I don't see a reason. force_set_code_hash will still do further checks and reject if the authorized code is incorrect.

Actually, do_force_set_current_code_update or force_set_current_code does not do any validations.
So the only validation is here "if code is authorized".

I have the only doubt here:

Open questions

* [ ]  Do we need something like `poke_authorized_code_hash`? E.g. in case that we authorize code hash, but nobody would apply it and the parachain starts working with old/other_new code? Is this possible?

Could use the feeless_if attribute.

Could use the feeless_if attribute.

I don't see much example of feeless_if, but iiuc it can do calculation just based on the inputs?
Or should I do something like:

#[pallet::feeless_if(|_: &OriginFor<T>, para: ParaId, validation_code: ValidationCode| -> bool {
            // check that the code was applied
            Self::current_code(para) == Some(validation_code.hash())
})]

But this way, we allow spamming the chain for free, because I cannot check Self::current_code(para) before and after.

because I cannot check Self::current_code(para) before and after.

What you mean by this?

If I understand correctly, the purpose of using feeless_if here was to allow free execution when the code is actually applied, essentially the same effect as the PostDispatchInfo hack at the end (which should be removed when using feeless_if):

let post = PostDispatchInfo {
    // Consume the rest of the block to prevent further transactions
    actual_weight: Some(T::BlockWeights::get().max_block),
    // No fee for a valid upgrade
    pays_fee: Pays::No,
};
Ok(post)

However, in this case, the PostDispatchInfo hack is applied after validations, when do_force_set_current_code_update is actually executed.

Is this really enough? Is it ok to access storage and calculate hash again inside feeless_if?

#[pallet::feeless_if(|_: &OriginFor<T>, para: ParaId, validation_code: ValidationCode| -> bool {
            // check that the code was applied
            Self::current_code(para) == Some(validation_code.hash())
})]

because I cannot check Self::current_code(para) before and after.

Forget about it, I'm probably overthinking. My idea was to check the result of the extrinsic inside #[pallet::feeless_if], something like (but that's not possible):

let code_before = Self::current_code(para);
.. wait extrinsic to do the job
let code_after = Self::current_code(para);

if code_before ! code_after {
   PaysFee::No
} else {
   PaysFee::Yes
}

In other words, I’m not sure how to properly use feeless_if here. 😅