix, owner, spender, supply, approve) {

From 00ed155e3f75587235c1404e50b88a0f9a23ddc6 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 5 Dec 2022 13:52:22 -0400
Subject: [PATCH 19/42] update ERC20Test

---
 test/token/ERC20/ERC20.behavior.js | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/test/token/ERC20/ERC20.behavior.js b/test/token/ERC20/ERC20.behavior.js
index a1884a72ddf..0404a2941bf 100644
--- a/test/token/ERC20/ERC20.behavior.js
+++ b/test/token/ERC20/ERC20.behavior.js
@@ -152,11 +152,11 @@ function shouldBehaveLikeERC20 (errorPrefix, initialSupply, initialHolder, recip
       describe('when the recipient is the zero address', function () {
         const amount = initialSupply;
         const to = ZERO_ADDRESS;
-  
+
         beforeEach(async function () {
           await this.token.approve(spender, amount, { from: tokenOwner });
         });
-  
+
         it('reverts', async function () {
           await expectRevert(this.token.transferFrom(
             tokenOwner, to, amount, { from: spender }), `${errorPrefix}: transfer to the zero address`,
@@ -238,8 +238,8 @@ function shouldBehaveLikeERC20Transfer (errorPrefix, from, to, balance, transfer
           { from, to, value: amount },
         );
       });
-    }); 
-  }); 
+    });
+  });
 }
 
 function shouldBehaveLikeERC20Approve (errorPrefix, owner, spender, supply, approve) {

From 0d74d6622ee08114d181176571aba27cb073986c Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 5 Dec 2022 17:49:33 -0400
Subject: [PATCH 20/42] Update changelog

---
 CHANGELOG.md | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 79005af6bf2..645c6a7e375 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,31 @@
  * `ProxyAdmin`: Removed `getProxyAdmin` and `getProxyImplementation` getters. ([#3820](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3820))
  * `ERC20`: Deleted `_beforeTokenTransfer` and `_afterTokenTransfer` hooks, and refactor all extensions using those hooks for customization, by using `transfer` instead. ([#3838](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3838))
 
+### How to upgrade from 4.x
+These breaking changes will require additional modifications in your implementation of ERC20, ERC721, and ERC1155, since the `afterTokenTransfer` and `beforeTokenTransfer` were removed. Any customization made through those hooks should now use the `transfer` function instead, keeping in mind that `_mint` and `_burn` are no longer virtual, so they are not overrideable.
+
+For example, a contract using `ERC20`'s `afterTokenTransfer` hook would have to be changed in the following way.
+
+```diff
+-function _beforeTokenTransfer(
+-         address from,
+-         address to,
+-         uint256 amount
+-     ) internal virtual override {
+-         super._beforeTokenTransfer(from, to, amount);
+-
+-         require(!condition(), "ERC20: wrong condition");
+-     }
++function _transfer(
++         address from,
++         address to,
++         uint256 amount
++     ) internal virtual override {
++         require(!condition(), "ERC20: wrong condition");
++         super._transfer(from, to, amount);
++     }
+```
+
 ## Unreleased
 
  * `ReentrancyGuard`: Add a `_reentrancyGuardEntered` function to expose the guard status. ([#3714](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3714))

From 7110896b5a7a45f43c4a6d64ac3c0296a69cf6d2 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 5 Dec 2022 17:52:18 -0400
Subject: [PATCH 21/42] Update CHANGELOG

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 645c6a7e375..039b0ed2b51 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,7 +11,7 @@
  * `ERC20`: Deleted `_beforeTokenTransfer` and `_afterTokenTransfer` hooks, and refactor all extensions using those hooks for customization, by using `transfer` instead. ([#3838](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3838))
 
 ### How to upgrade from 4.x
-These breaking changes will require additional modifications in your implementation of ERC20, ERC721, and ERC1155, since the `afterTokenTransfer` and `beforeTokenTransfer` were removed. Any customization made through those hooks should now use the `transfer` function instead, keeping in mind that `_mint` and `_burn` are no longer virtual, so they are not overrideable.
+These breaking changes will require additional modifications in your implementation of ERC20, ERC721, and ERC1155, since the `afterTokenTransfer` and `beforeTokenTransfer` were removed. Any customization made through those hooks should now use the `transfer` function instead, keeping in mind that `_mint` and `_burn` are no longer virtual, so they are not overridable.
 
