You can add an arg to make a test a fuzz test and use that as the seed

You can add an arg to make a test a fuzz test and use that as the seed

Given vm.shuffle() does not currently accept a salt parameter, that's not possible.

Anyone taking this yet? Would be happy to take a look

Gm, I'm working on this!

I don't think we should have a seed parameter for each individual rng function, but it could be set globally/for the current test with a setSeed or similar

As mentioned the seed will be the fuzz/invariant one if the test is one of those; we could also add a global test seed config

I think I prefer the config since it can be specified inline which would fulfill the same purpose as a cheatcode

cc @grandizzy @zerosnacks

Gm, @DaniPopes
So the focus of this issue would then be to implement a cheatcode that updates the RNG seed in CheatsConfig, right?

Do you have any suggestions or preferences for how to approach this?
I'm thinking of exposing something like vm.setSeed(uint256) that internally updates the config, similar to how other cheatcodes modify global state.

I just added a method to overwrite the cheatsConfig seed via the new cheat vm.setSeed(uint256). Hopefully that’s enough for rng() to return an instance using the provided seed. Could you review it and let me know what I should fix or improve? This is my first contribution to Foundry 😅.

I also wrote a test under testdata, but I’m a bit in the dark on how to run only that one with the forge binary. Sorry if that’s a trivial question!

I don't think we should have a seed parameter for each individual rng function, but it could be set globally/for the current test with a setSeed or similar

As mentioned the seed will be the fuzz/invariant one if the test is one of those; we could also add a global test seed config

I think I prefer the config since it can be specified inline which would fulfill the same purpose as a cheatcode

cc @grandizzy @zerosnacks

Thanks for the input! I agree that having a salted alias (like vm.shuffle(array,salt) might not be the best solution.

However, relying solely on a global config setting for the RNG seed wouldn’t solve the issue I'm facing. Having vm.setSeed(seed) would allow precise control while keeping the interface simple and composable.

My above example would become:

uint256 seed = vm.randomUint();

vm.setSeed(seed);
vm.shuffle(strategies);

// Ensure shuffled `balances` align with `strategies`.
vm.setSeed(seed);
vm.shuffle(balances);

May also be nice to fetch the current fuzz seed via vm.getSeed() or something, so you could use the current randomness twice.