This library provides some useful functions to deal with years.
let year = 2020;
let month = 2;
let leap_year = year_helper::is_leap_year(year);
let days_in_month = year_helper::get_days_in_month(year, month);
let days_in_year = year_helper::get_days_in_year(year);
// or use the following functions if the year has been determined whether it is a leap year
let days_in_month = year_helper::get_days_in_month_2(leap_year, month);
let days_in_year = year_helper::get_days_in_year_2(leap_year);