"vm.setBlockhash" cheatcode

[zomglings]

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.

Additional context

No response

[zomglings]

Developer documentation for cheat codes: https://github.com/foundry-rs/foundry/blob/master/docs/dev/cheatcodes.md#cheatcodes-implementation

[onbjerg]

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

[zomglings]

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]

yeah for setting a slot this will still be useful imo