[7.x] [Java.time] Calculate week of a year with ISO rules BACKPORT(#48209) (#48349)

Reverting the change introducing IsoLocal.ROOT and introducing IsoCalendarDataProvider that defaults start of the week to Monday and requires minimum 4 days in first week of a year. This extension is using java SPI mechanism and defaults for Locale.ROOT only.
It require jvm property java.locale.providers to be set with SPI,COMPAT

closes #41670
backport #48209

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -842,6 +842,12 @@ class BuildPlugin implements Plugin<Project> {
                     if ((ext.get('runtimeJavaVersion') as JavaVersion) >= JavaVersion.VERSION_1_9) {
                         test.jvmArgs '--illegal-access=warn'
                     }
+                    //TODO remove once jvm.options are added to test system properties
+                    if ((ext.get('runtimeJavaVersion') as JavaVersion) == JavaVersion.VERSION_1_8) {
+                        test.systemProperty ('java.locale.providers','SPI,JRE')
+                    } else if ((ext.get('runtimeJavaVersion') as JavaVersion) >= JavaVersion.VERSION_1_9) {
+                        test.systemProperty ('java.locale.providers','SPI,COMPAT')
+                    }
                 }
 
                 test.jvmArgumentProviders.add(nonInputProperties)
@@ -876,6 +882,7 @@ class BuildPlugin implements Plugin<Project> {
                         'tests.security.manager': 'true',
                         'jna.nosys': 'true'
 
+
                 // ignore changing test seed when build is passed -Dignore.tests.seed for cacheability experimentation
                 if (System.getProperty('ignore.tests.seed') != null) {
                     nonInputProperties.systemProperty('tests.seed', project.property('testSeed'))

server/src/main/java/org/elasticsearch/common/time/DateFormatters.java

@@ -37,7 +37,6 @@ import java.time.format.SignStyle;
 import java.time.temporal.ChronoField;
 import java.time.temporal.IsoFields;
 import java.time.temporal.TemporalAccessor;
-import java.time.temporal.TemporalAdjusters;
 import java.time.temporal.TemporalQueries;
 import java.time.temporal.TemporalQuery;
 import java.time.temporal.WeekFields;
@@ -53,6 +52,7 @@ import static java.time.temporal.ChronoField.NANO_OF_SECOND;
 import static java.time.temporal.ChronoField.SECOND_OF_MINUTE;
 
 public class DateFormatters {
+    public static final WeekFields WEEK_FIELDS = WeekFields.of(DayOfWeek.MONDAY,4);
 
     private static final DateTimeFormatter TIME_ZONE_FORMATTER_NO_COLON = new DateTimeFormatterBuilder()
         .appendOffset("+HHmm", "Z")
@@ -946,14 +946,14 @@ public class DateFormatters {
      * Returns a formatter for a four digit weekyear
      */
     private static final DateFormatter STRICT_WEEKYEAR = new JavaDateFormatter("strict_weekyear", new DateTimeFormatterBuilder()
-        .appendValue(WeekFields.ISO.weekBasedYear(), 4, 10, SignStyle.EXCEEDS_PAD)
+        .appendValue(WEEK_FIELDS.weekBasedYear(), 4, 10, SignStyle.EXCEEDS_PAD)
         .toFormatter(Locale.ROOT)
         .withResolverStyle(ResolverStyle.STRICT));
 
     private static final DateTimeFormatter STRICT_WEEKYEAR_WEEK_FORMATTER = new DateTimeFormatterBuilder()
-        .appendValue(WeekFields.ISO.weekBasedYear(), 4, 10, SignStyle.EXCEEDS_PAD)
+        .appendValue(WEEK_FIELDS.weekBasedYear(), 4, 10, SignStyle.EXCEEDS_PAD)
         .appendLiteral("-W")
-        .appendValue(WeekFields.ISO.weekOfWeekBasedYear(), 2, 2, SignStyle.NOT_NEGATIVE)
+        .appendValue(WEEK_FIELDS.weekOfWeekBasedYear(), 2, 2, SignStyle.NOT_NEGATIVE)
         .toFormatter(Locale.ROOT)
         .withResolverStyle(ResolverStyle.STRICT);
 