 For example, a contract using `ERC20`'s `afterTokenTransfer` hook would have to be changed in the following way.
 

From 4e09ef84170e5ce83085efa5c078e85b9adc0632 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Fri, 9 Dec 2022 10:13:49 -0400
Subject: [PATCH 22/42] Update CHANGELOG.md

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 CHANGELOG.md | 27 ++++++++++-----------------
 1 file changed, 10 insertions(+), 17 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 039b0ed2b51..c92c0d90469 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,23 +16,16 @@ These breaking changes will require additional modifications in your implementat
 For example, a contract using `ERC20`'s `afterTokenTransfer` hook would have to be changed in the following way.
 
 ```diff
--function _beforeTokenTransfer(
--         address from,
--         address to,
--         uint256 amount
--     ) internal virtual override {
--         super._beforeTokenTransfer(from, to, amount);
--
--         require(!condition(), "ERC20: wrong condition");
--     }
-+function _transfer(
-+         address from,
-+         address to,
-+         uint256 amount
-+     ) internal virtual override {
-+         require(!condition(), "ERC20: wrong condition");
-+         super._transfer(from, to, amount);
-+     }
+- function _beforeTokenTransfer(
++ function _transfer(
+      address from,
+      address to,
+      uint256 amount
+  ) internal virtual override {
+-     super._beforeTokenTransfer(from, to, amount);
+      require(!condition(), "ERC20: wrong condition");
++     super._transfer(from, to, amount);
+  }
 ```
 
 ## Unreleased

From ed853fae9494731bca535f1911c93ac2782f94ad Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Fri, 9 Dec 2022 10:14:03 -0400
Subject: [PATCH 23/42] Update CHANGELOG.md

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c92c0d90469..cb851e2074f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,7 +13,7 @@
 ### How to upgrade from 4.x
 These breaking changes will require additional modifications in your implementation of ERC20, ERC721, and ERC1155, since the `afterTokenTransfer` and `beforeTokenTransfer` were removed. Any customization made through those hooks should now use the `transfer` function instead, keeping in mind that `_mint` and `_burn` are no longer virtual, so they are not overridable.
 
