How to fix broken trait bounds when instantiating a pallet?

Question

I'm trying to change pallet_assets to pallet_assets::<Instance1> in preparation for more pallet instances. Commit here and compilation error here.

The trouble seems to come from the HandleCredit impl, which assumes some pallet_assets::Config, but doesn't reference any instance. I don't understand what it would need to do with an instance; it should take the assets from any configured Assets pallet (even if there are many). How can I fix this?

/// A `HandleCredit` implementation that naively transfers the fees to the block author.
/// Will drop and burn the assets in case the transfer fails.
pub struct AssetsToBlockAuthor<R>(PhantomData<R>);
impl<R> HandleCredit<AccountIdOf<R>, pallet_assets::Pallet<R>> for AssetsToBlockAuthor<R>
where
    R: pallet_authorship::Config + pallet_assets::Config,
    AccountIdOf<R>:
        From<polkadot_primitives::v2::AccountId> + Into<polkadot_primitives::v2::AccountId>,
{
    fn handle_credit(credit: CreditOf<AccountIdOf<R>, pallet_assets::Pallet<R>>) {
        if let Some(author) = pallet_authorship::Pallet::<R>::author() {
            // In case of error: Will drop the result triggering the `OnDrop` of the imbalance.
            let _ = pallet_assets::Pallet::<R>::resolve(&author, credit);
        }
    }
}

Answer 1

This should solve your problem:

/// A `HandleCredit` implementation that naively transfers the fees to the block author.
/// Will drop and burn the assets in case the transfer fails.
pub struct AssetsToBlockAuthor<R, I = ()>(PhantomData<(R, I)>);
impl<R, I> HandleCredit<AccountIdOf<R>, pallet_assets::Pallet<R, I>> for AssetsToBlockAuthor<R>
where
    I: 'static,
    R: pallet_authorship::Config + pallet_assets::Config<I>,
    AccountIdOf<R>:
        From<polkadot_primitives::v2::AccountId> + Into<polkadot_primitives::v2::AccountId>,
{
    fn handle_credit(credit: CreditOf<AccountIdOf<R>, pallet_assets::Pallet<R, I>>) {
        if let Some(author) = pallet_authorship::Pallet::<R>::author() {
            // In case of error: Will drop the result triggering the `OnDrop` of the imbalance.
            let _ = pallet_assets::Pallet::<R, I>::resolve(&author, credit);
        }
    }
}