[SPARK-15613] [SQL] Fix incorrect days to millis conversion due to Daylight Saving Time

## What changes were proposed in this pull request?

Internally, we use Int to represent a date (the days since 1970-01-01), when we convert that into unix timestamp (milli-seconds since epoch in UTC), we get the offset of a timezone using local millis (the milli-seconds since 1970-01-01 in a timezone), but TimeZone.getOffset() expect unix timestamp, the result could be off by one hour (in Daylight Saving Time (DST) or not).

This PR change to use best effort approximate of posix timestamp to lookup the offset. In the event of changing of DST, Some time is not defined (for example, 2016-03-13 02:00:00 PST), or could lead to multiple valid result in UTC (for example, 2016-11-06 01:00:00), this best effort approximate should be enough in practice.

## How was this patch tested?

Added regression tests.

Author: Davies Liu <[email protected]>

Closes apache#13652 from davies/fix_timezone.

Author: Davies Liu

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala

@@ -100,8 +100,8 @@ object DateTimeUtils {
 
   // reverse of millisToDays
   def daysToMillis(days: SQLDate): Long = {
-    val millisUtc = days.toLong * MILLIS_PER_DAY
-    millisUtc - threadLocalLocalTimeZone.get().getOffset(millisUtc)
+    val millisLocal = days.toLong * MILLIS_PER_DAY
+    millisLocal - getOffsetFromLocalMillis(millisLocal, threadLocalLocalTimeZone.get())
   }
 
   def dateToString(days: SQLDate): String =
@@ -850,6 +850,41 @@ object DateTimeUtils {
     }
   }
 
+  /**
+   * Lookup the offset for given millis seconds since 1970-01-01 00:00:00 in given timezone.
+   */
+  private def getOffsetFromLocalMillis(millisLocal: Long, tz: TimeZone): Long = {
+    var guess = tz.getRawOffset
+    // the actual offset should be calculated based on milliseconds in UTC
+    val offset = tz.getOffset(millisLocal - guess)
+    if (offset != guess) {
+      guess = tz.getOffset(millisLocal - offset)
+      if (guess != offset) {
+        // fallback to do the reverse lookup using java.sql.Timestamp
+        // this should only happen near the start or end of DST
+        val days = Math.floor(millisLocal.toDouble / MILLIS_PER_DAY).toInt
+        val year = getYear(days)
+        val month = getMonth(days)
+        val day = getDayOfMonth(days)
+
+        var millisOfDay = (millisLocal % MILLIS_PER_DAY).toInt
+        if (millisOfDay < 0) {
+          millisOfDay += MILLIS_PER_DAY.toInt
+        }
+        val seconds = (millisOfDay / 1000L).toInt
+        val hh = seconds / 3600
+        val mm = seconds / 60 % 60
+        val ss = seconds % 60
+        val nano = millisOfDay % 1000 * 1000000
+
+        // create a Timestamp to get the unix timestamp (in UTC)
+        val timestamp = new Timestamp(year - 1900, month - 1, day, hh, mm, ss, nano)
+        guess = (millisLocal - timestamp.getTime).toInt
+      }
+    }
+    guess
+  }
+
   /**
    * Returns a timestamp of given timezone from utc timestamp, with the same string
    * representation in their timezone.
@@ -866,7 +901,17 @@ object DateTimeUtils {
    */
   def toUTCTime(time: SQLTimestamp, timeZone: String): SQLTimestamp = {
     val tz = TimeZone.getTimeZone(timeZone)
-    val offset = tz.getOffset(time / 1000L)
+    val offset = getOffsetFromLocalMillis(time / 1000L, tz)
     time - offset * 1000L
   }
+
+  /**
+   * Re-initialize the current thread's thread locals. Exposed for testing.
+   */
+  private[util] def resetThreadLocals(): Unit = {
+    threadLocalGmtCalendar.remove()
+    threadLocalLocalTimeZone.remove()
+    threadLocalTimestampFormat.remove()
+    threadLocalDateFormat.remove()
+  }
 }

sql/catalyst/src/main/scala/org/apache/spark/sql/types/DateType.scala

@@ -30,7 +30,7 @@ import org.apache.spark.sql.catalyst.ScalaReflectionLock
  *
  * Please use the singleton [[DataTypes.DateType]].
  *
- * Internally, this is represented as the number of days from epoch (1970-01-01 00:00:00 UTC).
+ * Internally, this is represented as the number of days from 1970-01-01.
  */
 @DeveloperApi
 class DateType private() extends AtomicType {