-For example, a contract using `ERC20`'s `afterTokenTransfer` hook would have to be changed in the following way.
+For example, a contract using `ERC20`'s `_afterTokenTransfer` hook would have to be changed in the following way.
 
 ```diff
 - function _beforeTokenTransfer(

From a2bc30c23158d8a35846bf3d518c527e7cf0cce9 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Fri, 9 Dec 2022 10:14:45 -0400
Subject: [PATCH 24/42] Update CHANGELOG.md

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 CHANGELOG.md | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index cb851e2074f..776262b16d9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,7 +11,12 @@
  * `ERC20`: Deleted `_beforeTokenTransfer` and `_afterTokenTransfer` hooks, and refactor all extensions using those hooks for customization, by using `transfer` instead. ([#3838](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3838))
 
 ### How to upgrade from 4.x
-These breaking changes will require additional modifications in your implementation of ERC20, ERC721, and ERC1155, since the `afterTokenTransfer` and `beforeTokenTransfer` were removed. Any customization made through those hooks should now use the `transfer` function instead, keeping in mind that `_mint` and `_burn` are no longer virtual, so they are not overridable.
+
+#### ERC20, ERC721, and ERC1155
+
+These breaking changes will require modifications to ERC20, ERC721, and ERC1155 contracts, since the `_afterTokenTransfer` and `_beforeTokenTransfer` functions were removed. Any customization made through those hooks should now be done overriding the `_transfer` function instead.
+
+Minting and burning are implemented by `_transfer` and customizations should be done by overriding this function as well. `_mint` and `_burn` are no longer virtual (meaning they are not overridable) to guard against possible inconsistencies.
 
 For example, a contract using `ERC20`'s `_afterTokenTransfer` hook would have to be changed in the following way.
 

From ed66c580397a2f87ee778bde58db918c42661f82 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 12 Dec 2022 13:43:17 -0400
Subject: [PATCH 25/42] update test

---
 test/token/ERC20/ERC20.behavior.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/test/token/ERC20/ERC20.behavior.js b/test/token/ERC20/ERC20.behavior.js
index 0404a2941bf..701ec2e6d5e 100644
--- a/test/token/ERC20/ERC20.behavior.js
+++ b/test/token/ERC20/ERC20.behavior.js
@@ -158,8 +158,9 @@ function shouldBehaveLikeERC20 (errorPrefix, initialSupply, initialHolder, recip
         });
 
         it('reverts', async function () {
-          await expectRevert(this.token.transferFrom(
-            tokenOwner, to, amount, { from: spender }), `${errorPrefix}: transfer to the zero address`,
+          await expectRevert(
+            this.token.transferFrom(tokenOwner, to, amount, { from: spender }),
+            `${errorPrefix}: transfer to the zero address`,
           );
         });
       });

From 5e671709f0c0d99083908aa52967e2d2a6d44fa9 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 12 Dec 2022 13:48:52 -0400
Subject: [PATCH 26/42] update ERC20

---
 contracts/token/ERC20/ERC20.sol | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 8586d9984d2..dd33cb85c29 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -245,8 +245,11 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
             }
         } else {
             require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
-            _balances[from] = fromBalance - amount;
-            _balances[to] += amount;
+            unchecked {
+                // Overflow not possible: fromBalance - amount is at most 0, which is checked above.
+                _balances[from] = fromBalance - amount;
+                _balances[to] += amount;
+            }
         }
 
         emit Transfer(from, to, amount);

From fe5abf40e76e3a96e27cc2bbc03a370d48855194 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Mon, 12 Dec 2022 16:19:06 -0400
Subject: [PATCH 27/42] Handle zero address parameters

---
 contracts/mocks/ERC20VotesMock.sol            |  4 ++--
 contracts/token/ERC20/ERC20.sol               | 24 ++++++++++++++++---
 .../token/ERC20/extensions/ERC20Capped.sol    |  4 ++--
 .../token/ERC20/extensions/ERC20Pausable.sol  |  6 ++---
 .../token/ERC20/extensions/ERC20Snapshot.sol  |  4 ++--
