Test build #39109 has finished for PR 7806 at commit fc01f2d.

• This patch fails SparkR unit tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • case class DateAdd(startDate: Expression, days: Expression)
  • case class DateSub(startDate: Expression, days: Expression)
  • case class TimeAdd(start: Expression, interval: Expression)
  • case class TimeSub(start: Expression, interval: Expression)
  • case class AddMonths(startDate: Expression, numMonths: Expression)
  • case class MonthsBetween(date1: Expression, date2: Expression)

Test build #39135 has finished for PR 7806 at commit e8eb86f.

• This patch fails SparkR unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

Test build #39293 has finished for PR 7806 at commit 72600f7.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

Thanks @falaki -- LGTM. Merging this