Add interfaces to ERC20 base contracts (#371)

* add interfaces & add burnable extension

* add burnable interface

* add Burnable & Mintable interfaces

* prettier

Author: ciaranightingale

contracts/base/ERC20Base.sol

@@ -8,6 +8,8 @@ import "../openzeppelin-presets/token/ERC20/extensions/ERC20Permit.sol";
 import "../extension/ContractMetadata.sol";
 import "../extension/Multicall.sol";
 import "../extension/Ownable.sol";
+import "../extension/interface/IMintableERC20.sol";
+import "../extension/interface/IBurnableERC20.sol";
 
 /**
  *  The `ERC20Base` smart contract implements the ERC20 standard.
@@ -24,7 +26,7 @@ import "../extension/Ownable.sol";
  *                             presenting a message signed by the account.
  */
 
-contract ERC20Base is ContractMetadata, Multicall, Ownable, ERC20Permit {
+contract ERC20Base is ContractMetadata, Multicall, Ownable, ERC20Permit, IMintableERC20, IBurnableERC20 {
     /*//////////////////////////////////////////////////////////////
                             Constructor
     //////////////////////////////////////////////////////////////*/
@@ -62,6 +64,22 @@ contract ERC20Base is ContractMetadata, Multicall, Ownable, ERC20Permit {
         _burn(msg.sender, _amount);
     }
 
+    /**
+     *  @notice          Lets an owner burn a given amount of an account's tokens.
+     *  @dev             `_account` should own the `_amount` of tokens.
+     *
+     *  @param _account  The account to burn tokens from.
+     *  @param _amount   The number of tokens to burn.
+     */
+    function burnFrom(address _account, uint256 _amount) external virtual override {
+        require(_canBurn(), "Not authorized to burn.");
+        require(balanceOf(_account) >= _amount, "not enough balance");
+        uint256 decreasedAllowance = allowance(_account, msg.sender) - _amount;
+        _approve(_account, msg.sender, 0);
+        _approve(_account, msg.sender, decreasedAllowance);
+        _burn(_account, _amount);
+    }
+
     /*//////////////////////////////////////////////////////////////
                         Internal (overrideable) functions
     //////////////////////////////////////////////////////////////*/
@@ -76,6 +94,11 @@ contract ERC20Base is ContractMetadata, Multicall, Ownable, ERC20Permit {
         return msg.sender == owner();
     }
 
+    /// @dev Returns whether tokens can be burned in the given execution context.
+    function _canBurn() internal view virtual returns (bool) {
+        return msg.sender == owner();
+    }
+
     /// @dev Returns whether owner can be set in the given execution context.
     function _canSetOwner() internal view virtual override returns (bool) {
         return msg.sender == owner();

contracts/base/ERC20Drop.sol

@@ -10,6 +10,7 @@ import "../extension/Multicall.sol";
 import "../extension/Ownable.sol";
 import "../extension/PrimarySale.sol";
 import "../extension/DropSinglePhase.sol";
+import "../extension/interface/IBurnableERC20.sol";
 
 import "../lib/CurrencyTransferLib.sol";
 
@@ -33,7 +34,7 @@ import "../lib/CurrencyTransferLib.sol";
  *
  */
 
-contract ERC20Drop is ContractMetadata, Multicall, Ownable, ERC20Permit, PrimarySale, DropSinglePhase {
+contract ERC20Drop is ContractMetadata, Multicall, Ownable, ERC20Permit, PrimarySale, DropSinglePhase, IBurnableERC20 {
     /*//////////////////////////////////////////////////////////////
                             Constructor
     //////////////////////////////////////////////////////////////*/
@@ -62,6 +63,22 @@ contract ERC20Drop is ContractMetadata, Multicall, Ownable, ERC20Permit, Primary
         _burn(msg.sender, _amount);
     }
 
+    /**
+     *  @notice          Lets an owner burn a given amount of an account's tokens.
+     *  @dev             `_account` should own the `_amount` of tokens.
+     *
+     *  @param _account  The account to burn tokens from.
+     *  @param _amount   The number of tokens to burn.
+     */
+    function burnFrom(address _account, uint256 _amount) external virtual override {
+        require(_canBurn(), "Not authorized to burn.");
+        require(balanceOf(_account) >= _amount, "not enough balance");
+        uint256 decreasedAllowance = allowance(_account, msg.sender) - _amount;
+        _approve(_account, msg.sender, 0);
+        _approve(_account, msg.sender, decreasedAllowance);
+        _burn(_account, _amount);
+    }
+
     /*//////////////////////////////////////////////////////////////
                         Internal (overrideable) functions
     //////////////////////////////////////////////////////////////*/
@@ -114,6 +131,11 @@ contract ERC20Drop is ContractMetadata, Multicall, Ownable, ERC20Permit, Primary
         return msg.sender == owner();
     }
 
+    /// @dev Returns whether tokens can be burned in the given execution context.
+    function _canBurn() internal view virtual returns (bool) {
+        return msg.sender == owner();
+    }
+
     /// @dev Returns whether owner can be set in the given execution context.
     function _canSetOwner() internal view virtual override returns (bool) {
         return msg.sender == owner();

contracts/base/ERC20Vote.sol

@@ -6,6 +6,8 @@ pragma solidity ^0.8.0;
 import "../openzeppelin-presets/token/ERC20/extensions/ERC20Votes.sol";
 
 import "./ERC20Base.sol";
+import "../extension/interface/IMintableERC20.sol";
+import "../extension/interface/IBurnableERC20.sol";
 
 /**
  *  The `ERC20Vote` smart contract implements the ERC20 standard and ERC20Votes.
@@ -24,7 +26,7 @@ import "./ERC20Base.sol";
  *                             presenting a message signed by the account.
  */
 
-contract ERC20Vote is ContractMetadata, Multicall, Ownable, ERC20Votes {
+contract ERC20Vote is ContractMetadata, Multicall, Ownable, ERC20Votes, IMintableERC20, IBurnableERC20 {
     /*//////////////////////////////////////////////////////////////
                             Constructor
     //////////////////////////////////////////////////////////////*/
@@ -62,6 +64,22 @@ contract ERC20Vote is ContractMetadata, Multicall, Ownable, ERC20Votes {
         _burn(msg.sender, _amount);
     }
 
+    /**
+     *  @notice          Lets an owner burn a given amount of an account's tokens.
+     *  @dev             `_account` should own the `_amount` of tokens.
+     *
+     *  @param _account  The account to burn tokens from.
+     *  @param _amount   The number of tokens to burn.
+     */
+    function burnFrom(address _account, uint256 _amount) external virtual override {
+        require(_canBurn(), "Not authorized to burn.");
+        require(balanceOf(_account) >= _amount, "not enough balance");
+        uint256 decreasedAllowance = allowance(_account, msg.sender) - _amount;
+        _approve(_account, msg.sender, 0);
+        _approve(_account, msg.sender, decreasedAllowance);
+        _burn(_account, _amount);
+    }
+
     /*//////////////////////////////////////////////////////////////
                         Internal (overrideable) functions
     //////////////////////////////////////////////////////////////*/
@@ -76,6 +94,11 @@ contract ERC20Vote is ContractMetadata, Multicall, Ownable, ERC20Votes {
         return msg.sender == owner();
     }
 
+    /// @dev Returns whether tokens can be burned in the given execution context.
+    function _canBurn() internal view virtual returns (bool) {
+        return msg.sender == owner();
+    }
+
     /// @dev Returns whether owner can be set in the given execution context.
     function _canSetOwner() internal view virtual override returns (bool) {
         return msg.sender == owner();