@@ -972,7 +972,7 @@ public class DateFormatters {
         new DateTimeFormatterBuilder()
             .append(STRICT_WEEKYEAR_WEEK_FORMATTER)
             .appendLiteral("-")
-            .appendValue(WeekFields.ISO.dayOfWeek())
+            .appendValue(WEEK_FIELDS.dayOfWeek())
             .toFormatter(Locale.ROOT)
             .withResolverStyle(ResolverStyle.STRICT));
 
@@ -1162,7 +1162,7 @@ public class DateFormatters {
      * Returns a formatter for a four digit weekyear. (YYYY)
      */
     private static final DateFormatter WEEK_YEAR = new JavaDateFormatter("week_year",
-        new DateTimeFormatterBuilder().appendValue(WeekFields.ISO.weekBasedYear()).toFormatter(Locale.ROOT)
+        new DateTimeFormatterBuilder().appendValue(WEEK_FIELDS.weekBasedYear()).toFormatter(Locale.ROOT)
                                       .withResolverStyle(ResolverStyle.STRICT));
 
     /*
@@ -1591,9 +1591,9 @@ public class DateFormatters {
      */
     private static final DateFormatter WEEKYEAR_WEEK = new JavaDateFormatter("weekyear_week", STRICT_WEEKYEAR_WEEK_FORMATTER,
         new DateTimeFormatterBuilder()
-            .appendValue(WeekFields.ISO.weekBasedYear())
+            .appendValue(WEEK_FIELDS.weekBasedYear())
             .appendLiteral("-W")
-            .appendValue(WeekFields.ISO.weekOfWeekBasedYear())
+            .appendValue(WEEK_FIELDS.weekOfWeekBasedYear())
             .toFormatter(Locale.ROOT)
             .withResolverStyle(ResolverStyle.STRICT)
     );
@@ -1606,15 +1606,15 @@ public class DateFormatters {
         new DateTimeFormatterBuilder()
             .append(STRICT_WEEKYEAR_WEEK_FORMATTER)
             .appendLiteral("-")
-            .appendValue(WeekFields.ISO.dayOfWeek())
+            .appendValue(WEEK_FIELDS.dayOfWeek())
             .toFormatter(Locale.ROOT)
             .withResolverStyle(ResolverStyle.STRICT),
         new DateTimeFormatterBuilder()
-            .appendValue(WeekFields.ISO.weekBasedYear())
+            .appendValue(WEEK_FIELDS.weekBasedYear())
             .appendLiteral("-W")
-            .appendValue(WeekFields.ISO.weekOfWeekBasedYear())
+            .appendValue(WEEK_FIELDS.weekOfWeekBasedYear())
             .appendLiteral("-")
-            .appendValue(WeekFields.ISO.dayOfWeek())
+            .appendValue(WEEK_FIELDS.dayOfWeek())
             .toFormatter(Locale.ROOT)
             .withResolverStyle(ResolverStyle.STRICT)
     );
@@ -1858,7 +1858,7 @@ public class DateFormatters {
         } else if (isLocalDateSet) {
             return localDate.atStartOfDay(zoneId);
         } else if (isLocalTimeSet) {
-            return of(getLocaldate(accessor), localTime, zoneId);
+            return of(getLocalDate(accessor), localTime, zoneId);
         } else if (accessor.isSupported(ChronoField.YEAR) || accessor.isSupported(ChronoField.YEAR_OF_ERA) ) {
             if (accessor.isSupported(MONTH_OF_YEAR)) {
                 return getFirstOfMonth(accessor).atStartOfDay(zoneId);
@@ -1868,19 +1868,9 @@ public class DateFormatters {
             }
         } else if (accessor.isSupported(MONTH_OF_YEAR)) {
             // missing year, falling back to the epoch and then filling
-            return getLocaldate(accessor).atStartOfDay(zoneId);
+            return getLocalDate(accessor).atStartOfDay(zoneId);
-        } else if (accessor.isSupported(WeekFields.ISO.weekBasedYear())) {
+        } else if (accessor.isSupported(WEEK_FIELDS.weekBasedYear())) {
-            if (accessor.isSupported(WeekFields.ISO.weekOfWeekBasedYear())) {
+            return localDateFromWeekBasedDate(accessor).atStartOfDay(zoneId);
-                return Year.of(accessor.get(WeekFields.ISO.weekBasedYear()))
-                    .atDay(1)
-                    .with(WeekFields.ISO.weekOfWeekBasedYear(), accessor.getLong(WeekFields.ISO.weekOfWeekBasedYear()))
-                    .atStartOfDay(zoneId);
-            } else {
-                return Year.of(accessor.get(WeekFields.ISO.weekBasedYear()))
-                    .atDay(1)
-                    .with(TemporalAdjusters.firstInMonth(DayOfWeek.MONDAY))
-                    .atStartOfDay(zoneId);
-            }
         }
 
