SERVER-55224 Fix $dateDiff for timezones with non-whole hour Daylight Savings Time UTC offset changes for minute and second units

2 files changed, 111 insertions, 13 deletions

diff --git a/src/mongo/db/query/datetime/date_time_support.cpp b/src/mongo/db/query/datetime/date_time_support.cpp
index a78715d96cf..fb38063b0af 100644
--- a/src/mongo/db/query/datetime/date_time_support.cpp
+++ b/src/mongo/db/query/datetime/date_time_support.cpp
@@ -644,15 +644,29 @@ inline long long daysBetweenYears(long startYear, long endYear) {
 
 /**
  * Determines a correction needed in number of hours when calculating passed hours between two time
- * instants 'startInstant' and 'endInstant' due to the Daylight Savings Time. Returns 0, if both
- * time instants 'startInstant' and 'endInstant' are either in Standard Time (ST) or in Daylight
- * Saving Time (DST); returns 1, if 'endInstant' is in ST and 'startInstant' is in DST and
- * 'endInstant' > 'startInstant' or 'endInstant' is in DST and 'startInstant' is in ST and
- * 'endInstant' < 'startInstant'; otherwise returns -1.
+ * instants 'startInstant' and 'endInstant' due to different UTC offsets.
  */
-inline long long dstCorrection(timelib_time* startInstant, timelib_time* endInstant) {
+inline long long utcOffsetCorrectionForHours(timelib_time* startInstant, timelib_time* endInstant) {
     return (startInstant->z - endInstant->z) / (kMinutesPerHour * kSecondsPerMinute);
 }
+
+/**
+ * Determines a correction needed in number of minutes when calculating passed minutes between two
+ * time instants 'startInstant' and 'endInstant' due to different UTC offsets.
+ */
+inline long long utcOffsetCorrectionForMinutes(timelib_time* startInstant,
+                                               timelib_time* endInstant) {
+    return (startInstant->z - endInstant->z) / kSecondsPerMinute;
+}
+
+/**
+ * Determines a correction needed in number of seconds when calculating passed seconds between two
+ * time instants 'startInstant' and 'endInstant' due to different UTC offsets.
+ */
+inline long long utcOffsetCorrectionForSeconds(timelib_time* startInstant,
+                                               timelib_time* endInstant) {
+    return startInstant->z - endInstant->z;
+}
 inline long long dateDiffYear(Date startInstant, Date endInstant) {
     return endInstant.year - startInstant.year;
 }
@@ -698,18 +712,27 @@ inline long long dateDiffWeek(Date startInstant, Date endInstant, DayOfWeek star
             dayOfWeek(endInstant, startOfWeek)) /
         kDaysPerWeek;
 }
+inline long long dateDiffHourWithoutUTCOffsetCorrection(timelib_time* startInstant,
+                                                        timelib_time* endInstant) {
+    return endInstant->h - startInstant->h + dateDiffDay(*startInstant, *endInstant) * kHoursPerDay;
+}
 inline long long dateDiffHour(timelib_time* startInstant, timelib_time* endInstant) {
-    return endInstant->h - startInstant->h +
-        dateDiffDay(*startInstant, *endInstant) * kHoursPerDay +
-        dstCorrection(startInstant, endInstant);
+    return dateDiffHourWithoutUTCOffsetCorrection(startInstant, endInstant) +
+        utcOffsetCorrectionForHours(startInstant, endInstant);
 }
-inline long long dateDiffMinute(timelib_time* startInstant, timelib_time* endInstant) {
+inline long long dateDiffMinuteWithoutUTCOffsetCorrection(timelib_time* startInstant,
+                                                          timelib_time* endInstant) {