 .../token/ERC20/extensions/ERC20Votes.sol     |  4 ++--
 test/token/ERC20/ERC20.test.js                |  4 ++--
 7 files changed, 34 insertions(+), 16 deletions(-)

diff --git a/contracts/mocks/ERC20VotesMock.sol b/contracts/mocks/ERC20VotesMock.sol
index d60e13be842..c52c5b073a7 100644
--- a/contracts/mocks/ERC20VotesMock.sol
+++ b/contracts/mocks/ERC20VotesMock.sol
@@ -8,11 +8,11 @@ contract ERC20VotesMock is ERC20Votes {
     constructor(string memory name, string memory symbol) ERC20(name, symbol) EIP712(name, "1") {}
 
     function mint(address account, uint256 amount) public {
-        _transfer(address(0), account, amount);
+        _update(address(0), account, amount);
     }
 
     function burn(address account, uint256 amount) public {
-        _transfer(account, address(0), amount);
+        _update(account, address(0), amount);
     }
 
     function getChainId() external view returns (uint256) {
diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index dd33cb85c29..c2e3c2dc572 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -227,8 +227,24 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         address to,
         uint256 amount
     ) internal virtual {
-        require(!(from == address(0) && to == address(0)), "ERC20: invalid transfer operation");
+        require(from != address(0), "ERC20: transfer from the zero address");
+        require(to != address(0), "ERC20: transfer to the zero address");
+        _update(from, to, amount);
+    }
 
+    /**
+     * @dev Moves `amount` of tokens from `from` to `to`.
+     *
+     * Will mint (or burn) if `from` (or `to`) is the zero address.
+     *
+     * Emits a {Transfer} event.
+     *
+     */
+    function _update(
+        address from,
+        address to,
+        uint256 amount
+    ) internal virtual {
         uint256 fromBalance = _balances[from];
         if (from == address(0)) {
             _totalSupply += amount;
@@ -264,7 +280,8 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      *
      */
     function _mint(address account, uint256 amount) internal {
-        _transfer(address(0), account, amount);
+        require(account != address(0), "ERC20: mint to the zero address");
+        _update(address(0), account, amount);
     }
 
     /**
@@ -277,7 +294,8 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      *
      */
     function _burn(address account, uint256 amount) internal {
-        _transfer(account, address(0), amount);
+        require(account != address(0), "ERC20: burn from the zero address");
+        _update(account, address(0), amount);
     }
 
     /**
diff --git a/contracts/token/ERC20/extensions/ERC20Capped.sol b/contracts/token/ERC20/extensions/ERC20Capped.sol
index 8acc7248c2c..3be9ff805d7 100644
--- a/contracts/token/ERC20/extensions/ERC20Capped.sol
+++ b/contracts/token/ERC20/extensions/ERC20Capped.sol
@@ -30,7 +30,7 @@ abstract contract ERC20Capped is ERC20 {
     /**
      * @dev See {ERC20-_transfer}.
      */
-    function _transfer(
+    function _update(
         address from,
         address to,
         uint256 amount
@@ -39,6 +39,6 @@ abstract contract ERC20Capped is ERC20 {
             require(ERC20.totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
         }
 
-        super._transfer(from, to, amount);
+        super._update(from, to, amount);
     }
 }
diff --git a/contracts/token/ERC20/extensions/ERC20Pausable.sol b/contracts/token/ERC20/extensions/ERC20Pausable.sol
index 97410fb9320..92d764932a9 100644
--- a/contracts/token/ERC20/extensions/ERC20Pausable.sol
+++ b/contracts/token/ERC20/extensions/ERC20Pausable.sol
@@ -15,18 +15,18 @@ import "../../../security/Pausable.sol";
  */
 abstract contract ERC20Pausable is ERC20, Pausable {
     /**
-     * @dev See {ERC20-_transfer}.
+     * @dev See {ERC20-_update}.
      *
      * Requirements:
      *
      * - the contract must not be paused.
      */
-    function _transfer(
+    function _update(
         address from,
         address to,
         uint256 amount
     ) internal virtual override {
         require(!paused(), "ERC20Pausable: token transfer while paused");
-        super._transfer(from, to, amount);
+        super._update(from, to, amount);
     }
 }
diff --git a/contracts/token/ERC20/extensions/ERC20Snapshot.sol b/contracts/token/ERC20/extensions/ERC20Snapshot.sol
