Fix date_nanos in composite aggs (elastic#53315)

It looks like `date_nanos` fields weren't likely to work properly in
composite aggs because composites iterate field values using points and
we weren't converting the points into milliseconds. Because the doc
values were coming back in milliseconds we ended up geting very confused
and just never collecting sub-aggregations.

This fixes that by adding a method to `DateFieldMapper.Resolution` to
`parsePointAsMillis` which is similarly in name and function to
`NumberFieldMapper.NumberType`'s `parsePoint` except that it normalizes
to milliseconds which is what aggs need at the moment.

Closes elastic#53168

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/230_composite.yml

@@ -8,6 +8,8 @@ setup:
                 properties:
                   date:
                     type: date
+                  date_nanos:
+                    type: date_nanos
                   keyword:
                     type: keyword
                   long:
@@ -886,6 +888,57 @@ setup:
   - match: { aggregations.test.buckets.0.key.date: "2017-10-21T00:00:00.000-02:00" }
   - match: { aggregations.test.buckets.0.doc_count: 2 }
 
+---
+"date_histogram on date_nanos":
+  - skip:
+      version: " - 7.6.99"
+      reason: Fixed in 7.7.0
+  - do:
+      index:
+        index:   test
+        id:      7
+        body:    { "date_nanos": "2017-11-21T01:00:00" }
+        refresh: true
+  - do:
+      index:
+        index:   test
+        id:      8
+        body:    { "date_nanos": "2017-11-22T01:00:00" }
+        refresh: true
+  - do:
+      index:
+        index:   test
+        id:      9
+        body:    { "date_nanos": "2017-11-22T02:00:00" }
+        refresh: true
+  - do:
+      search:
+        index: test
+        body:
+          aggregations:
+            test:
+              composite:
+                sources:
+                  - date:
+                      date_histogram:
+                        field: date_nanos
+                        calendar_interval: 1d
+                        format: iso8601 # Format makes the comparisons a little more obvious
+              aggregations:
+                avg:
+                  avg:
+                    field: date_nanos
+
+  - match: { hits.total.value: 9 }
+  - match: { hits.total.relation: eq }
+  - length: { aggregations.test.buckets: 2 }
+  - match: { aggregations.test.buckets.0.key.date: "2017-11-21T00:00:00.000Z" }
+  - match: { aggregations.test.buckets.0.doc_count: 1 }
+  - match: { aggregations.test.buckets.0.avg.value_as_string: "2017-11-21T01:00:00.000Z" }
+  - match: { aggregations.test.buckets.1.key.date: "2017-11-22T00:00:00.000Z" }
+  - match: { aggregations.test.buckets.1.doc_count: 2 }
+  - match: { aggregations.test.buckets.1.avg.value_as_string: "2017-11-22T01:30:00.000Z" }
+
 ---
 "Terms source from sorted":
   - do:

server/src/main/java/org/elasticsearch/index/mapper/DateFieldMapper.java

@@ -94,6 +94,11 @@ public Instant toInstant(long value) {
             public Instant clampToValidRange(Instant instant) {
                 return instant;
             }
+
+            @Override
+            public long parsePointAsMillis(byte[] value) {
+                return LongPoint.decodeDimension(value, 0);
+            }
         },
         NANOSECONDS("date_nanos", NumericType.DATE_NANOSECONDS) {
             @Override
@@ -110,6 +115,11 @@ public Instant toInstant(long value) {
             public Instant clampToValidRange(Instant instant) {
                 return DateUtils.clampToNanosRange(instant);
             }
+
+            @Override
+            public long parsePointAsMillis(byte[] value) {
+                return DateUtils.toMilliSeconds(LongPoint.decodeDimension(value, 0));
+            }
         };
 
         private final String type;
@@ -138,8 +148,17 @@ NumericType numericType() {
          */
         public abstract Instant toInstant(long value);
 
+        /**
+         * Return the instant that this range can represent that is closest to
+         * the provided instant.
+         */
         public abstract Instant clampToValidRange(Instant instant);
 
+        /**
+         * Decode the points representation of this field as milliseconds.
+         */
+        public abstract long parsePointAsMillis(byte[] value);
+
         public static Resolution ofOrdinal(int ord) {
             for (Resolution resolution : values()) {
                 if (ord == resolution.ordinal()) {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/composite/LongValuesSource.java

@@ -269,7 +269,8 @@ SortedDocsProducer createSortedDocsProducerOrNull(IndexReader reader, Query quer
             }
             return new PointsSortedDocsProducer(fieldType.name(), toBucketFunction, lowerPoint, upperPoint);
         } else if (fieldType instanceof DateFieldMapper.DateFieldType) {
-            final ToLongFunction<byte[]> toBucketFunction = (value) -> rounding.applyAsLong(LongPoint.decodeDimension(value, 0));
+            ToLongFunction<byte[]> decode = ((DateFieldMapper.DateFieldType) fieldType).resolution()::parsePointAsMillis;
+            ToLongFunction<byte[]> toBucketFunction = value -> rounding.applyAsLong(decode.applyAsLong(value));
             return new PointsSortedDocsProducer(fieldType.name(), toBucketFunction, lowerPoint, upperPoint);
         } else {
             return null;

server/src/main/java/org/elasticsearch/search/aggregations/metrics/MinAggregator.java

@@ -18,15 +18,14 @@
  */
 package org.elasticsearch.search.aggregations.metrics;
 
-import org.apache.lucene.document.LongPoint;
 import org.apache.lucene.index.IndexOptions;
 import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.PointValues;
 import org.apache.lucene.search.CollectionTerminatedException;
 import org.apache.lucene.search.MatchAllDocsQuery;
-import org.apache.lucene.util.Bits;
 import org.apache.lucene.search.ScoreMode;
+import org.apache.lucene.util.Bits;
 import org.elasticsearch.common.lease.Releasables;
 import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.common.util.DoubleArray;
@@ -191,11 +190,7 @@ static Function<byte[], Number> getPointReaderOrNull(SearchContext context, Aggr
                 converter = ((NumberFieldMapper.NumberFieldType) fieldType)::parsePoint;
             } else if (fieldType.getClass() == DateFieldMapper.DateFieldType.class) {
                 DateFieldMapper.DateFieldType dft = (DateFieldMapper.DateFieldType) fieldType;
-                /*
-                 * Makes sure that nanoseconds decode to milliseconds, just
-                 * like they do when you run the agg without the optimization.
-                 */
-                converter = (in) -> dft.resolution().toInstant(LongPoint.decodeDimension(in, 0)).toEpochMilli();
+                converter = dft.resolution()::parsePointAsMillis;
             }
             return converter;
         }