Add SafeERC20.forceApprove()

.changeset/small-terms-sleep.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`SafeERC20`: Add a `forceApprove` function to improve compatibility with tokens behaving like USDT.

contracts/mocks/token/ERC20ForceApproveMock.sol

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../../token/ERC20/ERC20.sol";
+
+// contract that replicate USDT (0xdac17f958d2ee523a2206206994597c13d831ec7) approval beavior
+abstract contract ERC20ForceApproveMock is ERC20 {
+    function approve(address spender, uint256 amount) public virtual override returns (bool) {
+        require(amount == 0 || allowance(msg.sender, spender) == 0, "USDT approval failure");
+        return super.approve(spender, amount);
+    }
+}

contracts/mocks/token/ERC20NoReturnMock.sol

@@ -2,20 +2,27 @@
 
 pragma solidity ^0.8.0;
 
-contract ERC20NoReturnMock {
-    mapping(address => uint256) private _allowances;
+import "../../token/ERC20/ERC20.sol";
 
-    function transfer(address, uint256) public {}
-
-    function transferFrom(address, address, uint256) public {}
-
-    function approve(address, uint256) public {}
+abstract contract ERC20NoReturnMock is ERC20 {
+    function transfer(address to, uint256 amount) public override returns (bool) {
+        super.transfer(to, amount);
+        assembly {
+            return(0, 0)
+        }
+    }
 
-    function setAllowance(address account, uint256 allowance_) public {
-        _allowances[account] = allowance_;
+    function transferFrom(address from, address to, uint256 amount) public override returns (bool) {
+        super.transferFrom(from, to, amount);
+        assembly {
+            return(0, 0)
+        }
     }
 
-    function allowance(address owner, address) public view returns (uint256) {
-        return _allowances[owner];
+    function approve(address spender, uint256 amount) public override returns (bool) {
+        super.approve(spender, amount);
+        assembly {
+            return(0, 0)
+        }
     }
 }

contracts/mocks/token/ERC20PermitNoRevertMock.sol

@@ -5,9 +5,7 @@ pragma solidity ^0.8.0;
 import "../../token/ERC20/ERC20.sol";
 import "../../token/ERC20/extensions/draft-ERC20Permit.sol";
 
-contract ERC20PermitNoRevertMock is ERC20, ERC20Permit {
-    constructor() ERC20("ERC20PermitNoRevertMock", "ERC20PermitNoRevertMock") ERC20Permit("ERC20PermitNoRevertMock") {}
-
+abstract contract ERC20PermitNoRevertMock is ERC20Permit {
     function permitThatMayRevert(
         address owner,
         address spender,

contracts/mocks/token/ERC20ReturnFalseMock.sol

@@ -2,26 +2,18 @@
 
 pragma solidity ^0.8.0;
 
-contract ERC20ReturnFalseMock {
-    mapping(address => uint256) private _allowances;
+import "../../token/ERC20/ERC20.sol";
 
-    function transfer(address, uint256) public pure returns (bool) {
+abstract contract ERC20ReturnFalseMock is ERC20 {
+    function transfer(address, uint256) public pure override returns (bool) {
         return false;
     }
 
-    function transferFrom(address, address, uint256) public pure returns (bool) {
+    function transferFrom(address, address, uint256) public pure override returns (bool) {
         return false;
     }
 
-    function approve(address, uint256) public pure returns (bool) {
+    function approve(address, uint256) public pure override returns (bool) {
         return false;
     }
-
-    function setAllowance(address account, uint256 allowance_) public {
-        _allowances[account] = allowance_;
-    }
-
-    function allowance(address owner, address) public view returns (uint256) {
-        return _allowances[owner];
-    }
 }

contracts/mocks/token/ERC20ReturnTrueMock.sol

@@ -2,26 +2,21 @@
 
 pragma solidity ^0.8.0;
 
-contract ERC20ReturnTrueMock {
-    mapping(address => uint256) private _allowances;
+import "../../token/ERC20/ERC20.sol";
 
-    function transfer(address, uint256) public pure returns (bool) {
+abstract contract ERC20ReturnTrueMock is ERC20 {
+    function transfer(address to, uint256 amount) public override returns (bool) {
+        super.transfer(to, amount);
         return true;
     }
 
-    function transferFrom(address, address, uint256) public pure returns (bool) {
+    function transferFrom(address from, address to, uint256 amount) public override returns (bool) {
+        super.transferFrom(from, to, amount);
         return true;
     }
 
