From 4c45d5a1854dd14fd0c1fc8c2a0ad1ac0222646e Mon Sep 17 00:00:00 2001
From: Ivan Zhelyazkov <ivan.y.zhelyazkov@gmail.com>
Date: Thu, 16 Nov 2023 12:02:33 +0200
Subject: [PATCH] carbon pol eth conversion - burn bnt directly

---
 contracts/helpers/TestBNT.sol | 12 ++++++++++++
 contracts/pol/CarbonPOL.sol   |  4 ++--
 test/forge/CarbonPOL.t.sol    | 15 +++++++++------
 3 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/contracts/helpers/TestBNT.sol b/contracts/helpers/TestBNT.sol
index 14172ff6..031f509d 100644
--- a/contracts/helpers/TestBNT.sol
+++ b/contracts/helpers/TestBNT.sol
@@ -29,6 +29,18 @@ contract TestBNT is TestERC20Token {
         return true;
     }
 
+    function transferFrom(address _from, address _to, uint256 _value) public override(ERC20) returns (bool success) {
+        assert(super.transferFrom(_from, _to, _value));
+
+        // transferring to the contract address destroys tokens
+        if (_to == address(this)) {
+            _burn(address(this), _value);
+            emit Destruction(_value);
+        }
+
+        return true;
+    }
+
     function issue(address recipient, uint256 amount) external {
         _mint(recipient, amount);
     }
diff --git a/contracts/pol/CarbonPOL.sol b/contracts/pol/CarbonPOL.sol
index 0e374c1d..9311a959 100644
--- a/contracts/pol/CarbonPOL.sol
+++ b/contracts/pol/CarbonPOL.sol
@@ -328,8 +328,8 @@ contract CarbonPOL is ICarbonPOL, Upgradeable, ReentrancyGuardUpgradeable, Utils
         if (ethAmountRequired == 0) {
             revert InvalidTrade();
         }
-        // transfer the tokens from the user
-        _bnt.safeTransferFrom(msg.sender, address(this), amount);
+        // transfer the tokens from the user to the bnt address (burn them directly)
+        _bnt.safeTransferFrom(msg.sender, Token.unwrap(_bnt), amount);
 
         // transfer the eth to the user
         payable(msg.sender).sendValue(ethAmountRequired);
diff --git a/test/forge/CarbonPOL.t.sol b/test/forge/CarbonPOL.t.sol
index 8423a34f..6a37b1f5 100644
--- a/test/forge/CarbonPOL.t.sol
+++ b/test/forge/CarbonPOL.t.sol
@@ -7,7 +7,7 @@ import { TestFixture } from "./TestFixture.t.sol";
 import { POLTestCaseParser } from "./POLTestCaseParser.t.sol";
 
 import { AccessDenied, ZeroValue, InvalidAddress } from "../../contracts/utility/Utils.sol";
-import { Token, NATIVE_TOKEN } from "../../contracts/token/Token.sol";
+import { Token, toERC20, NATIVE_TOKEN } from "../../contracts/token/Token.sol";
 import { TestReenterCarbonPOL } from "../../contracts/helpers/TestReenterCarbonPOL.sol";
 
 import { ICarbonPOL } from "../../contracts/pol/interfaces/ICarbonPOL.sol";
@@ -811,8 +811,8 @@ contract CarbonPOLTest is TestFixture {
         vm.stopPrank();
     }
 
-    /// @dev test trading should increase the contract's bnt balance
-    function testTradingETHShouldIncreaseContractBNTBalance() public {
+    /// @dev test trading eth should burn bnt
+    function testTradingETHShouldBurnBNT() public {
         // enable trading and set price for the native token
         vm.prank(admin);
         Token token = NATIVE_TOKEN;
@@ -830,7 +830,8 @@ contract CarbonPOLTest is TestFixture {
         uint128 tradeAmount = 1000 * 1e18;
         uint128 expectedTradeInput = carbonPOL.expectedTradeInput(token, tradeAmount);
 
-        uint256 bntBalanceBefore = bnt.balanceOf(address(carbonPOL));
+        uint256 bntBalanceBefore = bnt.balanceOf(user1);
+        uint256 bntSupplyBefore = toERC20(bnt).totalSupply();
 
         // approve bnt for eth -> bnt trades
         bnt.safeApprove(address(carbonPOL), tradeAmount);
@@ -838,9 +839,11 @@ contract CarbonPOLTest is TestFixture {
         // trade
         carbonPOL.trade{ value: expectedTradeInput }(token, tradeAmount);
 
-        uint256 bntBalanceAfter = bnt.balanceOf(address(carbonPOL));
+        uint256 bntBalanceAfter = bnt.balanceOf(user1);
+        uint256 bntSupplyAfter = toERC20(bnt).totalSupply();
 
-        assertEq(bntBalanceAfter - bntBalanceBefore, tradeAmount);
+        assertEq(bntBalanceBefore - bntBalanceAfter, tradeAmount);
+        assertEq(bntSupplyBefore - bntSupplyAfter, tradeAmount);
 
         vm.stopPrank();
     }