bug: vm.etch does not work in forge script simulation[/-]

[wjmelements]

Component

Forge

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

• Foundry
• Foundryup

What version of Foundry are you on?

forge Version: 1.3.5-stable Commit SHA: 9979a41 Build Timestamp: 2025-09-09T04:49:14.583356000Z (1757393354) Build Profile: maxperf

What version of Foundryup are you on?

foundryup: 1.1.0

What command(s) is the bug in?

forge script

Operating System

macOS (Intel)

Describe the bug

I'm using vm.etch to mock filecoin precompiles (FilOzone/filecoin-pay#234). It works fine in forge test but fails in forge script.

Here is the relevant part of the script:

contract Profile is Script {
    function endAuction(address sender, Payments payments, uint256 railId) public {
        Payments.RailView memory railView = payments.getRail(railId);
        IERC20 token = railView.token;

        (uint256 fullAmount,,,) = payments.accounts(token, address(payments));

        address recipient = address(0x4a6f6B9fF1fc974096f9063a45Fd12bD5B928AD1);

        FVMPrecompileMock precompileMock = new FVMPrecompileMock();
        vm.etch(0xfe00000000000000000000000000000000000005, address(precompileMock).code);

        vm.startBroadcast();

        payments.burnFILForFees{value: AUCTION_START_PRICE}(token, recipient, fullAmount);
    }
}

The output is

[⠊] Compiling...
No files changed, compilation skipped
Script ran successfully.

## Setting up 1 EVM.
  [19407] 0xF6990c51dC94B36c5D5184BF60107EFe99DDE592::burnFILForFees{value: 31320000000000000000}(0xe9AE74E0C182AAb11bdDb483227CC1F6600b3625, 0x4a6f6B9fF1fc974096f9063a45Fd12bD5B928AD1, 5000)
    ├─ [0] 0xfe00000000000000000000000000000000000005::00000000{value: 31320000000000000000}(00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001b2a6fe0f3d3c00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000c000000000000000000000000000000000000000000000000000000000000000630000000000000000000000000000000000000000000000000000000000000000) [delegatecall]
    │   └─ ← [Stop]
    └─ ← [Revert] FVM precompile invalid response

Error: Simulated execution failed.

Based on the [Stop] I don't think etch is working in the simulation. I also believe it is not working because when I intercept the rpc with a reverse proxy I see it fetching the actual code.

[::1]:60468: POST http://localhost:1234/rpc/v1
    content-type: application/json
    accept: */*
    user-agent: foundry/1.3.5
    accept-encoding: gzip
    host: localhost:1234
    content-length: 111

    {
        "method": "eth_getCode",
        "params": [
            "0xfe00000000000000000000000000000000000005",
            "0x1c"
        ],
        "id": 37,
        "jsonrpc": "2.0"
    }

 << 200 OK 40b
    Date: Fri, 19 Sep 2025 21:16:23 GMT
    Content-Length: 40
    Content-Type: text/plain; charset=utf-8

    {"id":37,"jsonrpc":"2.0","result":"0x"}

I also believe that vm.deal doesn't work for the simulation either, though this is less important to me.

[grandizzy]

@wjmelements I don't think vm.etch could work in this scenario (as you broadcast) but we added support for custom network precompiles (Celo transfer for now, https://github.com/foundry-rs/foundry/tree/master/crates/evm/networks/src/celo) The best way to support this is to add Filecoin precompiles, is this something that you could contribute / suggest what needs to be implemented? thank you

[wjmelements]

I don't think vm.etch could work in this scenario (as you broadcast)

I don't understand this part. Do you mean that the estimated gas will be wrong? Because it already is and I've been tolerating that. Really I just want to mock this precompile so that the simulation will pass and have approximately correct EVM gas.