Use ISO standard for week of week based year

[pgomulka]

In java.time week of weekbased year is depending on Locale. The locale we use is ROOT, and it does not define the start of the week.
Therefore start of the week can be either Sunday or Monday.
ISO 8601 defines start of the week as Monday, and that standard was used in Joda for week of week based year.
This would fail because of that change.
2019-21 (ok joda) vs 2019-22 (java)

 ZonedDateTime now = LocalDateTime.of(2019,5,26,1,32,8,328402)
                                         .atZone(ZoneOffset.UTC);
        DateFormatter jodaFormatter = Joda.forPattern("xxxx-ww").withLocale(Locale.ROOT).withZone(ZoneOffset.UTC);
        DateFormatter javaFormatter = DateFormatter.forPattern("8YYYY-ww").withLocale(Locale.ROOT).withZone(ZoneOffset.UTC);
        assertThat(jodaFormatter.format(now), equalTo(javaFormatter.format(now)));

[elasticmachine]

Pinging @elastic/es-core-infra

[pgomulka]

This behaviour is described in jdk javadoc

    w       1      append special localized WeekFields element for numeric week-of-year

It mentioned that this is localized. The code that is responisble for this is here:

1 = {StackTraceElement@4560} "java.base/java.time.temporal.WeekFields.of(WeekFields.java:299)"
2 = {StackTraceElement@4561} "java.base/java.time.format.DateTimeFormatterBuilder$WeekBasedFieldPrinterParser.printerParser(DateTimeFormatterBuilder.java:4882)"
3 = {StackTraceElement@4562} "java.base/java.time.format.DateTimeFormatterBuilder$WeekBasedFieldPrinterParser.format(DateTimeFormatterBuilder.java:4866)"
4 = {StackTraceElement@4563} "java.base/java.time.format.DateTimeFormatterBuilder$CompositePrinterParser.format(DateTimeFormatterBuilder.java:2345)"
5 = {StackTraceElement@4564} "java.base/java.time.format.DateTimeFormatter.formatTo(DateTimeFormatter.java:1846)"
6 = {StackTraceElement@4565} "java.base/java.time.format.DateTimeFormatter.format(DateTimeFormatter.java:1820)"
7 = {StackTraceElement@4566} 

[pgomulka]

raising this for the record. Will update known issues
related to this bug #41670 and fixed in v7.6+ PR fix #48349
affecting 6.8 - 7.5

week based dates like 2020-01 were not correctly translated to a long epoch value and throwing an exception. Week based values should be defaulted to start of the week.
reproduce

curl --request PUT \
  --url http://localhost:9200/test \
  --header 'authorization: Basic ZWxhc3RpYzpwYXNzd29yZA==' \
  --header 'content-type: application/json' \
  --data '{
	"mappings" :{

			"properties": {
				"timestamp": {
					"type": "date",
						"format":"YYYY-ww",
					"store": true
					}
			}
		}

}'

curl --request POST \
  --url http://localhost:9200/test/_doc \
  --header 'authorization: Basic ZWxhc3RpYzpwYXNzd29yZA==' \
  --header 'content-type: application/json' \
  --data '{
	"timestamp": "2020-33"
	
}'

results in

{
  "error": {
    "root_cause": [
      {
        "type": "mapper_parsing_exception",
        "reason": "failed to parse field [timestamp] of type [date] in document with id 'Q9-p5XIBy0lAoBkyOJdN'"
      }
    ],
    "type": "mapper_parsing_exception",
    "reason": "failed to parse field [timestamp] of type [date] in document with id 'Q9-p5XIBy0lAoBkyOJdN'",
    "caused_by": {
      "type": "illegal_argument_exception",
      "reason": "temporal accessor [{WeekBasedYear[WeekFields[SUNDAY,1]]=2020, WeekOfWeekBasedYear[WeekFields[SUNDAY,1]]=33},ISO] cannot be converted to zoned date time"
    }
  },
  "status": 400
}

should not, and since 7.6 it returns fine.
then when searching

curl --request GET \
  --url http://localhost:9200/test/_search \
  --header 'authorization: Basic ZWxhc3RpYzpwYXNzd29yZA==' \
  --header 'content-type: application/json' \
  --data '{
	  "stored_fields": [ "timestamp" ] 

}'

correct

{
  "took": 4,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 1,
      "relation": "eq"
    },
    "max_score": 1.0,
    "hits": [
      {
        "_index": "test",
        "_type": "_doc",
        "_id": "1Pqe5XIB1L6riJIjbO85",
        "_score": 1.0,
        "fields": {
          "timestamp": [
            "2020-33"
          ]
        }
      }
    ]
  }
}