Merge pull request #2762 from readdle/win-tz-daylight

[Windows] Fix TimeZone display name and daylight saving time check

Author: compnerd

CoreFoundation/NumberDate.subproj/CFTimeZone.c

@@ -1663,9 +1663,10 @@ CFStringRef CFTimeZoneCopyAbbreviation(CFTimeZoneRef tz, CFAbsoluteTime at) {
     }
     ucal_setMillis(ucal, (at + kCFAbsoluteTimeIntervalSince1970) * 1000.0, &status);
 
+    UCalendarDisplayNameType nameType = ucal_inDaylightTime(ucal, &status) ? UCAL_SHORT_DST : UCAL_SHORT_STANDARD;
     UChar buffer[64];
     int32_t length;
-    length = ucal_getTimeZoneDisplayName(ucal, UCAL_SHORT_STANDARD, "C", buffer, sizeof(buffer), &status);
+    length = ucal_getTimeZoneDisplayName(ucal, nameType, "C", buffer, sizeof(buffer), &status);
 
     ucal_close(ucal);
 
@@ -1678,10 +1679,22 @@ CFStringRef CFTimeZoneCopyAbbreviation(CFTimeZoneRef tz, CFAbsoluteTime at) {
 }
 
 Boolean CFTimeZoneIsDaylightSavingTime(CFTimeZoneRef tz, CFAbsoluteTime at) {
-    CFIndex idx;
     __CFGenericValidateType(tz, CFTimeZoneGetTypeID());
+#if TARGET_OS_WIN32
+    UErrorCode status = U_ZERO_ERROR;
+    UCalendar *ucal = __CFCalendarCreateUCalendar(NULL, CFSTR("C"), tz);
+    if (ucal == NULL) {
+      return FALSE;
+    }
+    ucal_setMillis(ucal, (at + kCFAbsoluteTimeIntervalSince1970) * 1000.0, &status);
+
+    UBool isDaylightTime = ucal_inDaylightTime(ucal, &status);
+    return isDaylightTime ? TRUE : FALSE;
+#else
+    CFIndex idx;
     idx = __CFBSearchTZPeriods(tz, at);
     return __CFTZPeriodIsDST(&(tz->_periods[idx]));
+#endif
 }
 
 CFTimeInterval CFTimeZoneGetDaylightSavingTimeOffset(CFTimeZoneRef tz, CFAbsoluteTime at) {

Tests/Foundation/Tests/TestTimeZone.swift

@@ -256,6 +256,16 @@ class TestTimeZone: XCTestCase {
         XCTAssertEqual(aest.nextDaylightSavingTimeTransition(after: dt2)?.description, "2018-10-06 16:00:00 +0000")
     }
 
+    func test_isDaylightSavingTime() throws {
+        let eukv = try XCTUnwrap(TimeZone(identifier: "Europe/Kiev"))
+        
+        let dateNoDST = Date(timeIntervalSince1970: 1585432800.0) // March 29, 2020
+        let dateDST = Date(timeIntervalSince1970: 1585515600.0) // March 30, 2020
+        
+        XCTAssertFalse(eukv.isDaylightSavingTime(for: dateNoDST))
+        XCTAssertTrue(eukv.isDaylightSavingTime(for: dateDST))
+    }
+
     static var allTests: [(String, (TestTimeZone) -> () throws -> Void)] {
         var tests: [(String, (TestTimeZone) -> () throws -> Void)] = [
             ("test_abbreviation", test_abbreviation),
@@ -275,6 +285,7 @@ class TestTimeZone: XCTestCase {
             ("test_systemTimeZoneName", test_systemTimeZoneName),
             ("test_autoupdatingTimeZone", test_autoupdatingTimeZone),
             ("test_nextDaylightSavingTimeTransition", test_nextDaylightSavingTimeTransition),
+            ("test_isDaylightSavingTime", test_isDaylightSavingTime),
         ]
 
         #if !os(Windows)