Native (All): Fixes and new SharedImmutable annotations

Testing revealed that accessing even immutable fields concurrently
is not supported out-of-the-box and instead crashes the Kotlin
Native runtime.

Author: dkhalanskyjb

core/commonMain/src/DayOfWeek.kt

@@ -5,6 +5,8 @@
 
 package kotlinx.datetime
 
+import kotlin.native.concurrent.*
+
 public expect enum class DayOfWeek {
     MONDAY,
     TUESDAY,
@@ -17,6 +19,7 @@ public expect enum class DayOfWeek {
 
 public val DayOfWeek.number: Int get() = ordinal + 1
 
+@SharedImmutable
 private val allDaysOfWeek = DayOfWeek.values().asList()
 public fun DayOfWeek(number: Int): DayOfWeek {
     require(number in 1..7)

core/commonMain/src/Month.kt

@@ -5,6 +5,8 @@
 
 package kotlinx.datetime
 
+import kotlin.native.concurrent.*
+
 public expect enum class Month {
     JANUARY,
     FEBRUARY,
@@ -24,7 +26,9 @@ public expect enum class Month {
 
 public val Month.number: Int get() = ordinal + 1
 
+@SharedImmutable
 private val allMonths = Month.values().asList()
+
 public fun Month(number: Int): Month {
     require(number in 1..12)
     return allMonths[number - 1]

core/nativeMain/cinterop/cpp/cdate.cpp

@@ -32,6 +32,14 @@ static char * timezone_name(const T& zone)
 
 static const time_zone *zone_by_id(TZID id)
 {
+    /* The `date` library provides a linked list of `tzdb` objects. `get_tzdb()`
+       always returns the head of that list. For now, the list never changes:
+       a call to `reload_tzdb()` would be required to load the updated version
+       of the timezone database. We never do this because for now (with use of
+       `date`) this operation is not even present for the configuration that
+       uses the system timezone database. If we move to C++20 support for this,
+       it may be feasible to call `reload_tzdb()` and construct a more elaborate
+       ID scheme. */
     auto& tzdb = get_tzdb();
     try {
         return &tzdb.zones.at(id);

core/nativeMain/src/Instant.kt

@@ -25,8 +25,8 @@ public actual enum class DayOfWeek {
 }
 
 // org.threeten.bp.format.DateTimeFormatterBuilder.InstantPrinterParser#parse
-private val instantParser: Parser<Instant> =
-    localDateParser
+private val instantParser: Parser<Instant>
+    get() = localDateParser
         .chainIgnoring(concreteCharParser('T').or(concreteCharParser('t')))
         .chain(intParser(2, 2)) // hour
         .chainIgnoring(concreteCharParser(':'))

core/nativeMain/src/LocalDate.kt

@@ -42,7 +42,7 @@ public actual class LocalDate actual constructor(actual val year: Int, actual va
 
         // org.threeten.bp.LocalDate#toEpochDay
         internal fun ofEpochDay(epochDay: Long): LocalDate {
-            require(epochDay in -365243219162L..365241780471L)
+            require(epochDay >= -365243219162L && epochDay <= 365241780471L)
             var zeroDay: Long = epochDay + DAYS_0000_TO_1970
             // find the march-based year
             zeroDay -= 60 // adjust to 0000-03-01 so leap day is at end of four year cycle

core/nativeMain/src/Parser.kt

@@ -26,6 +26,7 @@ internal fun <T, S> Parser<T>.chainIgnoring(other: Parser<S>): Parser<T> =
 internal fun <T, S> Parser<T>.chainSkipping(other: Parser<S>): Parser<S> =
     chain(other).map { (_, s) -> s }
 
+@SharedImmutable
 internal val eofParser: Parser<Unit> = { str, pos ->
     if (str.length > pos) {
         throw ParseException("extraneous input", pos)

core/nativeMain/src/TimeZone.kt

@@ -18,28 +18,18 @@ public actual open class TimeZone internal constructor(val tzid: TZID, actual va
 
     private val asciiName = id.cstr
 
-    @ThreadLocal
     actual companion object {
 
-        private var systemTimeZoneCached: TimeZone? = null
-
-        actual val SYSTEM: TimeZone
-            get() {
-                val cached = systemTimeZoneCached
-                if (cached != null) {
-                    return cached
-                }
-                val systemTimeZone = memScoped {
-                    val tzid = alloc<TZIDVar>()
-                    val string = get_system_timezone(tzid.ptr) ?: throw RuntimeException("Failed to get the system timezone.")
-                    val kotlinString = string.toKString()
-                    free(string)
-                    TimeZone(tzid.value, kotlinString)
-                }
-                systemTimeZoneCached = systemTimeZone
-                return systemTimeZone
-            }
+        @SharedImmutable
+        actual val SYSTEM: TimeZone = memScoped {
+            val tzid = alloc<TZIDVar>()
+            val string = get_system_timezone(tzid.ptr) ?: throw RuntimeException("Failed to get the system timezone.")
+            val kotlinString = string.toKString()
+            free(string)
+            TimeZone(tzid.value, kotlinString)
+        }
 
+        @SharedImmutable
         actual val UTC: TimeZone = ZoneOffset.UTC
 
         // org.threeten.bp.ZoneId#of(java.lang.String)
@@ -140,6 +130,7 @@ public actual class ZoneOffset internal constructor(actual val totalSeconds: Int
 
     companion object {
         // org.threeten.bp.ZoneOffset#UTC
+        @SharedImmutable
         val UTC = ZoneOffset(0, "Z")
 
         // org.threeten.bp.ZoneOffset#of