Refactor SafeTransferLib and interfaces

src/interfaces/IERC20.sol

@@ -4,7 +4,5 @@ pragma solidity >=0.5.0;
 /// @title IERC20
 /// @author Morpho Labs
 /// @custom:contact [email protected]
-interface IERC20 {
-    function transfer(address to, uint256 value) external returns (bool);
-    function transferFrom(address from, address to, uint256 value) external returns (bool);
-}
+/// @dev Empty because we only call library functions. It prevents calling transfer (transferFrom) instead of safeTransfer (safeTransferFrom).
+interface IERC20 {}

src/libraries/SafeTransferLib.sol

@@ -5,26 +5,27 @@ import {ErrorsLib} from "../libraries/ErrorsLib.sol";
 
 import {IERC20} from "../interfaces/IERC20.sol";
 
+interface IERC20Internal {
+    function transfer(address to, uint256 value) external returns (bool);
+    function transferFrom(address from, address to, uint256 value) external returns (bool);
+}
+
 /// @title SafeTransferLib
 /// @author Morpho Labs
 /// @custom:contact [email protected]
 /// @notice Library to manage tokens not fully ERC20 compliant:
 ///         not returning a boolean for `transfer` and `transferFrom` functions.
+/// @dev It is the responsibility of the market creator to make sure that the address of the token has non-zero code.
 library SafeTransferLib {
     function safeTransfer(IERC20 token, address to, uint256 value) internal {
-        (bool success, bytes memory returndata) = address(token).call(abi.encodeCall(token.transfer, (to, value)));
-        require(
-            success && address(token).code.length > 0 && (returndata.length == 0 || abi.decode(returndata, (bool))),
-            ErrorsLib.TRANSFER_FAILED
-        );
+        (bool success, bytes memory returndata) =
+            address(token).call(abi.encodeCall(IERC20Internal.transfer, (to, value)));
+        require(success && (returndata.length == 0 || abi.decode(returndata, (bool))), ErrorsLib.TRANSFER_FAILED);
     }
 
     function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
         (bool success, bytes memory returndata) =
-            address(token).call(abi.encodeCall(token.transferFrom, (from, to, value)));
-        require(
-            success && address(token).code.length > 0 && (returndata.length == 0 || abi.decode(returndata, (bool))),
-            ErrorsLib.TRANSFER_FROM_FAILED
-        );
+            address(token).call(abi.encodeCall(IERC20Internal.transferFrom, (from, to, value)));
+        require(success && (returndata.length == 0 || abi.decode(returndata, (bool))), ErrorsLib.TRANSFER_FROM_FAILED);
     }
 }

test/forge/SafeTransferLib.t.sol

@@ -59,13 +59,6 @@ contract SafeTransferLibTest is Test {
         tokenWithBooleanAlwaysFalse = new ERC20WithBooleanAlwaysFalse();
     }
 
-    function testSafeTransferShouldRevertOnTokenWithEmptyCode(address noCode) public {
-        vm.assume(noCode.code.length == 0);
-
-        vm.expectRevert(bytes(ErrorsLib.TRANSFER_FAILED));
-        this.safeTransfer(noCode, address(0), 0);
-    }
-
     function testSafeTransfer(address to, uint256 amount) public {
         tokenWithoutBoolean.setBalance(address(this), amount);