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Add offset-based fallback for local-zone abbreviation resolution

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* Fix a GitHub CI failure on a UTC-configured runner. Name-based resolution previously found no candidate, and abbreviationForDate returned no value.

* Add a fallback mechanism that uses the system's current UTC offset when a name match fails.

* Ensure correct abbreviation resolution, regardless of the zone name string that the runtime reports.
This commit is contained in:
David Richardson
2026-08-28 19:07:32 -06:00
parent c39f03823a
commit d717e07d5c
1 changed files with 21 additions and 8 deletions
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Foundation/CPTimeZone.j
+21 -8
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@@ -47,7 +47,7 @@ var abbreviationDictionary,
function abbreviationForDate(date)
{
// Strategy 1: ask Intl directly for the short time zone name (e.g. "PDT") of
// First, ask Intl directly for the short time zone name (e.g. "PDT") of
// the runtime's local zone, which correctly reflects DST for this date.
// Replaces the previous date.toString() parenthesis-scraping and
// long-name-to-acronym regex guessing, which broke for locales and
@@ -59,14 +59,13 @@ function abbreviationForDate(date)
if (tzPart && [abbreviationDictionary objectForKey:tzPart.value])
return tzPart.value;
} catch (e) {
// Intl API not supported, or it failed. Fall through to strategy 2.
// Intl API not supported, or it failed. Fall through to the next attempt.
}
// Strategy 2: if the short name Intl returned isn't one of our known
// abbreviations (e.g. it returned "GMT-04:00" for a zone with no common
// three/four-letter abbreviation), resolve the runtime's IANA zone and
// pick whichever known abbreviation for that zone matches the date's
// current UTC offset.
// If that short name isn't one of our known abbreviations (e.g. it
// returned "GMT-04:00" for a zone with no common three/four-letter
// abbreviation), resolve the runtime's IANA zone and pick whichever
// known abbreviation for that zone matches the date's current UTC offset.
try {
var ianaName = new Intl.DateTimeFormat().resolvedOptions().timeZone;
var currentOffset = -date.getTimezoneOffset(); // in minutes
@@ -94,8 +93,22 @@ function abbreviationForDate(date)
if (possibleAbbrs.length > 0) {
return possibleAbbrs[0];
}
// Neither attempt above found a match by name. Fall back to any
// known abbreviation whose stored offset matches the system's
// current UTC offset. Several abbreviations legitimately share an
// offset (GMT, UTC, and WET all correctly resolve to 0, for example),
// so this returns one of them rather than none.
var offsetKeys = [timeDifferenceFromUTC keyEnumerator],
offsetKey;
while (offsetKey = [offsetKeys nextObject]) {
if ([timeDifferenceFromUTC valueForKey:offsetKey] === currentOffset) {
return offsetKey;
}
}
} catch (e) {
// Intl API not supported, or it failed. We cannot proceed with this strategy.
// Intl API not supported, or it failed.
}
// Return nil if no valid abbreviation could be determined.