         // we should not reach this piece of code, everything being parsed we should be able to
@@ -1888,6 +1878,19 @@ public class DateFormatters {
         throw new IllegalArgumentException("temporal accessor [" + accessor + "] cannot be converted to zoned date time");
     }
 
+    private static LocalDate localDateFromWeekBasedDate(TemporalAccessor accessor) {
+        if (accessor.isSupported(WEEK_FIELDS.weekOfWeekBasedYear())) {
+            return LocalDate.ofEpochDay(0)
+                            .with(WEEK_FIELDS.weekBasedYear(), accessor.get(WEEK_FIELDS.weekBasedYear()))
+                            .with(WEEK_FIELDS.weekOfWeekBasedYear(), accessor.get(WEEK_FIELDS.weekOfWeekBasedYear()))
+                            .with(ChronoField.DAY_OF_WEEK, WEEK_FIELDS.getFirstDayOfWeek().getValue());
+        } else {
+            return LocalDate.ofEpochDay(0)
+                            .with(WEEK_FIELDS.weekBasedYear(), accessor.get(WEEK_FIELDS.weekBasedYear()))
+                            .with(ChronoField.DAY_OF_WEEK, WEEK_FIELDS.getFirstDayOfWeek().getValue());
+        }
+    }
+
     /**
      * extending the java.time.temporal.TemporalQueries.LOCAL_DATE implementation to also create local dates
      * when YearOfEra was used instead of Year.
@@ -1915,9 +1918,11 @@ public class DateFormatters {
         }
     };
 
-    private static LocalDate getLocaldate(TemporalAccessor accessor) {
+    private static LocalDate getLocalDate(TemporalAccessor accessor) {
-        int year = getYear(accessor);
+        if (accessor.isSupported(WEEK_FIELDS.weekBasedYear())) {
-        if (accessor.isSupported(MONTH_OF_YEAR)) {
+            return localDateFromWeekBasedDate(accessor);
+        } else if (accessor.isSupported(MONTH_OF_YEAR)) {
+            int year = getYear(accessor);
             if (accessor.isSupported(DAY_OF_MONTH)) {
                 return LocalDate.of(year, accessor.get(MONTH_OF_YEAR), accessor.get(DAY_OF_MONTH));
             } else {

server/src/main/java/org/elasticsearch/common/time/IsoCalendarDataProvider.java

@@ -0,0 +1,41 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.elasticsearch.common.time;
+
+import java.util.Calendar;
+import java.util.Locale;
+import java.util.spi.CalendarDataProvider;
+
+public class IsoCalendarDataProvider extends CalendarDataProvider {
+
+    @Override
+    public int getFirstDayOfWeek(Locale locale) {
+        return Calendar.MONDAY;
+    }
+
+    @Override
+    public int getMinimalDaysInFirstWeek(Locale locale) {
+        return 4;
+    }
+
+    @Override
+    public Locale[] getAvailableLocales() {
+        return new Locale[]{Locale.ROOT};
+    }
+}

server/src/main/java/org/elasticsearch/script/JodaCompatibleZonedDateTime.java

@@ -23,6 +23,7 @@ import org.apache.logging.log4j.LogManager;
 import org.elasticsearch.common.SuppressForbidden;
 import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.common.time.DateFormatter;
+import org.elasticsearch.common.time.DateFormatters;
 import org.elasticsearch.common.time.DateUtils;
 import org.joda.time.DateTime;
 
