bug: `forge test` deletes any existing `snapshots` directory by design

[smartcontracts]

Component

Forge

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

• Foundry
• Foundryup

What version of Foundry are you on?

forge 0.2.0 (e5dbb7a 2024-12-03T00:25:01.006590000Z)

What command(s) is the bug in?

forge test

Operating System

macOS (Apple Silicon)

Describe the bug

Running forge test in our repository seems to delete any existing "snapshots" folder if it already exists. We use a folder called "snapshots" to contain all of our snapshots, so this folder isn't exclusive to forge things. I've gotten around this for now by changing our foundry.toml to set the configured snapshots folder to a fake directory.

From a quick glance it looks like this is the source of the issue:

foundry/crates/config/src/lib.rs

Lines 1042 to 1046 in 805d7ce

	// Remove snapshot directory.
	let snapshot_dir = project.root().join(&self.snapshots);
	if snapshot_dir.exists() {
	let _ = fs::remove_dir_all(&snapshot_dir);
	}

I haven't checked what this is actually being used for but if I have some time later I might take a stab at a fix.

[grandizzy]

@smartcontracts that dir is cleaned up to make sure gas snapshots are properly recorded for tests, @zerosnacks maybe we could pattern match and remove only the foundry gas snapshot files? Or should be reserved dir and should be reconfigured as above?

[zerosnacks]

Hi @smartcontracts

Thanks for flagging this, for context this is the relevant code section:

foundry/crates/forge/bin/cmd/test/mod.rs

Lines 309 to 318 in 3a1e76b

	// Remove the snapshots directory if it exists.
	// This is to ensure that we don't have any stale snapshots.
	// If `FORGE_SNAPSHOT_CHECK` is set, we don't remove the snapshots directory as it is
	// required for comparison.
	if std::env::var_os("FORGE_SNAPSHOT_CHECK").is_none() {
	let snapshot_dir = project_root.join(&config.snapshots);
	if snapshot_dir.exists() {
	let _ = fs::remove_dir_all(project_root.join(&config.snapshots));
	}
	}

This is an edge case that wasn't considered, I'll have a look at how best to handle this:

Some possible approaches:

• Detect whether the gas snapshot cheatcode is used and only then clear out (unreliable due to parallelism, hence why it was moved up)
• Use a *.gas.json or *.snapshot.json extension and only clear those out (breaking for current users, not very reliable either)
• To mark snapshots as a reserved directory, similar to .cache or out.

In the base case the snapshots directory should not be cleaned out if the developer does not use Foundry's gas snapshot cheatcodes.

The configured snapshots directory will also be cleaned upon forge clean.

For context: https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/snapshots

For now the workaround you are using should work and continue to work but it is clearly less than ideal.