Gem::Specification#date=

# File tmp/rubies/ruby-3.0.5/lib/rubygems/specification.rb, line 1687
def date=(date)
  # We want to end up with a Time object with one-day resolution.
  # This is the cleanest, most-readable, faster-than-using-Date
  # way to do it.
  @date = case date
          when String then
            if DateTimeFormat =~ date
              Time.utc($1.to_i, $2.to_i, $3.to_i)
            else
              raise(Gem::InvalidSpecificationException,
                    "invalid date format in specification: #{date.inspect}")
            end
          when Time, DateLike then
            Time.utc(date.year, date.month, date.day)
          else
            TODAY
          end
end