Add burnFrom burning function (#41)

src/interfaces/IBurnableERC20.sol

@@ -4,4 +4,5 @@ pragma solidity 0.8.15;
 
 interface IBurnableERC20 {
     function burn(uint256 amount) external;
+    function burnFrom(address user, uint256 amount) external;
 }

src/token/ERC20MintBurn.sol

@@ -3,7 +3,6 @@
 pragma solidity 0.8.15;
 
 import "../utils/Ownable.sol";
-import "../interfaces/IMintableERC20.sol";
 import "./BaseERC20.sol";
 import "../interfaces/IMintableERC20.sol";
 import "../interfaces/IBurnableERC20.sol";
@@ -58,4 +57,18 @@ abstract contract ERC20MintBurn is IMintableERC20, IBurnableERC20, Ownable, Base
 
         _burn(msg.sender, _value);
     }
+
+    /**
+     * @dev Burns pre-approved tokens from the other address.
+     * Callable only by one of the burner addresses.
+     * @param _from account to burn tokens from.
+     * @param _value amount of tokens to burn. Should be less than or equal to account balance.
+     */
+    function burnFrom(address _from, uint256 _value) external virtual {
+        require(isBurner(msg.sender), "ERC20MintBurn: not a burner");
+
+        _spendAllowance(_from, msg.sender, _value);
+
+        _burn(_from, _value);
+    }
 }

test/BobToken.t.sol

@@ -94,6 +94,30 @@ contract BobTokenTest is Test, EIP2470Test {
         assertEq(bob.balanceOf(user2), 0 ether);
     }
 
+    function testBurnFrom() public {
+        vm.prank(user1);
+        bob.mint(user1, 1 ether);
+
+        vm.expectRevert("ERC20MintBurn: not a burner");
+        bob.burnFrom(user1, 1 ether);
+
+        vm.prank(user2);
+        vm.expectRevert("ERC20: insufficient allowance");
+        bob.burnFrom(user1, 1 ether);
+
+        vm.prank(user1);
+        bob.approve(user2, 10 ether);
+
+        vm.prank(user2);
+        vm.expectEmit(true, true, false, true);
+        emit Transfer(user1, address(0), 1 ether);
+        bob.burnFrom(user1, 1 ether);
+
+        assertEq(bob.totalSupply(), 0);
+        assertEq(bob.balanceOf(user1), 0);
+        assertEq(bob.allowance(user1, user2), 9 ether);
+    }
+
     function testMinterChange() public {
         vm.expectRevert("Ownable: caller is not the owner");
         bob.updateMinter(user3, true, true);