feat(docs): EIP-712 Tutorial

[kulkarohan]

resolves #159

[gakonst]

Love the example - thank you for taking the time for this.

But maybe something that is easier for people to grok would be just showing how to use permit in ERC2612 / DAI? That is something that you'll encounter more frequently!

i.e. show that instead of doing approve-> function that calls transferFrom you can do permit off-chain and then function that calls transferFrom including the v,r,s or the signature?

On the code pattern:

Can you replace DSTest with forge-std/Test? Would let you remove the need to specify VM internal vm and instantiate it.

Also would recommend moving EIP_712_DOMAIN_SEPARATOR and SIGNED_TICKET_TYPEHASH into helper fns / state vars?

some helper fns which make it clearer:
https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/cryptography/ECDSA.sol#L228
https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/cryptography/draft-EIP712.sol#L53-L103

[kulkarohan]

hmmm yeah agreed. i'll update

[gigamesh]

Sorry to jump in on this thread but something I've been trying to figure out is how to use forge to test a signed message that is provided to the function as a single string:
https://github.com/soundxyz/protocol/blob/63f5219dca6e91ef27e2922c96473dfacaccb400/contracts/ArtistV4.sol#L450

Is there a way to convert the v, r, s returned from vm.sign() into a bytes signature?

For context, the way I'm creating the signature off chain is with ethers.js's wallet._signTypedData

[kulkarohan]

hey @gigamesh! bytes signature = abi.encodePacked(r, s, v) should do the trick

[gigamesh]

ah ok super easy - thank you!

[kulkarohan]

@gakonst @onbjerg sorry for the absurd delay on this. let me know if any further changes are desired and i'll update ASAP!!

[onbjerg]

LGTM, let's iterate on it if needed :)