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/DateTimeTestUtils.scala

@@ -0,0 +1,40 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.util
+
+import java.util.TimeZone
+
+/**
+ * Helper functions for testing date and time functionality.
+ */
+object DateTimeTestUtils {
+
+  val ALL_TIMEZONES: Seq[TimeZone] = TimeZone.getAvailableIDs.toSeq.map(TimeZone.getTimeZone)
+
+  def withDefaultTimeZone[T](newDefaultTimeZone: TimeZone)(block: => T): T = {
+    val originalDefaultTimeZone = TimeZone.getDefault
+    try {
+      DateTimeUtils.resetThreadLocals()
+      TimeZone.setDefault(newDefaultTimeZone)
+      block
+    } finally {
+      TimeZone.setDefault(originalDefaultTimeZone)
+      DateTimeUtils.resetThreadLocals()
+    }
+  }
+}

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/DateTimeUtilsSuite.scala

@@ -492,6 +492,13 @@ class DateTimeUtilsSuite extends SparkFunSuite {
     test("2011-12-25 09:00:00.123456", "JST", "2011-12-25 18:00:00.123456")
     test("2011-12-25 09:00:00.123456", "PST", "2011-12-25 01:00:00.123456")
     test("2011-12-25 09:00:00.123456", "Asia/Shanghai", "2011-12-25 17:00:00.123456")
+
+    // Daylight Saving Time
+    test("2016-03-13 09:59:59.0", "PST", "2016-03-13 01:59:59.0")
+    test("2016-03-13 10:00:00.0", "PST", "2016-03-13 03:00:00.0")
+    test("2016-11-06 08:59:59.0", "PST", "2016-11-06 01:59:59.0")
+    test("2016-11-06 09:00:00.0", "PST", "2016-11-06 01:00:00.0")
+    test("2016-11-06 10:00:00.0", "PST", "2016-11-06 02:00:00.0")
   }
 
   test("to UTC timestamp") {
@@ -503,5 +510,38 @@ class DateTimeUtilsSuite extends SparkFunSuite {
     test("2011-12-25 18:00:00.123456", "JST", "2011-12-25 09:00:00.123456")
     test("2011-12-25 01:00:00.123456", "PST", "2011-12-25 09:00:00.123456")
     test("2011-12-25 17:00:00.123456", "Asia/Shanghai", "2011-12-25 09:00:00.123456")
+
+    // Daylight Saving Time
+    test("2016-03-13 01:59:59", "PST", "2016-03-13 09:59:59.0")
+    // 2016-03-13 02:00:00 PST does not exists
+    test("2016-03-13 02:00:00", "PST", "2016-03-13 10:00:00.0")
+    test("2016-03-13 03:00:00", "PST", "2016-03-13 10:00:00.0")
+    test("2016-11-06 00:59:59", "PST", "2016-11-06 07:59:59.0")
+    // 2016-11-06 01:00:00 PST could be 2016-11-06 08:00:00 UTC or 2016-11-06 09:00:00 UTC
+    test("2016-11-06 01:00:00", "PST", "2016-11-06 09:00:00.0")
+    test("2016-11-06 01:59:59", "PST", "2016-11-06 09:59:59.0")
+    test("2016-11-06 02:00:00", "PST", "2016-11-06 10:00:00.0")
+  }
+
+  test("daysToMillis and millisToDays") {
+    // There are some days are skipped entirely in some timezone, skip them here.
+    val skipped_days = Map[String, Int](
+      "Kwajalein" -> 8632,
+      "Pacific/Apia" -> 15338,
+      "Pacific/Enderbury" -> 9131,
+      "Pacific/Fakaofo" -> 15338,
+      "Pacific/Kiritimati" -> 9131,
+      "Pacific/Kwajalein" -> 8632,
+      "MIT" -> 15338)
+    for (tz <- DateTimeTestUtils.ALL_TIMEZONES) {
+      DateTimeTestUtils.withDefaultTimeZone(tz) {
+        val skipped = skipped_days.getOrElse(tz.getID, Int.MinValue)
+        (-20000 to 20000).foreach { d =>
+          if (d != skipped) {
+            assert(millisToDays(daysToMillis(d)) === d)
+          }
+        }
+      }
+    }
   }
 }