Rename some ERC20 parameters to match the standard document. (#3167)

* Renames `sender` to `source`.

The naming variable was incorrect.  The source of the funds is *not* necessarily (and in most cases isn't) the sender of the transaction.  Also, this code has a `msgSender` which further adds confusion.

* Changes to `from/to` instead of `source`.

* Function documentation matches new names

* Changed other instances of sender/recipient to from/to.

Also changed `msgSender` to `owner` in the approval related methods.

* apply changes to IERC20.sol + minor renaming in ERC20.sol

Co-authored-by: Daniel Von Fange <daniel@leancoder.com>
Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
(cherry picked from commit 63b4669)

contracts/token/ERC20/ERC20.sol

@@ -107,11 +107,12 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      *
      * Requirements:
      *
-     * - `recipient` cannot be the zero address.
+     * - `to` cannot be the zero address.
      * - the caller must have a balance of at least `amount`.
      */
-    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
-        _transfer(_msgSender(), recipient, amount);
+    function transfer(address to, uint256 amount) public virtual override returns (bool) {
+        address owner = _msgSender();
+        _transfer(owner, to, amount);
         return true;
     }
 
@@ -133,7 +134,8 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      * - `spender` cannot be the zero address.
      */
     function approve(address spender, uint256 amount) public virtual override returns (bool) {
-        _approve(_msgSender(), spender, amount);
+        address owner = _msgSender();
+        _approve(owner, spender, amount);
         return true;
     }
 
@@ -148,25 +150,26 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      *
      * Requirements:
      *
-     * - `sender` and `recipient` cannot be the zero address.
-     * - `sender` must have a balance of at least `amount`.
-     * - the caller must have allowance for ``sender``'s tokens of at least
+     * - `from` and `to` cannot be the zero address.
+     * - `from` must have a balance of at least `amount`.
+     * - the caller must have allowance for ``from``'s tokens of at least
      * `amount`.
      */
     function transferFrom(
-        address sender,
-        address recipient,
+        address from,
+        address to,
         uint256 amount
     ) public virtual override returns (bool) {
-        uint256 currentAllowance = _allowances[sender][_msgSender()];
+        address spender = _msgSender();
+        uint256 currentAllowance = allowance(from, spender);
         if (currentAllowance != type(uint256).max) {
             require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
             unchecked {
-                _approve(sender, _msgSender(), currentAllowance - amount);
+                _approve(from, spender, currentAllowance - amount);
             }
         }
 
-        _transfer(sender, recipient, amount);
+        _transfer(from, to, amount);
 
         return true;
     }
@@ -184,7 +187,8 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      * - `spender` cannot be the zero address.
      */
     function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
-        _approve(_msgSender(), spender, _allowances[_msgSender()][spender] + addedValue);
+        address owner = _msgSender();
+        _approve(owner, spender, _allowances[owner][spender] + addedValue);
         return true;
     }
 
@@ -203,10 +207,11 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      * `subtractedValue`.
      */
     function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
-        uint256 currentAllowance = _allowances[_msgSender()][spender];
+        address owner = _msgSender();
+        uint256 currentAllowance = _allowances[owner][spender];
         require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
         unchecked {
-            _approve(_msgSender(), spender, currentAllowance - subtractedValue);
+            _approve(owner, spender, currentAllowance - subtractedValue);
         }
 
         return true;
@@ -222,30 +227,30 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      *
      * Requirements:
      *
-     * - `sender` cannot be the zero address.
-     * - `recipient` cannot be the zero address.
-     * - `sender` must have a balance of at least `amount`.
+     * - `from` cannot be the zero address.
+     * - `to` cannot be the zero address.
+     * - `from` must have a balance of at least `amount`.
      */
     function _transfer(
-        address sender,
-        address recipient,
+        address from,
+        address to,
         uint256 amount
     ) internal virtual {
-        require(sender != address(0), "ERC20: transfer from the zero address");
-        require(recipient != address(0), "ERC20: transfer to the zero address");
+        require(from != address(0), "ERC20: transfer from the zero address");
+        require(to != address(0), "ERC20: transfer to the zero address");
 
-        _beforeTokenTransfer(sender, recipient, amount);
+        _beforeTokenTransfer(from, to, amount);
 
-        uint256 senderBalance = _balances[sender];
-        require(senderBalance >= amount, "ERC20: transfer amount exceeds balance");
+        uint256 fromBalance = _balances[from];
+        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
         unchecked {
-            _balances[sender] = senderBalance - amount;
+            _balances[from] = fromBalance - amount;
         }
-        _balances[recipient] += amount;
+        _balances[to] += amount;
 
-        emit Transfer(sender, recipient, amount);
+        emit Transfer(from, to, amount);
 
-        _afterTokenTransfer(sender, recipient, amount);
+        _afterTokenTransfer(from, to, amount);
     }
 
     /** @dev Creates `amount` tokens and assigns them to `account`, increasing

contracts/token/ERC20/IERC20.sol

@@ -18,13 +18,13 @@ interface IERC20 {
     function balanceOf(address account) external view returns (uint256);
 
     /**
-     * @dev Moves `amount` tokens from the caller's account to `recipient`.
+     * @dev Moves `amount` tokens from the caller's account to `to`.
      *
      * Returns a boolean value indicating whether the operation succeeded.
      *
      * Emits a {Transfer} event.
      */
-    function transfer(address recipient, uint256 amount) external returns (bool);
+    function transfer(address to, uint256 amount) external returns (bool);
 
     /**
      * @dev Returns the remaining number of tokens that `spender` will be
@@ -52,7 +52,7 @@ interface IERC20 {
     function approve(address spender, uint256 amount) external returns (bool);
 
     /**
-     * @dev Moves `amount` tokens from `sender` to `recipient` using the
+     * @dev Moves `amount` tokens from `from` to `to` using the
      * allowance mechanism. `amount` is then deducted from the caller's
      * allowance.
      *
@@ -61,8 +61,8 @@ interface IERC20 {
      * Emits a {Transfer} event.
      */
     function transferFrom(
-        address sender,
-        address recipient,
+        address from,
+        address to,
         uint256 amount
     ) external returns (bool);