index fcb65d09f53..2c34e226809 100644
--- a/contracts/token/ERC20/extensions/ERC20Snapshot.sol
+++ b/contracts/token/ERC20/extensions/ERC20Snapshot.sol
@@ -120,7 +120,7 @@ abstract contract ERC20Snapshot is ERC20 {
 
     // Update balance and/or total supply snapshots before the values are modified. This is executed
     // for _mint, _burn, and _transfer operations.
-    function _transfer(
+    function _update(
         address from,
         address to,
         uint256 amount
@@ -138,7 +138,7 @@ abstract contract ERC20Snapshot is ERC20 {
             _updateAccountSnapshot(from);
             _updateAccountSnapshot(to);
         }
-        super._transfer(from, to, amount);
+        super._update(from, to, amount);
     }
 
     function _valueAt(uint256 snapshotId, Snapshots storage snapshots) private view returns (bool, uint256) {
diff --git a/contracts/token/ERC20/extensions/ERC20Votes.sol b/contracts/token/ERC20/extensions/ERC20Votes.sol
index 0a7bb70385b..7f9f36b7603 100644
--- a/contracts/token/ERC20/extensions/ERC20Votes.sol
+++ b/contracts/token/ERC20/extensions/ERC20Votes.sol
@@ -35,12 +35,12 @@ abstract contract ERC20Votes is ERC20, Votes {
      *
      * Emits a {IVotes-DelegateVotesChanged} event.
      */
-    function _transfer(
+    function _update(
         address from,
         address to,
         uint256 amount
     ) internal virtual override {
-        super._transfer(from, to, amount);
+        super._update(from, to, amount);
         if (from == address(0)) {
             require(totalSupply() <= _maxSupply(), "ERC20Votes: total supply risks overflowing votes");
         }
diff --git a/test/token/ERC20/ERC20.test.js b/test/token/ERC20/ERC20.test.js
index e8fa042dd1e..46ee5ab6373 100644
--- a/test/token/ERC20/ERC20.test.js
+++ b/test/token/ERC20/ERC20.test.js
@@ -203,7 +203,7 @@ contract('ERC20', function (accounts) {
     const amount = new BN(50);
     it('rejects a null account', async function () {
       await expectRevert(
-        this.token.mint(ZERO_ADDRESS, amount), 'ERC20: invalid transfer operation',
+        this.token.mint(ZERO_ADDRESS, amount), 'ERC20: mint to the zero address',
       );
     });
 
@@ -244,7 +244,7 @@ contract('ERC20', function (accounts) {
   describe('_burn', function () {
     it('rejects a null account', async function () {
       await expectRevert(this.token.burn(ZERO_ADDRESS, new BN(1)),
-        'ERC20: invalid transfer operation');
+        'ERC20: burn from the zero address');
     });
 
     describe('for a non zero account', function () {

From 1083de9520fae091f28ad0b3145fd4361eb71b98 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Tue, 13 Dec 2022 15:45:29 -0400
Subject: [PATCH 28/42] Update CHANGELOG.md

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 776262b16d9..60ce13b1954 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,7 +8,7 @@
  * Removed presets in favor of [OpenZeppelin Contracts Wizard](https://wizard.openzeppelin.com/).
  * `TransparentUpgradeableProxy`: Removed `admin` and `implementation` getters, which were only callable by the proxy owner and thus not very useful. ([#3820](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3820))
  * `ProxyAdmin`: Removed `getProxyAdmin` and `getProxyImplementation` getters. ([#3820](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3820))
- * `ERC20`: Deleted `_beforeTokenTransfer` and `_afterTokenTransfer` hooks, and refactor all extensions using those hooks for customization, by using `transfer` instead. ([#3838](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3838))
+ * `ERC20`: Deleted `_beforeTokenTransfer` and `_afterTokenTransfer` hooks, and refactor all extensions using those hooks for customization, by using `_update` instead. ([#3838](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3838))
 
 ### How to upgrade from 4.x
 

From a7a9ff16d9f42fb58ad5351c47ce2d7a7e39dffc Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 08:01:40 -0400
Subject: [PATCH 29/42] Update CHANGELOG.md

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 CHANGELOG.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 60ce13b1954..3fdf6c09d1b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,14 +22,14 @@ For example, a contract using `ERC20`'s `_afterTokenTransfer` hook would have to
 
