Detect SystemTime overflow in debug mode

[dtolnay]

use std::time::{Duration, UNIX_EPOCH};
use std::u64;

fn main() {
    let t = UNIX_EPOCH + Duration::new(u64::MAX, 0) + Duration::new(2, 0);
    println!("{}", t.duration_since(UNIX_EPOCH).unwrap().as_secs()); // 1
}

For me (Linux + Rust 1.19.0-nightly) this program prints 1. In debug mode I would expect this overflow to be caught and panic, similar to u64::MAX + 2.

[cuviper]

There are explicit checks regardless of debug mode, but the overflow occurs silently when add_duration first converts your u64::MAX to i64. So it basically sees the signed addition UNIX_EPOCH + (-1) + 2 = 1.

Your example starting with i64::MAX instead does panic, "overflow when adding duration to time".