On empty blocks, who is paying timestamp fees?

Question

On empty blocks you can see such transactions where paysFee: Yes. What does it mean though? Who is paying the fees for the timestamp module?

Answer 1

timestamp.set is an unsigned extrinsic:

pub fn set(origin: OriginFor<T>, #[pallet::compact] now: T::Moment) -> DispatchResult {
    ensure_none(origin)?;
    ...
}

So even though the UI reports paysFee: Yes, there is actually no fee being taken:

You can see some of that logic being represented here:

/// Query the detailed fee of a given `call`.
pub fn query_fee_details<Extrinsic: sp_runtime::traits::Extrinsic + GetDispatchInfo>(
    unchecked_extrinsic: Extrinsic,
    len: u32,
) -> FeeDetails<BalanceOf<T>>
where
    T::Call: Dispatchable<Info = DispatchInfo>,
{
    let dispatch_info = <Extrinsic as GetDispatchInfo>::get_dispatch_info(&unchecked_extrinsic);

    let tip = 0u32.into();

    if unchecked_extrinsic.is_signed().unwrap_or(false) {
        Self::compute_fee_details(len, &dispatch_info, tip)
    } else {
        // Unsigned extrinsics have no inclusion fee.
        FeeDetails { inclusion_fee: None, tip }
    }
}