 ```diff
 - function _beforeTokenTransfer(
-+ function _transfer(
++ function _update(
       address from,
       address to,
       uint256 amount
   ) internal virtual override {
 -     super._beforeTokenTransfer(from, to, amount);
       require(!condition(), "ERC20: wrong condition");
-+     super._transfer(from, to, amount);
++     super._update(from, to, amount);
   }
 ```
 

From d6fdf53df4ad15f43d19e9691796a40c8400e6d0 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 08:01:48 -0400
Subject: [PATCH 30/42] Update CHANGELOG.md

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 CHANGELOG.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3fdf6c09d1b..a0848ba6d99 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,9 +14,9 @@
 
 #### ERC20, ERC721, and ERC1155
 
-These breaking changes will require modifications to ERC20, ERC721, and ERC1155 contracts, since the `_afterTokenTransfer` and `_beforeTokenTransfer` functions were removed. Any customization made through those hooks should now be done overriding the `_transfer` function instead.
+These breaking changes will require modifications to ERC20, ERC721, and ERC1155 contracts, since the `_afterTokenTransfer` and `_beforeTokenTransfer` functions were removed. Any customization made through those hooks should now be done overriding the new `_update` function instead.
 
-Minting and burning are implemented by `_transfer` and customizations should be done by overriding this function as well. `_mint` and `_burn` are no longer virtual (meaning they are not overridable) to guard against possible inconsistencies.
+Minting and burning are implemented by `_update` and customizations should be done by overriding this function as well. `_mint` and `_burn` are no longer virtual (meaning they are not overridable) to guard against possible inconsistencies.
 
 For example, a contract using `ERC20`'s `_afterTokenTransfer` hook would have to be changed in the following way.
 

From 5e0688b92860e778d66e8bea3857c8ae3bfc5b20 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 08:02:09 -0400
Subject: [PATCH 31/42] Update contracts/token/ERC20/ERC20.sol

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 contracts/token/ERC20/ERC20.sol | 1 -
 1 file changed, 1 deletion(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index c2e3c2dc572..0fdeeeb8727 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -262,7 +262,6 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         } else {
             require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
             unchecked {
-                // Overflow not possible: fromBalance - amount is at most 0, which is checked above.
                 _balances[from] = fromBalance - amount;
                 _balances[to] += amount;
             }

From b66eb88f93ddeb029952896ab49422ca62ad4e7f Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 08:02:15 -0400
Subject: [PATCH 32/42] Update contracts/token/ERC20/ERC20.sol

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 contracts/token/ERC20/ERC20.sol | 1 -
 1 file changed, 1 deletion(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 0fdeeeb8727..4dbbc574877 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -110,7 +110,6 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      * - the caller must have a balance of at least `amount`.
      */
     function transfer(address to, uint256 amount) public virtual override returns (bool) {
-        require(to != address(0), "ERC20: transfer to the zero address");
         address owner = _msgSender();
         _transfer(owner, to, amount);
         return true;

From d55e714fd4f3a21585ef835ac5ebed59ca1a1b26 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 08:02:25 -0400
Subject: [PATCH 33/42] Update contracts/token/ERC20/ERC20.sol

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 contracts/token/ERC20/ERC20.sol | 2 --
 1 file changed, 2 deletions(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 4dbbc574877..bd1b2138f2e 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -159,8 +159,6 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         address to,
         uint256 amount
     ) public virtual override returns (bool) {
-        require(from != address(0), "ERC20: transfer from the zero address");
-        require(to != address(0), "ERC20: transfer to the zero address");
         address spender = _msgSender();
         _spendAllowance(from, spender, amount);
         _transfer(from, to, amount);

From 8abfed7eae032a74078e037fda8220b978b0e5eb Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 08:05:31 -0400
Subject: [PATCH 34/42] Update unchecked reason

---
 contracts/token/ERC20/ERC20.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index bd1b2138f2e..12cabe32af8 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -253,7 +253,7 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
             require(fromBalance >= amount, "ERC20: burn amount exceeds balance");
             _totalSupply -= amount;
             unchecked {
-                // Overflow not possible: balance - amount is at most totalSupply - amount, which is checked above.
+                // Overflow not possible: amount <= accountBalance <= totalSupply.
                 _balances[from] = fromBalance - amount;
             }
         } else {

From 278c6d0c43b4f44e69043141f77ac58980205af6 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 12:34:09 -0400
Subject: [PATCH 35/42] Update contracts/token/ERC20/ERC20.sol

Co-authored-by: Francisco <frangio.1@gmail.com>
