Optimize implementation of ERC20Capped (#2524)

CHANGELOG.md

@@ -14,6 +14,7 @@
  * `AccessControl`: removed enumerability by default for a more lightweight contract. It is now opt-in through `AccessControlEnumerable`. ([#2512](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2512))
  * Meta Transactions: add `ERC2771Context` and a `MinimalForwarder` for meta-transactions. ([#2508](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2508))
  * Overall reorganisation of the contract folder to improve clarity and discoverability. ([#2503](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2503))
+ * `ERC20Capped`: optimize gas usage of by enforcing te check directly in `_mint`. ([#2524](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2524))
 
 ### How to upgrade from 3.x
 

contracts/token/ERC20/extensions/ERC20Capped.sol

@@ -27,17 +27,10 @@ abstract contract ERC20Capped is ERC20 {
     }
 
     /**
-     * @dev See {ERC20-_beforeTokenTransfer}.
-     *
-     * Requirements:
-     *
-     * - minted tokens must not cause the total supply to go over the cap.
+     * @dev See {ERC20-_mint}.
      */
-    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override {
-        super._beforeTokenTransfer(from, to, amount);
-
-        if (from == address(0)) { // When minting tokens
-            require(totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
-        }
+    function _mint(address account, uint256 amount) internal virtual override {
+        require(ERC20.totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
+        super._mint(account, amount);
     }
 }