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fix(date): NaN-revive setters seed from raw +0, not LocalTime(0) (#4927) #5055

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Merged
proggeramlug merged 1 commit into from
Jun 13, 2026
Merged

fix(date): NaN-revive setters seed from raw +0, not LocalTime(0) (#4927) #5055

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11 changes: 8 additions & 3 deletions crates/perry-runtime/src/date.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -876,7 +876,12 @@ pub extern "C" fn js_date_apply_setter(
if t.is_nan() && !is_full_year {
return f64::NAN;
}
let base = if t.is_nan() { 0.0 } else { t };
// #4927: a NaN time value is passed through to the rebuild AS NaN — its
// NaN branch seeds the spec's `t = +0` substitution from the RAW +0
// components (1970-01-01 00:00:00), per Date.prototype.setFullYear step 2,
// which skips LocalTime(t). Substituting 0.0 here ran the epoch through
// timestamp_to_local_components, so a CET process revived
// `new Date(NaN).setFullYear(2020)` to local 01:00 instead of 00:00.
// The leading component is required: an omitted call (`setHours()`) coerces
// `undefined` → NaN, so the leading slot is always `Some`.
let lead = Some(coerced.first().copied().unwrap_or(f64::NAN));
Expand All @@ -895,9 +900,9 @@ pub extern "C" fn js_date_apply_setter(
_ => return date_cell_store(date, f64::NAN),
};
if is_utc != 0 {
rebuild_with(date, base, year, month0, day, hour, minute, second, ms)
rebuild_with(date, t, year, month0, day, hour, minute, second, ms)
} else {
rebuild_local_with(date, base, year, month0, day, hour, minute, second, ms)
rebuild_local_with(date, t, year, month0, day, hour, minute, second, ms)
}
}

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