bug(`cheatcodes`): mockCall does not mock correctly when methods does not return a value

[lemunozm]

Component

Forge

Have you ensured that all of these are up to date?

• Foundry
• Foundryup

What version of Foundry are you on?

forge Version: 1.2.2-nightly

What version of Foundryup are you on?

forge Version: 1.2.2-nightly

What command(s) is the bug in?

forge test

Operating System

macOS (Apple Silicon)

Describe the bug

If I do the following, it will revert:

// SPDX-License-Identifier: BUSL-1.1
pragma solidity 0.8.28;

import "forge-std/Test.sol";

interface IExample {
    function foo(uint a) external;
}

contract MyTest is Test {
    function testFoo() public {
        IExample(address(1)).foo(42);
    }
}

because address(1) is not a contract.

Nevertheless, if I use mockCall like this:

// SPDX-License-Identifier: BUSL-1.1
pragma solidity 0.8.28;

import "forge-std/Test.sol";

interface IExample {
    function foo(uint a) external;
}

contract MyTest is Test {
    function testFoo() public {
        vm.mockCall(address(1), "randomvalue", abi.encode());
        IExample(address(1)).foo(42); // passes, but foo is not mocked
    }
}

it will pass and I do not understand why. This behavior is pretty obscure and makes tests pass when they shouldn't.

NOTE: this only happens when methods does not return a value. It works as expected in the method return some value

[lemunozm]

Actually, this also reverts:

// SPDX-License-Identifier: BUSL-1.1
pragma solidity 0.8.28;

import "forge-std/Test.sol";

interface IExample {
    function foo(uint a) external;
}

contract MyContract { }

contract MyTest is Test {
    function testFoo() public {
        IExample(address(new MyContract())).foo(42);
    }
}

So my real question is, why, if I use mockCall() on an address that is not a contract, the call passes, when it shouldn't?

[grandizzy]

hey @lemunozm thanks for report! the reason why this happens is that we're etching a single byte onto the account in order to circumvent the extcodesize check Solidity might perform, see below

foundry/crates/cheatcodes/src/evm/mock.rs

Lines 211 to 223 in dc43e2c

	// Etches a single byte onto the account if it is empty to circumvent the `extcodesize`
	// check Solidity might perform.
	fn make_acc_non_empty(callee: &Address, ecx: &mut CheatsCtxt) -> Result {
	let acc = ecx.journaled_state.load_account(*callee)?;
	let empty_bytecode = acc.info.code.as_ref().is_none_or(Bytecode::is_empty);
	if empty_bytecode {
	let code = Bytecode::new_raw(Bytes::from_static(&[0u8]));
	ecx.journaled_state.set_code(*callee, code);
	}
	Ok(Default::default())
	}

We could add a sig for mockCalls to bypass this, but I think you could use different cheatcodes for your scenario, like etch or mockFunction (which executes only the mocked function with different bytecode https://getfoundry.sh/reference/cheatcodes/mock-function#description)

[lemunozm]

Thanks for the answer!

In my case, I have different dependencies that I want to mock. For me, it's really convenient just to do vm.mockCall in the same test case to do this, without the need to create another contract with extra functionality, as, IIUC, I need it if I go with etch or mockFunction.

This current behavior feels a bit odd with what one expects after playing with mockCall

[grandizzy]

got it, will add sig to bypass that, CC @zerosnacks wdyt?

[zerosnacks]

That makes sense to me 👍