dev: check that class exist before using it in BuildGenesisConfig

[tdelabro]

Problem

    #[pallet::genesis_build]
    impl<T: Config> BuildGenesisConfig for GenesisConfig<T> {
        fn build(&self) {
            <Pallet<T>>::store_block(0);
            frame_support::storage::unhashed::put::<StarknetStorageSchemaVersion>(
                PALLET_STARKNET_SCHEMA,
                &StarknetStorageSchemaVersion::V1,
            );

            for (class_hash, contract_class) in self.contract_classes.iter() {
                ContractClasses::<T>::insert(class_hash, contract_class);
            }

            for (sierra_class_hash, casm_class_hash) in self.sierra_to_casm_class_hash.iter() {
                CompiledClassHashes::<T>::insert(sierra_class_hash, CompiledClassHash(casm_class_hash.0));
            }

            for (address, class_hash) in self.contracts.iter() {
                ContractClassHashes::<T>::insert(address, class_hash);
            }

            for (key, value) in self.storage.iter() {
                StorageView::<T>::insert(key, value);
            }

            LastKnownEthBlock::<T>::set(None);
            // Set the fee token address from the genesis config.
            FeeTokenAddress::<T>::set(self.fee_token_address);
            SeqAddrUpdate::<T>::put(true);
        }
    }

Here we "declare" classes:

 for (class_hash, contract_class) in self.contract_classes.iter() {
        ContractClasses::<T>::insert(class_hash, contract_class);
}

Here we map them to their sierra

for (sierra_class_hash, casm_class_hash) in self.sierra_to_casm_class_hash.iter() {
       CompiledClassHashes::<T>::insert(sierra_class_hash, CompiledClassHash(casm_class_hash.0));
}

And here we "deploy" new contracts:

            for (address, class_hash) in self.contracts.iter() {
                ContractClassHashes::<T>::insert(address, class_hash);
            }

It would be nice for "declare", "map ot sierra" and "deploy" to make sure we are refering to ContractClass that actually exist. Meaning that have been stored in the first storage ContractClasses.

What to do?

Add those checks, panic if we are using a ClassHash which don't have been declared before in the first for loop

[kfastov]

I would like to take this

[tdelabro]

Rather than checking it is in the storage. You can check it is in the in-memory array. I will probably be a bit more efficient

[kfastov]

I've implemented it using ContractClasses::<T>::contains_key(class_hash), I am a bit worried about O(n^2) complexity in the case of array, not sure how storage lookup is implemented though. I will test this simple implementation compared to an in-memory array and choose the best option

[tdelabro]

I think the storage lookup is a kind of hashmap. Due to caching. So probably better performances.
Forget what I said

[tdelabro]

Hey, @kfastov, do you have an ETA for opening a PR? understood you were quite close

[kfastov]

Hey, sorry for delaying it so hard, will open PR tomorrow (Jan 21st)