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fix(timezone): resolve the abbreviation via java.util, not java.time

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The abbreviation came from java.time's "zzz" formatter, which on Android
has no short specific-zone names and silently degrades every zone to a
"GMT-4" form — so on device New York showed "GMT-04:00" instead of "EDT".
Desktop couldn't catch it: there "zzz" and java.util.TimeZone agree, and
that agreement is the whole trap.

Resolve through java.util.TimeZone.getDisplayName(inDst, SHORT, locale)
instead — ICU-backed, so it returns the real abbreviation on both Android
and the JVM. Zones with no named abbreviation still fall back to a GMT
form, which zoneDescriptor already collapses to a single token.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Jean-Luc Makiola
2026-07-19 11:01:25 +02:00
parent 01ac61185b
commit 629896b74d
1 changed files with 18 additions and 12 deletions
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30
app/src/main/java/de/jeanlucmakiola/calendula/domain/TimeZoneCatalog.kt
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@@ -3,8 +3,6 @@ package de.jeanlucmakiola.calendula.domain
import java.text.Normalizer
import java.time.Instant
import java.time.ZoneId
import java.time.ZonedDateTime
import java.time.format.DateTimeFormatter
import java.time.format.TextStyle
import java.util.Locale
@@ -35,16 +33,24 @@ data class TimeZoneOption(
val region: String get() = id.substringBeforeLast('/', missingDelimiterValue = "")
}
private fun optionFor(zone: ZoneId, locale: Locale, at: Instant) = TimeZoneOption(
id = zone.id,
displayName = zone.getDisplayName(TextStyle.FULL, locale),
// "zzz" resolves the DST-correct abbreviation at [at] (CET vs CEST); zones
// with no named abbreviation fall back to a "GMT+05:30" form, which is
// exactly what we'd want to show them as anyway.
shortName = ZonedDateTime.ofInstant(at, zone)
.format(DateTimeFormatter.ofPattern("zzz", locale)),
offsetMinutes = zone.rules.getOffset(at).totalSeconds / 60,
)
private fun optionFor(zone: ZoneId, locale: Locale, at: Instant): TimeZoneOption {
val offsetSeconds = zone.rules.getOffset(at).totalSeconds
return TimeZoneOption(
id = zone.id,
displayName = zone.getDisplayName(TextStyle.FULL, locale),
// The abbreviation ("EDT"/"CEST", DST-correct at [at]). Resolved through
// java.util.TimeZone, NOT java.time's "zzz" formatter: on Android the
// latter has no short specific-zone names and silently degrades every
// zone to a "GMT-4" form (it agrees with java.util only on desktop), so
// "zzz" cost us the real abbreviation on the one platform that ships.
// java.util is ICU-backed and returns the abbreviation on both. Zones
// with genuinely no named abbreviation still fall back to a GMT form,
// which is what we'd show anyway.
shortName = java.util.TimeZone.getTimeZone(zone.id)
.getDisplayName(zone.rules.isDaylightSavings(at), java.util.TimeZone.SHORT, locale),
offsetMinutes = offsetSeconds / 60,
)
}
/**
* Every zone the JVM knows, resolved at [at]. This is ~600 entries, so build it