Editorial: Avoid dividing by zero in ZonedDateTime#round.

Ref. #1502.
tc39 · Jun 28, 2021 · cd616a1 · cd616a1
1 parent 0e24fd3
commit cd616a1
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diff --git a/polyfill/lib/zoneddatetime.mjs b/polyfill/lib/zoneddatetime.mjs
@@ -644,6 +644,9 @@ export class ZonedDateTime {
  const instantStart = ES.BuiltinTimeZoneGetInstantFor(timeZone, dtStart, 'compatible');
  const endNs = ES.AddZonedDateTime(instantStart, timeZone, calendar, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0);
  const dayLengthNs = endNs.subtract(GetSlot(instantStart, EPOCHNANOSECONDS));
+ if (dayLengthNs.isZero()) {
+ throw new RangeError('can not round a ZonedDateTime in a calendar with zero-length days');
+ }
  ({ year, month, day, hour, minute, second, millisecond, microsecond, nanosecond } = ES.RoundISODateTime(
  year,
  month,

diff --git a/polyfill/test/ZonedDateTime/prototype/round/div-zero.js b/polyfill/test/ZonedDateTime/prototype/round/div-zero.js
@@ -0,0 +1,23 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.round
+features: [Temporal]
+---*/
+
+class Calendar extends Temporal.Calendar {
+ constructor() {
+ super("iso8601")
+ }
+ dateAdd(d) {
+ return d;
+ }
+};
+
+const zdt = new Temporal.ZonedDateTime(0n, "UTC", new Calendar());
+
+const units = ["day", "hour", "minute", "second", "millisecond", "microsecond", "nanosecond"];
+for (const smallestUnit of units) {
+ assert.throws(RangeError, () => zdt.round({ smallestUnit }));
+}
diff --git a/spec/zoneddatetime.html b/spec/zoneddatetime.html
@@ -789,6 +789,8 @@ <h1>Temporal.ZonedDateTime.prototype.round ( _options_ )</h1>
  1. Let _startNs_ be _instantStart_.[[Nanoseconds]].
  1. Let _endNs_ be ? AddZonedDateTime(_startNs_, _timeZone_, _zonedDateTime_.[[Calendar]], 0, 0, 0, 1, 0, 0, 0, 0, 0, 0).
  1. Let _dayLengthNs_ be _endNs_ − _startNs_.
+ 1. If _dayLengthNs_ is 0, then
+ 1. Throw a *RangeError* exception.
  1. Let _roundResult_ be ? RoundISODateTime(_temporalDateTime_.[[ISOYear]], _temporalDateTime_.[[ISOMonth]], _temporalDateTime_.[[ISODay]], _temporalDateTime_.[[ISOHour]], _temporalDateTime_.[[ISOMinute]], _temporalDateTime_.[[ISOSecond]], _temporalDateTime_.[[ISOMillisecond]], _temporalDateTime_.[[ISOMicrosecond]], _temporalDateTime_.[[ISONanosecond]], _roundingIncrement_, _smallestUnit_, _roundingMode_, _dayLengthNs_).
  1. Let _offsetNanoseconds_ be ? GetOffsetNanosecondsFor(_timeZone_, _instant_).
  1. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_roundResult_.[[Year]], _roundResult_.[[Month]], _roundResult_.[[Day]], _roundResult_.[[Hour]], _roundResult_.[[Minute]], _roundResult_.[[Second]], _roundResult_.[[Millisecond]], _roundResult_.[[Microsecond]], _roundResult_.[[Nanosecond]], _offsetNanoseconds_, _timeZone_, *"compatible"*, *"prefer"*).