Bundle ERC20Detailed (#2161)

* Merge ERC20Detailed into ERC20, make derived contracts abstract

* Fix Create2 tests

* Fix failing test

* Default decimals to 18

* Add tests for setupDecimals

* Add changelog entry

* Update CHANGELOG.md

* Update CHANGELOG.md

* Replace isConstructor for !isContract

* Update CHANGELOG.md

Co-Authored-By: Francisco Giordano <frangio.1@gmail.com>

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

contracts/token/ERC20/ERC20.sol

@@ -3,6 +3,7 @@ pragma solidity ^0.6.0;
 import "../../GSN/Context.sol";
 import "./IERC20.sol";
 import "../../math/SafeMath.sol";
+import "../../utils/Address.sol";
 
 /**
  * @dev Implementation of the {IERC20} interface.
@@ -30,6 +31,7 @@ import "../../math/SafeMath.sol";
  */
 contract ERC20 is Context, IERC20 {
     using SafeMath for uint256;
+    using Address for address;
 
     mapping (address => uint256) private _balances;
 
@@ -37,6 +39,57 @@ contract ERC20 is Context, IERC20 {
 
     uint256 private _totalSupply;
 
+    string private _name;
+    string private _symbol;
+    uint8 private _decimals;
+
+    /**
+     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
+     * a default value of 18.
+     *
+     * To select a different value for {decimals}, use {_setupDecimals}.
+     *
+     * All three of these values are immutable: they can only be set once during
+     * construction.
+     */
+    constructor (string memory name, string memory symbol) public {
+        _name = name;
+        _symbol = symbol;
+        _decimals = 18;
+    }
+
+    /**
+     * @dev Returns the name of the token.
+     */
+    function name() public view returns (string memory) {
+        return _name;
+    }
+
+    /**
+     * @dev Returns the symbol of the token, usually a shorter version of the
+     * name.
+     */
+    function symbol() public view returns (string memory) {
+        return _symbol;
+    }
+
+    /**
+     * @dev Returns the number of decimals used to get its user representation.
+     * For example, if `decimals` equals `2`, a balance of `505` tokens should
+     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
+     *
+     * Tokens usually opt for a value of 18, imitating the relationship between
+     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
+     * called.
+     *
+     * NOTE: This information is only used for _display_ purposes: it in
+     * no way affects any of the arithmetic of the contract, including
+     * {IERC20-balanceOf} and {IERC20-transfer}.
+     */
+    function decimals() public view returns (uint8) {
+        return _decimals;
+    }
+
     /**
      * @dev See {IERC20-totalSupply}.
      */
@@ -223,6 +276,18 @@ contract ERC20 is Context, IERC20 {
         emit Approval(owner, spender, amount);
     }
 
+    /**
+     * @dev Sets {decimals} to a value other than the default one of 18.
+     *
+     * Requirements:
+     *
+     * - this function can only be called from a constructor.
+     */
+    function _setupDecimals(uint8 decimals_) internal {
+        require(!address(this).isContract(), "ERC20: decimals cannot be changed after construction");
+        _decimals = decimals_;
+    }
+
     /**
      * @dev Hook that is called before any transfer of tokens. This includes
      * minting and burning.

contracts/token/ERC20/ERC20Burnable.sol

@@ -8,7 +8,7 @@ import "./ERC20.sol";
  * tokens and those that they have an allowance for, in a way that can be
  * recognized off-chain (via event analysis).
  */
-contract ERC20Burnable is Context, ERC20 {
+abstract contract ERC20Burnable is Context, ERC20 {
     /**
      * @dev Destroys `amount` tokens from the caller.
      *

contracts/token/ERC20/ERC20Capped.sol

@@ -5,7 +5,7 @@ import "./ERC20.sol";
 /**
  * @dev Extension of {ERC20} that adds a cap to the supply of tokens.
  */
-contract ERC20Capped is ERC20 {
+abstract contract ERC20Capped is ERC20 {
     uint256 private _cap;
 
     /**

contracts/token/ERC20/ERC20Detailed.sol

@@ -1,54 +0,0 @@
-pragma solidity ^0.6.0;
-
-import "./IERC20.sol";
-
-/**
- * @dev Optional functions from the ERC20 standard.
- */
-abstract contract ERC20Detailed is IERC20 {
-    string private _name;
-    string private _symbol;
-    uint8 private _decimals;
-
-    /**
-     * @dev Sets the values for `name`, `symbol`, and `decimals`. All three of
-     * these values are immutable: they can only be set once during
-     * construction.
-     */
-    constructor (string memory name, string memory symbol, uint8 decimals) public {
-        _name = name;
-        _symbol = symbol;
-        _decimals = decimals;
-    }
-
-    /**
-     * @dev Returns the name of the token.
-     */
-    function name() public view returns (string memory) {
-        return _name;
-    }
-
-    /**
-     * @dev Returns the symbol of the token, usually a shorter version of the
-     * name.
-     */
-    function symbol() public view returns (string memory) {
-        return _symbol;
-    }
-
-    /**
-     * @dev Returns the number of decimals used to get its user representation.
-     * For example, if `decimals` equals `2`, a balance of `505` tokens should
-     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
-     *
-     * Tokens usually opt for a value of 18, imitating the relationship between
-     * Ether and Wei.
-     *
-     * NOTE: This information is only used for _display_ purposes: it in
-     * no way affects any of the arithmetic of the contract, including
-     * {IERC20-balanceOf} and {IERC20-transfer}.
-     */
-    function decimals() public view returns (uint8) {
-        return _decimals;
-    }
-}

contracts/token/ERC20/ERC20Pausable.sol

@@ -11,7 +11,7 @@ import "../../utils/Pausable.sol";
  * period, or having an emergency switch for freezing all token transfers in the
  * event of a large bug.
  */
-contract ERC20Pausable is ERC20, Pausable {
+abstract contract ERC20Pausable is ERC20, Pausable {
     /**
      * @dev See {ERC20-_beforeTokenTransfer}.
      *

contracts/token/ERC20/ERC20Snapshot.sol

@@ -17,7 +17,7 @@ import "./ERC20.sol";
  * account address.
  * @author Validity Labs AG <info@validitylabs.org>
  */
-contract ERC20Snapshot is ERC20 {
+abstract contract ERC20Snapshot is ERC20 {
     // Inspired by Jordi Baylina's MiniMeToken to record historical balances:
     // https://github.com/Giveth/minimd/blob/ea04d950eea153a04c51fa510b068b9dded390cb/contracts/MiniMeToken.sol