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Add warning about MappedLocalTime and wasm

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Warns about https://github.com/chronotope/chrono/issues/1701.
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Ohad Lutzky 2025-05-05 21:06:33 +01:00 committed by Dirkjan Ochtman
parent c5c22a357d
commit 3b4af71f0b
1 changed files with 20 additions and 0 deletions
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20
src/offset/mod.rs
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@ -46,6 +46,26 @@ pub use self::utc::Utc;
/// DST.
/// * No result when the clock is turned forwards during a transition due to for example DST.
///
/// <div class="warning">
///
/// In wasm, when using [`Local`], only the [`LocalResult::Single`] variant is returned.
/// Specifically:
///
/// * When the clock is turned backwards, where `Ambiguous(earliest, latest)` would be expected,
/// `Single(earliest)` is returned instead.
/// * When the clock is turned forwards, where `None` would be expected, `Single(t)` is returned,
/// with `t` being the requested local time represented as though there is no transition on that
/// day (i.e. still "summer time")
///
/// This is caused because of limitations in the JavaScript
/// [`Date`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date)
/// API, which always parses a local time as a single, valid time - even for an
/// input which describes a nonexistent or ambiguous time.
///
/// See further discussion and workarounds in <https://github.com/chronotope/chrono/issues/1701>.
///
/// </div>
///
/// When the clock is turned backwards it creates a _fold_ in local time, during which the local
/// time is _ambiguous_. When the clock is turned forwards it creates a _gap_ in local time, during
/// which the local time is _missing_, or does not exist.