c4626dd64d
- Add MIT LICENSE file - Expand .gitignore with standard Rust/Linux entries - Remove dangling symlinks (breadmancli, breadpadcli) and dev scratchpad (svgs.txt) from git tracking - Replace unsafe unwrap() calls with expect() in breadman CLI (guarded by prior filter)
63 lines
2.4 KiB
Rust
63 lines
2.4 KiB
Rust
use chrono::{DateTime, Duration, Local, LocalResult, NaiveDateTime, TimeZone, Utc};
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/// Resolve a naive *local* datetime to UTC without panicking on DST transitions.
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///
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/// `NaiveDateTime::and_local_timezone` (and `Local.from_local_datetime`) returns a
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/// `LocalResult`, which is not always `Single`:
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/// - `Single` — the normal case.
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/// - `Ambiguous` (a fall-back hour that occurs twice) — pick the earliest instant.
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/// - `None` (a spring-forward gap where the wall-clock time never happens) — advance
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/// an hour at a time until a valid instant is found, then fall back to treating the
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/// naive value as UTC.
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///
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/// Calling `.unwrap()` on the `None`/`Ambiguous` cases panics, which is what this helper
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/// exists to avoid (it bit us on the ~2 DST transition days per year).
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pub fn local_naive_to_utc(naive: NaiveDateTime) -> DateTime<Utc> {
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match Local.from_local_datetime(&naive) {
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LocalResult::Single(dt) => dt.with_timezone(&Utc),
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LocalResult::Ambiguous(earliest, _latest) => earliest.with_timezone(&Utc),
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LocalResult::None => {
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let mut shifted = naive;
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for _ in 0..3 {
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shifted += Duration::hours(1);
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if let LocalResult::Single(dt) = Local.from_local_datetime(&shifted) {
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return dt.with_timezone(&Utc);
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}
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}
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// Last resort: interpret the wall-clock value as UTC so we still return a time.
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Utc.from_utc_datetime(&naive)
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use chrono::NaiveDate;
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#[test]
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fn ordinary_time_round_trips() {
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let naive = NaiveDate::from_ymd_opt(2026, 6, 15)
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.unwrap()
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.and_hms_opt(9, 30, 0)
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.unwrap();
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let utc = local_naive_to_utc(naive);
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// Converting back to local should yield the same wall-clock time.
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let local: DateTime<Local> = utc.with_timezone(&Local);
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assert_eq!(local.naive_local(), naive);
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}
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#[test]
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fn never_panics_across_a_full_year_of_hours() {
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// Walk every hour of a year through the helper; it must never panic regardless
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// of the host timezone's DST rules.
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let mut dt = NaiveDate::from_ymd_opt(2026, 1, 1)
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.unwrap()
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.and_hms_opt(0, 0, 0)
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.unwrap();
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for _ in 0..(366 * 24) {
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let _ = local_naive_to_utc(dt);
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dt += Duration::hours(1);
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}
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}
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}
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