[WIP][Android][CoreCLR] Filter legacy TimeZone IDs using ICU if tzlookup.xml isn't available

src/libraries/Common/src/Interop/Interop.TimeZoneInfo.cs

@@ -21,5 +21,8 @@ internal static unsafe partial ResultCode GetTimeZoneDisplayName(
 
         [LibraryImport(Libraries.GlobalizationNative, EntryPoint = "GlobalizationNative_IanaIdToWindowsId", StringMarshalling = StringMarshalling.Utf16)]
         internal static unsafe partial int IanaIdToWindowsId(string ianaId, char* windowsId, int windowsIdLength);
+
+        [LibraryImport(Libraries.GlobalizationNative, EntryPoint = "GlobalizationNative_GetCanonicalTimeZoneId", StringMarshalling = StringMarshalling.Utf16)]
+        internal static unsafe partial int GetCanonicalTimeZoneId(string timeZoneId, char* canonicalId, int canonicalIdLength);
     }
 }

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Unix.Android.cs

@@ -308,6 +308,23 @@ public AndroidTzData()
                 return tzLookupIDs;
             }
 
+            private static unsafe bool IsLegacyTimeZoneId(string timeZoneId)
+            {
+                const int TimeZoneIdLength = 64; // Arbitrarily large, to be safe.
+                char* buffer = stackalloc char[TimeZoneIdLength];
+
+                int canonicalIdLength = Interop.Globalization.GetCanonicalTimeZoneId(timeZoneId, buffer, TimeZoneIdLength);
+
+                if (canonicalIdLength <= 0)
+                {
+                    return false; // If we can't get canonical ID, assume it's not legacy
+
+                }
+
+                ReadOnlySpan<char> canonicalIdSpan = new ReadOnlySpan<char>(buffer, canonicalIdLength);
+                return !timeZoneId.AsSpan().SequenceEqual(canonicalIdSpan);
+            }
+
             [MemberNotNullWhen(true, nameof(_ids))]
             [MemberNotNullWhen(true, nameof(_byteOffsets))]
             [MemberNotNullWhen(true, nameof(_lengths))]
@@ -391,7 +408,13 @@ private void ReadIndex(string tzFileDir, Stream fs, int indexOffset, int dataOff
                     _ids[i] = id;
                     _lengths[i] = length;
                     if (tzLookupIDs != null)
+                    {
                         _isBackwards[i] = !tzLookupIDs.Contains(id);
+                    }
+                    else
+                    {
+                        _isBackwards[i] = IsLegacyTimeZoneId(id);
+                    }
 
                     if (length < 24) // Header Size
                     {

src/native/libs/System.Globalization.Native/pal_icushim_internal.h

@@ -95,6 +95,7 @@ extern ucol_safeClone_func ucol_safeClone_ptr;
     PER_FUNCTION_BLOCK(ucal_close, libicui18n, true) \
     PER_FUNCTION_BLOCK(ucal_get, libicui18n, true) \
     PER_FUNCTION_BLOCK(ucal_getAttribute, libicui18n, true) \
+    PER_FUNCTION_BLOCK(ucal_getCanonicalTimeZoneID, libicui18n, true) \
     PER_FUNCTION_BLOCK(ucal_getKeywordValuesForLocale, libicui18n, true) \
     PER_FUNCTION_BLOCK(ucal_getLimit, libicui18n, true) \
     PER_FUNCTION_BLOCK(ucal_getNow, libicui18n, true) \
@@ -232,6 +233,7 @@ FOR_ALL_ICU_FUNCTIONS
 #define ucal_close(...) ucal_close_ptr(__VA_ARGS__)
 #define ucal_get(...) ucal_get_ptr(__VA_ARGS__)
 #define ucal_getAttribute(...) ucal_getAttribute_ptr(__VA_ARGS__)
+#define ucal_getCanonicalTimeZoneID(...) ucal_getCanonicalTimeZoneID_ptr(__VA_ARGS__)
 #define ucal_getKeywordValuesForLocale(...) ucal_getKeywordValuesForLocale_ptr(__VA_ARGS__)
 #define ucal_getLimit(...) ucal_getLimit_ptr(__VA_ARGS__)
 #define ucal_getNow(...) ucal_getNow_ptr(__VA_ARGS__)

src/native/libs/System.Globalization.Native/pal_icushim_internal_android.h

@@ -448,6 +448,7 @@ void ucal_add(UCalendar * cal, UCalendarDateFields field, int32_t amount, UError
 void ucal_close(UCalendar * cal);
 int32_t ucal_get(const UCalendar * cal, UCalendarDateFields field, UErrorCode * status);
 int32_t ucal_getAttribute(const UCalendar * cal, UCalendarAttribute attr);
+int32_t ucal_getCanonicalTimeZoneID(const UChar * id, int32_t len, UChar * result, int32_t resultCapacity, UBool * isSystemID, UErrorCode * status);
 UEnumeration * ucal_getKeywordValuesForLocale(const char * key, const char * locale, UBool commonlyUsed, UErrorCode * status);
 int32_t ucal_getLimit(const UCalendar * cal, UCalendarDateFields field, UCalendarLimitType type, UErrorCode * status);
 UDate ucal_getNow(void);

src/native/libs/System.Globalization.Native/pal_timeZoneInfo.c

@@ -336,3 +336,21 @@ ResultCode GlobalizationNative_GetTimeZoneDisplayName(const UChar* localeName, c
 
     return GetResultCode(err);
 }
+
+/*
+Get the canonical timezone ID for a given timezone ID.
+*/
+int32_t GlobalizationNative_GetCanonicalTimeZoneId(const UChar* timeZoneId, UChar* canonicalId, int32_t canonicalIdLength)
+{
+    UErrorCode status = U_ZERO_ERROR;
+    UBool isSystemID = 0;
+
+    int32_t actualLength = ucal_getCanonicalTimeZoneID(timeZoneId, -1, canonicalId, canonicalIdLength, &isSystemID, &status);
+
+    if (U_SUCCESS(status))
+    {
+        return actualLength;
+    }
+
+    return 0;
+}

src/native/libs/System.Globalization.Native/pal_timeZoneInfo.h

@@ -23,6 +23,7 @@ typedef enum
 PALEXPORT int32_t GlobalizationNative_WindowsIdToIanaId(const UChar* windowsId, const char* region, UChar* ianaId, int32_t ianaIdLength);
 PALEXPORT int32_t GlobalizationNative_IanaIdToWindowsId(const UChar* ianaId, UChar* windowsId, int32_t windowsIdLength);
 PALEXPORT ResultCode GlobalizationNative_GetTimeZoneDisplayName(const UChar* localeName, const UChar* timeZoneId, TimeZoneDisplayNameType type, UChar* result, int32_t resultLength);
+PALEXPORT int32_t GlobalizationNative_GetCanonicalTimeZoneId(const UChar* timeZoneId, UChar* canonicalId, int32_t canonicalIdLength);
 #if defined(APPLE_HYBRID_GLOBALIZATION)
 PALEXPORT int32_t GlobalizationNative_GetTimeZoneDisplayNameNative(const uint16_t* localeName, int32_t lNameLength, const uint16_t* timeZoneId, int32_t timeZoneIdLength,
                                                                    TimeZoneDisplayNameType type, uint16_t* result, int32_t resultLength);