-    function approve(address, uint256) public pure returns (bool) {
+    function approve(address spender, uint256 amount) public override returns (bool) {
+        super.approve(spender, amount);
         return true;
     }
-
-    function setAllowance(address account, uint256 allowance_) public {
-        _allowances[account] = allowance_;
-    }
-
-    function allowance(address owner, address) public view returns (uint256) {
-        return _allowances[owner];
-    }
 }

contracts/token/ERC20/utils/SafeERC20.sol

@@ -19,10 +19,18 @@ import "../../../utils/Address.sol";
 library SafeERC20 {
     using Address for address;
 
+    /**
+     * @dev Transfer `value` amount of `token` from the calling contract to `to`. If `token` returns no value,
+     * non-reverting calls are assumed to be successful.
+     */
     function safeTransfer(IERC20 token, address to, uint256 value) internal {
         _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
     }
 
+    /**
+     * @dev Transfer `value` amount of `token` from `from` to `to`, spending the approval given by `from` to the
+     * calling contract. If `token` returns no value, non-reverting calls are assumed to be successful.
+     */
     function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
         _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
     }
@@ -45,20 +53,45 @@ library SafeERC20 {
         _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
     }
 
+    /**
+     * @dev Increase the calling contract's allowance toward `spender` by `value`. If `token` returns no value,
+     * non-reverting calls are assumed to be successful.
+     */
     function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
-        uint256 newAllowance = token.allowance(address(this), spender) + value;
-        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
+        uint256 oldAllowance = token.allowance(address(this), spender);
+        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, oldAllowance + value));
     }
 
+    /**
+     * @dev Decrease the calling contract's allowance toward `spender` by `value`. If `token` returns no value,
+     * non-reverting calls are assumed to be successful.
+     */
     function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
         unchecked {
             uint256 oldAllowance = token.allowance(address(this), spender);
             require(oldAllowance >= value, "SafeERC20: decreased allowance below zero");
-            uint256 newAllowance = oldAllowance - value;
-            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
+            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, oldAllowance - value));
+        }
+    }
+
+    /**
+     * @dev Set the calling contract's allowance toward `spender` to `value`. If `token` returns no value,
+     * non-reverting calls are assumed to be successful. Compatible with tokens that require the approval to be set to
+     * 0 before setting it to a non-zero value.
+     */
+    function forceApprove(IERC20 token, address spender, uint256 value) internal {
+        bytes memory approvalCall = abi.encodeWithSelector(token.approve.selector, spender, value);
+
+        if (!_callOptionalReturnBool(token, approvalCall)) {
+            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, 0));
+            _callOptionalReturn(token, approvalCall);
         }
     }
 
+    /**
+     * @dev Use a ERC-2612 signature to set the `owner` approval toward `spender` on `token`.
+     * Revert on invalid signature.
+     */
     function safePermit(
         IERC20Permit token,
         address owner,
@@ -87,9 +120,24 @@ library SafeERC20 {
         // the target address contains contract code and also asserts for success in the low-level call.
 
         bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
-        if (returndata.length > 0) {
-            // Return data is optional
-            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
-        }
+        require(returndata.length == 0 || abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
+    }
+
+    /**
+     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
+     * on the return value: the return value is optional (but if data is returned, it must not be false).
+     * @param token The token targeted by the call.
+     * @param data The call data (encoded using abi.encode or one of its variants).
+     *
+     * This is a variant of {_callOptionalReturn} that silents catches all reverts and returns a bool instead.
+     */
+    function _callOptionalReturnBool(IERC20 token, bytes memory data) private returns (bool) {
+        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
+        // we're implementing it ourselves. We cannot use {Address-functionCall} here since this should return false
+        // and not revert is the subcall reverts.
+
+        (bool success, bytes memory returndata) = address(token).call(data);
+        return
+            success && (returndata.length == 0 || abi.decode(returndata, (bool))) && Address.isContract(address(token));
     }
 }

package.json

@@ -72,7 +72,7 @@
     "glob": "^8.0.3",
     "graphlib": "^2.1.8",
     "hardhat": "^2.9.1",
-    "hardhat-exposed": "^0.3.1",
+    "hardhat-exposed": "^0.3.2",
     "hardhat-gas-reporter": "^1.0.4",
     "hardhat-ignore-warnings": "^0.2.0",
     "keccak256": "^1.0.2",