     return endInstant->i - startInstant->i +
-        dateDiffHour(startInstant, endInstant) * kMinutesPerHour;
+        dateDiffHourWithoutUTCOffsetCorrection(startInstant, endInstant) * kMinutesPerHour;
+}
+inline long long dateDiffMinute(timelib_time* startInstant, timelib_time* endInstant) {
+    return dateDiffMinuteWithoutUTCOffsetCorrection(startInstant, endInstant) +
+        utcOffsetCorrectionForMinutes(startInstant, endInstant);
 }
 inline long long dateDiffSecond(timelib_time* startInstant, timelib_time* endInstant) {
     return endInstant->s - startInstant->s +
-        dateDiffMinute(startInstant, endInstant) * kSecondsPerMinute;
+        dateDiffMinuteWithoutUTCOffsetCorrection(startInstant, endInstant) * kSecondsPerMinute +
+        utcOffsetCorrectionForSeconds(startInstant, endInstant);
 }
 inline long long dateDiffMillisecond(Date_t startDate, Date_t endDate) {
     long long result;
diff --git a/src/mongo/db/query/datetime/date_time_support_test.cpp b/src/mongo/db/query/datetime/date_time_support_test.cpp
index 40a85150788..049b7fee220 100644
--- a/src/mongo/db/query/datetime/date_time_support_test.cpp
+++ b/src/mongo/db/query/datetime/date_time_support_test.cpp
@@ -1218,6 +1218,9 @@ const TimeZone kAustraliaSydneyTimeZone =
     kDefaultTimeZoneDatabase.getTimeZone("Australia/Sydney");  // UTC offset +11:00.
 const TimeZone kUTCMinus10TimeZone =
     kDefaultTimeZoneDatabase.getTimeZone("-10:00");  // UTC offset -10:00.
+const TimeZone kAustraliaLordHoweTimeZone =
+    kDefaultTimeZoneDatabase.getTimeZone("Australia/Lord_Howe");
+const TimeZone kEuropeMadridTimeZone = kDefaultTimeZoneDatabase.getTimeZone("Europe/Madrid");
 const std::vector<const TimeZone*> kTimezones{&kDefaultTimeZone,
                                               &kNewYorkTimeZone,
                                               &kAustraliaEuclaTimeZone,
@@ -1499,6 +1502,27 @@ TEST(DateDiff, Hour) {
                        kNewYorkTimeZone.createFromDateParts(2001, 1, 1, 1, 0, 0, 0),
                        TimeUnit::hour,
                        kNewYorkTimeZone));
+
+    // Tests with Australia/Lord_Howe time zone that has 00:30 hour Daylight Savings Time (DST) UTC
+    // offset change. 'startDate' and 'endDate' parameters span a transition from/to DST.
+    //
+    // Verify that even when the UTC offset change is 30 minutes on transition from DST to Standard
+    // Time, time difference in hours is based on the local time. In the test 1.5h of real time
+    // passes, but the returned difference is 1h.
+    ASSERT_EQ(1,
+              dateDiff(kAustraliaLordHoweTimeZone.createFromDateParts(2021, 4, 4, 1, 0, 0, 0),
+                       kAustraliaLordHoweTimeZone.createFromDateParts(2021, 4, 4, 2, 0, 0, 0),
+                       TimeUnit::hour,
+                       kAustraliaLordHoweTimeZone));
+
+    // Verify that even when the UTC offset change is 30 minutes on transition from Standard Time to
+    // DST, time difference in hours is based on the local time. In the test 1h of real time passes
+    // and the returned difference is 1h.
+    ASSERT_EQ(1,
+              dateDiff(kAustraliaLordHoweTimeZone.createFromDateParts(2021, 10, 3, 1, 0, 0, 0),
+                       kAustraliaLordHoweTimeZone.createFromDateParts(2021, 10, 3, 2, 30, 0, 0),
+                       TimeUnit::hour,
+                       kAustraliaLordHoweTimeZone));
 }
 