@@ -50,7 +51,6 @@ import java.time.temporal.TemporalField;
 import java.time.temporal.TemporalQuery;
 import java.time.temporal.TemporalUnit;
 import java.time.temporal.ValueRange;
-import java.time.temporal.WeekFields;
 import java.util.Locale;
 import java.util.Objects;
 
@@ -474,14 +474,14 @@ public class JodaCompatibleZonedDateTime
 
     @Deprecated
     public int getWeekOfWeekyear() {
-        logDeprecatedMethod("getWeekOfWeekyear()", "get(WeekFields.ISO.weekOfWeekBasedYear())");
+        logDeprecatedMethod("getWeekOfWeekyear()", "get(DateFormatters.WEEK_FIELDS.weekOfWeekBasedYear())");
-        return dt.get(WeekFields.ISO.weekOfWeekBasedYear());
+        return dt.get(DateFormatters.WEEK_FIELDS.weekOfWeekBasedYear());
     }
 
     @Deprecated
     public int getWeekyear() {
-        logDeprecatedMethod("getWeekyear()", "get(WeekFields.ISO.weekBasedYear())");
+        logDeprecatedMethod("getWeekyear()", "get(DateFormatters.WEEK_FIELDS.weekBasedYear())");
-        return dt.get(WeekFields.ISO.weekBasedYear());
+        return dt.get(DateFormatters.WEEK_FIELDS.weekBasedYear());
     }
 
     @Deprecated

server/src/main/resources/META-INF/services/java.util.spi.CalendarDataProvider

@@ -0,0 +1 @@
+org.elasticsearch.common.time.IsoCalendarDataProvider

server/src/test/java/org/elasticsearch/common/joda/JavaJodaTimeDuellingTests.java

@@ -37,9 +37,9 @@ import java.time.format.DateTimeFormatter;
 import java.time.temporal.TemporalAccessor;
 import java.util.Locale;
 
+import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.is;
-import static org.hamcrest.core.IsEqual.equalTo;
 
 public class JavaJodaTimeDuellingTests extends ESTestCase {
     @Override

server/src/test/java/org/elasticsearch/common/time/DateFormattersTests.java

@@ -19,6 +19,7 @@
 
 package org.elasticsearch.common.time;
 
+import org.elasticsearch.bootstrap.JavaVersion;
 import org.elasticsearch.test.ESTestCase;
 
 import java.time.Clock;
@@ -40,6 +41,35 @@ import static org.hamcrest.Matchers.sameInstance;
 
 public class DateFormattersTests extends ESTestCase {
 
+    public void testWeekBasedDates() {
+        assumeFalse("won't work in jdk8 " +
+                "because SPI mechanism is not looking at classpath - needs ISOCalendarDataProvider in jre's ext/libs",
+            JavaVersion.current().equals(JavaVersion.parse("8")));
+
+        // as per WeekFields.ISO first week starts on Monday and has minimum 4 days
+        DateFormatter dateFormatter = DateFormatters.forPattern("YYYY-ww");
+
+        // first week of 2016 starts on Monday 2016-01-04 as previous week in 2016 has only 3 days
+        assertThat(DateFormatters.from(dateFormatter.parse("2016-01")) ,
+            equalTo(ZonedDateTime.of(2016,01,04, 0,0,0,0,ZoneOffset.UTC)));
+
+        // first week of 2015 starts on Monday 2014-12-29 because 4days belong to 2019
+        assertThat(DateFormatters.from(dateFormatter.parse("2015-01")) ,
+            equalTo(ZonedDateTime.of(2014,12,29, 0,0,0,0,ZoneOffset.UTC)));
+
+
+        // as per WeekFields.ISO first week starts on Monday and has minimum 4 days
+         dateFormatter = DateFormatters.forPattern("YYYY");
+
+        // first week of 2016 starts on Monday 2016-01-04 as previous week in 2016 has only 3 days
+        assertThat(DateFormatters.from(dateFormatter.parse("2016")) ,
+            equalTo(ZonedDateTime.of(2016,01,04, 0,0,0,0,ZoneOffset.UTC)));
+
+        // first week of 2015 starts on Monday 2014-12-29 because 4days belong to 2019
+        assertThat(DateFormatters.from(dateFormatter.parse("2015")) ,
+            equalTo(ZonedDateTime.of(2014,12,29, 0,0,0,0,ZoneOffset.UTC)));
+    }
+
     // this is not in the duelling tests, because the epoch millis parser in joda time drops the milliseconds after the comma
     // but is able to parse the rest
     // as this feature is supported it also makes sense to make it exact