---
 contracts/token/ERC20/ERC20.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 12cabe32af8..cb73e7b6479 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -253,7 +253,7 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
             require(fromBalance >= amount, "ERC20: burn amount exceeds balance");
             _totalSupply -= amount;
             unchecked {
-                // Overflow not possible: amount <= accountBalance <= totalSupply.
+                // Overflow not possible: amount <= fromBalance <= totalSupply.
                 _balances[from] = fromBalance - amount;
             }
         } else {

From 56e648aad08578c01b142ee276ae173712d53fc3 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 12:36:06 -0400
Subject: [PATCH 36/42] Update ERC20.sol

---
 contracts/token/ERC20/ERC20.sol | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index cb73e7b6479..b3cabfa5454 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -242,7 +242,7 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         address to,
         uint256 amount
     ) internal virtual {
-        uint256 fromBalance = _balances[from];
+
         if (from == address(0)) {
             _totalSupply += amount;
             unchecked {
@@ -250,6 +250,7 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
                 _balances[to] += amount;
             }
         } else if (to == address(0)) {
+            uint256 fromBalance = _balances[from];
             require(fromBalance >= amount, "ERC20: burn amount exceeds balance");
             _totalSupply -= amount;
             unchecked {
@@ -257,6 +258,7 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
                 _balances[from] = fromBalance - amount;
             }
         } else {
+            uint256 fromBalance = _balances[from];
             require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
             unchecked {
                 _balances[from] = fromBalance - amount;

From 2fc018eaf1ab7acc9196199e63625f63845f8cc8 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 12:42:46 -0400
Subject: [PATCH 37/42] run lint

---
 contracts/token/ERC20/ERC20.sol | 1 -
 1 file changed, 1 deletion(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index b3cabfa5454..529f5936484 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -242,7 +242,6 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         address to,
         uint256 amount
     ) internal virtual {
-
         if (from == address(0)) {
             _totalSupply += amount;
             unchecked {

From fa58b35ff5fb113c3411b5c2b28755f63a2fdd94 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 14:25:41 -0400
Subject: [PATCH 38/42] Add unchecked comment

---
 contracts/token/ERC20/ERC20.sol | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 529f5936484..978da3a431e 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -261,6 +261,8 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
             require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
             unchecked {
                 _balances[from] = fromBalance - amount;
+                // Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
+                // decrementing then incrementing.
                 _balances[to] += amount;
             }
         }

From 58a28b9d0b16c9084e1109ca4926dcd4e3585007 Mon Sep 17 00:00:00 2001
From: Francisco <frangio.1@gmail.com>
Date: Wed, 14 Dec 2022 15:43:14 -0300
Subject: [PATCH 39/42] Update CHANGELOG.md

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a0848ba6d99..83ba8498d14 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,7 +8,7 @@
  * Removed presets in favor of [OpenZeppelin Contracts Wizard](https://wizard.openzeppelin.com/).
  * `TransparentUpgradeableProxy`: Removed `admin` and `implementation` getters, which were only callable by the proxy owner and thus not very useful. ([#3820](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3820))
  * `ProxyAdmin`: Removed `getProxyAdmin` and `getProxyImplementation` getters. ([#3820](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3820))
- * `ERC20`: Deleted `_beforeTokenTransfer` and `_afterTokenTransfer` hooks, and refactor all extensions using those hooks for customization, by using `_update` instead. ([#3838](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3838))
+ * `ERC20`: Deleted `_beforeTokenTransfer` and `_afterTokenTransfer` hooks, added a new internal `_update` function for customizations, and refactored all extensions using those hooks to use `_update` instead. ([#3838](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3838))
 
 ### How to upgrade from 4.x
 

From a6ce9e1a6a8166805d7c588f81a4f8e6c0a90dbb Mon Sep 17 00:00:00 2001
From: Francisco <frangio.1@gmail.com>
Date: Wed, 14 Dec 2022 15:55:13 -0300
Subject: [PATCH 40/42] Update CHANGELOG.md

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 83ba8498d14..9450563faf5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,7 +18,7 @@ These breaking changes will require modifications to ERC20, ERC721, and ERC1155
 
 Minting and burning are implemented by `_update` and customizations should be done by overriding this function as well. `_mint` and `_burn` are no longer virtual (meaning they are not overridable) to guard against possible inconsistencies.
 
-For example, a contract using `ERC20`'s `_afterTokenTransfer` hook would have to be changed in the following way.
+For example, a contract using `ERC20`'s `_beforeTokenTransfer` hook would have to be changed in the following way.
 
