Find the next Friday from today in Rust

next_friday.rs

use chrono::{offset::Utc, Datelike, Duration}; // 0.4.19

fn main() {
    let today_naive = Utc::today()
        .naive_utc()
        .checked_add_signed(Duration::days(0))
        .unwrap();

    let num_days_from_monday = today_naive.weekday().num_days_from_monday();

    // Using an if ... block here avoids any signed arithmetic.
    let next_friday = if num_days_from_monday < 4 {
        today_naive
            .checked_add_signed(Duration::days((4 - num_days_from_monday) as _))
            .unwrap()
    } else {
        today_naive
            .checked_add_signed(Duration::days((11 - num_days_from_monday) as _))
            .unwrap()
    };

    println!("Today is {}, next Friday is {}", today_naive, next_friday,);
}

Bonus: if you want to return the current day if it is Friday, the if ... block needs to look like this:

if num_days_from_monday < 4 {
    today_naive
        .checked_add_signed(chrono::Duration::days((4 - num_days_from_monday) as _))
        .unwrap()
} else if 4 < num_days_from_monday {
    today_naive
        .checked_add_signed(chrono::Duration::days((11 - num_days_from_monday) as _))
        .unwrap()
} else {
    today_naive
}