Function scan_block 

pub fn scan_block<P, AccountId, IvkTag, E>(
    params: &P,
    block: CompactBlock,
    scanning_keys: &ScanningKeys<AccountId, IvkTag>,
    spend_ids: &SpendIdentifiers<AccountId>,
    prior_block_metadata: Option<&BlockMetadata>,
    find_account_for_address: impl Fn(&TransparentAddress) -> Result<Option<(AccountId, Option<TransparentKeyScope>)>, E>,
) -> Result<ScannedBlock<AccountId>, ScanBlockError<E>>
where
    P: Parameters + Send + 'static,
    AccountId: Default + Eq + Hash + ConditionallySelectable + Send + Sync + 'static,
    IvkTag: Copy + Hash + Eq + Send + 'static,

Scans a CompactBlock with a set of ScanningKeys.

Returns a vector of WalletTxs decryptable by any of the given keys. If an output is decrypted by a full viewing key, the nullifiers of that output will also be computed.