fix: Date_add throws or produces wrong results when the result would …

…be nonexistent time in the time zone (facebookincubator#11845)

Summary:
Pull Request resolved: facebookincubator#11845

Date_add is computed on top of Unix timestamps (millis since epoch). When the unit being added is at least a
day, this calculation is done in the "local" time zone (the session time zone in the case of Timestamps and the
time zone associated with the value in the case of TImestampWithTimeZones). This local time is then converted
back to a system time.

When this calculation is done in a "local" time zone, the resulting local millis since epoch may not exist, e.g. in
U.S. time zones that respect daylight savings time, it may fall in the hour 2:00-3:00 am on the day when the
clocks move forward. In this case, date_add will throw an exception when this is done with Timestamps, and
return the next valid time (e.g. 3 am in the example above) when this is done with TimestampWithTimeZones.

To fix this I added a function correct_nonexistent_time to TimeZoneMap which can take a local timestamp and
adjust it by the difference between the to time zones (e.g. moves it forward an hour in the case of the example
above) and returns a timestamp that exists. This gets us behavior that is consistent with Presto Java.

Reviewed By: HeidiHan0000

Differential Revision: D67154813

fbshipit-source-id: eb56ee93ade8da29eeec2ecec3004f5fd7ac12fd

velox/functions/prestosql/DateTimeFunctions.h

@@ -1269,8 +1269,13 @@ struct DateAddFunction : public TimestampWithTimezoneSupport<T> {
         result = Timestamp(
             resultTimestamp.getSeconds() + offset, resultTimestamp.getNanos());
       } else {
-        resultTimestamp.toGMT(*sessionTimeZone_);
-        result = resultTimestamp;
+        result = Timestamp(
+            sessionTimeZone_
+                ->correct_nonexistent_time(
+                    std::chrono::seconds(resultTimestamp.getSeconds()))
+                .count(),
+            resultTimestamp.getNanos());
+        result.toGMT(*sessionTimeZone_);
       }
     } else {
       result = addToTimestamp(timestamp, unit, (int32_t)value);

velox/functions/prestosql/DateTimeImpl.h

@@ -268,6 +268,12 @@ FOLLY_ALWAYS_INLINE int64_t addToTimestampWithTimezone(
                                     .count());
       auto updatedTimeStamp =
           addToTimestamp(originalTimestamp, unit, (int32_t)value);
+      updatedTimeStamp = Timestamp(
+          timeZone
+              ->correct_nonexistent_time(
+                  std::chrono::seconds(updatedTimeStamp.getSeconds()))
+              .count(),
+          updatedTimeStamp.getNanos());
       finalSysMs =
           timeZone
               ->to_sys(

velox/functions/prestosql/tests/DateTimeFunctionsTest.cpp

@@ -2375,6 +2375,16 @@ TEST_F(DateTimeFunctionsTest, dateAddTimestamp) {
           "year",
           -2,
           Timestamp(1582970400, 500'999'999) /*2020-02-29 10:00:00.500*/));
+
+  // Test cases where the result would end up in the nonexistent gap between
+  // daylight savings time and standard time. 2023-03-12 02:30:00.000 does not
+  // exist in America/Los_Angeles since that hour is skipped.
+  EXPECT_EQ(
+      Timestamp(1678617000, 0), /*2023-03-12 03:30:00*/
+      dateAdd("day", 45, Timestamp(1674729000, 0) /*2023-01-26 02:30:00*/));
+  EXPECT_EQ(
+      Timestamp(1678617000, 0), /*2023-03-12 03:30:00*/
+      dateAdd("day", -45, Timestamp(1682501400, 0) /*2023-04-26 02:30:00*/));
 }
 
 TEST_F(DateTimeFunctionsTest, dateAddTimestampWithTimeZone) {
@@ -2553,6 +2563,17 @@ TEST_F(DateTimeFunctionsTest, dateAddTimestampWithTimeZone) {
       "2023-03-11 00:00:00.000 America/Los_Angeles",
       dateAddAndCast(
           "year", -1, "2024-03-11 00:00:00.000 America/Los_Angeles"));
+
+  // Test cases where the result would end up in the nonexistent gap between
+  // daylight savings time and standard time. 2023-03-12 02:30:00.000 does not
+  // exist in America/Los_Angeles since that hour is skipped.
+  EXPECT_EQ(
+      "2023-03-12 03:30:00.000 America/Los_Angeles",
+      dateAddAndCast("day", 45, "2023-01-26 02:30:00.000 America/Los_Angeles"));
+  EXPECT_EQ(
+      "2023-03-12 03:30:00.000 America/Los_Angeles",
+      dateAddAndCast(
+          "day", -45, "2023-04-26 02:30:00.000 America/Los_Angeles"));
 }
 
 TEST_F(DateTimeFunctionsTest, dateDiffDate) {

velox/type/tz/TimeZoneMap.cpp

@@ -445,6 +445,24 @@ TimeZone::milliseconds TimeZone::to_local(
   return toLocalImpl(timestamp, tz_, offset_);
 }
 
+TimeZone::seconds TimeZone::correct_nonexistent_time(
+    TimeZone::seconds timestamp) const {
+  // If this is an offset time zone.
+  if (tz_ == nullptr) {
+    return timestamp;
+  }
+
+  const auto localInfo = tz_->get_info(date::local_time<seconds>{timestamp});
+
+  if (localInfo.result != date::local_info::nonexistent) {
+    return timestamp;
+  }
+
+  const auto adjustment = localInfo.second.offset - localInfo.first.offset;
+
+  return timestamp + adjustment;
+}
+
 std::string TimeZone::getShortName(
     TimeZone::milliseconds timestamp,
     TimeZone::TChoose choose) const {

velox/type/tz/TimeZoneMap.h

@@ -143,6 +143,14 @@ class TimeZone {
   seconds to_local(seconds timestamp) const;
   milliseconds to_local(milliseconds timestamp) const;
 
+  /// If a local time is nonexistent, i.e. refers to a time that exists in the
+  /// gap during a time zone conversion, this returns the time adjusted by
+  /// the difference between the two time zones, so that it lies in the later
+  /// time zone.
+  ///
+  /// If the local time exists then the same time is returned.
+  seconds correct_nonexistent_time(seconds timestamp) const;
+
   const std::string& name() const {
     return timeZoneName_;
   }