Function sp_trie::read_child_trie_first_descedant_value

pub fn read_child_trie_first_descedant_value<L: TrieConfiguration, DB>(
    keyspace: &[u8],
    db: &DB,
    root: &TrieHash<L>,
    key: &[u8],
    recorder: Option<&mut dyn TrieRecorder<TrieHash<L>>>,
    cache: Option<&mut dyn TrieCache<L::Codec>>
) -> Result<Option<MerkleValue<TrieHash<L>>>, Box<TrieError<L>>>where
    DB: HashDBRef<L::Hash, DBValue>,

Read the trie_db::MerkleValue of the node that is the closest descendant for the provided child key.