server/src/test/java/org/elasticsearch/common/time/JavaDateMathParserTests.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.common.time;
 
 import org.elasticsearch.ElasticsearchParseException;
+import org.elasticsearch.bootstrap.JavaVersion;
 import org.elasticsearch.test.ESTestCase;
 
 import java.time.Instant;
@@ -50,6 +51,24 @@ public class JavaDateMathParserTests extends ESTestCase {
         assertDateEquals(gotMillis, "297276785531", "297276785531");
     }
 
+    public void testWeekDates() {
+        assumeFalse("won't work in jdk8 " +
+                "because SPI mechanism is not looking at classpath - needs ISOCalendarDataProvider in jre's ext/libs",
+            JavaVersion.current().equals(JavaVersion.parse("8")));
+
+        DateFormatter formatter = DateFormatter.forPattern("YYYY-ww");
+        assertDateMathEquals(formatter.toDateMathParser(), "2016-01", "2016-01-04T23:59:59.999Z", 0, true, ZoneOffset.UTC);
+
+        formatter = DateFormatter.forPattern("YYYY");
+        assertDateMathEquals(formatter.toDateMathParser(), "2016", "2016-01-04T23:59:59.999Z", 0, true, ZoneOffset.UTC);
+
+        formatter = DateFormatter.forPattern("YYYY-ww");
+        assertDateMathEquals(formatter.toDateMathParser(), "2015-01", "2014-12-29T23:59:59.999Z", 0, true, ZoneOffset.UTC);
+
+        formatter = DateFormatter.forPattern("YYYY");
+        assertDateMathEquals(formatter.toDateMathParser(), "2015", "2014-12-29T23:59:59.999Z", 0, true, ZoneOffset.UTC);
+    }
+
     public void testBasicDates() {
         assertDateMathEquals("2014-05-30", "2014-05-30T00:00:00.000");
         assertDateMathEquals("2014-05-30T20", "2014-05-30T20:00:00.000");

server/src/test/java/org/elasticsearch/index/mapper/DateFieldMapperTests.java

@@ -235,7 +235,7 @@ public class DateFieldMapperTests extends ESSingleNodeTestCase {
         mapper.parse(new SourceToParse("test", "type", "1", BytesReference
                 .bytes(XContentFactory.jsonBuilder()
                         .startObject()
-                        .field("field", "Mi., 06 Dez. 2000 02:55:00 -0800")
+                        .field("field", "Mi, 06 Dez 2000 02:55:00 -0800")
                         .endObject()),
                 XContentType.JSON));
     }

server/src/test/java/org/elasticsearch/script/JodaCompatibleZonedDateTimeTests.java