 ```diff
 - function _beforeTokenTransfer(

From ee4b86a2f8c6a603bfb0052d84ffff5a10f091b8 Mon Sep 17 00:00:00 2001
From: JulissaDantes <julissadcj@gmail.com>
Date: Wed, 14 Dec 2022 15:00:52 -0400
Subject: [PATCH 41/42] update mock

---
 contracts/mocks/ERC20VotesMock.sol | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/contracts/mocks/ERC20VotesMock.sol b/contracts/mocks/ERC20VotesMock.sol
index c52c5b073a7..654a089acf1 100644
--- a/contracts/mocks/ERC20VotesMock.sol
+++ b/contracts/mocks/ERC20VotesMock.sol
@@ -8,11 +8,11 @@ contract ERC20VotesMock is ERC20Votes {
     constructor(string memory name, string memory symbol) ERC20(name, symbol) EIP712(name, "1") {}
 
     function mint(address account, uint256 amount) public {
-        _update(address(0), account, amount);
+        _mint(account, amount);
     }
 
     function burn(address account, uint256 amount) public {
-        _update(account, address(0), amount);
+        _burn(account, amount);
     }
 
     function getChainId() external view returns (uint256) {

From 30876ac29a8b263f2d3376b46dfa6ec0639ea82b Mon Sep 17 00:00:00 2001
From: Francisco Giordano <frangio.1@gmail.com>
Date: Wed, 14 Dec 2022 16:27:51 -0300
Subject: [PATCH 42/42] update docs

---
 contracts/token/ERC20/ERC20.sol | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 978da3a431e..c10f659d019 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -214,28 +214,25 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      * This internal function is equivalent to {transfer}, and can be used to
      * e.g. implement automatic token fees, slashing mechanisms, etc.
      *
-     * Will mint (or burn) if `from` (or `to`) is the zero address.
-     *
      * Emits a {Transfer} event.
      *
+     * NOTE: This function is not virtual, {_update} should be overridden instead.
      */
     function _transfer(
         address from,
         address to,
         uint256 amount
-    ) internal virtual {
+    ) internal {
         require(from != address(0), "ERC20: transfer from the zero address");
         require(to != address(0), "ERC20: transfer to the zero address");
         _update(from, to, amount);
     }
 
     /**
-     * @dev Moves `amount` of tokens from `from` to `to`.
-     *
-     * Will mint (or burn) if `from` (or `to`) is the zero address.
+     * @dev Transfers `amount` of tokens from `from` to `to`, or alternatively mints (or burns) if `from` (or `to`) is
+     * the zero address. All customizations to transfers, mints, and burns should be done by overriding this function.
      *
      * Emits a {Transfer} event.
-     *
      */
     function _update(
         address from,
@@ -270,13 +267,13 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         emit Transfer(from, to, amount);
     }
 
-    /** @dev Creates `amount` tokens and assigns them to `account`, by transferring it from address(0).
-     * Relies on the `_transfer` mechanism
+    /**
+     * @dev Creates `amount` tokens and assigns them to `account`, by transferring it from address(0).
+     * Relies on the `_update` mechanism
      *
      * Emits a {Transfer} event with `from` set to the zero address.
      *
-     * Note: this function is not virtual, {_transfer} should be overridden instead.
-     *
+     * NOTE: This function is not virtual, {_update} should be overridden instead.
      */
     function _mint(address account, uint256 amount) internal {
         require(account != address(0), "ERC20: mint to the zero address");
@@ -285,12 +282,11 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
 
     /**
      * @dev Destroys `amount` tokens from `account`, by transferring it to address(0).
-     * Relies on the `_transfer` mechanism.
-     *
-     * Note: this function is not virtual, {_transfer} should be overridden instead
+     * Relies on the `_update` mechanism.
      *
      * Emits a {Transfer} event with `to` set to the zero address.
      *
+     * NOTE: This function is not virtual, {_update} should be overridden instead
      */
     function _burn(address account, uint256 amount) internal {
         require(account != address(0), "ERC20: burn from the zero address");