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"vm.setBlockhash" cheatcode #7929

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zomglings opened this issue May 14, 2024 · 8 comments · Fixed by #8258
Closed

"vm.setBlockhash" cheatcode #7929

zomglings opened this issue May 14, 2024 · 8 comments · Fixed by #8258
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@jrmncos
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good first issue Good for newcomers T-feature Type: feature

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@zomglings
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zomglings commented May 14, 2024 •
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Component

cheatcodes

Describe the feature you would like

A vm.setBlockhash cheat code would be very convenient for testing code that uses the Solidity blockhash function.

This is how it would be used:

vm.roll(block.number + 1);
vm.setBlockhash(block.number - 1, "1234");
assertEq(blockhash(block.number - 1), "1234");

Currently, the easiest way to test code that calls blockhash is to wrap the blockhash call in a virtual, internal method and then create a test class that overrides that method to mock blockhash calls.

I'd rather just have the mocking performed at the level of the vm.

If this is considered sufficiently useful, I would be happy to try my hand at adding this cheat code. Just don't want to learn rust, etc. to add this only to have a PR rejected if the feature isn't seen as useful.

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@zomglings zomglings added the T-feature Type: feature label May 14, 2024
@zomglings
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Developer documentation for cheat codes: https://github.com/foundry-rs/foundry/blob/master/docs/dev/cheatcodes.md#cheatcodes-implementation

@onbjerg
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onbjerg commented May 14, 2024

Unsure if this makes sense to add if https://eips.ethereum.org/EIPS/eip-2935 is included in Prague, as this could be emulated with just setting the appropriate slot on the contract

@mattsse mattsse added the good first issue Good for newcomers label May 14, 2024
@zomglings
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Unsure if this makes sense to add if https://eips.ethereum.org/EIPS/eip-2935 is included in Prague, as this could be emulated with just setting the appropriate slot on the contract

In that case, wouldn't vm.setBlockhash still be a useful shorthand to set that slot?

@mattsse
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mattsse commented May 15, 2024

yeah for setting a slot this will still be useful imo

@jrmncos
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jrmncos commented Jun 11, 2024

Hello, is it still available? I would like to work on this one

@mattsse
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mattsse commented Jun 11, 2024 •
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this is available and should be similar to

foundry/crates/cheatcodes/spec/src/vm.rs

Lines 415 to 420 in 29e5112

/// Gets the current `block.timestamp`.
/// You should use this instead of `block.timestamp` if you use `vm.warp`, as `block.timestamp` is assumed to be constant across a transaction,
/// and as a result will get optimized out by the compiler.
/// See https://github.com/foundry-rs/foundry/issues/6180
#[cheatcode(group = Evm, safety = Safe)]
function getBlockTimestamp() external view returns (uint256 timestamp);

foundry/crates/cheatcodes/src/evm.rs

Lines 362 to 367 in 29e5112

impl Cheatcode for getBlockTimestampCall {
fn apply_full<DB: DatabaseExt>(&self, ccx: &mut CheatsCtxt<DB>) -> Result {
let Self {} = self;
Ok(ccx.ecx.env.block.timestamp.abi_encode())
}
}

the impl would need to update the hash of the number argument in the database

if you need more pointers, please open a draft pr and we take it from there

@TropicalDog17 TropicalDog17 mentioned this issue Jun 26, 2024
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@TropicalDog17
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Hi @mattsse, it appears the previous assignee hasn't started on this task yet so I'd like to work on it. I've created a draft PR but I'm having trouble accessing the database in apply_full to update the blockhash. Could you provide some guidance on this? Thank you!

@jrmncos
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jrmncos commented Jun 26, 2024

hey @mattsse you can re-assign the issue to @TropicalDog17 . Sorry for delay

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good first issue Good for newcomers T-feature Type: feature
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feat(cheatcodes): add vm.setBlockhash orbitorg/foundry
5 participants
@zomglings @onbjerg @mattsse @jrmncos @TropicalDog17