@@ -213,12 +213,12 @@ public class JodaCompatibleZonedDateTimeTests extends ESTestCase {
 
     public void testWeekOfWeekyear() {
         assertMethodDeprecation(() -> assertThat(javaTime.getWeekOfWeekyear(), equalTo(jodaTime.getWeekOfWeekyear())),
-            "getWeekOfWeekyear()", "get(WeekFields.ISO.weekOfWeekBasedYear())");
+            "getWeekOfWeekyear()", "get(DateFormatters.WEEK_FIELDS.weekOfWeekBasedYear())");
     }
 
     public void testWeekyear() {
         assertMethodDeprecation(() -> assertThat(javaTime.getWeekyear(), equalTo(jodaTime.getWeekyear())),
-            "getWeekyear()", "get(WeekFields.ISO.weekBasedYear())");
+            "getWeekyear()", "get(DateFormatters.WEEK_FIELDS.weekBasedYear())");
     }
 
     public void testYearOfCentury() {

server/src/test/java/org/elasticsearch/search/query/SearchQueryIT.java

@@ -1678,21 +1678,21 @@ public class SearchQueryIT extends ESIntegTestCase {
                 .endObject().endObject().endObject()));
 
         indexRandom(true,
-            client().prepareIndex("test", "type1", "1").setSource("date_field", "Mi., 06 Dez. 2000 02:55:00 -0800"),
+            client().prepareIndex("test", "type1", "1").setSource("date_field", "Mi, 06 Dez 2000 02:55:00 -0800"),
-            client().prepareIndex("test", "type1", "2").setSource("date_field", "Do., 07 Dez. 2000 02:55:00 -0800")
+            client().prepareIndex("test", "type1", "2").setSource("date_field", "Do, 07 Dez 2000 02:55:00 -0800")
         );
 
         SearchResponse searchResponse = client().prepareSearch("test")
             .setQuery(QueryBuilders.rangeQuery("date_field")
-                .gte("Di., 05 Dez. 2000 02:55:00 -0800")
+                .gte("Di, 05 Dez 2000 02:55:00 -0800")
-                .lte("Do., 07 Dez. 2000 00:00:00 -0800"))
+                .lte("Do, 07 Dez 2000 00:00:00 -0800"))
             .get();
         assertHitCount(searchResponse, 1L);
 
         searchResponse = client().prepareSearch("test")
             .setQuery(QueryBuilders.rangeQuery("date_field")
-                .gte("Di., 05 Dez. 2000 02:55:00 -0800")
+                .gte("Di, 05 Dez 2000 02:55:00 -0800")
-                .lte("Fr., 08 Dez. 2000 00:00:00 -0800"))
+                .lte("Fr, 08 Dez 2000 00:00:00 -0800"))
             .get();
         assertHitCount(searchResponse, 2L);
     }

x-pack/plugin/core/src/test/java/org/elasticsearch/license/LicenseServiceTests.java

@@ -17,23 +17,11 @@ import static org.hamcrest.Matchers.startsWith;
 /**
  * Due to changes in JDK9 where locale data is used from CLDR, the licence message will differ in jdk 8 and jdk9+
  * https://openjdk.java.net/jeps/252
+ * We run ES with -Djava.locale.providers=SPI,COMPAT and same option has to be applied when running this test from IDE
  */
 public class LicenseServiceTests extends ESTestCase {
 
-    public void testLogExpirationWarningOnJdk9AndNewer() {
+    public void testLogExpirationWarning() {
-        assumeTrue("this is for JDK9+", JavaVersion.current().compareTo(JavaVersion.parse("9")) >= 0);
-
-        long time = LocalDate.of(2018, 11, 15).atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli();
-        final boolean expired = randomBoolean();
-        final String message = LicenseService.buildExpirationMessage(time, expired).toString();
-        if (expired) {
-            assertThat(message, startsWith("LICENSE [EXPIRED] ON [THU, NOV 15, 2018].\n"));
-        } else {
-            assertThat(message, startsWith("License [will expire] on [Thu, Nov 15, 2018].\n"));
-        }
-    }
-
-    public void testLogExpirationWarningOnJdk8() {
         assumeTrue("this is for JDK8 only", JavaVersion.current().equals(JavaVersion.parse("8")));
 
         long time = LocalDate.of(2018, 11, 15).atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli();
@@ -45,5 +33,4 @@ public class LicenseServiceTests extends ESTestCase {
             assertThat(message, startsWith("License [will expire] on [Thursday, November 15, 2018].\n"));
         }
     }
-
 }

x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/filestructurefinder/TimestampFormatFinderTests.java

