[SPARK-30688][SQL] Week based dates not being parsed with TimestampFormatter

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

@@ -68,6 +68,17 @@ private object DateTimeFormatterHelper {
     new DateTimeFormatterBuilder().parseCaseInsensitive()
   }
 
+  def toWeekBasedFormatter(builder: DateTimeFormatterBuilder, locale: Locale): DateTimeFormatter = {
+    builder
+      .parseDefaulting(ChronoField.ERA, 1)
+      .parseDefaulting(ChronoField.DAY_OF_WEEK, 1)
+      .parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
+      .parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0)
+      .toFormatter(locale)
+      .withChronology(IsoChronology.INSTANCE)
+      .withResolverStyle(ResolverStyle.STRICT)
+  }
+
   def toFormatter(builder: DateTimeFormatterBuilder, locale: Locale): DateTimeFormatter = {
     builder
       .parseDefaulting(ChronoField.ERA, 1)
@@ -80,9 +91,20 @@ private object DateTimeFormatterHelper {
       .withResolverStyle(ResolverStyle.STRICT)
   }
 
+  def isWeekBasedPattern(pattern: String): Boolean = {
+    Seq("YY", "w").exists(pattern.contains)
+  }
+
   def buildFormatter(pattern: String, locale: Locale): DateTimeFormatter = {
     val builder = createBuilder().appendPattern(pattern)
-    toFormatter(builder, locale)
+    // Default values for parser needs to be changed when the pattern
+    // is week/year based.
+    // DAY_OF_MONTH and MONTH_OF_YEAR will be added by the week of the year.
+    if (isWeekBasedPattern(pattern)) {
+      toWeekBasedFormatter(builder, locale)
+    } else {
+      toFormatter(builder, locale)
+    }
   }
 
   lazy val fractionFormatter: DateTimeFormatter = {

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/DateExpressionsSuite.scala

@@ -811,6 +811,7 @@ class DateExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper {
     val fmt3 = "yy-MM-dd"
     val sdf3 = new SimpleDateFormat(fmt3, Locale.US)
     sdf3.setTimeZone(TimeZoneGMT)
+    val fmt4 = "YYYY-ww"
 
     withDefaultTimeZone(TimeZoneGMT) {
       for (tz <- Seq(TimeZoneGMT, TimeZonePST, TimeZoneJST)) {
@@ -853,6 +854,14 @@ class DateExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper {
           MILLISECONDS.toSeconds(DateTimeUtils.daysToMillis(DateTimeUtils.fromJavaDate(date1), tz)))
         checkEvaluation(
           ToUnixTimestamp(Literal("2015-07-24"), Literal("not a valid format"), timeZoneId), null)
+        val expectedResults = Map(
+          TimeZoneGMT -> 1580688000L,
+          TimeZoneJST -> (1580688000L - 32400L),
+          TimeZonePST -> (1580688000L + 28800L))
+        // Sixth week from 2020 is: Monday, February 3, 2020 0:00:00 GMT: 1580688000
+        checkEvaluation(
+          ToUnixTimestamp(Literal("2020-06"), Literal(fmt4), timeZoneId),
+          expectedResults.get(tz).head)
 
         // SPARK-28072 The codegen path for non-literal input should also work
         checkEvaluation(