Function try_read_variable 

fn try_read_variable<'a>(
    sql: &'a str,
    bytes: &[u8],
    i: usize,
) -> Option<(&'a str, VarKind, usize)>

Try to read a variable reference starting at position i (which must be :).

Returns (name, kind, end_position) or None if this isn’t a variable.