Forge Gas Snapshot

Flexible, checked-in gas snapshotting for Foundry.

Forge has native gas reporting with forge snapshot and forge test --gas-report, but neither perfectly fit my needs. Specifically, forge-gas-snapshot aims to allow for:

• Gas reports over specific, known flows
  • not entire tests and not an average of all calls
• Check gas diffs into version control
• See gas changes over time through commit history

Installation

forge install marktoda/forge-gas-snapshot

• NOTE: foundry.toml must be updated to allow forge to write the snapshots

[profile.default]
...
ffi = true
fs_permissions = [{ access = "read-write", path = ".forge-snapshots/"}]

Usage

By default, gas snapshots are automatically written to ./forge-snapshots/<test-name>.snap on run.

Snapshot modes

Wrap

Wrap arbitrary code in snapStart(testName) and snapEnd to snapshot gas usage.

import {GasSnapshot} from "forge-gas-snapshot/GasSnapshot.sol";

contract MyTest is GasSnapshot {
    function test() public {
        snapStart("test name");
        // do stuff
        snapEnd();
    }
}

Closure

Snapshot a zero-parameter function pointer with snap

import {GasSnapshot} from "forge-gas-snapshot/GasSnapshot.sol";

contract MyTest is GasSnapshot {
    function doStuff() internal {
        // do stuff
    }

    function test() public {
        snap("test name", doStuff);
    }
}

Arbitrary values

Snapshot arbitrary values with snap

import {GasSnapshot} from "forge-gas-snapshot/GasSnapshot.sol";

contract MyTest is GasSnapshot {
    function test() public {
        uint256 value = getValue()
        snap("test name", value);
    }
}

Contract Size

Snapshot contract size with snapSize

import {GasSnapshot} from "forge-gas-snapshot/GasSnapshot.sol";

contract MyTest is GasSnapshot {
    function test() public {
        address addr = new Contract();
        snapSize("test name", addr);
    }
}

Check Mode

Snapshots can be run in check-mode where they revert on mismatch by setting an environment variable FORGE_SNAPSHOT_CHECK=true

TODO Improvements

• Introspection for file / function name
• Group related snapshots in a single file
• Check overhead and accuracy
• Env config for snap dir