 // Verifies 'dateDiff()' with TimeUnit::minute.
@@ -1518,11 +1542,28 @@ TEST(DateDiff, Minute) {
                        kNewYorkTimeZone.createFromDateParts(2020, 11, 8, 1, 30, 59, 999),
                        TimeUnit::minute,
                        kNewYorkTimeZone));
-    ASSERT_EQ(234047495,
+    ASSERT_EQ(234047498,
               dateDiff(kNewYorkTimeZone.createFromDateParts(1585, 11, 8, 1, 55, 0, 0),
                        kNewYorkTimeZone.createFromDateParts(2030, 11, 8, 1, 30, 59, 999),
                        TimeUnit::minute,
                        kNewYorkTimeZone));
+
+    // Tests with Australia/Lord_Howe time zone that has 00:30 hour Daylight Savings Time (DST) UTC
+    // offset change. 'startDate' and 'endDate' parameters span a transition from/to DST.
+    ASSERT_EQ(90,
+              dateDiff(kAustraliaLordHoweTimeZone.createFromDateParts(
+                           2021, 4, 4, 1, 0, 0, 0),  // UTC 2021-04-03T14:00:00
+                       kAustraliaLordHoweTimeZone.createFromDateParts(
+                           2021, 4, 4, 2, 0, 0, 0),  // UTC 2021-04-03T15:30:00
+                       TimeUnit::minute,
+                       kAustraliaLordHoweTimeZone));
+    ASSERT_EQ(60,
+              dateDiff(kAustraliaLordHoweTimeZone.createFromDateParts(
+                           2021, 10, 3, 1, 0, 0, 0),  // UTC 2021-10-02T14:30:00
+                       kAustraliaLordHoweTimeZone.createFromDateParts(
+                           2021, 10, 3, 2, 30, 0, 0),  // UTC 2021-10-02T15:30:00
+                       TimeUnit::minute,
+                       kAustraliaLordHoweTimeZone));
 }
 
 // Verifies 'dateDiff()' with TimeUnit::second.
@@ -1547,6 +1588,40 @@ TEST(DateDiff, Second) {
                        kDefaultTimeZone.createFromDateParts(2020, 11, 10, 1, 30, 16, 0),
                        TimeUnit::second,
                        kNewYorkTimeZone));
+
+    // Verify that negative milliseconds from the Unix Epoch are properly handled.
+    ASSERT_EQ(2,
+              dateDiff(kDefaultTimeZone.createFromDateParts(1969, 12, 31, 23, 59, 59, 999),
+                       kDefaultTimeZone.createFromDateParts(1970, 1, 1, 0, 0, 1, 0),
+                       TimeUnit::second,
+                       kDefaultTimeZone));
+
+    // Tests with Australia/Lord_Howe time zone that has 00:30 hour Daylight Savings Time (DST) UTC
+    // offset change. 'startDate' and 'endDate' parameters span a transition from/to DST.
+    const int secondsPerMinute{60};
+    ASSERT_EQ(90 * secondsPerMinute,
+              dateDiff(kAustraliaLordHoweTimeZone.createFromDateParts(
+                           2021, 4, 4, 1, 0, 0, 0),  // UTC 2021-04-03T14:00:00
+                       kAustraliaLordHoweTimeZone.createFromDateParts(
+                           2021, 4, 4, 2, 0, 0, 0),  // UTC 2021-04-03T15:30:00
+                       TimeUnit::second,
+                       kAustraliaLordHoweTimeZone));
+    ASSERT_EQ(60 * secondsPerMinute,
+              dateDiff(kAustraliaLordHoweTimeZone.createFromDateParts(
+                           2021, 10, 3, 1, 0, 0, 0),  // UTC 2021-10-02T14:30:00
+                       kAustraliaLordHoweTimeZone.createFromDateParts(
+                           2021, 10, 3, 2, 30, 0, 0),  // UTC 2021-10-02T15:30:00
+                       TimeUnit::second,
+                       kAustraliaLordHoweTimeZone));
+
+    // Verify that UTC offset adjustments are properly accounted for when calculating the time
+    // difference. Time zone Europe/Madrid skips 0:14:44 hours at 1900-12-31 23:45:15 to change the
+    // timezone to UTC.
+    ASSERT_EQ(1,
+              dateDiff(kEuropeMadridTimeZone.createFromDateParts(1900, 12, 31, 23, 45, 15, 0),
+                       kEuropeMadridTimeZone.createFromDateParts(1901, 1, 1, 0, 0, 0, 0),
+                       TimeUnit::second,
+                       kEuropeMadridTimeZone));
 }
 
 // Verifies 'dateDiff()' with TimeUnit::millisecond.