Add IERC20Metadata with name, symbol and decimals

CHANGELOG.md

@@ -18,6 +18,7 @@
  * Rename `UpgradeableProxy` to `ERC1967Proxy`. ([#2547](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2547))
  * `ERC777`: Optimize the gas costs of the constructor. ([#2551](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2551))
  * `ERC721URIStorage`: Add a new extension that implements the `_setTokenURI` behavior as it was available in 3.4.0. ([#2555](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2555))
+ * `ERC20Metadata`: Add a new extended interface that includes the non standard `name()`, `symbol()` and `decimals()` functions. ([#2561](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2561))
 
 ### How to upgrade from 3.x
 

contracts/token/ERC20/ERC20.sol

@@ -3,6 +3,7 @@
 pragma solidity ^0.8.0;
 
 import "./IERC20.sol";
+import "./extensions/IERC20Metadata.sol";
 import "../../utils/Context.sol";
 
 /**
@@ -29,7 +30,7 @@ import "../../utils/Context.sol";
  * functions have been added to mitigate the well-known issues around setting
  * allowances. See {IERC20-approve}.
  */
-contract ERC20 is Context, IERC20 {
+contract ERC20 is Context, IERC20, IERC20Metadata {
     mapping (address => uint256) private _balances;
 
     mapping (address => mapping (address => uint256)) private _allowances;
@@ -56,15 +57,15 @@ contract ERC20 is Context, IERC20 {
     /**
      * @dev Returns the name of the token.
      */
-    function name() public view virtual returns (string memory) {
+    function name() public view virtual override returns (string memory) {
         return _name;
     }
 
     /**
      * @dev Returns the symbol of the token, usually a shorter version of the
      * name.
      */
-    function symbol() public view virtual returns (string memory) {
+    function symbol() public view virtual override returns (string memory) {
         return _symbol;
     }
 
@@ -81,7 +82,7 @@ contract ERC20 is Context, IERC20 {
      * no way affects any of the arithmetic of the contract, including
      * {IERC20-balanceOf} and {IERC20-transfer}.
      */
-    function decimals() public view virtual returns (uint8) {
+    function decimals() public view virtual override returns (uint8) {
         return 18;
     }
 

contracts/token/ERC20/extensions/IERC20Metadata.sol

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../IERC20.sol";
+
+/**
+ * @dev Interface of the ERC20 standard as defined in the EIP.
+ */
+interface IERC20Metadata is IERC20 {
+    /**
+     * @dev Returns the name of the tokens.
+     */
+    function name() external view returns (string memory);
+
+    /**
+     * @dev Returns the symbol of the tokens.
+     */
+    function symbol() external view returns (string memory);
+
+    /**
+     * @dev Returns the decimals places of the tokens.
+     */
+    function decimals() external view returns (uint8);
+}