Function block_entity_providers 

pub fn block_entity_providers<T>(
    key: &CapabilityKey<T>,
    host: &dyn Host,
    at: BlockSide,
) -> Option<BlockEntityProviders<T>>
where
    T: 'static + ?Sized,

The providers mods registered for capability key and the type of the block entity at at, for the game’s own lookups (a hopper’s): none where no mod registered one, so a vanilla container’s lookup costs one table check and allocates nothing, and the game needn’t work out its own answer. BlockEntityProviders::ask then asks them.