SQL: Make sure now() always uses milliseconds precision (#36877)

* This change is to account for different system clock implementations
or different Java versions (for Java 8, milliseconds precision is used;
for Java 9+ a system specific clock implementation is used which can
have greater precision than what we need here).

x-pack/plugin/sql/src/test/java/org/elasticsearch/xpack/sql/TestUtils.java

@@ -11,11 +11,27 @@
 import org.elasticsearch.xpack.sql.session.Configuration;
 import org.elasticsearch.xpack.sql.util.DateUtils;
 
+import java.time.Clock;
+import java.time.Duration;
+import java.time.ZonedDateTime;
+
 public class TestUtils {
 
     private TestUtils() {}
 
     public static final Configuration TEST_CFG = new Configuration(DateUtils.UTC, Protocol.FETCH_SIZE,
             Protocol.REQUEST_TIMEOUT, Protocol.PAGE_TIMEOUT, null, Mode.PLAIN, null, null);
 
+    /**
+     * Returns the current UTC date-time with milliseconds precision.
+     * In Java 9+ (as opposed to Java 8) the {@code Clock} implementation uses system's best clock implementation (which could mean
+     * that the precision of the clock can be milliseconds, microseconds or nanoseconds), whereas in Java 8
+     * {@code System.currentTimeMillis()} is always used. To account for these differences, this method defines a new {@code Clock}
+     * which will offer a value for {@code ZonedDateTime.now()} set to always have milliseconds precision.
+     * 
+     * @return {@link ZonedDateTime} instance for the current date-time with milliseconds precision in UTC
+     */
+    public static final ZonedDateTime now() {
+        return ZonedDateTime.now(Clock.tick(Clock.system(DateUtils.UTC), Duration.ofMillis(1)));
+    }
 }

x-pack/plugin/sql/src/test/java/org/elasticsearch/xpack/sql/type/DataTypeConversionTests.java

@@ -7,9 +7,9 @@
 
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.xpack.sql.SqlIllegalArgumentException;
+import org.elasticsearch.xpack.sql.TestUtils;
 import org.elasticsearch.xpack.sql.expression.Literal;
 import org.elasticsearch.xpack.sql.type.DataTypeConversion.Conversion;
-import org.elasticsearch.xpack.sql.util.DateUtils;
 
 import java.time.ZonedDateTime;
 
@@ -79,7 +79,6 @@ public void testConversionToLong() {
         assertEquals("cannot cast [0xff] to [Long]", e.getMessage());
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/35683")
     public void testConversionToDate() {
         DataType to = DATE;
         {
@@ -111,7 +110,7 @@ public void testConversionToDate() {
         assertEquals(dateTime(18000000L), conversion.convert("1970-01-01T00:00:00-05:00"));
 
         // double check back and forth conversion
-        ZonedDateTime dt = ZonedDateTime.now(DateUtils.UTC);
+        ZonedDateTime dt = TestUtils.now();
         Conversion forward = conversionFor(DATE, KEYWORD);
         Conversion back = conversionFor(KEYWORD, DATE);
         assertEquals(dt, back.convert(forward.convert(dt)));