Attempt to extrapolate the earliest piece of historical data

Fixes #440
Kotlin · Jan 9, 2025 · 475c66a · 475c66a
1 parent 1e339e7
commit 475c66a
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Showing 2 changed files with 12 additions and 4 deletions.
diff --git a/core/windows/src/internal/TzdbInRegistry.kt b/core/windows/src/internal/TzdbInRegistry.kt
@@ -166,8 +166,11 @@ private fun HKEYVar.readHistoricDataFromRegistry(
     withRegistryKey(tzHKey, "Dynamic DST", { emptyList() }) { dynDstHKey ->
         val firstEntry = dwordBuffer.readValue(dynDstHKey, "FirstEntry")
         val lastEntry = dwordBuffer.readValue(dynDstHKey, "LastEntry")
-        (firstEntry..lastEntry).map { year ->
-            year to zoneRulesBuffer.readZoneRules(dynDstHKey, year.toString())
+        val registryData = (firstEntry..lastEntry).map { year ->
+            zoneRulesBuffer.readZoneRules(dynDstHKey, year.toString())
+        }
+        (1970..lastEntry).map { year ->
+            year to registryData[(year - firstEntry).coerceAtLeast(0)]
         }
     }
 

diff --git a/core/windows/test/TimeZoneRulesCompleteTest.kt b/core/windows/test/TimeZoneRulesCompleteTest.kt
@@ -95,7 +95,7 @@ class TimeZoneRulesCompleteTest {
                                 val firstTransitionYear = Instant.fromEpochSeconds(
                                     rules.transitionEpochSeconds.firstOrNull() ?: 0 // arbitrary time
                                 ).toLocalDateTime(TimeZone.UTC).year
-                                val yearsToCheck = ((firstTransitionYear - 15)..<firstTransitionYear) +
+                                val yearsToCheck = (maxOf(firstTransitionYear - 15, 1970)..<firstTransitionYear) +
                                         ((lastTransitionYear + 1)..(lastTransitionYear + 15))
                                 for (year in yearsToCheck) {
                                     val rulesForYear = rules.recurringZoneRules!!.rulesForYear(year)
@@ -184,8 +184,13 @@ private fun SYSTEMTIME.toLocalDateTime(): LocalDateTime =
     )
 
 private val strangeTimeZones = listOf(
+    // These report transitions in the future that are not in the registry:
     "Morocco Standard Time", "West Bank Standard Time", "Iran Standard Time", "Syria Standard Time",
-    "Paraguay Standard Time"
+    "Paraguay Standard Time",
+    // This one reports transitions on Jan 1st for years 1970..2003, but the registry contains transitions
+    // on the first Thursday of January.
+    // Neither of these is correct: https://en.wikipedia.org/wiki/Daylight_saving_time_in_Brazil
+    "Central Brazilian Standard Time"
 )
 
 private fun binarySearchInstant(instant1: Instant, instant2: Instant, predicate: (Instant) -> Boolean): Instant {