@@ -430,7 +430,6 @@ public class TimestampFormatFinderTests extends FileStructureTestCase {
     }
 
     public void testGuessIsDayFirstFromLocale() {
-
         TimestampFormatFinder timestampFormatFinder = new TimestampFormatFinder(explanation, true, true, true, NOOP_TIMEOUT_CHECKER);
 
         // Locale fallback is the only way to decide

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/function/scalar/datetime/NonIsoDateTimeProcessor.java

@@ -10,14 +10,12 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 
 import java.io.IOException;
-import java.time.LocalDateTime;
+import java.time.DayOfWeek;
 import java.time.ZoneId;
 import java.time.ZonedDateTime;
 import java.time.temporal.ChronoField;
-import java.util.Calendar;
+import java.time.temporal.WeekFields;
-import java.util.Locale;
 import java.util.Objects;
-import java.util.TimeZone;
 import java.util.function.Function;
 
 public class NonIsoDateTimeProcessor extends BaseDateTimeProcessor {
@@ -30,15 +28,7 @@ public class NonIsoDateTimeProcessor extends BaseDateTimeProcessor {
             return dayOfWeek == 8 ? 1 : dayOfWeek;
         }),
         WEEK_OF_YEAR(zdt -> {
-            // by ISO 8601 standard, the first week of a year is the first week with a majority (4 or more) of its days in January.
+            return zdt.get(WeekFields.of(DayOfWeek.SUNDAY, 1).weekOfWeekBasedYear());
-            // Other Locales may have their own standards (see Arabic or Japanese calendars).
-            LocalDateTime ld = zdt.toLocalDateTime();
-            Calendar cal = Calendar.getInstance(TimeZone.getTimeZone(zdt.getZone()), Locale.ROOT);
-            cal.clear();
-            cal.set(ld.get(ChronoField.YEAR), ld.get(ChronoField.MONTH_OF_YEAR) - 1, ld.get(ChronoField.DAY_OF_MONTH),
-                    ld.get(ChronoField.HOUR_OF_DAY), ld.get(ChronoField.MINUTE_OF_HOUR), ld.get(ChronoField.SECOND_OF_MINUTE));
-
-            return cal.get(Calendar.WEEK_OF_YEAR);
         });
 
         private final Function<ZonedDateTime, Integer> apply;

x-pack/plugin/sql/src/test/java/org/elasticsearch/xpack/sql/expression/function/scalar/datetime/NonIsoDateTimeProcessorTests.java

@@ -17,7 +17,6 @@ import static org.elasticsearch.xpack.sql.util.DateUtils.UTC;
 
 public class NonIsoDateTimeProcessorTests extends AbstractSqlWireSerializingTestCase<NonIsoDateTimeProcessor> {
 
-
     public static NonIsoDateTimeProcessor randomNonISODateTimeProcessor() {
         return new NonIsoDateTimeProcessor(randomFrom(NonIsoDateTimeExtractor.values()), UTC);
     }
@@ -45,6 +44,8 @@ public class NonIsoDateTimeProcessorTests extends AbstractSqlWireSerializingTest
 
     public void testNonISOWeekOfYearInUTC() {
         NonIsoDateTimeProcessor proc = new NonIsoDateTimeProcessor(NonIsoDateTimeExtractor.WEEK_OF_YEAR, UTC);
+        // 1 Jan 1988 is Friday - under Sunday,1 rule it is the first week of the year (under ISO rule it would be 53 of the previous year
+        // hence the 5th Jan 1988 Tuesday is the second week of a year
         assertEquals(2, proc.process(dateTime(568372930000L)));  //1988-01-05T09:22:10Z[UTC]
         assertEquals(6, proc.process(dateTime(981278530000L)));  //2001-02-04T09:22:10Z[UTC]
         assertEquals(7, proc.process(dateTime(224241730000L)));  //1977-02-08T09:22:10Z[UTC]