[CI] Fix year of week formatting when using joda time

[ywangd]

Based on the joda-time documentation, the symbol for "year of the week" is x as opposed to Y (used by java's DateTimeFormatter). This PR fixes the test code to use the correct date formatting symbol.

Resolves: #66907

[elasticmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[romseygeek]

I'm not sure this is the correct fix. Why is {now/M{YYYY.MM}} getting resolved to 2020.01 when we're in 2021?

[romseygeek]

OK, having read https://www.alexcorrigan.co.uk/blog/20191231-0644-javas-week-based-year-datetimeformatter/ I understand what the issue is - {now/M{YYYY.MM}} is resolving the week-based year as of the first of January, which falls in a week in which the Thursday is in 2020. I think this might be better fixed by changing the expression to be {now/M{yyyy.MM}} which looks like something a user might actually want to do?

[pgomulka]

This test is based on joda format (was possibly missed when migrating) and Y meant year of era in joda.
It should be changed to uuuu when using java.time

[pgomulka]

I'm not sure this is the correct fix. Why is {now/M{YYYY.MM}} getting resolved to 2020.01 when we're in 2021?

in week based calendar 01-03.01.2021 are still in 2020. The first week of 2021 starts on Monday 4th. This is because it requires first week to contain minimum 4 days in new year. Also Monday is the first day fo the week per ISO rule.
http://www.whatweekisit.org/

This is all because YYYY (week based year) was used instead of yyyy (year of era) or uuuu (year)

[ywangd]

This test is based on joda format (was possibly missed when migrating) and Y meant year of era in joda.
It should be changed to uuuu when using java.time

If the intention is to use "year-of-era", I can change the date-math-expression to use yyyy (year-of-era for java DateTimeFormmatter) instead of changing the assertion code, i.e. something like the follows:

@@ -115,7 +115,7 @@ public class DateMathExpressionResolverTests extends ESTestCase {

     public void testExpression_MixedArray() throws Exception {
         List<String> result = expressionResolver.resolve(context, Arrays.asList(
-                "name1", "<.marvel-{now/d}>", "name2", "<.logstash-{now/M{YYYY.MM}}>"
+                "name1", "<.marvel-{now/d}>", "name2", "<.logstash-{now/M{yyyy.MM}}>"
         ));
         assertThat(result.size(), equalTo(4));
         assertThat(result.get(0), equalTo("name1"));

Alternatively, we can change both date-math-expression and the assertion to use simply "year", i.e. uuuu for java DateTimeFormatter and yyyy for the assertion. Which one would you suggest that is closer to the actual intention?

[pgomulka]

@ywangd edit - you are right. it should be uuuu in the date math, and yyyy in assertion as the assertion is still using joda. We should migrate this test in another PR

[ywangd]

@ywangd edit - you are right. it should be uuuu in the date math, and yyyy in assertion as the assertion is still using joda. We should migrate this test in another PR

Thanks @pgomulka The PR is updated as discussed.

[pgomulka]

LGTM, thanks!